Formation of supramolecular synthons in the crystalline structure of the dinitrosyl iron complexes with aliphatic thiourea ligands

By means of quantum-chemical calculations using Density Functional Theory, Quantum Theory of Atoms in Molecules, and Natural Bond Orbitals, theoretical modeling of intermolecular interactions has been performed for eight nitrosyl iron complexes with aliphatic thiourea ligands, which was aimed at discovering the presence of the NO…NO intermolecular interactions and at studying the possibility of the NO…NO supramolecular synthon formation in their crystalline structure for explaining their unusual magnetic properties. Such interactions were shown to be either stacking or T-like interactions, depending on the relative position of nitrosyl ligands and energetically corresponding to Van der Waals bonds. Mainly LP(O), π (NO), and π*(NO) orbitals in various combinations participate in their formation, with π (FeN), π(FeО), and LP(N) orbitals hardly being participants. The involvement of the NO bond orbitals results in quenching the orbital moment of the NO groups. If NO groups are isolated from intermolecular interactions, they can preserve the unquenched orbital moment.