PHOTOPHYSICAL PROPERTIES OF HEXANUCLEAR COPPER(I) AND SILVER(I) CLUSTERS

Thc spectroscopic properties, including emission spectra and lifetimes, absorption and diffuse reflectance spectra and excitation spectra, of thc hexanuclear copper(I) and silver(I) clusters Cu6(mtc)6 (1), Ag6(mtc) (2), and Ag6(dtc)6 (3) (mtc = di-n-propylmonothiocarbamate, dtc = di-n-propyldithiocarbamate) are reported. At room temperature 1 exhibits a strong single emission (e.g., in toluene lambda(max)em = 725 nm, tau = 1.0-mu-s), while at 77 K each of these is a bright emitter (spectral properties: 1 in toluene, lambda(max)em = 762 nm, tau = 20-mu-s; 2 in toluene, lambda(max)em = 607 nm, tau = 131-mu-s; 3 in toluene, lambda(max)em = 550 nm, tau = 21-mu-s). In analogy to previous assignments in tetranuclear Cu(I) clusters, the emission bands in the octahedral (M(I))6 clusters are assigned to spin-forbidden transitions from triplet excited states which are mixed d --> s and LMCT (ligand to metal charge transfer) in character modified by metal-metal interactions.