Heterospin molecular complexes of Cu(hfac)2 with pyridyl-substituted nitronyl nitroxides: peculiarities of structure and magnetic properties

Abstract

A series of binuclear and tetranuclear Cu(hfac)₂ complexes with pyridyl-substituted nitroxide radicals L^R, where L^R is 2-(4-R-pyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (R = Cl, Br, CF₃, OMe, OEt, i-Pr, n-Pr, Ph, cyclopentyl (CP), cyclohexyl (Cy), thiophen-2-yl (Thio)), were synthesized. The crystal structures of these complexes are formed by centrosymmetric molecules with the bridging paramagnetic ligand L^R, connecting two Cu(hfac)₂ units. In the tetranuclear complexes, the other two O_NO atoms that are not involved in the formation of the binuclear unit are bound to additional Cu(hfac)₂ or Cu(hfac)L^R fragments. It was found that only for complexes with L^Thio and L^Ph, changing the temperature induces structural transformations in the environment of Cu atoms in the binuclear units. This is reflected in the anomalous behavior of the effective magnetic moment μ_eff with temperature. Magneto-structural correlations were established linking the rigidity of a pyridine fragment substituent with the possibility of a spin transition.