(7)Li NMR and two-dimensional exchange study of lithium dynamics in monoclinic Li(3)V(2)(PO(4))(3)

High-resolution solid-state (7)Li NMR was used to characterize the structure and dynamics of lithium ion transport in monoclinic Li(3)V(2)(PO(4))(3). Under fast magic-angle spinning (MAS) conditions (25 kHz), three resonances are clearly resolved and assigned to the three unique crystallographic sites. This assignment is based on the Fermi-contact delocalization interaction between the unpaired d-electrons at the vanadium centers and the lithium ions. One-dimensional variable-temperature NMR and two-dimensional exchange spectroscopy (EXSY) are used to probe Li mobility between the three sites. Very fast exchange, on the microsecond time scale, was observed for the Li hopping processes. Activation energies are determined and correlated to structural properties including interatomic Li distances and Li-O bottleneck sizes.     

Electrochemical property: Structure relationships in monoclinic Li(3-y)V2(PO4)3

Monoclinic lithium vanadium phosphate, alpha-Li(3)V(2)(PO(4))(3), is a highly promising material proposed as a cathode for lithium-ion batteries. It possesses both good ion mobility and high lithium capacity because of its ability to reversibly extract all three lithium ions from the lattice. Here, using a combination of neutron diffraction and (7)Li MAS NMR studies, we are able to correlate the structural features in the series of single-phase materials Li(3-y)V(2)(PO(4))(3) with the electrochemical voltage-composition profile. A combination of charge ordering on the vanadium sites and lithium ordering/disordering among lattice sites is responsible for the features in the electrochemical curve, including the observed hysteresis. Importantly, this work highlights the importance of ion-ion interactions in determining phase transitions in these materials.     

OFF沸石中锂离子在骨架外的分布及可接近性

对OFF沸石进行离子交换制备出NH4-OFF沸石,然后通过Li2CO3/NH4-OFF体系的固态反应制备了不同锂离子交换度的Li-OFF沸石。对吸附氮气和氧气的Li-OFF样品进行了7Li MAS NMR表征。研究发现,所有吸附氧气样品的部分7Li MAS NMR共振峰均发生了顺磁位移。通过对实验谱的拟合,得知Li-OFF沸石中的锂离子可分布在三类阳离子位置（A、B和C）上,对应于三个不同位移的谱峰。Li+离子并非等比例地进入三个可交换的位置,而是优先占据主孔道中的A位置,随着交换度的升高,位能较高的C和B位置上的Li离子占有率逐渐增加。在100％固态交换度样品中,Li+离子在不同离子位的占有率分别为17％(位置B)、29％(位置C)和54％(位置A)。其中,位置B是O2分子不可接近的,所以Li-OFF沸石中有83％的阳离子是可以接近的。     

Transport and structural properties of pure and Cr doped Li3VO4

This study deals with the effects of 5 and 10% chromium additions on the transport and structural properties of Li3VO4. The Cr substitution is easily obtained without impurity phases and does not affect the room- and high-temperature host crystal structure, as evidenced by X-ray powder diffraction and micro-Raman analysis. The EPR signals are interpreted in terms of quantified amounts of Cr ions in 5+ and 3+ valence states. Suitable 7Li and 51V MAS NMR spectra simulations agree with the EPR results about the relative amount of Cr5+ and Cr3+ ions substituted in V5+ and Li+ sites, respectively. The Cr3+ presence on Li site, also suggested by Raman results and Rietveld refinements, requires Li vacancies to maintain the charge neutrality. The p-type conductivity, suggested by the positive thermoelectric power coefficients, significantly increases by the cation doping up to an order of magnitude.     

Solvation of LiClO4 and NaClO4 in deuterated acetonitrile studied by means of infrared and Raman spectroscopy

Vibrational characteristics of CD3CN solutions of LiClO4 and NaClO4 have been studied by means of infrared and Raman spectroscopy. Blue shifts of 22 and 11 cm(-1) of the v2 C[triple bond]N stretch are observed resulting from interaction of CD3CN with Li+ and Na+, respectively. The number of primary solvation sites of both Li+ and Na+ in acetonitrile is believed to be four from the comparison of the Raman intensities of the C[triple bond]N stretch for free CD3CN and those coordinated to Li+ and Na+. Evidently formation of contact ion pairs of the cation (Li+ or Na+) and anion (ClO4-) is more probable at a higher concentration of the salt. The characteristics of the v2 C[triple bond]N stretch, v4 C-C stretch, and v8 CCN deformation bands vary substantially upon coordination, while other vibrational bands are relatively immune to the donor-acceptor interaction. DFT calculations have also been performed at the BLYP/6-31 + G(2d,p) level to examine the structures and vibrational characteristics of CD3CN coordinated to Li+ and Na+. The calculated results are in good agreement with the observed vibrational characteristics.     

