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PubMed2001

Ternary lanthanoid ruthenium gallides with a high gallium content: Ln(2)Ru(3)Ga(10) (Ln = Yb, Lu) with a new structure type and LnRu(2)Ga(8) (Ln = La-Nd) with CaCo(2)Al(8)-type structure.

The title compounds were prepared by reaction of the elemental components at high temperatures. The compounds Yb(2)Ru(3)Ga(10) and Lu(2)Ru(3)Ga(10) crystallize with a new structure type, which has been determined from the single-crystal X-ray data of Yb(2)Ru(3)Ga(10): P4/mbm, Z = 2, a = 881.9(1) pm, c = 632.5(1) pm. In this structure the gallium atoms form two-dimensionally infinite double layers that extend perpendicular to the tetragonal axis. They contain two-thirds of the ruthenium atoms. The other ruthenium and the ytterbium atoms are situated between the gallium double layers. The structure is closely related to that of Mn(2)Hg(5). The latter compound may be written with the formula Mn(2)Mn(2)(square)Hg(10), thus indicating that its structure may be regarded as a defect-variant of the presently reported structure of Yb(2)Ru(3)Ga(10). The four gallides of the series LnRu(2)Ga(8) (Ln = La-Nd) crystallize with the orthorhombic CaCo(2)Al(8)-type structure (Pbam, Z = 4). This structure has been refined from single-crystal X-ray data of the cerium and neodymium compounds. Slight deviations from the ideal composition for one of the two ruthenium sites resulted in the formulas CeRu(1.913(4))Ga(8) and NdRu(1.858(4))Ga(8). Magnetic susceptibility measurements with a SQUID magnetometer indicate diamagnetism for LaRu(2)Ga(8), which is partially compensated by the expected Pauli paramagnetism. The cerium atoms in CeRu(2)Ga(8) show mixed or intermediate valent behavior, and PrRu(2)Ga(8) follows the Curie-Weiss law with no magnetic order down to 4 K.

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PubMed2002

Synthesis and characterization of an air-stable gallium hydride, [t-Bu(H)Ga(mu-NEt(2))](2), and related chloride derivatives.

The synthesis of [t-Bu(H)Ga(mu-NEt(2))](2) (1) was accomplished by the addition of 4 t-BuLi to [Cl(2)Ga(mu-NEt(2))](2). Evidence suggests that two tert-butyl groups are lost as isobutylene and result in Ga-H bond formation. The gallium hydride 1 is remarkably stable toward ambient air, oxygen, photolysis, and moderate heating; however, in CHCl(3) the hydride is replaced by chloride, producing [t-Bu(Cl)Ga(mu-NEt(2))](2) (2). Compound 1 may also be synthesized by sequential tert-butyl additions to [Cl(2)Ga(mu-NEt(2))](2). A singly substituted tert-butyl dimer, t-Bu(Cl)Ga(mu-NEt(2))(2)GaCl(2) (3), was also isolated, and interconversions between 1, 2, and 3 are described. Compound 1 was tested for utility in the chemical vapor deposition of GaN and produced gallium-rich films at low temperatures (<250 degrees C) with limited nitrogen incorporation due to facile Et(2)NH elimination.

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PubMed2002

Synthesis and structures of gallium amido imido phenyl clusters (PhGa)(4)(NH(i)Bu)(4)(N(i)Bu)(2) and (PhGa)(7)(NHMe)(4)(NMe)(5).

The phenylgallium-containing clusters constructed with bridging imido and amido ligands, (PhGa)(4)(NH(i)Bu)(4)(N(i)Bu)(2) (1) (51% yield) and (PhGa)(7)(NHMe)(4)(NMe)(5) (2) (31% yield), were synthesized from the room-temperature reactions of bis(dimethylamido)phenylgallium, [PhGa(NMe(2))(2)](2), with isobutylamine and methylamine, respectively. The reaction of [PhGa(NMe(2))(2)](2) in refluxing isobutylamine (85 degrees C) afforded (Ph(2)GaNH(i)Bu)(2) as one of the products, while the reaction of [PhGa(NMe(2))(2)](2) with methylamine at 150 degrees C afforded compound 2 in only 9% yield. Compound 1 possessed an admantane-like Ga(4)N(6) core, whereas compound 2 had a novel Ga(7)N(9) core constructed with both chair- and boat-shaped Ga(3)N(3) rings. The presence of several isomers of compounds 1 and 2 in solution is discussed along the structural similarities with other known gallium-nitrogen clusters and with gallium nitride.

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PubMed2003

Gallium and indium hydrazides. Molecular and electronic structure of In[N(SiMe3)NMe2]3 and related compounds.

