Thermodynamic investigation on M–Te–O (M = Sc, Y) system

The standard Gibbs energy of formation of M₂TeO₆ and M₆TeO₁₂ (where M = Sc, Y), was determined from its vapor pressure measurements by employing thermogravimetry-based transpiration technique. This technique was validated by measuring the vapor pressure of well-studied substances such as TeO₂(s) and CdCl₂(s). The temperature dependence of the vapor pressure of TeO₂(g) over the mixtures M₆TeO₁₂ + M₂O₃ (where M = Sc, Y), generated by the incongruent vaporization reaction, M₆TeO₁₂(s) → 3M₂O₃(s) + TeO₂(g) + ½O₂(g) were measured in the temperature range 1,413–1,473 K and 1,623–1,743 K for Sc₆TeO₁₂(s) and Y₆TeO₁₂(s), respectively. Similarly, the vapor pressure of TeO₂(g) over the mixtures M₂TeO₆(s) + M₆TeO₁₂(s) generated by the vaporization reaction, 3M₂TeO₆(s) → M₆TeO₁₂(s) + 2TeO₂(g) + O₂(g) was measured in the temperature range (1,223–1,293 K) and (1,333–1,423 K) for Sc₂TeO₆(s) and Y₂TeO₆(s), respectively. From the vapor pressure measurements, the standard Gibbs energy of formation of M₆TeO₁₂ and M₂TeO₆ were derived.     

Synthesis,crystal structures,and magnetic properties of three K[M(bpb)(CN)2]-based trinuclear sandwich-like heterobimetallic M(III)–Ni(II) (M = Fe,Cr, Co) complexes

Three trinuclear sandwich-type cyanide-bridged M^III–Ni^II complexes, {[Ni(cyclm)[Fe(bpb)(CN)₂]₂}·8H₂O (1), {[Ni(cyclm)[Cr(bpb)(CN)₂]₂}·2H₂O (2), and {[Ni(cyclm)[Co(bpb)(CN)₂]₂}·CH₃OH·2H₂O (3) (cyclm?=?1,4,8,11-tetraazacyclotetradecane), have been synthesized using K[M(bpb)(CN)₂] (M?=?Fe, Cr, Co; bpb?=?1,2-bis(pyridine-2-carboxamido)benzenate) as building block and one Ni(II) compound containing a 14-membered macrocycle ring as assembling segment. All the complexes have been characterized by elemental analysis, IR spectroscopy, and X-ray structure determination. Single X-ray diffraction analysis shows similar sandwich-like structures, in which the two cyanide-containing building blocks are monodentate through one of their two cyanides, coordinated face to face to the central Ni(II). Investigation of the magnetic properties of 1 and 2 reveals ferromagnetic magnetic coupling between the neighboring Fe(III)/Cr(III) and Ni(II) through the bridging cyanide. A best-fit to the magnetic susceptibilities of 1 and 2 based on the trinuclear M₂Ni model leads to magnetic coupling constants J?=?5.47(1)?cm^?1 for 1 and J?=?6.37(2)?cm^?1 for 2.     

ChemInform Abstract: Are Cyclogallenes (M2(GaH)3) (M: Li,Na, K) Aromatic?

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Theoretical study of group 11 metal–silonyl complexes: M–SiO and M–(SiO)2 (M = Cu, Ag, or Au)

 The spectroscopic properties of M–SiO and M–(SiO)₂ (1–1 and 1–2 complexes with M = Cu, Ag, or Au) have been theoretically studied. It has been shown that both M–SiO and M–(SiO)₂ compounds in their ground state are bent with a metal–Si bonded structure. The calculated M(ns) spin density agrees well with the electron spin resonance experimental data. From a topological analysis, it has been shown that a rather large charge transfer occurs from the metal towards the SiO moiety, and that the M–Si bond energy correlates with the electron density located at the M–Si bond path (bond critical point). Received: 6 July 2000 / Accepted: 11 October 2000 / Published online: 19 January 2001     

Thermodynamic studies on the systems M–Te–O (M = Nd,Sm)

