Noncovalent Bonding in d and f‐Type Coordination Compounds and Lattices. A Case Study

Abstract

Using as example the [Fe(bpca)(μ‐bpca)Gd(NO3)4]×4CH3NO2×CH3OH system, where Hbpca=bis(2‐pyridilcarbonyl)amine), we perform the analysis of bonding components inside the d and f coordination units and between molecular entities from crystal. Aside the nominal long‐range interactions between molecular components of the crystal, we considered that the bonding inside the coordination units is also not a covalent regime. We performed Density Functional Theory (DFT) calculations, with plane‐waves (PW), in band‐structure mode, and with atom‐centred bases, by molecular procedures. Observing that the PW‐DFT frame is free of basis set superposition errors, which is an important methodological hint underlined here, we estimated various non‐covalent terms. E.g. the interaction between inversion‐related FeGd units amounts ‐394.47 kcal/mol, only about ‐37 kcal/mol being due to Coulomb effects, the remainder being assignable to dispersion forces. One FeGd binuclear interacts with the closest methanol molecule by ‐9.30 kcal/mol and by ‐36.57 kcal/mol with the set of four nitromethane molecules. The energy decomposition analysis of molecular calculations showed, aside the expected ionic character (about 82% of the total cohesion energy of lanthanide ion in molecule), the important role of empty 5d orbitals. The d virtuals are contributing with 68.4 kcal/mol, out of 97.15 kcal/mol quantity estimated as ligand‐to‐metal donor‐acceptor effects.