pH-selective synthesis and structures of alkynyl, acyl, and ketonyl intermediates in anti-Markovnikov and Markovnikov hydrations of a terminal alkyne with a water-soluble iridium aqua complex in water

Chemoselective synthesis and isolation of alkynyl [Cp*Ir(III)(bpy)CCPh]+ (2, Cp* = eta5-C5Me5, bpy = 2,2'-bipyridine), acyl [Cp*Ir(III)(bpy)C(O)CH2Ph]+ (3), and ketonyl [Cp*Ir(III)(bpy)CH2C(O)Ph]+ (4) intermediates in anti-Markovnikov and Markovnikov hydration of phenylacetylene in water have been achieved by changing the pH of the solution of a water-soluble aqua complex [Cp*Ir(III)(bpy)(H2O)]2+ (1) used as the same starting complex. The alkynyl complex [2]2.SO4 was synthesized at pH 8 in the reaction of 1.SO4 with H2O at 25 degrees C, and was isolated as a yellow powder of 2.X (X = CF3SO3 or PF6) by exchanging the counteranion at pH 8. The acyl complex [3]2.SO4 was synthesized by changing the pH of the aqueous solution of [2]2.SO4 from 8 to 1 at 25 degrees C, and was isolated as a red powder of 3.PF6 by exchanging the counteranion at pH 1. The hydration of phenylacetylene with 1.SO4 at pH 4 at 25 degrees C gave a mixture of [2]2.SO4 and [4]2.SO4. After the counteranion was exchanged from SO4(2-) to CF3SO3-, the ketonyl complex 4.CF3SO3 was separated from the mixture of 2.CF3SO3 and 4.CF3SO3 because of the difference in solubility at pH 4 in water. The structures of 2-4 were established by IR with 13C-labeled phenylacetylene (Ph12C13CH), electrospray ionization mass spectrometry (ESI-MS), and NMR studies including 1H, 13C, distortionless enhancement by polarization transfer (DEPT), and correlation spectroscopy (COSY) experiments. The structures of 2.PF6 and 3.PF6 were unequivocally determined by X-ray analysis. Protonation of 3 and 4 gave an aldehyde (phenylacetaldehyde) and a ketone (acetophenone), respectively. Mechanism of the pH-selective anti-Markovnikov vs Markovnikov hydration has been discussed based on the effect of pH on the formation of 2-4. The origins of the alkynyl, acyl, and ketonyl ligands of 2-4 were determined by isotopic labeling experiments with D2O and H2(18)O.     

Asymmetric cationic coordination environments in new oxide materials: synthesis and characterization of Pb(4)Te(6)M(10)O(41) (M = Nb(5+) or Ta(5+))

Two new isostructural tellurites, Pb(4)Te(6)M(10)O(41) (M = Nb(5+) or Ta(5+)), have been synthesized by standard solid-state techniques using PbO, Nb(2)O(5) (or Ta(2)O(5)), and TeO(2) as reagents. The structures of Pb(4)Te(6)Nb(10)O(41) and Pb(4)Te(6)Ta(10)O(41) were determined by single-crystal and powder X-ray diffraction. The materials exhibit a three-dimensional framework consisting of layers of corner-shared NbO(6) octahedra connected by TeO(3) and PbO(6) polyhedra. The Nb(5+), Te(4+), and Pb(2+) cations are in asymmetric coordination environments attributable to second-order Jahn-Teller effects. The Nb(5+) cations undergo an intraoctahedral distortion either toward a face or a corner, whereas the Te(4+) and Pb(2+) cations are in distorted environments attributable to their lone pair. In addition, the TeO(3) polyhedra strongly influence the direction of the Nb(5+) intraoctahedral distortion. Infrared and Raman spectroscopy, thermogravimetric analysis, and dielectric measurements are also presented. Crystal data: Pb(4)Te(6)Nb(10)O(41), monoclinic, space group C2/m (No. 12), with a = 23.412(3) A, b = 20.114(3) A, c = 7.5008(10) A, beta = 99.630(4) degrees, V = 3482.4(8) A(3), and Z = 4; Pb(4)Te(6)Ta(10)O(41), monoclinic, space group C2/m (No. 12), with a = 23.340(8) A, b = 20.068(5) A, c = 7.472(2) A, beta = 99.27(3) degrees, V = 3453.8(2) A(3), and Z = 4.     

