K3(U3O6)(Si2O7) and Rb3(U3O6)(Ge2O7): a pentavalent-uranium silicate and germanate

A new uranium(V) silicate, K3(U3O6)(Si2O7), and the germanate analogue, Rb3(U3O6)(Ge2O7), have been synthesized under high-temperature, high-pressure hydrothermal conditions and characterized by single-crystal X-ray diffraction. Their structures contain uranate columns formed of triple octahedral chains of the alpha-UF5 type linked by disilicate (or digermanate) units to form a 3-D framework structure. The valence state of uranium is confirmed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and magnetic susceptibility.     

Structural and thermochemical chemisorption of CO2 on Li(4+x)(Si(1-x)Al(x))O4 and Li(4-x)(Si(1-x)V(x))O4 solid solutions

Different Li(4)SiO(4) solid solutions containing aluminum (Li(4+x)(Si(1-x)Al(x))O(4)) or vanadium (Li(4-x)(Si(1-x)V(x))O(4)) were prepared by solid state reactions. Samples were characterized by X-ray diffraction and solid state nuclear magnetic resonance. Then, samples were tested as CO(2) captors. Characterization results show that both, aluminum and vanadium ions, occupy silicon sites into the Li(4)SiO(4) lattice. Thus, the dissolution of aluminum is compensated by Li(1+) interstitials, while the dissolution of vanadium leads to lithium vacancies formation. Finally, the CO(2) capture evaluation shows that the aluminum presence into the Li(4)SiO(4) structure highly improves the CO(2) chemisorption, and on the contrary, vanadium addition inhibits it. The differences observed between the CO(2) chemisorption processes are mainly correlated to the different lithium secondary phases produced in each case and their corresponding diffusion properties.     

Exchange interactions and electron delocalization in the mixed-valence cluster V(4)(IV)V(2)(V)O(7)(OC(2)H(5))(12)

The mixed-valence cluster compound V4IVV2VO7(OC2H5)12 was studied by X-band electron paramagnetic resonance (EPR) in the temperature range of 4.2-293 K. According to X-ray diffraction study, the crystal structure of the compound was described by a R3m space group at 295 K (four d1 electrons are equally delocalized on all vanadium ions) and changed to a P21/n space group on cooling the crystals to 173 K (the electrons are preferably localized on the four equatorial vanadium ions). The EPR spectra originate from the S = 1 total spin states with the fine structure averaged to a single Lorentzian line and from the S = 2 total spin states with fine structure partly averaged in the temperature range of 295-200 K and well averaged below 45-50 K. The states of S = 1 and S = 2 of comparable energy (DeltaE approximately 2 cm(-1); ES=1 < ES=2) were shown to be the lowest ones. The VIV <--> VV unpaired electron transfers together with isotropic Heisenberg exchange were shown to determine the total spin states composition and the intracluster dynamics of the compound. Two types of electron transfers were assumed: the single-jump transfer leading to the averaged configurations of the V4IVV2V <--> V3IVVV VIVVV type and to the splitting of the total spin states by intervals comparable in magnitude with the isotropic exchange parameter J approximately 100 cm-1 and the double-jump transfer resulting in dynamics. Temperature dependence of the transition rates nutr was observed. In the range of 295-210 K, the value of nutr = (0.5-0.6) x 10(10) s(-1) is sufficient for averaging the fine structure of the S = 1 states, and below 45 K the value of nutr approximately 1.5 x 10(10) s(-1) also averages the fine structure of the S = 2 state. A change in the localization plane of the VIV ions in the temperature range of 40-50 K was discovered.     

Two caesium vanadium hydrogenphosphates with tunnelled structures: Cs2V2O3(PO4)(HPO4) and Cs2[(VO)3(HPO4)4(H2O)]·H2O

Dicaesium divanadium trioxide phosphate hydrogenphosphate, Cs₂V₂O₃(PO₄)(HPO₄), (I), and dicaesium tris[oxidovanadate(IV)] hydrogenphosphate dihydrate, Cs₂[(VO)₃(HPO₄)₄(H₂O)]·H₂O, (II), crystallize in the monoclinic system with all atoms in general positions. The structures of the two compounds are built up from VO₆ octahedra and PO₄ tetrahedra. In (I), infinite chains of corner‐sharing VO₆ octahedra are connected to V₂O₁₀ dimers by phosphate and hydrogenphosphate groups, while in (II) three vanadium octahedra share vertices leading to V₃O₁₅(H₂O) trimers separated by hydrogenphosphate groups. Both structures show three‐dimensional frameworks with tunnels in which Cs⁺ cations are located.     

