Mixed-metal clusters with a {Re 3 Mo 3 Se 8 } core: from a polymeric solid to soluble species with multiple redox transitions.

Cluster compounds based on a new {Re3 Mo3 Se8 }n core were obtained and studied. The polymeric solid K6 [Re3 Mo3 Se8 (CN)4 (CN)2/2 ] (1) containing 24 cluster valence electrons (CVE) was isolated as a result of high-temperature reaction. Water-soluble salts K5 [Re3 Mo3 Se8 (CN)6 ]·11H2 O (2) and Cs5 [Re3 Mo3 Se8 (CN)6 ]·H2 O (3) were prepared from compound 1. Crystal structures of the diamagnetic compounds 2 and 3 contain a cluster anion [Re3 Mo3 Se8 (CN)6 ]5- with a 22-electronic core {Re3 Mo3 Se8 }+ . Metathesis reaction followed by recrystallization from CH3 CN yielded paramagnetic salt (Ph4 P)4 [Re3 Mo3 Se8 (CN)6 ]·2CH3 CN (4) containing the {Re3 Mo3 Se8 }2+ core with 21 CVE. Cyclic voltammetry of the solution of 4 displayed three quasi-reversible waves with E1/2 = -0.325, -0.818 and -1.410 V vs. Ag/AgCl electrode indicating the presence of [Re3 Mo3 Se8 (CN)6 ]4-/5-/6-/7- transitions. Electronic structure calculations showed that both mer- and fac-isomers of [Re3 Mo3 Se8 (CN)6 ]n- clusters undergo great distortion when the number of CVE decreases.