Five New Cobalt(II) and Copper(II)-1,2,4,5-benzenetetracarboxylate Supramolecular Architectures: Syntheses, Structures, and Magnetic Properties

Five New Cobalt(II) and Copper(II)-1,2,4,5-benzenetetracarboxylateSupramolecular Architectures: Syntheses, Structures, and MagneticProperties

Arpi Majumder,† Volker Gramlich,‡ Georgina M. Rosair,§ Stuart R. Batten,|

Jason D. Masuda,⊥ M. S. El Fallah,*,O Joan Ribas,O Jean-Pascal Sutter,#

Cedric Desplanches,3 and Samiran Mitra*,†

Department of Chemistry, JadaVpur UniVersity, Kolkata-700 032, India, Department of Chemistry,Laboratorium fur Kristallographie ETH, Eidgeno¨ssische Technische Hochschule Zu¨rich,CH-8092 Zu¨rich, Switzerland, Department of Chemistry, Heriot-Watt UniVersity,Edinburgh EH14 4AS, U.K., School of Chemistry, P. O. Box 23, Monash UniVersity, 3800, Australia,Department of Chemistry and Biochemistry, UniVersity of Windsor, 401 Sunset AVenue,Windsor, Ontario, Canada, Departament de Quı´mica Inorganica, 25 UniVersitat de Barcelona,Martı i Franques, 1-11, 08028-Barcelona, Spain, Laboratoire de Chimie de Coordination du CNRS,UniVersitePaul Sabatier, 205 route de Narbonne, F-31077 Toulouse, France, and Institut de Chimiede la Matiere Condenseé de Bordeaux-CNRS, UniVersiteBordeaux, 187 aVenue du Dr Schweitzer,33 608 Pessac, Cedex, France

ReceiVed June 6, 2006; ReVised Manuscript ReceiVed July 23, 2006

ABSTRACT: 1,2,4,5-Benzenetetracarboxylic acid (H4btec) and a combination ofN-donorcoligands, such as 4-aminopyridine (4-apy), pyrazine (pyz), 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), and 4,4′-bipyridine (4,4′-bipy) with transition metal ions Co(II) andCu(II), give rise to five coordination complexes namely, [{Co(H2btec)(H2O)4}‚4-apy‚(H2O)2]n (1), [{Cu(btec)(4-apy)2}‚(4-Hapy)2‚(H2O)4]n (2), [{Cu(H3btec)2(pyz)‚(H2O)2}‚H2O]n (3), [Co(tptz)(H2O)2(H2btec)]‚(H2O)2 (4), and [{Co2(4,4′-bipy)2(H2O)8}‚(btec)‚(H2O)2]n (5). All these complexes form supramolecular frameworks through ligand-based hydrogen bonding interactions. They havebeen characterized by a combination of analytical, spectroscopic, and crystallographic methods. These highly crystalline complexeshave been obtained under different pH conditions at room temperature and the btec binding mode differs in these five complexes.Complex1 is a one-dimensional (1D) layered solid consisting of alternating neutral metal-organic coordination polymeric chains,[Co(H2btec)(H2O)4]n, and amines whereas the molecular structure of2 is made up of alternating layers of anionic [Cu(btec)(4-apy)2]2-

n coordination polymers and 4-apy cations (4-Hapy). In both1 and2, btec links the metal centers. Complex3 is composedof zigzag 1D copper chains, and complex4 is a mononuclear cobalt complex. In both3 and4, btec binds as a monodentate ligand.In the crystal structure of5, btec4- is present unbound in the lattice and linked to 1D chains of [Co(4,4′-bipy)(H2O)4]2+ throughstrong hydrogen bonding interactions. The magnetic properties of the polymers were investigated in the temperature range 300-2K. The values for the spin coupling constantJ were estimated to be-0.60,-0.50,-0.79, and-5.72 cm-1 for 1-3 and5, respectively,indicative of antiferromagnetic interactions.

Introduction

The design and synthesis of supramolecular coordinationpolymeric networks has received much attention recently, andhydrogen bonding andπ-π stacking interactions are oftenemployed in their construction.1 Such rational design based oncovalent or supramolecular contacts is a key part of self-assembly supramolecular chemistry.2 One synthetic strategy usedin this area is the controlled assembly of donor and acceptorbuilding blocks in order to generate supramolecular polymers.1a,3

Finding molecular materials from organic ligands and metal ionbuilding blocks to generate new supramolecular architecturesis still a challenge.2 The high directionality of hydrogen bondspresent in supramolecular architectures makes them useful inthe crystalline design of functional materials with controlledphysical, chemical, physicochemical, catalytic, and optical

properties.4,5 The interactions of hydrogen bonds also play vitalroles for molecular recognition in a wide variety of biologicalsystems and have also been applied in the synthesis of molecularmagnetic materials.6

Aromatic polycarboxylate ligands have proved to be goodbuilding blocks for the construction of coordination polymersand multidimensional supramolecular networks.7 Interest inaromatic polycarboxylate transition metal complexes also stemsfrom biochemical applications of some oligonuclear carboxylato-bridged complexes, the study of long-range magnetic interac-tions between magnetic centers, and numerous industrialapplications.8 Among the various aromatic polycarboxylateligands, 1,2,4,5-benzenetetracarboxylic acid (H4btec) has beenproved to be a good candidate due to its various bridging abilitiesand strong coordination tendency with transition metals to form2- and 3D moderately robust networks exhibiting tunable ferro-or antiferromagnetic exchange. H4btec is of particular interestbecause it has four COOH groups which can be fully or partiallydeprotonated, resulting in versatile coordination behavior tometal ions. Moreover, the COOH and the COO- groups can behydrogen bond donors and/or hydrogen bond acceptors, afford-ing the possibilities of participation in intermolecular and/orintramolecular hydrogen bonding interactions to form complexeswith higher dimensionalities.9 Finally, the COOH and/or theCOO- groups can be tilted from the phenyl ring plane upon

* To whom all correspondence should be addressed. E-mail:[email protected]. Fax: 91-33-2414-6414. Tel.:+91-33-2668-2017(S.M.). E-mail: [email protected] (M.S.E.F.).

† Jadavpur University.‡ Eidgenossische Technische HochschuleZurich.§ Heriot-Watt University.| Monash University.⊥ University of Windsor.O 25 Universitat de Barcelona.# UniversitePaul Sabatier.3 UniversiteBordeaux.

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10.1021/cg060337y CCC: $33.50 © 2006 American Chemical SocietyPublished on Web 09/16/2006

coordination to metal ions, mainly due to the types of hydrogenbonding interactions and steric hindrance, allowing lots ofpossible coordination modes.7c,10On the other hand, the presenceof many uncoordinated water molecules within the lattice may,in turn, lead to interesting possibilities for the preparation ofporous solids. The H4btec ligand has been used to create 1Dpolymeric chains, 2D polymeric sheets, and 3D polymericnetworks with a variety of metal ions reported in the literature.11

Additionally, the assembly of H4btec and the transition metalions is highly influenced by the multitopic organic spacer lig-ands, judicious selection of the pH value, solvent system, tem-perature, counteranions, and metal-to-ligand ratio as well as thecoordination nature of the metal ions. All these factors have asignificant effect on the formation of desirable frameworks.

In our laboratory, we have focused our efforts on combiningvarious aromatic carboxylates (1,3,5-benzenetricarboxylic acid)with transition metals to create supramolecular architectures withintriguing structures.12 Keeping in mind the aforementionedpoints, we have investigated the ability of H4btec to formextended solids with divalent first row transition metal ions,such as Co2+ and Cu2+ in the presence of theN-donorcoligands.In these complexes, the classic synthon R2

2(7) (involving bothO-H‚‚‚N and C-H‚‚‚O interactions) is present, involving thebest-donor (carboxylic group) and the best-acceptor (the het-erocyclic nitrogen atom) in the composition of hydrogen bonds.The number of copper and cobalt complexes is greater than forother metal ions. Copper(II) complexes with btec to formmononuclear systems with, for example, 3,4-dimethyl-2,6,13,-17-tetrazatricyclo[14.4.01.18.07.2]docosane13 and 3,10-bis(2-hy-droxyethyl)-1,3,5,810,12-hexaazacyclotetradecane.14 Most nu-merous are the one-dimensional systems, such as those with3,10-bis(2-hydroxyethyl)-1,3,5,810,12-hexaazacyclotetrade-cane,14 1,4,8,11-tetraaza-cyclotetradecane,11c 1,10-phanthroline(phen),15 and 2,2′-bipyridine (2,2′-bipy).16 Other more compli-cated structures are less numerous such as the ladderlikeframework derived with 2,2′:6′,2′′-terpyridine (terpy),17 or thedouble-chain framework with phen (with the less commontetrahedral coordination geometry for copper(II) ions).18 2Dstructures are even less frequent, such as with that observedwith N-methylpyrazole.11a 3D nets are found either with btecas the sole ligand19,20 or with pyridine (py).21

Cobalt(II) ions form mononuclear complexes with phen(where btec acts as a counteranion).22 One-dimensional networksare less numerous for Co(II) than for copper(II), such as onesystem with btec as the sole ligand species.23 Two-dimensionalnetworks are, by far, the most numerous, containing bridgingOH- groups,24 chelating bpy,25 phen,26 with N-methylimidazole,which is similar to the copper analogue,11a and with homopip-erazonium as the countercation.5b Finally, some 3D systems arereported; a hydrogen bonded 3D network27 and several systemswith btec and oxalato as bridging ligands.28 The synthesis,structural features, and magnetic properties of four new coor-dination polymers and one mononuclear complex using btec asone of the elements are described in this paper. To the best ofour knowledge, there are no reports concerning the use ofboth btec and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) as com-ponents in molecular lattices; these two components are bothpresent in4.

