Structural and spectroscopic studies of transition metal nitrite complexes. VII. Crystal structures and spectra of two dinuclear and trinuclear species with stoichiometry [Ni(methylpyridine)₂(NO₂)₂] containing bridging nitrite groups

Abstract

The crystal structures of the dimer [Ni(γmpy)₂(NO₂)₂]₂,2C₆H₆ and the trimer [Ni(βmpy)₂(NO₂)₂]₃,- C₆H_s (γmpy = 4-methylpyridine, βmpy = 3-methylpyridine) are reported, the latter being the redetermination of a structure described previously. The ligand coordination geometry in each oligomer is essentially octahedral, with neighbouring nickel(II) ions being bridged by two nitrite groups, one through a single oxygen atom and the second through an oxygen and the nitrogen atom. The amine ligands occupy trans coordination sites with the terminal bond positions in both species being taken up by chelating nitrite ions. In both compounds the oligomers pack so that the amine rings form sheets with potential voids in the lattice being filled by clathrated benzene molecules. The electronic spectra of the complexes in the visible region are unusual, showing peaks centred at c. 17500 and c. 20500 cm^-1, and the assignment of these is discussed. The infrared stretching frequencies of the nitrite groups in these and other compounds are found to correlate well with the observed nitrogen-oxygen bond lengths.