New molybdenum(V) complexes based on the {Mo2O4}2+ structural core with esters or anions of malonic and succinic acid

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Inorganica Chimica Acta 360 (2007) 663–678

New molybdenum(V) complexes based on the {Mo2O4}2+

structural core with esters or anions of malonic and succinic acid

Barbara Modec *, Darko Dolenc, Jurij V. Brencic

Department of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, 1000 Ljubljana, Slovenia

Received 9 May 2006; received in revised form 16 August 2006; accepted 30 August 2006Available online 19 September 2006

Abstract

A series of malonato complexes of molybdenum(V) was prepared by reacting (PyH)5[MoOCl4(H2O)]3Cl2 or (PyH)n[MoOBr4]n withmalonic acid (H2mal) or a half-neutralized acid, hydrogen malonate (Hmal�), at ambient conditions: (PyH)3[Mo2O4Cl4(l2-Hmal)] ÆCH3CN (1), (PyH)3[Mo2O4Br4(l2-Hmal)] Æ CH3CN (2), (PyH)2[Mo2O4Cl(g2-mal)(l2-Hmal)Py] (3), (3,5-LutH)2(H3O) [Mo2O4(g2-mal)2-(l2-Hmal)] (4), (PyH)[Mo2O4Cl2(l2-Memal)Py2] (5), (3,5-LutH)[Mo2O4Cl2(l2-Memal)(3,5-Lut)2] (6), (PyH)[Mo2O4Cl2(l2-Etmal)Py2](7), (3,5-LutH)[Mo2O4Cl2(l2-Prmal)(3,5-Lut)2] (8) and [{Mo2O4(l2-Memal)Py2}2(l2-OCH3)2] (9) (where Py = pyridine, C5H5N;PyH+ = pyridinium cation, C5H5NH+; 3,5-Lut = 3,5-lutidine, C7H9N; 3,5-LutH+ = 3,5-lutidinium cation, C7H9NH+; mal2� = malon-ate, �OOCCH2COO�; Memal� = monomethyl malonate, �OOCCH2COOCH3; Etmal� = monoethyl malonate, �OOCCH2COOC2H5

and Prmal� = monopropyl malonate, �OOCCH2COOC3H7). The complex anions of compounds 1–8 have a common structural feature:a dinuclear, singly metal–metal bonded {Mo2O4}2+ core with the carboxylate moiety of the malonato ligand coordinated in a syn–syn

bidentate bridging manner to the pair of metal atoms. The remaining four coordination sites of the {Mo2O4}2+ core are occupiedwith halides in 1 and 2, with halides/pyridine ligands in 5–8, with a pair of bidentate malonate ions in 4 and with the combination ofall in 3. The neutral molecules of 9 consist of two {Mo2O4}2+ cores linked with a pair of methoxide ions into a chain-like, tetranuclearcluster. An esterification of malonic acid was observed to take place in the reaction mixtures containing alcohols. Solvothermal reactionswith malonic acid carried out at 115 �C produced anionic acetato complexes as found in (PyH)[Mo2O4Cl2(l2-OOCCH3)Py2] Æ Py (10),(PyH)[Mo2O4Cl2(l2-OOCCH3)Py2] (11), (3,5-LutH)[Mo2O4Cl2(l2-OOCCH3)(3,5-Lut)2] (12) and (4-MePyH)3[Mo2O4Cl2-(l2-OOCCH3)(4-MePy)2]2Cl (13) (4-MePy = 4-methylpyridine, C6H7N). The acetate coordinated in the syn–syn bidentate bridging modein all. Reactions of (PyH)5[MoOCl4(H2O)]3Cl2 with succinic acid (H2suc) at ambient conditions resulted in a complex with a half-neu-tralized acid, (PyH)[Mo2O4Cl2(l2-Hsuc)Py2] Æ Py (14) (Hsuc� = hydrogen succinate, �OOC(CH2)2COOH), while those carried out at115 �C in a tetranuclear succinato complex, (4-MePyH)2[{Mo2O4Cl2(4-MePy)2}2(l4-suc)] (15) (suc2� = succinate, �OOC(CH2)2COO�).The tetranuclear anion of 15 consists of two {Mo2O4}2+ cores covalently linked with a tetradentate succinato ligand. The compoundswere fully characterized by infrared vibrational spectroscopy, elemental analyses and X-ray diffraction studies.� 2006 Elsevier B.V. All rights reserved.

Keywords: Molybdenum(V) complexes; Dicarboxylates; Malonate; Succinate; Esterification

1. Introduction

The designed synthesis of supramolecular arrays con-structed from the labile metal cations and polyfunctionalorganic molecules has been an area of active research overthe past decade [1]. Appropriately designed dimetal units,

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doi:10.1016/j.ica.2006.08.047

* Corresponding author. Tel.: +386 1 2419 114; fax: +386 1 2419 220.E-mail address: [email protected] (B. Modec).

e.g. Mo24þ, also served as preformed molecular building

blocks in the formation of higher order structures [2]. Adinuclear {Mo2O4}2+ core (Fig. 1) presents itself asanother building block. Not only does it dominate thechemistry of this oxidation state, but it preserves its struc-tural integrity upon the coordination. Its most relevantgeometric parameters are (i) a metal–metal separation of2.5–2.6 A, and (ii) a non-planar Mo(l2-O)2Mo moiety witha fold angle of ca. 150� [3]. The direct bonding interaction

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Mo

O

Mo

O

OO

O OC

R

Fig. 2. The syn–syn bidentate bridging coordination of the carboxylate tothe {Mo2O4}2+ core.

1 The X-ray structure analysis of PyHHmal Æ H2mal [K. Djinovic, L.Golic, Acta Cryst. C 48 (1992) 1046] revealed hydrogen-bondedHmal�� H+� � �Hmal� anions with approximately the same degree ofionization of both malonate moieties.

Mo

O

Mo

O

OO

Fig. 1.

664 B. Modec et al. / Inorganica Chimica Acta 360 (2007) 663–678

between two d1 metal centres, described as a single metal–metal bond, accounts for the experimentally observed dia-magnetism of the {Mo2O4}2+-containing compounds [4].Of the six sites of the {Mo2O4}2+ core open for coordina-tion, two are positioned trans relative to the Mo@O groupsand four are positioned cis. With few exceptions only, ithas been observed that the bonding of ligands to the transsites is weaker [4c,5]. The phenomenon has been explainedin terms of the trans influence of molybdenyl groups. Thebonding to the trans site is stabilized in the case of multid-entate ligands which can coordinate in the chelating man-ner. The ligand attaches with one donor atom to thetrans site and with the other (two) atom(s) to cis site(s).This type of coordination is exemplified by the oxalate intrans- and cis-[Mo2O4(g2-C2O4)2(R–Py)2]2� [6]. Dependingon the ligand-to-metal ratio, the oxalate adopted two otherbinding modes: (i) a bischelating one in the polymericanion with the ½Mo2O4ðl2-C2O4ÞCl2�n2n� composition [7],and (ii) a l4-bridging coordination in a discrete tetranu-clear anion with the [{Mo2O4(g2-C2O4)2}2(l4-C2O4)]6�

composition [8]. The coordination of the l4-oxalate differsfrom the previous binding modes: all four donor atoms ofthe ligand occupy only trans sites of two {Mo2O4}2+ cores.Another multidentate oxygen donor ligand, the squaratewhich is a dianion of 3,4-dihydroxycyclobut-3-ene-1,2-dione and which can not bind in a chelating manner tomolybdenum, coordinated in [Mo2O4(l2-C4O4)(R–Py)4]also by occupying only trans sites [9].

The well-known versatility of the carboxylate bindingmodes [10] and the recent application of ligands with twoor more carboxylate groups in the construction of thesupramolecular assemblies [11] prompted us to try theseligands as well. Preliminary research in our laboratory onmaleic, heptanedioic and 1,3,5-benzenetricarboxylic acidsproduced interesting results [12,13]. In no instance, the car-boxylate bonded in the chelating manner which is typicalfor complexes of many transition metals [14]. Instead, inthe majority of complexes only one carboxylate functioncoordinated, while the other(s) remained protonated. Thecarboxylate coordinated in the syn–syn bidentate bridgingmanner to a pair of trans sites (Fig. 2). Herein we presentresults of the research on two other dicarboxylic acids:malonic (H2mal) and succinic acid (H2suc). In order to pro-vide a definite description of the carboxylate functional-ities, the X-ray structure analysis was employed whereverpossible. In the course of the reactions of molybdenum(V)starting materials in the alcohol solutions, an esterificationof malonic acid took place. The isolated complexes con-tained coordinated monoalkyl malonate esters. Additional

experiments were undertaken to assess the possible role ofmolybdenum(V) species in the latter process.

2. Experimental

2.1. General remarks

All manipulations and procedures were conducted inair. Chemicals were purchased from Aldrich and used with-out further purification. (PyH)5[MoOCl4(H2O)]3Cl2 and(PyH)n[MoOBr4]n were prepared as reported [15]. Mono-and dimethyl esters of malonic and succinic acid were alsoprepared as reported [16]. The solvothermal reactions werecarried out at 115 �C in sealed glass tubes under autoge-nous pressure. The infrared spectra were measured on solidsamples as Nujol or poly(chlorotrifluoroethylene) mullsusing a Perkin Elmer 2000 Fourier Transform infraredspectrometer. NMR spectra of DMSO-d6 solutions wererecorded on a Bruker Avance DPX 300 spectrometer(1H, 300 MHz) using tetramethylsilane as an internal stan-dard. Elemental analyses were carried out by the ChemistryDepartment service at the University of Ljubljana. EGAanalysis was performed in a thermogravimetric analyzerNetzsch STA 409 coupled with a quadrupole mass spec-trometer Leybold-Heraeus Inficon QMS 200. The gaseswere transferred through a deactivated and heated quartzcapillary with an inner diameter of 0.250 mm and a lengthof 1 m. Crucible containing 500.0 mg of 1 was heated at4 �C min�1 under argon atmosphere.

