Study of Sb‐doped SnO2 Gray Ceramic Pigment with Cassiterite Structure

In this study, Sb_xSn_1?xO₂ (0 ≤ x ≤ 0.5) compositions were synthesized by the ceramic method from Sb₂O₃‐SnO₂ and Sb₂O₅‐SnO₂ mixtures and characterized by Differential thermal analysis (DTA) and thermogravimetric analysis (TG), X‐ray diffraction, UV‐V‐NIR spectroscopy and CIE L*a*b* (Commission Internationale de l'Eclairage L*a*b*) parameters measurements. Solid solutions with cassiterite structure were obtained at 1300 °C. These solid solutions are stable into glazes. From Sb₂O₃, light gray coloured materials were obtained. From Sb₂O₅, bluish gray coloured materials were obtained at 1300 °C/6h when x ≥ 0.3. Sb_xSn_1?xO₂ with 0.3 ≤ x < 0.5, T = 1300 °C and Sb₂O₅ might be established as compositional range, fired temperature and antimony precursor to obtain gray ceramic pigments in this system.     

Inclusion of nickel(<Emphasis Type="SmallCaps">II</Emphasis>) and copper(<Emphasis Type="SmallCaps">II</Emphasis>) complexes with aliphatic polyamines in cucurbit[8]uril

The inclusion compound of macrocyclic cavitand cucurbit[8]uril (CB[8]) with the nickel(II) complex containing the tetraazamacrocyclic ligand cyclam, {[Ni(cyclam)]@CB[8]}Cl₂··16H₂O (1), and the inclusion compounds of CB[8] with the copper(II) bis-ethylene-diamine complex, {trans-[Cu(en)₂(H₂O)₂]@CB[8]}Cl₂·{CB[8]}·42H₂O (2a) and {trans-[Cu(en)₂(H₂O)₂]@CB[8]}Cl₂·17H₂O (2b), were synthesized and characterized by X-ray diffraction analysis, IR and ESR spectroscopy, and electrospray mass spectrometry. Guest—host inclusion compounds can be directly synthesized starting from a metal complex and cucurbit[8]uril, as was exemplified by the preparation of compounds 2a and 2b.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2414–2419, November, 2004.     

Synthesis and structure of the incomplete cuboidal clusters [W3Se4H3(dmpe)3]+, [W3Se4H(3-x)(OH)x(dmpe)3]+ and [W3Se4(OH)3(dmpe)3]+, and the mechanism of the acid-assisted substitution of the coordinated hydrides

The novel incomplete cuboidal cluster [W3Se4H3(dmpe)3](PF6), [1](PF6), has been prepared by reduction of [W3Se4Br3(dmpe)3](PF6) with LiBH4 in THF solution. The trihydroxo complex [W3Se4(OH)3(dmpe)3](PF6), [2](PF6), was obtained by reacting [W3Se4Br3(dmpe)3](PF6) with NaOH in MeCN-H2O solution. The complexes [1](PF6) and [2](PF6) were converted to their BPh4- salts by treatment with NaBPh4. Recrystallisation of [1](BPh4) in the presence of traces of water affords the mixed dihydride hydroxo complex [W3Se4H2(OH)(dmpe)3](BPh4). The crystal structures of [1](BPh4), [2](BPh4) and [W3Se4H2(OH)(dmpe)3](BPh4) have been resolved. Although the [1]+ trihydride does not react with an excess of halide salts, reaction with HX leads to [W3Se4X3(dmpe)3]+ (X = Cl, Br). The kinetics of this reaction has been studied at 25 degrees C in MeCN-H2O solution (1:1, v/v) and found to occur with two consecutive kinetic steps. The first step is independent of the nature and concentration of the X(-) anion but shows a first order dependence on the concentration of acid (k1 = 12.0 mol(-1) dm(3) s(-1)), whereas the second one is independent of the nature and concentration of both the acid and added salts (k2 = 0.024 s(-1)). In contrast, the reaction of [2]+ with acids occurs in a single step with kobs = 0.63 s(-1)(HCl) and 0.17 s(-1)(HBr). These kinetic results are discussed on the basis of the mechanism previously proposed for the reactions of the analogous [W3S4H3(dmpe)3]+ cluster, with special emphasis on the effects caused by the change of S by Se on the rate constants for the different processes involved.     