Mixed-metal tellurites: synthesis, structure, and characterization of Na1.4Nb3Te4.9O18 and NaNb3Te4O16

Two new mixed-metal tellurites, Na1.4Nb3Te4.9O18 and NaNb3Te4O16, have been synthesized by standard solid-state techniques using Na2CO3, Nb2O5, and TeO2 as reagents. The structures of Na1.4Nb3Te4.9O18 and NaNb3Te4O16 were determined by single-crystal X-ray diffraction. Both of the materials exhibit three-dimensional structures composed of NbO6 octahedra, TeO4, and TeO3 polyhedra. The Nb5+ and Te4+ cations are in asymmetric coordination environments attributable to second-order Jahn-Teller (SOJT) effects. The Nb5+ cations undergo an intraoctahedral distortion toward a corner (local C4 direction), whereas the Te4+ cations are in distorted environments owing to their nonbonded electron pair. Infrared and Raman spectroscopy, UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dielectric measurements were also performed on the reported materials. Crystal data: Na1.4Nb3Te4.9O18, monoclinic, space group C2/m (No. 12), with a = 32.377(5) A, b = 7.4541(11) A, c = 6.5649(9) A, beta = 95.636(5) degrees, V = 1576.7(4) A3, and Z = 4; NaNb3Te4O16, monoclinic, space group P2(1)/m (No. 11), with a = 6.6126(13) A, b = 7.4738(15) A, c = 14.034(3) A, beta = 102.98(3) degrees, V = 675.9(3) A3, and Z = 2.     

Synthesis and Characterization of Polyether Adducts of Barium and Strontium Carboxylates and Their Use in the Formation of MTiO(3) Films

The synthesis, characterization, and reactivity of new polyether adducts of strontium and barium carboxylates of general composition M(O(2)CCF(3))(n)()(L) (M = Ba, L = 15-crown-5, (1); M = Ba (2), Sr (3), respectively, with L = tetraglyme are reported. The compounds were synthesized by reaction of BaCO(3) or MH(2) (M = Sr or Ba) with organic acids in the presence of the polyether ligands. These compounds have been characterized by IR and (13)C and (1)H NMR spectroscopies, elemental analyses, and thermogravimetric analysis. The species Ba(2)(O(2)CCF(3))(4)(15-crown-5)(2) (1) and [Ba(2)(O(2)CCF(3))(4)(tetraglyme)](infinity) (2), were also characterized by single-crystal X-ray diffraction. Ba(2)(O(2)CCF(3))(4)(15-crown-5)(2) (1) crystallizes in the orthorhombic space group Cccm with cell dimensions of a = 13.949(1) ?, b = 19.376(2) ?, c = 16.029(1) ?, and Z = 8. [Ba(2)(O(2)CCF(3))(4)(tetraglyme)](infinity) (2) crystallizes in the monoclinic space group C2/c with cell dimensions of a = 12.8673(12) ?, b = 16.6981(13) ?, c = 15.1191(12) ?, beta = 99.049(8) degrees, and Z = 4. Compounds 1-3 thermally decompose at high temperatures in the solid state to give MF(2). However, solutions of compounds 1-3 dissolved in ethanol with Ti(O-i-Pr)(4) give crystalline perovskite phase MTiO(3) films, or in the case of mixtures of 2 and 3, Ba(1)(-)(x)()Sr(x)()TiO(3) films below 600 degrees C when spin coated onto silicon substrates and thermally treated. The crystallinity, purity, and elemental composition of the films was determined by glancing angle X-ray diffraction and Auger electron spectroscopy.     

