Spin transition in the molecular heterospin complex of Cu(hfac)2 with 4,4,5,5-tetramethyl-2-(1-methylpyrazol-5-yl)-4,5-dihydroimidazole-1-oxyl 3-oxide

The synthesis, structure, and magnetic properties of the products of the reaction for Cu(hfac)2 (hfac is hexafluoroacetylacetonate) with spin-labeled nitronyl nitroxides 4,4,5,5-tetramethyl-2-(1-R-1H-pyrazol-5-yl)-3-imidazoline-1-oxyl 3-oxides L5/R (R = Me, Et, Pr, Bu), viz., binuclear complex [Cu(hfac)2L5/Me]2 and chain polymer complexes [Cu(hfac)2L5/R]n, are described. The polymer heterospin chains are built according to “head-to-head” (R = Me, Et, Pr, Bu) and “head-to-tail” (R = Pr, Bu) motifs. Compound [Cu(hfac)2L5/Me]2 is characterized by the ability to reveal the reversible effect of thermally induced spin transition at a temperature about 75 K (without hysteresis). In the set of heterospin CuII compounds with spin-labeled pyrazoles, this is the earlier unknown example of a molecular complex exhibiting a similar magnetic anomaly.