Cu(II) Complexes with Fluoroalkyl-Pyrazolyl-Substituted Nitronyl Nitroxides

Abstract

Synthetic methods of heterospin compounds based on copper hexafluoroacetylacetonate [Cu(hfac)2] and nitronyl nitroxide radicals containing fluorinated alkyl substituents in the pyrazole ring 2-(1-R-3-pyrazol-4-yl)-4,4,5,5-tetramethyl-2-imidazoline-3-oxide-1-oxyl, where R = CHF2 (L12), CH2CH2F (L21), CH2CHF2 (L22) or CH2CF3 (L23) were developed. Single crystals of two chain polymers [Cu(hfac)2(L12)]n and [Cu(hfac)2L23]n·0.5C6H14 and solvates of molecular [Cu3(hfac)6(L21)2]·C6H14, [Cu3(hfac)6(L22)2]·2CH2Cl2, [Cu5(hfac)10(L21)4]·solv (solv = C6H14, 2CH2Cl2) and [Cu5(hfac)10(L22)4]·C6H14 complexes were grown. Their structures and magnetic properties were studied. It was established that upon cooling of the [Cu5(hfac)10(L21)4]·2CH2Cl2 crystal, a magneto-structural phase transition associated with a reduction in the Cu−ONO distances in the environment of the central Cu atom is realized. The transformation of this three-spin exchange cluster {>N−O•−Cu(II)−•O−N<} leads to a change in the nature of the exchange interactions from ferro-to antiferromagnetic, which is reflected in the type of temperature dependence of the effective magnetic moment.