LDI mass spectrometry and quantum chemical calculations of four, five, and six atomic clusters of tantalum oxochloride anion-radicals

Abstract

Quantum-chemical calculations of isomers of bulk closed “cage” structures of four, five and six atomic clusters of tantalum oxochloride anion-radicals, identified by LDI mass spectrometry in the gas phase, have been performed. The structure and relative thermodynamic stability of the isomers of clusters [Ta4OxCly]- (x = 6–9; y = 9, 7, 5,3), [Ta5OxCly]- (x = 8–12; y = 8, 6, 4, 2) and [Ta6OxCly]- (x = 12–15; y = 7, 5, 3, 1) of various configurations (tetrahedron, trigonal bipyrmide, tetragonal pyramid, trigonal prism, pentagonal pyramid and octahedron position of tantalum atoms) and different positions of oxygen and chlorine atoms have been studied. Some patterns of relative thermodynamic stability of isomers have been established. In the series of cluster radical anions of the same geometric configuration [TanOxCly]- (n = 4–6), the relative stability of geometric isomers depends on the ratio of the number of oxygen and chlorine atoms. For all anion-radicals [TanOxCly]- (n = 4–6) isomers having an anionic fragment with terminal oxygen and chlorine atoms (≡ТаOCl-) are energetically more favorable, than those with three of thes chlorine atoms (≡ TaCl3-). The average length of the Ta–Ta distances, in a series of cluster anions of tantalum oxochlorides [TanOxCly]- (n = 4–6) of the same geometric configuration, increases with a decrease in the number of oxygen atoms (an increase in the number of chlorine atoms). In the closed “cage” structures of the cluster anion radicals of tantalum oxochlorides, together with the oxygen, the chlorine can also act as a bridging atom, but the total binding energy of such isomer is higher.