Thermal study of the Ce<Subscript>0.9</Subscript>Tb<Subscript>0.1</Subscript>O<Subscript>2</Subscript> pigment prepared by different synthesis

The inorganic ceramic compounds based on the CeO₂ belong into the group of high-temperature pigments. The pigments have been prepared by the classical dry process (i.e. solid-state reaction) in the temperature range from 1,300 to 1,600 °C and by the coprecipitation at the three different temperatures: 400, 600 and 1,100 °C. The principal of these pigments makes the host lattice of the CeO₂, which is doped by terbium ions. This incorporation of the doped ions leads to obtaining of the interesting dark orange colour after application into ceramic glaze. The aim of our research was to improve and optimize the synthesis conditions of these pigments. The samples were submitted to thermal analysis (TG–DTA) for determination of the temperature interval of the pigment formation and the thermal stability of pigments. The compounds were also measured from the point of view of their colouring, structure and particle size distribution.     

General and selective iron-catalyzed transfer hydrogenation of nitroarenes without base

The first well-defined iron-based catalyst system for the reduction of nitroarenes to anilines has been developed applying formic acid as reducing agent. A broad range of substrates including other reducible functional groups were converted to the corresponding anilines in good to excellent yields at mild conditions. Notably, the process constitutes a rare example of base-free transfer hydrogenations.     

Distinctive unimolecular gas-phase reactivity of [M(en)2]2+ (M=Ni, Cu) dications and their inclusion complexes with the macrocyclic cavitand Cucurbit[8]uril

Electrospray ionization mass spectrometry makes it possible to generate gas-phase bis-ethylenediamine nickel and copper dications, [M(en)(2)](2+) (M = Ni, 1; M = Cu, 2), as well as their {[M(en)(2)]@cuc[8]}(2+) inclusion complexes with the macrocyclic cavitand cucurbit[8]uril (cuc[8]). The unimolecular gas-phase reactivity of these species has been investigated by electrospray ionization tandem mass spectrometry with a quadrupole-time-of-flight configuration. Distinctive fragmentation pathways have been observed for the free and encapsulated [M(en)(2)](2+) (M = Ni, Cu) dications under collision-induced dissociation (CID) conditions. The dications [M(en)(2)](2+) (M = Ni, Cu) dissociate according to several competitive pathways that involve intra-complex hydrogen or electron-transfer processes. Most of these channels are suppressed after encapsulation inside the cucurbit[8]uril macrocycle and, as a consequence, a simplification of the {[M(en)(2)]@cuc[8]}(2+) fragmentation pattern is observed. The results obtained demonstrate that the encapsulation of a coordination complex inside a host molecule can be used to alter the nature of the product ions generated under CID conditions.     

Synthesis, crystal structure, aqueous speciation, and kinetics of substitution reactions in a water-soluble Mo3S4 cluster bearing hydroxymethyl diphosphine ligands

The [Mo3S4Cl3(dhmpe)3]Cl ([1]Cl) cluster has been prepared from [Mo3S7Cl6]2- and the water-soluble 1,2-bis(bis(hydroxymethyl)-phosphino)ethane (dhmpe, L) ligand. The crystal structure has been determined by X-ray diffraction methods and shows the incomplete cuboidal structure typical of the M3Q4 clusters (M=Mo, W; Q=S, Se), with a capping sulfide ligand to the three metal centers and the other three sulfides acting as bridges between two Mo atoms. The octahedral coordination around each metal center is completed with a chlorine and two phosphorus atoms of one L ligand. The chemistry of aqueous solutions of [1]Cl is dominated by the formation of the [Mo3S4L(L-H)2(H2O)]2+ complex ([2]2+), where the three chlorides have been replaced by one water molecule and two alkoxo groups of two different dhmpe ligands, thus leading to a solution structure where the three metal centers are not equivalent. A detailed study based on stopped-flow, 31P{1H} NMR, and electrospray ionization mass spectrometry techniques has been carried out to understand the behavior of [2]2+ in aqueous solution. In this way, it has been established that the addition of an excess of X- (Cl-, SCN-) leads to [Mo3S4X3(dhmpe)3]+ complexes in three resolved kinetic steps that correspond to the sequential coordination of X- at the three metal centers. However, whereas the first two steps involve the opening of the chelate rings formed with the alkoxo groups of the dhmpe ligands, the third one corresponds to the substitution of the coordinated water molecule. These results demonstrate that the asymmetry introduced by the closure of chelate rings at only two of the three Mo centers makes the kinetics of the reaction deviate significantly from the statistical behavior typically associated with M3Q4 clusters. The results obtained for the reaction of [2]2+ with acid and base are also described, and they complete the picture of the aqueous speciation of this cluster.     