Cd3(H2O)3((O3PCH2)2NH-CH2C6H4-COOH)2].11H2O: a layered cadmium phosphonate with reversible dehydration/hydration properties

In a recent systematic study on the influence of the reaction temperature on the structure formation in the system CdCl2/H(HO3PCH2)2NH-CH2C6H4-COOH (H5L) /NaOH, [Cd3(H2O)3((O3PCH2)2NH-CH2C6H4-COOH)2].11H2O was obtained as a microcrystalline compound. We have now been able to elucidate the structure from single-crystal data: triclinic, P; a=5.4503(9), b=12.880(2), and c=16.417(3) A; alpha=67.841(6) degrees, beta=80.633(6) degrees, gamma=87.688(8) degrees, V=1052.9(3) A3; Z=1; R1=0.1143, R2=0.2108 (all data); 0.0705, 0.1823 ((I>2sigmaI)). The structure of [Cd3(H2O)3((O3PCH2)2NH-CH2C6H4-COOH)2].11H2O is built up of cadmium phosphonate layers connected by water-mediated hydrogen bonds between aryl-carboxylic acid groups and water molecules coordinated to Cd2+ ions of adjacent layers (C-OH...H2O...H2O-Cd2+). The title compound was characterized by IR spectroscopy and energy dispersive X-ray, elemental, and thermogravimetric analyses. Furthermore, temperature-dependent X-ray diffraction data are presented. [Cd3(H2O)3((O3PCH2)2NH-CH2C6H4-COOH)2].11H2O can be reversibly dehydrated, and mechanical stress and grinding in the presence of water leads to the intercalation of additional water molecules.     

Novel gallium phosphate framework encapsulating trinuclear Mn3(H2O)6O8 cluster: hydrothermal synthesis and characterization of Mn3(H2O)6Ga4(PO4)6

A new manganese gallium phosphate, Mn3(H2O)6Ga4(PO4)6, has been synthesized under hydrothermal conditions at 150 degrees C and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, magnetic susceptibility, and electron paramagnetic resonance (EPR) spectroscopy. It crystallized in the monoclinic space group, P2(1)/n, with a = 8.9468(4) A, b = 10.148(5) A, c = 13.5540(7) A, beta = 108.249(1) degrees, and Z = 2. The compound is unusual in that it is not only the first nonoranically templated MnGaPO phase but also the first instance where edge-shared trinuclear manganese-oxygen clusters are encapsulated in a metal phosphate lattice. The trimer involves a central Mn(H2O)4O2 octahedron, which links to two Mn (H2O)2O4 octahedra at trans edges. The Mn3(H2O)6O8 clusters reside in tunnels built from GaO5 trigonal bipyramids and PO4 tetrahedra. Our magnetic study revealed that superexchange interactions occurred between the neighboring MnII centers. A good fit of the magnetic susceptibility data for the isolated trimers was obtained by using a derived expression based on Van Vleck's equation. Unlike all existing linear trinuclear MnII complexes, the chi MT product in the range 8-4 K remains at a constant value corresponding to one spin S = 5/2 per three MnII centers. The Curie behavior at such low temperatures has been confirmed by EPR data. According to the thermogravimetric analysis/differential thermal analysis (TGA/DTA) results, the title compound is thermally stable up to ca. 200 degrees C.     

Syntheses, structures and fluorescent properties of two novel coordination polymers in the U-Cu-H3pdc system

Two novel coordination polymers, UO2(C5H2N2O4)(H2O) (1) and (UO2)Cu(C5H2N2O4)2(H2O)2 (2), have been prepared by the hydrothermal reaction of uranyl nitrate hexahydrate [(UO2(NO3)2.6H2O], 3,5-pyrazoledicarboxylic acid (H3pdc) and copper(II) nitrate hemipentahydrate (Cu(NO3)2.2.5H2O) and characterized by single-crystal X-ray diffraction, thermogravimetric analyses (TGA) and fluorescence spectroscopy. Compound 1 (monoclinic, P2(1)/c, a=6.9556(6)A, b=11.302(1)A, c= 10.5288(9)A, beta=90.057(2) degrees and Z=4) consists of a two-dimensional sheet containing uranyl hexagonal bipyramids. Compound 2 (triclinic, P-1, a=5.1014(7)A, b=7.6067(11)A, c=10.2910(15)A, alpha=72.380(3) degrees, beta=86.796(3) degrees, gamma=84.447(3) degrees and Z=1) consists of two-dimensional sheets. Both structures contain the linear UO2(2+) moiety and have extended networks built up from the H3pdc ligand. Compound 1 exhibits the characteristic UO(2)2+ emission spectra when it is excited at the ligand or uranium excitation wavelength. With the addition of the copper metal center in compound 2, the uranium emission is absent regardless of the excitation wavelength.     

