Transition metal complexes with fractionally charged TCNQ radical anions as structural templates for multifunctional molecular conductors

Abstract

Structures that combine transition metal complexes with fractionally charged organic cations or anions are of interest as potential multifunctional materials, in which conducting behavior of the organic substructure is supplemented by other properties, provided by the transition metal component. Here we review such hybrid structures prepared with ligand-capped transition metal cations and radical anions derived from the organic acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) or its analogs. Our analysis of the Cambridge Structural Database has revealed 520 structures of this type, among which only 35 contain fractionally charged organic anions. The requirement of fractional charge on the organic anion is paramount for achieving high electrical conductivity. After introducing a few basic concepts, we provide classification of such structures and a detailed summary of their properties.