Combined theoretical and experimental analysis of the bonding in the heterobimetallic cubane-type Mo(3)NiS(4) and Mo(3)CuS(4) core clusters

X-ray structural data for the cubane-type clusters [Mo3CuS4(dmpe)3Cl4](+) and Mo3NiS4(dmpe)3Cl4 (dmpe = 1,2-bis(dimethylphosphino)ethane) with 16 metal electrons have been compared with optimized structural parameters calculated using "ab initio" methodologies. Compound Mo3NiS4(dmpe)3Cl4 crystallizes in the cubic noncentrosymmetric space group P213 with a Mo-Ni distance of 2.647 Angstrom, that is 0.2 Angstrom shorter than the Mo-Cu bond length in the isoelectronic copper cluster. The best agreement between theory and experiments has been obtained using the B3P86 method. In order to validate the B3P86 results, accurate infrared and Raman spectra have been acquired and the vibrational modes associated to the cubane-type Mo3M'S4 (M' = Cu or Ni) unit have been assigned theoretically. The electronic changes taking place when incorporating the M' into the Mo3S4 unit have been analyzed from a theoretical and experimental perspective. The bond dissociation energies between M'-Cl and Mo3S4 fragments show that formation of [Mo3CuS4(dmpe)3Cl4](+) is 135 kcal/mol energetically less favorable than the Ni incorporation. The more robust nature of the Mo3NiS4 fragment has been confirmed by mass spectrometry. The X-ray photoelectron spectroscopy (XPS) spectra of the trimetallic and tetrametallic complexes have been measured and the obtained binding energies compared with the computed electronic populations based on topological approaches of the electron localization function (ELF). The energies and shapes of the Cu 2p and Ni 2p lines indicate formal oxidation states of Cu(I) and Ni(II). However, the reductive addition of nickel into [Mo3S4(dmpe)3Cl3](+) causes a small decrease in the Mo 3d binding energies. This fact prevents an unambiguous assignment of an oxidation state in a conventional way, a circumstance that has been analyzed through the covariance of the electronic populations associated to the C(M') core and V(Mo3Ni) and V(S(2)') valence basins where Mo3NiS4 is a particularly electronically delocalized chemical entity.     

4,2-Ribbon like ferromagnetic cyano-bridged Fe(III)2Ni(II) chains: a magneto-structural study

The low-spin iron(III) complex AsPh(4)[Fe(III)(bpy)(CN)(4)].CH(3)CN (1) [AsPh(4) = tetraphenylarsonium cation] and the heterobimetallic chains [{Fe(III)(L)(CN)(4)}(2)Ni(II)(H(2)O)(2)].4H(2)O with L = bpy (2) and phen (3) [bpy = 2,2'-bipyridine and phen = 1,10-phenanthroline] have been prepared and their structures determined by X-ray diffraction methods. The structure of 1 consists of mononuclear [Fe(bpy)(CN)(4)](-) anions, tetraphenylarsonium cations and acetonitrile molecules of crystallization. The iron(III) is hexacoordinated with two nitrogen atoms of the bidentate bpy and four carbon atoms of four terminal cyanide groups building a distorted octahedral surrounding around the metal atom. 2 and 3 are isomorphous compounds whose structure is made up of neutral 4,2-ribbon like bimetallic chains of formula [{Fe(III)(L)(CN)(4)}(2)Ni(II)(H(2)O)(2)] where the [Fe(III)(L)(CN)(4)](-) unit acts as a bis-monodentate bridging ligand toward the trans-diaquanickel(II) units through two of its four cyanide groups in cis positions. The chains exhibit two orientations in the unit cell and they interact with each other through hydrogen bonds involving the coordination and crystallization water molecules together with the uncoordinated cyanide nitrogen atoms of the [Fe(L)(CN)(4)](-) units. Compounds 2 and 3 behave as ferromagnetic Fe(III)(2)Ni(II) chains which interact ferromagnetically at very low temperatures in the case of 2, whereas metamagnetic-like behaviour is observed for with a critical field (H(c)) around 200 G. For H > H(c) the ferromagnetic Fe(III)(2)Ni(II) chains of 3 exhibit a frequency dependence of the out-of-phase ac susceptibility signal at T < 3.5 K.