Diversity of Structural Motifs in Cu(hfac)₂ Complexes with Spin-Labeled Polyalkylpyrazoles

The extension of a series of polyalkylpyrazolyl-substituted 2-imidazoline nitronyl nitroxide radicals L^R1/R2/R3 (R = Me, Et, Pr, Bu) enables the synthesis of a number of coordination polymers based on copper(II) bis(hexafluoroacetylacetonate) Cu(hfac)₂ with L^R1/R2/R3. As compared to breathing crystals (Cu(hfac)₂ complexes with monoalkyl-substituted nitroxides L^R1 with bridging μ₂-O,N coordination), the introduction of the second substituent L^R1/R2 into the pyrazole ring allows the performance of the tritopic function of the paramagnetic ligand (μ₃-O,O,N) and the formation of 1D and 2D polymers with original structures and different combinations of [CuO₆], [CuO₅N], [CuO₄N₂], and [CuO₅] coordination cores. Only molecular complexes are obtained with single 3-substituted nitroxide L^R1/R2/R3–L^Me3. The single crystal X-ray diffraction study of the structures of these compounds shows that as in the case of L^Me3, an increase in the size of one of substituents in L^R1/R2 to Pr or Bu causes an increase in distances between paramagnetic centers in two- and three-spin exchange clusters, and correspondingly, spin transitions are absent.