Altering Charges on Heterobimetallic Transition-Metal Carbonyl Clusters.

The homoleptic group 5 carbonylates [M(CO) ] (M=Nb, Ta) serve as ligands in carbonyl-terminated heterobimetallic Ag M clusters containing 3 to 11 metal atoms. Based on our serendipitous [Ag {Nb(CO) } ] (4 a ) precedent, we established access to such Ag M clusters of the composition [Ag {M(CO) } ] (M=Nb, Ta; m=1, 2, 6; n=2, 3, 4, 5; x=1-, 1+, 2+). Salts of those molecular cluster ions were synthesized by the reaction of [NEt ][M(CO) ] and Ag[Al(OR ) ] (R =C(CF ) ) in the correct stoichiometry in 1,2,3,4-tetrafluorobenzene at -35 °C. The solid-state structures were determined by single-crystal X-ray diffraction methods and, owing to the thermal instability of the clusters, a limited scope of spectroscopic methods. In addition, DFT-based AIM calculations were performed to provide an understanding of the bonding within these clusters. Apparently, the clusters 3 (m=6, n=5) and 4 (m=6, n=4) are superatom complexes with trigonal-prismatic or octahedral Ag superatom cores. The [M(CO) ] ions then bind through three CO units as tridentate chelate ligands to the superatom core, giving overall structures related to tetrahedral AX (4 ) or trigonal bipyramidal AX molecules (3 ).