Experimental Section

General Remarks. All the chemicals and solvents used for thesynthesis were of reagent grade. H4btec, tptz, 4-apy (Aldrich), CoCl2‚6H2O and Cu(ClO4)2‚6H2O (Merck), 4,4′-bipy, and pyrazine (Merck)were used as received.Caution! Although no problems were encoun-

tered in this work, perchlorate salts are potentially explosiVe. Theyshould be prepared in small quantities and handled with care. Elementalanalyses were carried out on all the complexes using a Perkin-Elmer2400 II elemental analyzer. The infrared spectra of the complexes wererecorded on a Perkin-Elmer RX 1 Fourier transform infrared (FT-IR)spectrophotometer with KBr disk. The electronic spectra were obtainedas Nujol mulls on a Perkin-Elmer Lambda 40 (UV-vis) spectropho-tometer for1-3 and5 and dimethylformamide for4. Magnetic studieswere carried out on polycrystalline samples in the temperature domain2-300 K. These have been conducted on a Quantum Design SQUIDMPMS-XL magnetometer for compounds1 and5 whereas compound2 and 3 have been investigated with a Quantum Design MPMS-5SSQUID magnetometer. For all compounds, the applied magnetic fieldwas 5000 Oe. The magnetic susceptibility of complex4 was measuredon a powder sample in a vibrating sample magnetometer using mercury-(tetrathiocyanato) cobaltate as the standard. Diamagnetic correctionswere estimated from Pascal tables and magnetic data were correctedfor diamagnetic contributions of the sample holder.

Synthesis. [{Co(H2btec)(H2O)4}‚4-apy‚(H2O)2]n (1). To a 5 mLhot aqueous solution of H4btec (0.508 g, 2 mmol), 10 mL of an aqueoussolution of NaOH (0.16 g, 4 mmol) was added. An aqueous solution(10 mL) of CoCl2‚6H2O (0.237 g, 1 mmol) and the methanolic solution(5 mL) of 4-apy (0.188 g, 2 mmol) were then added to the abovesolution, at pH≈ 7.0. Pink crystals of1 were obtained in good yielddirectly from the reaction mixture after 4 days. Yield: 376 mg, (62%).Elemental analysis for C20 H28 Co O14 N4. Found (calcd): C 39.42(39.51); H 4.57 (4.61); N 9.19 (9.22).

[{Cu(btec)(4-apy)2}‚(4-Hapy)2‚(H2O)4]n (2). An aqueous solution(5 mL) of H4btec (0.508 g, 2 mmol) was slowly added to a 10 mLaqueous solution of NaOH (0.32 g, 8 mmol) with stirring. The pH wasadjusted with 4-apy (0.94 g, 10 mmol) until the pHg 9.0. Cu(ClO4)2‚6H2O (0.365 g, 1 mmol) was dissolved in 5 mL of water and added tothe above-mentioned solution with stirring. The solution was filteredand allowed to stand at room temperature. Blue single crystals of2were obtained after 2 days. Yield: 477 mg, (65%). Elemental analysisfor C30H36CuN8O12. Found (calcd): C 47.04 (47.10); H 4.68 (4.71); N14.65 (14.61).

[Cu(H3btec)2(pyz)‚(H2O)2]‚H2O (3). About 5 mL of H4btec (0.508g, 2 mmol) was slowly added to a 10 mL aqueous solution of NaOH(0.04 g, 1 mmol). Then, CuCl2‚2H2O (0.170 g, 1 mmol) in 5 mL ofwater was added followed by 5 mL of methanolic solution of pyz (0.152g, 2 mmol) with stirring, and finally, the pH was adjusted to≈7.0.The resultant solution was allowed to stand at room temperature. Bluesingle crystals of3 were obtained after 2 days. Yield: 451 mg, (62.5%).Elemental analysis for C24 H22 Cu N2 O20. Found (calcd): C 39.85(39.89); H 2.97 (3.04); N 3.84 (3.87).

[Co(tptz)(H2O)2(H2btec)]‚(H2O)2 (4). CoCl2‚2H2O (0.237 g, 1.0mmol) and tptz (0.312 g, 1.0 mmol) were dissolved in 10 mL ofmethanol. To this orange colored reaction mixture, 5 mL of an aqueoussolution of H4btec (0.254 g, 1 mmol) and NaOH (0.24 g, 6 mmol) wasadded at pH≈ 7.5. Slow evaporation of the solvent at room temperatureafforded brownish yellow single crystals of4 after 2 days. Yield: 422mg, (64%). Elemental analysis for C28 H20 Co N6 O10. Found (calcd):C 50.90 (50.95); H 2.98 (3.03); N 12.65(12.73).

[{Co2(4,4′-bipy)2(H2O)8}‚(btec)‚(H2O)2]n (5). To 5 mL of anaqueous solution of H4btec (0.508 g, 2 mmol), 10 mL of an aqueoussolution of NaOH (0.32 g, 8 mmol) was slowly added with stirringuntil the pH≈ 7.5. CoCl2‚2H2O (0.474 g, 1 mmol) was dissolved in 5mL of water and added to the above solution. A methanolic solutionof 4,4′-bipy (0.312 g, 10 mmol) was then slowly added with stirring.Pink single crystals of5 were obtained from the standing solution after4 days. Yield: 497 mg (60%). Elemental analysis for C30H38Co2N4O18.Found (calcd): C 41.78 (41.83); H 4.38 (4.41); N 6.46 (6.53).

As is common with supramolecular polymers and coordinationpolymers, the complexes1-3, 5 are insoluble in common solvents suchas methanol, water, acetonitrile, andN,N-dimethylformamide (DMF).Complex4 is soluble in DMF.

X-ray Structure Determination. The X-ray single crystal data forcomplexes1, 3, and5 were collected on a Picker-Stoe diffractometer.Crystallographic data, experimental conditions, and some features ofthe structural refinements are listed in Table 1. Graphite-monochro-matized (Cu KR) radiation (λ ) 1.54178 Å) andω-scans were used tocollect the data sets. The stability of the crystals was checked bymeasuring standard reflections at fixed intervals during the datacollection. However, no significant loss of intensity was noted for the

2356 Crystal Growth & Design, Vol. 6, No. 10, 2006 Majumder et al.

crystals. The data were corrected for Lorentz and polarization effects.The structures were solved by direct methods using the SHELXTLPLUS29 system and refined by full-matrix least-squares methods basedon F2 using SHELXL93.30 All the non-hydrogen atoms were refinedanisotropically. All aromatic hydrogen atoms were placed at geometricpositions and not refined.

Blue colored crystals of2 were mounted with vacuum grease onglass fibers on a Bruker Nonius X8Apex2 diffractometer. Data werecollected with Mo KR radiation (λ ) 0.7107 Å) at 100 K cooled by anOxford Cryosystems Cryostream. No significant crystal decay wasfound. The structure of2 was solved by direct and different Fouriermethods and refined by full-matrix least-squares onF2. All non-hydrogen atoms were refined with anisotropic displacement parametersand other atoms were constrained to idealized geometries and refinedwith riding isotropic displacement parameters. Crystallographic comput-ing was performed using SHELXTL programs.31 Further details aregiven in Table 1.

Intensity data on4 were collected using SMART32 software on aBruker APEX (CCD) diffractometer using a graphite monochrom-ator with Mo KR radiation (λ ) 0.71069 Å). A hemisphere of datawas collected in 1448 frames with 10 s exposure times. Data re-duction was performed using the SAINT32 software package, andabsorption corrections were applied using SADABS.32 The struc-ture was solved by direct methods using XS and refined by full-matrix least-squares onF2 using XL as implemented in the SHELXTLsuite of programs.32 All non-H atoms were refined anisotropically.Hydrogen atoms were placed in calculated positions using an appro-priate riding model. All packing diagrams and thermal ellipsoidplots were produced using ORTEP-3.33 Further details are given inTable 1.

