Mixed-metal clusters with a {Re3Mo3Se8} core: from a polymeric solid to soluble species with multiple redox transitions

Abstract

Cluster compounds based on a new {Re₃Mo₃Se₈}ⁿ core were obtained and studied. The polymeric solid K₆[Re₃Mo₃Se₈(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[Re₃Mo₃Se₈(CN)₆]·11H₂O (2) and Cs₅[Re₃Mo₃Se₈(CN)₆]·H₂O (3) were prepared from compound 1. Crystal structures of the diamagnetic compounds 2 and 3 contain a cluster anion [Re₃Mo₃Se₈(CN)₆]⁵⁻ with a 22-electronic core {Re₃Mo₃Se₈}⁺. Metathesis reaction followed by recrystallization from CH₃CN yielded paramagnetic salt (Ph₄P)₄[Re₃Mo₃Se₈(CN)₆]·2CH₃CN (4) containing the {Re₃Mo₃Se₈}²⁺ core with 21 CVE. Cyclic voltammetry of the solution of 4 displayed three quasi-reversible waves with E_1/2 = −0.325, −0.818 and −1.410 V vs. Ag/AgCl electrode indicating the presence of [Re₃Mo₃Se₈(CN)₆]^{4−/5−/6−/7−} transitions. Electronic structure calculations showed that both mer- and fac-isomers of [Re₃Mo₃Se₈(CN)₆]ⁿ⁻ clusters undergo great distortion when the number of CVE decreases.