A New Method for the Synthesis of Heterospin Complexes

The interaction of binuclear Co(II) pivalate [Co-2(H2O)Piv(4)(HPiv)(4)] with nitronyl nitroxide HL1 (2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl) in organic solvents led to the formation of a pentanuclear heterospin complex [Co-5(Piv)(4)(L4L22)-L-1]. A nontrivial peculiarity of the complex is the presence of both the starting nitronyl nitroxide L-1 and its deoxygenated derivative imino nitroxide L-2 (HL2: 2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl) in its coordination sphere. Based on this, a new synthetic approach was developed, which suggests the use of both the starting radical and the product of its reduction in the reaction with the metal. The suggested approach is a new method for the synthesis of heterospin compounds, including those that cannot be obtained by other methods. It was shown that the reaction of Co(II) pivalate with a mixture of HL1 and HL2 can give a trinuclear heterospin complex [Co-3(Piv)(2)(L2L22)-L-1]. The replacement of Co(II) by Ni(II) completely suppresses the reduction of HL1 into HL2, and Ni(II) pivalate does not react with HL1. The use of a known mixture of HL1 and HL2 in the reaction with [Ni-2(H2O)Piv(4)(HPiv)(4)], however, led to the formation of a heterospin complex [(Ni3LL22)-L-1(Piv)(3)(HPiv)(3)] also containing both nitronyl nitroxide and imino nitroxide.