Strong Ferromagnetic Exchange Couplings in Copper(II) and Nickel(II) Complexes with a Paramagnetic Tridentate Chelate Ligand, 2,2‘-Bipyridin-6-yl <i>tert</i>-Butyl Nitroxide

A paramagnetic ligand 6bpyNO (2,2‘-bipyridin-6-yl tert-butyl nitroxide) is a newcomer in the field of metal-radical hybrid magnetic materials. Complexes [CuII(6bpyNO)Cl2] and [NiII(6bpyNO)2](PF6)2 having highly planar chelate rings showed considerably strong ferromagnetic exchange couplings J/kB = 202 and 192 K, respectively, across the direct radical oxygen coordination bonds (the spin Hamiltonian is defined as −2JSi·Sj).