Dimeric nature of N-coordinated Mg and Ca ions in metaloorganic compounds. The topological analysis of ELF functions for Mg–Mg and Ca–Ca bonds

Abstract

The local electronic structure of the Mg–Mg and Ca–Ca bonds have been investigated in the model dimeric magnesium(I) and calcium(I) molecules: [C10H18Mg2N4], and [C10H18Ca2N4] using the topological analysis of Electron Localisation Function (ELF). The wave function has been approximated by the DFT method and PBE, B3LYP, M052X, M062X, ωB97XD, CAM-B3LYP, LC-ωPBE and B2PLYP functionals. The investigated bonds are covalent, and are represented by disynaptic bonding attractors V(Mg,Mg) and V(Ca,Ca). The basin population of the Ca–Ca bond (1.84–1.89e) is about 0.1e smaller than population of the Mg–Mg bond (1.95–1.98e). The results of ELF-analysis support classical Lewis representation of the 2c–2e bonds (single bond). The topological analysis of electron density field, ρ(r) shows that both the Mg–Mg and Ca–Ca bonds are characterised by the non-nuclear attractor (NNA) and pseudo-basin localised in midpoint of the bond. However, in the case of the Ca–Ca bond its localisation depends on the used functional. The median ELF-basin population of the Mg–Mg bond (1.96e) is about 2.5 larger than the population (0.79e) of pseudo-atomic basin associated with NNA of the ρ(r) field. The analysis performed for the nitrogen – magnesium and nitrogen–calcium bonds showed the dative bonds N→Mg and N→Ca with very large values of the polarity index, pNMg, pNCa, 0.96 and median ELF-basin population 3.40e.