| Abstract
| - A number of main group element (E)−transition metal (M) clustercompunds based upon a hexacapped M8 cubehave been reported in two configurations: empty and with interstitialmetal atoms in the center of the cube.Related molecules arise upon slow oxidation of the reactionproduct that forms when[Bi2Co4(CO)11]-is treatedwith Mo(CO)3(toluene) giving Bi−Co clustersbased upon tetragonally distorted tetracapped cubic metalarrayswith interstitial metal atoms. These compounds formulated as[PPN]2[Bi4Co9(CO)16]·2THF([PPN]2[1]·2THF)and[PPN]2[Bi8Co14(CO)20]·1.08THF([PPN]2[2]·1.08THF)have been characterized via single-crystal X-raydiffraction. An alternative description ascribes the metal coresto close-packed arrays based upon the cuboctahedron.The complexes are electron rich via conventional electron-countingformalisms. To understand these moleculesmore fully, a thorough theoretical analysis of compounds[1]2- and[2]2- was undertaken. Thecalculations indicatethat the bonding of the interstitial metal atom with the metallic hostsomewhat differs from that found in theirrelated metal-centered cubic speciesM9(μ4-E)6L8, dueto stretching along the 4-fold axis. The HOMO−LUMOregion is slightly antibonding between the Coi atoms (i =interstitial) and the surrounding Bi and Cop (p=peripheral) atoms. As with other members of this cubic clusterclass, no HOMO−LUMO gaps are observed.The actual electron counts for[1]2- and[2]2-, however, favor strongerCop−Coi and Bi−Coi bonding thanwouldbe observed for the allowed higher electron counts.Crystallographic data for[PPN]2[1]·2THF: triclinicspacegroup P1̄; a = 13.560(5),b = 15.893(5), c =11.884(4) Å; α= 105.26(2), β = 98.25(3), γ = 83.25(3)°;Z = 1.Crystallographic data for[PPN]2[2]·1.08THF: triclinic spacegroup P1̄; a = 17.445(5),b = 18.234(3), c =9.033(3) Å; α = 92.74(2), β = 102.59(3), γ= 78.52(2)°; Z = 1.
- Extended Hückel anddensity functional theoretical analyses of the tetragonally distortedcubic clusters[Bi4Co9(CO)16]2-and[Bi8Co14(CO)20]2-indicate that the HOMO/LUMO region is slightly antibonding between theinterstitial Co atoms and the surrounding Bi and peripheral Co atoms.Although no HOMO−LUMO gaps are observed, the actual electroncounts for these compounds seem the best compromise for having strongbonding to the interstitial cobalt atoms. This observation isconsistent with reported electron counts for related cubic clusters,which in general also tend to have open-shellconfigurations.
|
