title: Al(6)(2-) - fusion of two aromatic Al(3)(-) units. A combined photoelectron spectroscopy and ab initio study of M(+)[Al(6)(2-)] (M = Li, Na, K, Cu, and Au).
abstract: Photoelectron spectroscopy is combined with ab initio calculations to elucidate the structure and chemical bonding of a series of MAl(6)(-) (M = Li, Na, K, Cu, and Au) bimetallic clusters. Well-resolved photoelectron spectra were obtained for MAl(6)(-) (M = Li, Na, Cu, and Au) at several photon energies. The ab initio calculations showed that all of the MAl(6)(-) clusters can be viewed as an M(+) cation interacting with an Al(6)(2-) dianion. Al(6)(2-) was found to possess an O(h) ground-state structure, and all of the MAl(6)(-) clusters possess a C(3v) ground-state structure derived from the O(h) Al(6)(2-). Careful comparison between the photoelectron spectral features and the ab initio one-electron detachment energies allows us to establish firmly the C(3v)ground-state structures for the MAl(6)(-) clusters. A detailed molecular orbital (MO) analysis is conducted for Al(6)(2-) and compared with Al(3)(-). It was shown that Al(6)(2-) can be considered as the fusion of two Al(3)(-) units. We further found that the preferred occupation of those MOs derived from the sums of the empty 2e' MOs of Al(3)(-), rather than those derived from the differences between the occupied 2a(1)' and 2a(2)' ' MOs of Al(3)(-), provides the key bonding interactions for the fusion of the two Al(3)(-) into Al(6)(2-). Because there are only four bonding MOs (one pi and three sigma MOs), an analysis of resonance structures was performed for the O(h)Al(6)(2-). It is shown that every face of the Al(6)(2-) octahedron still possesses both pi- and sigma-aromaticity, analogous to Al(3)(-), and that in fact Al(6)(2-) can be viewed to possess three-dimensional pi- and sigma-aromaticity with a large resonance stabilization.
authors.affiliation: Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322-0300, USA.
authors.forename: Aleksey E
authors.initials: AE
authors.lastname: Kuznetsov
authors.forename: Alexander I
authors.initials: AI
authors.lastname: Boldyrev
authors.forename: Hua-Jin
authors.initials: HJ
authors.lastname: Zhai
authors.forename: Xi
authors.initials: X
authors.lastname: Li
authors.forename: Lai-Sheng
authors.initials: LS
authors.lastname: Wang