M(μ-CN)Fe(μ-CN)M‘ Chains with Phthalocyanine Iron Centers: Redox, Spin-State, and Mixed-Valence Properties

Abstract

Dinuclear complexes with M−CN−ZnPc and M−CN−FePc−CN arrays and trinuclear complexes with M(μ-CN)Fe(μ-CN)M‘ arrays containing central metal phthalocyaninato (Pc) and external Cp(dppe)Fe or Cp(PPh₃)₂Ru building blocks (M) and having all possible orientations of the bridging cyanide ligands were subjected to electrochemical and preparative redox reactions. The species with unpaired electrons show characteristic MMCT bands in the near-IR spectra, the energies of which depend in a typical fashion on the nature of the building blocks and the orientation of the cyanide bridges and can be correlated with the redox potentials. Cyclic voltammetry has revealed electronic communication between the external organometallic units. An analysis of the MMCT spectra allows the assignment of the odd-electron complexes as class II mixed-valence species. The magnetic moments of the complexes with central Fe(III)Pc units are characteristically higher than the spin-only value for one unpaired electron. A Mössbauer investigation has shown that the M−CN−Fe(III)Pc−NC−M complexes undergo a low-spin-to-high-spin crossover of the Fe(III) component above room temperature.