2.1.1. Preparation of pyridinium hydrogen malonate,

PyHHmal Æ H2mal1

Pyridine (0.75 cm3, 9.30 mmol) and malonic acid(1.936 g, 18.6 mmol) were dissolved in acetonitrile(50 cm3). The solvent was evaporated under reduced pres-sure until white, crystalline solid started to precipitate.Yield: 86% (2.3 g). Anal. Calc. for C11H13NO8: C, 46.00;H, 4.56; N, 4.88. Found: C, 46.16; H, 4.43; N, 4.82%.

B. Modec et al. / Inorganica Chimica Acta 360 (2007) 663–678 665

2.1.2. Preparation of (PyH)3[Mo2O4Cl4(l2-Hmal)] ÆCH3CN (1)

(PyH)5[MoOCl4(H2O)]3Cl2 (150 mg, 0.350 mmol of Mo)was dissolved in acetonitrile (20 cm3). To this solutionPyHHmal Æ H2mal (225 mg, 0.783 mmol) was added. Thecolour of the solution changed from green to orange.Orange, needle-shaped crystals, which grew within a fewhours, were collected by filtration. Yield: 70% (96 mg).Note: The compound 1 was found to decompose on pro-longed exposure to the air. Anal. Calc. forC18H21Cl4Mo2N3O8 (dried sample): C, 29.17; H, 2.86; N,5.67. Found: C, 28.93; H, 2.80; N, 5.43%.

2.1.3. Preparation of (PyH)3[Mo2O4Br4(l2-Hmal)] ÆCH3CN (2)

(PyH)n[MoOBr4]n (180 mg, 0.352 mmol) was dissolvedin acetonitrile (20 cm3). To this solution PyHHmal Æ H2mal(225 mg, 0.783 mmol) was added. Colour of the solutionchanged from yellow to dark red. In order to reduce thesolubility of the product, tetraphenylphosphonium bro-mide (170 mg, 0.398 mmol) was added. The solution in astoppered flask was stored in the refrigerator. Yellow, needle-shaped crystals, which deposited from the solution over-night, were collected by filtration. Yield: 60% (102 mg).Note: No elemental analysis was performed, since the crys-tals quickly lost the acetonitrile solvent of crystallizationwhen removed from the mother liquor.

2.1.4. Preparation of (PyH)2[Mo2O4Cl(g2-mal)-

(l2-Hmal)Py] (3)The acetonitrile (20 cm3) solution of pyridine (9.30 mmol)

and malonic acid (9.30 mmol) was added to the acetonitrile(30 cm3) solution of (PyH)5[MoOCl4(H2O)]3Cl2 (600 mg,1.40 mmol of Mo). Dark red solution in a closed flask wasleft to stand at ambient conditions overnight. Red crystallineproduct was isolated by filtration. Yield: 47% (242 mg).Anal. Calc. for C21H22ClMo2N3O12: C, 34.28; H, 3.01; N,5.71. Found: C, 34.56; H, 3.11; N, 5.92%.

2.1.5. Preparation of (3,5-LutH)2(H3O)[Mo2O4(g2-mal)2-

(l2-Hmal)] (4)

Malonic acid (104 mg, 1.00 mmol) was dissolved in themixture of 3,5-lutidine (1 cm3), methanol (5 cm3) andacetonitrile (0.5 cm3), followed by the addition of(PyH)n[MoOBr4]n (300 mg, 0.586 mmol). After the colourof the reaction mixture turned orange, diethyl ether(9 cm3) was added while stirring. The mixture was allowedto stand for two days at ambient conditions to let theproduct deposit from the solution. Orange crystals werecollected by filtration. Yield: 18% (43 mg). Note: No ele-mental analysis was performed, since the crystals quicklydecomposed when removed from the mother liquor.

2.1.6. Preparation of (PyH)[Mo2O4Cl2(l2-Memal)Py2](5)

Malonic acid (104 mg, 1.00 mmol) was dissolved inthe mixture of pyridine (1 cm3), methanol (5 cm3) and

acetonitrile (0.5 cm3), followed by the addition of(PyH)5[MoOCl4(H2O)]3Cl2 (200 mg, 0.466 mmol of Mo).After the colour of the reaction mixture turned orange,diethyl ether (8 cm3) was added while stirring. The mixturewas allowed to stand at ambient conditions for a week. Twocrystalline phases crystallized from the solution: either red,block-shaped crystals of (PyH)[Mo2O4Cl2(l2-Memal)Py2](5) (yield: 84% (133 mg)) or orange, needle-shaped crystals(155 mg).

Compound 5. Anal. Calc. for C19H21Cl2Mo2N3O8: C,33.45; H, 3.10; N, 6.16. Found: C, 33.34; H, 2.92; N,6.28%. Orange, needle-shaped crystals. Found: C, 33.10;H, 3.34; N, 5.88%. Selected IR bands (cm�1): 1731vvs,1557vvs, 1450vvs, 1434vvs, 1394vvs. 1H NMR (DMSO-d6, 300 MHz), d (ppm): 3.38 (2H, s, �OOCCH2COOCH3),3.64 (3H, s, �OOCCH2COOCH3), 7.55 (6H, m, H3,5), 7.97(3H, t, J = 7.9 Hz, H4) and 8.69 (6H, d, J = 6.0 Hz, H2,6).Only one set of pyridine signals was observed indicating thesubstitution of coordinated pyridine with the solvent.

2.1.7. Preparation of (3,5-LutH)[Mo2O4Cl2(l2-Memal)-

(3,5-Lut)2] (6)Malonic acid (104 mg, 1.00 mmol) was dissolved in the

mixture of 3,5-lutidine (1 cm3), methanol (5 cm3) and ace-tonitrile (0.5 cm3), followed by the addition of (PyH)5-[MoOCl4(H2O)]3Cl2 (200 mg, 0.466 mmol of Mo). Afterthe colour of the reaction mixture turned orange, diethylether (15 cm3) was added while stirring. The mixture wasallowed to stand at ambient conditions for a week. Red,needle-shaped crystals were collected by filtration. Yield:65% (116 mg). Anal. Calc. for C25H33Cl2Mo2N3O8: C,39.18; H, 4.34; N, 5.48. Found: C, 39.69; H, 4.64; N, 4.98%.

2.1.8. Preparation of (PyH)[Mo2O4Cl2(l2-Etmal)Py2]

(7)

Malonic acid (104 mg, 1.00 mmol) was dissolved in themixture of pyridine (1 cm3), ethanol (5 cm3) and acetoni-trile (0.5 cm3), followed by the addition of (PyH)5-[MoOCl4(H2O)]3Cl2 (200 mg, 0.466 mmol of Mo). Afterthe colour of the reaction mixture turned orange, diethylether (8 cm3) was added while stirring. The mixture wasallowed to stand at ambient conditions for two weeks.Orange, block-shaped crystals were collected by filtration.Yield: 76% (124 mg). Anal. Calc. for C20H23Cl2Mo2N3O8:C, 34.50; H, 3.33; N, 6.04. Found: C, 34.64; H, 3.39; N,5.48%.

2.1.9. Preparation of (3,5-LutH)[Mo2O4Cl2(l2-Prmal)-

(3,5-Lut)2] (8)

Malonic acid (104 mg, 1.00 mmol) was dissolved in themixture of 3,5-lutidine (1 cm3), 2-propanol (5 cm3) and ace-tonitrile (0.5 cm3), followed by the addition of (PyH)5-[MoOCl4(H2O)]3Cl2 (200 mg, 0.466 mmol of Mo). Thereaction mixture was left in a stoppered flask at ambientconditions for 3 days. Meanwhile its colour changed toorange. To this solution diethyl ether (1.5 cm3) was addedwhile stirring until a precipitate was observed. After 4 days


a small amount of orange block-shaped crystals of 8 wasseparated manually from white crystalline material.

2.1.10. Preparation of [{Mo2O4(l2-Memal)Py2}2-

(l2-OCH3)2] (9)

Malonic acid (104 mg, 1.00 mmol) was dissolved inthe mixture of pyridine (1 cm3), methanol (5 cm3) andacetonitrile (0.5 cm3), followed by the addition of(PyH)n[MoOBr4]n (300 mg, 0.586 mmol). The colour ofthe reaction mixture turned orange. The flask containingthe reaction mixture was stoppered and left to stand atambient conditions for one week. Yellow crystals were col-lected by filtration. Yield: 58% (95 mg). Anal. Calc. forC30H36Mo4N4O18: C, 32.05; H, 3.23; N, 4.98. Found: C,32.64; H, 3.21; N, 5.08%.

2.1.11. Reaction with monomethyl hydrogen malonate

(PyH)5[MoOCl4(H2O)]3Cl2 (200 mg, 0.466 mmol of Mo)was dissolved in the solution of monomethyl hydrogenmalonate (124 mg, 1.05 mmol) in methanol (5 cm3), pyri-dine (1 cm3) and acetonitrile (0.5 cm3). Orange solution ina stoppered flask was left to stand at ambient conditionsfor 24 h. Orange crystalline product was isolated by filtra-tion. The product was identified as compound 9 by itsinfrared spectrum. Yield: 36% (47 mg).

2.1.12. Reaction of (PyH)3[Mo2O4Cl4(l2-Hmal)] ÆCH3CN (1) with the mixture of malonic acid, methanol and

pyridine

Malonic acid (80 mg, 0.769 mmol) was dissolved inthe mixture of pyridine (1 cm3), methanol (5 cm3) andacetonitrile (0.5 cm3). To this solution (PyH)3[Mo2O4Cl4-(l2-Hmal)] Æ CH3CN (1) (280 mg, 0.358 mmol) was added.The flask was stoppered and left to stand at ambient con-ditions. Diethyl ether (5 cm3) was added on the followingday. The mixture was allowed to stand for ten days atambient conditions to let the product deposit from thesolution. Orange, crystalline product was isolated by filtra-tion. The product was identified as compound 9 by itsinfrared spectrum. Yield: 23% (46 mg).