Polymorphism of heptalithium nitridovanadate(V) Li7[VN4

The system Li-V-N was studied by means of X-ray and neutron powder diffraction, thermal and chemical analyses, and XAS spectroscopy at the vanadium K-edge. Three polymorphs of Li(7)[VN(4)] have been established from X-ray and neutron powder diffraction (gamma-Li(7)[VN(4)], space group Pfourmacr;3n, No. 218, a = 960.90(4) pm, V = 887.23(6) x 10(6) pm(3), Z = 8; beta-Li(7)[VN(4)], space group Pathremacr;, No. 205, a = 959.48(3) pm, V = 883.31(5) x 10(6) pm(3), Z = 8; alpha-Li(7)[VN(4)], P4(2)/nmc, No. 137, a = 675.90(2) pm, c = 488.34(2) pm, V = 223.09(1) x 10(6) pm(3), Z = 2). Crystallographic and phase relations are discussed. All three modifications are diamagnetic, indicating vanadium in the oxidation state +5. The V-K XAS spectra support the oxidation state assignment, the non-centrosymmetric coordination (tetrahedral), and the nearly identical second coordination sphere of vanadium, made up from Li in all three phases. The 3d-related features of the spectra display strongly localized properties. The phase transitions appear to be reconstructive; no direct group-subgroup symmetry relations of the crystal structures exist. The formation of solid solutions between Li(2)O and beta-Li(7)[VN(4)] with the general formula Li(1.75)((V(0.25(1)(-)(x))Li(0.25)(x))(N(1)(-)(x)O(x)())) with 0 相似文献   

Magnetism and structural chemistry of the n = 1 Ruddlesden-Popper phases La4LiMnO8 and La3SrLiMnO8.

Polycrystalline samples of La4LiMnO8 and La3SrLiMnO8 have been studied by a combination of X-ray diffraction (XRD), neutron diffraction (ND), 6Li MAS NMR, electron microscopy (EM), and magnetometry. Room-temperature XRD and ND measurements suggest that both compounds have the K2NiF4 structure, with a disordered arrangement of Li and Mn over the six-coordinate sites. However, MAS NMR and EM demonstrate the presence of local 1:1 Li:Mn order on these sites, and EM shows that although cation order is well-developed in each xy sheet of corner-sharing octahedra, the sheets are stacked randomly along z. The structures are best described as paracrystalline, and many of the concepts of conventional crystallography are inapplicable. Magnetometry and low-temperature ND experiments show that, despite their paracrystallinity, the two compounds are ordered antiferromagnetically with susceptibility maxima at 26 and 18 K, respectively, and with ordered magnetic moments of 3.61(6) and 2.3(1) muB per Mn cation at 2 K. Anisotropic peak broadening reveals a 2D character in the magnetic behavior of both compounds, and La3SrLiMnO8 is well-modeled as a quadratic layer S = 3/2 Heisenberg antiferromagnet.     

Synthesis,crystal structure,and solid state NMR spectroscopy of NH(4)[(V(2)O(3))(2)(4,4'-bpy)(2)(H(2)PO(4))(PO(4))(2)].0.5H(2)O,a mixed-valence vanadium(IV,V) phosphate with a pillared layer structure

A mixed-valence vanadium phosphate, NH(4)[(V(2)O(3))(2)(4,4'-bpy)(2)(H(2)PO(4))(PO(4))(2)].0.5H(2)O, has been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the monoclinic space group C2/c (No. 15) with a = 12.6354(8) A, b = 9.9786(6) A, c = 23.369(1) A, beta = 92.713(1) degrees, and Z = 4 with R(1) = 0.0389. The structure consists of dimers of edge-sharing vanadium(IV,V) octahedra that are connected by corner-sharing phosphate tetrahedra to form layers in the ab-plane, which are further linked through 4,4'-bipyridine pillars to generate a 3-D framework. Magnetic susceptibility confirms the valence of the vanadium atoms. The (31)P MAS NMR spectrum shows a resonance centered at 80 ppm with a shoulder at ca. 83 ppm in an intensity ratio close to 1:2, which correspond to two distinct P sites. The observed large downfield (31)P NMR shifts can be ascribed to magnetic exchange coupling involving phosphorus atoms. The unpaired electron spin density at the phosphorus nucleus was determined from variable-temperature (31)P NMR spectra. The (1)H MAS NMR spectrum was fitted to six components in accordance with the structure as determined from X-ray diffraction.     

