Ligand hierarchy on driving the crystal packing. Effect of supramolecular interactions on solid-state conformations adopted by saccharinate Pd(II) complexes

CrystEngComm

PAPER

7124 | CrystEngComm, 2014, 16, 7124–7132 This journal is © The R

aDpto de Ingeniería Minera, Geológica y Cartográfica. Universidad Politécnica

de Cartagena. Área de Química Inorgánica, Regional Campus of International

Excellence “Campus Mare Nostrum”, Universidad Politécnica de Cartagena,

30203, Cartagena, Spain. E-mail: [email protected] ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire, OX11 0QX UKcDpto de Química Orgánica, Universidad de Murcia, Campus de Espinardo,

E-30071 Murcia, Spain

† Electronic supplementary information (ESI) available: CCDC 982563–982567.For ESI and crystallographic data in CIF or other electronic format see DOI:10.1039/c4ce00518j

Cite this: CrystEngComm, 2014, 16,

7124

Received 12th March 2014,Accepted 15th May 2014

DOI: 10.1039/c4ce00518j

www.rsc.org/crystengcomm

Ligand hierarchy on driving the crystal packing.Effect of supramolecular interactions on solid-stateconformations adopted by saccharinate Pd(II)complexes†

José Pérez,*a J. Luis Serrano,a Ivan da Silva,b Arturo Espinosa,c Eduardo Péreza

and Luis Garcíaa

The potential of saccharinate as a supramolecular organizer in selected palladium complexes has been

thoroughly evaluated from the perspective of those relevant interactions operating in organic salts and

co-crystals in which saccharinate is involved. With this purpose, molecular and supramolecular structures

of a series of bis-saccharinate complexes with the general formula trans-[Pd(sac)2(L)2] [L = pyridine (1),

pyridazine (2), PPh3 (3), SMe2 (4) or nicotinamide (6)] containing co-ligands with different polarities and

abilities to form intermolecular bonds have been studied by X-ray diffraction. These X-ray diffraction data

were either previously reported (1 and 3), or obtained from newly determined crystal structures (2, 4

and 6). The new crystal structures of closely related complexes [Pd(sac)2(SMe2)(OH2)]·dmso (5) and

[Pd(succinimide)2(nicot)2] (7) have also been elucidated and provide an additional structural discussion.

We have disclosed that the anti-configuration is preferred for saccharinate ligands and that the CO

group defines the most important supramolecular interactions in the crystal packing of 1, 2 and 4. The

saccharinate ligand drives crystal packing when pyridine (1), pyridazine (2), PPh3 (3), or SMe2 (4) are

the co-ligands, but the crystal packing orienting role relies on water (5) or nicotinamide (6 and 7) when

these ligands are present. These results have been compared with other previously reported examples.

Molecular geometries have been optimized by DFT, with the interesting output of the energetic

preference by the syn-configuration. Supramolecular interactions distort conformations from those

optimized ones so that complexes with stronger interacting ligands display larger distortions.

Introduction

Since its serendipitous discovery in 1879,1 invariably found atthe top of any list of accidental inventions, saccharin hasattracted continuous interest, updated from time to time dueto the advent of new and striking applications. It is bestknown as an artificial sweetener, its widespread use not freefrom controversy, as concisely described in the excellentreviews of Baran and Yilmaz that are devoted to metal

complexes of saccharin.2 Apart from the biological, bio-chemical and pharmacological interest in saccharin and itscomplexes,2,3 they have also been used as additives in electro-chemical deposition4 or as electroplating brighteners.3

Recently, novel saccharinate-based functional ionic liquidshave emerged in the field of these neoteric solvents, with thehydrogen-bonding ability of the saccharinate anion playing acrucial role in its performance.5 The wide variety of coordina-tion modes produced by its three different functional groups,and the good crystalline habits of its metal derivatives,have also turned saccharine into a valuable ligand for crystalengineering6 and the aim of several fundamental structuralstudies.7 Regarding crystal engineering, saccharine definitelybroke into this field less than a decade ago when Desirajuand co-workers demonstrated its use as a weak acid inpharmaceutical chemistry, forming salts with basic activepharmaceutical ingredients (APIs) that exhibited the highlysought-after property of enhanced water solubility.8 Since thisseminal work was published in 2005, robust supramolecular