Tetranuclear and Pentanuclear Vanadium(IV/V) Carboxylate Complexes: [V(4)O(8)(NO(3))(O(2)CR)(4)](2-) and [V(5)O(9)X(O(2)CR)(4)](2-) (X = Cl(-), Br(-)) Salts

The syntheses and properties of tetra- and pentanuclear vanadium(IV,V) carboxylate complexes are reported. Reaction of (NBzEt(3))(2)[VOCl(4)] (1a) with NaO(2)CPh and atmospheric H(2)O/O(2) in MeCN leads to formation of (NBzEt(3))(2)[V(5)O(9)Cl(O(2)CPh)(4)] 4a; a similar reaction employing (NEt(4))(2)[VOCl(4)] (1b) gives (NEt(4))(2)[V(5)O(9)Cl(O(2)CPh)(4)] (4b). Complex 4a.MeCN crystallizes in space group P2(1)2(1)2(1) with the following unit cell dimensions at -148 degrees C: a = 13.863(13) ?, b = 34.009(43) ?, c = 12.773(11) ?, and Z = 4. The reaction between (NEt(4))(2)[VOBr(4)] (2a) and NaO(2)CPh under similar conditions gives (NEt(4))(2)[V(5)O(9)Br(O(2)CPh)(4)] (6a), and the use of (PPh(4))(2)[VOBr(4)] (2b) likewise gives (PPh(4))(2)[V(5)O(9)Br(O(2)CPh)(4)] (6b). Complex 6b crystallizes in space group P2(1)2(1)2(1) with the following unit cell dimensions at -139 degrees C: a = 18.638(3) ?, b = 23.557(4) ?, c = 12.731(2) ?, and Z = 4. The anions of 4a and 6b consist of a V(5) square pyramid with each vertical face bridged by a &mgr;(3)-O(2)(-) ion, the basal face bridged by a &mgr;(4)-X(-) (X = Cl, Br) ion, and a terminal, multiply-bonded O(2)(-) ion on each metal. The RCO(2)(-) groups bridge each basal edge to give C(4)(v)() virtual symmetry. The apical and basal metals are V(V) and V(IV), respectively (i.e., the anions are trapped-valence). The reaction of 1b with AgNO(3) and Na(tca) (tca = thiophene-2-carboxylate) in MeCN under anaerobic conditions gives (NEt(4))(2)[V(4)O(8)(NO(3))(tca)(4)] (7). Complex 7.H(2)O crystallizes in space group C2/c with the following unit cell dimensions at -170 degrees C: a = 23.606(4) ?, b = 15.211(3) ?, c = 23.999(5) ?, and Z = 4. The anion of 7 is similar to those of 4a and 6b except that the apical [VO] unit is absent, leaving a V(4) square unit, and the &mgr;(4)-X(-) ion is replaced with a &mgr;(4),eta(1)-NO(3)(-) ion. The four metal centers are now at the V(IV), 3V(V) oxidation level, but the structure indicates four equivalent V centers, suggesting an electronically delocalized system. Variable-temperature magnetic susceptibility data were collected on powdered samples of 4b, 6a, and 7 in the 2.00-300 K range in a 10 kG applied field. 4b and 6a both show a slow increase in effective magnetic moment (&mgr;(eff)) from approximately 3.6-3.7 &mgr;(B) at 320 K to approximately 4.5-4.6 &mgr;(B) at 11.0 K and then a slight decrease to approximately 4.2 &mgr;(B) at 2.00 K. The data were fit to the theoretical expression for a V(IV)(4) square with two exchange parameters J = J(cis)() and J' = J(trans)() (H = -2JS(i)()S(j)()): fitting of the data gave, in the format 4b/6a, J= +39.7/+46.4 cm(-)(1), J' = -11.1/-18.2 cm(-)(1) and g = 1.83/1.90, with the complexes possessing S(T) = 2 ground states. The latter were confirmed by magnetization vs field studies in the 2.00-30.0 K and 0.500-50.0 kG ranges: fitting of the data gave S(T) = 2 and D = 0.00 cm(-)(1) for both complexes, where D is the axial zero-field splitting parameter. Complex 7 shows a nearly temperature-independent &mgr;(eff) (1.6-2.0 &mgr;(B)) consistent with a single d electron per V(4) unit. The (1)H NMR spectra of 4b and 6a in CD(3)CN are consistent with retention of their pentanuclear structure on dissolution. The EPR spectrum of 7 in a toluene/MeCN (1:2) solution at approximately 25 degrees C yields an isotropic signal with a 29-line hyperfine pattern assignable to hyperfine interactions with four equivalent I = (7)/(2) (51)V nuclei.     