The standard Gibbs energies of formation of Nd₂TeO₆ and M₆TeO₁₂ (where M = Nd, Sm) were determined from vapour pressure measurements. The vapour pressure of TeO₂(g) was measured by employing thermogravimetry-based transpiration technique. The temperature dependence of the vapour pressure of TeO₂(g) over the mixtures Nd₂TeO₆+Nd₆TeO₁₂, generated by the incongruent vapourisation reaction, 3Nd₂TeO₆(s) → Nd₆TeO₁₂(s)+2TeO₂(g)+O₂(g), was measured in the temperature range 1,408–1,495 K. Similarly, the vapour pressure of TeO₂(g) over the mixtures M₆TeO₁₂+M₂O₃ (where M = Nd, Sm), generated by the incongruent vapourisation reaction, M₆TeO₁₂(s) → 3M₂O₃(s)+TeO₂(g)+½O₂(g), was measured in the temperature range 1,703–1,773 and 1,633–1,753 K for Nd₆TeO₁₂(s) and Sm₆TeO₁₂(s), respectively. Enthalpy increments of M₂TeO₆(s) (where M = Nd, Sm) were determined by inverse drop calorimetric method in the temperature range 573–1,273 K. The thermodynamic functions, viz., heat capacity, entropy and free energy functions, were derived from the measured values of enthalpy increments. A mean value of ?2,426.2 ± 0.6 and ?2,417.9 ± 1.1 kJ mol^?1 was obtained for $ \Updelta_{\text{f} } H_{298}^{\text{o}} $ (Nd₂TeO₆, s) and $ \Updelta_{\text{f}} H_{298}^{\text{o}} $ (Sm₂TeO₆, s), respectively, by combining the value of $ \Updelta_{\text{f}} G^{\text{o}} $ (Nd₂TeO₆, s) and $ \Updelta_{\text{f}} G^{\text{o}} $ (Sm₂TeO₆, s) derived from vapour pressure data and the free energy functions derived from the drop calorimetric data.     

Electroconductivity of Solid Electrolytes in the Systems K3–2x M x PO4 (M = Ca, Sr, Ba)

Solid electrolytes K_{3 – 2x} M _x PO₄ (M = Ca, Sr, Ba) are synthesized and the temperature and concentration dependences of their electroconductivity are studied. Adding calcium and strontium stabilizes the high-temperature -form of K₃PO₄ at room temperature, while barium-containing solid electrolytes undergo an eutectoid decomposition below 430°C. Maximum electroconductivity is exhibited by K_{3 – 2x} Sr _x PO₄ (7.1 × 10^–3 and 1.25 × 10^–1 S cm^–1 at 300 and 700°C).     

三元体系MCl-M′Cl-HOAc(25℃)的研究(M,M′=K、Rb、Cs,M≠M′)

测定了25℃下KCl-RbCl-HOAc,KCl-CsCl-HOAc,RbCl-CsCl-HOAc三个体系的溶度数据,绘制了相应的相图以及分配图。第一个体系中只有一种固相存在,属于Roozeboom第Ⅰ型;后两个体系互溶性都有十分明鲜的裂隙,但比以水为溶剂的体系中的互溶性显著增强,二者均属Roozeboom第Ⅳ型。     

Avoided crossings in metal (M)–gas (X) reactions (M = Hg, and X = SiH4, GeH4)

A study of nonadiabatic transitions through avoided crossings between two potential energy curves, associated to the approach of a mercury atom to an organic gas molecule (silane or germane) is presented. We study the Si–H and Ge–H bond breaking in the molecules SiH₄ and GeH₄, which are an important subject in the production of hydrogenated amorphous thin films. We here emphasize the importance of the excited states, the avoided crossings generated during the molecule–metal approach and the nonadiabatic transition probabilities. We have developed a model to extend the Landau–Zener theory utilizing the angle instead of the distance as the main parameter of the reaction, which is particularly adapted for tetrahedral molecules (as silane and germane). The activation process of these molecules requires several stages; first, we solve the Schrödinger equation (within the Born-Oppenheimer approximation) for the metal–molecule system during interaction. We always take into account all those states that can play a role in the reaction, even those that because of their energetic separation from the ground state are forgotten by other groups. The calculations begin at a LCAO-MO approximation and thenceforth variational and perturbative CI including of the order of a million determinants are carried out. Usually, some states of the metal repel the gas molecule and others attract it. This produces a series of avoided crossings among the curves, demanding that the nonadiabatic transition probabilities are obtained. This is the ultimate goal of the present study.     