Supplementary Material. Crystallographic data for the structuralanalysis of1-5 have been deposited with the Cambridge Crystal-lographic Data Centre, CCDC nos. 268344-268348. A copy of thisinformation may be obtained free of charge from this address: TheDirector, 12 Union Road, Cambridge, CB2 1EZ, UK. (Fax:+44-1223-336033. E-mail: [email protected]. Website: http://www.ccdc.cam.ac.uk.)

Results and Discussion

The chemistry of transition metals with benzenetetracarboxy-late as a ligand has wide scope for variation. The various stablecharges, geometries, and modes of coordination of benzenetet-racarboxylic acids provide a wealth of compounds with verydiverse structures and properties. Six-coordinate octahedral

geometries are common for d7 cobalt(II) complexes, whereasthe Jahn-Teller distortion of d9 copper(II) favors four-coordinate square planar or tetragonally distorted geometries.34

This difference in coordination number and geometry betweencobalt(II) and copper(II) leads to significant differences in thepolymeric structures. Moreover, the assembly with metal ionshas been highly influenced by the pH value and the metal-to-ligand ratio of the reactants. It has been suggested that thedimensionality of the resulting coordination framework topologyconstructed by metal ions and polycarboxylates is extremelydependent on the deprotonation level of the COOH groups. Thebasicity strength of the reactants influences the deprotonationof carboxylate groups and therefore the coordination sphere ofthe metal centers, resulting in the different coordinationarchitectures assembled.35

Description of Crystal Structures. [{Co(H2btec)(H2O)4}‚4-apy‚(H2O)2]n (1). A perspective view of the repeating unitof 1 is depicted in Figure 1; selected structural parameters suchas bond distances and angles are listed in Table 2. The varioustypes of hydrogen bonds present in these coordination polymericnetworks are listed in Table 3. The repeating unit consists of acentral Co2+ ion having its axial positions occupied by watermolecules (O3W) while the other two water molecules (O2W)and carboxylate groups (O1) are in the equatorial plane whichgives a slightly distorted octahedral environment. Thus, the

Table 1. Crystallographic Data for Complexes 1-5

1 2 3 4 5

chemical formula C20 H28 Co N4 O14 C30 H36 Cu N8 O12 C24 H22 Cu N2 O20 C28 H20 Co N6 O10 C30 H38 Co2 N4 O18

formula weight 607.39 764.22 721.98 659.43 860.50crystal system triclinic monoclinic triclinic monoclinic monoclinictemperature (K) 293(2) 100(2) 293(2) 296(2) 293(2)space group P1h P21/c P1h P21/c C2/ca (Å) 7.272(6) 11.043(1) 6.836(6) 14.537(2) 20.078(4)b (Å) 9.361(6) 9.506(1) 9.705(12) 7.628(1) 11.349(2)c (Å) 10.642(9) 32.266(3) 11.504(13) 23.864(3) 15.609(3)R (deg) 115.08(5) 90 107.70(9) 90 90â (deg) 105.96(6) 96.365(4) 103.57(7) 102.827(3) 95.33(3)γ (deg) 95.38(6) 90 99.80(9) 90 90V (Å3) 612.2(9) 3366.5(5) 682.3(13) 2580.2(6) 3541.4(12)Z 1 4 1 4 4reflections collected 1268 30226 2130 12055 1828independent reflections 1268 10180 1398 3724 1828density (calcd) 1.648 1.508 1.757 1.703 1.614absorption coefficient 6.234 0.724 2.062 0.742 8.097F(000) 315 1716 369 1356 1776crystal size (mm) 0.05× 0.07× 0.10 0.22× 0.20× 0.15 0.09× 0.07× 0.06 0.20× 0.50× 0.60 0.1× 0.1× 0.1θ range for data collection 4.9-50.0 1.27-30.44 4.24-49.98 1.8-23.3 4.42-49.99unique data (Rint) 0.0000 0.0668 0.0136 0.1065 0.0000R indices (all data) R1) 0.0429 R1) 0.1173 R1) 0.0364 R1) 0.1130 R1) 0.0802

wR2 ) 0.1114 wR2) 0.1412 wR2) 0.0895 wR2) 0.1220 wR2) 0.1628final R indices [I > 2σ(I)] R1 ) 0.0429 R1) 0.0499 R1) 0.0330 R1) 0.0503 R1) 0.0602

wR2 ) 0.1114 wR2) 0.1083 wR2) 0.0865 wR2) 0.0969 wR2) 0.1471largest diff. peak and hole (e Å-3) 0.625,-0.386 0.480,-0.605 0.255,-0.332 0.357,-0.521 0.602,-0.650

Figure 1. Asymmetric unit of1 with atom numbering scheme. Thehydrogen atoms have been omitted for clarity.

Five New Supramolecular Architectures Crystal Growth & Design, Vol. 6, No. 10, 20062357

H2btec2- ligand acts as a bridge in a unidentate binding modelinking adjacent metal ions through itspara positioned car-boxylate groups, resulting in the formation of a coordinationpolymer. The Co atom sits on an inversion center. The car-boxylate groups on each H2btec2- participate in an N-H‚‚‚Ohydrogen bond with intercalated 4-apy. Thus, a layered solidconsisting of alternating neutral cobalt-carboxylate coordinationpolymer chains and 4-apy layers is formed (Figure 2). Adjacentlayers of uncoordinated 4-apy and cobalt-carboxylate coordina-tion polymer chains stack over one another in a staggeredfashion and are held together by N-H‚‚‚O interactions betweenthe free carboxylate of the H2btec2- and 4-apy, thus yieldinga rigid and stable extended network. Apart from the N-H‚‚‚Ointeractions linking the metal-organic and amine layers, numer-ous O-H‚‚‚O hydrogen bonding interactions involving thecoordinated water molecules of one cobalt-H2btec2- and thefree carboxylate groups of the adjacent cobalt-H2btec2- throughuncoordinated water molecules are established. Moreover, thereare two water molecules per unit cell which are also involvedin hydrogen bonding with coordinated water. These hydrogenbond interactions combine to give a tightly held 3D supramo-lecular metal-organic framework. Another type of O-H‚‚‚Ohydrogen bonds exist between the coordinated water moleculesand the uncoordinated carboxylate groups of the H2btec2-

ligands in the same chain, strengthening it through intramo-lecular hydrogen bonding. Besides the strong N-H‚‚‚O andO-H‚‚‚O hydrogen bonds, weak C-H‚‚‚O hydrogen bonds arealso present between the water ligands and the carbon atomson the 4-apy. This hydrogen bonding scheme is an importantfactor in the supramolecular assembly and stabilization of lattice.

1D zigzag chains run along the [110] plane with an intrachainCo‚‚‚Co distance of 11.302(10) Å. The distance between twocobalt-carboxylate polymer layers is 9.03(8) Å, while thedistance between the two adjacent cobalt-carboxylate and 4-apylayers is 4.51(6) Å.

Two bridging COO- groups of the four carboxylato groupson each btec ligand are twisted out of the plane of the aromaticring by approximately 54°. The other two free carboxylatogroups are nearly coplanar with the aromatic ring, havingdihedral angles of approximately 46°. The bond distances and

angles found in1 do not deviate appreciably from the expectedvalues found in similar carboxylate complexes of Co2+.5b,8,24

Thecis O-M-O angles around the metal atom in1 vary from89.17° to 94.90° with an average value of 90°.

The critical difference between1 and related coordina-tion polymers24 is the presence of the neutral 1D chains of[Co2(H2btec)(H2O)8]n that alternate with the layers containinguncoordinated 4-apy molecules (that are found in1) instead ofan anionic 1D chain [Co(btec)(H2O)4]2- interspersed withpiperazonium cataions.24

[{Cu(btec)(4-apy)2}‚(4-Hapy)2‚(H2O)4]n (2). Although theamino group of the 4-apy ligand is a potential lone pair donor,there are no structures reported where 4-apy acts as a bridgingligand. In many structures, 4-apy exists as the 4-aminopyri-dinium cation.36 Only a few structures are known in which 4-apyis coordinated to Cu2+ ion as a coligand with carbonate,37

phenanthroline,38 bis(2-aminoethyl)oxamide,39 and formate.40

A single crystal X-ray diffraction study of2 reveals that thiscompound is made up of infinite chains of copper atoms

Table 2. Selected Bond Distances (Å) and Angles (deg) ofComplex 1a

Bond DistancesCo(1)-O(1)#1 2.082(3) Co(1)-O(2W)#1 2.104(3)Co(1)-O(1) 2.082(3) Co(1)-O(3W) 2.116(3)Co(1)-O(2W) 2.104(3) Co(1)-O(3W)#1 2.116(3)

Bond AnglesO(1)#1-Co(1)-O(1) 180.0 O(2W)-Co(1)-O(3W) 93.0(2)O(1)#1-Co(1)-O(2W) 95.01(13) O(2W)#1-Co(1)-O(3W) 87.0(2)O(1)-Co(1)-O(2W) 84.99(13) O(1)#1-Co(1)-O(3W)#1 87.03(12)O(1)#1-Co(1)-(2W)#1 84.99(13) O(1)-Co(1)-O(3W)#1 92.97(12)O(1)-Co(1)-O(2W)#1 95.01(13) O(2W)-Co(1)-O(3W)#1 87.0(2)O(2W)-Co(1)-(2W)#1 180.0 O(2W)#1-Co(1)-O(3W)#1 93.0(2)O(1)#1-Co(1)-O(3W) 92.97(12) O(3W)-Co(1)-O(3W)#1 180.0O(1)-Co(1)-O(3W) 87.03(12)

a Symmetry operations: (#1)-x, -y, -z.

