Quantum-Chemical Calculations and Stability Analysis of Copper(II) Complexes with Cryptand[2.2.2]

The analysis of stability constants of mononuclear, protonated, and binuclear copper(II) complexes with cryptand[2.2.2] and quantum-chemical calculations of the structure of cryptand[2.2.2] and its protonated forms and copper(II) complexes have been reported. It has been found that the formation of mononuclear copper(II) cryptate is associated with a significant contraction of the macrocycle in the direction of the nitrogen–nitrogen axis, while the formation of the binuclear complex, on the contrary, leads to the stretching of the cavity. Using the literature data on the stability of complexes of divalent d metals with N-donor ligands, the ratio of cryptate and chelate effects in the formation of coordination compounds with macrocyclic ligands and open-chain ligands is considered. It is shown that during the formation of cryptand [2.2.2] complexes of with Zn2+, Co2+, Ni2+, and Cu2+ ions, the chelate effect significantly exceeds the cryptate effect. The presence of the cryptate effect is compared with the geometric dimensions of the cation and macrocycle.