Crystal structure of diaquabis(N,N-diethylnicotinamide-κN 1)bis(2,4,6-trimethylbenzoato-κO 1)cobalt(II)

The CoII atom in the crystal structure of diaquabis(N,N-diethylnicotinamide)bis(2,4,6-trimethylbenzoato)cobalt(II) is located on an inversion centre and exhibits a slightly distorted octahedral N2O4 coordination set. Hydrogen bonds of the type O—H⋯O and C—H⋯O lead to the formation of a three-dimensional network.

The centrosymmetric molecule in the monomeric title cobalt complex, [Co(C 10 H 11 O 2 ) 2 (C 10 H 14 N 2 O) 2 (H 2 O) 2 ], contains two water molecules, two 2,4,6-trimethylbenzoate (TMB) ligands and two diethylnicotinamide (DENA) ligands. All ligands coordinate to the Co II atom in a monodentate fashion. The four O atoms around the Co II atom form a slightly distorted square-planar arrangement, with the distorted octahedral coordination sphere completed by two pyridine N atoms of the DENA ligands. The dihedral angle between the planar carboxylate group and the adjacent benzene ring is 84.2 (4) , while the benzene and pyridine rings are oriented at a dihedral angle of 38.87 (10) . The water molecules exhibit both intramolecular (to the non-coordinating carboxylate O atom) and intermolecular (to the amide carbonyl O atom) O-HÁ Á ÁO hydrogen bonds. The latter lead to the formation of layers parallel to (100), enclosing R 4 4 (32) ring motifs. These layers are further linked via weak C-HÁ Á ÁO hydrogen bonds, resulting in a three-dimensional network. One of the two ethyl groups of the DENA ligand is disordered over two sets of sites with an occupancy ratio of 0.490 (13):0.510 (13).
The structure-function-coordination relationships of arylcarboxylate ions in Co II complexes of benzoic acid derivatives may 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 conditions and temperature of synthesis (Shnulin et al., 1981;Nadzhafov et al., 1981;Antsyshkina et al., 1980;Adiwidjaja et al., 1978). When pyridine or its derivatives are used instead of water molecules, the resulting structure is completely different (Catterick et al., 1974). In this context, we synthesized a Co II -containing compound with 2,4,6-trimethylbenzoate (TMB) and DENA ligands, namely diaquabis(N,Ndiethylnicotinamide-N 1 )bis(2,4,6-trimethylbenzoato-O 1 )cobalt(II), [Co(DENA) 2 (TMB) 2 (H 2 O) 2 ], and report herein its crystal structure.

Structural commentary
The asymmetric unit of the mononuclear title complex contains one Co II atom located on an inversion centre, one TMB ligand, one DENA ligand and one water molecule, with all ligands coordinating to the metal ion in a monodentate fashion (Fig. 1).

Figure 2
Part of the crystal structure viewed approximately down [100]. Intra-and intermolecular O-HÁ Á ÁO hydrogen bonds, shown as dashed lines, enclose R 4 4 (32) ring motifs. Only one part of the disordered group and only H atoms involved in hydrogen bonding have been included for clarity.

Synthesis and crystallization
The title compound was prepared by the reaction of CoSO 4 Á7H 2 O (1.41 g, 5 mmol) in H 2 O (100 ml) and N,N-diethylnicotinamide (1.78 g, 10 mmol) in H 2 O (10 ml) with sodium 2,4,6-trimethylbenzoate (1.86 g, 10 mmol) in H 2 O (150 ml). The mixture was filtered and set aside to crystallize at ambient temperature for three weeks, giving pink single crystals.

Refinement
Experimental details including crystal data, data collection and refinement are summarized in Table 3. Atoms H1W and H2W (of the water molecule) were located in a difference Fourier map. Their coordinates were refined freely, with U iso (H) = 1.5U eq (O   (7) and R 4 4 (32) ring motifs, are shown as dashed lines (see Table 2). Only one part of the disordered group and only H atoms involved in hydrogen bonding have been included for clarity. geometrically, with C-H = 0.93, 0.96 and 0.97 Å for aromatic, methyl and methylene H atoms, respectively, and constrained to ride on their parent atoms, with U iso (H) = k Â U eq (C), where k = 1.5 for methyl H atoms and k = 1.2 for other H atoms. The disordered ethyl group (C19, C20) was refined over two sets of sites with distance restraints and SIMU and DELU restraints (Sheldrick, 2008). The refined occupancy ratio of the two orientations is 0.490 (13):0.510 (13).

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (