Zhao-Hui Zhou

Oxidative dehydrogenation of propane over a series of low-temperature rare earth orthovanadate catalysts prepared by the nitrate method

A series of high‐purity rare earth orthovanadates were prepared by the nitrate method and found to be effective low‐temperature catalysts for the oxydehydrogenation of propane at 320°C, at which no reactions occurred over the catalysts reported in the literature, and, thus, may be of practical significance. The catalytic performances of LnVO4 (Ln = Y, Ce–Yb) at 500°C were much better than those of rare earth orthovanadate catalysts and also slightly exceeded that of magnesium orthovanadate Mg3(VO4)2 reported in the literature. LnVO4 (Ln = Y, Ce–Yb) materials were tetragonal active phases which could stabilize the existence of active sites for the oxydehydrogenation of propane. Some catalysts with a certain amount of LnVO3 reduced from LnVO4 (Ln = Ho–Yb) under reaction atmosphere exhibited better redox properties and catalytic performances possibly due to the existence of biphasic catalytic synergy. LaVO4 was a monoclinic unstable active phase, although its bulk structure did not change after reaction. The remarkable deactivation of the LaVO4 catalyst was probably due to that LaVO4 could not stabilize the existence of surface active sites.

Consistent approaches to van der Waals radii for the metallic elements

Abstract Due to the paucity of data on non-bonding interactions for metal atoms, no complete tabulation is available for crystallographic van der Waals radii for metallic elements. In this work several sets of van der Waals radii for metal atoms are derived indirectly. Unique data resources used for the derivation are (i) average volumes of elements in crystals, (ii) single covalent radii, (iii) Allinger´s van der Waals radii, as well as (iv) bond valence parameters for metal-oxygen bonds. The van der Waals radii for metal atoms deduced from these various approaches are basically comparable with each other, but are strikingly different from those from Bondi’s system of van der Waals radii. A complete set of new values for metallic elements up to Am, derived from bond valence parameters, are recommended.

SYNTHESES AND STRUCTURES OF THE POTASSIUM-AMMONIUM DIOXOCITRATOVANADATE(V) AND SODIUM OXOCITRATOVANADATE(IV) DIMERS

Abstract The two dimers potassium-ammonium dioxocitratovanadate (V), K2(NH4)4[VO2(cit)]2·6H2O (1) and sodium oxocitratovanadate (IV), Na4[VO(cit)]2·6H2O (2) have been prepared by the reactions of citric acid and metavanadate in neutral solution. Complex 1 crystallizes in the triclinic space group P 1 with unit cell parameters: α = 8.894(1), b = 9.783(1), c = 9.930(2) A , σ = 70.00(1), β = 88.09(1), γ = 68.42(1)°, V = 750.8 A 3 , Z = 1, R = 0.035 for 2622 observed reflections. The dimeric anion contains a centrosymmetric planar four-member V2O2 ring with the bridging hydroxyl oxygens. The citrate ion is coordinated via oxygen atoms of the hydroxyl and α-carboxylato groups, and the two acetato branches are not coordinated to vanadium. The principal V-O dimensions are: V-O(hydroxy), 1.961(2), 2.005(2) A; V-O(σ-carboxy), 1.981(3) A. Complex 2 crystallizes in the monoclinic space group P21/n with unit cell parameters: a = 10.120(2), b = 10.822(4), c = 11.934(4) A , β = 111.57(2)°, V = 1215.4 A 3 , Z = 2, R = 0.035 for 2255 observed reflections. The dimer contains a similar planar V2O2 ring with bridging hydroxyl oxygens. The tetradentate citrato ligands coordinate via hydroxyl and α-carboxylato oxygens to one vanadium, and via two acetato branches to the two vanadiums in the dimer. The principal V-O dimensions are: V-O(hydroxy), 1.971(2), 2.206(2) A; V-O (α-carboxy), 2.038(2) A: V-O(β-carboxy), 2.017(2), 2.032(2) A. The coordination number of the vanadium ions in complex 1 and complex 2 is therefore five and six, respectively.

Highly Enantioselective Henry Reactions of Aromatic Aldehydes Catalyzed by an Amino Alcohol-Copper(II) Complex

Amino alcohol-Cu(II) catalyst: Highly enantioselective Henry reactions between aromatic aldehydes and nitromethane have been developed. The reactions were catalyzed by an easily available and operationally simple amino alcohol-copper(II) catalyst. In total, 38 substrates were tested and the R-configured products were obtained in good yields with excellent enantioselectivities.

SYNTHESES, STRUCTURES AND SPECTROSCOPIC PROPERTIES OF NICKEL(II) CITRATO COMPLEXES, (NH4)2[Ni(Hcit)(H2O)2]2-2H2O AND (NH4)4[Ni(Hcit)2]-2H2O

Abstract Dimeric ammonium diaquocitratonickelate (II) dihydrate (NH4)2[Ni(Hcit)(H,O)2]2 -2H2O, 1, and its sodium and potassium salts, as well as ammonium dicitratonickelate (II) dihydrate (NH4)4[Ni(Hcit)2] ·2H2O, 2, (H4cit = citric acid) have been synthesized and characterized by spectroscopic methods. The crystal structures of 1 and 2 were determined by X-ray methods. Compound 1 is triclinic. space group Pl with a = 6.4071(7), b = 9.4710(7), c = 9.6904(5) A, α = 105.064(5), β = 91.992(7). γ = 89.334(8)°, V = 567.5(1) A Z = 1, R = 0.037 for 1714 observed reflections. The structure consists of centrosymmetric dimers, [Ni(Hcit)(H2O)2]2 2- The principal Ni[sbnd]O dimensions are Ni[sbnd]O(hydroxy), 2.074(2)A, Ni[sbnd]O(α-carboxy), 2.020(3)A, Ni[sbnd]O(β-carboxy), 2.031(2). 2.037(2)A, Ni[sbnd]O(water), 2.065(2), 2.072(3)A. Compound 2 crystallizes in the monocliruc space group P 21/a with a = 9.361(1), b= 13.496(1), c = 9.4238(7)A, (3= 115.475(6)°, V= 1074.9(3)A;. Z= 2, R = 0.052 for 1507 observed reflections. ...