Gallium and indium hydrazides, Ga[N(SiMe(3))NMe(2)](3) (1) and In[N(SiMe(3))NMe(2)](3) (2), were synthesized from the reactions of metal chlorides and Li[N(SiMe(3))NMe(2)]. Single crystal X-ray crystallographic analysis revealed that compound 2 was monomeric with trigonal planar geometries on the indium and the indium-bonded nitrogen atoms. The average In[bond]N distance of 2.078(3) A and the N[bond]In[bond]N[bond]N dihedral angles did not provide clear structural evidence of In[bond]N pi-bonding. The electronic absorption spectra of the indium hydrazido complex revealed transitions at significantly lower energies compared to those observed in the tris(amido) compounds, In[N(SiMe(3))(2)](3) (3) and In[N((t)Bu)(SiMe(3))](3) (4). The absorptions of the indium and gallium compounds were attributed to ligand-metal charge transfer transitions. Trends in the electronic transitions for compounds 2 and 3 calculated at the time-dependent density functional and configuration interaction including single excitations levels, both using a minimal basis set, were consistent with the experimental data, and Mulliken charge analyses support the assignment to ligand-to-metal charge transfer transitions. These calculations also demonstrated the presence of pi-bonding between the In and N p-orbitals, and an analogy is drawn to the frontier molecular orbitals of trimethylenemethane. The low-lying spectroscopic transition in 2, and thus its yellow color, results from mixing of the lone pair electrons on the beta-nitrogens of the hydrazido ligands with the HOMO of the InN(3) core.

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PubMed2003

Neutral and ionic aluminum, gallium, and indium compounds carrying two or three terminal ethynyl groups.

The syntheses of the ionic compounds [Li(+).2 dioxane (2,6-iPr(2)C(6)H(3)N(SiMe(3))Al(C triplebond CSiMe(3))(3))(-)].0.75 dioxane (1), [(Li(+))(2).(dioxane)(7)](0.5) [2,6-iPr(2)C(6)H(3)N(SiMe(3))Ga(C triplebond CSiMe(3))(3)(-)].1.5 dioxane (2), and [(Li(+))(2).(dioxane)(7)](0.5) [2,6-iPr(2)C(6)H(3)N(SiMe(3))In(C triplebond CSiMe(3))(3)(-)].1.5 dioxane (3) by the reaction of the corresponding organo metal chloride with LiC triplebond CSiMe(3) are reported. The neutral ethynyl compounds Br-Al(C triplebond CtBu)(2).2 THF (4), Cl-Ga(C triplebond CtBu)(2).THF (5), Cl-In(C triplebond CtBu)(2).2 THF (6), Al(C triplebond CtBu)(3).C[N(Me)CMe](2) (7), Ga(C triplebond CtBu)(3).dioxane (8), and In(C triplebond CtBu)(3).NEt(3) (9) have been obtained in good yields from the reaction of AlBr(3), GaCl(3), and InCl(3) with LiC triplebond CtBu in the presence of a Lewis base. Compound 7 is the first heterocyclic carbene substituted ethynyl derivative. Aluminum and gallium compounds with three terminal ethynyl groups Al(C triplebond CPh)(3).NMe(3) (10) and Ga(C triplebond CPh)(3).NMe(3) (11) have been prepared by the reaction of AlH(3).NMe(3) or GaH(3).NMe(3) with three equivalents of phenylethyne. All the above-mentioned compounds have been structurally studied. In compound 1 the lithium ion is coordinated to the three terminal ethynyl groups, whereas in compounds 2 and 3 the lithium is coordinated to the solvent (dioxane). Compound 8 crystallizes as a coordination polymer with dioxane molecules bridging the individual gallium units.

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PubMed2004

Ga(2,2'-bipy)(HPO(4))(H(2)PO(4)): first layered inorganic-organic hybrid gallium phosphate with a neutral framework.

A novel gallium phosphate, Ga(2,2'-bipy)(HPO(4))(H(2)PO(4)) (denoted FJ-12; FJ = Fujian Institute of Research on the Structure of Matter), which is the first example of layered inorganic-organic hybrid gallium phosphate with neutral framework, has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. This compound crystallizes in the monoclinic system, space group P2(1)/c (No. 14), with a = 10.9443(9), b = 15.8253(13), and c = 8.4201(7) A, beta = 108.898(2) degrees, V = 1379.7(2) A(3), and Z = 4. The structure consists of HPO(4) and H(2)PO(4) tetrahedra and unusual GaO(4)N(2) octahedra which are linked through their vertexes forming an undulated sheetlike structure with 4.12-net. The adjacent layers are stably packed together and exhibit interesting 3-D supramolecular arrays pi-pi interactions of the 2,2'-bipy groups.

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PubMed2005

Syntheses, structures, and ion-exchange properties of the three-dimensional framework uranyl gallium phosphates, Cs4[(UO2)2(GaOH)2(PO4)4].H2O and Cs[UO2Ga(PO4)2].

