New model of the electronic structure of the [Mo₆X₈(CN)₆]⁶⁻ clusters (XS, Se) based on the study of electron density distribution in the inner part of the Mo₆ polyhedron

Abstract

ABSTRACT:The geometric structure and bonding in [Mo 6 S 8 (CN) 6 ] 6Ϫ cluster were studied on the basis of quantum chemical ab initio and DFT (B3LYP) calculations with different basis sets. The geometry parameters of the Mo 6 S 8 core are in good agreement with the available crystal structure data. The electron density in the inner part of the Mo 6 octahedron is almost constant (ϳ0.04 -0.06 e/au 3 ). There is also noticeable electron density on the edges and faces of the Mo 6 S 8 polyhedron. The model of the electronic structure of the cluster under consideration starts from the mobile electrons moving in the potential well of the spherical symmetry. The resulting states are classified according to orbital quantum number l (e.g., 1s, 1p, 1d, 1f). Subsequent crystal field splitting leads to observable consequence of the one electron states of the O h point group symmetry.

Quantum chemical study of the addition effect on the geometry of the [Mo6S8(CN)6]6− cluster

“…There are some changes in the composition of the t 2u highest occupied molecular orbital (HOMO) as compared with the parent [Mo 6 S 8 (CN) 6 ] 6À cluster: in the latter this orbital is almost completely localized in the Mo 6 octahedron [6], whereas in the adducts 2-5 the Mo 6 contribution to the highest energy orbitals is reduced to about 50-75%. The energies of the orbitals with the noticeable contributions from the atoms of the Cr(CO) 4 L group and/or the bridging CN ligand are 3-5 eV lower than those of HOMOs.…”

“…Our study of the [Mo 6 S 8 (CN) 6 ] 6À cluster [6,7] showed that in this compound the electron density is concentrated on the Mo-Mo bonds and on the faces of the Mo 6 polyhedron. Moreover, there is uniformly distributed electron density of 0.06 e/a.u.…”

“…Analysis of the bonding between these very different structural units and electronic structure of the resulting complexes is of principle importance for development of the corresponding synthetic chemistry. In the present paper, we describe the results of quantum chemical studies on [Mo 6 S 8 (CN) 6 ] 6À (1) and on the following series of bimetallic compounds-[Mo 6 S 8 (CN) 6 -Cr(CO) 4 L] 6À , L = CO (2), PH 3 (3), P(OCH 3 ) 3 (4), PF 3 (5). The structure of (2) together with the atoms numbering scheme is shown in Fig.…”

“…Recently synthesized [1,2] family of octahedral chalcocyanide clusters [M 6 X 8 (CN) 6 ] nÀ (M = Mo, Re) is particularly promising in the synthesis of heterometallic polymers containing {M 0 (H 2 O) n } units, which link the cluster fragments forming infinite 1D chains and 2D networks [2]. One of the perspective directions of the chalcocyanide clusters chemistry consists in the synthesis of heterometallic compounds by direct coupling of the octahedral cluster [M 6 X 8 (CN) 6 ] nÀ fragments with mononuclear organometallic complexes, like for example, carbonyl compounds and their substituted derivatives. Analysis of the bonding between these very different structural units and electronic structure of the resulting complexes is of principle importance for development of the corresponding synthetic chemistry.…”

“…The energies of the orbitals with the noticeable contributions from the atoms of the Cr(CO) 4 L group and/or the bridging CN ligand are 3-5 eV lower than those of HOMOs. The total molecular orbital scheme is an overlap of the set of the [Mo 6 S 8 (CN) 6 ] orbitals and of the molecular orbitals of the Cr(CO) 4 L group.…”