Bis[μ-N′-(2-methyl-1-oxidopropanylidene)-2-oxidobenzohydrazidato]tetrapyridinetrinickel(II)

The asymmetric unit of the title trinuclear NiII compound, [Ni3(C11H11N2O3)(C5H5N)4], contains two independent molecules which are located on individual inversion centres. The central Ni atom, located on an inversion centre, is coordinated by two pyridine N atoms and is further N,O-chelated by two N-(2-methylpropanoyl)salicyloylhydrazidate anions in an elongated octahedral coordination geometry. The terminal Ni atom is coordinated by a pyridine ligand and is further N,N′,O-chelated by an N-(2-methylpropanoyl)salicyloylhydrazidate anion in a distorted square-planar coordination geometry. Weak intramolecular C—H⋯O hydrogen bonding is observed in the structure.


Comment
In the recent years, much attention has been paid to the coordination chemistry of the trianionic pentadentate N-acyl-salicylhydrazide ligands and their metal complexes. These kinds of pentadentate ligands have been utilized in the system of self-assembly in metallacrowns with different ring-sizes and nuclearities based on trivalent 3d metal ions such as Fe(III), Gd(III), Co(III) and Mn(III) (Dou et al., 2006;John et al., 2005;Li et al., 2005;Xiao et al., 2007), and a few trinuclear complexes based on bivalent 3d metal ions such as Ni(II), Cu(II) and Zn(II) (Chen et al., 2011;Lin et al., 2007;Luo et al., 2007;Luo et al., 2008;Yang et al., 2005). Some of these complexes have potential application in chemically modified electrodes, anion-selective separation agents, magnetic materials and biological activities.
There are two crystallographically independent molecules of (I) in the asymmetric unit ( Fig. 1). Each independent molecule is composed of three Ni(II) ions, two L 3and four pyridine molecules. The ligand serves as both bidentate for the central Ni(II) ion and, at the same time, tridentate for the two terminal Ni(II) ions, forming a linear trinuclear nickel structure. The neighboring Ni···Ni interatomic distances are 4.605 (2)Å and 4.589 (2)Å, respectively. The coordination geometry of the three Ni(II) atoms in each trinuclear molecule follows a square-planar/octahedral/square-planar mode. The central Ni(II) atom located on the crystallographic inversion is six-coordinated by two pyridine N atoms in axial positions, and the two hydrazine N atoms and carbonyl O atoms of two ligands in the equatorial plane, conferring an elongated octahedral geometry. Each basal plane of the two octahedra is ideally planar and each Ni(II) ion complexly lies in the equatorial plane.
The terminal Ni(II) atom is coordinated in a square-planar configuration composed of the other hydrazine nitrogen carbonyl oxygen and phenolic oxygen of one ligand, as well as one pyridine N atom. The distances in the coordination planes around the Ni(II) ions (Table 1) and the bond lengths in the ligand moieties are comparable with the related Ni(II) complexes based on the similar pentadentate N-acyl-salicylhydrazide ligands (Xiao & Jin 2008;Yang et al., 2003).

Refinement
All H atoms were placed at calculated positions and treated as riding on their parent atoms with C-H = 0.93-0.98 Å , and U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for the others.

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. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.