Coordination polymers of VIV—MII (MII = Mn,Co, Ni,Cd) with ethylmalonate anions

Russian Chemical Bulletin - A series of heterometallic 1D coordination polymers {[MII(VIVO)(Etmal)2(H2O)5] ? 2 H2O}n (MII = Mn (1), Co (2), Ni (3), Cd (4)) were synthesized. These compounds...     

2D coordination polymers of AgI—MII (MII = Ni,Cu) with anions of substituted malonic acids

Russian Chemical Bulletin - Heterometallic malonate complexes [Ag2Ni(H2O)2(R2mal)2]n (R2mal2– is the dimethylmalonate dianion (Me2mal2–) (1) or the cyclobutane-1,1-dicarboxylate dianion...     

State of uranyl silicates MII(HSiUO6)2 ·6H2O (MII=Mn, Co, Ni, Cu, Zn) in aqueous solutions

Uranyl silicates with formula M^II(HSiUO₆)₂·6H₂O (M^II=Mn, Co, Ni, Cu, Zn) were investigated in aqueous solutions in the pH range of 0÷14. The pH interval was established where compounds preserve their composition and structure. It varies in the pH range of (3.5–4.0)÷(10.8–11.4) and depends on M^II type. Out of this pH interval investigated uranyl silicates convert to the compounds of other composition and structure, such as amorphous silica, polyuranates and hydroxides of 3d-transition elements. The solubility of M^II(HSiUO₆)₂·6H₂O was determined, it’s value changes on the several orders of magnitude from 10^?6 M in subalkali solutions to 10^?3 M in acid and strongly alkaline media. Using obtained experimental data the solubility products and solubility curves of uranyl silicates were calculated by mathematical modeling. Also the speciation diagrams of uranium (VI), silicon (IV) and M (II) in solutions and solids were plotted.     

Study of the state of uranogermanates MII(HGeUO6)2·6H2O in Aqueous Solutions (MII = Mn, Co, Ni, Cu, Zn)

The state of d-elements uranogermanates M^II(HGeUO₆)₂·6H₂O in aqueous salt solutions in a wide range of ionic strength, ionic composition, and acidity has been investigated. The pH ranges of the uranogermanates stability have been determined, and products of their transformation have been identified. Solubility, solubility equilibrium constant, and Gibbs energy of formation have been determined for the studied uranogermanates. Diagrams of uranium(VI), germanium(IV), and M(II) state in aqueous solutions and in equilibrium solid phases have been plotted.     

Isodimorphism of the salts 2RbCl · MIICl2 · 2H2O (MII = Mn,Fe, Co,Cu)

The three-component systems RbClMnCl₂H₂O, 2RbCl · CoCl₂ · 2H₂O2RbCl · CuCl₂ · 2H₂OH₂O, 2RbCl · CoCl₂ · 2H₂O2RbCl · MnCl₂ · 2H₂OH₂O have been studied at 25°C. In the 2RbCl · CoCl₂ · 2H₂O2RbCl · CuCl₂ · 2H₂OH₂O system, a discontinuous series of mixed crystals is formed and in the 2RbCl · CoCl₂ · 2H₂O2RbCl · MnCl₂ · 2H₂OH₂O system, a continuous series is present.The unit cell parameters of the 2RbCl · CoCl₂ · 2H₂O double salt were determined: a = 5.586(2) Å, b = 6.469(3) Å, c = 6.988(2) Å, α = 65.31(3)°, β = 87.69(3)°, γ = 84.65(4)°, volume 228.4 ų, Z = 1.The results obtained and discussed in conjunction with the crystal structure data suggest that for 2M^ICl · M^IICl₂ · 2H₂O type salts the triclinic structure is stable only when the large rubidium and cesium ions participate in combinations with non-Jahn-Teller metal(II) ions. In the cases of Jahn-Teller metal(II) ions or with potassium or ammonium ions a tetragonal structure is always stable.     

