Significant geometry and charge difference between the E54− bare clusters of group 14 Zintl anions and their coordinated form in [E5{M(CO)3}2]4− (E = Si, Ge, Sn, Pb; M = Cr, Mo, W) complexes

Abstract

In this paper, at first, the possible structures for E₅ⁿ Zintl ions (E = Si, Ge, Sn, Pb; n = 0, 2−, 4−) were investigated at the BP86/def2-TZVPP and M06-2X/def2-TZVPP levels of theory. The results showed that E₅²⁻ bare clusters, in agreement with their solid state structures, have the minimum energy in the trigonal bipyramid (D_3h), while the neutral E₅ and also E₅⁴⁻ ions, which have not been characterized structurally to date, are stabilized in the oblate trigonal bipyramid (D_3h) and square pyramid (C_4v) geometries, respectively. Then [E₅{M(CO)₃}₂]⁴⁻ complexes (M = Cr, Mo, W) containing a planar E₅⁴⁻ ring were investigated at the same levels of theory. The results show that the strong interaction of the planar E₅⁴⁻ ring with the two {M(CO)₃} fragments and significant charge donation from it is the reason for its strained planar geometry. This was further confirmed by NBO and Energy Decomposition Analysis-Natural Orbital for Chemical Valence (EDA-NOCV) as well as analysis of carbonyl vibrational frequencies. The EDA analysis indicated that the interaction energy values (ΔE_int) in the series of these complexes show the same trend as the term for orbital interactions (ΔE_orb).