Synthesis and characterisation of second-generation metallodithiolene complexes of the type [Tp*ME(dithiolene)](M=Mo, W; E=O, S) and a novel 'organoscorpionate' complex of tungsten

Paramagnetic, chalcogenido-M(v) dithiolene complexes, [Tp*ME{S2C2(CO2Me)2}][M=Mo, E=O, S; M=W, E=O, S; Tp*=hydrotris(3,5-dimethylpyrazol-1-yl)borate] are generated in the reactions of dimethyl acetylenedicarboxylate (DMAC) and the sulfur-rich complexes NEt4[Tp*MoS(S4)] and NEt4[Tp*WS3]; the oxo complexes result from hydrolysis of the initial sulfido products. As well, a novel 'organoscorpionate' complex, [W{S2C2(CO2Me)2}{SC2(CO2Me)2-Tp*}], has been isolated from the reactions of NEt4[Tp*WS3] with excess DMAC. Complexes , and have been isolated and characterised by microanalytical, mass spectrometric, spectroscopic and (for and) X-ray crystallographic techniques. Complexes and have been partially characterised by mass spectrometry and IR and EPR spectroscopy. Six-coordinate, distorted-octahedral contains a terminal sulfido ligand (W=S=2.108(3)A), a bidentate dithiolene ligand (S-Cav=1.758 A, C=C=1.332(10)A) and a fac-tridentate Tp* ligand. Seven-coordinate contains a planar, bidentate dithiolene ligand (S-Cav=1.746 A, C=C=1.359(5)A) and a novel pentadentate 'organoscorpionate' ligand formed by the melding of DMAC, sulfido and trispyrazolylborate units. The latter is coordinated through two pyrazolyl N atoms (kappa2-N,N') and a tridentate kappa3-S,C,C' unit appended to N-beta of the third (uncoordinated) pyrazolyl group. The second-generation [Tp*ME(dithiolene)] complexes represent a refinement on first-generation [Tp*ME(arene-1,2-dithiolate)] complexes and their synthesis affords an opportunity to compare and contrast the electronic structures of true vs. pseudo-dithiolene ligands in otherwise analogous complexes.     

New d0 transition metal iodates: synthesis, structure, and characterization of BaTi(IO3)6, LaTiO(IO3)5, Ba2VO2(IO3)4.(IO3), K2MoO2(IO3)4, and BaMoO2(IO3)4.H2O

Five new d0 transition metal iodates, BaTi(IO3)6, LaTiO(IO3)5, Ba2VO2(IO3)4.(IO3), K2MoO2(IO3)4, and BaMoO2(IO3)4.H2O, have been synthesized by hydrothermal methods using Ba(OH)2.8H2O, La2O3, K2CO3, TiO2, V2O5, MoO3, and HIO3 as reagents. The structures of these compounds were determined by single-crystal X-ray diffraction. All of the reported materials have zero-dimensional or pseudo-one-dimensional crystal structures composed of MO6 (M = Ti4+, V5+, or Mo6+) octahedra connected to IO3 polyhedra. Infrared and Raman spectroscopy, thermogravimetric analysis, and UV-vis diffuse reflectance spectroscopy are also presented. Crystal data: BaTi(IO3)6, trigonal, space group R-3 (No. 148), with a = b = 11.4711(10) A, c = 11.1465(17) A, V = 1270.2(2) A3, and Z = 3; LaTiO(IO3)5, monoclinic, space group P2(1)/n (No. 14), with a = 7.4798(10) A, b = 18.065(2) A, c = 10.4843(14) A, beta = 91.742(2) degrees , V = 1416.0(3) A3, and Z = 4; Ba2VO2(IO3)4.(IO3), monoclinic, space group P2(1)/c (No. 14), with a = 7.5012(9) A, b = 33.032(4) A, c = 7.2150(9) A, beta = 116.612(2) degrees , V = 1598.3(3) A3, and Z = 4; K2MoO2(IO3)4, monoclinic, space group C2/c (No. 15), with a = 12.959(2) A, b = 6.0793(9) A, c = 17.748(3) A, beta = 102.410(4) degrees , V = 1365.5(4) A3, and Z = 4; BaMoO2(IO3)4.H(2)O, monoclinic, space group P2(1)/n (No. 14), with a = 13.3368(17) A, b = 5.6846(7) A, c = 18.405(2) A, beta = 103.636(2) degrees , V = 1356.0(3) A3, and Z = 4.     