Synthesis,crystal structures,and properties of two heterometallic Cu(II)–M(II) (M = Zn,Ni) oxamidato-bridged coordination complexes

Two heterometallic coordination complexes, {[Cu(aeop)Zn(H₂O)₃]₂?·?3H₂O} _n (1) and [Cu(aeop)Ni(H₂O)₄]?·?4H₂O (2) (H₄aeop?=?N-(2-aminoterephthalic acid)-N′-(1,3-propanediamine)oxamidate), have been synthesized and characterized by elemental analyses, IR, UV spectroscopy, thermogravimetric analysis, and X-ray crystal diffraction. Complex 1 features a 1-D chain constructed from neutral tetranuclear units. Complex 2 is a neutral binuclear complex. Through intermolecular hydrogen-bonding interactions, 2 gives a 3-D network structure. The variable temperature magnetic susceptibility measurements (2–300?K) of 2 show a pronounced antiferromagnetic interaction between the copper(II) and nickel(II), and the exchange integral J is equal to ?42.7?cm^?1.     

Quantum-chemical modeling of the molecular structures of (555)macrotricyclic chelates in M(II) ion–thiooxamide–glyoxal ternary systems (M = Mn,Fe, Co,Ni, Cu,Zn)

The thermodynamic and geometric parameters of isomeric macrotricyclic Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes that can form upon the complexation of the corresponding hexacyanoferrates( II) with thiooxamide H₂N–C(=S)–C(=O)–NH₂ and glyoxal HC(=O)–CH(=O) in gelatin-immobilized matrices have been calculated by the OPBE/TZVP DFT method with the use of the Gaussian09 program package. It has been found that a complex with the MN₄ chelate core is most stable for M = Mn, Fe, Co, Ni, and Zn, and the MN₂S₂ core is most stable for M = Cu. Bond lengths and bond angles have been reported, and it has been noted that in all complexes, except the Zn(II) one, the chelate core and three fivemembered chelate rings are almost planar.     

Preparation and photoluminescent properties of Eu(III) containing M-layered silicates (M = Li,Na, K,Rb, Cs)

Eu(III) containing M-layered silicates (M = Li, Na, K, Rb, Cs) were prepared using the layered silicates, such as ilerite, magadiite, and kenyaite, as a host matrix and the luminescence properties were investigated. The results from the luminescence measurements indicated that the luminescence properties in the EuM-layered silicate system depended strongly on the types of host matrices and alkali cations. Among the EuM-layered silicates, EuM-ilerite exhibited the strongest luminescence intensity for all alkali cations, whereas EuM-kenyaite exhibited relatively weak luminescence intensity. The luminescence intensity was significantly increased by heat treatment at high temperature, mainly due to the phase change of host matrices and the presence of alkali cations in the host matrices. Particularly, the luminescence intensity of EuM-layered silicate calcined at 1,000 °C increased with the increase of the ion size of alkali cations.     

Aqueous sol–gel synthesis,thermoanalytical study and luminescent properties of M0.05Eu0.05Ca0.9MoO4 (M=Li,Na, K,Rb, Cs) nanocrystallites

Nano-sized M_0.05Eu_0.05Ca_0.9MoO₄ (M=Li, Na, K, Rb, Cs) ceramics have been successfully synthesized by an aqueous sol–gel synthesis method using a tartaric acid as a ligand. In order to reveal the influence of the peculiarities of the nature of dopants effect into the crystallization of CaMoO₄ double oxide, the thermal analysis of the as-prepared gels was performed. In addition, infrared spectroscopy was used in order to identify the functional groups from the characteristic stretching vibrations in the M–Eu–Ca–Mo–O tartrate gel precursors. Besides, to confirm the dynamics of growing crystallites in the final ceramics and to reveal the morphological changes on the surface, the x-ray diffraction and scanning electron microscopy were applied. Finally, photoluminescence measurements were used to estimate the optical properties of europium oxide as a dopant in the samples according to the nature of alkali metal. Therefore, according to the obtained results, it was estimated that luminescence intensity of Eu³⁺ ions is mainly affected by the chemical reaction, which takes place at about 973 K of temperature. This effect was partly confirmed from the results of the thermal decomposition of M–Eu–Ca–Mo–O tartrate gel precursors with an endothermic behaviour in the DSC curve, which indicates the crystallization mechanism of the CaMoO₄ double oxide.

