A complex cascade of solid-state processes initiated by variation of temperature was found for the heterospin complex [Cu(hfac)(2)L(Me/E)t] formed in the reaction of copper(II) hexafluoroacetylacetonate [Cu(hfac)(2)] with stable nitronyl nitroxide 2-(1-methy1-3-ethy1-1H-pyrazol-4yl)-4,4,5, 5-t etrame thyk-4,5-dihydro-1H-imidazol e-3-oxi de-1oxyl (L-Me/Et). The cooling of the compound below 260 K initiated a solid-state chemical reaction, which led to a depolymerization of chains and formation of a pair heterospin complex [Cu(hfac)(2)L-Me/Et2] [Cu(hfac)(2)](3)Le(2)(Me/Et)]. Further decrease in temperature below 144 K led to a spin transition accompanied by a drastic decrease in the effective magnetic moment from 2.52 to 2.24 mu(B). When the compound was heated, the order of effects was reversed: at first, the magnetic moment abruptly increased, and then the molecular fragments of the pair cluster united into polymer chains. Two hysteresis loops correspond to this cascade of temperature-induced structural transformations on the experimental dependence mu(eff)(T): one at high (T up arrow = 283 K and T down arrow = 260 K) and the other at low (T up arrow = 161 K, T down arrow = 144 K) temperature. The spin transitions were also recorded for the [[Cu(hfac)(2)](3)LE2Bu/Et] and [[Cu(hfac)(2)](5)L-Bu/Et] molecular complexes, which are models of the trinuclear fragment of the I[Cu(hfac)(2)](3)L-Me/Et pair cluster.