{N,N′-Bis[1-(2-pyridyl)ethylidene]propane-1,2-diamine}bis(thiocyanato-κN)nickel(II)

In the title complex, [Ni(NCS)2(C17H20N4)], the Ni2+ ion (site symmetry 2) is coordinated by the N,N,N,N-tetradentate Schiff base ligand and two thiocyanate ligands, forming a distorted NiN6 octahedral geometry, with the thiocyanate N atoms in a trans orientation. The pendant methyl group of the central propane-1,2-diamine fragment of the ligand is statistically disordered over two sets of positions. In the crystal, weak aromatic π–π stacking between pyridine rings [centroid–centroid separation = 3.7081 (17) Å] may help to establish the packing.

In the title complex, [Ni(NCS) 2 (C 17 H 20 N 4 )], the Ni 2+ ion (site symmetry 2) is coordinated by the N,N,N,N-tetradentate Schiff base ligand and two thiocyanate ligands, forming a distorted NiN 6 octahedral geometry, with the thiocyanate N atoms in a trans orientation. The pendant methyl group of the central propane-1,2-diamine fragment of the ligand is statistically disordered over two sets of positions. In the crystal, weak aromaticstacking between pyridine rings [centroid-centroid separation = 3.7081 (17) Å ] may help to establish the packing.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB5571).

Comment
The bis-Schiff bases formed from aldehydes with diamines have been widely investigated in coordination chemistry (Yin et al., 1999;Costes et al., 2002;Haikarainen et al., 2001;Miyasaka et al., 2002;Ryazanov et al., 2002). The complexes with such Schiff bases have proved to be of significant interest in the areas of catalysis, magnetism, medicinal and material chemistry. Although there have been numerous studies on the preparation and crystal structures of such complexes, the complexes with the Schiff base ligand N',N''-Bis(1-pyridin-2-ylethylidene)propane-1,2-diamine have never been reported.
In the present paper, the title nickel(II) complex with the Schiff base ligand and thiocyanate is reported.
The molecule of the title complex, Fig. 1, possesses a crystallographic twofold rotation axis symmetry. The Ni atom is coordinated by four N atoms of a Schiff base ligand and two N atoms from two thiocyanate ligands, forming an octahedral geometry. The bond lengths (Table 1) related to the central Ni atom are comparable to those observed in other nickel(II) complexes with Schiff bases (Liu et al., 2006;Li & Wang, 2007;Liu et al., 2007;Ali et al., 2006;Knight et al., 2007).

Experimental
To an ethanolic solution (30 ml) of 1,2-diaminopropane (0.074 g, 1 mmol) was added an ethanolic solution (30 ml) of 2acetylpyridine (0.242 g, 2 mmol). The mixture was stirred at room temperature for 30 minutes. Then a solution of ammonium thiocyanate (0.152 g, 2 mmol) and nickel(II) nitrate hexahydrate (0.291 g, 1 mmol) in a minimum amount of ethanol was added, and the final mixture was further stirred at room temperature for 1 h. The clear solution was set aside for a week, yielding green blocks of (I).

Refinement
The H8A and H8B atoms attached to C8 in the complex were located in a difference Fourier map and were refined with distance restraints of C-H = 0.97 (1) Å, and H···H = 1.55 (2) Å. All other H atoms were positioned geometrically and were constrained as riding atoms, with C-H distances of 0.93-0.96 Å, and U iso (H) set to 1.2 or 1.5U eq (C) of the parent atom.
Rotating group models were used for the methyl groups. Fig. 1. The molecular structure of the title compound, showing displacement ellipsoids drawn at the 30% probability level. Unlabeled atoms are related to labeled atoms by the symmetry operation -x, y, 1/2 -z. Only one orientation of C9 and its attached H atoms is shown.