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synthons have been identified9 and several solid-statestructural studies have been carried out on saccharin salts10

or saccharin derivatives.11

Although we have always paid attention to the valuableinformation provided by the supramolecular interactions inthe new complexes that we have synthesized,12,13 our initialinterest in saccharine comes, however, from its potential as aligand that is able to bond transition metals in a wide varietyof coordination modes.2 The acidic imino hydrogen of sac-charin (pKa 2.2) and the adjacent carbonyl group make itsimilar to imidates like phthalimide or succinimide in theirreactions with palladium precursors containing Pd–OH orPd–OAc groups. Imidates are a variety of pseudohalidesshowing mixed σ-donating and π-accepting properties14 thatduring the past years have shown in our hands an incrediblepotential for cross-coupling reactions.15 Our most recentcontribution to this field has focused on the use of trans-[Pd(PPh3)2(sac)2] as a general catalyst for the Suzuki–Miyauracross-coupling, Negishi cross-coupling and C–H bondfunctionalization of challenging substrates.16 The superiorperformance of this complex containing N-bonded saccharinate,compared to others with related imidates, attracted our atten-tion, which was definitely focused on the supramolecularfeatures of saccharinate coordinated to palladium when wedisclosed the promising solid-state luminescence propertiesin some saccharinate-bridged palladium complexes.17 Saccha-rine is a polyfunctional ligand with potential hydrogen bondacceptor and donor groups, which could play a prominentrole in the crystal packing of such complexes and thereforein their solid-state properties. Surprisingly, and in clear con-trast with the attention paid to its organic salts, co-crystalsand other derivatives, the crystal packing in saccharinatecomplexes has been scarcely studied and not in a compre-hensive way.2,3,18 We report herein a systematic study on thesupramolecular properties of saccharinate in several palla-dium complexes {[Pd(sac)2(L)2]}. The structures of 1 and 3

This journal is © The Royal Society of Chemistry 2014

Schem

have been previously published,15i and the new crystal struc-tures were obtained either by powder (6 and 7) or single-crystal X-ray diffraction (2, 4 and 5). In all these complexesthe ability of saccharinate to organize the supramolecularstructures has been compared against selected ligands alsopresent in the coordination sphere of palladium. The func-tion played in the crystal packing of saccharinate complexesby those synthons that are relevant in other saccharine/saccharinate compounds has been evaluated.

Results and discussion

In order to the study molecular and supramolecularproperties of saccharinate palladium complexes in a compre-hensive manner, the following trans-derivatives were selected:[Pd(sac)2(py)2] (1), [Pd(sac)2(pyz)2] (2), [Pd(sac)2(PPh3)2] (3),[Pd(sac)2(SMe2)2] (4), [Pd(sac)2(SMe2)(OH2)]·dmso (5) and[Pd(sac)2(nicot)2] (6) (Scheme 1).

Regarding organic salt formation or co-crystal preparation,saccharine has three key interaction points. It is able totransfer the N–H hydrogen to a basic counterpart, with for-mation of a saccharinate anion. Otherwise saccharine bearsstrong hydrogen bond donor (N–H) and acceptor groups(SO and CO) available for hydrogen bonding, and it hasbeen profusely used to prepare co-crystals when the othercomponent is not basic enough to form a salt.9,10

In the palladium complexes under study here thedeprotonated heterocyclic N-atom is involved in the coordina-tion to the metal, so its usual prominent role in the crystalpacking would give priority to other interactions.

In order to study the supramolecular interactions ofsaccharinate ligand (sac) in metal complexes, a square-planarcoordination would particularly favour the intermolecularinteractions, due to its low steric impediment, offering bothsides of the coordination plane for this purpose. Among thesquare-planar complexes, we have chosen for our specific

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e 1

Scheme 2

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study trans-isomers because a trans-disposition avoids intra-molecular interactions between the sac ligands. Having fixedthe trans-(sac)2Pd core, in order to determine the crystalpacking driving hierarchy of the ligands we have selected asequence with different abilities to generate non-bonded links:py (pyridine), pyz (pyridazine), PPh3 (triphenylphosphine),SMe2 (dimethylsulfide), H2O (water) and nicot (nicotinamide).

Molecular structure

A major objective of this work is to determine the effect ofthe crystal packing in the molecular geometry of the studiedcomplexes, which in turn requires a systematic moleculargeometry description. Given the rigidity of ligands, themolecular configuration and conformation can be character-ized by (i) the relative orientation of the saccharinate ligands,(ii) the symmetry of the complexes, and (iii) the anglebetween the mean coordination plane (CP) and the ligands(Table 1).

