On the theory of exchange interactions in organometallic compounds. Part I

Abstract

Recently magnetic order has been found in organometallic donor (D)-acceptor (A) compounds, with a localized spin on a transition-metal ion (donor) and a localized spin on an organic group (acceptor). We call these magnetic d/p systems. The magnetic order is often ferromagnetic. Many of these systems are one-dimensional magnets with a simple structure: ··· D +A −D +A −D + ··· . There are two types of such systems. First, systems in which the localized spins on the donor and acceptor are in orbitals which are not separated by other organic groups, and second systems where there is an intermediate organic group between the donor and acceptor. In this paper we discuss the various contributions to the exchange interaction in the first type of d/p systems. We use the molecular orbital (MO) model applied already successfully by the author and others for the discussion of exchange interactions in transition-metal compounds and rare-earth compounds. The most important contributions to the nearest-neighbour exchange interaction in these compounds come from single-ion exchange on the transition-metal ion between the unpaired spins and spin transferred from the unpaired acceptor spin to occupied and empty atomic transition-metal orbitals. This is the old ferromagnetic Kramers-Anderson mechanism.