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A dichlorophenyl substituted nitronyl nitroxide radical 2-(2,6-dichlorophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L) is prepared, its structure and magnetic properties are studied. It is shown that the interaction of bis(hexafluoroacetylacetonato)copper(II) [Cu(hfac)2] with L leads to the formation of the {[Cu(hfac)2][Cu(hfac)2L2]} heterospin complex whose crystal structure consists of pseudo-polymer chains formed by alternating single-spin [Cu(hfac)2] and three-spin [Cu(hfac)2L2] fragments. It is established that the temperature dependence of magnetic susceptibility of {[Cu(hfac)2][Cu(hfac)2L2]} is determined by ferromagnetic exchange interactions between unpaired electrons of Cu(II) ions and the axially coordinated L in three-spin fragments. [ABSTRACT FROM AUTHOR]

A method for the synthesis of solvates of dinuclear heterospin complexes of bis(hexafluoroacetylacetonato)copper(ii) with 2-(4-methylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LMe) and 2-(4-ethylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LEt) of the composition [Cu(hfac)2LR]2 · Solv (Solv = benzene, bromobenzene, toluene, o-xylene, p-xylene) was developed. It was found that a decrease in temperature induces structural transformations of the solid phases of the complexes followed by significant changes in the distances between the paramagnetic centers in the intramolecular exchange clusters {Cu2+-O·-} from 2.321 to 1.974 Å. As a result, the temperature dependences of the effective magnetic moment μeff(T) exhibit magnetic features similar to spin transitions. An analysis of the shape of the μeff(T) curves suggested that the magnetic properties of the compounds under study depend primarily on the molecular packing. A comparison of the magneto-structural correlations typical of the [Cu(hfac)2LR]2 · Solv complexes studied in this work with the data obtained earlier for analogous solvates of heterospin polymer chain complexes showed that the spin transition characteristics of the [Cu(hfac)2LR]2 · Solv systems are much less sensitive to the change of the solvent than the corresponding characteristics of the heterospin polymers containing solvate molecules in the interchain space. The magnetic characteristics of the heterospin dimer molecules depend primarily on which cavity between the dimers is filled with solvate molecules. For solvates with monoclinic symmetry, changes in the solvent molecules occupying same-type cavities have almost no effect on the spin transition characteristics in the heterospin exchange cluster. [ABSTRACT FROM AUTHOR]

The reaction of Cu(hfac)2 with a spirocyclic nitronyl nitroxide 2-(1-ethylpyrazol-4-yl)-4,5-bis(spirocyclopentane)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LEt) gave a heterospin complex [Cu(hfac)2LEt]-I, whose solid state is formed by polymer chains with a head-to-tail motif (the bridging function inside the chains is performed by the paramagnetic organic ligand). At 295 K the distance from the Cu atom to the N atom of the pyrazole ring and to the O atom of the NO group is 2.333(2) and 2.451(2) Å, respectively. The cooling of the compound to 110 K leads to a structural transition, as a result of which the unit cell volume decreases by more than 7%. The elongated axis of the octahedron changes from N–Cu–ONO to Ohfac–Cu–Ohfac in all coordination units as a result of a significant decrease in the Cu–ONO and Cu–N bond lengths to 2.002(4) and 2.034(5) Å, respectively, and an increase in the two Cu–Ohfac distances from 1.950(2) and 1.955(2) Å to 2.263(4) and 2.213(4) Å, respectively. The [Cu(hfac)2LEt]-I crystals are elastic and stable during the thermally induced spin crossover. The transition from the high-temperature to low-temperature phase is accompanied by a spin transition at 125 K at 1.0 × 10−4 GPa, as a result of which [Cu(hfac)2LEt]-I transforms from a paramagnetic compound to a diamagnetic one due to the complete spin coupling in the {Cu(ii)–OṖ–N＜} exchange clusters inside the polymer chains. The reversible phase transformation is accompanied by a reversible contrastive change of color from blue to dark brown upon cooling and vice versa from dark brown to blue upon heating. The spin crossover temperature is very sensitive to the change of external pressure: when pressure increases from 1.0 × 10−4 GPa to 0.48 GPa, it increases to 325 K. The increase of pressure provokes a transition from a high-spin to low-spin state, which again transforms into the high-spin state when the external load is removed. The [Cu(hfac)2LEt]-I crystals are the first examples of polymer-chain breathing crystals whose paramagnetic properties are suppressed by the lowering of temperature and/or increase of pressure. [ABSTRACT FROM AUTHOR]