Table 3. Hydrogen Bonding Contacts for Complex 1a

D‚‚‚A (Å) D ‚‚‚A (Å)

O(2W)-H(2W2)‚‚‚O(1W) 2.696(6) O(1W)-H(1W1)‚‚‚O(3)#2 2.686(6)O(3W)-H(3W1)‚‚‚O(4) 2.749(5) O(3W)-H(3W2)‚‚‚O(4)#3 2.726(5)O(3)-H(3H)‚‚‚O(1W) 2.926(6) N(2)-H(21)‚‚‚O(2)#4 2.857(6)O(2W)-H(2W1)‚‚‚O(2)#1 2.652(5) N(2)-H(22)‚‚‚O(1W)#5 3.056(7)O(1W)-H(1W2)‚‚‚O(3) 2.926(6) C(10)-H(10)‚‚‚O(3W)#5 3.330(7)

a Symmetry operations: (#1)-x, -y, -z; (#2) 1- x, 1 - y, 1 - z; (#3)1 - x, -y, -z; (#4) x, 1 + y, 1 + z; (#5) x, 1 + y, z.

Figure 2. (a) Packing of the adjacent 1D chains in the structure of1.Interchain hydrogen bonds are depicted by the dashed bonds, andhydrogen atoms are not shown for the sake of clarity. (b) Hydrogenbonding interactions existing within a layer in1.


connected by btec4- ligands along the [101] plane. Thecoordination environment around the copper(II) ions, illustratedin Figure 3, is four-coordinate, with a slightly distorted squareplanar geometry. The two carboxylato oxygen atoms and two4-apy ligands are in atrans, trans arrangement with the N2O2

ligand set. The metal-ligand bond lengths and angles are allwithin expected limits for copper(II) complexes with carboxy-lates andN-heterocycles11a,b,38a,41and are summarized in Table4 with hydrogen bond parameters in Table 5. The Cu atom sitson an inversion center. The btec4- ligand is centrosymmetric-ally bound to two copper atoms. The btec4- ligands arecoordinated via twopara-carboxylato groups in aµ2-trans-syn manner. Unlike1, 2 contains uncoordinated 4-apy cationsand is comprised of alternating anionic metal-organic coor-dination polymer chains and cationic pyridinium layers. Theanionic chains are made up with the basic unit [Cu(btec)-(4-apy)2]2-

n. The 4-aminopyridinium cations are packed be-tween anionic chains (Figure 4a). The chains run parallel tothe plane created by the crystallographica axis and thebc

diagonal. The separation between the adjacent copper-car-boxylate layers and 4-aminopyridinium cationic layers is about3.1 Å.

Two of the four carboxylato groups (O10-C10-O1 andO30-C30-O31) on each btec ligand are twisted out ofthe plane of the aromatic ring by approximately 36.3° and41.2°, respectively. The other two carboxylato groups(C1-C6-C40-O40 and C2-C3-C20-O20) with the aromaticring, are twisted by approximately 123.5° and 52.2°. Theintralayer Cu1‚‚‚Cu2 distance is 11.043(11) Å while theinterlayer Cu‚‚‚Cu distance is 9.38(8) Å which are in goodagreement with the values found in structurally related com-plexes.11

Adjacent layers stack over one another in a staggered fashionand are held together by N-H‚‚‚O interactions between thecoordinated 4-apy, the 4-aminopyridinium cations, and the freecarboxylates of the btec4- and the lattice water molecules, thusyielding a rigid and stable extended network. An extensive array

Figure 3. One chain, with atom labeling, in the structure of2.


Bond DistancesCu(1)-O(10) 1.9420(17) Cu(1)-N(21) 1.997(2)Cu(1)-O(30)#1 1.9500(17) Cu(1)-N(11) 1.988(2)

Bond AnglesO(10)-Cu(1)-O(30)#1 175.89(8) O(10)-Cu(1)-N(21) 89.42(8)O(10)-Cu(1)-N(11) 90.70(8) O(30)#1-Cu(1)-N(21) 89.81(8)O(30)#1-Cu(1)-N(11) 89.99(8) N(11)-Cu(1)-N(21) 178.88(9)

a Symmetry operations: (#1)x - 1, y, z.


D‚‚‚A (Å) D ‚‚‚A (Å)

N(10)-H(10B)‚‚‚O(4S)#1 2.988(3) N(30)-H(30B)‚‚‚O(31)#8 3.017(3)N(10)-H(10A)‚‚‚O(11)#2 3.163(3) O(3S)-H(31S)‚‚‚O(40)#9 2.908(3)N(10)-H(10A)‚‚‚O(41)#2 3.178(3) O(3S)-H(32S)‚‚‚O(11)#9 2.892(3)O(1S)-H(11S)‚‚‚O(20)#3 2.836(3) N(34)-H(34)‚‚‚O(40)#10 2.673(3)O(1S)-H(12S)‚‚‚O(21)#4 2.782(3) N(40)-H(40A)‚‚‚O(3S)#6 3.040(4)N(20)-H(20A)‚‚‚O(2S)#5 3.064(3) N(40)-H(40B)‚‚‚O(41)#6 2.942(3)N(20)-H(20B)‚‚‚O(21)#6 2.972(3) O(4S)-H(41S)‚‚‚O(11)#11 2.776(3)N(20)-H(20B)‚‚‚O(31)#6 3.288(3) O(4S)-H(42S)‚‚‚O(3S)#8 3.260(3)O(2S)-H(21S)‚‚‚O(1S)#6 3.075(3) N(44)-H(44A)‚‚‚O(20) 2.669(3)O(2S)-H(22S)‚‚‚O(31)#7 2.755(3) C(35)-H(35A)‚‚‚O(41) 3.204(3)N(30)-H(30A)‚‚‚O(1S)#8 2.979(3)

a Symmetry operations: (#1)x - 1, y + 1, z; (#2) -x, -y + 1, -z;(#3) -x + 1, y + 1/2, -z + 1/2; (#4) x, y + 1, z; (#5) x, y - 1, z; (#6) -x+ 1, y - 1/2, -z + 1/2; (#7) x - 1, y, z; (#8) -x + 1, -y + 1, -z + 1; (#9)-x + 1, -y + 1, -z; (#10) x, y, z + 1; (#11)x + 1, y, z.

Figure 4. (a) Packing diagram viewed down theb axis. The4-aminopyridinium cations are shown in a different style from the rest,and the hydrogen bonds are depicted by striped bonds. (b) Closeup oftheπ‚‚‚π and C-H‚‚‚π interactions involving the 4-aminopyridiniumcations. Closest contacts are shown by the thin bonds.


of O-H‚‚‚O hydrogen bonds also exists between the uncoor-dinated water molecules and the uncoordinated carboxylategroup of the btec4- ligands (Table 5). Apart from theN-H‚‚‚O interactions holding the copper-carboxylate andcationic amine layers, numerous O-H‚‚‚O hydrogen bondinginteractions involving the coordinated water molecules of onecopper-carboxylate layer and the carboxylate group of theadjacent copper-carboxylate layer lead to the formation of atightly held metal-organic framework. The [Cu(btec)(4-apy)2]2-

n chains are reinforced and cross-linked into a compli-cated 3D network by extensive hydrogen bonding interactionsbetween coordinated and free btec4-, 4-apy ligands, anduncoordinated 4-aminopyridinium cations as well as watermolecules. Besides the strong N-H‚‚‚O and O-H‚‚‚O hydrogenbonds, weak C-H‚‚‚O hydrogen bonds are also present betweenthe carboxylate of unbound btec4- and the carbon atoms on the4-aminopyridinium cations.