Several conclusions can be extracted from the data inTable 1: (i) the anti-configuration is the most frequent one,(ii) a symmetrical overall arrangement is most frequentlyobserved, and (iii) saccharinate ligands tend to lie roughlyperpendicular to the coordination plane.

Supramolecular structure

In the analysis of intermolecular interactions there aresophisticated treatments, such as Hirshfeld surfaces,19 thatuse a whole-molecule approach. However, for simplicity, therelevant short contacts in the structures were used herein.Table 2 summarizes the most relevant interactions found inthe complexes under study. All the data are displayedtogether here in a logical increasing-distances order.

The packing of 1 ([Pd(sac)2(py)2]) can be describedas chains of molecules connected by C–Hpy⋯OC andC–Hsac⋯OS bonds. In turn, these chains are connected byC–H⋯OS bonds. In this case, the saccharinate ligand canbe considered as the driving ligand of the packing because itis involved in most of the intermolecular contacts, in particu-lar in the strongest ones (Table 2).

The most important supramolecular interaction (Table 2)is a C–H⋯OC bond (dC⋯O = 3.142(2) Å) that accounts forthe formation of a polymeric chain where each complex

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Table 1 Most relevant molecular features in the solid-state structures of [P

Complex Relative orientation

[Pd(sac)2(py)2] (1) anti[Pd(sac)2(pyz)2] (2) anti[Pd(sac)2(PPh3)2] (3) syn[Pd(sac)2(SMe2)2] (4) anti[Pd(sac)2(SMe2)(OH2)]·dmso (5) syn[Pd(sac)2(nicot)2] (6) anti

a CP (coordination plane): mean plane defined by the four atoms coordin

molecule takes part in sixteen C–H⋯OC and C–H⋯OSintermolecular hydrogen bonds (HBs) (dC⋯O ranging from3.142(2) to 3.245(2) Å), Fig. 1.

Each complex molecule is surrounded by four moremaking use of eight C–H⋯OS hydrogen bonds (C⋯Odistances ranging from 3.285(2) to 3.477(2) Å) (Fig. 1). All ofthese are weak HBs of C–H⋯A type. In addition, there arealso π⋯π interactions between sac phenyl rings of neigh-bouring molecules (the distance between centroids is 3.567 Å).

The packing of 2 ([Pd(sac)2(pyz)2]) can be described aschains of molecules along the a direction connected byC–Hpyz⋯OC and C–Hpyz⋯OS bonds (Fig. 2). The saccharinateligand can be considered as the driving ligand of the pack-ing. This is similar to the polymeric arrangement found in 1,and noticeably the additional N atom of pyz is not involvedin the bonding of this main chain.

The most important supramolecular interaction is aC–H⋯OC bond (dC⋯O = 3.120(6) Å), leading to a polymericchain where each molecule takes part in eight C–H⋯OC orC–H⋯OS hydrogen bonds.

Each complex is surrounded by four more molecules, witheach one linking by a Cpyz–H⋯OS bond (dC⋯O = 3.165(7) Å);the orientation of the pyz and sac ligands suggests an R2

2 (8)ring involving the non-coordinated N atom in spite of the factthat the C⋯N distance is very long (Table 2). This is shown inFig. 3 (only two of the four additional molecules are shown).In addition, there are also C–H⋯π interactions between pyzand sac ligands of neighbouring molecules.

The packing of 3 ([Pd(sac)2(PPh3)2] can be described as a3D arrangement where each molecule is surrounded by sixothers. C–H⋯OS, C–H⋯OC hydrogen bonds and CH⋯π

interactions connect each molecule with the others aroundit. As shown in Table 2, based on distances, these


d(sac)2(L)2] complexesa

Symmetry CP–sac angle (°) CP–L angle (°)

Ci 88.2 64.6Ci 75.7 66.8~C2v 75.7, 66.3 —Ci 83.7 —Cs 74.7 —Ci 84.0 68.5

ated to palladium.

