Broken symmetry approach and density functional theory calculations for heterospin system consisting of copper(II) and aminoxyl radicals

The magnetic-structural correlation in metal-radical heterospin system such as bis(hexafluoroacetylacetonato)copper(II) [Cu(hfac)2] ligated with 3- and 4-(N-oxyl-tert-butylamino)-pyridines (3NOPy and 4NOPy) complexes has been investigated on the basis of unrestricted density functional theory (UDFT) and unrestricted Hartree-Fock (UHF) calculations combined with the broken symmetry (BS) approach, in order to study the magnetic properties of the complexes [Cu(hfac)2(4NOPy)2] and [Cu(hfac)2(3NOPy)2]. The effective exchange coupling constants J1 have been obtained by different methods (UPBE, UB3PW91, UB3LYP, UB3P86, UPBE0 and UHF). The best calculated exchange coupling constant for complex [Cu(hfac)2(4NOPy)2] was found to be J = 55.8 K, while the smallest magnitude calculated exchange coupling constant for complex [Cu(hfac)2(3NOPy)2] was found to be J = −33.1 K. For both two complexes UPBE0, UB3PW91, UB3LYP, and UB3P86 methods with LANL2DZ basis set are suitable for the calculation of exchange coupling constant.