Synthesis and chemical characterization of the new anions [Rh3(µ3-E)2(CO)6]–(E = S or Se). Crystal and molecular structures of [PPh4][Rh3(µ3-S)2(CO)6] and [NMe4][Rh3(µ3-Se)2(CO)6]

Abstract

Reactions of [Rh₄(CO)₁₂] or [Rh₆(CO)₁₆] in tetrahydrofuran with [SCN]^–, [SeCN]^–, or with polysulphides give, together with the decanuclear clusters [Rh₁₀E(CO)₂₂]^2–, the trinuclear anions [Rh₃(µ₃-E)₂(CO)₆]^–(E = S or Se). The latter species have been isolated and investigated by X-ray analysis. The salt [PPh₄][Rh₃(µ₃-S)₂(CO)₆](1) crystallizes in the orthorhombic space group Pbc2₁, (no. 29) with a= 13.529(2), b= 16.965(2), c= 28.365(6)Å, and Z= 8; [NMe₄][Rh₃(µ₃-Se)₂(CO)₆](2) crystallizes in the orthorhombic space group Ccm2₁(no. 36) with a= 14.029(2), b= 10.889(1), c= 12.748(2)Å, and Z= 4. Both structures were solved by conventional Patterson and Fourier methods and refined on the basis of 3 438 and 1 032 significant independent counter data, respectively, to final conventional R values of 0.042 for compound (1) and 0.026 for (2). Both anions consist of a Rh₃ triangle bicapped by triply bridging chalcogenide atoms and each rhodium atom, bearing two terminal CO groups, displays an almost square-planar geometry. The Rh–Rh distances are long [mean values 3.053 and 3.135 Å for compounds (1) and (2), respectively] and suggest very weak, if any, metal–metal interaction. The two anions can therefore be considered as trinuclear rhodium(I) aggregates rather than triangular clusters.