Trigonal-bipyramidal and square-pyramidal chromium-manganese chalcogenide clusters, [E₂CrMn₂(CO)_n]^2- (E=S, Se, Te; N=9, 10): Synthesis, electrochemistry, UV/Vis absorption, and computational studies

The reactions of E powder (E=S, Se) with a mixture of Cr(CO)₆ and Mn₂(CO)₁₀ in concentrated solutions of KOH/MeOH produced two new mixed Cr-Mn-carbonyl clusters, [E₂CrMn ₂(CO)₉]^2- (E=S,; Se,). Clusters and were isostructural with one another and each displayed a trigonal-bipyramidal structure, with the CrMn₂ triangle axially capped by two μ₃-E atoms. The analogous telluride cluster, [Te ₂CrMn₂(CO)₉]^2- (), was obtained from the ring-closure of Te₂Mn₂ ring complex [Te ₂Mn₂Cr₂(CO)₁₈]^2- (). Upon bubbling with CO, clusters and were readily converted into square-pyramidal clusters, [E₂CrMn₂(CO)₁₀]^2- (E=Se,; Te,), accompanied with the cleavage of one Cr-Mn bond. According to SQUID analysis, cluster was paramagnetic, with S=1 at room temperature; however, the Se analogue () was spectroscopically proposed to be diamagnetic, as verified by TD-DFT calculations. Cluster could be further carbonylated, with cleavage of the Mn-Mn bond to produce a new arachno-cluster, [Te₂CrMn ₂(CO)₁₁]^2- (). The formation and structural isomers, as well as electrochemistry and UV/Vis absorption, of these clusters were also elucidated by DFT calculations. Show and tellurium: Cr-Mn trigonal-bipyramidal clusters, [E₂CrMn₂(CO) ₉]^2- (E=S, Se, Te), their carbonylated square-pyramidal (SP) clusters, [E₂CrMn₂(CO)₁₀]^2- (E=Se, Te), and an arachno-cluster, [Te₂CrMn₂(CO) ₁₁]^2-, are reported. The Te SP cluster was an electron-precise paramagnetic species, whilst the Se analogue diamagnetic. DFT calculations were performed to elucidate their formation, electrochemistry, and UV/Vis absorption.