     

Ion-Exchange Processes M(II) → Fe(III) and Fe(III) → M(II) in Metal Hexacyanoferrate(II) Gelatin-Immobilized Matrices (M = Mn,Co, Ni,Cu, Zn,Cd)

Ion-exchange reactions M²⁺ Fe³⁺ and Fe³⁺ M²⁺ (M = Mn, Co, Ni, Cu, Zn, Cd) were studied in metal(II) hexacyanoferrate(II) gelatin-immobilized matrices M₂[Fe(CN)₆] in contact with aqueous FeCl₃ solutions and Fe₄[Fe(CN)₆]₃ in contact with aqueous MCl₂ solutions. It was shown that in both cases, M²⁺ was replaced by Fe³⁺ and Fe³⁺ was replaced by M²⁺ to some extent, but no complete replacement was observed in the M₂[Fe(CN)₆]–FeCl₃ or Fe₄[Fe(CN)₆]₃–MCl₂ systems under study. No electrophilic substitution Fe³⁺ Mn²⁺ was found to occur in any noticeable degree during the contact of Fe₄[Fe(CN)₆]₃ with aqueous MnCl₂ solutions even when this contact occurred for 1 h and longer.     

Tunability of the M(II)M(III)/M(II)(2) and M(III)(2)/M(II)M(III) (M=Mn, Co) couples in bis-μ-O,O'-carboxylato-μ-OR bridged complexes

A comparison of the electrochemical properties of a series of dinuclear complexes [M(2)(L)(RCO(2))(2)](+) with M = Mn or Co, L = 2,6-bis(N,N-bis-(2-pyridylmethyl)-sulfonamido)-4-methylphenolato (bpsmp(-)) or 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato (bpbp(-)) and R = H, CH(3), CF(3) or 3,4-dimethoxybenzoate demonstrates: (i) The electron-withdrawing sulfonyl groups in the backbone of bpsmp(-) stabilize the [M(2)(bpsmp)(RCO(2))(2)](+) complexes in their M(II)(2) oxidation state compared to their [M(2)(bpbp)(RCO(2))(2)](+) analogues. Manganese complexes are stabilised by approximately 550 mV and cobalt complexes by 650 mV. (ii) The auxiliary bridging carboxylato ligands further attenuate the metal-based redox chemistry. Substitution of two acetato for two trifluoroacetato ligands shifts redox couples by 300-400 mV. Within the working potential window, reversible or quasi-reversible M(II)M(III)? M(II)(2) processes range from 0.31 to 1.41 V for the [Co(2)(L)(RCO(2))(2)](+/2+) complexes and from 0.54 to 1.41 V for the [Mn(2)(L)(RCO(2))(2)](+/2+) complexes versus Ag/AgCl for E(M(II)M(III)/M(II)(2)). The extreme limits are defined by the complexes [M(2)(bpbp)(CH(3)CO(2))(2)](+) and [M(2)(bpsmp)(CF(3)CO(2))(2)](+) for both metal ions. Thus, tuning the ligand field in these dinuclear complexes makes possible a range of around 0.9 V and 1.49 V for the one-electron E(M(II)M(III)/M(II)(2)) couple of the Mn and Co complexes, respectively. The second one-electron process, M(II)M(III)? M(III)(2) was also observed in some cases. The lowest potential recorded for the E°(M(III)(2)/M(II)M(III)) couple was 0.63 V for [Co(2)(bpbp)(CH(3)CO(2))(2)](2+) and the highest measurable potential was 2.23 V versus Ag/AgCl for [Co(2)(bpsmp)(CF(3)CO(2))(2)](2+).     

Metalloligand-induced Synthesis of Two Cu(I)–M (M=Ni,Co) Heterobimetallic Coordination Polymers: Structures,Thermal and Luminescence Properties

Two interesting heterobimetallic coordination polymers (CPs), {[Ni(4-pytpy)₂]₂[Cu₄(N(CN)₂)₇](NO₃)(DMF)(DMSO)(H₂O)₄}_n (1) and {[Co(4-pytpy)(N(CN)₂)]₂[Cu₂(N(CN)₂)₄]}_n (2), have been synthesized based on different metalloligands [M(4-pytpy)₂]²⁺ (M=Ni 1, Co 2) (4-pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine). CPs 1 and 2 have been well characterized by elemental analysis, IR spectroscopy, thermal analysis and single-crystal X-ray diffraction. Both CPs 1 and 2 crystallize in the triclinic crystal system with the P-1 space group but feature different structures. CP 1 exhibits a unique one dimensional double-chain structure, while CP 2 possesses an infinite 2D network structure. It is interesting to note that the metalloligand [Co(4-pytpy)₂]²⁺ in CP 2 was decomposed into [Co(4-pytpy)]²⁺. Thermal analysis indicates that the chain structure of CP 1 begins to collapse after about 360 °C, while CP 2 can be stable up to 300 °C. The solid-state luminescence properties of CPs 1 and 2 have also been investigated.     

