Structural and spectroscopic studies of transition metal nitrite complexes. IX.Crystal structures and spectroscopic properties of polymeric [Ni(C₂H₈N₂)₂-(NO₂)] ClO₄, its mononuclear zinc analogue, cis-Bis(ethane-1,2-diamine)(nitrito-O,O')zinc(II) perchlorate, and the complexes cis-(N,N,N',N'-Tetramethylethane-1,2-diamine)di(nitrito-O,O')-nickel(II) and -zinc(II)

Abstract

The crystal structures of the title compounds are reported. The complex [Ni(C₂H₈N₂)₂(NO₂)] ClO₄ is found to be an infinite polymer with trans N,O-bridging nitrite groups. The zinc analogue of this contains mononuclear units involving a symmetrically chelated nitrite group. The two compounds formed with N,N,N',N'-tetramethylethane-1,2-diamine are isostructural, with the metal having a distorted octahedral ligand environment provided by the amine nitrogen atoms and two chelating nitrite groups. However, while the nitrite ions in the nickel complex are chelated approximately symmetrically, the Zn-O bonds trans to the amine nitrogen atoms (2.30 Å) are much longer than those in the cis positions (2.07 Å), and an alternative description of the geometry of the zinc complex is as a highly distorted tetrahedral arrangement involving essentially monodentate nitrito groups. The difference in stereochemistry between these two complexes is apparently caused by electronic rather than steric factors, and comparison is also made with the geometry reported for the iso-structural copper complex. The electronic spectra of the two nickel(II) complexes are discussed in relation to their structures, and the infrared frequencies reported for the nitrite groups are correlated with the observed coordination geometries.