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.     

Oxidation state of vanadium introduced in dealuminated beta zeolite by impregnation with VIVOSO4 solution: influence of preparation parameters

Vanadium was introduced in dealuminated beta zeolite by impregnation with a VIVOSO4 aqueous solution at 353 K in air or argon (to prevent oxidation of VIV), leading to VSibeta and VSibeta-Ar zeolites, respectively. The samples were characterized by spectroscopy, XRD, and N2-physisorption. The oxidation state and environment of V in Sibeta zeolite depend on the preparation parameters (i.e., on the way the solid is recovered after impregnation and on the drying temperature). In solids recovered by centrifugation, washed with distilled water, and then dried overnight at 298 K in argon, vanadium is found as extra-lattice octahedral VIV ions as evidenced by EPR. In contrast, in solids not washed but directly dried overnight at 353 K in air or argon, vanadium is found in both cases as lattice tetrahedral VV ions. These ions are incorporated into vacant T sites associated with SiOH, SiO-, oxygen vacancies (OVs) or nonbridging oxygen (NBOs) defects as shown by diffuse reflectance UV-visible, 51V MAS NMR, FT-IR, and photoluminescence. The oxidation to VV ions is suggested to be due to an electron transfer from VO2+ to trigonal identical with Si+ defect sites followed by reaction of the resulting VO2+ ions with particular defects of vacant T sites. These processes occur already upon drying of V-impregnated Sibeta at 353 K. 51V MAS NMR allows detection of one kind of lattice tetrahedral V ions in VSibeta and two kinds in VSibeta-Ar. The formation of different kinds of tetrahedral V species is related to the presence in vacant T sites of Sibeta zeolite of different types of defect sites such as trigonal identical with Si+ defect or SiOH and SiO- groups.     

New mercury vanadium phosphate hydrate Hg(4)(-)(x)()O(1-)(y)()((VO)(PO(4))(2).H(2)O with unprecedented tetrahedral oxo-cluster [Hg( approximately )(4)O( approximately )(5)

The new mercury vanadium phosphate hydrate Hg(4)(-)(x)()O(1)(-)(y)()(VO)(PO(4))(2).H(2)O has been synthesized under hydrothermal conditions. X-ray investigations led to orthorhombic symmetry, space group P2(1)2(1)2(1) (No. 19), a = 6.3632(2) A, b = 12.4155(5) A, c = 14.2292(6) A, Z = 4. The crystal structure was solved and refined from single-crystal diffractometer data to residuals R[F(2) > 2sigmaF(2)] = 0.039, R(w)(F(2)) = 0.055. The VPO framework consists of infinite one-dimensional [VO(PO(4))(2)]( infinity ) chains with corner-connected VO(6) octahedra and PO(4) tetrahedra. The chains run along the [100] direction and are held together by the unprecedented tetrahedral cationic units [Hg(4)(-)(x)()O(1)(-)(y)()](4+). Presence of Hg-Hg bonding contacts is proved from theoretical calculations.     

Probing the vanadyl and molybdenyl bonds in complex vanadomolybdate structures

A solid solution was found to exist in the quaternary Li(2)O-MgO-V(2)O(5)-MoO(3) system between the two phases Mg(2.5)VMoO(8) and Li(2)Mg(2)(MoO(4))(3). Both Mg(2.5)VMoO(8) and Li(2)Mg(2)(MoO(4))(3) are isostructural with the mineral lyonsite, and substitution according to the formula square(1/4-x/6)Li(4x/3)Mg(15/4-7x/6)V(3/2-x)Mo(3/2+x)O(12) (0 < or = x < or = 1.5, where square denotes a cation vacancy) demonstrates that a complete solid solution exits coupling the addition of molybdenum and lithium with the subtraction of cation vacancies, magnesium, and vanadium and vice versa. Vibrational Raman spectroscopy indicates that molybdenum-oxo double bonds preferentially associate with the cation vacancies.     

