Excited Triplet States of [{Mo6Cl8}Cl6]2-, [{Re6S8Cl6]4-, and [{W6Cl8}Cl6]2- Clusters

The temperature (T) dependences of the emission spectra and lifetimes of octahedral hexanuclear molybdenum(II) ([{Mo6Cl8} Cl-6](2-) = [1](2-)), rhenium(III) ([{Re6S8}Cl-6](4-) = [2](4-)), and tungsten(II) clusters ([Mo6Cl8} Cl-6](2-) = [3](2-)) in crystalline or poly(methyl methacrylate) (PMMA) phases were studied. The emission spectrum of the cluster showed a lowerenergy shift upon heating from 3 to 70K, 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.