Crystal structure of catena-poly[[[diaquabis(2,4,6-trimethylbenzoato-κO)cobalt(II)]-μ-aqua-κ2 O:O] dihydrate]

In {[Co(C10H11O2)2(H2O)3]·2H2O}n, the CoII atom is coordinated by two TMB anions and two water molecules in the basal plane, while another water molecule bridges the CoII atoms in the apical directions, forming polymeric chains running along [001].


Chemical context
Transition metal complexes with ligands of biochemical interest, such as imidazole and some N-protected amino acids, show interesting physical and/or chemical properties, through which they may find applications in biological systems (Antolini et al., 1982). Some benzoic acid derivatives, such as 4-aminobenzoic acid, have been extensively reported in coordination chemistry, as bifunctional organic ligands, due to the varieties of their coordination modes (Chen & Chen, 2002;Amiraslanov et al., 1979;Hauptmann et al., 2000).
The structure-function-coordination relationships of the arylcarboxylate ion in Zn II complexes of benzoic acid derivatives change depending on the nature and position of the substituted groups on the benzene ring, the nature of the additional ligand molecule or solvent, and the pH and temperature of the synthesis Nadzhafov et al., 1981;Antsyshkina et al., 1980;Adiwidjaja et al., 1978). When pyridine and its derivatives are used instead of water molecules, the structure is completely different (Catterick et al., 1974).
The structures of some mononuclear polymeric complexes obtained from the reactions of transition metal(II) ions with nicotinamide (NA) and/or some benzoic acid derivatives as ligands have been determined, e.g. {Mn (C 11 H 14 Bozkurt et al., 2013)], where the transition metal(II) cations are bridged by water molecules in (II), 4-fluorobenzoate anions in (III), nicotinamide ligands in (IV), 3-hydroxybenzoate anions in (V) and 3-chlorobenzoate anions in (VI). The synthesis and structure determination of the title compound, (I), a one-dimensional polymeric cobalt(II) complex with two 2,4,6-trimethylbenzoate (TMB) ligands and four coordinating and two non-coordinating water molecules, was undertaken in order to compare the results obtained with those reported previously. Its crystal structure is reported herein.

Structural commentary
The asymmetric unit of the title one-dimensional polymeric compound, (I), contains one Co II cation situated on a centre of inversion, one-half of a coordinating water molecule, one 2,4,6-trimethylbenzoate (TMB) anion together with the one coordinating and one non-coordinating water molecules; the TMB anion acts as a monodentate ligand (Fig. 1).
The Co II atom is coordinated by two TMB anions and two water molecules in the basal plane while another water molecule bridges the Co II atoms in the axial directions, resulting in a slightly distorted octahedral coordination sphere around each Co 2+ cation, and forming polymeric chains (Fig. 2    The asymmetric unit of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 3
A partial packing diagram of the title one-dimensional polymeric compound in a view approximately along the b axis, where the c axis is horizontal and the a axis is vertical. H atoms have been omitted for clarity.
bridging water molecules rather than bridging hydroxide groups. This is confirmed by softness-sensitive BVS calculations (Adams, 2001), which identify the BVS for the Co atom to be 2.05 (5).
Neighboring Co II atoms are bridged by H 2 O molecules ( Fig. 2) and they are also coordinated by monodentate carboxylate groups. The non-coordinating oxygen atoms of the carboxylate groups interact with the bridging water molecules via short hydrogen bonds (Table 1 and  View of the hydrogen bonding and packing of the title one-dimensional polymeric compound along the c axis. H atoms not involved in classical hydrogen bonds have been omitted for clarity. Table 1 Hydrogen-bond geometry (Å , ).
Cg1 is the centroid of the C2-C7 ring.

Figure 5
Part of the crystal structure. Intramolecular and intermolecular O-HÁ Á ÁO hydrogen bonds, enclosing S(6), R 2 2 (8) and R 3 increasing the Lewis basicity of the bridging water molecules by attracting the protons of the water molecules to the oxygen atoms of the carboxylate groups. Intramolecular O-H brdW Á Á ÁO c and intermolecular O-H coordW Á Á ÁO c (brdW = bridging water, coordW = coordinating water and c = carboxylate) hydrogen bonds (Table 1) link the bridging and coordinating water molecules to the carboxylate oxygen atoms, enclosing S(6) ring motifs (Fig. 5).

Comparison with related structures
In the crystal structure of a similar complex, catena-poly- , which had previously been reported by Chen et al. (2007). In (VIII), the Mn II atom and the bridging water O atom are located on a centre of symmetry and the Mn II atom is coordinated by two 2,4,6-trimethylbenzoate (TMB) anions and two water molecules in the basal plane, while another water molecule

catena-Poly[[[diaquabis(2,4,6-trimethylbenzoato-κO)cobalt(II)]-µ-aqua-κ 2 O:O] dihydrate]
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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. Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, y, −z+1/2; (iii) x, −y+1, z−1/2; (iv) −x+1, y, −z+3/2; (v) −x+1/2, y+3/2, −z−1/2.