2.1.13. Preparation of (PyH)[Mo2O4Cl2(l2-OOCCH3)Py2] ÆPy (10) and (PyH)[Mo2O4Cl2(l2-OOCCH3)Py2]

(11)

A mixture of (PyH)5[MoOCl4(H2O)]3Cl2 (400 mg,0.933 mmol of Mo), malonic acid (480 mg, 4.62 mmol)and pyridine (4 cm3) was placed in a glass tube whichwas sealed and heated for 5 days in an electric oven main-tained at 115 �C. The tube was allowed to cool slowly toroom temperature. A few, red crystals of 10, grew from adark violet solution over a period of one week. Crystalswere separated by decantation. The solvent was removedfrom the solution under vacuum. The residue was dissolvedin the mixture of pyridine (3 cm3) and methanol (1 cm3).To this solution diethyl ether (3.5 cm3) was added. A smallamount of orange plate-like crystals of 11 was obtainedafter one day.

Compound 10: Anal. Calc. for C22H24Cl2Mo2N4O6: C,37.57; H, 3.44; N, 7.97. Found: C, 37.41; H, 3.29; N,7.92%. Compound 11. Anal. Calc. for C17H19Cl2Mo2N3O6:C, 32.71; H, 3.07; N, 6.73. Found: C, 32.65; H, 2.88; N,6.55%. Same procedure was used for the preparation of(3,5-LutH)[Mo2O4Cl2(l2-OOCCH3)(3,5-Lut)2] (12) and(4-MePyH)3[Mo2O4Cl2(l2-OOCCH3)(4-MePy)2]2Cl (13)with 3,5-lutidine or 4-methylpyridine in place of pyridine.The yields were low, typically a few large, red crystals.Compound 12. Anal. Calc. for C23H31Cl2Mo2N3O6: C,39.00; H, 4.41; N, 5.93. Found: C, 39.08; H, 4.11; N,5.81%. Compound 13: Anal. Calc. for C23H29Cl2.5-Mo2N3.5O6: C, 37.79; H, 4.00; N, 6.71. Found: C, 37.66;H, 3.89; N, 6.80%. Note: The acetato complexes can be pre-pared in good yields following a more rational syntheticpathway, i.e., either by using acetate or acetic acid directly.The exact procedures will be described in a forthcomingmanuscript.

2.1.14. Preparation of (PyH)[Mo2O4Cl2(l2-Hsuc)Py2] ÆPy (14)

Succinic acid (118 mg, 1.00 mmol) was dissolved in themixture of pyridine (1 cm3), ethanol (5 cm3) and acetoni-trile (1.5 cm3). To this solution (PyH)5[MoOCl4(H2O)]3Cl2(200 mg, 0.466 mmol of Mo) was added. On the followingday diethyl ether (4 cm3) was added. The mixture wasallowed to stand for two weeks at ambient conditions.Orange crystalline product was collected by filtration andwashed with the hexanes. Yield: 65% (116 mg). Anal. Calc.for C24H26Cl2Mo2N4O8: C, 37.87; H, 3.44; N, 7.36. Found:C, 37.31; H, 3.37; N, 7.00%.

2.1.15. Reaction with monomethyl hydrogen succinate

(PyH)5[MoOCl4(H2O)]3Cl2 (200 mg, 0.466 mmol of Mo)was dissolved in the solution of monomethyl hydrogen suc-cinate (145 mg, 1.10 mmol) in methanol (5 cm3), pyridine(1 cm3) and acetonitrile (0.5 cm3). The mixture was allowedto stand for two days at ambient conditions. Orange, crys-talline product (54 mg) was separated by filtration. SelectedIR bands (cm�1): 2816w, 1739vs, 1575vs, 1566vs, 1447vvs,1422vvs, 1408vvs, 1361m, 560vs, 470s. 1H NMR (mixtureof D2O and DMSO-d6 in the volume ratio 1:3,300 MHz), d (ppm): 3.25 (3H, s, �OCH3), 3.64 (3H, s,�OOC(CH2)2COOCH3), 7.54 (4H, m, H3,5), 7.96 (2H, t,H4) and 8.57 (4H, d, H2,6). Note: The resonances are shiftedwhen compared to those in pure DMSO-d6. The resonanceof the methylene protons of monomethyl succinate over-laps with the DMSO signal (d = 2.57 ppm). The signal at3.25 ppm indicates the presence of methoxide ions in theproduct.

2.1.16. Preparation of (4-MePyH)2-

[{Mo2O4Cl2(4-MePy)2}2(l4-suc)] (15)

A glass tube was charged with (PyH)5[MoOCl4(H2O)]3Cl2 (400 mg, 0.933 mmol of Mo), succinic acid(200 mg, 1.70 mmol) and 4-methylpyridine (4 cm3). Thetube was sealed and heated for 5 days in an electric oven


maintained at 115 �C. The tube was allowed to cool slowlyto room temperature. The reaction mixture consisted of adark brown solution and small orange crystals of 15 whichgrew on the wall of the tube. Yield: 11% (34 mg). Anal.Calc. for C40H48Cl4Mo4N6O12: C, 36.11; H, 3.64; N,6.32. Found: C, 35.97; H, 3.75; N, 6.24%.

2.1.17. NMR spectra1H NMR spectra of the DMSO-d6 solutions, d (ppm): (i)

malonic acid: 3.27 (s); (ii) monomethyl hydrogen malonate:3.39 (2H, s, HOOCCH2COOCH3), 3.64 (3H, s, HOO-CCH2COOCH3); (iii) dimethyl malonate: 3.53 (2H, s,CH3OOCCH2COOCH3), 3.65 (6H, s, CH3OOCCH2-COOCH3); (iv) succinic acid: 2.46 (s); (v) monomethylhydrogen succinate: 2.52 (4H, m, HOOCCH2CH2-COOCH3), 3.60 (3H, s, HOOCCH2CH2COOCH3).

2.1.18. Esterification of malonic acid with methanol at

ambient conditions

Three flasks, labelled A, B and C, were each chargedwith malonic acid (104 mg, 1.0 mmol), methanol(5 cm3), pyridine (1 cm3) and acetonitrile (0.5 cm3).(PyH)5[MoOCl4(H2O)]3Cl2 (200 mg, 0.466 mmol of Mo)was added to flask B. Pyridinium chloride (310 mg,2.68 mmol) was added to flask C. The flasks were stopperedand left to stand at ambient conditions for 10 days. A400 mg aliquot from each flask was concentrated on therotary evaporator. The non-volatile residue was dissolvedin 0.7 cm3 of deuterated DMSO. The solutions wereinspected by NMR spectroscopy for the presence of unre-acted malonic acid, monomethyl and dimethyl malonate.The yields were determined from the ratios of the integralsof selected signals.

2.1.19. Esterification of succinic acid with methanol at

ambient conditions

Two flasks, labelled D and E, were each charged withsuccinic acid (118 mg, 1.00 mmol), methanol (5 cm3), pyri-dine (1 cm3) and acetonitrile (0.5 cm3). (PyH)5[MoOCl4-(H2O)]3Cl2 (200 mg, 0.466 mmol of Mo) was added to flaskE. The flasks were stoppered and left to stand at ambientconditions for 10 days. A 700 mg aliquot from each flaskwas concentrated on the rotary evaporator. The non-vola-tile residue was dissolved in 0.7 cm3 of deuterated DMSO.The solutions D and E were inspected by NMR spectros-copy for the presence of unreacted succinic acid, monom-ethyl and dimethyl succinate. The yields were determinedfrom the ratios of the integrals of selected signals.

2.1.20. X-ray crystallographic study

Data for compounds 1–15 were collected on a NoniusKappa CCD diffractometer using graphite monochro-mated Mo Ka radiation. Data reduction and integrationwere performed with the software package DENZO-SMN

[17]. Averaging of the symmetry-equivalent reflectionslargely compensated for the absorption effects. For allcompounds, the coordinates of some or all of the non-

hydrogen atoms were found via direct methods using thestructure solution program SHELXS [18]. The positions ofthe remaining non-hydrogen atoms were located by useof a combination of least-squares refinement and differenceFourier maps in the SHELXL-97 program [18]. All the calcu-lations were performed using the WinGX System Version1.64.05 [19]. Figures depicting the structures were preparedby ORTEP3 [20] and SHELXTL [21].The displacement ellipsoidsof all ORTEP figures were drawn at the 30% probability level.Cell parameters and refinement results are summarized inTable 1. The modest quality of the crystal of 4 resultedin large R1 and wR2 residuals. Consequently, the formula-tion of 4 as (3,5-LutH)2(H3O)[Mo2O4(g2-mal)2(l2-Hmal)]is not unambiguous. The lone oxygen atom as revealedfrom the solved structure is assumed to be actually ahydroxonium cation. In this way, the charges are balanced.The positions of hydrogen atoms of H3O+, which wouldsupport such a formulation, unfortunately could not belocated from the residual electron density map. Repeatedattempts to obtain crystals with better diffraction data havenot been successful. The systematic absences (0k0, k 6¼ 2n)for 13 allowed two space groups, P21/m and P21. The latterwas found to be correct after structure refinement.

3. Results and discussion

3.1. Structural data

The crystals of (PyH)3[Mo2O4Cl4(l2-Hmal)] Æ CH3CN(1) and (PyH)3[Mo2O4Br4(l2-Hmal)] Æ CH3CN (2) are iso-morphous. A dinuclear anion [Mo2O4Br4(l2-Hmal)]3� asfound in 2 is depicted in Fig. 3. Selected bond lengthsand angles for both compounds are given in Table 2. Theanion consists of the {Mo2O4}2+ structural core with fourhalo ligands and a Hmal� ligand, a half-neutralized acid,bound with its carboxylate moiety to a pair of metal atomsin the syn–syn bidentate bridging manner. The geometricparameters of the {Mo2O4}2+ core are (i) a separation of2.5859(3) A (compound 1) and 2.5767(4) A (compound 2)between a pair of metal atoms, and (ii) a nonplanarMo(l2-O)2Mo moiety with the fold angle of 160.08(5)�(1) and 158.77(6)� (2). The monoprotonated dicarboxylicacid function forms a six-membered ring (deviation fromplanarity, ±0.16 A) with the hydrogen atom locatedbetween O(6) and O(7) atoms, separated by 2.552(4) (1)and 2.568(4) A (2). This separation is indicative of a strongintramolecular hydrogen bond. Similar hydrogen-bondingmotif was observed for [Cu(Hmal)(Ph3P)2], where the sep-aration between the corresponding oxygen atoms is evenshorter, 2.500 A [22].