Synthesis and characterization of MIIU3O10 · nH2O (MII = Mg, Mn, Co, Ni, Cu, Zn, Cd) triuranates

Individual crystalline phases of composition M^IIU₃O₁₀ · nH₂O were prepared by reacting schoepite UO₃ · 2.25H₂O with aqueous solutions of Mg, Mn, Co, Ni, Cu, Zn, or Cd nitrates under hydrothermal conditions at 200°C. The composition and structure of the resultant compounds were determined by hightemperature X-ray diffraction, IR spectroscopy, scanning calorimetry, and chemical analysis; the dehydration and thermal destruction of the compounds were studied.     

Polarography��past, present, and future

Polarography was first developed as an automated method of voltage-controlled electrolysis with dropping mercury electrode. The spontaneously renewed pure electrode surface provided reproducible electrochemical results which enabled scientists to work out adequate theory and rich analytical applications. The original method was then instrumentally modified in various ways. Later, hanging mercury drop was added as an alternative indicator electrode??in this way, polarography turned formally into voltammetry with mercury drop electrodes. Beside, in potential-controlled electrolysis, the mercury drop electrodes have been also used in current-controlled electrolysis (chronopotentiometry)??there, it has provided new experimental effects. Polarography has thus gradually covered a wide field of electrolytic methods based on the use of mercury electrodes, in which it continues developing.     

Heterometallic trinuclear {CdII—MII—CdII} pivalates (M = Mg,Ca, or Sr): ways of assembly and structural features

Conditions for chemical assembly of new heterometallic trinuclear pivalates [Cd₂M(piv)₆L₂] (M = Mg, Ca, or Sr; piv is pivalate) were found. Reactions with the nonchelating ligand 2,4-lutidine (lut) gave the crystals of heterometallic complexes [Cd₂M(piv)₆(lut)₂] (M = Mg (1), Ca (2), and Sr (3)). With the chelating ligand 1,10-phenanthroline (phen), only the homometallic dimer [Cd₂(piv)₄(phen)₂] (4) was obtained under these conditions. Yet heterometallic trinuclear complexes with 1,10-phenanthroline ([Cd₂Mg(piv)₆(H₂O)(phen)₂] (5), [CaCd₂(piv)₆(phen)₂] (6), and [Cd₂Sr(piv)₆(phen)₂]?2MeCN (7)) were synthesized by reactions of phen with complexes 1—3. For all the complexes obtained, the molecular and crystal structures as well as the details of their molecular architecture were determined. The thermal behavior of aqua complex 5 was studied by TG and DSC. The complex eliminated the water molecule between 130 and 180 °C with a high endothermic effect (Q = 101 kJ mol^–1) due to (1) intramolecular hydrogen bonds that stabilize its molecular architecture and (2) subsequent structural rearrangements.     

Low frequency vibrational spectra of crystalline and glassy metaborates Ba2MII(B3O6)2 (MII  Mg,Ca, Ni,Co, Cd)

The low frequency vibrational spectra (Raman and IR) of crystalline metaborates Ba₂M^II(B₃O₆)₂ (M^II  Mg, Ca, Ni, Co, Cd) are interpreted on the basis of a factor group analysis and with the help of ²⁴Mg²⁶Mg and ⁴⁰Ca⁴⁴Ca isotopic shifts. The far-IR spectra of the glasses appear as the envelope of the spectra of the corresponding crystalline compounds for M^II  Mg, Ca and Cd, but they exhibit an additional broad absorption centred near 400 cm⁻¹ for M^II  Co, Ni and Zn. This absorption is assigned to a fourfold coordination of part of the M^II cations, the remaining being in sixfold coordination (as in the crystal) and responsible for a broad absorption in the 300-200 cm⁻¹ region. The possible existence of correlations between coordination and vibrational frequencies is discussed for either alkali and alkaline-earth cations, or transition elements.     

