Crystal structure of catena-poly[calcium-di-μ3-benzoato-κ6 O,O′:O-μ2-(dimethyl sulfoxide)-κ2 O:O]

A novel calcium benzoate complex, [Ca(C7H5O2)2(C2H6OS)], has been synthesized and structurally characterized. The compound has a chain polymeric structure stabilized by C—H⋯π interactions.

In the title complex, [Ca(C 7 H 5 O 2 ) 2 (C 2 H 6 OS)] n , the Ca 2+ ion (site symmetry m..) is surrounded by eight O atoms, six from two bridging-chelating tridentate benzoate carboxyl groups and two from a bridging dimethyl sulfoxide molecule (point group symmetry m..), giving an irregular coordination geometry [Ca-O bond length range = 2.345 (2)-2.524 (2) Å ]. One-dimensional coordination complex chains extending parallel to c are generated in which the triply 2 -Obridged Ca 2+ cations are separated by 3.6401 (5) Å . In the crystal, weak intrachain C-HÁ Á Á hydrogen bonds are present between the methyl H atoms of the dimethyl sulfoxide molecules as donors and the aromatic rings as acceptors [C-HÁ Á ÁCg = 3.790 (4) Å ].

Chemical context
Compounds of benzoic acid with calcium are of special interest due to their wide-ranging applications, for example as a preservative in the food industry, in cosmetics and in medicine. In spite of that, the crystal structures of such compounds have been poorly investigated. Searches of the Cambridge Structural Database (CSD; Version 5.35, November 2013 + 2 updates; Groom & Allen, 2014)  Here we report the synthesis of a new calcium benzoatedimethyl sulfoxide complex, [Ca(benz) 2 (dmso)] n , which was obtained as a by-product of an attempted synthesis of an Mn/ ISSN 2056-9890 Cu heterometallic complex (in crystalline form available for X-ray analysis) from the system: Mn-Cu-(bhz-sal)-CaO-KSCN-dmso (in open air), where manganese and copper were used as unactivated metal powders, bhz = benzohydrazide and sal = salicylaldehyde. The investigation of the system was carried out as a part of systematic research on the elaboration the 'direct synthesis' approach to both homo-and heterometallic coordination compounds (Babich et al., 1996;Buvaylo et al., 2005;Vassilyeva et al., 1997). It is worth noting that an alternative method of synthesis using a classical reaction between calcium oxide and benzoic acid in dmso, affords the same complex in good yield (up to 90%), but does not give X-ray quality crystals. The crystal structure of the title complex, [Ca(benz) 2 (dmso)] n , is reported herein.

Structural commentary
The asymmetric unit of [Ca(benz) 2 (dmso)] n comprises one Ca 2+ cation (site symmetry m..), one benzoate ligand and half of a dmso molecule, the other half being generated by mirror symetry. The irregular CaO 8 coordination polyhedron consists of six O atom donors from two O,O 0 chelating-bridging benzoate carboxyl groups with the same coordination modes, [2.1 1 1 12 ] in the Harris notation (Coxall et al., 2000), and two from 2 -bridging dmso molecules (Fig. 1). The coordination geometry deviates strongly from ideal, the Ca-O bond lengths varying from 2.345 (2) to 2.524 (2) Å (Table 1) and the O-Ca-O angles from 52.19 (7) to 156.06 (8) . The bridging Ca1-O1 i and Ca1-O1 ii (carboxyl) bond lengths are considerably shorter than the chelate ones, as is usually observed in polymeric benzoates. For the title complex, the bond-valence index [BVS (Ca)] (Allmann, 1975) is 2.03.

Supramolecular features
The triple-O-bridged CaO 8 polyhedra form one-dimensional coordination polymeric chains which extend parallel to the caxis direction (Figs. 2-4). The CaÁ Á ÁCa i and Ca1Á Á ÁCa1 iv separation in the chain is 3.6401 (5) Å [symmetry code (iv): Àx + 1, Ày, z À 1 2 ]. To the best of our knowledge, this is the first Ca carboxylate polymer based on non-centrosymmetric bridges (-2 : 1 ) 2 . For bridging modes in coordination poly- A fragment of the [Ca(benz) 2 (dmso)] n chain with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity. For symmetry codes, see Table 1. Table 1 Selected bond lengths (Å ).
Cg is the centroid of the benzoate ring.

Figure 2
Bridging interactions observed in the title complex polymer which extends along the c-axis direction. Phenyl rings and H atoms have been omitted for clarity. meric structures, reference should be made to Deacon et al. (2007) and Busskamp et al. (2007). The polymer chains in the title compound are additionally stabilized by weak C-HÁ Á Á interactions between the methyl groups of the dmso molecule and the benzoate rings (centroid Cg) (

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.