Table 2 Most relevant supramolecular features in [Pd(sac)2(L)2] complexes

ComplexNumber of moleculessurrounding each one Geometrical parameters Interaction type

1 8 D–H⋯A D⋯A (Å) H⋯A (Å) D–H⋯A (°) Hydrogen bondsa,b

(4) C1py–H⋯OC 3.142(2) 2.47 129.2

(4) C2py–H⋯OC 3.245(2) 2.70 118.2

(4) C4sac–H⋯OS 3.195(2) 2.65 118.0

(4) C3sac–H⋯OS 3.193(2) 2.68 115.7

(4) C5sac–H⋯OS 3.285(2) 2.60 130.9

(4) C4py–H⋯OS 3.477(2) 2.70 142.3

Centroid distance (Å) Angle between rings (°) π⋯π stackinga

(2) 3.567 0

2 8 D–H⋯A D⋯A (Å) H⋯A (Å) D–H⋯A (°) Hydrogen bondsa,b

(4) C3pyz–H⋯OC 3.120(6) 2.39 132.9

(4) C3sac–H⋯OS 3.388(6) 2.60 140.1

(4) C6pyz–H⋯OS 3.165(7) 2.59 119.0

(4) C6sac–H⋯Npyz 3.611(7) 2.75 150.3

H⋯centroid (Å) C–H–centroid angle (°) C–H⋯ π(4) Cpyz–H⋯πsac 2.734 150.7

3 6 D–H⋯A D⋯A (Å) H⋯A (Å) D–H⋯A (°) Hydrogen bondsCsac–H⋯OS 3.048(2) 2.38 128.7CPh–H⋯OS 3.590(3) 2.72 156.2CPh–H⋯OS 3.589(2) 2.68 165.5CPh–H⋯OS 3.487(2) 2.71 141.8CPh–H⋯OC 3.127(2) 2.66 111.7

H⋯centroid (Å) C–H–centroid (°) C–H⋯ πCPh–H⋯πsac 3.049 164.8

4 4 CO⋯S O⋯S (Å) CO⋯S (°) Hypervalent non-bondedinteraction of sulfura

(4) CO⋯SMe2 2.958(6) 174.8(3)D–H⋯A D⋯A (Å) H⋯A (Å) D–H⋯A (°) Hydrogen bondsa

(4) Csac–H⋯OS 3.266(6) 2.40 155.0

5 4 D–H⋯A D⋯A (Å) H⋯A (Å) D–H⋯A (°) Hydrogen bondsa

(4) O–H⋯OC 2.640(4) 1.83 166.7(4) SMe⋯OC 3.246(6) 2.50 134.5(4) SMe⋯OS 3.187(5) 2.44 135.0

6 4 D–H⋯A D⋯A (Å) H⋯A (Å) D–H⋯A (°) Hydrogen bondsa

(4) NH2⋯OCNH2 2.84(4) 1.87(4) 163(2)(4) –NH2⋯OS 3.08(2) 2.08(3) 168(3)

a In brackets, the number of bonds around each molecule. b Numbering of carbon atoms according to Scheme 2.

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interactions are weak. A cooperative effect rather than a spe-cific interaction controls the packing in this structure, withthe voluminous phosphine ligands preventing the orientationcapability of polar functional groups on the saccharinateligands.

The packing of 4 ([Pd(sac)2(SMe2)2] (Fig. 4) can bedescribed as a 3D arrangement where each molecule issurrounded by four others. The main interactions betweenneighbouring molecules are SMe2⋯OC and C–H⋯OS.Molecules of 1, 2 and 4 lie on a center of symmetry, but theSMe2 ligand allows a closer intermolecular approach so thatthe number of molecules around any given one is lower andthe shortest Pd⋯Pd distance in 4 is 7.007 Å (in 1 and 2 theseare 7.991 and 8.053 Å, respectively).

In the packing of 5·dmso, [Pd(sac)2(SMe2)(OH2)]·dmso canbe described as chains of complexes linked by hydrogenbonds (Scheme 3, Fig. 5). Each molecule in the chain


participates in two R12 (10) rings constituted by H2O and

CO groups and in two R22 (12) rings defined by SMe2 and

CO groups. These are interactions between consecutivemolecules in the chain; in addition, molecules in relativepositions 1 and 3 in the chain interact by R2

2 (12) ringsdefined by SMe2 and SO groups. The most intense supra-molecular interaction is the ring defined by H2O (Table 2)which could account for the syn-configuration of thesaccharinate ligands in this case. Moreover, the low stericimpediment of the H2O ligand together with the strongsupramolecular interaction lead to the shortest Pd⋯Pd dis-tance among the complexes studied in this paper (5.476 Å).Solvent molecules appear linking chains by weak HBs.

