Multicomponent supramolecular devices: synthesis, optical and electronic properties of bridged bis-dirhodium and -diruthenium complexes.

Four ruthenium- and rhodium-based metal–metal-bonded multicomponent systems have been synthesized, and their absorption, redox, spectroelectrochemical and structural properties have been studied. The absorption spectra of the four bis-dimetallic compounds M2LM2, where L is a bridging ligand and M is rhodium or ruthenium, exhibit very strong bands in the UV, visible and, for the diruthenium species, near-IR region. The low-energy absorption bands are as- signed to charge-transfer transitions involving a metal–metal bonding orbital as the donor and an orbital centered on the bis-tetradentate aromatic ligands as the acceptor (metal– metal to ligand charge transfer, M2LCT). Each compound ex- hibits reversible bridging-ligand-centered reductions at mild potentials and several reversible oxidation processes. The oxidation signals of the two equivalent dimetallic centers of each bis-dimetallic compound are split, with the splitting - a measure of the electronic coupling - depending on both the metal and bridging ligand. The mixed-valence species of the dirhodium species was investigated, and the electronic coup- ling matrix element calculated from the experimental inter- valence band parameters for one of them (86 cm–1) indicates a significant inter-component electronic interaction which compares well with good electron conducting anionic brid- ges such as cyanides. Although none of these compounds is luminescent, the M2LCT excited state of one of the bis- dirhodium complexes is relatively long-lived (about 6 microseconds) in degassed acetonitrile at room temperature. The results pre- sented here are promising for the development of linear poly- dimetallic complexes built on longer naphthyridine-based strands, with significant long-range electronic coupling and molecular-wire-like behavior.