Structural and spectroscopic studies of transition metal nitrite complexes. III. Crystal structures and spectra of Aquabis(meso-1,2-diphenylethane-1,2-diamine)-nitronickel(II) perchlorate and Bis(meso-1,2-diphenylethane-1,2-diamine)-(nitrito-O,O')nickel(II) chloride

Abstract

The crystal and molecular structures of the complexes [Ni(mstien),(NO₂)(H₂O)] ClO₄ and [Ni(mstien)₂(O₂N)] Cl are reported (mstien = meso-stilbenediamine, 1,2-diphenylethane-1,2-di-amine). Both compounds contain nickel(II) in an essentially octahedral ligand environment. In the latter complex, the nitrite ion chelates, while in the former it is present as a nitro group situated trans to a coordinated water molecule. In both complexes the conformations observed for the amine chelate rings can be rationalized on the basis that they minimize intramolecular ligand repulsions. The complex [Ni(mstien)₂(O₂N)] NO₂ is isomorphous with the analogous chloride compound, and spectral evidence suggests that the complex [Ni(mstien)₂(O₂N)] ClO₄ also contains a chelating nitrite group. The electronic spectra of single crystals of [Ni(mstien),(O₂N)] X (X = Cl^- and NO₂^-) show bands centred at c. 25000 cm^-l which exhibit vibrational fine structure. The energies of the progressional spacings are c.600cm^-l, which suggests that the bands are probably due to n → π* internal nitrite transitions. The band centred at c. 20500 cm^-1 in [Ni(mstien)₂(NO₂)(H₂O)] ClO₄ also shows well resolved vibrational fine structure with a progressional spacing of c. 630 cm^-1. This implies that the band is not due to a 'd-d' transition, but must be caused by the excitation of an electron into the nitrite π* orbital, either from a non-bonding nitrite orbital, or more probably from the nickel ion.