Polynuclear Ni<Superscript>II</Superscript> and Co<Superscript>II</Superscript> hexafluoroacetylacetonates

Hydrolysis of [M₄(hfac)₄(MeO)₄(MeOH)₄] (М = Сo, Ni and hfac is hexafluoroacetylaceton ate) is a convenient way of obtaining polynuclear complexes [Ni₇(hfac)₆(OH)₈(H₂O)₆]?2H₂O, [Co₁₂(hfac)₁₀(OH)₁₄(H₂O)₈]?2H₂O?2MePh, [Co₁₂(hfac)₁₀(OH)₁₄(H₂O)₄(Me₂CO)₄]?3PhMe, and [Co₁₂(hfac)₁₀(OH)₁₄(H₂O)₆(Me₂CO)₂]?2H₂O?2Me₂CO, whose structures were confirmed by X-ray analysis.     

Complexes of CuII with nitroxides and their magnetochemical behavior

The synthesis, structures, and magnetochemical data for the heterospin chain polymer complexes Cu(hfac)₂L^All and Cu(hfac)₂L^Bu·0.5Solv, where hfac is the hexafluoroacetylacetonate anion, L^All and L^Bu are 2-(1-allyl-1H-pyrazol-4-yl)- and 2-(1-butyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyls, respectively, Solv is isopropylbenzene or tert-butylbenzene, were described. These polycrystalline solids were found to exhibit similar magnetic anomalies. Thus, the effective magnetic moment first decreases and then increases with temperature, resulting in the specific minimum in the curve μ_eff(T). The study of the magneto-structural correlations showed that the appearance of the minimum is attributed to different factors. For Cu(hfac)₂L^All, this is the phase transition accompanied by the structural rearrangement of the exchange cluster >N—·O—Cu^II—O·—N<, which leads to a change in the energy of the exchange interaction between the unpaired electrons of the paramagnetic centers. By contrast, for Cu(hfac)₂L^Bu·0.5PrⁱPh and Cu(hfac)₂L^Bu·0.5Bu^tPh, the appearance of the minimum is a consequence of the coexistence of exchange interaction energies with opposite signs, while the structure of the solid phase remains unchanged.     

Spirocyclic derivatives of nitronyl nitroxides in the design of heterospin CuII complexes manifesting spin transitions

A method was developed for the synthesis of a nitronyl nitroxide containing cyclopentane substituents in positions 4 and 5 of the imidazoline ring, viz., 2-(3-pyridyl)-4,5-bis(spiropentyl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L^CP). The reaction of Cu^II hexafluoroacetylacetonate with L^CP affords different products depending on the reaction conditions: mononuclear [Cu(hfac)₂(L^CP)₂], binuclear [Cu(hfac)₂L^CP]₂, tetranuclear {[Cu(hfac)₂]₄(L^CP)₂}, or chain polymer {[Cu(hfac)₂]₃(L^CP)₂} _n . Temperature changes induce structural transformations accompanied by a change in the spin state in exchange clusters in the solid [Cu(hfac)₂L^CP]₂ and {[Cu(hfac)₂]₄(L^CP)₂}.     

Crystal structure of polynuclear pivalate Ni(II) complexes with butanediol

Using single crystal X-ray diffraction the structure of polynuclear [Ni₆(OH)₄(Piv)₇(HOC₄H₈O)(HPiv)₄], {K₄[Ni₁₂(CO₃)₂(Piv)₁₆(OH)₈(HOC₄H₈OH)₂]}HPiv, {[Ni₆(OH)₄(Piv)₆(HOC₄H₈O)(Me₂CO)(HOC₄H₈OH)₂]₄×(Piv)₄}, and {K[Ni₂L₂(Piv)₃]}_∞ complexes, where HOC₄H₈OH is 1,4-butanediol, HPiv is pivalic acid, and L is the anion of nitroxyl radical 2,2,5,5-tetramethyl-4-(3′,3′,3′-trifluoro-2′-oxy-1′-propenyl)-3-imidazolin-1-oxyl is determined.     

Detection of trielectronic recombination of In<Superscript>+</Superscript> ion

The trielectronic recombination of an In⁺ (4d ¹⁰5s ^{2 1} S ₀) ion in collisions with slow electrons, including the two-electron excitation of the 5s2 core of the ion with the simultaneous capture of the triply excited 5p ³ intermediate autoionizing state with its subsequent radiative stabilization 5p ³ → 5s5p ² + hν has been detected and experimentally examined for the first time. The maximum effective cross section of trielectronic recombination is 1.6 × 10⁻¹⁶ cm², which is comparable to the effective cross sections for both dielectronic recombination and electron excitation of the In⁺ ion.     

Study of mechanisms of formation of X-ray emission bands in crystals by the density functional method: The Mg <Emphasis Type="Italic">L</Emphasis><Subscript>2,3</Subscript> bands in metal and in MgO

Using the density functional method in the pseudopotential approximation, we calculate the probabilities of X-ray emission transitions and shapes of the L _2,3 X-ray emission bands of Mg in crystals of metallic magnesium and monoxide MgO. We have paid special attention to the study of mechanisms by which these bands were formed; therefore, along with the total intensities, we determine the partial s- and d-contributions. In addition, the intensities of the L _2,3 bands of Mg have been separated into contributions from direct (intra-atomic) transitions and charge-transfer crossover transitions. We show that an unexpectedly large contribution of partial d-transitions in magnesium oxide is caused by crossover transitions of electrons of valence states of ligands to the core 2p-level of Mg, i.e., charge-transfer transitions. In metallic magnesium, the contribution of these transitions proved to be insignificant. An appreciable contribution of crossover transitions has also been revealed in s-contributions of X-ray emission bands. To estimate the calculation accuracy, we have compared the shapes of theoretical spectra with the shapes of experimental L _2,3 X-ray emission bands of Mg.     

Interpretation of X-ray photoelectron spectra of free nitroxyl radicals

N1s and O1s X-ray photoelectron spectra of stable nitroxyl radicals (substituted piperidine-1-oxyl, 2-imidazoline-1-oxyl, and 2-imidazoline-3-oxide-1-oxyl) and also diamagnetic derivatives with a {ONCNO} fragment are measured. It is shown that the structure of N1s and O1s X-ray photoelectron spectra of nitroxyls is determined by charge transfer processes between different parts of the molecule to screen the X-ray hole and the spin-spin interaction of unpaired electrons on the HOMO and 1s level.