N. K. Kochetkov (18.05.1915–21.12.2005)

In Memoriam

N. K. Kochetkov (18.05.1915–21.12.2005)     

Syntheses and structures of the MOF-type series of metal 1,4,5,8,-naphthalenetetracarboxylates M2(OH)2[C14O8H4] (Al,Ga, In) with infinite trans-connected M–OH–M chains (MIL-122)

Three new isostructural MOF-type compounds (named MIL-122) have been obtained from the hydrothermal reaction at 210 °C for 24 h of the 1,4,5,8-naphthalenetetracarboxylic acid with aluminum, gallium or indium source in water. The structures of the compounds M₂(OH)₂[C₁₄H₄O₈] (M = Al, Ga, In) have been solved ab initio from powder X-ray diffraction analysis using the synchrotron radiation (Soleil; station CRISTAL). The three-dimensional organic–inorganic framework exhibits infinite straight chains of metal-centered octahedra sharing trans corners linked to each other through the 1,4,5,8-naphthalenetetracarboxylate ligand. The cations Al, Ga or In, are coordinated by four oxygen atoms coming from the carboxyl groups and two bridging hydroxyl groups μ₂-OH, located in trans position in the octahedral surrounding. The compounds characterized by thermogravimetric and thermodiffraction analyses are thermally stable up to 440, 460 and 380 °C, for Al, Ga and In, respectively. Crystal data: monoclinic cell; P2₁/c (n°14); for MIL-122 (Al): a = 9.5174(2), b = 10.0706(1), c = 6.6465(2) Å, β = 91.2614(5)°, V = 636.878(2) Å³, Z = 2; for MIL-122 (Ga): a = 9.6501(1), b = 10.0585(1), c = 6.75069(9) Å, β = 92.4786(9)°, V = 654.65(1) Å³, Z = 2; for MIL-122 (In): a = 9.92359(5), b = 10.19765(7), c = 7.19357(4) Å, β = 727.034(8)°, V = 727.034(8)ų, Z = 2.     

Structures and luminescent properties of two heterotrimetallic Ln(III)–Sr(II)–K(I) complexes

Eu(III)–Sr(II)–K(I) and Tb(III)–Sr(II)–K(I) heterotrimetallic metal-organic frameworks with 2,4,6-pyridinetricarboxylic acid have been synthesized under hydrothermal conditions. The complexes are isomorphic and both in triclinic space group P-1. The ligands bond with three metal ions with two coordination modes. One connects seven metal ions and the other connects eight metal ions. IR spectra, thermal analysis, and photoluminescent properties have been studied. The results display strong characteristic emissions of Eu(III) or Tb(III) ions with excitation of ultraviolet radiation.     

Electroconductivity of Solid Solutions Cs3–2x M x PO4 (M = Ba, Sr, Ca, Mg)

Solid solutions Cs_{3 – 2x} M _x PO₄ (M = Ba, Sr, Ca, Mg) are synthesized and their thermal behavior and electroconductivity are examined. Adding elements of Subgroup IIA of the periodic table into cesium orthophosphate shifts the phase transition, which occurs in pure Cs₃PO₄ at 450–620°, towards lower temperatures and raises the cesium cation conductivity at low temperatures. The electroconductivity of a high-temperature modification of Cs₃PO₄ is weakly dependent on the presence and concentration of such additives, which points to structural disordering of the cesium sublattice.     

Co-cation Conduction in Solid Solutions (K1 – xRbx)4P2O7–M2P2O7(M = Ca,Sr, Cd,Ba): Transport Numbers and Partial Ionic Conductivities

Transport numbers for potassium and rubidium cations in solid electrolytes (K_{1 – x} Rb _x )_3.8M_0.1P₂O₇(M = Ca, Cd, Ba) are measured, and the co-cation nature of the electrolytes" conduction is confirmed. The concentration dependences of transport numbers are used to draw a conclusion about the ratio between mobilities of potassium and rubidium cations. The presence of an extremum in the concentration dependence of the activation energy for the rubidium-cation constituent of conduction is confirmed by the NMR method. The obtained results are explained by assuming that the polyalkaline effect is largely due to an ordering of mobile alkali cations.