Combined EPR and DFT study of the copper(II) complexes with N-phosphoryl thioureas

Copper(II) bis-complexes with N-phosphoryl thioureas, RN^'HC(S)NP(O)(OPrⁱ)2- {R = phenyl ( I), cyclohexyl ( II)}, have been obtained and investigated in liquid and frozen toluene solutions. Equilibria between trans-S,N and cis-S,N-isomers have been revealed and described by EPR method. In contrast to more usual S,O-forms, trans-S,N-isomers demonstrate large superhyperfine splitting from N and P atoms simultaneously. From EPR spectra anisotropic hyperfine, superhyperfine, and g-tensor parameters obtained and the symmetry of the metal ion surrounding analyzed. Rhombic anisotropy of copper(II) hyperfine and axial symmetry of N and P superhyperfine splitting resolved. Structural, hydrodynamic, and magnetic characteristics of the complexes established experimentally were supported by DFT calculations. According to EPR and DFT studies, tetrahedral distortion is higher in cis-S,N than in trans-S,N forms for steric reasons and slightly higher in I(S,N- trans) isomer than in II(S,N- trans) one due to the electron-donating effect of cyclohexyl substituent. The domination of S,N- over S,O-coordination is explained by the effects of the crystal field stabilization and the formation of the intramolecular hydrogen bonds.