Structure of N-substituted copper(II) hydroxamates in crystalline state and frozen solution

Two CuL2 complexes, where L = R1N(O)-(O)CR2, R1 = tert-Bu, R2 = Me (I) and R1 = Me, and R2 = tert-Bu (II) have been structurally studied by X-ray diffraction. According to electron paramagnetic resonance (EPR) data, the complexes exist in dichloromethane at 77 K as two mononuclear isomeric species. The species whose spectrum is described by a spin Hamiltonian with a high hyperfine structure (HFS) constant is a cis-isomer. The species with a smaller HFS constant is classified as a trans-isomer. The trans-isomer of compound II forms an associate with dichloromethane molecules.