Structural characterization of moganite-type AlPO4 by NMR and powder X-ray diffraction

Structural characterization of a new high-pressure AlPO(4) phase synthesized at 5 GPa and 1500 °C is reported. The phase is monoclinic (P2/a) with a = 8.7437(1) ?, b = 4.8584(1) ?, c = 10.8600(2) ?, β = 90.124(1)° (Z = 6). (31)P MAS NMR and two-dimensional (2D) (27)Al triple-quantum (3Q) MAS NMR revealed that it contains two tetrahedral P sites of 1:2 abundance ratio, and two tetrahedral Al sites with 1:2 ratio. 2D (31)P dipolar-recoupled double-quantum (DQ) MAS NMR and (27)Al → (31)P dipolar-based (through-space) and J coupling-based (through-bond) 3Q-heteronuclear correlation (HETCOR) experiments provided direct information on the linkages of these sites. The crystal structure was solved and refined from synchrotron powder X-ray diffraction data utilizing the information from NMR. The phase is isostructural to moganite, a rare SiO(2) polymorph, and its structure can be derived from the latter via an ordered replacement of tetrahedral Si sites by Al and P. The NMR parameters of the phase were also calculated by first-principles method, which are consistent with those observed. Contrary to the other moganite phases known to date (i.e., SiO(2) and PON), moganite-AlPO(4) has a higher-pressure stability field than the corresponding quartz phase. This is the first moganite-type phase found in the ABX(4) system.     

Superweak complexes of tetrahedral P4 molecules with the silver cation of weakly coordinating anions

The silver aluminates AgAl[OC(CF3)2(R)]4 (R = H, CH3, CF3) react with solutions of white phosphorus P4 to give complexes that bind one or two almost undistorted tetrahedral P4 molecules in an fashion: [Ag(P4)2]+[Al(OC(CF3)3)4]+ (1) containing the first homoleptic metal-phosphorus cation, the molecular species (P4)AgAl[OC(CH3)(CF3)2]4 (2), and the dimeric Ag(mu,eta2-P4)Ag bridged [(P4)AgAl[OC(H)(CF3)2]4]2 (3). Compounds 1-3 were characterized by variable-temperature (VT) 31P NMR spectroscopy (1 also by VT 32P MAS-NMR spectroscopy), Raman spectroscopy, and single-crystal X-ray crystallography. Other Ag:P4 ratios did not lead to new species, and this observation was rationalized on thermodynamic grounds. The Ag(P4)2+ ion has an almost planar coordination environment around the Ag+ ion due to d(x2 - y2)(Ag) --> sigma*(P-P) backbonding. Calculations (HF-DFT) on six Ag(P4)2+ isomers 4a-f showed that the planar eta2 form 4a is only slightly favored by 5.2 kJ mol(-1) over the tetrahedral eta2 species 4b; eta1-P4 and eta3-P4 complexes are less favorable (27-76 kJ mol(-1)). The bonding of the P4 moiety in [RhCl(eta2-P4)(PPh3)2], the only compound in which an eta2 bonding mode of a tetrahedral P4 molecule has been claimed, must be regarded as a tetraphosphabicyclobutane, and not as a tetrahedro-P4 complex, on the basis of the published NMR and vibrational spectra, the calculated geometry of [RhCl(P4)(PH3)2] (10), the highly endothermic (385 kJ mol(-1)) calculated dissociation enthalpy of 10 into P4 and RhCl(PH3)2 (11), as well as atoms in molecules (AIM) and natural bond orbital (NBO) population analyses of 10 and the Ag(P4)2+ ion. Therefore, 1-3 are the first examples of species containing eta2-coordinated tetrahedral P4 molecules.     

The structural and spectroscopic characterisation of three actinyl complexes with coordinated and uncoordinated perrhenate: [UO2(ReO4)2(TPPO)3], [[(UO2)(TPPO)3]2(mu2-O2)][ReO4]2 and [NpO2(TPPO)4][ReO4

