Synthesis, reactivities, and electrochemical properties of pyridinecarboxamide complexes of rhodium(III) and iridium(III). Crystal structure of [Rh(bpb)(py)2]ClO4[H2bpb = 1,2-bis(2-pyridinecarboxamido)benzene, py = pyridine]

Abstract

A series of organo and non-organo rhodium and iridium complexes of bpb and bpc ligands [H₂bpb = 1,2-bis(2-pyridinecarboxamido)benzene, H₂bpc = 4,5-dichloro-1,2-bis(2-pyridinecarboxamido)benzene] have been synthesized. These complexes display reversible one-electron oxidation couples. Stable one-electron-oxidized species have been generated both chemically and electrochemically. The oxidation potentials are affected dominantly by the charge effect but are relatively independent of the nature of the central metal ions and axial ligands. On the contrary, [Rh(bpe)R]·H₂O complexes [R = Me or Et; H₂bpe = 1,2-bis(2-pyridinecarboxamido)ethane] can only be oxidized irreversibly at a potential of about 0.3 V more anodic than that of the corresponding bpb complexes. The involvement of the equatorial ligand in the oxidation of the bpb and bpc complexes has been suggested. The complex [Rh(bpb)(py)₂]ClO₄ has been characterized by X-ray crystallography: space group P, a= 8.316(1), b= 9.620(2), c= 17.405(6)Å, α= 98.87(2), β= 99.57(2), γ= 90.55(2)°Z= 2, and R= 0.039 for 4 788 observed reflections.