Further insights on the high–low spin interconversion in nickel(ii) tetramine complexes. Solvent and temperature effects

Abstract

The spin interconversion equilibrium involving the [Ni^II(cyclam)]²⁺ complex has been investigated in a variety of polar solvents, at varying temperatures. The greater the donor tendencies of the solvent, the higher the endothermicity of the high-to-low-spin conversion. In particular, a positive linear relationship exists between ΔH° and Gutmann's Donor Number (DN). In the same way, higher donor tendencies of the solvent favour the occurrence of the Ni^II-to-Ni^III oxidation process and negative linear relationship has been found between the E_1/2(Ni^III/Ni^II) and DN. General behaviour is related to the intensity of the metal–solvent axial bonds in the octahedrally elongated cyclam complexes (of both Ni^II and Ni^III).