Cu⋯Cl semi-coordinate bond flexibility; synthesis, theoretical and crystallographic studies on two copper dimers and their solvates

Two new copper dimers, [Cu(L)(μ-Cl)]_2, (1–2) have been synthesized, where L = 2(RS)C₆H₄N=NC(COCH₃)-SC₆H₅ with R being either C₆H₅ (1) or CH₃ (2). Complexes 1 and 2 are penta-coordinated with a distorted square pyramidal geometry, supported by the Cu(II) ion coordinated to the SNS ligand in a meridional arrangement. Complex 1 is crystallized as an anhydrous dimer (1) and as a hydrate (1·H₂O). Complex 2 is crystallized as pure phase 2 and as two solvates, with dichloromethane as solvent in the first (2.DCM) and acetonitrile in the second (2.ACN). The crystal structures of all five phases have been determined. The flexibility of the Cu⋯Cl semi-coordinate bond was demonstrated through the crystallographic and theoretical calculations. These interactions were analyzed using the Quantum Theory of Atoms in Molecules (QTAIM). Data analysis indicated that the Cu⋯Cl bond is easily stretchable; the distances of the Cu⋯Cl semi-coordinate bonds vary significantly between 1 phases, and between 2 phases. In the case of 1·H₂O, water molecules acted like molecular pliers, with hydrogen bonding interactions pushing the copper ion closer. This resulted in a shorter Cu⋯Cl bond in 1·H₂O, which is 0.05 Å shorter than in 1. Consequently, the Cu-S bond distances were elongated by 0.03 Å. Additionally, the S1-Cu1-S2 angles in 1·H₂O are 5° closer to a linear arrangement compared to the non-hydrated complex 1, due to the proximity of the two copper centers. For the three phases of 2, the Cu⋯Cl semi-coordinate variation range is 0071 Å. Furthermore, the two dimers were analyzed using various techniques, including spectroscopic methods (UV–visible, IR), thermal analysis (TGA), and electrochemistry.