(PyH)2[Mo2O4Cl(g2-mal)(l2-Hmal)Py] (3) and(3,5-LutH)2(H3O)[Mo2O4(g2-mal)2(l2-Hmal)] (4) containtwo types of malonato ligands: apart from a bridginghydrogen malonate also a chelating malonate, which iscoordinated via two oxygen atoms, each from a differentcarboxylate group. The Hmal� ligand occupies a pair oftrans sites in both. Two out of four cis sites of the

Table 1Crystal data for compounds 1–15

1 2 3 4

Empirical formula C20H24Cl4Mo2N4O8 C20H24Br4Mo2N4O8 C21H22ClMo2N3O12 C23H30Mo2N2O17

Formula mass 782.11 959.95 735.75 794.34Crystal system monoclinic monoclinic monoclinic monoclinicSpace group P21/n P21/n Cc C2/mT (K) 150(2) 150(2) 293(2) 150(2)a (A) 10.9701(2) 11.0730(1) 8.6476(1) 22.1010(5)b (A) 13.8687(2) 13.8871(1) 34.8281(5) 15.5236(4)c (A) 18.9100(3) 19.3530(2) 9.0579(1) 10.9321(3)a (�) 90 90 90 90b (�) 90.422(7) 91.0208(5) 109.2387(6) 90.063(1)c (�) 90 90 90 90V (A3) 2876.91(8) 2975.47(5) 2575.70(6) 3750.7(2)Z 4 4 4 4k (A) 0.71073 0.71073 0.71073 0.71073l (mm�1) 1.292 6.262 1.146 0.733Collected reflections 11245 13143 20658 6291Unique reflections, Rint 5836, 0.0171 6787, 0.0239 5580, 0.0380 3509, 0.0192Observed reflections 5009 5740 5293 3071R1 [I > 2r(I)] 0.0325 0.0299 0.0278 0.0638wR2 (all data) 0.0869 0.0764 0.0633 0.2063

5 6 7 8

Empirical formula C19H21Cl2Mo2N3O8 C25H33Cl2Mo2N3O8 C20H23Cl2Mo2N3O8 C27H37Cl2Mo2N3O8

Formula mass 682.17 766.32 696.19 794.38Crystal system triclinic orthorhombic triclinic triclinicSpace group P�1 Pbna P�1 P�1T (K) 150(2) 293(2) 150(2) 150(2)a (A) 8.7050(1) 13.7954(1) 8.6597(1) 9.1522(2)b (A) 9.8779(1) 19.2171(2) 10.1523(2) 13.4384(3)c (A) 29.2861(3) 25.8494(4) 29.3712(5) 14.4757(3)a (�) 88.3971(4) 90 87.7225(7) 106.5433(8)b (�) 84.5570(5) 90 87.3314(7) 101.2021(8)c (�) 84.1830(5) 90 81.9421(8) 96.0479(9)V (A3) 2493.54(5) 6852.9(1) 2552.49(7) 1649.54(6)Z 4 8 4 2k (A) 0.71073 0.71073 0.71073 0.71073l (mm�1) 1.268 0.932 1.241 0.971Collected reflections 14346 11396 11565 13479Unique reflections, Rint 11138, 0.0198 6032, 0.0205 8529, 0.0217 7482, 0.0358Observed reflections 10544 4180 7861 6628R1 [I > 2r(I)] 0.0340 0.0564 0.0677 0.0450wR2 (all data) 0.1152 0.2313 0.2006 0.1261

9 10 11 12

Empirical formula C30H36Mo4N4O18 C22H24Cl2Mo2N4O6 C17H19Cl2Mo2N3O6 C23H31Cl2Mo2N3O6

Formula mass 1124.39 703.23 624.13 708.29Crystal system monoclinic monoclinic monoclinic triclinicSpace group P21/c P21/a P21/n P�1T (K) 150(2) 150(2) 293(2) 150(2)a (A) 9.2596(1) 16.5796(2) 8.76510(1) 8.8059(1)b (A) 12.6649(1) 8.8003(1) 19.1095(3) 11.2507(1)c (A) 16.1035(2) 18.6227(2) 27.3296(4) 15.1326(2)a (�) 90 90 90 74.1464(6)b (�) 95.3082(5) 100.0686(4) 98.2016(1) 85.5063(6)c (�) 90 90 90 69.6012(6)V (A3) 1880.39(3) 2675.31(5) 4530.8(1) 1351.52(3)Z 2 4 8 2k (A) 0.71073 0.71073 0.71073 0.71073l (mm�1) 1.386 1.181 1.380 1.168Collected reflections 8324 11660 12731 11255Unique reflections, Rint 4284, 0.0119 6125, 0.0144 7621, 0.0292 6174, 0.0149Observed reflections 3835 5475 6004 5552R1 [I > 2r(I)] 0.0246 0.0227 0.0471 0.0228wR2 (all data) 0.0719 0.0605 0.1025 0.0574


Table 1 (continued)

13 14 15

Empirical formula C23H29Cl2.5Mo2N3.5O6 C24H26Cl2Mo2N4O8 C40H48Cl4Mo4N6O12

Formula mass 731.00 761.27 1330.40Crystal system monoclinic triclinic monoclinicSpace group P21 P�1 P21/cT (K) 150(2) 150(2) 150(2)a (A) 9.2731(1) 8.8889(1) 9.7165(1)b (A) 30.7073(3) 9.8798(2) 27.7921(3)c (A) 10.0534(1) 17.8751(3) 28.6521(3)a (�) 90 100.1909(7) 90b (�) 96.1257(5) 102.0207(7) 98.2497(4)c (�) 90 95.8447(7) 90V (A3) 2846.38(5) 1495.39(4) 7657.2(1)Z 4 2 6k (A) 0.71073 0.71073 0.71073l (mm�1) 1.158 1.068 1.231Collected reflections 24232 12196 24850Unique reflections, Rint 10696, 0.025 6769, 0.0167 13442, 0.0307Observed reflections 10155 6154 10147R1 [I > 2r(I)] 0.0250 0.0285 0.0328wR2 (all data) 0.0714 0.0752 0.0756

Fig. 3. A drawing of [Mo2O4Br4(l2-Hmal)]3�, an anion of 2. A hydrogen bond within the hydrogen malonate is drawn in dashed lines. Same labellingscheme pertains to 1.


{Mo2O4}2+ core are occupied by the chelating malonate inthe anion of 3 (Fig. 4), while in the anion of 4 two malo-nates occupy all four cis sites (Fig. 5). Six-numbered che-late rings are formed with the angle of 84.36(9) (3) or86.4(2) and 85.2(3)� (4) subtended at molybdenum atoms.This type of malonate coordination has a widespreadoccurrence among complexes with several transition metal

cations [14]. The malonato chelate rings are known toadopt different conformations [23]. A boat conformationis observed in 3 with molybdenum and methylene carbondisplaced from the plane of the other four ring atoms.The malonato ligands in 4 are found in two different con-formations: one is in a boat conformation, while the otheradopts an envelope conformation with the methylene

Table 2Relevant geometric parameters (A, �) for [Mo2O4X4(l2-Hmal)]3�, anionsof 1 and 2

1 2

Mo–Mo 2.5859(3) 2.5767(4)Mo–Xa 2.4505(8)–2.4789(9) 2.5977(4)–2.6307(5)Fold angle 160.08(5) 158.77(6)Mo–O (Hmal�) 2.330(2), 2.357(2) 2.323(2), 2.364(2)C–C–C (Hmal�) 118.2(3) 118.3(3)C–O (COO� group) 1.259(4), 1.274(4) 1.260(4), 1.271(4)C@O (COOH group) 1.204(4) 1.193(5)C–O (COOH group) 1.317(5) 1.317(5)

a X = Cl for 1, X = Br for 2.


group significantly displaced from the plane of the otherfive atoms. The chelating malonates bind with bond lengthsof 2.078(2) and 2.081(2) A in 3 and 2.066(4) and 2.075(4) Ain 4. As a consequence of the trans influence of the Mo@Obonds, the l2-Hmal� ligand binds with significantly longerbond lengths, 2.286(3) and 2.293(3) A in 3 and 2.335(7) and2.345(7) A in 4. In contrast to compounds 1 and 2, the l2-Hmal� ligands of the anions in 3 and 4 do not form intra-molecular hydrogen bonds. Instead, an intermolecularhydrogen bond to the C@O group of the chelating malon-ate of the neighbouring anion is formed in 3. Infinite chainswhich propagate along the c-axis are thus formed (Fig. 6).The corresponding O� � �O separations are 2.558(4) A. Apair of non-equivalent C–O bond lengths within theCOOH moiety supports the hydrogen atom location whichwas deduced from the difference electron density map. It isof interest to note that the l2-Hmal� ligand in 4 partici-pates in no hydrogen bonds at all. The dinuclear anion

Fig. 4. A drawing of [Mo2O4Cl(g2-mal)(l2-Hmal)Py]2�, an anion of 3. Seangle = 161.9(2), Mo(1)–Cl(1) = 2.443(1), Mo(1)–N(1) = 2.261(3), Mo(2)–O(2O(12) = 2.286(3), C(4)–O(21) = 1.283(5), C(4)–O(23) = 1.234(4), C(6)–O(22O(11) = 1.263(4), C(1)–O(12) = 1.259(5), C(3)–O(13) = 1.316(4), C(3)–O(14) =

of 4, [Mo2O4(g2-mal)2(l2-Hmal)]3�, is located with someof its atoms on the mirror plane in the C 2/m space group.Consequently, the C–O bond lengths of the COOH groupare averaged. The separation between the carboxylic oxy-gen atoms and the nearest oxygen atom of the coordinatedcarboxylate, i.e., O(4)� � �O(6) = 3.180(11) A, is too long tosuggest a hydrogen-bonding interaction. The type of thehydrogen-bonding interaction of hydrogen malonate withits environment manifests in the overall conformation ofthe ligand. The pair of carboxylate groups of the Hmal�

ligand in 3 and 4 are thus not coplanar, as observed for 1

and 2, but almost (3) or exactly (4) perpendicular to eachother. An intricate hydrogen-bonding network involvingthe hydroxonium cations is observed in 4. Each hydroxo-nium cation forms four hydrogen bonds in an almost tetra-hedral arrangement, implying a disorder of hydrogenatoms. Bonds are formed to non-coordinated oxygens ofthe chelating malonates (Fig. 7). Layers, which are copla-nar with the ab plane, are thus formed. The correspondingO� � �O separations are 2.777(7) and 2.846(7) A.