Structure, Magnetism and Spin Coupling Mechanism of Cyano-Bridged LnIII–FeIII Binuclear Metal Complexes

A series of binuclear metal complexes [Ln(L)₄(H₂O)₃Fe(CN)₆]·nH₂O (Ce(1), Pr(2), Nd(3), Sm(4), Eu(5), Gd(6), Tb(7), Dy(8), Er(9), L=2-pyrrolidinone) were prepared and the X-ray crystal structures of complexes 4, 6, and 8 were determined. All the compounds consist of an Ln–CN–Fe unit, in which an octahedral coordinated Fe^III is bridged to an Ln^III ion located in square antiprism environment by a cyano group. The magnetic properties of 3, 4, 5, 6, 7, 9 show an overall antiferromagnetic behavior. The fitting to the experimental magnetic susceptibilities of complex 6 gave g=1.99, J=0.735 cm^–1, zJ=–0.080 cm^–1 on the basis of a binuclear spin system (S _Gd=7/2, S _Fe=1/2), revealing a ferromagnetic intra-molecular Gd–Fe interaction and an antiferromagnetic inter-molecular interaction. Results on the quantum chemical density functional theory (DFT) calculation for 6 showed that the calculated magnetic coupling constant is 8.1 cm^–1, supporting the occurrence of weak ferromagnetic intra-molecular interaction in 6. The spin density maps for 6 in the high spin ground state and broken symmetry state were obtained, and the spin–spin coupling mechanism is discussed.     

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.     

Four tri-spin lanthanide–nitronyl nitroxide (LnIII = GdIII,DyIII, ErIII,and HoIII) complexes: syntheses,structures, and magnetic properties

Four radical–Ln(III)–radical complexes, [Ln(hfac)₃(NITPhSCH₃)₂] (Ln?=?Gd (1), Dy (2), Er (3), Ho (4); hfac?=?hexafluoroacetylacetonate; NITPhSCH₃?=?4′-thiomethylphenyl-4,4,5,5tetramethyl-imidazoline-1-oxyl-3-oxide), have been synthesized, and structurally and magnetically characterized. The X-ray crystal structures show that the structures of the four complexes are similar, consisting of isolated molecules in which Ln(III) ions are coordinated by six oxygen atoms from three hfac and two oxygen atoms from nitronyl radicals. The temperature dependencies of magnetic susceptibilities for the four complexes show that in the Gd(III) complex, ferromagnetic interactions between Gd(III)–radical and antiferromagnetic interactions between the radicals coexist with J _Rad–Gd?=?1.09?cm^?1, J _Rad–Rad?=??1.85?cm^?1.     

连续二氧化碳激光敏化氧化CF2HCL,CF2=CF2,CF2=CFCl,CHCl3,CHCl=CCl2和CH2=CH2

本文报道了连续二氧化碳激光敏化氧化CF_2HCl,CF_2==CF_2,CF_2==CFCL,CHCl_3,CHCl==CCl_2和CH_2==CH_2的反应,讨论了某些反应的机制。结果表明,激光敏化方法可以使不能直接吸收激光的反应物分子在气相中发生反应,并有可能产生卡宾。     

CH_2=CH(XM)(X=S,Se,Te;M=H,Li,Na,K,Rb,Cs,-)的从头算研究

应用相对论有效势在ＭＰ２水平上对ＣＨ２ＣＨ（ＸＭ）（Ｘ＝Ｓ，Ｓｅ，Ｔｅ；Ｍ＝Ｈ，Ｌｉ，Ｎａ，Ｋ，Ｒｂ，Ｃｓ，－）进行了从头计算研究．结果表明，所研究的化合物都有平面式和非平面桥式两种构型．分析了碱金属离子对两可亲核底物ＣＨ２ＣＨＸ－（Ｘ＝Ｓ，Ｓｅ，Ｔｅ）离域化的影响，并用自然布局分析方法（ＮＰＡ）研究了电荷分布的变化，得出了有价值的结论．     

