Importance of non-covalent interactions in a nitrile anion metal-complex based on pyridine ligands: a theoretical and experimental approach

Abstract

The solvothermal synthesis and crystal structure of [bis(thiocyanato-κN)bis(tris(pyridin-2-yl-κN)amine)iron(II)] (1) are described. The structure obtained was i subjected to theoretical analysis of interaction energies and intra- and intermolecular bonding. This comprehensive study illustrates the richness of non-covalent interactions that are exhibited by nitrile anionmetal complexes. The neutral complex lies on a crystallographic two-fold axis. The iron atom is octahedrally coordinated, with two thiocyanato ligands in cis positions, and the two trispyridine ligands coordinated via the nitrogen atoms of just two of the three pyridine rings. Energy analysis of five significant dimers, supplemented by a detailed analysis of the Hirshfeld surfaces, indicates attractive interaction energies of up to 101 kJ, with the strongest dimer stabilized by bifurcated C–H⋯S hydrogen bonds and additional π⋯π interactions. Solid-state and molecular quantum mechanical calculations confirm the high-spin nature of the complex, which is also reflected in the Fe–N bond lengths, and highlights the relevance of intramolecular ligand-ligand interactions. From a combined analysis using the Quantum Theory of Atoms in Molecules and the Non-Covalent Interaction index it was possible to identify further specific intermolecular interactions contributing the stability of the crystal structure, such as the H⋯H bonds, as well as the presence of several delocalized van der Waals forces, which are mainly of dispersive origin.