The dinuclear anions of (PyH)[Mo2O4Cl2(l2-Memal)-Py2] (5), (3,5-LutH)[Mo2O4Cl2(l2-Memal)(3,5-Lut)2] (6),(PyH)[Mo2O4Cl2(l2-Etmal)Py2] (7) and (3,5-LutH)-[Mo2O4Cl2(l2-Prmal)(3,5-Lut)2] (8) consist of the central{Mo2O4}2+ core whose six coordination sites are distrib-uted among two chloro ligands, two pyridine/3,5-lutidineligands and monoalkyl malonate ester. The latter is coordi-nated via its carboxylate group in the syn–syn bidentatebridging manner. The conformation of the malonato ligandin all is such that the plane of one carboxylate functionforms a dihedral angle in the 80.5(5)–89.6(1.3)� range with

lected bond lengths (A) and angles (�): Mo(1)–Mo(2) = 2.5603(4), fold1) = 2.078(2), Mo(2)–O(22) = 2.081(2), Mo(1)–O(11) = 2.293(3), Mo(2)–) = 1.275(4), C(6)–O(24) = 1.230(4), C(4)–C(5)–C(6) = 120.1(3), C(1)–1.208(5) and C(1)–C(2)–C(3) = 113.9(3).

Fig. 5. A drawing of [Mo2O4(g2-mal)2(l2-Hmal)]3�, an anion of 4. Selected bond lengths (A) and angles (�): Mo(1)–Mo(2) = 2.5807(10), foldangle = 160.3(3), Mo(1)–O(11) = 2.066(4), Mo(2)–O(21) = 2.075(4), Mo(1)–O(4) = 2.335(7), Mo(2)–O(5) = 2.345(7), C(2)–O(11) = 1.299(8), C(2)–O(12) = 1.232(8), C(2)–C(1)–C(2)a = 118.8(8), C(4)–O(21) = 1.266(8), C(4)–O(22) = 1.218(9), C(4)–C(3)–C(4)a = 118.7(13), C(5)–O(4) = 1.276(12),C(5)–O(5) = 1.242(13), C(7)–O(6) = 1.233(14) and C(5)–C(6)–C(7) = 113.3(10); asymmetry operation: x, �y, z.

Fig. 6. Dinuclear anions of 3 are hydrogen-bonded into infinite chains which propagate along the c-axis. Molybdenum atoms are cross-hatched; chlorineatoms are lined bottom right to top left; nitrogen atoms are lined bottom left to top right; oxygen atoms are unshaded and carbon atoms are shaded,medium-sized spheres. Hydrogen atoms are represented by open, small-sized spheres.


the plane of the other. Both chloro ligands or both pyridineligands lie on the same side of the plane defined by a pair ofmolybdenyl groups. A complex anion with coordinatedmonoethyl malonate is depicted in Fig. 8. Selected bondlengths and angles for 5–8 are given in Tables 3 and 4.

The crystal structure of 9 consists of neutral, tetranu-clear molecules with the [{Mo2O4(l2-Memal)Py2}2-(l2-OCH3)2] composition (Fig. 9). A pair of methoxide ionsbridges two {Mo2O4}2+ moieties into a chain-like frag-ment. The metal–metal bond distance within the{Mo2O4}2+ moieties is as usually observed for singleMoV–MoV bonds, 2.5405(3) A, while the distance betweena pair of molybdenum atoms bridged by methoxide groupsis beyond any significant bonding interactions, 3.3540(4) A.The Mo(l2-OCH3)2Mo bridge is planar in contrast to thefolded Mo(l2-O)2Mo bridge with the fold angle of159.14(9)�. The monomethyl malonate occupies a pair oftrans positions within the {Mo2O4}2+ core. It is coordi-nated in the usual manner, via two oxygen atoms in thesyn–syn bidentate bridging mode. A pair of carboxylateplanes in the Memal� ligand forms a dihedral angle of75.8(3)�. The sixfold coordination environment of the ter-minal molybdenum atoms is completed by a pair of pyri-

dine ligands. All four metal atoms are thus in distortedoctahedral environments.

The anions [Mo2O4Cl2(l2-OOCCH3)(R-Py)2]�, as foundin compounds (PyH)[Mo2O4Cl2(l2-OOCCH3)Py2] Æ Py(10), (PyH)[Mo2O4Cl2(l2-OOCCH3)Py2] (11), (3,5-LutH)-[Mo2O4Cl2(l2-OOCCH3)(3,5-Lut)2] (12) and (4-MePyH)3-[Mo2O4Cl2(l2-OOCCH3)(4-MePy)2]2Cl (13), consist of thecentral {Mo2O4}2+ core. The distribution of ligands overthe six coordination sites of the {Mo2O4}2+ core is the samein all: the trans sites are occupied by the acetato oxygenatoms and the remaining four sites by two chloro and twopyridine/3,5-lutidine/4-methylpyridine ligands. The relativearrangement of chloro or aromatic ligands with respect toeach other is cis in all four complexes. A dinuclear anionof 13 is depicted in Fig. 10. Selected bond lengths and anglesfor compounds 10–13 are given in Table 5.

The dinuclear anion of (PyH)[Mo2O4Cl2(l2-Hsuc)Py2] ÆPy (14) consists of the central {Mo2O4}2+ structural corewith two chloro ligands, two pyridine ligands and ahydrogen succinate completing distorted octahedralenvironments of both metal atoms. The complex anion isdepicted in Fig. 11. The conformation of the Hsuc� ligandis such that a dihedral angle of 76.1(3)� is formed between a

Fig. 7. Hydroxonium cations connect dinuclear anions into infinite layersin 4.

Fig. 8. A drawing of [Mo2O4Cl2(l2-Etmal)Py2]�, an anion of 7.

Table 3Relevant geometric parameters (A, �) for [Mo2O4Cl2(l2-Memal)(R-Py)2]�,anions of 5 and 6

5a 6

Mo–Mo 2.5610(4), 2.5686(4) 2.5646(9)Fold angle 159.5(1), 160.4(1) 160.9(3)Mo–Cl 2.4440(9)–2.4503(9) 2.450(2), 2.465(2)Mo–N 2.234(3)–2.242(3) 2.230(6), 2.229(6)Mo–O (malonato ligand) 2.273(2) vs. 2.310(2),

2.260(2) vs. 2.322(2)2.285(5) vs. 2.298(5)

C–C–C (malonato ligand) 109.9(3), 108.2(3) 111.5(6)C–O (COO� group) 1.257(4), 1.265(4) 1.249(8), 1.266(8)

1.254(4), 1.263(4)C@O (methyl ester) 1.201(5), 1.198(5) 1.204(9)C(O)–O (methyl ester) 1.318(5), 1.339(5) 1.320(10)

a The asymmetric unit of 5 contains two dinuclear anions.

Table 4Relevant geometric parameters (A, �) for [Mo2O4Cl2(l2-Etmal)Py2]� (7)and [Mo2O4Cl2(l2-Prmal)(3,5-Lut)2]� (8)

7a 8

Mo–Mo 2.5589(12), 2.5689(12) 2.5730(4)Fold angle 159.0(4), 159.9(4) 160.4(1)Mo–Cl 2.441(3)–2.449(3) 2.4474(8), 2.4583(8)Mo–N 2.231(8)–2.252(9) 2.231(3), 2.241(3)Mo–O (malonato ligand) 2.248(7) vs. 2.312(7),

2.281(7) vs. 2.308(7)2.275(2) vs. 2.283(2)

C–C–C (malonato ligand) 108.9(9), 111.3(9) 110.3(3)C–O (COO� group) 1.260(12), 1.296(12) 1.265(4), 1.265(4)

1.251(12), 1.270(12)C@O (ester group) 1.184(15), 1.200(15) 1.200(5)C(O)–O (ester group) 1.329(16), 1.343(15) 1.329(5)

a The asymmetric unit of 7 contains two dinuclear anions.



pair of carboxylate planes. The carboxylic group is engagedin a hydrogen-bonding interaction with a pyridine solventmolecule, N� � �O = 2.636(4) A.

The tetranuclear anion of (4-MePyH)2[{Mo2O4Cl2-(4-MePy)2}2(l4-suc)] (15) consists of two {Mo2O4}2+ moi-eties linked together with a tetradentate succinate(Fig. 12). Succinate is coordinated with both carboxylategroups in the syn–syn bidentate bridging manner. Thegeometric parameters of the [{Mo2O4Cl2(4-MePy)2}2-(l4-suc)]2� anions are listed in Table 6. All four metalatoms lie in the plane. The succinato ligand with theexception of its hydrogen atoms also lies in this plane.Metal atoms are in distorted octahedral environmentswhich consist apart from the terminal oxo group, a pairof bridging oxo groups and a carboxylate oxygen, alsoof a chloro and a 4-methylpyridine ligand. The lattertwo ligands occupy the cis positions of the {Mo2O4}2+

core. The position of a pair of 4-methylpyridine ligandsin the dinuclear subunit is also cis with respect to eachother. The separations between molybdenum atoms fromthe {Mo2O4}2+ cores bridged by the succinate are in the9.300(1)–10.071(1) A range.

