[Fe2(μ-SC5H4N)2(NO)4] as a New Potential NO Donor: Synthesis,Structure, and Properties

A new potential donor of nitrogen monoxide, a binuclear iron sulfur nitroso complex, was prepared by exchange reaction of Na₂Fe₂(S₂O₃)₂(NO)₄ with pyridine-2-thiol in the presence of sodium thiosulfate at pH 12. The molecular and crystal structures of [Fe₂(-SC₅H₄N)₂(NO)₄] were studied by X-ray diffraction analysis. The type of iron coordination by pyridine-2-thiol in the presence of a coordinated NO molecule was determined. In vacuum, the structure of the complex is destroyed, which is accompanied by NO evolution, while exposure to UV radiation results in decomposition of the complex and in a release of N₂O.     

Supertransferred hyperfine interaction in magnetic insulators (II)

The important mechanisms of supertransferred hyperfine (STHF) interactions in N–O–M chains are briefly discussed: (i) spin polarization ofns states in the N-ion due to the s-d exchange interaction,H _STHF ^sd ; (ii) contributions of spin-polarized states of the intervening O-ion,H _STHF ^II ; (iii) transfer of d-electrons of the M-ion to emptyns states in the N-ion,H _STHF ^III . The dependence ofH _STHF upon the N–O–M bond configuration, electronic structure, and orbital state of the M-ion is presented in a convenient form. The STHF interactions in the chains Sn⁴⁺–O^2––Fe³⁺, Cr³⁺ in compounds with slightly distorted Perovskite structure are considered. The STHF field in the chain Sn⁴⁺–O^2––Cr³⁺ is shown to change the sign within the range of angles near 170°. This conclusion is in line with published data on the isoelectronic chain Sn⁴⁺–O²–Mn⁴⁺ in the compounds Ca_1–x Sr _x MnO₃. The results obtained for the N–O–Fe³⁺ chain are rationalized by the predicted angular dependence ofH _STHF=+ cos + cos². Features of the STHF interactions in N–O–M chains with an M-ion in an orbital degenerate state are examplified by a preliminary analysis of N–O^2––V³⁺ chains in orthovanadites.     

Synthesis of molecular ferromagnetics [R3R′X]MCr(C2O4)3 (X = N,R = Bun,R′ = Prn,Et, Me; X = P,R = Ph,R′ = Bun; M = Mn,Fe, Co,Ni, Cu)

The synthesis, IR spectra, and the temperatures of the transition into a ferromagnetic state (T _c) of layered ferromagnetics [R₃RX[MCr(C₂O₄)₃ (M = Mn, Fe, Co, Cu, and Ni) with the [Ph₃BuP]⁺, [Bu₃RN]⁺ (R = Pr, Et, and Me) cations capable of subsequently changing the distances between metallooxalate layers have been considered. The temperatureT _c has been found to be independent of the size of the organic cation. It is believed that the determining factors in the transition to a ferromagnetic state are exchange interactions inside the metallooxalate layer.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2327–2330, September, 1996.     

Synthesis and reactivity of metal-containing monomers

Acid and neutral Co^II, Cu^II, Ni^II, Zn^II, Fe^II, and Fe^III maleates, fumarates, and itaconates were obtained and characterized. The methods for their synthesis were optimized, and the valence state and coordination of metals were studied. Co^II and Fe^II hydrogen maleates, Co^II maleate, and Co^II fumarate were examined by X-ray diffraction analysis. The ligands based on unsaturated dicarboxylic acids can be mono-, bi-, and tetradentate, which results in the formation of acid salts, chain and three-dimensional coordination polymers, whose double bond is not involved in the coordination. The strong antiferromagnetic exchange (μ_elf=1.41 and 0.34 μ_B at 290 and 80 K, respectively) was detected in Cu^II itaconate. Based on the data of Mössbauer spectroscopy, the partial reduction of Fe^III to Fe^II during the synthesis of Fe^III maleate was shown to occur: δFe=0.43 and 1.27 mm s^?1, ΔE _Q=0.57 and 3.13 mm s^?1 and Γ=0.37 and 0.28 mm s^?1 atT=298 K for Fe^III and Fe^II, respectively.     

Synthesis and some properties of anionic chloranilate complexes of iron(iii). Crystal and molecular structure of rubidium and cesium chloranilatoferrates