Cluster self-organization of silicate and germanate systems: Suprapolyhedral precursor nanoclusters and self-assembly of tetrahedral structures of the family A2T2O5 (A = Li, Na; T = Si, Ge): Li2T2O5, Li4Ge3SiO10, Li2Si2O5, and A2Si2O5

Modeling of atomic species (An clusters in the form of atoms or Kn polyhedra, where n is the number of atoms or polyhedra) corresponding to the initial stage of evolution of a chemical system has been carried out. Three series of K4 clusters built of different T tetrahedra (L and T) have been recognized. For L₂T₂ clusters, six geometrically and symmetrically different types of suprapolyhedral clusters have been discovered. The model has been used to identify precursor clusters in A₂T₂O₅ (A = Li, Na; T = Si, Ge) framework structures: A-type Li₂T₂O₅ with space group Cc, B-type Li₄Ge₃SiO₁₀ with space group Abm2, C-type Li₂Si₂O₅ with space group Ccc2, and D-type A₂Si₂O₅ with space group Pbcn. Three (of the six possible) types of suprapolyhedral precursor nanoclusters K4 in the four structures have been identified. The full 3D reconstruction of the self-assembly scenario of crystal structures is as follows: precursor nanocluster ?? primary chain ?? microlayer ?? microframework ?? ?? framework. The bifurcation of structural evolution pathways (structural branching points) at the suprapolyhedral level for type A and B structures is found to occur only when a microframework is formed of equivalent microlayers.     

Photoelectron imaging of Ag(-)(H2O)x and AgOH(-)(H2O)y (x=1,2, y=0-4)

The photoelectron images of Ag(-)(H(2)O)(x) (x=1,2) and AgOH(-)(H(2)O)(y) (y=0-4) are reported. The Ag(-)(H(2)O)(1,2) anionic complexes have similar characteristics to the other two coinage metal-water complexes that can be characterized as metal atomic anion solvated by water molecules with the electron mainly localized on the metal. The vibrationally well-resolved photoelectron spectrum allows the adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of AgOH(-) to be determined as 1.18(2) and 1.24(2) eV, respectively. The AgOH(-) anion interacts more strongly with water molecules than the Ag(-) anion. The photoelectron spectra of Ag(-)(H(2)O)(x) and AgOH(-)(H(2)O)(y) show a gradual increase in ADE and VDE with increasing x and y due to the solvent stabilization.     

Cs2USi6O15: a tetravalent uranium silicate

A uranium(IV) silicate has been synthesized under high-temperature, high-pressure hydrothermal conditions. The structure consists of unbranched dreier single layers with the composition [Si(2)O(5)] that are connected by UO(6) octahedra to form a 3D framework with 7-ring channels where the Cs(+) cations are located. Each UO(6) octahedron spans four neighboring dreier single chains and, therefore, introduces a high degree of corrugation in the silicate layers. The U 4f X-ray photoelectron spectroscopy spectrum was measured to confirm the valence state of the uranium. A comparison of related metal silicate structures is made. After the synthesis of this compound, all members in the family of uranium silicates and germanates with oxidation states of uranium from 4+ to 6+ have been observed.     

Electrochemical Properties and ESR Characterization of Mixed Valence alpha-[XMo(3)(-)(x)()V(x)()W(9)O(40)](n)()(-) Heteropolyanions with X = P(V) and Si(IV), x = 1, 2, or 3

Electrochemical behavior of the alpha-[SiMo(3)(-)(x)()V(x)()W(9)O(40)]((4+)(x)()())(-) and alpha-[PMo(3)(-)(x)()V(x)()W(9)O(40)]((3+)(x)()())(-) anions with x = 1, 2, or 3 were studied. Electrochemical reduction of each compounds was consistent with its Mo/V ratio, reduction of vanadium and molybdenum atoms occurring in the +0.6 to -0.6 V potential range. The one-electron-reduced species were prepared by electrolysis and then characterized by ESR spectroscopy. The g and A values for V(4+)ions appeared to depend on the nature of the surrounding atoms (Mo(VI), W(VI), and V(V)). In solution at 330 K, the ESR spectrum of the protonated alpha-H[SiMoV(IV)VW(9)O(40)](6)(-) anion displayed 29 superhyperfine lines which were related to the partial localization of the electron on one vanadium nucleus. The ESR spectra at room temperature for the divanadium-substituted anions showed a strong anisotropy of the A tensor which would be related to the electron transfer along a preferential axis. An isolated V(4+) signal was not observed, even at 12 K, indicating that the electron is never firmly trapped on one single vanadium atom.     

