Binuclear chromium(III), manganese(III), iron(III) and cobalt(III) complexes bridged by diaminopyridine

Abstract

Trivalent chromium, manganese, iron and bivalent cobalt salts react with 2,6-diaminopyridine and acetylacetone to give complexes of the type [M(C 15H 17N 3O 2)X] [where X  Cl, Br, NO 3 or NCS for M = chromium(III) and iron(III); X  Cl, Br, OAc or NCS for manganese(III)]. Conductance measurements show the complexes to be non-electrolytes. Molecular weights determined cryoscopically suggest the dimeric nature of these complexes. Magnetic measurements above 85 K reveal the presence of some antiferromagnetic exchange via 2,6-diaminopyridine moieties. The complexes are dimeric five-coordinate square-pyramidal with 2,6-diaminopyridine residues acting as bridges. The electronic spectra are interpreted in terms of the normalized spherical harmonic Hamiltonian theory and the DT/DQ values which indicate that chromium complexes are slightly distorted, whereas those of manganese are severely distorted.