In addition to hydrogen bonding, intersheet contacts arestrengthened byπ-π interactions42 between uncoordinated4-Hapy rings pairs (closest non-hydrogen contact is 3.378 Å)which also make C-H‚‚‚π contacts to the btec4- anions ofthe surrounding chains (Figure 4b; closest contact (C)H‚‚‚C )2.522 and 2.572 Å). The 4-apy rings are parallel with theirsymmetry-related partners on adjacent sheets. The 4-apy lig-and containing N10 and N11 has the closest contact with acentroid-centroid vector of 4.36 Å and an offset angle of120.8°.

The structure of2 is similar to those of coordination polymerssynthesized with tetracarboxylate, piperazine, and divalenttransition metals, M2+ (M ) Co, Ni, Zn),24 and contains anionicchains of [M(btec)(H2O)4]2-

n interspersed with piperazoniumcations.

[Cu(H3btec)2(pyz)‚(H2O)2]‚H2O (3). An ORTEP drawingshows that the coordination environment around the copper(II)ions illustrated in Figure 5 is six-coordinate, with a distortedoctahedral geometry, while selected bond distances and anglesare listed in Table 6. The Cu chromophore is comprised of twonitrogen (from twoµ-N, N donor pyz) and four oxygen atoms,two from H3btec- and another two from aqua ligands in atrans,trans, transarrangement. The Cu-O bond lengths are consistentwith those found for related complexes,43 and Cu-N bonddistances were found to be shorter than the bonds found in thesimilar compounds, e.g., Cu(NCS)2(pyz),44 but fall in the samerange as seen in other systems.7 Figure 6 shows molecular chainsrunning along the crystallographica axis where pyrazine is thebridging ligand. The H3btec- anion is not exactly planar sincethe dihedral angle between the carboxylate and aromatic ring

is 4.3(2)° (O1-C7-C1-C6) and the torsion angles betweenthe carboxylic acid and the aromatic ring of H3btec- are-124.4-(3)° (O8-C10-C5-C4), 148.1(4)° (O6-C9-C4-C3), and177.0(5)° (O4-C8- C2-C1).

The coordination sphere of each Cu site is Jahn-Tellerdistorted to give the typical 4 short+ 2 long bond geometry.The axial Cu-O distance (2.297(4) Å) is significantly longerthan those of the basal Cu-O (2.000(4) Å) or Cu-N (2.035(3)Å) due to the Jahn-Teller effect. Only one of the four COOHgroups in the H4btec is deprotonated under the reactionconditions, resulting in the formation of a rare H3btec- anion.The most common are the btec4- and the H2btec2- anions.14

The deprotonated COO- group participates in catemeric hy-drogen bonding interactions (Table 7) to the neighboring COOHgroup in an intramolecular fashion to form a seven-membered

Figure 5. ORTEP drawing of the coordination environment aroundthe coper(II) ions.


Bond DistancesCu(1)-O(1W) 2.000(4) Cu(1)-N 2.035(3)Cu(1)-O(1W)#1 2.000(4) Cu(1)-O(1)#1 2.297(4)Cu(1)-N#1 2.035(3) Cu(1)-O(1) 2.297(4)

Bond AnglesO(1W)-Cu(1)-O(1W)#1 180.0 N#1-Cu(1)-O(1)#1 89.43(12)O(1W)-Cu(1)-N#1 87.97(14) N-Cu(1)-O(1)#1 90.57(12)O(1W)#1-Cu(1)-N#1 92.03(14) O(1W)-Cu(1)-O(1) 91.8(2)O(1W)-Cu(1)-N 92.03(14) O(1W)#1-Cu(1)-O(1) 88.2(2)O(1W)#1-Cu(1)-N 87.97(14) N#1-Cu(1)-O(1) 90.57(12)N#1-Cu(1)-N 180.0 N-Cu(1)-O(1) 89.43(12)O(1W)-Cu(1)-O(1)#1 88.2(2) O(1)#1-Cu(1)-O(1) 180.0O(1W)#1-Cu(1)-O(1)#1 91.8(2)

a Symmetry operations: (#1)-x, -y, -z.

Figure 6. One 1D chain in the structure of3.


D‚‚‚A (Å) D ‚‚‚A (Å)

O(5)-H(5)‚‚‚O(6)#1 2.672(5) O(2W)-H(22W‚‚‚O(7)#4 2.803(7)O(8)-H(8)‚‚‚O(4)#2 2.627(6) O(2)-H(23)‚‚‚O(3)#2 2.386(5)O(1W)-H(11W)‚‚‚O(2)#3 2.724(5) C(3)-H(3)‚‚‚O(4) 2.674(6)O(1W)-H(12W)‚‚‚O(2W) 2.643(6) C(6)-H(6)‚‚‚O(1) 2.652(5)O(2W)-H(22W)‚‚‚O(3) 3.016(7) C(6)-H(6)‚‚‚O(7) 3.258(6)

a Symmetry operations: (#1) 1- x, 1 - y, 2 - z; (#2) x, 1 + y, z; (#3)-x, -y, -z; (#4) 1 - x, 1 - y, 1 - z.


ring (Figure 7a). The 1D chains are connected by extensivehydrogen bonding (Table 7) between the H3btec- ligands andthe water molecules (both coordinated and intercalated), to givean overall 3D network. The hydrogen bonding may be under-stood in terms of sheets (Figure 7b) in thebc plane with themolecular chains running in thea direction. Each sheet involvesevery second chain in thec direction, which is connected toeach other via hydrogen bonds between the carboxylate groups(via a carboxylate dimer interaction and a single O-H...Ointeraction). These sheets are then connected to identical sheetsinvolving the “missing” chains in thec direction via the guestwater molecules which bridge between the coordinated watermolecules of one sheet and a carboxylate oxygen of theadjoining sheets. The sheets are, of course, further connectedby the pyrazine bridges of the chains. Also visible in Figure 7care theπ stacked columns of H3btec- ligands (closest non-hydrogen contacts are 3.435 Å on one side of the ligand and3.442 Å on the other).

The intrachain Cu‚‚‚Cu distance in the 1D zigzag chain is6.836(8) Å, and the shortest interchain Cu‚‚‚Cu distance is9.70(3) Å. In addition to hydrogen bonding, intersheet contactsare strengthened byπ-π interactions between H3btec- (closestnon-hydrogen contact is 3.43(2) Å).

[Co(tptz)(H2O)2(H2btec)]‚(H2O)2 (4). A perspective view ofcomplex4 with an atom numbering scheme is shown in Figure

8, and selected bond lengths and angles are summarized in Table8. In this structure, the tptz acts as a tridentate ligand throughits major coordination site.14 One nitrogen from triazine andtwo from pyridyl moieties along with the two water moleculesand one H2btec2- anion form the distorted octahedral geometryaround Co(II). Three nitrogen atoms (N4, N1, and N5) fromthe tptz ligand and a carboxylate oxygen atom (O3) form theequatorial base, while O1 and O2 (water molecules) occupythe axial positions. The deviation from the ideal octahedralgeometry is indicated by the difference incisoid [74.22(16)-

Figure 7. (a) Same 2D sheet with the intra- and intermolecular hydrogen bonding interactions. (b) Hydrogen bonding of every second chain in thec direction into a 2D sheet, viewed down thea axis. Guest water molecules and carboxylate groups belonging to adjoining layers (which link tothe sheet shown) are shown in a different style. Pyrazine ligands are not shown. (c) Overall hydrogen bonding connections between chains to givean overall 3D network. The view is the same as part b, except all chains are shown, as are pyrazine bridges (chains run into the page).

Figure 8. Asymmetric unit of4 with atom numbering scheme.


118.57(16)°] and transoid angles [148.43(15)-175.45(18)°].The deviations of the atoms N4, N1, N5, and O5 from the meanbasal plane are-0.034(5), 0.046(6),-0.039(6), and-0.026-(5) Å. The source of distortion primarily comes from the ligandbite angles; N4-Co1-N1 and N1-Co1-N5 are 74.38(16)° and74.22(16)°, respectively, significantly smaller than the idealvalue of 90°. The bond distance of Co1 to the middle nitrogenN1 (2.069(4) Å) is significantly shorter than that to N4 [2.205-(4) Å] and N5 [2.244(4) Å], a pattern usually observed in thistype of three point attachment of tptz-type ligands.45,46 TheCo1-O (water) distances are almost same, 2.096(4) and 2.097-(4) Å, and Co1-O (H2btec2-) is 2.000(4) Å. In the tptz ligand,the C(sp2)-C(sp2) distances within the ring are normal [1.370-(7)-1.387(7) Å], and the exterior bond distances, 1.459(7)-1.478(7) Å, are also normal. The tptz ligands deviate little fromplanarity;45 the three pyridyl rings are twisted with respect tothe central triazine ring by angles of 4.2(2)°, 4.8(2)°, and 6.9-(3)° with the noncoordinating ring displaying the highest degreeof twisting. The two monomeric units of4 form dimers throughintermolecular hydrogen bonding interactions making a 12-membered ring shown in Figure 9a. Finally, these dimericentities are assembled into a 3D network by further hydrogenbonds between the coordinated water and free water moleculesand the carboxylate and pyridyl hydrogens with the distancesfrom 2.388(6) to 3.279(7) Å (Table 9). The packing diagramof complex4 is shown in Figure 9b.