ChemInform Abstract: Two Caesium Vanadium Hydrogenphosphates,with Tunnelled Structures: Cs2V2O3(PO4)(HPO4) and Cs2 [(VO)3(HPO4)4(H2O)] ·H2O.

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.     

Cs3UGe7O18: a pentavalent uranium germanate containing four- and six-coordinate germanium

A pentavalent uranium germanate, Cs(3)UGe(7)O(18), was synthesized under high-temperature, high-pressure hydrothermal conditions at 585 °C and 160 MPa and structurally characterized by single-crystal X-ray diffraction and infrared spectroscopy. The valence state of uranium was confirmed by X-ray photoelectron spectroscopy and electron paramagnetic resonance. The room-temperature EPR spectrum can be simulated with two components using an axial model that are consistent with two distinct sites of uranium(V). In the structure of the title compound, each ([6])GeO(6) octahedron is bonded to six three-membered single-ring ([4])Ge(3)O(9)(6-) units to form germanate triple layers in the ab plane. Each layer contains nine-ring windows; however, these windows are blocked by adjacent layers. The triple layers are further connected by UO(6) octahedra to form a three-dimensional framework with intersecting six-ring channels along the <1 ?10> directions. The Cs(+) cation sites are fully occupied, ordered, and located in the cavities of the framework. Pentavalent uranium germanates or silicates are very rare, and only two uranium silicates and one germanate analogue have been published. However, all of them are iso-structural with those of the Nb or Ta analogues. In contrast, the title compound adopts a new structural type and contains both four- and six-coordinate germanium. Crystal data of Cs(3)UGe(7)O(18): trigonal, P3?c1 (No. 165), a = 12.5582(4) ?, c = 19.7870(6) ?, V = 2702.50(15) ?(3), Z = 6, D(calc) = 5.283 g·cm(-3), μ(Mo Kα) = 26.528 mm(-1), R(1) = 0.0204, wR(2) = 0.0519 for 1958 reflections with I > 2σ(I). GooF = 1.040, ρ(max,min) = 1.018, and -1.823 e·?(-3).     

Zur Kenntnis eines Alkali-Erdalkalimetall-Cadmium-Oxovanadats: KBaCd2(VO4)(V2O7)

On an Alkali Alkaline-Earth Cadmium Oxovanadate: KBaCd₂(VO₄)(V₂O₇) Single crystals of KBaCd₂(VO₄)(V₂O₇) have been prepared by crystallization from melts. X-ray investigations led to monoclinic symmetry, space group C? P2₁/n, a = 10.359(3), b = 6.986(2), c = 15.331(3) Å, β = 94.77(2), Z = 4. The hitherto unknown compound represents a new structure type and is one of those few examples containing VO₄ and V₂O₇ groups.     

Anion-directed crystallization of coordination polymers: syntheses and characterization of Cu(4)(2-pzc)(4)(H(2)O)(8)(Mo(8)O(26)).2H(2)O and Cu(3)(2-pzc)(4)(H(2)O)(2)(V(10)O(28)H(4)).6.5H(2)O (2-pzc = 2-pyrazinecarboxylate)

Two new copper 2-pyrazinecarboxylate (2-pzc) coordination polymers incorporating [Mo(8)O(26)](4-) and [V(10)O(28)H(4)](2-) anions were synthesized and structurally characterized: Cu(4)(2-pzc)(4))(H(2)O)(8)(Mo(8)O(26)).2H(2)O (1) and Cu(3)(2-pzc)(4)(H(2)O)(2)(V(10)O(28)H(4)).6.5H(2)O (2). Crystal data: 1, monoclinic, space group P2(1)/n, a = 11.1547(5) A, b = 13.4149(6) A, c = 15.9633(7) A, beta = 90.816(1) degrees; 2, triclinic, space group P1, a = 10.5896(10) A, b = 10.7921(10) A, c = 13.5168(13) A, alpha = 104.689(2) degrees, beta = 99.103(2) degrees, gamma = 113.419(2) degrees. Compound 1 contains [Cu(2-pzc)(H(2)O)(2)] chains charge-balanced by [Mo(8)O(26)](4-) anions. In compound 2, layers of [Cu(3)(2-pzc)(4)(H(2)O)(2)] form cavities that are filled with [V(10)O(28)H(4)](2-) anions. The magnetic properties of both compounds are described.     