The packing of 6 ([Pd(sac)2(nicot)2], Fig. 6) can bedescribed as a 3D arrangement where each molecule issurrounded by four others owing to strong –NH2⋯nicotOChydrogen bonds with a N⋯O distance of 2.84(4) Å. With

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Fig. 1 Crystal packing of [Pd(sac)2(py)2] (1). Molecules added to polymeric chain are in wireframe style.

Fig. 2 Polymeric chain of [Pd(sac)2(pyz)2] (2).

Fig. 3 Crystal packing of [Pd(sac)2(pyz)2] (2).

Fig. 4 Crystal packing of [Pd(sac)2(SMe2)2] (4).

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them, the central molecular unit forms one more hydrogenbond NH2⋯OS, with a longer N⋯O distance of 3.08(2) Å.In this case, the ligand that directs the packing is nicotin-amide. The strong capacity of nicotinamide to control thecrystal packing has been previously reported.20

The power of nicotinamide to orientate the crystal packingis confirmed in the structure of [Pd(succinimide)2(nicot)2](7), as in this case the packing is very similar to that observedin 6. Each molecule is surrounded by four others throughstrong –NH2⋯OC hydrogen bonds with a N⋯O distance of2.934 Å. ESI† includes a figure showing the crystal packing of 7.

Effect of supramolecular interactionsin the molecular conformation

Regarding the relative orientation of ligands, it can beconcluded that anti- is the most frequent one among


Table 3 Dihedral angles (°) between CP and ligand mean planes inexperimental versus computed (B3LYP-D3/def2-TZVPecp) [Pd(sac)2(L)2]

complexesa

Complex CP–sac CP–L

1 88.2 (83.9) 64.6 (61.7)2 75.7 (74.7), 66.3 (71.8) —3 75.7 (71.2) 66.8 (62.2)4 83.7 (81.9) —5 74.7 (64.9), 74.8 (66.3) —6 84.0 (74.6) 68.5 (79.3)

a Computed values in parentheses.

Scheme 3

Fig. 5 Crystal packing of [Pd(sac)2(SMe2)(OH2)]·dmso (5·dmso).Molecules of dmso have been omitted for clarity.

Fig. 6 Crystal packing of [Pd(sac)2(nicot)2] (6). Hydrogen atoms areomitted for clarity.

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complexes under study, with only [Pd(sac)2(PPh3)2] (3) and[Pd(sac)2(SMe2)(OH2)] (5) showing the syn-configuration.To confirm this, the Cambridge Structural Database (CSD)v. 5.34 was searched for all the structures containing


coordination complexes with two sac ligands. All theplanar18g,21 or octahedral22 trans-structures found show ananti-configuration. Intramolecular hydrogen bonding hasbeen used to justify the syn-configuration in [Pd(sac)2(2-aampy)2], where 2-aampy = 2-acetylaminopyridine.21c

Quantum chemical calculations have allowed the com-parison of both syn- and anti-orientations for the molecu-lar species [Pd(sac)2(PPh3)2] (3), [Pd(sac)2(SMe2)2] (4) and[Pd(sac)2(SMe2)(OH2)] (5). In all the cases syn-orientation ismore stable than the anti-one, but intermolecular interac-tions could play a key role in the observed configuration.Thus, in the complex [Pd(sac)2(SMe2)2] (4), which has lowsteric hindrance, the syn-isomer is more stable than theanti-one by only 1.84 kcal mol−1, which can be compen-sated by the higher availability of the Ci-symmetric (anti)isomer to form supramolecular interactions on both sidesof the coordination plane. Most probably this is also the casefor complexes 1, 2 and 6. By contrast, the high stabilization ofsyn-complex 3 over the anti-isomer (3.09 kcal mol−1) seems tobe enough to compensate all possible supramolecular smallinteractions in the latter. In the case of model complex 5the syn-isomer is only slightly stabilized over the anti-form(by 1.45 kcal mol−1) but in this case supramolecular inter-actions provide additional strength to the syn-form asexplained below.

The most significant differences between optimized geom-etries and molecular structures in the solid state are relatedto the dihedral angles between the coordination plane (CP)and the heterocyclic ligand (sac or L) mean planes (Table 3).

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Supramolecular interactions are strong enough to tilt theangles between the CP and saccharinate or co-ligands. Thestronger intermolecular interactions, the higher deviationsare observed.