Reactivity of the isolable disilene R*PhSi=SiPhR* (R* = SitBu3)

The disilene R*PhSi=SiPhR* (R* = supersilyl = SitBu3), which can be quantitatively prepared by dehalogenation of the disilane R*PhClSi-SiBrPhR* with NaR* (yellow, water- and air-sensitive crystals; decomp at ca. 70 degrees C; Si=Si distance 2.182 A), is comparatively reactive. It transforms 1) with Cl2, Br2, HCl, HBr, and HOH under 1,2-addition into disilanes R*PhXSi-SiX'PhR* (X/X' = Hal/Hal, H/Hal, H/OH), 2) with O2, S8, and Sen under insertion into 1,3-disiletanes R*PhSi(-Y-)2SiPhR* (Y = O, S, Se), 3) with Me2C=CH2 under ene reaction into the disilane R*PhRSi-SiHPhR* (R = CH2-CMe=CH2), 4) with N2O, Ten, tBuN identical to C, and Me3SiN=N=N under [2 + 1] cycloaddition into disiliranes -R*PhSi-Y-SiPhR*- (Y = O, Te, C=NtBu, NSiMe3; P4 adds 2 molecules of disilene), 5) with CO2, COS, PhCHO, and Ph2CS under [2 + 2] cycloaddition into disiletanes -R*PhSi-SiPhR*-Y-CO- (Y = O, S) as well as -R*PhSi-SiPhR*-Y-CRPh- (Y/R = O/H, S/Ph), 6) with CS2 and CSe2 under [2 + 3] cycloaddition into ethenes R*2Ph2Si2Y2C = CY2Si2Ph2R*2 (Y = S, Se), and 7) with CH2 = CMe-CMe=CH2 and Ph2CO under [2 + 4] cycloaddition into "Diels-Alder adducts". X-ray structure analyses of seven of these compounds are presented.     

UF3(H2O)(C2O4)0.5: a fluorooxalate of tetravalent uranium with a three-dimensional framework structure

A new uranium(IV) fluorooxalate, UF3(H2O)(C2O4)0.5, has been synthesized by a hydrothermal method and structurally characterized by single-crystal X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The structure consists of two-dimensional layers of corner- and edge-sharing tricapped trigonal prisms with the composition UF(4/2)F(2/2)O3 linked by bisbidentate oxalate ligands to form a three-dimensional framework. Magnetic susceptibilities were measured to confirm the tetravalent state of uranium. Crystal data: monoclinic, space group C2/c, a = 17.246(3) Angstroms, b = 6.088(1) Angstroms, c = 8.589(2) Angstroms, beta = 95.43(3) degrees, and Z = 8.     

Nitrogen atom insertion into Ir-S and C-S bonds initiated by photolysis of iridium(III)-azido-dithiocarbamato complexes

Photolysis of acetonitrile solutions of Cp*Ir(R2dtc)(N3) [Cp* = eta5-C5Me5, R2dtc = S2CNR2; R = Me (1) or Et (1')] at temperatures below 0 degrees C afford five-coordinate complexes Cp*Ir{NSC(NR2)S} (2 or 2'), where a nitrogen atom has been inserted into one of the Ir-S bonds. In solution, complex 2 thermally convert to the azaethene-1,2-dithiolate complex, Cp*Ir[SN=C(NMe2)S] (3), which could be crystallized as the corresponding dimer, {Cp*Ir[mu-SN=C(NMe2)S-kappa3S:S,S']}2 (4). As a result, a nitrogen atom that originated in the azide ligand is transferred into a C-S bond of the dithiocarbamate.     