Molybdenum(VI) complex with citric acid: synthesis and structural characterization of 1:1 ratio citrato molybdate K2Na4[(MoO2)2(cit)2]·5H2O

Abstract Sodium potassium citrato molybdate K 2 Na 4 [(MoO 2 ) 2 O(cit) 2 ]·5H 2 O has been prepared by the reaction of potassium trihydrogen citrate and sodium molybdate. Analysis of the crystal structure reveals that the anion of the complex contains a bent (MoO 2 )O(MoO 2 ) core with an MoOMo angle 142°. Each molybdenum has a distorted octahedral coordination and citrato ligands are tridentate to the two molybdenum atoms via the deprotonated hydroxy-, α- and β-carboxyl groups. Principal dimensions are: [MoO(t)] av , 1.706(4); [MoO(b)] av , 1.899(3); [MoO(hydroxy)] av , 1.944(3); [Mo Oα-carboxyl)] av , 2.207(3), and [MoO(β-carboxyl)] av , 2.264(3) A. The IR, 1 H and 13 C NMR spectra are in agreement with this structure.

syn‐ and Enantioselective Henry Reactions of Aliphatic Aldehydes and Application to the Synthesis of Safingol

Fundamental Research Funds for the Central Universities [2010121014]; Natural Science Foundation of Fujian Province [2013J10011]

Stereocontrolled syntheses of (-)-goniofufurone and (-)-8-epi-goniofufurone

Abstract The absolute configurations of natural goniofufurone and 8- epi -goniofufurone are shown to be 2 and 4 respectively by unambiguous syntheses of their enantiomers 1 and 3 from d - glycero - d - gulo -heptono-γ-lactone 7 involving an intramolecular Michael reaction as the key step. The diol 6 , readily availble from d - glycero - d - gulo -heptono-γ-lactone, has been converted by six sequential reactions (acetylation, hydrolysis, deacetylation, glycol cleavage, Wittig reaction, and hydrolysis) into the γ-lactone 5 which underwent an intramolecular Michael reaction to yield (-)-goniofufurone 1 . Likewise reactions of the monoacetate 12 gave (-)-8- epi -goniofufurone 3 .

PH- and mol-ratio dependent tungsten(VI) - citrate speciation from aqueous solutions: syntheses, spectroscopic properties and crystal structures

Abstract Investigation of the aqueous coordination chemistry for citrate and tungsten(VI) resulted in the isolation of three new monomeric and dimeric tungsten(VI) citrate NaK3[W2O5(Hcit)2]·4H2O (1), (Hphen)3[WO2(H2cit)(Hcit)]·6H2O (2) and K4[WO3(cit)]·2H2O (3), (H4citcitric acid). The three complexes have been characterized by elemental analyses, IR and NMR spectroscopies. The IR and NMR spectra are consistent with monomeric species or a monooxo-bridged dinuclear structure as revealed by single crystal X-ray diffraction study. The dimeric anion of complex 1 contains a bent (O2W)O(WO2) core with an angle of WObW 162.3(3)°. Each citrate ligand is tridentately coordinated to one tungsten atom through the α-alkoxyl, α-carboxyl, and one β-carboxyl group, making each metal atom six-coordinate and forming a mesomer with configuration of ΔSΛR. The mononuclear tungstate 2 consists of a cis-dioxo partially protonated citrato tungstate(VI) anion and three phenanthrolinium cations. The W(VI) atom is coordinated by two acid oxo groups and two bidentate citrate ligands through α-alkoxyl and α-carboxyl groups, while the other two β-carboxyl or carboxylic groups remain free. The tungsten atom in the complex 3 forms an octahedral coordination with three fac-oxo groups and one tridentate citrate, in which the later is coordinated through the α-alkoxyl and α-carboxyl groups, and much more weakly by one of the two terminal β-carboxyl groups [2.348(4) A]. Interconversion of citrato tungstate(VI) with pH value and the molar ratio of the reactant are discussed.

Monomeric and polymeric nickel complexes of malate: X-ray crystal structure of polymeric homochiral S-malato nickel(II), [Δ-Ni(S-Hmal)(H2O)2]n·nH2O

Abstract Polymeric S-malate nickel(II) [Δ-Ni(S-Hmal)(H2O)2]n·nH2O (1) was prepared from the reaction of nickel chloride and malate salt. By prolonging the reaction time and heating, the kinetic monomeric product cis-[Ni(S-H2mal)2(H2O)2]·2H2O (2) can be converted into the thermodynamic polymeric product 1. The coordination polymer is linked strongly by the tetradentate malate ligand, forming an homochiral zigzag chain. It is proposed that the chiral metal center of the complex may also be involved in the enantioselective synthesis as well as the chiral ligand.