Magnetic and spectral properties of nickel(II) complexes with bridging nitrite groups

Abstract

The preparations and magnetic and spectral properties of the compounds NiD(NO₂)₂(D = ethylenediamine, and N-methyl- and NN-diethyl-ethylenediamine) and NiL₂(NO₂)₂(L = pyridine, isoquinoline, and 3- and 4-methylpyridine), the latter as benzene solvates in some cases, are reported. The nitrite groups in the ethylenediamine (en) and N-methylethylenediamine (men) complexes are thought to be present as M–ON(O)–M [type (I)] bridges. The spectral properties of the rest of the compounds are similar to those of the trimer [Ni(3-Mepy)₂(NO₂)₂]₃, C₆H₆(Mepy = methylpyridine) which is known to contain M–O(NO)–M [type (II)] bridges, type (I) bridges, and chelating nitrite groups. The type (II) bridges give rise to ν(NO) bands in the regions 1007–1026 and 1470–1490 cm^–1.

Single-crystal polarized electronic spectra of [Ni(3-Mepy)₂(NO₂)₂]₃, C₆H₆ are reported and discussed. The magnetic properties of this compound over the range 90–300 K are interpreted in terms of J=–11 cm^–1(for the coupling between adjacent metal atoms of the trimer). For the compound [Ni(en)₂(NO₂)]ClO₄, which contains chains of nickel atoms connected by type (I) bridges, J=–18 cm^–1.