Fluorescence lifetime studies of no a 2Σ+(ν = 5, N = 9), B2Π32(ν = 8, J = 8.5), CwΠ32(ν = 1, J = 8.5), D2Σ+ (ν = 0, N = 5) and D2Σ+(ν = 1, N = 9)

Fluorescence decay profiles of NO excited levels slightly above the dissociation limit have been measured by a single-photon counting technique with nanosecond pulse excitation using an iodine flash lamp. Three iodine atomic lines in the vicinity of 180 nm are found to bring NO molecules into the levels A²Σ⁺(ν = 5, N = 9), B²²Π_{$\text{3}\text{2}$}(ν = 8, J = 8.5), C²Π_{$\text{3}\text{2}$}(ν = 1, J = 8.5), D²Σ⁺(ν = 0, N = 5) and D²Σ⁺(ν = 1, N = 9). Extrapolated zero-pressure lifetimes for single rotational levels are obtained, except for the C state where only a lifetime of ⩽0.4 ns was obtained. Self-quenching rate constants are also determined under higher-pressure conditions. Helium was found to quench the NO A²Σ⁺(ν′ = 5) fluorescence very efficiently.     

Cyano-bridged Ln^3＋-Cr^3＋ Binuclear Complexes [Ln（L）x（H2O）y^- Cr（CN）6]·mL·nH2O （Ln=La-Nd,x=5, y=2, m=1 or 2, n=2 or 2.5; Ln-Sm-Dy,Er, x=4, y=3, m=0, n=1.5 or 2.0; L= 2-pyrrolidinone）： Structure,Magnetism and Spin Density Map

In order to shed light upon the nature and mechanism of 4f-3d magnetic exchange interactions, a series of binuclear complexes of lanthanide（3＋） and chromium（3＋） with the general formula [Ln（L）5（H2O）2Cr（CN）6]·mL· nH2O （Ln=La （1）, Ce （2）, Pr （3）, Nd （4）; x=5, y=2, m=1 or 2, n=2 or 2.5; L=2-pyrrolidinone） and [Ln（L）4（H2O）3Cr（CN）6] ·nH2O （Ln=Sm （5）, Eu （6）, Gd （7）, Tb （8）, Dy （9）, Er （10）; x=4, y=3, m=0, n= 1.5 or 2.0; L=2-pyrrolidinone） were prepared and the X-ray crystal structures of complexes 2, 6 and 7 were determined. All the compounds consist of a Ln-CN-Cr unit, in which Ln^3＋ in a square antiprism environment is bridged to an octahedral coordinated Cr^3＋ ion through a cyano group. The magnetic properties of the complexes 3 and 6-10 show an overall antiferromagnetic behavior. The fitting to the experimental magnetic susceptibilities of 7 give g= 1.98, J=0.40 cm^-1, zJ＇= -0.21 cm^-1 on the basis of a binuclear spin system （Scd=7/2, Scr=3/2）, revealing an intra-molecular Gd^3＋-Cr^3＋ ferromagnetic interaction and an inter-molecular antiferromagnetic interaction. For 7 the calculation of quantum chemical density functional theory （DFT）, combined with the broken symmetry approach, showed that the calculated spin coupling constant was 20.3 cm^-1, supporting the observation of weak ferromagnetic intra-molecular interaction in 7. The spin density distributions of 7 in both the high spin ground state and the broken symmetry state were obtained, and the spin coupling mechanism between Gd^3＋ and Cr^3＋ was discussed.     

