PHOTOMECHANICAL PROPERTIES OF RHODIUM(I) SEMIQUINONE COMPLEXES - THE STRUCTURE, SPECTROSCOPY, AND MAGNETISM OF (3,6-DI-TERT-BUTYL-1,2-SEMIQUINONATO)DICARBONYLRHODIUM(I)

Crystals of Rh(CO)2(3,6-DBSQ) [3,6-DBSQ = 3,6-di-tert-butyl-1,2-semiquinone] have been reported to bend reversibly when exposed to light in thc near-IR. Structural characterization on the complex has confirmed the Rh(I)-DBSQ charge distribution for the complex and shown that molecules are stacked in columns in the solid state with a slightly nonlinear oligomeric rhodium core. Magnetic features show marked temperature dependence with both ferromagnetic and antiferromagnetic interactions apparent over the temperature range between 330 and 5 K. Coupling between radical semiquinone ligands is propagated through Rh-Rh interactions along the column. Solution (pentane) UV-vis-NIR spectra recorded over the temperature range from 300 to 150 K show evidence for oligomer formation with spectral changes resulting in a dramatic color change for the solution, from orange-brown at room temperature to dark green at lower temperatures. Strong transitions that appear in the NIR in solution at the lower temperatures also appear in the solid-state spectrum of the complex at room temperature. These properties reflect the strength of interactions between Rh(CO)2(3,6-DBSQ) molecules in the polymeric chain. The low-energy MLCT transition that is characteristic of the oligomeric structure may contribute to the unique photomechanical property of the complex in the solid state.