In [Pd(sac)2(py)2] (1) the anti-molecular structure ofthe complex is conformationally fixed by two identical(Ci-symmetry-related) C–Hpy⋯OC interactions (H⋯A distance2.69 Å, calc. 2.46 Å; D⋯A distance 3.451 Å, calc. 3.390 Å;where the discrepancy arises from the inexistence in thecomputed molecular (isolated) structure of any other HB ofintermolecular nature, whereas in the crystal there exist cor-respondingly short intermolecular contacts). The most signif-icant deviation of the experimental molecular conformationis that ligands lie more orthogonal to the coordination planethan in the calculated structure. This can be explained bysmall distortions effected to maximize the supramolecularinteractions C–Hpy⋯OC and C–Hsac⋯OS as describedabove.

In [Pd(sac)2(pyz)2] (2) the effect is similar to that in 1, asthe supramolecular C–Hpyz⋯OC and C–Hpyz⋯OS interac-tions account for differences in the dihedral angles betweenthe ligands and CP between the calculated and experimentalstructures.

In [Pd(sac)2(SMe2)2] (4) deviations between calculatedan experimental conformations are smaller than in 1 or 2.This can be explained by the much weaker strength of theSMe2⋯OC and C–H⋯S interactions with respect to typicalHBs present in complexes with py or pyz ligands.

By contrast, for 5 and 6 the largest differences betweencalculated and experimental conformations are found. Thiscan be ascribed to the occurrence of the strongest supramo-lecular interactions. In [Pd(sac)2(SMe2)(OH2)] (5) the maineffects on the molecular conformation are that: (i) the experi-mental saccharinate ligands are more orthogonal to the CP(ca. 10°) than in the calculated one, and (ii) the SMe2 ligandis rotated significantly about the Pd–S axis (ca. 59°), and thisrotation allows the simultaneous link by HBs to a CO andtwo SO2 groups (Scheme 3 and Fig. 5). Fig. 7 shows the over-lay of calculated and experimental molecular structures of[Pd(sac)2(SMe2)(OH2)].

In [Pd(sac)2(nicot)2] (6) the highest differences betweenthe calculated and experimental conformations are found,which can be attributed to the occurrence of the strongestsupramolecular interactions in this particular case. Inthis regard, –NH2⋯OC and –NH2⋯OS HBs seem to beable to modify the angles between ligands and the CP by upto ca. 10°.

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Fig. 7 Overlay of experimental and calculated (green) molecularconformation of [Pd(sac)2(SMe2)(OH2)].

ExperimentalSynthesis and crystallization

The saccharinate complexes trans-[Pd(sac)2(L)2] [L = pyridine(1), pyridazine (2), PPh3 (3), SMe2 (4) or nicotinamide (6)] wereobtained by reacting the precursor [Pd(sac)2(SMe2)2] with thecorresponding neutral monodentate ligand (molar ratio 1 : 2)according to the procedure previously described.15i Complex 7was obtained by a similar method using [Pd(succ)2(SMe2)2] asthe precursor.15i

Single crystals were obtained by slow evaporation ofchloroform (2 and 4) or dimethyl sulfoxide (5) solutions ofthe complexes. In the case of complexes 6 and 7, single crys-tals could not be obtained and powder diffraction was usedfor their structural elucidation. Crystal structures of 1 and 3have been published previously,15i and the structural datahave been deposited with the Cambridge CrystallographicData Centre: CCDC reference numbers 817742 (1), 817739 (3).

X-ray data collection and structure determination

For 2, 4 and 5, diffraction data were collected using a BrukerSmart Apex diffractometer with graphite-monochromatedMo-Kα radiation (λ = 0.71073 Å). The diffraction frames wereintegrated using the SAINT package23 and corrected forabsorption with SADABS.24 Crystallographic data are shownin Table S1.† The structures were solved by direct methodsand refined anisotropically on F2.25 Hydrogen atoms wereintroduced in calculated positions. In complex 4, the crystalswere of poor quality, probably related to the labile and low-boiling-point ligand SMe2. This fact produces a high atomicdisplacement parameter of the S atom and a high absolutevalue for the deepest hole in the electronic density locatedclose by the S atom (0.58 Å).