Two-dimensional metal-organic frameworks (MOFs) constructed from heterotrinuclear coordination units and 4,4'-biphenyldicarboxylate ligands

Three novel metal-organic frameworks (MOFs) formulated as [Zn(2)M(BPDC)(3)(DMF)(2)].4DMF (M = Co(II), Ni(II) or Cd(II); BPDC = 4,4'-biphenyldicarboxylate; DMF = N,N'-dimethylformamide) have been prepared via solvothermal synthesis from mixtures of the corresponding transition metal salts and 4,4'-biphenyldicarboxylic acid (H(2)BPDC). The framework structures are characterized by single-crystal X-ray diffraction analysis, IR and UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis (TGA), and X-ray powder diffraction (XRPD). All three compounds possess essentially the same 2-D layered coordination framework consisting of linear heterotrinuclear secondary building units (SBUs) connected by rigid bridging BPDC ligands. Crystal data: for (C(60)H(66)CoN(6)O(18)Zn(2)): monoclinic, space group P2(1)/n, M = 1348.86, a = 20.463(4), b = 14.819(3), c = 23.023(5) A, beta = 111.75(3) degrees , V = 6484(2) A(3), Z = 4, D(c) = 1.382 Mg m(-3). For (C(60)H(66)N(6)NiO(18)Zn(2)): monoclinic, space group P2(1)/n, M = 1348.64, a = 11.670(2), b = 14.742(3), c = 19.391(4) A, beta = 102.29(3) degrees , V = 3259.5(11) A(3), Z = 2, D(c) = 1.374 Mg m(-3). For (C(60)H(66)CdN(6)O(18)Zn(2)): monoclinic, space group P2(1)/n, M = 1402.33, a = 11.491(2), b = 14.837(3), c = 19.386(4) A, beta = 101.53(3) degrees , V = 3238.3(11) A(3), Z = 2, D(c) = 1.438 Mg m(-3).     

Synthesis and characterization of new Mg(2)Al-paratungstate layered double hydroxides

Layered double hydroxides (LDHs, or hydrotalcites) with Mg(2+) and Al(3+) cations in the mixed metal hydroxide layer and paratungstate anions in the interlayer have been prepared. Different methods have been followed: anion exchange with Mg,Al LDHs originally containing nitrate or adipate, reconstruction of the LDH structure from a mildly calcined Mg(2)Al-CO(3) LDH, and coprecipitation. In all cases, the tungsten precursor salt was (NH(4))(10)H(2)W(12)O(42). The prepared solids have been characterized by elemental chemical analysis, powder X-ray diffraction (PXRD), FT-IR spectroscopy, thermogravimetric (TG) and differential thermal (DTA) analyses, scanning electron microscopy (SEM) with EDX (energy-dispersive X-ray analysis), and nitrogen adsorption at -196 degrees C for surface area and surface texture. Most of the synthesis methods used, especially anion exchange starting from a Mg(2)Al-NO(3) precursor at low temperature and short reaction times, lead to formation of a hydrotalcite with a gallery height of 9.8 A; increasing the reaction temperature to 70-100 degrees C and maintaining short contact times leads to a solid with a gallery height of 7.8 A. Both phases have been identified as a result of the intercalation of W(7)O(24)(6)(-) species in different orientations in the interlayer space. If the time of synthesis or the temperature is increased, a more stable phase, with a gallery height of 5.2 A corresponding to a solid with intercalated W(7)O(24)(6)(-), is formed, probably with grafting of the interlayer anion on the brucite-like layers. All systems are microporous. Calcination at 300 degrees C leads to amorphous species, and crystallized MgWO(4) is observed at 700 degrees C.     

Detection of the singlet and triplet MM δδ* states in quadruply bonded dimetal tetracarboxylates (M = Mo, W) by time-resolved infrared spectroscopy

