Excited Triplet States of [{Mo6Cl8}Cl6]2−, [{Re6S8}Cl6]4−, and [{W6Cl8}Cl6]2− Clusters

Abstract The temperature (T) dependences of the emission spectra and lifetimes of octahedral hexanuclear molybdenum(II) ([{Mo6Cl8}Cl6]2− = [1]2−), rhenium(III) ([{Re6S8}Cl6]4− = [2]4−), and tungsten(II) clusters ([{W6Cl8}Cl6]2− = [3]2−) in crystalline or poly(methyl methacrylate) (PMMA) phases were studied. The emission spectrum of the cluster showed a lower-energy shift upon heating from 3 to 70 K, while that shifted gradually to higher-energy above 70 K. The emission spectral shifts of the cluster upon T-elevation accompanied sharp (<50 K) and gradual decreases (>50 K) in the emission lifetime. Such T-dependent emission characteristics, commonly observed for these three cluster complexes, were analyzed by assuming the contribution of the emissions from the excited triplet state spin-sublevels. The large T dependences of the emission lifetimes and spectra of the hexanuclear Mo(II), Re(III), and W(II) clusters can be understood by a single context of the contributions of the emissions from the excited triplet state spin-sublevels.