Hexakis(thiourea-κS)nickel(II) nitrate: a redetermination

A preliminary X-ray study of the title molecular salt, [Ni(CH4N2S)6](NO3)2, has been reported twice previously, by Maďar [Acta Cryst. (1961), 14, 894] and Rodriguez, Cubero, Vega, Morente & Vazquez [Acta Cryst. (1961), 14, 1101], using film methods. We confirm the previous studies, but to modern standards of precision and with all H atoms located. The central Ni atom (site symmetry ) of the dication is octahedrally coordinated by six S-bound thiourea molecules. The crystal structure is stabilized by intra- and intermolecular N—H⋯S and N—H⋯O hydrogen bonds.

A preliminary X-ray study of the title molecular salt, [Ni(CH 4 N 2 S) 6 ](NO 3 ) 2 , has been reported twice previously, by Maď ar [Acta Cryst. (1961), 14, 894] and Rodriguez, Cubero, Vega, Morente & Vazquez [Acta Cryst. (1961), 14, 1101], using film methods. We confirm the previous studies, but to modern standards of precision and with all H atoms located. The central Ni atom (site symmetry 1) of the dication is octahedrally coordinated by six S-bound thiourea molecules. The crystal structure is stabilized by intra-and intermolecular N-HÁ Á ÁS and N-HÁ Á ÁO hydrogen bonds.

Comment
The coordination chemistry of thiourea type ligands has been a matter of interest in view of their biological (Arslan et al., 2009) and non-linear optical (Bhaskaran et al., 2007) properties, and because of their potential use as selective reagents for concentration and separation of metal ions (Emre et al., 2009). The complexes of nickel(II) with thioureas were shown to have a variety of stereochemistries (octahedral, tetragonal, square planar and tetrahedral) both in the solid state and in solution form (Eaton et al., 1975;Figgis et al., 1986;Suescun et al., 2000;Zhu et al., 2009). In order to investigate further about the structures of nickel(II)-thiourea systems, we present here a structural study of a Tu complex with nickel(II) nitrate, which consists of [Ni(Tu) 6 ] +2 molecular ions and nitrate counter ions.
A preliminary X-ray study of complex (I) has been reported twice previously, but with incomplete crystallographic data (Maďar, 1961;Rodriguez et al., 1961). We redetermined the crystal structure of complex (I), which we present in this paper.
In (I), the central Ni atom is located on a centre of inversion and is six-coordinated by six thiourea groups in a octahedral geometry (Fig. 1). The values of the geometrical parameters of the title molecule are as expected (Allen et al., 1987). The Ni-S bond lengths vary from 2.4708 (7) to 2.4995 (6) Å.
In the crystal packing of (I), adjacent molecules are linked by intra and intermolecular N-H···S and N-H···O hydrogen bonds (Table 2, Fig. 2), forming a three-dimensional network and a supramolecular structure.

Experimental
The complex was prepared by adding 4 equivalents of thiourea in 10 ml methanol to 1 mmole (0.29 g) solution of nickel(II) nitrate hexa hydrate in 10 ml methanol. After stirring the solution for half an hour, the green solution was filtered and the filtrate was kept for crystallization. As a result light green needles of (I) were formed.

Refinement
H atoms were positioned geometrically and were treated as riding on their parent C atoms, with N-H = 0.86 Å and U iso (H) = 1.2U eq (N).
supplementary materials sup-2 Figures   Fig. 1. View of (I) with displacement ellipsoids depicted at the 30% probability level for all non-H atoms. Fig. 2. Partial view of the intra and intermolecular N-H···S and N-H···O hydrogen bonds in the crystal structure of (I), forming a three-dimensional network.