Trigonal‐Bipyramidal and Square‐Pyramidal ChromiumManganese Chalcogenide Clusters, [E 2 CrMn 2 (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 Mn 2 (CO) 10 in concentrated solutions of KOH/MeOH produced two new mixed CrMncarbonyl clusters, [E 2 CrMn 2 (CO) 9 ] 2− (E=S, 1 ; Se, 2 ). Clusters 1 and 2 were isostructural with one another and each displayed a trigonal‐bipyramidal structure, with the CrMn 2 triangle axially capped by two μ 3 ‐E atoms. The analogous telluride cluster, [Te 2 CrMn 2 (CO) 9 ] 2− ( 3 ), was obtained from the ring‐closure of Te 2 Mn 2 ring complex [Te 2 Mn 2 Cr 2 (CO) 18 ] 2− ( 4 ). Upon bubbling with CO, clusters 2 and 3 were readily converted into square‐pyramidal clusters, [E 2 CrMn 2 (CO) 10 ] 2− (E=Se, 5 ; Te, 6 ), accompanied with the cleavage of one CrMn bond. According to SQUID analysis, cluster 6 was paramagnetic, with S =1 at room temperature; however, the Se analogue ( 5 ) was spectroscopically proposed to be diamagnetic, as verified by TD‐DFT calculations. Cluster 6 could be further carbonylated, with cleavage of the MnMn bond to produce a new arachno ‐cluster, [Te 2 CrMn 2 (CO) 11 ] 2− ( 7 ). The formation and structural isomers, as well as electrochemistry and UV/Vis absorption, of these clusters were also elucidated by DFT calculations.