The electronic structures and aromaticities for zinc sandwich, half-sandwich and zinc-zinc (Zn-2(2+)) sandwich complexes within density functional theory

摘要

The equilibrium geometries, energies, harmonic frequencies, and nucleus-independent chemical shifts of the zinc sandwich, the half-sandwich, and the zinc-zinc (Zn-2(2+)) sandwich complexes are computed by B3LYP/6-311 + + G(d,p) within the density functional theory. The staggered [(eta(5) -C5H5)(2)Zn-2] ((1)A(1), D-5d) is the most stable minimum with higher binding energy and slightly stronger aromaticity than those of the eta(5)-C5H5- ((1)A(1), D-5h). The eclipsed [(eta(5) -C5H5)(2)Zn-2] ((1)A(1), D-5h) is a transition state with a small ring rotation barrier. The Zn-containing half-sandwich complexes are minima while with different stabilities and aromaticity. Particularly, the [(eta(5) -C5H5)Zn] ((2)A(1), C-5 nu) has larger binding energy with aromaticity slightly weaker than eta(5) -C5H5-, this compound features a simple while bona fide monovalent zinc molecular compound. The Zn2+ sandwich complex, [Zn(eta(5) -C5H5)(2)] ((1)A(1), D-5h and D-5d), with aromaticity weaker than that of the slip-sandwich complex, is a saddle point on potential energy surface. The slip-sandwich complex, (eta(1) -C5H5)Zn(eta(5) -C5H5) ((1)A(1), C-1), with aromaticity close to that of eta(5) - C5H5- ((1)A(1), D-5h), is a local minimum. Both the eclipsed and the staggered [(C-5(CH3)(5))(2)Zn-2](C-1) are aromatic with aromaticity close to that of [(eta(5) -C5H5)(2)Zn-2] (D-5d). According to the analysis of molecular orbitals, the Wiberg bond indices, the magnitude of charge transfer, the total nucleus-independent chemical shifts distributions, and the nucleus-independent chemical shifts contribution distributions of various bonds manifests, the stabilities of all the Zn-containing sandwich, the half-sandwich, and the Zn-2(2+) sandwich complexes are accredited to both ionic electrostatic interactions and covalent binding, especially the ionic electrostatic interactions, between the metal center and the eta(5)-C5H5- building blocks. (c) 2005 Elsevier B.V. All rights reserved.