The reaction of UO(2)(NO(3))(2).6H(2)O with Cs(2)CO(3) or CsCl, H(3)PO(4), and Ga(2)O(3) under mild hydrothermal conditions results in the formation of Cs(4)[(UO(2))(2)(GaOH)(2)(PO(4))(4)].H(2)O (UGaP-1) or Cs[UO(2)Ga(PO(4))(2)] (UGaP-2). The structure of UGaP-1 was solved from a twinned crystal revealing a three-dimensional framework structure consisting of one-dimensional (1)(infinity)[Ga(OH)(PO(4))(2)](4-) chains composed of corner-sharing GaO(6) octahedra and bridging PO(4) tetrahedra that extend along the c axis. The phosphate anions bind the UO(2)(2+) cations to form UO(7) pentagonal bipyramids. The UO(7) moieties edge-share to create dimers that link the gallium phosphate substructure into a three-dimensional (3)(infinity)[(UO(2))(2)(GaOH)(2)(PO(4))(4)](4-) anionic lattice that has intersecting channels running down the b and c axes. Cs(+) cations and water molecules occupy these channels. The structure of UGaP-2 is also three-dimensional and contains one-dimensional (1)(infinity)[Ga(PO(4))(2)](3-) gallium phosphate chains that extend down the a axis. These chains are formed from fused eight-membered rings of corner-sharing GaO(4) and PO(4) tetrahedra. The chains are in turn linked together into a three-dimensional (3)(infinity)[UO(2)Ga(PO(4))(2)](1-) framework by edge-sharing UO(7) dimers as occurs in UGaP-1. There are channels that run down the a and b axes through the framework. These channels contain the Cs(+) cations. Ion-exchange studies indicate that the Cs(+) cations in UGaP-1 and UGaP-2 can be exchanged for Ca(2+) and Ba(2+). Crystallographic data: UGaP-1, monoclinic, space group P2(1)/c, a = 18.872(1), b = 9.5105(7), c = 14.007(1) A, beta = 109.65(3)(o) , Z = 4 (T = 295 K); UGaP-2, triclinic, space group P, a = 7.7765(6), b = 8.5043(7), c = 8.9115(7) A, alpha = 66.642(1)(o), beta = 70.563(1)(o), gamma = 84.003(2)(o), Z = 2 (T = 193 K).

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PubMed2005

Synthesis and crystal structure of unprecedented oxo/hydroxo-bridged polynuclear gallium(III) aqua complexes.

Two new polynuclear oxo/hydroxo-bridged polynuclear gallium(III) aqua complexes are obtained upon treatment of Ga(3+)(aq) with pyridine: the supramolecular compound of macrocyclic cavitand cucurbit[6]uril with gallium complex containing 32 metal atoms [Ga(32)(mu(4)-O)(12)(mu(3)-O)(8)(mu(2)-O)(7)(mu(2)-OH)(39)(H(2)O)(20)](PyH subsetC(36)H(36)N(24)O(12))(3)(NO(3))(6).53H(2)O (1) and the tridecanuclear complex [Ga(13)(mu(3)-OH)(6)(mu(2)-OH)(18)(H(2)O)(24)](NO(3))(15).12H(2)O (2). It follows that two modes of nucleation exist when Ga(3+)(aq) is hydrolyzed: one around the tetrahedral GaO(4) units (complex 1) and the other around the octahedral GaO(6) units (complex 2). This is the first time that polynuclear oxo/hydroxo-bridged aqua complexes of Ga(III) have been isolated without the use of other ligands to control or block olygomerization.

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PubMed1996

N-Methyl-2-(methylamino)troponiminate Complexes of Tin(II), Gallium(III), and Indium(III). Syntheses of [(Me)(2)ATI](2)GaI and [(Me)(2)ATI](2)InCl Using the Tin(II) Reagent [(Me)(2)ATI](2)Sn.

