Electronic structure of two isostructural `paddle‐wheel' complexes: a comparative study. Issue 6 (27th November 2018)

• Record Type: Journal Article
• Authors: Herich, Peter; Bučinský, Lukáš; Breza, Martin; Gall, Marián; Fronc, Marek; Petřiček, Václav; Kožíšek, Jozef
• Is Part Of: Acta crystallographica. Volume 74:Issue 6(2018:Dec.)
• Page Start: 681
• Page End: 692
• Publication Date: 2018-11-27
• Subjects: electronic structure -- charge density -- valence‐shell electron‐pair repulsion (VSEPR) -- quantum crystallography -- classical coordination bond
• DOI: 10.1107/S2052520618013707
• Languages: English
• ISSNs: 2052-5206

Abstract

Abstract : The experimental electron‐density distribution in two isostructural complexes, tetrakis(μ2 ‐acetato)diaquadicopper(II) [H2 OCu(ac)2 Cu(ac)2 H2 O] and tetrakis(μ2 ‐acetato)diaquadichromium(II) [H2 OCr(ac)2 Cr(ac)2 H2 O], has been studied and compared. Abstract : The experimental electron density distribution in two isostructural and isomorphous complexes, tetrakis(μ2 ‐acetato)diaquadicopper(II) [H2 OCu(ac)2 Cu(ac)2 H2 O] (I) and tetrakis(μ2 ‐acetato)diaquadichromium(II), [H2 OCr(ac)2 Cr(ac)2 H2 O] (II), has been obtained from high‐resolution X‐ray diffraction data in order to shed light on the bonding properties in the compounds studied. It has been shown that from accurate X‐ray data it is possible to discuss the bonding capability of the metal atom (Cu/Cr) and the ligands in these complexes. A comparison of results obtained from averaged and non‐averaged X‐ray data demonstrates that using the non‐averaged data and introducing an anisotropic correction for secondary extinction errors provides a more detailed distribution of the electron density in the area of the metal atoms. In both complexes studied, the bonding of the acetate oxygen atom to the central metal atom is significantly affected by the formation of hydrogen bonds. The electron density and its Laplacian at the bond critical point of metal–oxygen coordination bonds for those oxygen atoms not involved in the intermolecular hydrogen bonds are approximately 10% larger compared with the case when oxygen atoms take part in hydrogen bonds with the neighboring water molecules. It is shown that metal–oxygen bonds in a quasi‐equatorial plane are typical coordination bonds and differ significantly from the apical metal–oxygen bond. Metal–metal interaction with a small positive value of the electron density Laplacian at this bond critical point is mainly of electrostatic character. The metal–metal interaction is definitely not a bond according to the classical definition. Based on a search of the Cambridge Structural Database, it can be argued that there are four typical coordination bonds in the [CuO6 ] chromophore, similar to the four Cu—O coordination bonds in the basal plane of the CuO5 pyramid in one of the complexes under study.