Crystal structure of diaquabis(4-tert-butylbenzoato-κO)bis(nicotinamide-κN 1)cobalt(II) dihydrate

The asymmetric unit of the monomeric cobalt complex, [Co(C11H13O2)2(C6H6N2O)2(H2O)2]·2H2O, contains one half of the complex molecule, one coordinating and one non-coordinating water, one 4-tert-butylbenzoate (TBB) ligand and one nicotinamide (NA) ligand; the Co atom lies on an inversion centre. The coordinating water molecules are hydrogen bonded to the carboxyl O atoms [O ⋯ O = 2.6230 (17) Å], enclosing an S(6) hydrogen-bonding motif, while intermolecular O—H⋯O hydrogen bonds link two of the non-coordinating water molecules to the coordinating water molecules and NA anions. In the crystal, O—H⋯O and N—H⋯O hydrogen bonds link the molecules, enclosing (8), (10) and (12) ring motifs, forming layers parallel to (001).

The asymmetric unit of the mononuclear cobalt complex, [Co(C 11 H 13 O 2 ) 2 -(C 6 H 6 N 2 O) 2 (H 2 O) 2 ]Á2H 2 O, contains one half of the complex molecule, one coordinating and one non-coordinating water molecule, one 4-tert-butylbenzoate (TBB) ligand and one nicotinamide (NA) ligand; the Co atom lies on an inversion centre. All ligands coordinating to the Co atom are monodentate. The four nearest O atoms around the Co atom form a slightly distorted square-planar arrangement, with the distorted octahedral coordination completed by the two pyridine N atoms of the NA ligands at distances of 2.1638 (11) Å . The coordinating water molecules are hydrogen bonded to the carboxyl O atoms [O Á Á Á O = 2.6230 (17) Å ], enclosing an S(6) hydrogenbonding motif, while intermolecular O-HÁ Á ÁO hydrogen bonds link two of the non-coordinating water molecules to the coordinating water molecules and NA anions. The dihedral angle between the planar carboxylate group and the adjacent benzene ring is 29.09 (10) , while the benzene and pyridine rings are oriented at a dihedral angle of 88.53 (4) . In the crystal, O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds link the molecules, enclosing R 2 2 (8), R 2 2 (10) and R 4 4 (12) ring motifs, forming layers parallel to (001). The C and H atoms of the tert-butyl group of the TBB ligand are disordered over two sets of sites with an occupancy ratio of 0.631 (5):0.369 (5).

Chemical context
Nicotinamide (NA) is one form of niacin. A deficiency of this vitamin leads to loss of copper from the body: a condition known as pellagra disease. Victims of pellagra show unusually high serum and urinary copper levels (Krishnamachari, 1974). The NA ring is the reactive part of nicotinamide adenine dinucleotide (NAD) and its phosphate (NADP), which are the major electron carriers in many biological oxidation-reduction reactions (You et al., 1978). The nicotinic acid derivative N,Ndiethylnicotinamide (DENA) is an important respiratory stimulant (Bigoli et al., 1972) Transition metal complexes with biochemical molecules 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 Co II complexes of benzoic acid derivatives may change depending on the nature and position of the substituent groups on the benzene ring, the nature of the additional ligand molecule or solvent, and the pH and temperature of 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). In this context, we synthesized a Co II -containing compound with 4-tert-butylbenzoate (TBB) and NA ligands, namely diaquabis(4-tert-butylbenzoato-O)bis(nicotinamide-N 1 )cobalt(II) dihydrate, [Co(C 11 H 13 O 2 ) 2 (C 6 H 6 N 2 O) 2

Structural commentary
The asymmetric unit of the crystal structure of the mononuclear title complex contains one 4-tert-butylbenzoate (TBB) and one nicotinamide (NA) ligand together with one coordinating and one non-coordinating water molecule, all ligands coordinating in a monodentate manner (Fig. 1).
In the title complex, the two carboxylate O atoms (O2 and O2 i ) of the two symmetry-related monodentate TBB anions and the two symmetry-related coordinating water O atoms (O4 and O4 i ) around the Co1 (site symmetry 1) atom form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination sphere is completed by the two pyridine N atoms (N1 and N1 i ) of the two symmetry-related monodentate NA ligands in the axial positions [symmetry code: (i) Àx, Ày, Àz] (Fig. 1).
Intramolecular O-H w Á Á ÁO c (w = water, c = carboxylate) hydrogen bonds (Table 1) link the coordinating water molecules to the TBB anions, enclosing S(6) hydrogen-bonding motifs, while intermolecular O-H w Á Á ÁO w and O-H w Á Á ÁO na (na = nicotinamide) hydrogen bonds link two of the noncoordinating water molecules to the coordinating water molecules and NA anions ( Fig. 1).

Figure 1
The molecular structure of the title complex with the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. Intra-and intermolecular O-HÁ Á ÁO hydrogen bonds are shown as dashed lines. Table 1 Hydrogen-bond geometry (Å , ). (3) 3.0331 (19) 175 (3) mixture was filtered and set aside to crystallize at ambient temperature for five days, giving pink single crystals.

Refinement
Experimental details including the crystal data, data collection and refinement are summarized in Table 2. Atoms H21 and H22 (for NH 2 ), H41, H42, H51 and H52 (for H 2 O) were located in a difference Fourier map and were refined freely. The C-bound H atoms were positioned geometrically, with C-H = 0.93 and 0.96 Å for aromatic and methyl 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 aromatic H atoms. During the refinement process the disordered t-butyl group atoms were refined with major:minor occupancy ratios of 0.631 (5)   hydrogen bonds, enclosing R 2 2 (8), R 2 2 (10) and R 4 4 (12) ring motifs, are shown as dashed lines (see Table 1). For clarity, only the major disorder component and H atoms involved in hydrogen bonding are shown.   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. Refined as a 2-component inversion twin.

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