Synthesis, crystal structure, electrochemistry and electronic paramagnetic resonance spectroscopy of [M{(PPh2CH2)3CMe}(o-S2C6H4)][PF6]n(M = Fe, Co or Rh; n= 0 or 1)

Abstract

Monomeric thiolate complexes of formula [M{(PPh₂CH₂)₃CMe}(o-S₂C₆H₄)][PF₆]_n(M = Fe^II, Fe^III, Co^II, Co^III, Rh^II or Rh^III; n= 0 or 1) have been synthesized. The molecular structure of all these compounds has been established by single-crystal X-ray diffraction studies. All the complexes display a square-pyramidal geometry with differing degrees of distortion depending on the oxidation state and electronic configuration of the metal. Electrochemistry served to localize the formal electrode potentials of the different M^II–M^III couples. In dichloromethane solution, the iron(III) complex (E°=+0.04 V vs. saturated calomel electrode) is easier to reduce than the cobalt(III) complex (E°=–0.39 V), which in turn is easier to reduce than the rhodium(III) complex (E°=–0.69 V). In the case of the iron species, the possibility of obtaining the somewhat stable Fe^I congener has been realized. The paramagnetic Fe^I and Fe^III, Co^II and Rh^II derivatives have been studied by EPR spectroscopy under different experimental conditions, confirming that the unpaired electron is mainly localized on the metal centre. For cobalt and rhodium derivatives EPR results indicate the presence in solution of a chemical equilibrium between two different isomers.