trans-Tetraaquabis(nicotinamide-κN)cadmium(II) biphenyl-4,4′-disulfonate

In the title compound, [Cd(C6H6N2O)2(H2O)4](C10H8O6S2), the CdII ion is located on a crystallographic inversion centre. An octahedral coordination geometry is defined by four water molecules in one plane, and two trans N-atom donors of the nicotinamide ligands. The biphenyl-4,4′-disulfonate anion also lies on a crystallographic inversion centre. In the crystal structure, the complex cations are connected to the counter-anions via N—H⋯O and O—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title compound, [Cd(C 6 H 6 N 2 O) 2 (H 2 O) 4 ](C 10 H 8 O 6 S 2 ), the Cd II ion is located on a crystallographic inversion centre. An octahedral coordination geometry is defined by four water molecules in one plane, and two trans N-atom donors of the nicotinamide ligands. The biphenyl-4,4 0 -disulfonate anion also lies on a crystallographic inversion centre. In the crystal structure, the complex cations are connected to the counteranions via N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

Comment
The strong and directional nature of hydrogen bonds is exploited in the organized self-assembly of molecules in the solid state. Amides are commonly used functional groups in crystal engineering owing to the inherent coordination and hydrogen bonding donor/acceptor functionalities, and were used to construct extended frameworks sustained both by hydrogen bonds and coordination bonds (Beatty 2001;Christer et al., 2004). On the other hand, the sulfonate group is a suitable hydrogenbond acceptor, and has been used to build extended frameworks. (Holman et al., 2001;Lian & Li, 2007a,b,c,d) In this paper, we report the synthesis and crystal structure of the title compound.
In the title compound, the metal centre, located on a crystallographic inversion centre, is in an octahedral geometry Experimental Nicotinamide (0.050 g, 0.4 mmol) was added with constant stirring to an aqueous solution (10 mL) of Cd(CH 3 COO) 2 .2H 2 O (0.058 g, 0.2 mmol). The solution was then treated with disodium biphenyl-4,4'-disulfonate (0.070 g, 0.2 mmol). Colourless crystals of the title complex were collected by slow evaporation at room temperature after 7 days, (80% yield based on Cd).

Refinement
All the non-H atoms were refined with anisotropic thermal parameters.
H atoms attached to C or N atoms were placed in geometrically calculated positions (C-H = 0.93 Å, N-H=0.86 Å), and refined as riding with U iso (H) = 1.2U eq (C or N).
The O-bound H atoms were located in difference maps and refined as riding on the attached O atoms, with U iso (H) =  Fig. 1. The molecular structure of (1), with the atom labelling scheme. Displacement ellipsoids are drawn at the 40% probability level. H atoms are represented as spheres of arbitrary radii. Hydrogen bonds are shown as dashed lines. Symmetry codes:(i) -x, y, -z + 1/2; (ii): -x + 1, -y, -z + 1.