3.2. General structural considerations and comments on the

carboxylate ligation to the {Mo2O4}2+ core

The title complexes 1–15 possess the {Mo2O4(l2-OOCR)}+ structural fragment with the carboxylate moietybonded in the syn–syn bidentate bridging manner (Fig. 2).

Fig. 9. A drawing of [{Mo2O4(l2-Memal)Py2}2(l2-OCH3)2] (9). SelectedO(5) = 2.088(2), Mo(2)–O(5)a = 2.075(2), Mo(1)–N(1) = 2.260(2), Mo(1C(1)–O(11) = 1.285(3), C(1)–O(12) = 1.244(3), C(3)–O(13) = 1.325(3), C(3)–Oasymmetry operation: �x, 1 � y, �z.

The survey of the structurally characterized {Mo2O4}2+-containing compounds with the carboxylato ligands revealsthat this binding mode is the prevalent one [24]. The onlyother observed coordination mode is the unidentate one[25]. The rare {Mo2O4}2+ complexes with ligands withtwo or three carboxylate groups reveal the same bindingpatterns. For instance, the btcH2� ligand (an anion of1,3,5-benzenetricarboxylic acid with two deprotonated car-boxylic moieties) in [(Mo2O4Py3)2(l3-btcH)2] displays bothbinding modes: one of its carboxylate moieties is coordi-nated in the syn–syn bidentate bridging manner to one{Mo2O4}2+ core and the other in the unidentate mannerto another [13]. The protonated carboxylic group doesnot participate in coordination. On the other hand dicarb-oxylates in (Mo2O4Cl4)2(l4-hda)6� and [{Mo2O4(g2-mal)2}2(l4-mal)]6� fully exploited their binding abilities[13,26]. Both carboxylate groups of the bridging heptane-dioate/malonate coordinated in the syn–syn bidentatebridging manner, each to its own {Mo2O4}2+ moiety andthereby linked two dinuclear subunits into a tetranuclearcluster. Same type of dicarboxylate coordination isadopted by succinate in 15. To sum up, the series of dicarb-oxylates which serve as linkers between two {Mo2O4}2+

cores now includes oxalate, malonate, succinate and hep-tanedioate. In the case of two, oxalate and heptanedioate,a conformational isomerism of the l4-bridging ligand wasobserved. Two compounds of the [(Mo2O4Cl4)2(l4-hda)]6�

anion with different alkyl chain conformations wereisolated. Consequently, the two isomeric forms of the

bond lengths (A) and angles (�): Mo(1)–Mo(2) = 2.5405(3), Mo(2)–)–N(2) = 2.260(2), Mo(1)–O(11) = 2.192(2), Mo(2)–O(12) = 2.455(2),(14) = 1.202(3), O(13)–C(4) = 1.455(4) and C(1)–C(2)–C(3) = 112.2(2);

Fig. 10. A drawing of [Mo2O4Cl2(l2-OOCCH3)(4-MePy)2]�, an anion of 13.

Table 5Relevant geometric parameters (A, �) for [Mo2O4Cl2(l2-OOCCH3)(R-Py)2]�, anions of 10–13

10 11a 12 13a

Mo–Mo 2.5648(2) 2.5646(7), 2.5684(8) 2.5671(2) 2.5566(6), 2.5567(6)Fold angle 163.45(8) 161.5(2), 162.2(3) 163.64(7) 161.3(2), 159.6(2)Mo–Cl 2.4412(5), 2.4543(5) 2.439(2)–2.472(2) 2.4565(5), 2.4593(5) 2.455(1)–2.466(1)Mo–N 2.239(2), 2.241(2) 2.241(5)–2.245(4) 2.244(2), 2.243(2) 2.215(5)–2.239(4)Mo–O (acetate) 2.243(1) vs. 2.261(1) 2.265(4) vs. 2.278(4) 2.231(1) vs. 2.259(1) 2.263(4) vs. 2.271(4)

2.254(4) vs. 2.296(4) 2.281(3) vs. 2.285(4)C–O (COO� group) 1.265(2), 1.268(2) 1.266(7), 1.277(7) 1.264(2), 1.272(2) 1.269(6), 1.269(6)

1.245(7), 1.267(7) 1.264(6), 1.268(6)

a The asymmetric unit contains two dinuclear anions.

Fig. 11. A drawing of [Mo2O4Cl2(l2-Hsuc)Py2]�, an anion of 14, and a hydrogen-bonded pyridine molecule. Selected bond lengths (A) and angles (�):Mo(1)–Mo(2) = 2.5617(3), fold angle = 160.6(1), Mo(1)–Cl(1) = 2.4518(7), Mo(2)–Cl(2) = 2.4491(7), Mo(1)–N(1) = 2.234(2), Mo(2)–N(2) = 2.243(2),Mo(1)–O(5) = 2.257(2), Mo(2)–O(6) = 2.303(2), C(1)–O(5) = 1.267(3), C(1)–O(6) = 1.269(3), C(4)–O(7) = 1.317(4) and C(4)–O(8) = 1.213(4).


tetranuclear anion differ not only in the mutual orienta-tions of carboxylate moieties, but also in the separationsbetween the two {Mo2O4}2+ cores. The conformational

isomers of the oxalato-bridged complexes were of twotypes: the l4-oxalate adopted either a planar [27] or anextremely rare, completely staggered conformation [8].

Fig. 12. A drawing of [{Mo2O4Cl2(4-MePy)2}2(l4-suc)]2�, an anion of 15. Hydrogen atoms were omitted for clarity.

Table 6Relevant geometric parameters (A, �) for [{Mo2O4Cl2(4-MePy)2}2-(l4-suc)]2�, anions of 15

Mo–Mo 2.5628(4), 2.5726(4), 2.5712(4)Fold angle 163.6(1), 163.4(1), 163.3(1)Mo–Cl 2.4395(9)–2.466(1)Mo–N 2.229(3)–2.267(3)Mo–O (suc2�) 2.240(2) vs. 2.249(2)

2.234(2) vs. 2.277(2)2.251(2) vs. 2.275(2)

C–O (COO� group) 1.256(4), 1.276(4)1.267(4), 1.269(4)1.264(4), 1.264(4)


The structural features of the {Mo2O4(l2-OOCR)}+

fragment merit further comment. The fold angles,ca. 160� in compounds 1–15, are larger than in the{Mo2O4}2+-containing compounds without the thirdbridging ligand, for example a dihedral angle of149.62(6)� is formed by a pair of Mo(l2-O)2 planes in(MeNC5H5)2[Mo2O4(g2-C2O4)2Py2] [8]. The increase maybe attributed to the short O� � �O distance of the bridgingOCO group [26]. A series of squarato complexes[Mo2O4(l2-C4O4)(R-Py)4], where the distance between thecoordinated oxygen atoms of the bridging ligand is longer,displays normal fold angles of ca. 150� [9]. Although longermetal–metal bond lengths are expected with larger foldangles, the compounds 1–15 display bond lengths which fallwithin the normal range. The coordinated carboxylate moi-ety is almost coplanar with the plane of two molybdenylgroups. The largest misalignment of the two planes is found

in 15 with a dihedral angle of 17.9(3)� between the two planes.Furthermore, several complexes in the series 1–15 display anon-equivalence of the molybdenum-to-carboxylato-oxygenbond lengths. The most pronounced asymmetry is observedin 9 with the l2-Memal� ligand bonded at 2.192(2) and2.455(2) A. On the other hand, complex 13, where the ace-tate is bonded at 2.263(4)–2.285(4) A, shows very little or noasymmetry at all. Examples of the asymmetric binding mayalso be found among the literature examples, i.e., 2.277(7)versus 2.335(6) A in [Mo2O4(SCN)4(OOCCH3)]3�[24a].No explanation can be provided in either case.

Complex 9 possesses a rare tetranuclear core, which con-sists of two dinuclear subunits bridged by two methoxidegroups, {Mo2O4(l2-OCH3)2Mo2O4}2+. Alkoxide-assistedassembly of {Mo2O4}2+ units is a well-known process,but it usually results in a more condensed structure,{Mo4O4(l3-O)2(l2-O)2(l2-OCH3)2}2+ core with the rhombicarrangement of molybdenum atoms [3]. In contrast to severalcomplexes with the later structure, the literature reports ononly five more complexes with the chain-like {Mo2O4-(l2-OR)2Mo2O4}2+ (R = alkyl) fragment: methoxide-bridged ½Mo4O8ðOMeÞ2ðMeOHÞ2ðHBðpzÞ3Þ2�ðHBðpzÞ3�¼ hydrotripyrazolylborateÞ [28], i-propoxide-bridged[Mo4O10ðOiPrÞ12MVI

2] (M = Mo, W) [29,30] and [Mo4O8-ðOiPrÞ14MV

2] (M = Ta, Nb) [30].

3.3. Infrared spectroscopy

All the complexes show strong bands in the 1619–1529and 1449–1343 cm�1 regions attributable to the carboxylate

Table 7m(COO) frequencies (cm�1) for compounds 1–15

masym(COO) msym(COO)

1 1555, 1530 1411, 13782 1557, 1531 1413, 13733 1558, 1536 1442, 1411, 13684 1619, 1580 13705 1557 1448, 1415, 14026 1564 1434, 13927 1557 1449, 1418, 1401, 13659 1587 1447, 1428, 1378

10 1529 1445, 1434, 1410, 134611 1537 1435, 1427, 134913 1532 1433, 134314 1536 1446, 1432, 1414, 139515 1538 1406

2 The unit cell dimensions of the orange, needle-like crystals area = 7.3376(4), b = 10.5807(3), c = 18.6128(6) A, a = 94.981(2),b = 100.712(8), c = 98.682(7)�, V = 1393.74(4) A3.


masym(COO) and msym(COO) vibrations, respectively (seeTable 7) [31]. Additional absorptions due to the esterC@O stretching vibrations are observed in the spectra ofcomplexes with monoalkyl malonates: a single band for 6

(at 1723 cm�1) and 9 (at 1745 cm�1). Two distinct bandsare observed for compounds 5 and 7, at 1748 and1716 cm�1 for 5 and at 1739 and 1721 cm�1 for 7. Possibleexplanation for the appearance of two bands lies in the factthat the asymmetric unit of both compounds contains twodinuclear anions and therefore two ester moieties in slightlydifferent environments. A strong absorption at 1731 (com-pound 1), 1734 (2), 1717 (3) and 1729 (4) cm�1 confirmsthe presence of the non-ionized carboxylic moiety of theHmal� ligand. In the spectrum of 14, a complex with theHsuc� ligand, two bands occur in this spectral region, at1709 and 1682 cm�1.