Towards Binuclear Polyaminocarboxylate MRI Contrast Agents? Spectroscopic and MD Study of the Peculiar Aqueous Behavior of the LnIII Chelates of OHEC (Ln=Eu,Gd, and Tb): Implications for Relaxivity

We report the study of binuclear Ln(III) chelates of OHEC (OHEC=octaazacyclohexacosane-1,4,7,10,14,17,20,23-octaacetate). The interconversion between two isomeric forms, which occurs in aqueous solution, has been studied by NMR, UV/Vis, EPR, and luminescence spectroscopy, as well as by classical molecular dynamics (MD) simulations. For the first time we have characterized an isomerization equilibrium for a Ln(III) polyaminocarboxylate complex (Ln(III)=Y, Eu, Gd and Tb) in which the metal centre changes its coordination number from nine to eight, such that: [Ln(2)(ohec)(H(2)O)(2)](2-) r<==>[Ln(2)(ohec)](2-)+2 H(2)O. The variable temperature and pressure NMR measurements conducted on this isomerization reaction give the following thermodynamic parameters for Eu(III): K(298)=0.42+/-0.01, DeltaH(0)=+4.0+/-0.2 kJ mol(-1), DeltaS(0)=+6.1+/-0.5 J K(-1) mol(-1) and DeltaV(0)=+3.2+/-0.2 cm(3) mol(-1). The isomerization is slow and the corresponding kinetic parameters obtained by NMR spectroscopy are: k(298)(is)=73.0+/-0.5 s(-1), DeltaH++(is)=75.3+/-1.9 kJ mol(-1), DeltaS++(is)= +43.1+/-5.8 J K(-1) mol(-1) and DeltaV++(is)=+7.9+/-0.7 cm(3) mol(-1). Variable temperature and pressure (17)O NMR studies have shown that water exchange in [Gd(2)(ohec)(H(2)O)(2)](2-) is slow, k(298)(ex)=(0.40+/-0.02)x10(6) s(-1), and that it proceeds through a dissociative interchange I(d) mechanism, DeltaV( not equal )=+7.3+/-0.3 cm(3) mol(-1). The anisotropy of this oblong binuclear complex has been highlighted by MD simulation calculations of different rotational correlation times. The rotational correlation time directed on the Gd-Gd axis is 24 % longer than those based on the axes orthogonal to the Gd-Gd axis. The relaxivity of this binuclear complex has been found to be low, since 1) only [Gd(2)(ohec)(H(2)O)(2)](2-), which constitutes 70 % of the binuclear complex, contributes to the inner-sphere relaxivity and 2) the anisotropy of the complex prevents water molecules from having complete access to both Gd(III) cages; this decreases the outer-sphere relaxivity. Moreover, EPR measurements for the Gd(III) and for the mixed Gd(III)/Y(III) binuclear complexes have clearly shown that the two Gd(III) centres interact intramolecularly; this enhances the electronic relaxation of the Gd(III) electron spins.     

六聚同多酸阴离子M6On-19(M=Mo,W,n=2;M=Nb,Ta,n=8)电子结构和化学性质的密度泛函理论研究

采用B3LYP方法在Lanl2DZ水平上计算了六聚同多阴离子(M6On19^-(M=Mo和W,n=2;M=Nb和Ta,n=8)的电子结构,分析了它们的前线轨道、分子静电势(MEP)．计算结果表明,Nb6O19^8-和Ta6O19^8-是电子给体,而Nb6O19^2-和Ta6O19^2-则是电子受体,这与它们在溶液中具有不同的化学性质是一致的．     

OCH=CHR（R=H,BH2,CN,F,OH,NH2）自由基结构和稳定性的…

用ＵＨＦ／４－３１Ｇ基组，全构型优化ＯＣＨ＝ＣＨＲ（Ｒ＝Ｈ，ＢＨ２，ＣＮ，Ｆ，ＯＨ，ＮＨ２）６个氧自由基的构型并研究其稳定性化能△Ｅ，以ＯＣＨ＝ＣＨ２自由基为参考标准，它们的○Ｅ分别为０．００，－７５．９７，１．１１，０．７６，２２．０６和４０．６５ｋＪ／ｍｏｌ，说明供电子基团ＯＨ和ＮＨ２对氧自由基起稳定化作用，ＢＨ２对氧自由基起去稳定化作用，而ＣＮ和Ｆ对氧自由基的稳定性影响不大。