Tetrahedral Carbonylcobalt Clusters

A variety of general methods is available for the synthesis of tetrahedral heteronuclear cobalt clusters of type (CO)9Co3E(L)n (E=hetero element). The size of E has a limiting effect on the existence of such complexes. No compounds (CO)9Co3E(L)n have so far been prepared in which the covalent radius of E exceeds 1.30 Å;. Elements such as In, Sn, Pb, Sb, or Bi do not fit into the tetrahedral Co3E cluster unit and form open complexes E[Co(CO)4]n (n=3, 4). Structural variations among the heteronuclear clusters are encountered in the presence or absence of carbonyl bridges between the cobalt atoms: hetero atoms E bearing several ligands L favor bridging, whereas those bearing only one ligand or none at all permit terminal bonding of all the CO groups.