The heterospin solid phases of the chain polymer [Cu(hfac)2LEt]∞ and bicyclic molecule [Cu(hfac)2LEt]2-I (LR = pyrazolyl-substituted tert-butylnitroxide; 1-R-5-(tert-butyl-oxylamino)pyrazole,
R = Et, Pr) were found to undergo spontaneous transformation into
the bicyclic molecule [Cu(hfac)2LEt]2-II. The single-crystal to single-crystal (SC–SC) transformation
of [Cu(hfac)2LEt]2-I into [Cu(hfac)2LEt]2-II was recorded by X-ray diffraction
analysis of the crystal as a function of time. At 255–277 K,
the [Cu(hfac)2LEt]2-I → [Cu(hfac)2LEt]2-II SC–SC transformation
proceeded for 12–18 h. The [Cu(hfac)2LEt]∞ → [Cu(hfac)2LEt]2-II SC–SC phase transformation was accompanied
by a change in the crystal shape, spontaneous mechanical displacements
of crystals, and a change in color from orange to dark green. This
process started, to a certain extent, already in the crystals lying
under the layer of the mother solution. After the crystals were separated
from the solution, the SC–SC transformation [Cu(hfac)2LEt]∞ → [Cu(hfac)2LEt]2-II occurred completely within 4 h at
room temperature. Under normal conditions, [Cu(hfac)2LPr]2-I also undergoes transformation into [Cu(hfac)2LPr]2-II. At the macro level, the transformation
[Cu(hfac)2LPr]2-I → [Cu(hfac)2LPr]2-II is accompanied by spontaneous
fragmentation of crystals, visualized as a scatter of small particles
of the formed phase in different directions. The reverse transformation
[Cu(hfac)2LPr]2-II → [Cu(hfac)2LPr]2-I occurs when [Cu(hfac)2LPr]2-II is cooled below 225 K. When [Cu(hfac)2LPr]2-II was heated above 300 K, the
irreversible SC–SC phase transformation [Cu(hfac)2LPr]2-II → [Cu(hfac)2LPr]∞ was observed, which caused a pronounced
change in the color of the crystals from dark green to orange. Heat
treatment of the [Cu(hfac)2LPr]∞ single crystal at 303 K on a diffractometer for 1 day or more caused
partial melting of the starting crystal, disappearance of X-ray diffraction
reflections from the sample under study, and appearance of reflections
corresponding to the formation of the new polymer complex [Cu(hfac)2L*Pr]∞, where L*Pr is the product of transformation of the radical including the oxidation
of LPr and migration of the nitroxide O atom to the heterocycle,
leading to the formation of 5-(tert-butylimino)-1-propyl-1,5-dihydro-4H-pyrazol-4-one (L*Pr). The results of the X-ray
diffraction study of the phase transformations completely agreed with
the data of magnetochemical measurements for the complexes. Having
replaced the acyclic nitroxides LEt and LPr by
their diamagnetic structural analogues LPEt (2,2-dimethyl-1-(1-ethyl-1H-pyrazol-5-yl)propan-1-one) and LPPr (2,2-dimethyl-1-(1-propyl-1H-pyrazol-5-yl)propan-1-one), we obtained the complexes
[Cu(hfac)2LPEt]∞, [Cu(hfac)2(LPPr)2], and [(Cu(hfac)2)3(LPPr)2], for which the transformations
are absolutely not characteristic. It was also found that polymorphic
transformations are also uncharacteristic of complexes of other metals
with the acyclic nitroxides under study ([Zn(hfac)2LEt]2, [Zn(hfac)2LPr]...