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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]

The ternary TaIr2B2 boride was prepared by the reaction between iridium and TaB2 powders. It was shown that a choice in favor of any crystal structure of TaIr2B2 boride using only X-ray powder diffraction analysis and single-crystal XRD is rather difficult to make. The DFT calculations were carried out to predict the energetically preferred crystal structure of TaIr2B2. The 11B solid-state NMR spectrum of TaIr2B2 was recorded for the first time. A combination of diffraction and spectroscopic methods, as well as theoretical calculations, allowed us to make clear choice in favor of the triclinic space group for the crystal structure of TaIr2B2. The Vickers microhardness value for TaIr2B2 was found to be 17.9 ± 2.3 GPa, and the ternary TaIr2B2 boride can be considered a hard material. Therefore, the family of hard ternary boride phases got a new member. The coefficients of thermal expansion of TaIr2B2 measured by in situ high-temperature XRD analysis are independent of temperature along the a and b axes, but the CTE along the c axis deviates noticeably at elevated temperatures. The findings for the new ternary TaIr2B2 boride are of interest for the rational design of complex structural materials containing Ta–Ir–B-based components and prediction of their high-temperature behavior. Further research into this ternary boride as well as other iridium-containing ternary borides will provide a tool to solve the problems faced by high-temperature materials science. [ABSTRACT FROM AUTHOR]

The extension of a series of polyalkylpyrazolyl-substituted 2-imidazoline nitronyl nitroxide radicals LR1/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 LR1/R2/R3. As compared to breathing crystals (Cu(hfac)2 complexes with monoalkyl-substituted nitroxides LR1 with bridging μ2-O,N coordination), the introduction of the second substituent LR1/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 LR1/R2/R3–LMe3. The single crystal X-ray diffraction study of the structures of these compounds shows that as in the case of LMe3, an increase in the size of one of substituents in LR1/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. [ABSTRACT FROM AUTHOR]

The structure of previously unknown compounds NH4(HL•)(HL)·3H2O and NH4(L•)x(HL)1x·H2O (L• is a radical anion, HL is a deprotonated difurazanopyrazine derivative, HL• is a product of difurazanopyrazine oxidation) prepared by the oxidation of difurazanopyrazine (H2L) in aqueous ammonia is described. It is established that the shortest distances between the neighboring {L} in NH4(HL•)(HL)·3H2O and NH4(L•)x(HL)1–x·H2O fall within a fairly narrow range of 3.15-3.30 Å, despite the fact that they have substantially different stackings of {L} fragments. The bond lengths and bond angles of molecules {L} in all the studied compounds differ insignificantly. The energy of interaction between the paramagnetic centers in ammonium difurazanopyrazine salts is sharply diminished due to the decreased content of paramagnetic particles and, consequently, increased distances between these particles. [ABSTRACT FROM AUTHOR]

Crystalline Cs salts with the difurazanopyrazine radical anion are synthesized: Cs(L•)(H2O)2-I, Cs(L•)(H2O)2-II, Cs2(L•)2(HL•)(H2O), Cs3(L•)3(L••)2(H2O)3. In the solid phase, Cs ions are surrounded by water molecules and are located between the stacks of difurazanopyrazines, forming a framework. The study of the structure and magnetic properties of the compounds shows that Cs(L•)(H2O)2-I represents a metastable phase that transforms into Cs(L•)(H2O)2-II on cooling and differs from the initial compound by a shift of radical anions relative to each other in the stacks. It is found that in Cs(L•)(H2O)2-II there is strong antiferromagnetic exchange between paramagnetic centers. [ABSTRACT FROM AUTHOR]

New nitronyl nitroxide radicals, 2-(4′(5′)-methylimidazol-2′-yl)- and 2-(4′(5′)-trifluoromethylimidazol-2′-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide, were synthesized. The molecular and crystal structures of the paramagnetic trifluoromethyl derivative were determined. A previously unknown type of hydrogen bonding of imidazol-2-yl-substituted nitronyl nitroxides to form ribbons was established. Within the ribbons, the molecules face in the same direction, with all oxygen atoms of the paramagnetic moieties being involved in H-bonding. The spectral and electrochemical properties of the radicals were compared. The first quantum chemical calculations of the electronic spectra of nitronyl nitroxide radicals taking account of the vibrational structure were performed. [ABSTRACT FROM AUTHOR]

The reaction of metal hexafluoroacetylacetonates M(hfac)2, where M = Fe, Mn, and Co, with 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) in the inert atmosphere of a dry box is found to yield mixed-ligand complexes [M(hfac)2(3,6-Q)]. When the synthesis is performed under ambient conditions or the [M(hfac)2(3,6-Q)] mother liquor is kept in air in the case of Mn(II) and Co(II), crystals of [M(hfac)2(H2O)2](3,6-Q) aqua complexes precipitate into the solid phase, in which cis-coordinated H2O molecules are hydrogen bonded to o-quinone O atoms. Single crystal X-ray diffraction data for compounds, which correlate with the results of quantum chemical calculations, show that solid [M(hfac)2(3,6-Q)] and [M(hfac)2(H2O)2](3,6-Q), where M = Co(II) and Mn(II), contain initial o-quinone molecules. In the interaction of Fe(hfac)2 with 3,6-Q, there is an intramolecular redox process during which Fe(II) is oxidized to Fe(III) and o-quinone is reduced to the respective semiquinonate radical anion, which leads to the formation of [FeIII(hfac)2(3,6-SQ)]. According to the data of magnetic measurements, a strong antiferromagnetic exchange between high-spin Fe(III) unpaired electrons and SQ provide an almost complete compensation of spin of one of the unpaired electrons of the metal ion by SQ spin. For Co a complex with 3,5-di-tert-butyl-o-benzoquinone [Co(hfac)2(3,5-Q)] is also synthesized and its structure and magnetic properties are studied. The latter prove to be similar to those of [Co(hfac)2(3,6-Q)]. [ABSTRACT FROM AUTHOR]