3.4. Synthetic considerations

The starting materials, (PyH)5[MoOCl4(H2O)]3Cl2 and(PyH)n[MoOBr4]n, have demonstrated over their use inthe past decade, that they undergo an almost instantaneoussubstitution of halo ligands in moist solvents [3b]. This pro-cess ultimately results in the formation of species with the{Mo2O4}2+ core. Addition of a half-neutralized malonicacid, Hmal�, to the acetonitrile solution of either startingmaterial afforded complexes with hydrogen malonate,(PyH)3[Mo2O4X4(l2-Hmal)] Æ CH3CN (1 and 2). Acetoni-trile, with a weak coordinating ability, enables isolationof species with a relatively high content of halo ligands.In order to prevent the self-assembly of {Mo2O4}2+ units,an excess of the ligand has to be used. As a source ofHmal� ions, we used its pyridinium salt whose compositionwas PyH+Hmal� Æ H2mal.1 The initial attempts, when anacetonitrile solution of pyridine and malonic acid in a 1:1molar ratio was used, resulted in a complex with pyridine,(PyH)2[Mo2O4Cl(g2-mal)(l2-Hmal)Py] (3). Obviously, thesolution of reagents contained a sufficient amount of freepyridine to allow its coordination. Both (PyH)2[Mo2O4Cl-(g2-mal)(l2-Hmal)Py] (3) and (3,5-LutH)2(H3O)-[Mo2O4(g2-mal)2(l2-Hmal)] (4) contain fully deprotonated

malonate ions. The formation of 4 is rather surprising.It took place in a milieu which contained apart fromthe source of malonate ions two other strong ligands inexcessive amounts, 3,5-lutidine and methanol. This systemwas expected to produce a different product, a specieswith coordinated half-ester and 3,5-lutidine. Since(PyH)n[MoOBr4]n was used as a starting material, the antic-ipated product was [Mo2O4Br2(l2-Memal)(3,5-Lut)2]�.The use of the more reactive starting material providesan explanation for a different reaction course. The greaterlability of bromo ligands ensures their substitution to becomplete and consequently more sites of the {Mo2O4}2+

core are made available for coordination. It is unclearthough, why 3,5-lutidine ligands did not coordinate toany of these sites.

As stated above, the reaction mixtures containing alco-hols and malonic acid afforded complexes with monoalkylmalonate esters. The choice of alcohol as a solvent wasgoverned by the good alcohol solubility of both acids.The in situ formed monoalkyl malonate esters bondedwith their available carboxylate moiety in the usual syn–syn bidentate bridging manner. To the best of ourknowledge, these are the first structurally characterizedmonoalkyl malonato complexes. The esterification reac-tions took place at ambient conditions over a period ofone to two weeks. The yields were relatively good. Thereaction mixture of pyridine and methanol produced twocrystalline phases: red, block-shaped crystals of (PyH)-[Mo2O4Cl2(l2-Memal)Py2] (5) and orange, needle-likecrystals. Although the composition of the second phasewas not determined by X-ray crystallography, the resultsof elemental analysis, infrared and NMR spectra stronglysuggest its composition to be also (PyH)[Mo2O4Cl2-(l2-Memal)Py2], only a different polymorph.2 A changeof the starting material, when the more reactive (PyH)n-[MoOBr4]n was used in place of (PyH)5[MoOCl4(H2O)]3-Cl2, again resulted in a different product. A neutralcomplex, without any bromo ligands, [{Mo2O4(l2-Memal)-Py2}2(l2-OCH3)2] (9), was isolated instead of the antici-pated [Mo2O4Br2(l2-Memal)Py2]�. It is of interest to notethat a complex with hydrogen malonate, specifically(PyH)3[Mo2O4Cl4(l2-Hmal)] Æ CH3CN (1), also reacted atambient conditions with the mixture of malonic acid,pyridine and methanol. Surprisingly, the isolated productdid not contain [Mo2O4Cl2(l2-Memal)Py2]�, but it wasrather a neutral, tetranuclear complex [{Mo2O4(l2-Memal)Py2}2(l2-OCH3)2] (9). The latter result does notprovide an unambiguous proof that the coordinated hydro-gen malonate underwent the esterification since such a reac-tion outcome was observed only in the presence of malonicacid. Furthermore, when monomethyl hydrogen malonatewas used directly instead of malonic acid, the half-estercoordinated to the {Mo2O4}2+ core and the tetranuclear


compound 9 precipitated from the solution as the finalproduct. This result implies a different sequence of the pro-cesses, i.e., the esterification preceeding the coordination ofthe malonato ligand to the {Mo2O4}2+ core. In order toprovide answers to the question whether and to what extentthe molybdenum species affect the esterification, additionalexperiments were performed. Three reaction mixtures, sim-ilar to that used for the preparation of 5, were set up. Theywere labelled A, B and C. All three contained equalamounts of malonic acid, methanol, pyridine and acetoni-trile. (PyH)5[MoOCl4(H2O)]3Cl2 was added to flask B anda stoichiometric amount of pyridinium chloride to flaskC. Through molybdenum(V) starting material, a source ofpotential catalyst, a significant amount of pyridinium cat-ions is introduced into the system. Furthermore, the hydro-lysis of the [MoOCl4(H2O)]� ions entails a substantialacidification of the reaction medium. After ten days atambient conditions the contents of the flasks were inspectedby NMR spectroscopy for the presence of unreacted malo-nic acid, monomethyl and dimethyl malonate. No unre-acted malonic acid was found in flask B. In the presenceof molybdenum(V) species all malonic acid transformedinto monomethyl hydrogen malonate. On extending thereaction times dimethyl malonate formed. After two weeks,9.5% of malonic acid transformed into dimethyl ester.Reaction mixtures A and C were shown to contain mostlyunreacted malonic acid and monomethyl hydrogen malon-ate as a minor component (9.4% of all malonic acid in A,13.6% in C). The greater amount of monoalkyl ester inthe reaction mixture C is in accordance with the known cat-alytic role of Brønsted acids over the esterification. Analo-gous experiment was carried out also with succinic acid.(PyH)5[MoOCl4(H2O)]3Cl2 was added to one of the tworeaction mixtures which both contained equal amounts ofsuccinic acid, methanol, pyridine and acetonitrile. Afterten days at ambient conditions both mixtures containedmostly unreacted succinic acid and only small amounts ofmonomethyl hydrogen succinate (9.1% of all succinic acidtransformed into monomethyl hydrogen succinate whenmolybdenum(V) was present and 2.7% without it). The pre-sented results show that the extent of the esterification isincreased in the presence of molybdenum(V) species. Atthe same time, the extent of esterification of succinic acidis much smaller in comparison to malonic acid. This couldalso explain why a complex with hydrogen succinate andnot with monomethyl succinate was isolated from such areaction mixture (see Preparation of 14). Apparently theamount of the in situ formed half-ester was too small. Whenmonomethyl hydrogen succinate was used directly, themonomethyl ester coordinated as confirmed by the NMRspectrum of the isolated product. The catalytic role ofmolybdenum is not surprising, since many transition metalsalts are known to catalyze the esterification reactions [32].Of a particular relevance to our system is a recent study of acatalytic role of a very reactive molybdenum(V) ethoxidecomplex, [Mo2O2Cl4(l2-OC2H5)2(l2-HOC2H5)] [33]. Thealkoxide ligand which probably originated from the metal

coordination sphere attacked the carboxylic centre produc-ing the corresponding ester.

Solvothermal reactions at 115 �C were employed withthe aim to prepare complexes with less auxiliary ligationand higher dimensionality. The reactions with succinic acidyielded (4-MePyH)2[{Mo2O4Cl2(4-MePy)2}2(l4-suc)] (15),a complex with both carboxylate moieties of the ligandcoordinated in the syn–syn bidentate bridging manner.Although malonic acid is known to decarboxylate at ca.100–150 �C [34], we hoped that the thermal stability ofthe coordinated malonate would be greater and its decom-position would not take place at 115 �C. The thermogravi-metric analysis of 1, a complex with a hydrogen malonate,has shown that its decomposition with the evolution of car-bon dioxide starts around 120 �C. Nevertheless, from themixtures treated solvothermally only complexes with ace-tate, the decarboxylation product of malonic acid, wereisolated.

4. Conclusions

Several {Mo2O4}2+-containing complexes wereprepared by reacting (PyH)5[MoOCl4(H2O)]3Cl2 or(PyHn[MoOBr4]n with malonic or succinic acid. Theirstructures provide further evidence that the {Mo2O4-(l2-OOCR)}+ fragment represents a recurrent structuralmotif among the molybdenum(V) carboxylato complexes.One carboxylate function of the ligand bonded in the syn–syn bidentate bridging manner to the {Mo2O4}2+ core,while the other either remained protonated or formed anester when the reaction mixture contained alcohol. Reac-tions at elevated temperatures forced both carboxylatemoieties of the succinate to coordinate, each to its own{Mo2O4}2+ core. Analogous attempts with malonic acidresulted in its decarboxylation and formation of theacetato complexes.

5. Supplementary materials

CCDC 294405, 294406, 294407, 294408, 294409,294410, 294411, 294412, 294413, 294414, 294415,294416, 294417, 294418 and 294419 contain the supple-mentary crystallographic data for 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14 and 15. These data can be obtainedfree of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge CrystallographicData Centre, 12 Union Road, Cambridge CB2 1EZ,UK; fax: (+44) 1223-336-033; or e-mail: [email protected].