The first structural characterization of an actinide complex with coordinated perrhenate is reported, [UO2(ReO4)2(TPPO)3] (1). In this [UO2]2+ complex two [ReO4]- anions and three TPPO (triphenylphosphine oxide) P=O donor ligands are coordinated in the equatorial plane in a cisoid arrangement. This bonding arrangement, and apparent strain observed in the equatorially bonded ligands, is attributed to the solid state packing in adjacent molecules in which hydrophobic TPPO ligands form an effective "shell" around a hydrophilic core of two UO2(ReO4)2 moieties. Solid state vibrational spectroscopy (infrared and Raman), 31P CP MAS NMR and elemental analysis are also consistent with the formula of 1. Solution state vibrational spectroscopy and 31P NMR measurements in EtOH indicate the lability of the TPPO and [ReO4]- groups. The photolytic generation of peroxide in EtOH solutions of 1 leads to the formation of trace quantities of [[(UO2)(TPPO)3]2(mu2-O2)][ReO4]2, 2, in which the coordinated [ReO4]- groups of 1 have been displaced by bridging O2(2-), derived from atmospheric O2. Finally, attempts to synthesise a [NpO2]+ analogue of have resulted only in the formation of [NpO2(TPPO)4][ReO4], 3, in which [ReO4]- acts solely as a counter anion. From these results it can be concluded that [ReO4]- will bond to [UO2]2+, but will be readily displaced by a more strongly coordinating ligand (e.g. peroxide) and will not coordinate to an actinyl cation with a lower charge, [NpO2]+, under the same reaction conditions.     

Minerals from Macedonia XXIII. Spectroscopic and structural characterization of schorl and beryl cyclosilicates

IR and Raman spectroscopy study on two collected cyclosilicate species: schorl (from tourmaline group), Na(Fe,Mg)(3)Al(6)(BO(3))(3)Si(6)O(18)(OH,F)(4) and beryl (Be,Mg,Fe)(3)Al(2)Si(6)O(18) were carried out. Although beryl is nominally anhydrous mineral, vibrational results strongly indicate that H(2)O molecules exist in the structural channels. The number of vibrational bands and their frequencies revealed the presence of H(2)O type II, in which C(2) symmetry axis of the water molecule is parallel to the structural channel (and to the c-axis of beryl). On the other hand, it was found that observed bands in the IR and Raman OH stretching region of the other tourmaline varieties appear as a result of the cation combinations involving dominant presence of Mg and Fe cations in the Y structural sites. The strong indication derived from the vibrational spectroscopic results that the studied mineral represents a schorl variety, coincide very well with the results obtained by powder X-ray diffraction and X-ray microprobe analysis. Both minerals show IR spectral similarities in the region below 1500 cm(-1), whereas the resemblance between the Raman spectra (1500-100 cm(-1)) is less expressed confirming that these spectra are more sensitive to compositional changes and to structural disorder. The identification of both minerals was additionally supported by studying the powder X-ray diffraction diagrams.     

On the composition and crystal structure of the new quaternary hydride phase Li4BN3H10

X-ray data on single crystals of the quaternary metal hydride near the composition LiB(0.33)N(0.67)H(2.67), previously identified as "Li3BN2H8", reveal that its true composition is Li4BN3H10. The structure has body-centered-cubic symmetry [space group I2(1)3, cell parameter a = 10.679(1)-10.672(1) Angstroms] and contains an ordered arrangement of BH4- and NH2- anions in the molar ratio 1:3. The borohydride anion has an almost ideal tetrahedral geometry (angleH-B-H approximately 108-114 degrees), while the amide anion has a nearly tetrahedral bond angle (angleH-N-H approximately 106 degrees). Three symmetry-independent Li atom sites are surrounded by BH4- and NH2- anions in various distorted tetrahedral configurations, one by two B and two N atoms, another by four N atoms, and the third by one B and three N atoms. The Li configuration around B is nearly tetrahedral, while that around N resembles a distorted saddlelike configuration, similar to those in LiBH4 and LiNH2, respectively.     

Structural diversity in solvated lithium aryloxides. Syntheses, characterization, and structures of [Li(OAr)(THF)x]n and [Li(OAr)(py)x]2 complexes where OAr = OC6H5, OC6H4(2-Me), OC6H3(2,6-(Me))2, OC6H4(2-Pr(i)), OC6H3(2,6-Pr(i)))2, OC6h4(2-Bu(t)), OC6H3(2,6-Bu(t)))2

