Experimental and theoretical evidence for low-lying excited states in [Cr 6 E 8 (PEt 3 ) 6 ] (E = S, Se, Te) cluster molecules.

Three [Cr 6 E 8 (PEt 3 ) 6 ] cluster molecules with E = S, Se, and Te have been synthesized by reaction of stoichiometric mixtures of Cr(II) and Cr(III) metal salts with silylated chalcogen reagents E(SiMe 3 ) 2 (E = S, Se, Te) in the presence of L = PEt 3 = triethylphosphine. For the sulfide- and selenide-bridged clusters two crystallographic forms (trigonal R 3̄ and triclinic P 1̄), which differ in the presence of lattice solvent molecules, have been isolated. Structural data, optical spectra and quantum chemical calculations reveal the presence of low-lying excited states in [Cr 6 E 8 (PEt 3 ) 6 ] (E = S, Se), which would help in rationalizing the non-vanishing magnetic moments at 2 K revealed by DC magnetic measurements and EPR spectroscopy. These findings are partially in contrast to a previous report by Saito and co-workers (S. Kamiguchi, H. Imoto, T. Saito, Inorg. Chem. , 1998, 37 , 6852-6857.), who postulated an incorporated hydrogen atom as the source of paramagnetism at low temperatures for the trigonal forms of [Cr 6 E 8 (PEt 3 ) 6 ] (E = S, Se).