New anionic chloranilate complexes of iron(iii) Cs[Fe(C₆O₄Cl₂)₂(H₂O)₂]·4H₂O (1), Rb[Fe(C₆O₄Cl₂)₂(H₂O)₂]·4H₂O (2), Rb₂[Fe(C₆O₄Cl₂)₂(H₂O)₂]₂·5H₂O (3), Cs₃Fe(C₆O₄Cl₂)₃ (4), (Bu₄N)Fe(C₆O₄Cl₂)₂ (5), (Bu₄N)₄Fe₂(C₆O₄Cl₂)₅ (6), and (R₄N)₃Fe(C₆O₄Cl₂)₃ (R = Pr (7), Bu (8), C₅H₁₁ (9)) were synthesized in an aqueous medium. The Mössbauer spectra of the synthesized chloranilatoferrates are characteristic of the high-spin state of Fe^III in an octahedral oxygen coordination. The crystal and molecular structures of compounds 1–3 were determined by X-ray diffraction. The complex anions [Fe(C₆O₄Cl₂)₂(H₂O)₂]^2? involved in these compounds are composed of two chelate chloranilate ions and two water molecules trans-(1,2) or cis-coordinated (3) to the iron atom. Since tetraalkylammonium tris(chloranilato)ferrates 7–9 and binuclear complex 6 are soluble in many organic solvents, they are promising precursors for the synthesis of metal-organic coordination polymers. Tetrabutylammonium bis(chloranilato)ferrate (Bu₄N)Fe(C₆O₄Cl₂)₂ (5) is the first example of the preparation of an anionic chloranilate complex of iron(iii) with a plausible chain structure in an aqueous medium.     

Bridgman growth and site occupation in LuAG:Ce scintillator crystals

LuAG:Ce single crystals with various activator concentrations were grown by the vertical Bridgman technique. Characterization of crystals was done in terms of actual doping level, macroscopic defects and degree of non-equivalent substitutions by Lu for Al in octahedral lattice sites. Scintillation measurements were performed using 2×2×8 mm³ shaped samples with Ce concentration in the range 0.05–0.55 at%. Essential improvement of performance was demonstrated in samples containing ≥0.2 at% of Ce; the light yield measured in LuAG:Ce (0.55 at%) was about 26000 ph/MeV, or close to that of LSO.     

Angular dependence of the superexchange interaction Fe3+-O2−-Cr3+

The super-exchange interaction parametersI(Fe, Cr) of Fe³⁺ and Cr³⁺ in iron doped rate-earth orthochromitesRCr_0.99Fe_0.01 O₃ (R=La, La_0.5Nd_0.5, Nd, Sm, Gd, Dy, Y, Er, Yb or Lu) have been obtained from⁵⁷Fe magnetic hyperfine structure measurementsvia the Mössbauer effect.The dependence of the experimental valuesI(Fe, Cr) on the Fe–O–Cr average superexchange angle (depending upon the relative size of the rare-earth (RE) ionR ³⁺) is well described by the equationI(d⁵, d ^N ) = _N + _N cos + _N cos² .Within the accessible range of super-exchange angles 142°156°, the Fe³⁺–O^2––Cr³⁺ interaction is negative (antiferromagnetic). However, a theoretical analysis predicts a sign reversal forI(Fe, Cr.) at about 162° and thus ferromagnetic character of the interaction between 162° and 180°.The spin-only super-exchange interaction integrals fore _g andt _2g electrons, separately, are also calculated. Their angular dependence is accounted for by the behaviour of the antiferromagnetic kinetic and ferromagnetic potential exchange which are of different character when passing from 180° to 90° super-exchange geometry. The magnitude and the sign of the spin-only super-exchange integral for an arbitrary 3d cation, pair is predicted.     

Monoclinic centers of rare-earth <Emphasis Type="Italic">S</Emphasis> ions in yttrium orthoaluminate crystals

The ESR spectrum of Gd³⁺ and Eu²⁺ monoclinic centers, which substitute for yttrium ions in YAlO₃ crystals doped with europium and zirconium, has been investigated. Parameters of the fine structure of these centers are determined. The hyperfine-interaction parameters are determined for the centers with ¹⁵¹Eu isotope, and the hyperfine structure of the centers with ¹⁵³Eu isotope is discussed.     

Crystal structure of Na<Subscript>4</Subscript>[Na<Subscript>2</Subscript>Cr<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>6</Subscript>] · 10H<Subscript>2</Subscript>O

Single crystals of the Na₄[Na₂Cr₂(C₂O₄)₆] · 10H₂O complex were synthesized for the first time. The structure of the complex was determined by X-ray diffraction analysis. The compound crystallizes in the monoclinic crystal system with the unit cell parameters a = 17.290(4) Å, b = 12.521(3) Å, c = 15.149(3) Å, β = 100.45(3)°, Z = 4, space group Cc. Anionic layers [NaCr(C₂O₄)₃] _2n ^4n? can be distinguished in the crystal structure of the complex. The Na⁺ cations and water molecules, involved in the formation of a hydrogen bond network, are located between the anionic layers.     

The Enantioselective Role of the [N(C5H11)4]+Organic Cation in the Structure of the Molecular Magnet [N(C5H11)4][MnIIFeIII(C2O4)3]

A crystal of [N(C₅H₁₁)₄][Mn^IIFe^III(C₂O₄)₃] was studied by X-ray diffraction analysis: space group C222₁, a= 9.653(2) Å, b= 16.201(2) Å, c= 20.193(4) Å. The arrangement of the cations predetermines the formation of the crystal structure from anionic layers of the same chirality. The presence of two types of organic cation does not contradict the formation of crystals with left and right chirality and accounts for the data of Mössbauer spectroscopy, indicating two states of iron.