For 6 and 7, high resolution X-ray powder diffractionpatterns were collected at the SpLine beamline (BM25A) ofthe Spanish CRG at the European Synchrotron RadiationFacility (ESRF, Grenoble) with a fixed wavelength of 0.8269 Åat room temperature. Powder samples were placed inside a0.5 mm-diameter capillary, which was rotated during expo-sure. Data collection was done in a continuous 2θ-scan modewith 0.015° step and 2 s acquisition time per point. Thediffracted beam was detected using a scintillation counter.The incoming beam was also monitored to normalise thedecay of the primary beam.

The peak positions were identified using a derivative-based algorithm that is implemented in the peak searchutility of the WINPLOTR software package.26 The indexingwas carried out using the commonest indexing programs:ITO, TREOR90, DICVOL, KOHL, TAUP, FJZN, and LZON.To estimate the shape and width of the Bragg reflectionsas well as the instrumental shifts, we performed the Le Bailfit27 implemented as the profile-matching option in theFULLPROF program.28 A first approximation to the crystalstructure was obtained by Monte Carlo methods, using theparallel tempering algorithm implemented in the FOX


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software package.29 The atomic coordinates obtained byMonte Carlo methods were used to initialise the Rietveldrefinements, which were performed using the FULLPROFprogram.30 It is clear that the atomic fractional coordinatesobtained from single crystal diffraction technique will bemore accurate than those obtained from powder diffraction,mainly due to the use of molecular rigid block models in therefinement. However, the latter is also a powerful techniquesince precise lattice parameters can be obtained with anaccuracy comparable to that of the single crystal one.31 Also,its accuracy is enough to reveal the pattern of the crystalpacking of molecules in the solid state. ESI† shows plots forthe Rietveld refinement of 6 and 7.

The structural data (excluding structure factors) have beendeposited with the Cambridge Crystallographic Data Centre:CCDC reference numbers 982563 (2), 982564 (4), 982565 (5),982566 (6) and 982567 (7).

Computational details

Quantum chemical calculations were performed using theORCA electronic structure program package.32 All geometryoptimizations were run with tight convergence criteria usingthe B3LYP33 functional together with the new, efficientRIJCOSX algorithm34 and the def2-TZVP basis set35 togetherwith the [SD(28,MWB)] effective core potential (ECP) or Pdatoms.36 In all optimizations and energy evaluations, thelatest Grimme's semi-empirical atom-pair-wise correction,accounting for the major part of the contribution of disper-sion forces to the energy, was included.37 From these geome-tries all energy data were obtained by means of single-point(SP) calculations using the same functional as well as themore polarized def2-TZVPP basis set,34,38 and are notcorrected for the zero-point vibrational (ZPV) term.

Conclusion

In the saccharinate ligand the CO group produces shortersupramolecular interactions than SO2. This can be under-stood in the frame of the general chemical behaviour ofsaccharine/saccharinates: (i) The deprotonated nitrogen (N−)and carbonyl group have been reported9 as the groups ableto make the strongest synthons. (ii) Some uncommon com-plexes where saccharinate coordinates to metal by CO havebeen described,39 confirming the bonding ability of the car-bonyl group by means of covalent or non-covalent interac-tions. Overall, an observer role can be assigned to Pd in itssaccharinate complexes regarding supramolecular interac-tions, which allows the rationalization of saccharinate inter-actions in similar terms to those employed in well-documented organic salts. The saccharinate ligand linkscomplex molecules by hydrogen bonds, π⋯π interactionsor C–H⋯π interactions. We have concluded that thesaccharinate ligand has a stronger capability to organize thesupramolecular structure than py, pyz and PPh3 but weakerthan H2O or nicotinamide. Supramolecular interactions arestrong enough to modify molecular conformations (the angles


between the coordination plane and saccharinate orco-ligands) in the complexes studied. As expected, the strongerthe intermolecular interactions, the higher the deviations.

References

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https://www.researchgate.net/publication/273907043_SHELX-97_Programs_for_Crystal_Structure_Solution_and_Refinement?el=1_x_8&enrichId=rgreq-6f4cb2d3-495c-407e-b264-e5a29ee5e44e&enrichSource=Y292ZXJQYWdlOzI3MjI2NTU2MztBUzoyMTUxOTI1MDQ5MzQ0MDFAMTQyODMxNzI5OTg4NA==



Ligand hierarchy on driving the crystal packing. Effect of supramolecular interactions on solid-state conformations adopted by saccharinate Pd(II) complexes

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