Acknowledgements

This work was supported by the Ministry of HigherEducation, Science and Technology of the Republic ofSlovenia through research grant P1-0134. We are gratefulto Mrs. Barbara Novosel for the EGA analysis.

http://www.ccdc.cam.ac.uk

http://www.ccdc.cam.ac.uk


References

[1] S.L. James, Chem. Soc. Rev. 32 (2003) 276, and references citedtherein.

[2] (a) F.A. Cotton, A. de Meijere, C.A. Murillo, K. Rauch, R. Yu,Polyhedron 25 (2006) 219;(b) F.A. Cotton, J.P. Donahue, C. Lin, C.A. Murillo, Inorg. Chem.40 (2001) 1234;(c) F.A. Cotton, C. Lin, C.A. Murillo, Inorg. Chem. 40 (2001) 575;(d) F.A. Cotton, L.M. Daniels, C. Lin, C.A. Murillo, J. Am. Chem.Soc. 121 (1999) 4538;(e) F.A. Cotton, C. Lin, C.A. Murillo, Inorg. Chem. 40 (2001) 478;(f) F.A. Cotton, L.M. Daniels, C. Lin, C.A. Murillo, Chem.Commun. (1999) 841.

[3] (a) H.K. Chae, W.G. Klemperer, T.A. Marquart, Coord. Chem.Rev. 128 (1993) 209;(b) B. Modec, J.V. Brencic, J. Cluster Sci. 13 (2002) 279.

[4] (a) C.M. French, J.H. Garside, J. Chem. Soc. (1962) 2006;(b) P.C.H. Mitchell, J. Inorg. Nucl. Chem. 26 (1964) 1967;(c) F.A. Cotton, S.M. Morehouse, Inorg. Chem. 4 (1965) 1377;(d) P.C.H. Mitchell, Quart. Rev. 20 (1966) 103.

[5] (a) W.S. McDonald, Acta Crystallogr. B 34 (1978) 2850;(b) B. Kamenar, B. Kaitner, N. Strukan, Croat. Chem. Acta 64(1991) 329.

[6] B. Modec, D. Dolenc, J.V. Brencic, J. Koller, J. Zubieta, Eur. J.Inorg. Chem. (2005) 3224.

[7] B. Modec, J.V. Brencic, D. Dolenc, J. Zubieta, J. Chem. Soc., DaltonTrans. (2002) 4582.

[8] B. Modec, J.V. Brencic, J. Koller, Eur. J. Inorg. Chem. (2004) 1611.[9] B. Modec, J.V. Brencic, E.M. Burkholder, J. Zubieta, Dalton Trans.

(2003) 4618.[10] R.L. Rardin, W.B. Tolman, S.J. Lippard, New J. Chem. 15 (1991) 417.[11] (a) A.D. Burrows, A.S. Donovan, R.W. Harrington, M.F. Mahon,

Eur. J. Inorg. Chem. (2004) 4686;(b) C.A. Williams, A.J. Blake, P. Hubberstey, M. Schroder, Chem.Commun. (2005) 5435;(c) D. Sun, Y. Ke, T.M. Mattox, B.A. Ooro, H.-C. Zhou, Chem.Commun. (2005) 5447;(d) X. He, C.-Z. Lu, D.-Q. Yuan, L.-J. Chen, Q.-Z. Zhang, C.-D.Wu, Eur. J. Inorg. Chem. (2005) 4598;(e) Y.B. Go, X. Wang, E.V. Anokhina, A.J. Jacobson, Inorg. Chem.44 (2005) 8265;(f) A. Thirumurugan, M.B. Avinash, C.N.R. Rao, Dalton Trans.(2006) 221;(g) S. Zang, Y. Su, Y. Li, Z. Ni, Q. Meng, Inorg. Chem. 45 (2006)174;(h) M. Kurmoo, H. Kumagai, M. Akita-Tanaka, K. Inoue, S.Takagi, Inorg. Chem. 45 (2006) 1627;(i) D.A. Dickie, G. Schatte, M.C. Jennings, H.A. Jenkins, S.Y.L.Khoo, J.A.C. Clyburne, Inorg. Chem. 45 (2006) 1646.

[12] B. Modec, J.V. Brencic, Inorg. Chem. Commun. 7 (2004) 516.[13] B. Modec, J.V. Brencic, Eur. J. Inorg. Chem. (2005) 4325.[14] F.H. Allen, O. Kennard, R. Taylor, Acc. Chem. Res. 16 (1983) 146.[15] (a) B. Modec, J.V. Brencic, Eur. J. Inorg. Chem. (2005) 1698;

(b) G.R. Hanson, A.A. Brunette, A.C. McDonell, K.S. Murray,A.G. Wedd, J. Am. Chem. Soc. 103 (1981) 1953.

[16] (a) R.E. Strube, Org. Synth. IV (1963) 417;(b) S. Niwayama, J. Org. Chem. 65 (2000) 5834.

[17] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1997) 307.[18] G.M. Sheldrick, SHELXS-97 and SHELXL-97, Universitat Gottingen,

1997.[19] G.X. Win, L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.

[20] ORTEP3 for Windows L.J. Farrugia, J. Appl. Crystallogr. 30 (1997)565.

[21] SHELXTL version 5.03, Siemens Analytical X-ray Instrument Division,Madison, WI, 1994.

[22] D.J. Darensbourg, M.W. Holtcamp, B. Khandelwal, J.H. Reibens-pies, Inorg. Chem. 33 (1994) 531.

[23] (a) K.R. Butler, M.R. Snow, J. Chem. Soc., Dalton Trans. (1976)259;(b) C.G. van Kralingen, J. Reedijk, A.L. Spek, Inorg. Chem. 19(1980) 1481.

[24] (a) The syn–syn bidentate bridging coordination was observed for: (a)acetate in [Mo2O4(SCN)4(l2-OOCCH3)]3� T. Glowiak, M. Sabat, H.Sabat, M.F. Rudolf, J. Chem. Soc., Chem. Commun. (1975) 715;(b) Hglyc� (monoanion of glycolic acid) in [Mo8O16(glyc)6(Hglyc)2]6�

Z.-H. Zhou, S.-Y. Hou, Z.-X. Cao, H.-L. Wan, S.-W. Ng, J. Inorg.Biochem. 98 (2004) 1037;(c) zwitter ionic form of glycine in [Mo2O4(glycinato-N,O)2(l2-glycine)] G. Liu, J. Liu, Y.-G. Wei, Q. Lin, S.-W. Zhang, ActaCrystallogr. C 56 (2000) 822;(d) zwitter ionic form of 3-(2-thienyl)-DL-alanine (abbreviated asthala) in [Mo2O4(acac)2(l2-thala)] M. Cindric, N. Strukan, T. Kajfez,G. Giester, B. Kamenar, Inorg. Chem. Commun. 3 (2000) 281;(e) acetate and formate in oligonuclear pyrophosphate complexes[Na4(H2O)6{(Mo2O4)10(O3PCH2PO3)10(CH3COO)8(H2O)4}]24� and[Na2{(Mo2O4)10(O3PCH2PO3)10(HCOO)10}]28�, respectively C. duPeloux, A. Dolbecq, P. Mialane, J. Marrot, F. Secheresse, DaltonTrans. (2004) 1259.

[25] (a) The unidentate coordination of carboxylate was observed for: (a)formate in [Mo2O4(l2-OOCH)(OOCH)4]3� B. Kamenar, M. Penavic,B. Markovic, Acta Crystallogr. C 43 (1987) 2275;(b) difluoroacetate in [Mo2O4(OOCCHF2)2(2,20-bipy)2] T.R. Webb,E.S. Talbott, Acta Crystallogr. C 55 (1999) 370.

[26] T. Shibahara, H. Kuroya, K. Matsumoto, S. Ooi, Inorg. Chem. Acta54 (1981) L75.

[27] (a) T. Shibahara, S. Ooi, H. Kuroya, Bull. Chem. Soc. Jpn. 55 (1982)3742;(b) K. Mannemann, R. Mattes, J. Chem. Res. 100 (1979) 1343;(c) A. Dolbecq, B. Salignac, E. Cadot, F. Secheresse, Bull. Pol. Acad.Sci. 46 (1998) 237;(d) B. Kamenar, B. Kaitner, N. Strukan, Vestn. Slov. Kem. Drus. 39(1992) 357.

[28] S. Lincoln, S.A. Koch, Inorg. Chem. 25 (1986) 1594.[29] M.H. Chisholm, K. Folting, J.C. Huffman, C.C. Kirkpatrick, Inorg.

Chem. 23 (1984) 1021.[30] A. Johansson, M. Roman, G.A. Seisenbaeva, L. Kloo, Z. Szabo,

V.G. Kessler, J. Chem. Soc., Dalton Trans. (2000) 387.[31] (a) K. Nakamoto, Infrared and raman spectra of inorganic and

coordination compounds. Part B: Applications in coordination, fifthed. Organometallic and Bioinorganic Chemistry, John Wiley & Sons,Inc., New York, 1997, p. 59–62;(b) G. Socrates, Infrared Characteristic Group Frequencies. Tablesand Charts, second ed., John Wiley & Sons, New York, 1997, pp. 90–93, 96–98 and 236–237.

[32] K. Mantri, R. Nakamura, K. Komura, Y. Sugi, Chem. Lett. 34(2005) 1502.

[33] M. Hunger, C. Limberg, L. Zsolnai, Polyhedron 17 (1998) 3935.[34] (a) T.W.G. Solomons, Organic Chemistry, sixth ed., John Wiley &

Sons, Inc., New York, 1996, pp. 833–835;(b) M.B. Smith, J. March, March’s Advanced Organic Chemistry,fifth ed., Wiley, New York, 2001, pp. 808–811;(c) F.A. Carey, R.J. Sundberg, Advanced Organic Chemistry, Part B,second ed., Plenum Press, New York, 1984, p. 14.

New molybdenum(V) complexes based on the {Mo2O4}2+ structural core with esters or anions of malonic and succinic acid

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