Cs4UGe8O20: a tetravalent uranium germanate containing four- and five-coordinate germanium

A very rare tetravalent uranium germanate has been synthesized under hydrothermal conditions at 585 °C and 160 MPa. Its structure contains layers of single-ring Ge(3)O(9)(6-) germanate anions that are connected by UO(6) octahedra and dimers of edge-sharing GeO(5) trigonal bipyramids to form a three-dimensional framework with intersecting 6- and 7-ring channels. UV-visible, photoluminescence, and U 4f X-ray photoelectron spectroscopy were used to confirm the valence state of uranium.     

A variable Ag-Cr-Oxalate channel lattice: [M(x)Ag(0.5)(-)(x)(H(2)O)(3)]@[Ag(2.5)Cr(C(2)O(4))(3)], M = K, Cs, Ag

Reaction of aqueous AgNO(3) with aqueous M(3)[Cr(ox)(3)] in >or=3:1 molar ratio causes the rapid growth of large, cherry-black, light-stable crystals which are not Ag(3)[Cr(ox)(3)], but [M(0.5)(H(2)O)(3)]@[Ag(2.5)Cr(ox)(3)] (ox(2)(-) = oxalate, C(2)O(4)(2)(-); M = Na, K, Cs, Ag, or mixtures of Ag and a group 1 element). The structure of these crystals contains an invariant channeled framework, with composition [[Ag(2.5)Cr(ox)(3)](-)(0.5)]( infinity ), constructed with [Cr(ox)(3)] coordination units linked by Ag atoms through centrosymmetric [Cr-O(2)C(2)O(2)-Ag](2) double bridges. The framework composition [Ag(2.5)Cr(ox)(3)](-)(0.5) occurs because one Ag is located on a 2-fold axis. Within the channels there is a well-defined and ordered set of six water molecules, strongly hydrogen bonded to each other and some of the oxalate O atoms. This invariant channel plus water structure accommodates group 1 cations, and/or Ag cations, in different locations and in variable proportions, but always coordinated by channel water and some oxalate O atoms. The general formulation of these crystals is therefore [M(x)Ag(0.5-x)(H(2)O)(3)]@[Ag(2.5)Cr(ox)(3)]. Five different crystals with this structure are reported, with compositions 1 Ag(0.5)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), 2 Cs(0.19)Ag(0.31)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), 3 K(0.28)Ag(0.22)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), 4 Cs(0.41)Ag(0.09)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), and 5 Cs(0.43)Ag(0.07) [Ag(2.5)Cr(ox)(3)](H(2)O)(3). All crystallize in space group C2/c, with a approximately 18.4, b approximately 14.6, c approximately 12.3 A, beta approximately 113 degrees. Pure Ag(3)[Cr(ox)(3)](H(2)O)(3), which has the same crystal structure (1), was obtained from water by treating Li(3)[Cr(ox)(3)] with excess AgNO(3). Complete dehydration of all of these compounds occurs between 30 and 100 degrees C, with loss of diffraction, but rehydration by exposure to H(2)O(g) at ambient temperature leads to recovery of the original diffraction pattern. In single crystals, this reversible dehydration-hydration occurs without visually evident crystal change, but with loss of mechanical strength. We postulate a general mechanism for transport of water molecules along the channels, associated with local partial collapses of the channel framework, with concomitant bending but little breaking of the host Ag-O and Cr-O bonds, which is readily reversed.     

Ba2Gd2(Si4O13): a silicate with finite Si4O13 chains

The title compound, dibarium digadolinium(III) tetrasilicate, crystallized from a molybdate‐based flux. It represents a new structure type and contains finite zigzag‐shaped C₂‐symmetric Si₄O₁₃ chains and Gd₂O₁₂ dimers built of edge‐sharing GdO₇ polyhedra. The [9+1]‐coordinated Ba atoms are located in voids in the atomic arrangement. All atoms are in general positions except for one O atom, which lies on a twofold axis. The structure is compared with those of the few other known tetrasilicates.