Abstract
The experimental electron density distribution in two isostructural and isomorphous complexes, tetrakis(μ2-acetato)diaquadicopper(II) [H2OCu(ac)2Cu(ac)2H2O] (I) and tetrakis(μ2-acetato)diaquadichromium(II), [H2OCr(ac)2Cr(ac)2H2O] (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.
Highlights
It was necessary to have a good deal of imagination when Ronald James Gillespie and Ronald Sydney Nyholm developed the Valence-Shell Electron-Pair Repulsion (VSEPR) concept (Jolly, 1984)
We have proved by means of charge density studies that in the title compounds the metal atoms have four Classical Coordination Bond (CCB)
If the acetate donor oxygen atom is involved in hydrogen bonding, the strength of its bond with the central atom decreases
Summary
It was necessary to have a good deal of imagination when Ronald James Gillespie and Ronald Sydney Nyholm developed the Valence-Shell Electron-Pair Repulsion (VSEPR) concept (Jolly, 1984). Charge density studies of small molecules allowed us to characterize, both qualitatively and quantitatively, various intra- and intermolecular interactions existing in the crystal structure of the compound studied (Gatti & Macchi, 2012; Coppens, 2013; Zhurov & Pinkerton, 2015; Cenedese et al, 2015). In the literature (Gatti & Macchi, 2012) there are some studies of experimental electronic structures of 3d coordination compounds, but it is quite complicated to compare the particular results between each other. It is evident that further pursuit of this approach will lead to new insight in the nature of metal–ligand and metal–metal bonding, and in the effect of intermolecular interactions on the electronic structure of molecules in solids’ (Coppens et al, 2005)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
