Molecular magnet based on the FeII,III complex with squaric acid

The reaction of Fe^II and Fe^III salts with tetrabutylammonium squarate in an aqueous solution gives rise to a new molecular magnet (T _c = 8.6 K).     

1,3-Dipolar cycloaddition in the synthesis of pyrazolyl-substituted nitronyl nitroxides

A new approach to the synthesis of polyfunctional pyrazolyl-substituted nitronyl nitroxides was developed based on the presynthesized pyrazole derivatives prepared by 1,3-dipolar cycloaddition. The structures of the resulting mono-and biradicals were confirmed by X-ray diffraction. Dedicated to Academician A. L. Buchachenko on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2105–2116, September, 2005.     

Esters of 4,5-dihydro-1H-imidazole-1-oxyl-3-oxide-carboximidic acid

Esters of 4,5-dihydro-1H-imidazole-1-oxyl-3-oxide-carboximidic acid were synthesized. Their structures and magnetic properties were investigated.     

Synthesis, Crystal Structure Determination, and Physicochemical Study of the Nickel(II) Complex of 4-(Pyridyl-2)-1,2,4-triazole

A new trinuclear nickel(II) complex with 4-(pyridyl-2)-1,2,4-triazole (pytrz), [Ni₃(pytrz)₆(H₂O)₆](NO₃)₆, has been synthesized, and its crystal structure has been determined. The compound was studied by X-ray phase analysis (XRPA), magnetochemical measurements, and electronic and IR spectroscopy.     

Magnetic properties of aerugite Co<Subscript>10</Subscript>Ge<Subscript>3</Subscript>O<Subscript>16</Subscript>

This paper reports on the first study of the temperature and field dependences of the magnetization, heat capacity, and electrical properties of synthesized polycrystalline samples of aerugite Co₁₀Ge₃O₁₆, as well as on x-ray diffraction analysis of this compound. It is shown that the cobalt ions in this compound occupy three nonequivalent positions. The results of the experimental and theoretical studies suggest that aerugite is a ferrimagnet with two uncompensated magnetic moments of the cobalt atom per formula unit.     

Evolution of Cu-Zn-Si oxide catalysts in the course of reduction and reoxidation as studied by in situ X-ray diffraction analysis, transmission electron microscopy, and magnetic susceptibility methods

The reduced and reoxidized Cu-Zn-Si oxide catalysts as layered copper-zinc hydroxo silicates with the zincsilite structure were studied using in situ and ex situ X-ray diffraction analysis, transmission electron microscopy, and the temperature dependence of magnetic susceptibility. The catalysts were prepared by homogeneous deposition-precipitation. It was found that Cu⁰ particles were formed on the surface of a layered hydrosilicate with the zincsilite structure upon reduction with hydrogen. The reoxidation of the reduced samples with a mixture of oxygen and an inert gas, which contained no more than 0.05 vol % O₂, resulted in the formation of individual Cu₂O and CuO phases; copper ions did not return to the hydrosilicate structure. Catalytic tests of Cu-Zn-Si catalysts in methanol synthesis indicate that the specific catalytic activity of copper metal particles grows linearly with increasing zinc loading. This fact suggests that copper metal particles, which were obtained by the reduction of Cu²⁺ ions from the copper-zinc hydroxo silicate with the zincsilite structure, were responsible for activity in methanol synthesis. Consequently, the ability to return copper ions to a precursor compound in reoxidation with oxygen at low concentrations, which is known for reduced Cu/ZnO catalysts (these catalysts are highly active in methanol synthesis), is not related to the catalytic activity in methanol synthesis.     

Complexes Fe(HTrz)3B10H10 · H2O and Fe(NH2Trz)3B10H10 · H2O (HTrz = 1,2,4-triazole and NH2Trz = 4-amino-1,2,4-triazole). The spin transition 1 A 1 ⇆ 5 T 2 in Fe(HTrz)3B10H10 · H2O

Methods for the synthesis of iron(II) complexes with 1,2,4-triazole (HTrz) and 4-amino-1,2,4-triazole (NH₂Trz) containing the decahydro-closo-decaborate ion [B₁₀H₁₀]²-were developed. The empirical formulas of the complexes were Fe(HTrz)₃B₁₀H₁₀ · H₂O (I) and Fe(NH₂Trz)₃B₁₀H₁₀ · H₂O (II). The complexes were examined by static magnetic susceptibility measurements (2–300 K) and Moessbauer, IR, and electronic spectroscopy. Complex I exhibits the reversible spin transition ¹ A ₁ ? ⁵ T ₂ and pink ? white thermochromism. The temperatures of the forward and reverse transitions in complex I were 246 and 233 K, respectively. Complex II remained in the high-spin state over the whole temperature range. The sharp decrease in its effective magnetic moment at T < 78 K was attributed to antiferromagnetic exchange interactions between Fe²⁺ ions.     

New hexanuclear antiferromagnetic heterospin iron complex

Precise oxidation of Fe^II ₄(μ₃-OH)₂(OOCBu^t)₆(EtOH)₆ afforded the mixed-valent hexanuclear complex [Fe^II ₄Fe^III ₂(μ₄-O)₂(μ₃-OOCBu^t)₄(μ-OOCBu^t)₆(HOOCBu^t)₃(EtOH)]· ·HOOCBu^t. The structure of the latter was established by X-ray diffraction. The magnetic properties of the new complex were studied. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 900–903, May, 2006.     

Iron(II) Complexes with 4-R-1,2,4-Triazoles (R = Ethyl,Propyl, Isopropyl): Synthesis and Properties

Fe(II) complexes with 4-R-1,2,4-triazoles of compositions FeL₃A₂ · nH₂O (where L is 4-propyl-1,2,4-triazol; A is Br^- (n = 4), CF₃SO₃ ^- (n = 5)), and FeL₂A₂ · nH₂O (where L are 4-ethyl-, 4-propyl-, 4-isopropyl-1,2,4-triazoles (Ettrz, Prtrz, Iprtrz, respectively), A = NCS^-, NO₃ ^- (n = 0-2)) were synthesized. Magnetochemical studies revealed that FeL₃A₂ · nH₂O complexes exhibit reversible spin transition (ST) ¹ A ₁ ⁵ T ₂ that is accompanied by thermochromism (a reversible change of color rose white). The temperatures of direct (T _s) and reverse (T _s) spin transitions are, respectively, 252 and 247 K for Fe(rtrz)₃Br₂ · 4H₂O and 207 and 202 K for Fe(rtrz)₃(CF₃SO₃)₂ · 5H₂O. Dehydration of the complexes is attended by significant changes in the type and temperatures of ST.     

Spin Crossover 1 A 1⇔ 5 T 2 in Solid Fe(trz)3x(atrz)3-3x(NO3)2·H2O (trz = 1,2,4-triazole, atrz = 4-amino-1,2,4-triazole)

The reaction of Fe(NO ₃ ) ₂ , trz, and atrz in ethanol–water gave solid Fe(trz) _3x (atrz) _3-3x (NO ₃ ) ₂ ·H ₂ O (x = 0.1, 0.2, 0.4, 0.8). The solids were investigated by magnetic chemistry, X-ray diffraction, photoelectron (DRS), IR, and Mössbauer spectroscopy methods. The individual Fe(trz)₃(NO₃)₂ and Fe(atrz)₃(NO₃)₂ as well as the solid phases exhibit a reversible spin crossover ¹ , whose temperature and character depend on the phase composition. Due to this, T _c may be changed by introducing another ligand into the complex exhibiting a spin crossover effect.