A series of sterically varied aryl alcohols H-OAr [OAr = OC6H5 (OPh), OC6H4(2-Me) (oMP), OC6H3(2,6-(Me))2 (DMP), OC6H4(2-Pr(i)) (oPP), OC6H3(2,6-(Pr(i)))2 (DIP), OC6H4(2-Bu(t)) (oBP), OC6H3(2,6-(Bu(t)))2 (DBP); Me = CH3, Pr(i) = CHMe2, and Bu(t) = CMe3] were reacted with LiN(SiMe3)2 in a Lewis basic solvent [tetrahydrofuran (THF) or pyridine (py)] to generate the appropriate "Li(OAr)(solv)x". In the presence of THF, the OPh derivative was previously identified as the hexagonal prismatic complex [Li(OPh)(THF)]6; however, the structure isolated from the above route proved to be the tetranuclear species [Li(OPh)(THF)]4 (1). The other "Li(OAr)(THF)x" products isolated were characterized by single-crystal X-ray diffraction as [Li(OAr)(THF)]4 [OAr = oMP (2), DMP (3), oPP (4)], [Li(DIP)(THF)]3 (5), [Li(oBP)(THF)2]2, (6), and [Li(DBP)(THF)]2, (7). The tetranuclear species (1-4) consist of symmetric cubes of alternating tetrahedral Li and pyramidal O atoms, with terminal THF solvent molecules bound to each metal center. The trinuclear species 5 consists of a six-membered ring of alternating trigonal planar Li and bridging O atoms, with one THF solvent molecule bound to each metal center. Compound 6 possesses two Li atoms that adopt tetrahedral geometries involving two bridging oBP and two terminal THF ligands. The structure of 7 was identical to the previously reported [Li(DBP)(THF)]2 species, but different unit cell parameters were observed. Compound 7 varies from 6 in that only one solvent molecule is bound to each Li metal center of 7 because of the steric bulk of the DBP ligand. In contrast to the structurally diverse THF adducts, when py was used as the solvent, the appropriate "Li(OAr)(py)x" complexes were isolated as [Li(OAr)(py)2]2 (OAr = OPh (8), oMP (9), DMP (10), oPP (11), DIP (12), oBP (13)) and [Li(DBP)(py)]2 (14). Compounds 8-13 adopt a dinuclear, edge-shared tetrahedral complex. For 14, because of the steric crowding of the DBP ligand, only one py is coordinated, yielding a dinuclear fused trigonal planar arrangement. Two additional structure types were also characterized for the DIP ligand: [Li(DIP)(H-DIP)(py)]2 (12b) and [Li2(DIP)2(py)3] (12c). Multinuclear (6,7Li and 13C) solid-state MAS NMR spectroscopic studies indicate that the bulk powder possesses several Li environments for "transitional ligands" of the THF complexes; however, the py adducts possess only one Li environment, which is consistent with the solid-state structures. Solution NMR studies indicate that "transitional" compounds of the THF precursors display multiple species in solution whereas the py adducts display only one lithium environment.     

Mesoporous titanium phosphate molecular sieves with ion-exchange capacity.

Novel open framework molecular sieves, titanium(IV) phosphates named, i.e., TCM-7 and -8 (Toyota Composite Materials, numbers 7 and 8), with new mesoporous cationic framework topologies obtained by using both cationic and anionic surfactants are reported. The (31)P MAS NMR, UV-visible absorption, and XANES data suggest the tetrahedral state of P and Ti, and stabilization of the tetrahedral state of Ti in TCM-7/8 is due to the incorporation of phosphorus (at Ti/P = 1:1) vis-à-vis the most stable octahedral state of Ti in the pure mesoporous TiO(2). Mesoporous TCM-7 and -8 show anion exchange capacity due to the framework phosphonium cation and cation exchange capacity due to defective P-OH groups. The high catalytic activity in the liquid-phase partial oxidation of cyclohexene with a dilute H(2)O(2) oxidant supports the tetrahedral coordination of Ti in these materials.     

Tetrahydrometalate species VH(2)(H(2)), NbH(4), and TaH(4): matrix infrared spectra and quantum chemical calculations

Laser ablated V, Nb, and Ta atoms react with molecular hydrogen in excess neon at 4 K to give vanadium, niobium, and tantalum dihydrides that further react with H(2) to form VH(2)(H(2)), NbH(4), and TaH(4). The reaction products are identified by deuterium and deuterium hydride isotopic substitution. DFT and CCSD theoretical calculations are used to predict energies, geometries, and vibrational frequencies for these novel metal hydrides complex and molecules. The vanadium dihydride hydrogen complex, VH(2)(H(2)), is identified, while the niobium and tantalum tetrahydrides, NbH(4) and TaH(4,) with D(2d) symmetry structures are confirmed. Reactions of group 5 metal atoms with H(2) condensing in solid hydrogen gave VH(2)(H(2)) and the higher tetrahydride-hydrogen complexes NbH(4)(H(2))(4) and TaH(4)(H(2))(4).