The compounds M(2)(O(2)C(t)Bu)(4) and M(2)(O(2)CC(6)H(5))(4), where M = Mo or W, have been examined by femtosecond time-resolved IR (fs-TRIR) spectroscopy in tetrahydrofuran with excitation into the singlet metal-to-ligand charge-transfer ((1)MLCT) band. In the region from 1500 to 1600 cm(-1), a long-lived excited state (>2 ns) has been detected for the compounds M(2)(O(2)C(t)Bu)(4) and Mo(2)(O(2)C-C(6)H(5))(4) with an IR absorption at ~1540 cm(-1) assignable to the asymmetric CO(2) stretch, ν(as)(CO(2)), of the triplet metal-metal δ-δ star ((3)MM δδ*) state. The fs-TRIR spectra of W(2)(O(2)C-C(6)H(5))(4) are notably different and are assigned to decay of the MLCT states. In (3)MM δδ*, the removal of an electron from the δ orbital reduces MM δ to CO(2) π* back-bonding and causes a shift of ν(as)(CO(2)) to higher energy by ~30-60 cm(-1), depending on the metal. TRIR spectroscopy also provides evidence for M(2)(O(2)C(t)Bu)(4), where M = Mo or W, having MM δδ* S(1) states with ν(as)(CO(2)) distinct from those of the (3)MM δδ* states.     

Synthesis, thermal and spectral characterization of nanosized Ni(x)Mg(1-x)Al2O4 powders as new ceramic pigments via combustion route using 3-methylpyrozole-5-one as fuel

New Ni(x)Mg(1-x)Al(2)O(4) nanosized in different composition (0.1≤x≤0.8) powders have been synthesized successively for first time by using low temperature combustion reaction (LTCR) of corresponding metal chlorides, carbonates and nitrates as salts with 3-methylpyrozole-5-one (3MP5O) as fuel at 300°C in open air furnace. Magnesium aluminate spinel (MgAl(2)O(4)) was used as crystalline host network for the synthesis of nickel-based nano ceramic pigments. The structure of prepared samples was characterized by using different techniques such as thermal analysis (TG-DTG/DTA), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). UV/Visible and Diffuse reflectance spectroscopy (DRS) using CIE-L*a*b* parameters methods have been used for color measurements. The obtained results reveal that Ni(x)Mg(1-x)Al(2)O(4) powder of samples is formed in the single crystalline and pure phase with average particle size of 6.35-33.11 nm in the temperature range 500-1200°C. The density, particle size, shape and color are determined for all prepared samples with different calcination time and temperature.     

Crystal structures and topological aspects of the high-temperature phases and decomposition products of the alkali-metal oxalates M2[C2O4] (M=K, Rb, Cs)

The high-temperature phases of the alkali-metal oxalates M2[C2O4] (M = K, Rb, Cs), and their decomposition products M2[CO3] (M = K, Rb, Cs), were investigated by fast, angle-dispersive X-ray powder diffraction with an image-plate detector, and also by simultaneous differential thermal analysis (DTA)/thermogravimetric analysis (TGA)/mass spectrometry (MS) and differential scanning calorimetry (DSC) techniques. The following phases, in order of decreasing temperature, were observed and crystallographically characterized (an asterisk denotes a previously unknown modification): *alpha-K2[C2O4], *alpha-Rb2[C2O4], *alpha-Cs2[C2O4], alpha-K2[CO3], *alpha-Rb2[CO3], and *alpha-Cs2[CO3] in space group P6(3)/mmc; *beta-Rb2[C2O4], *beta-Cs2[C2O4], *beta-Rb2[CO3], and *beta-Cs2[CO3] in Pnma; gamma-Rb2[C2O4], gamma-Cs[C2O4], gamma-Rb2[CO3], and gamma-Cs2[CO3] in P2(1)/c; and delta-K2[C2O4] and delta-Rb2[C2O4] in Pbam. With respect to the centers of gravity of the oxalate and carbonate anions, respectively, the crystal structures of all known alkali-metal oxalates and carbonates belong to the AlB2 family, and adopt either the AlB2 or the Ni2In arrangement depending on the size of the cation and the temperature. Despite the different sizes and constitutions of the carbonate and oxalate anions, the high-temperature phases of the alkali-metal carbonates M2[CO3] (M = K, Rb, Cs), exhibit the same sequence of basic structures as the corresponding alkali-metal oxalates. The topological aspects and order-disorder phenomena at elevated temperature are discussed.     

