Geometry of Pentaphenylantimony in Solution: Support for a Trigonal Bipyramidal Assignment from X-ray Absorption Spectroscopy and Vibrational Spectroscopic Data

Abstract

A variety of methods are available to investigate the bonding in inorganic compounds. In contrast to wavefunction-based analyses, topological analysis of the electron density affords the advantage of analyzing a physical observable: the electron density. Classical topological analyses of bonding interactions within the Atoms in Molecules framework typically involve location of a bond path between two atoms and evaluation of a range of real-space functions at the (3, -1) critical point in the electron density that exists on that bond path. We show here that counter-intuitive trends are obtained from the analysis of the electron density (ρ), the Laplacian (∇ 2 ρ), and ellipticity (ε) at the O-E (3, -1) critical points in the CCSD electron densities of a series of compounds featuring a range of oxygen-pnictogen bond types: EO + , HEO, H2EOH, H3EOH + and H3EO (where E = N, P, As, Sb, or Bi). If, instead, these real-space functions are evaluated along the length of the bond path, the discrepancies in the trends are resolved. We show that robust results are also obtained using electron densities from less computationally demanding DFT calculations. The increased computational efficiency allowed us to also investigate organic derivatives of these oxygen-pnictogen bonded compounds and observe that the trends hold in these instances as well. We anticipate that these results will be of use to inorganic chemists engaged in the synthesis and evaluation of novel bonding interactions, particularly those involving heavy main-group elements.

Models of the putative antimony(v)–diolate motifs in antileishmanial pentavalent antimonial drugs

“…Such a lowering of symmetry would be expected to manifest in the NMR spectra of these compounds if not for the fact that pentasubstituted pnictogen molecules are frequently highly fluxional. 10,19,20…”

“…Such a lowering of symmetry would be expected to manifest in the NMR spectra of these compounds if not for the fact that pentasubstituted pnictogen molecules are frequently highly fluxional. 10,19,20 For example, under the assumption that 1, 2, and 4 are trigonal bipyramidal in solution, one would expect to see two distinct methyl resonances in the 1 H NMR spectrum of each: one for the methyl group(s) closest to the O atom that is bound axially, and one for the methyl group(s) closest to the O atom bound equatorially. For 2 and 4, these methyl peaks should be further split by the backbone CH units into doublets.…”

“…Based on our previous work, 10 we chose to use the Sb(tol) 3 fragment as the framework upon which to install the chelating diolate. The advantages of this organometallic framework include its stability, ease of synthesis, and solubility in a variety of solvents.…”

Isolation, bonding and reactivity of a monomeric stibine oxide

“…The oxidation state of 2a was probed with Sb X-ray absorption spectroscopy (XAS), which we have recently used to shed light on the structures of Sb-containing compounds 29 . The Sb K edge of 2a is 2 eV higher in energy than that of 1a (Fig.…”