The H2btec2- ligand in4 is not planar since the angle betweenthe planes containing the carboxylate group which is coordinatedto cobalt(II) (C7,O4,O3) and the aromatic ring is 21.5(4). Theother COO- and COOH groups which are not coordinated tothe central cobalt(II) ion make dihedral angles of (O10-C(10)-C6-C1), 6.4(4); (O7-C9-C5-C4), 0.9(4); and (O6-C8-C3-C4), 24.1(4). The carboxylate group O7-C9-O8 is likelyto be protonated as the C-O lengths are the most asymmetric,although the H atom was not located. To the best of ourknowledge, there are no reports concerning the use of btec andtptz as components in the molecular lattices, as observed in thecase of4. Recently, Newkome et al. have demonstrated theirinitial observations and results on the use of btec as element interpyridine-based constructs.47

[{Co2(4,4′-bipy)2(H2O)8}‚(btec)‚(H2O)2]n (5). The crystalstructure of5 consists of alternate inclined one-dimensional[Co(4,4′-bipy)(H2O)4]2+ chains that pack to form layers in thesolid state. The metal centers are six-coordinate, with thecoordination sphere consisting of two pyridyl nitrogen donorsfrom each of two 4,4′-bipy ligands and four oxygen atoms fromligated water molecules (Figure 10). The N(2)-Co(2)-N(3)bond angle is linear, which can be defined as the apex of theoctahedron, and the basal plane is formed by the four watermolecules. Selected bond distances and angles are presented inTable 10. Co-O(water) bond distances are consistent with those

found in related literature.6b,48 The 4,4′-bipy ligands act asbridges [Co‚‚‚Co distance of 11.349(3) Å] to neighboring metalions to form infinite trans-linear cationic chains along thecrystallographic [010] axis. Other Co-4,4′-bipy cationic chainspropagate along the crystallographic [110] and [-110] axis(Figure 6) with a Co‚‚‚Co distance of 11.532(2) Å which isinclined by an angle of+ and-60.5° with its adjacent layers.The two Co‚‚‚Co (bridging) bond distances on each metal areslightly different, and they are in accordance with the valueobserved for complex1.49 Along these layers, the pyridyl ringsof each bridging 4,4′-bipy ligand for the Co2 moiety are notcoplanar but twisted at an angle of 25.9(2)°, but for Co1, thebipy rings are not twisted. The distances between the inclined

Table 8. Selected Bond Distances (Å) and Angles (deg) ofComplex 4

Bond DistancesCo(1)-O(3) 2.000(4) Co(1)-O(2) 2.099(5)Co(1)-N(1) 2.069(4) Co(1)-N(4) 2.205(4)Co(1)-O(1) 2.100(3) Co(1)-N(5) 2.245(4)

Bond AnglesO(3)-Co(1)-N(1) 167.06(17) O(1)-Co(1)-N(4) 89.37(17)O(3)-Co(1)-O(1) 89.99(17) O(2)-Co(1)-N(4) 86.52(17)N(1)-Co(1)-O(1) 91.16(17) O(3)-Co(1)-N(5) 92.82(16)O(3)-Co(1)-O(2) 89.87(18) N(1)-Co(1)-N(5) 74.34(16)N(1)-Co(1)-O(2) 90.04(17) O(1)-Co(1)-N(5) 88.13(15)O(1)-Co(1)-O(2) 175.25(16) O(2)-Co(1)-N(5) 96.62(15)O(3)-Co(1)-N(4) 118.49(16) N(4)-Co(1)-N(5) 148.60(15)N(1)-Co(1)-N(4) 74.42(16)

Figure 9. (a) Hydrogen bonded dimeric unit of complex4. (b) Packingdiagram of complex4.


D‚‚‚A (Å) D ‚‚‚A (Å)

O(1)-H(1A)‚‚‚O(9)#1 2.720(6) C(1)-H(1B)‚‚‚O(3) 2.686(7)O(1)-H(1B)‚‚‚N(2)#2 3.207(6) C(1)-H(1B)‚‚‚O(10) 2.686(6)O(1)-H(1B)‚‚‚N(6)#2 2.815(6) C(4)-H(4A)‚‚‚O(6) 2.745(6)O(2)-H(2A)‚‚‚O(6)#3 2.753(5) C(4)-H(4A)‚‚‚O(7) 2.705(7)O(2)-H(2B)‚‚‚O(10)#4 2.705(6) C(14)-H(14A)‚‚‚O(8)#5 3.280(7)O(5)-H(5A)‚‚‚O(4) 2.434(6) C(15)-H(15A)‚‚‚O(7)#3 3.110(7)O(8)-H(8A)‚‚‚O(9) 2.392(6) C(26)-H(26A)‚‚‚O(5)#7 3.273(7)

a Symmetry operations: (#1) 1- x, 2 - y, -z; (#2) 1 - x, 2 - y, -z;(#3) 2- x, 1/2 + y, 1/2 - z; (#4) 2- x, 2 - y, -z; (#5) -1 + x, 1 + y, z;(#6) x, 3/2 - y, -1/2 + z.


adjacent chains and the parallel chains are 5.74 and 8.05 Å,respectively.

The Co(H2O)4(bipy) chains crisscross in three inclineddirections, with the bipy ligands overlapping and showing weakπ‚‚‚π interactions42 (closest non-hydrogen distance is 3.506 Å).This creates triangular channels which run in thec direction(Figure 11a). Within these channels, there is extensive hydrogenbonding (Figure 11b) between the water ligands of the chains,guest water molecules, and the guest btec4- anions (Figure 11c).The hydrophilic cavities contain two btec4- anions and twowater molecules which take part in extensive hydrogen bonding.In fact, the btec4- molecules are not in the plane of the sheetsbut protrude through the cavity, as shown in Figure 11b.Numerous hydrogen bonding interactions involving the unco-ordinated btec4-, the coordinated water molecules on adjacentchains, and the uncoordinated water molecules, combined withthe cation-anion electrostatic interaction throughout the chan-nels, act to hold the chains together within the 3D architecture(see Table 11). In this way, the fundamental building units,which are constructed by the [Co(4,4′-bipy)2(H2O)4]2+ chainsalong with the btec4- anions and water molecules present inthe lattice, are interconnected through hydrogen bonds. Indeed,

the supramolecular structure depends on two kinds of interac-tions: hydrogen bonding and electrostatic force. The bindingforce mainly comes from the electrostatic interaction betweenthe two building blocks, and the hydrogen bonding leads to theorientation and selectivity in the binding of the two units. Thecombined effects of both interactions make the crystal structuremore stable.

Two opposite COO- groups on each btec4- are twisted outof the plane of the aromatic ring by approximately 51°. Theother two carboxylato groups are twisted by approximately 47°relative to the aromatic ring.

IR Spectra. The bands above 3000 cm-1 are assigned to thestretching modes of the water molecules for all the complexes.There are more bands in this region for1, 3, 4, and5 comparedto 2, due to the presence of both coordinated and uncoordinatedwater molecules. The HsOsH bending modes are observed atca. 1665 cm-1. Bands centered about 1656-1550 cm-1 areassigned to the symmetric mode of the carboxylate groups, andthose at about 1440-1380 cm-1, to the asymmetric mode.11

The absence of any strong bands around 1720 cm-1 in com-plexes2 and5 indicates that all carboxylic groups are depro-tonated.50 The value of∆ν (the difference betweenνas(COO)andνs(COO) in complexes1, 3, and4 (185, 215, and 210 cm-1,respectively)) is larger than the corresponding value in Na4-btec (95 cm-1), indicating that the carboxylate groups behaveas monodentate ligands in these complexes.10b,51The bands at3210 for 1 (3212 for 2), 1660 for 1 (1656 for 2), and 1630cm-1 for 1 (1635 cm-1 for 2) are assigned to the stretchingmodes of 4-apy.52,39a 1213, 1153 1123, 1053, and 797 cm-1

are the characteristics bands of pyz observed in the spectrumof 3. The band at 472-486 cm-1, shifted from 417 cm-1 infree pyz, is particularly characteristic of bridging bidentate pyz,446 cm-1.53 Strong bands that appeared at 1560 and 1520 cm-1

for 4 correspond to the coordinated tptz ligand. Peaks at 1625,1593, 1530, 1479, 1461, 1443, 1369, and 973 cm-1 present in4 can be assigned for the CdC and CdN ring stretchingvibrations. Peaks are also observed at 766 cm-1 (CsH stretch-ing) and 586 cm-1 (pyridyl out-of-ring deformation) for all threecomplexes.54 Absorption bands at 1533, 1414, 1222, 1076, and827 cm-1 are attributable to 4,4′-bipy for 5.55

