Hexakis(N,N′-dimethylthiourea-κS)nickel(II) nitrate

The title complex salt, [Ni(C3H8N2S)6](NO3)2, consists of an [Ni(Dmtu)6]2+ (Dmtu is N,N′-dimethylthiourea) dication and two nitrate counter-anions. The NiII atom (site symmetry ) is coordinated by the S atoms of six Dmtu ligands within a slightly distorted octahedral environment. The crystal structure is characterized by weak intramolecular N—H⋯S interactions and by intermolecular N—H⋯O hydrogen bonds involving the nitrate anion (site symmetry 3.). These intermolecular interactions lead to the formation of two-dimensional networks lying parallel to the ab plane. The networks are linked via non-classical intermolecular C—H⋯O hydrogen bonds, forming a three-dimensional arrangement.

The title complex salt, [Ni(C 3 H 8 N 2 S) 6 ](NO 3 ) 2 , consists of an [Ni(Dmtu) 6 ] 2+ (Dmtu is N,N 0 -dimethylthiourea) dication and two nitrate counter-anions. The Ni II atom (site symmetry 3) is coordinated by the S atoms of six Dmtu ligands within a slightly distorted octahedral environment. The crystal structure is characterized by weak intramolecular N-HÁ Á ÁS interactions and by intermolecular N-HÁ Á ÁO hydrogen bonds involving the nitrate anion (site symmetry 3.). These intermolecular interactions lead to the formation of two-dimensional networks lying parallel to the ab plane. The networks are linked via non-classical intermolecular C-HÁ Á ÁO hydrogen bonds, forming a three-dimensional arrangement.

Comment
Several studies have been focused on the synthesis and structural characterization of nickel(II) complexes with thiourea type ligands. These studies showed that nickel(II) can adopt a variety of coordination geometries (octahedral, tetragonal, square-planar and tetrahedral) both in the solid state and in solution, which were prepared by varying the ligands or the anions (Ambujam et al., 2006;Bentley et al., 1974;Chiesi et al., 1971;Eaton & Zaw, 1975;El-Bahy et al., 2003;Figgis & Reynolds, 1986;Monim-ul-Mehboob et al., 2010;Sonar et al., 1979;Weininger et al. 1969, Weininger & Amma, 1976. When the anion is chloride, bromide or iodide, the predominant coordination about the nickel(II) atom in the crystalline solid state is tetragonal with the halide anions in the apical positions, leading to [NiL 4 ]X 2 complexes (Ambujam et al., 2006;Chiesi et al., 1971;Crane et al., 2004;Figgis & Reynolds, 1986;Weininger & Amma, 1976), although [NiL 6 ]X 2 complexes are also formed (El-Bahy et al., 2003;Weininger et al., 1969). The formation (in the solid state) of the octahedral species NiL 6 2+ is ascribed to crystal packing forces and extensive hydrogen bonding (Ambujam et al., 2006;El-Bahy et al., 2003;Monim-ul-Mehboob et al., 2010;Weininger et al., 1969). The coordination of nickel(II) in nitrate and the perchlorate salts is generally homoleptic octahedral in the solid state (Bentley et al., 1974;Monim-ul-Mehboob et al., 2010), but also can give such species as [NiL 2 (NO 3 ) 2 ] (Basso et al., 1969). We have recently reported on the crystal structure of a thiourea ( The molecular structure of the title complex is illustrated in Fig. 1. It is ionic and consists of a [Ni(Dmtu) 6 ] 2+ cationic unit (site symmetry 3) and two nitrate counter ions (site symmetry 3.). Atom Ni1 assumes a slightly distorted octahedral geometry, due to coordination with six sulfur atoms of the Dmtu ligands. In the cation there are weak N-H···S interactions linking adjacent ligand molecules (Table 1). The values of the bond lengths and bond angles observed in the title complex are comparable to those reported for related complexes (Ambujam et al., 2006;El-Bahy et al., 2003;Monim-ul-Mehboob et al., 2010;Weininger et al., 1969). In the only previously reported nickel(II) complex of N,N'-dimethylthiourea, [Ni(Dmtu) 4 ]Br 2 (Weininger & Amma, 1976), the nickel(II) atom is 4-coordinate, while in the title complex having the same ligand the nickel(II) atom is 6-coordinate, suggesting that in the presence of nitrate an octahedral coordination is preferred.
In the crystal of the title compound the [Ni(Dmtu) 6 ] +2 cations and the NO 3 ions are connected via N-H···O hydrogen bonds (Table 1) to form two-dimensional networks lying parallel to the ab-plane (Fig. 2). These two-dimensional sheets are linked via C-H···O hydrogen bonds (Table 1), resulting in the formation of a three-dimensional network.

Experimental
The title compound was prepared by adding 2 equivalents of N,N'-dimethylthiourea in 15 ml methanol to 0.29 g (1 mmol) of nickel(II) nitrate hexahydrate in 10 ml methanol. After stirring the mixture for 30 min the solution was filtered. The filtrate on slow evaporation yielded pale-green crystals, suitable for X-ray diffraction analysis.

Refinement
The NH H-atoms were located in difference electron-density maps. In the final cycles of least-squares refinement they was refined with a distance restraint of N-H = 0.87 (2) Å. The C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.97 Å for CH 3 H-atoms, with U iso (H) = 1.5U eq (parent C-atom).