Structures of Copper(II) N-tert-Butylbenzoyl and N-Phenylpivaloyl Hydroxamates in the Crystalline State and in a Frozen Solution

The geometric structures of compounds CuL2 (L = R1N(O)–(O)CR2; R1 = tert-Bu, R2 = Ph (I) and R1 = Ph, R2 = tert-Bu (II)) are studied by X-ray diffraction analysis (XRD) in the crystalline state and by stationary EPR spectroscopy in a dichloromethane solution. According to the XRD data (CIF files CCDC nos. 1875367 and 2022310, respectively), in the crystalline state the copper atoms of both complexes exist in the planar-square environment of the oxygen atoms with the trans-coordination of the hydroxamate ligands. According to the EPR data for frozen solutions of the complexes in dichloromethane, the compounds coexist as two mononuclear forms A and B differed in magnetic resonance parameters. It is shown that compound IB forms aggregates when freezing the solution. The form B of compound II is an associate of the copper complex with the solvent molecules. The EPR data indicate that both forms of compounds I and IIA form no associates with the solvent molecules.