Specific features of Copper(II) chloride complexes with Caffeine: Synthesis, Structure, DFT calculations

The present article is devoted to the consideration of the interconversions of copper(II) chloride complexes with caffeine (caf) ([CuII2(μ2-Cl)2(caf)2(H2O)2] (1),[CuII3(μ-Cl)6(caf)(H2O)]n (1a), [Cu4(μ2-Cl)6(μ4-O)(caf)4] (1b), 2[CuII(caf)Cl2].0·.25THF (1c), [CuII(caf)2Cl2] (2)), depending on the synthesis conditions, and to studies on the four-nuclear copper(II) bromide complex with acetamide (AcAm) ([Cu4(μ2-Br)6(μ4-O)(AcAm)4] (3)). The results obtained have been confirmed by different methods (powder XRD, single crystal XRD diffraction analysis, IR-, ESI-MS-, EPR-spectroscopy, and magnetic properties studies). Two bromide ions in (3) are non-equivalent to the other four and this fact may result in the modification of the exchange integral between bonded copper ions. Single crystal XRD data have been compared with the results of DFT calculations. It has been found that the thermodynamic stability of the complexes grows with an increase in the number of copper atoms and bridging chloride ions and a decrease in the number of water molecules in the formula unit of the compound. The calculation results for complexes with acetamide are in a good correlation with those of caffeine and experimental data.