The thermostability and reactivity of GaP nanocrystals in oxygen: from GaP nanocrystals to Ga2O3 nanocrystals

The thermostability and reactivity of GaP nanocrystals in O(2) were investigated using the thermogravimetric analysis (TGA), differential thermal analysis (DTA), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis techniques. alpha-Ga(2)O(3) nanoparticles, nano-hollow-particles, or nanorods and nanotubes can be separately obtained from the oxidation of nanocrystalline GaP at 400 degrees C for 30 min in dry O(2) atmosphere via manipulating different heating rates. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectrometry (EDX) analysis showed that the products were all alpha-Ga(2)O(3) but with different morphologies when different heating rates were applied. The formation mechanisms of the different morphological alpha-Ga(2)O(3) nanocrystals were discussed.     

AVSeO(5) (A = Rb, Cs) and AV(3)Se(2)O(12) (A = K, Rb, Cs, NH(4)): Hydrothermal Synthesis in the V(2)O(5)-SeO(2)-AOH System and Crystal Structure of CsVSeO(5)

Hydrothermal reactions in the V(2)O(5)-SeO(2)-AOH systems (A = Na, K, Rb, Cs, NH(4)) were studied with various reagent mole ratios. Typical millimole ratios were V(2)O(5)/SeO(2)/AOH = 5 or 3/15/x in 10-mL aqueous solutions, where x was 5, 10, 15, and 20. The reactions with x = 5 for A = K, Rb, Cs, and NH(4) at 230 degrees C produced single-phase products of the general formula AV(3)Se(2)O(12) with the (NH(4))(VO)(3)(SeO(3))(2) structure type. The x = 15 reactions for A = Rb and Cs yielded AVSeO(5) phases with a new structure type. The crystal structure for CsVSeO(5) was determined with X-ray single-crystal diffraction techniques to be monoclinic (P2(1) (No. 4), a = 7.887(3) ?, b = 7.843(2) ?, c = 9.497(3) ?, beta = 92.13(3) degrees, Z = 4). The structure of this compound consists of interwoven helixes extended in all three directions. The spires are composed of alternating SeO(3) and VO(5) units sharing common-edge oxygens in all three directions. For A = K and NH(4), the reactions of this mole ratio did not produce any identifiable phases. Each of the compounds is characterized by powder X-ray diffraction, infrared spectroscopic, and thermogravimetric techniques. The dependency of the synthesis results on the reaction conditions is discussed and rationalized.     

Ab initio study of the substituent effects on the relative stability of the E and Z conformers of phenyl esters. Stereoelectronic effects on the reactivity of the carbonyl group

Equilibria between the Z (tau1= 0 degrees) and E (tau1= 180 degrees) conformers of p-substituted phenyl acetates 4 and trifluoroacetates 5 (X = OMe, Me, H, Cl, CN, NO2) were studied by ab initio calculations at the HF/6-31G* and MP2/6-31G* levels of theory. The preference for the Z conformer, DeltaE(HF), was calculated to be 5.36 kcal mol(-1) and 7.50 kcal mol(-1) for phenyl acetate and phenyl trifluoroacetate (i.e., with X = H), respectively. The increasing electron-withdrawing ability of the phenyl substituent X increases the preference of the Z conformer. An excellent correlation with a negative slope was observed for both series between DeltaE of the E-Z equilibrium and the Hammett sigma constant. By using an appropriate isodesmic reaction, it was shown that electron-withdrawing substituents decrease the stability of both conformers, but the effect is higher with the E conformer. Electron-withdrawing phenyl substituents decrease the delocalization of the lone pair of the ether oxygen to the C=O antibonding orbital (nO--> pi*C=O) in both the E and Z forms and in both series studied; this effect is higher in the E conformer than in the Z conformer. The nO --> pi*C=O electron donation has a minimum value with tau1= 90 degrees and a maximum value with tau1= 0 degrees (the Z conformer), the value with tau1= 180 degrees (the E conformer) being between these two values, obviously due to steric hindrance. The effects of the phenyl substituents on the reactivity of the esters studied are discussed in terms of molecular orbital interactions. ED/EW substituents adjust the availability of the pi*C=O antibonding orbital to interact with the lone pair orbital of the attacking nucleophile and therefore affect the reactivity: EW substituents increase and ED substituents decrease it. Excellent correlations were observed between the rate coefficients of nucleophilic acyl substitutions and pi*C=O occupancies of the ester series 4 and 5.