UV-vis Spectra.The electronic spectra of all the complexeswere recorded in the range of 200-800 nm. Three absorptionpeaks at 320, 385, and 685 nm for2 (238, 390, and 671 nm for3) can be observed. The intense absorption at 320 nm for2(238 nm for3) may be assigned to intraligandπ-π* transitionof carboxylate for2 (pyz for 3).56 The absorption at 385 nm(390 nm for 3) may be assigned to a carboxylate-to-coppercharge-transfer band (ligand-metal charge transfer (LMCT))for 2 (pyz for 3) to copper. The weak absorption at 685 nm for2 may be assigned to the d-d transition band of copper(II),dxz,yz f dx2-y2 (2B1g f 2Eg).57 The broad band maxima at 671nm for 3 in the visible region can be attributed to a compositeof two possible transitions2B1g f 2B2g and2B1g f 2Eg out ofthree spin-allowed transitions of tetragonally elongated copper-(II) ions with approximateD4h symmetry.14

UV-visible spectra of cobalt complexes1, 4, and5 showthree absorption maxima in the visible region at 360, 503, and647 nm for1; 368, 542, and 656 nm for5; and 310 and 532nm for 4. While the strong absorption band at 503 nm (529 for4 and 542 nm for5) is easily assignable to the4T1g(F) f4T1g(P), the weak absorption at 647 nm for1 (656 nm for5)could be ascribed to the4T1g(F) f 4A2g(F) metal d-d transi-tion.36 With 4, d-d transition bands may be obscured by thecharge-transfer band.56

Figure 10. Asymmetric unit of5 with atom numbering scheme.


Bond DistancesCo(2)-O(3) 2.084(5) Co(1)-O(1) 2.038(5)Co(2)-O(3)#1 2.084(5) Co(1)-O(1)#2 2.038(5)Co(2)-O(4) 2.139(5) Co(1)-O(2) 2.144(6)Co(2)-O(4)#1 2.138(5) Co(1)-O(2)#2 2.144(6)Co(2)-N(2) 2.134(9) Co(1)-N(1) 2.211(6)Co(2)-N(3) 2.144(9) Co(1)-N(1)#2 2.211(6)

Bond AnglesO(3)-Co(2)-O(3)#1 176.7(3) O(1)-Co(1)-O(1)#2 180.0O(3)-Co(2)-N(2) 91.6(2) O(1)-Co(1)-O(2) 87.3(2)O(3)#1-Co(2)-N(2) 91.7(2) O(1)#2-Co(1)-O(2) 92.7(2)O(3)-Co(2)-O(4)#1 90.1(2) O(1)-Co(1)-O(2)#2 92.7(2)O(3)#1-Co(2)-O(4)#1 89.8(2) O(1)#2-Co(1)-O(2)#2 87.3(2)N(2)-Co(2)-O(4)#1 92.8(2) O(2)-Co(1)-O(2)#2 179.996(1)O(3)-Co(2)-O(4) 89.8(2) O(1)-Co(1)-N(1) 92.3(2)O(3)#1-Co(2)-O(4) 90.1(2) O(1)#2-Co(1)-N(1) 87.7(2)N(2)-Co(2)-O(4) 92.8(2) O(2)-Co(1)-N(1) 92.0(2)O(4)#1-Co(2)-O(4) 174.4(3) O(2)#2-Co(1)-N(1) 88.0(2)O(3)-Co(2)-N(3) 88.4(2) O(1)-Co(1)-N(1)#2 87.7(2)O(3)#1-Co(2)-N(3) 88.3(2) O(1)#2-Co(1)-N(1)#2 92.3(2)N(2)-Co(2)-N(3) 180.000(1) O(2)-Co(1)-N(1)#2 88.0(2)O(4)#1-Co(2)-N(3) 87.2(2) O(2)#2-Co(1)-N(1)#2 91.9(2)O(4)-Co(2)-N(3) 87.2(2) N(1)-Co(1)-N(1)#2 180.0

a Symmetry operations: (#1)-x + 1, y, -z + 1/2; (#2) -x + 3/2, -y -1/2, -z.


Figure 11. (a) Packing diagram viewed down thec axis, with the three different chain directions highlighted in different shades of gray. Only bipyligands and metal atoms are shown. Note the triangular channels. (b) Same view as before, but with all water molecules and btec4- anions addedto show the hydrogen bonding network. The btec4- anions are shown in a different style from the rest, and the hydrogen bonds are depicted bystriped bonds. (c) Closeup of the extensive hydrogen bonding interactions (striped bonds) between the coordinated water ligands, guest watermolecules, and btec4- anions (shown in a different style). A section of one triangular channel created by the crossing of Co(H2O)4(bipy) chains isshown.


Magnetic Studies.(A) Magnetic Study of Complexes 1 and5. The analysis of magnetic data for cobalt complexes iscomplicated by the fact that single-ion effects, such as spin-orbit coupling, distortion from regular stereochemistry, electrondelocalization, and crystal field mixing of excited states intothe ground state, affect the magnetic properties in addition to apossible magnetic exchange interaction.58 Considering thespin-orbit coupling due to the4T1g ground state for octahedralCo(II) complexes,58b-f exact calculations for deriving theJparameter from experimental data over the whole temperaturerange is not possible unless they are dinuclear complexes.59

Other small polynuclear systems can also be modeled usingsophisticated computer programs, based on full diagonalizationmethods in the low temperature region (where the effective spinS′) 1/2).60 One-dimensional systems of Co(II) are frequentlyassociated with anisotropic Ising systems, and they can be fittedin the low temperature zone assuming again an effective spinS′ ) 1/2.61 More recently, Rueff et al.61c,62 have proposed aphenomenological approach for some low-dimensional Co(II)systems that allows one to have an estimate of the strength ofthe antiferromagnetic exchange interactions. They postulate thefollowing phenomenological equation:

in which,A + B equals the Curie constant (≈2.8-3.4 cm3 mol-1

K for octahedral cobalt(II) ions), andE1 andE2 represent the“activation energies” corresponding to the spin-orbit cou-pling and the antiferromagnetic exchange interaction, respec-tively. TheE1/k which is the effect of spin-orbit coupling andsite distortion is of the order of+100 K.61c,62,63 Equation 1adequately describes the spin-orbit coupling, which results ina splitting between discrete levels, and the exponential lowtemperature divergence of the susceptibility. Good results havebeen reported for one- and, even, for two-dimensional cobalt-(II) complexes.61c,62

An important experimental feature in almost all octahedralcobalt(II) complexes is that theøMT (or µeff) values at roomtemperature (rt) are greater than those expected for one isolatedspin-only ion (øMT ) 1.87 cm3 mol-1 K for a S ) 3/2 ion),indicating that the commented orbital contribution is involved.58

Typical values oføMT (or µeff) are 2.75-3.4 cm3 mol-1 K (4.7-5.2 µâ).58,62 Lower values at rt indicate perturbation from theideal octahedral geometry.64

The magnetic properties of complexes1 and5 are shown inthe form of aøMT vs T plot, whereøM is the molar magneticsusceptibility for one Co(II) ion, and these are shown inFigures12 and 13, respectively. The value oføMT at 300 K is3.152 cm3 mol-1 K for 1 and 2.306 cm3 mol-1 K for 5, whichare both larger than that expected for the spin-only value (øMT) 1.87 cm3 mol-1 K, S) 3/2), indicating the important orbitalcontribution commented on in the previous paragraph. TheøMTvalues continuously decrease from room temperature to 1.585

cm3 mol-1 K at 2.0 K for 1 and 1.346 cm3 mol-1 K at 5.0 Kfor 5. The global feature is characteristic of a strong orbitalcontribution.65 The decrease oføMT with T can be attributed tothe intrinsic behavior of Co(II) rather than to antiferromagneticexchange interactions. This is confirmed by theøM curve thatstarts at room temperature from 0.010 cm3 mol-1 for 1 and0.0077 cm3 mol-1 for 5 and increases in a uniform way to 0.791cm3 mol-1 at 2.0 K for1 and 0.269 cm3 mol-1 at 5.0 K for5.The absence of a maximum in theseøM curves may indicatethat the possible antiferromagnetic coupling is very weak.

