Synthesis, structural characterization, and DFT investigation of a mixed-valence Co(iii)/Co(ii) complex stabilized by supramolecular interactions

Abstract

A dinuclear mixed-valence cobalt(III/II) complex, [(DMSO)(SCN)Co^IIILCo^II(NCS)₂(OH²)]·DMF, has been synthesized and structurally characterized by elemental analysis, spectroscopy, and single-crystal X-ray diffraction. The structure reveals a hexa-coordinated cobalt(III) center in an octahedral geometry and a penta-coordinated cobalt(II) center adopting a square pyramidal geometry. To support the oxidation state assignment, a spin density analysis was carried out, confirming spin localization on the cobalt(II) center. Additionally, a comprehensive DFT study was performed to evaluate key supramolecular interactions in the solid state. Theoretical analysis of selected assemblies using molecular electrostatic potential (MEP) mapping, QTAIM, and NCIplot methods reveals the energetic and directional features of dominant hydrogen bonds, including NH⋯S and OH⋯O interactions. The substantial interaction energies (up to −31.4 kcal mol⁻¹) and topological descriptors underscore the structure-directing role of these noncovalent contacts in the formation of one-dimensional supramolecular chains.