Complexes1 and 5 are basically one-dimensional systemsextended to give a more complicated structure by hydrogenbonds (see the structural part). Thus, in both cases, the Rueffformula (eq 1) can give an estimated (not exact) value ofJ.This equation is valid for any temperature greater than thepossibleTc,61c,62which does not exist at least atT > 2 K for 1and 5. The fitted values obtained with this procedure are asfollows: A + B ) 3.36 cm3 mol-1 K for 1 and 2.88 cm3 mol-1

K for 3, which perfectly agree with those given in the literaturefor the Curie constant (C ≈ 2.8-3.4 cm3 mol-1 K).61c,62Also,E1/k ) 52.93 K for 1 and 79.27 K for5 and are of the samemagnitude as those reported by Rueff et al. for several one-and two-dimensional cobalt(II) complexes.61 As for the valuesfound for the antiferromagnetic exchange interaction, it is veryweak (E2/k ) 0.43 K for1 and 0.57 K for3), corresponding toJ ) -0.86 K () -0.60 cm-1) for 1 and -1.14 K () -0.79cm-1) for 5, according to the Ising chain approximation,øMT∝ exp(J/2kT).

These weak magnetic exchange couplings can be understoodby considering the Co-benzenetetracarboxylate and Co-4,4′-bipyridine chains in1 and5, respectively, where the bridgingligands are separating the Co(II) atoms with large distances[11.302(10) in1 and 11.532(2) Å in5, respectively] leadingin, this way, to almost negligible coupling. These small values


D‚‚‚A (Å) D ‚‚‚A (Å)

O(1W)-H(1W)‚‚‚O(6) 2.788(9) O(3)-H(31)‚‚‚O(7#4) 2.705(8)O(1W)-H(2W)‚‚‚O(5) 3.349(8) O(3)-H(32)‚‚‚O(8) 2.656(8)O(1W)-H(2W)‚‚‚O(6) 2.788(9) O(4)-H(41)‚‚‚O(6) 2.735(8)O(1)-H(11)‚‚‚O(1W)#1 2.750(9) O(4)-H(42)‚‚‚O(7)#5 2.877(8)O(1)-H(12)‚‚‚O(7)#2 2.654(8) C(2)-H(2A)‚‚‚O(8)#6 3.292(10)O(2)-H(21)‚‚‚O(5)#1 2.793(9) C(6)-H(6A)‚‚‚O(4)#7 3.124(10)O(2)-H(22)‚‚‚O(6)#3 2.816(8) C(9)-H(9A)‚‚‚O(4) 3.056(10)

a Symmetry operations: (#1)x, -y, -1/2 + z; (#2) x, -1 + y, z; (#3) 3/2- x, 1/2 - y, -z; (#4) 1 - x, 1 - y, -z; (#5) x, 1 - y, 1/2 + z; (#6) 1 -x, -y, -z; (#7) 1 - x, y, 1/2 - z.

øMT ) A exp(-E1/kT) + B exp(-E2/kT) (1)

Figure 12. Plot of øMT vs T of polycrystalline sample of1. The solidline corresponds to the best fit.

Figure 13. Plot of øMT vs T of polycrystalline sample of3. The solidline corresponds to the best fit.


must be taken with great care because, being so small, theinterchain hydrogen bond connections are likely to contribute.

The reduced molar magnetization (M/Nâ) per Co(II) tendsto 2.22 electrons for1 (Figure 14) and 1.67 electrons for5(Figure 15). This value is less than that expected for an isolatedCo(II) ion not coupled (2.5-3 Nâ).62 This feature agrees withthe weak antiferromagnetic coupling within the Co(II) ionsreported in the literature.61c

(B) Magnetic Study of Complexes 2 and 3 (Copper(II)Systems).These two complexes are, actually, one-dimensionalones, forming much more complicated networks due to thehydrogen bonding network. The temperature dependence oføMTfor complex 2 is depicted Figure 16. These data have beenanalyzed by a model for chains of equally spacedS) 1/2 spins.The spin Hamiltonian in zero-field isH ) -J∑i)1

n-1 SA i‚SA i+1

where the summation runs overn sites of the chain. Whenntends to infinity, there is no analytical method to determine the

magnetic susceptibility. However, the results can be fitted usingthe numerical expression forJ < 0:66

The best fit was obtained for an isotropic interactionparameterJ ) -0.50 cm-1 and a Lande factorg ) 2.26. Thevery small value ofJ is in line with those usually found forthis carboxylate bridging ligand.67 For some compounds, thislinkage leads to stronger interactions.68 However, in these cases,the basal planes containing the CuN2O2 units are strictly coplanarwith the tetracarboxylato ligand. In the case of compound2,the benzene ring of the tetracarboxylato ligand is twisted relativeto the basal plane of the copper coordination sphere.

The temperature dependence for compound3 is depicted asøMT versusT in Figure 17. The steadily decrease of theøMTvalues below 100 K indicates that antiferromagnetic interactionsare operative between the Cu(II) centers. This curve is alsocharacterized by an anomaly visible around 200 K where thevalue oføMT drops suddenly from 0.46 cm3 mol-1 K at 205 Kto 0.44 cm3 mol-1 K at 200 K. Such a step in theøMT versusT behavior suggests a slight crystal lattice reorganizationaffecting the exchange interactions among the spin carriers.69

Assuming that the main exchange pathway involves the pyrazineligands bridging the Cu(II) units, the magnetic data wereanalyzed with the same model as compound2. The best fit tothe experimental points was obtained forJ ) -5.72 ( 0.04cm-1 and g ) 2.20. Only the data below 200 K have beenconsidered for the modeling process because of the stepexhibited by the curve. The value of the exchange parameterobtained is in good agreement with those usually observed forpyrazine bridged Cu(II) systems.70

The effective magnetic moment at 20°C for the mononuclearcomplex4 was 1.94 cm3 mol-1 K which is nearer to the spin-only value of cobalt(II) ions relative to mercury(tetrathiocy-anato)cobaltate as the standard.

Conclusion

It has been shown, in this context, that five new coordinationcomplexes can be readily synthesized under mild conditionsfrom H4btec and divalent late transition metal salts [cobalt(II)and copper(II)] in the presence of donor amines as a coligandswithout employing hydrothermal conditions. All the complexes(1-5) exhibit mixed-ligand supramolecular architectures through

Figure 14. Plot of the reduced magnetizationM/Nâ versus appliedfield H at 2 K for 1.

Figure 15. Plot of the reduced magnetizationM/Nâ versus appliedfield H at 2 K for 3.

Figure 16. Experimental (0) and calculated (s) temperature depen-dence oføMT for compound2.

Figure 17. Experimental (0) and calculated (s) øMT versusT curvefor compound4. The best fit was obtained forJ ) -5.72( 0.04 cm-1

andg ) 2.20.

øMT ) Ng2â2

k0.25+ 0.074975x + 0.075235x2

1.0+ 0.9931x + 0.172135x2 + 0.757825x3

with x ) -J/kT


numerous hydrogen bonding interactions involving the constitu-ent materials which enhance the stability of the complexes.Complex1 possesses a layered structure consisting of alternatingneutral cobalt-carboxylate and 4-apy layers in contrast to theanionic copper-carboxylates interspersed with 4-aminopyri-dinium cations in2 (here, the supramolecular framework alsodepends on the cation-anion electrostatic interactions). In both3 and4, tetracarboxylate acts as a terminal monodentate ligand.Complex3 is a pyz bridged 1D chain with a terminally attachedmonodentate tetracarboxylate. Mononuclear complex4 containsa H2btec2- ion (which binds to the cobalt(II) in a monodentatefashion) and tptz. The steric geometry of the tptz may beresponsible in the formation of this monomer. In complex5,though btec4- anions are not coordinated to cobalt(II), they arestrongly hydrogen bonded with coordinated and uncoordinatedwater molecules together with cation-anion electrostatic inter-actions. However, btec4- probably played a template orstructure-directing role on the constructing coordination frame-work. Complexes1-3 and 5 show weak antiferromagneticinteraction because of the longer distance between the twomagnetic centers.

Acknowledgment. The research was supported by a grantfrom DST, New Delhi, India. Prof. T. Matsushita is alsogratefully acknowledged, Department of Materials Chemistry,Faculty of Science and Technology, Ryukoku University, Japan,for the magnetic data collection of5. Our thanks are alsoextended to Mr. Deepak Chopra, IISC Bangalore, for hisassistance in developing the some figures. M.S.E.F. acknowl-edges the financial support of the Ministerio de Educacioń yCiencia (programa Ramoń y Cajal). Also, the Spanish Govern-ment (Grant BQU2003/00539) is acknowledged. The magneticmeasurements for2 and3 have been supported by the CentreFranco-Indien pour la promotion de la Recherche Avanceé/Indo-French Centre for the Promotion of Advanced research (Project3108-3).

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