The N-methyl-2-(methylamino)troponimine [(Me)(2)ATI]H reacts with bis[bis(trimethylsilyl)amido]tin(II) to yield [(Me)(2)ATI](2)Sn in excellent yield. The treatment of [(Me)(2)ATI](2)Sn with GaI and InCl led to the bis(ligand)gallium(III) and -indium(III) compounds [(Me)(2)ATI](2)GaI and [(Me)(2)ATI](2)InCl. These metal complexes were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, and X-ray crystallography. All three metal adducts show fluxional behavior in solution at room temperature. [(Me)(2)ATI](2)Sn exhibits a pseudo trigonal bipyramidal structure in the solid state. The gallium and indium atoms in [(Me)(2)ATI](2)GaI and [(Me)(2)ATI](2)InCl adopt trigonal bipyramidal geometry around the metal center with the halide occupying an equatorial site. A convenient, high-yield route to [(Me)(2)ATI]H is also reported. Crystal data with Mo Kalpha (lambda = 0.710 73 Å) at 183 K: [(Me)(2)ATI](2)Sn, C(18)H(22)N(4)Sn, a = 8.4347(11) Å, b = 10.5564(13) Å, c = 11.5527(11) Å, alpha = 66.931(8) degrees, beta = 73.579(9) degrees, gamma = 67.437(7) degrees, V = 863.3(2) Å(3), triclinic, space group P&onemacr;, Z = 2, R = 0.0224; [(Me)(2)ATI](2)GaI, C(18)H(22)GaIN(4), a = 12.947(2) Å, b = 9.5834(9) Å, c = 16.0132(12) Å, beta = 107.418(8) degrees, V = 1895.8(3) Å(3), monoclinic, space group P2(1)/c, Z = 4, R = 0.0214; [(Me)(2)ATI](2)InCl, C(18)H(22)ClInN(4), a = 24.337(3) Å, b = 8.004(2) Å, c = 19.339(3) Å, beta = 101.537(13) degrees, V = 3691.1(11) Å(3), monoclinic, space group C2/c, Z = 8, R = 0.0224.

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PubMed1997

Sulfur-Bridged Cubane-Type Molybdenum-Gallium Clusters with Mo(3)GaS(4)(n)(+) (n = 5, 6) Cores. X-ray Structures of [Mo(3)GaS(4)(H(2)O)(12)](CH(3)C(6)H(4)SO(3))(5).14H(2)O and [Mo(3)GaS(4)(H(2)O)(12)](CH(3)C(6)H(4)SO(3))(6).17H(2)O.

Sulfur-bridged cubane-type molybdenum-gallium clusters [Mo(3)GaS(4)(H(2)O)(12)](5+) (2) and [Mo(3)GaS(4)(H(2)O)(12)](6+) (3) have been synthesized from [Mo(3)S(4)(H(2)O)(9)](4+) (1) and gallium metal and have been isolated as 2(pts)(5).14H(2)O (2.pts) and 3(pts)(6).17H(2)O (3.pts) (Hpts = p-toluenesulfonic acid), whose structures have been characterized by X-ray crystallography. Crystal data for 3.pts: orthorhombic, space group Pca2(1), a = 11.188(1) Å, b = 30.936(4) Å, c = 23.987(2) Å, V = 8301(2) Å(3), Z = 4, D(calcd) = 1.628 g cm(-3), D(obsd) = 1.63 g cm(-3), R (R(w)) = 5.8% (6.3%) for 6102 reflections (I > 3.0sigma(I)). Crystal data for 2.pts: triclinic, space group P&onemacr;, a = 16.406(4) Å, b = 16.743(3) Å, c = 13.173(4) Å, alpha = 90.64 degrees, beta = 98.40(2) degrees, gamma = 89.32(2) degrees, V = 3579.2(14) Å(3), Z = 2, D(calcd) = 1.681 g cm(-3), D(obsd) = 1.68 g cm(-3), R (R(w)) = 6.7% (10.1%) for 7612 reflections (I > 3.0sigma(I)). The Mo-Ga distances (3.pts, 3.60[2] Å; 2.pts, 3.52[2] Å) are much longer than the corresponding Mo-Mo (3.pts, 2.679[7] Å; 2.pts, 2.713[3] Å) distances. At low H(+) concentrations, such as 0.5 M HCl, 2 is stable, and at H(+) concentration higher than 2 M HCl, 2 is oxidized by H(+) to give 3 with evolution of hydrogen gas. Chloride ion plays an important role in the oxidation of 2. Electronic spectra of 3.pts and 2.pts are very similar. Peak positions and epsilon values (lambda(max), nm (epsilon, M(-1) cm(-1))): 3.pts, 762 (447), 550 (204); 2.pts, 760 (404), 548 (205). The cyclic voltammogram of 3 shows three reduction processes (the cathodic peak potentials, E(pc), are -0.83, -1.20, and -1.74 V, respectively), where the first and second processes are quasi-reversible (the anodic peak potentials, E(pa), are -0.55 and -1.00 V, respectively). The reduction current of each process is close to 1:1:3.

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PubMed2000

Low-valent gallium, indium, and tin compounds that contain a highly fluorinated tris(pyrazolyl)borate ligand: syntheses and characterization of.

Syntheses and characterization of gallium(I), indium(I), and tin(II) complexes of the [HB(3,5-(CF3)2Pz)3]- ligand (where [HB(3,5-(CF3)2Pz)3]- = hydrotris(3,5-bis(trifluoromethyl)pyrazolyl)borate)) are reported. X-ray crystal structures of [HB(3,5-(CF3)2Pz)3]In and [HB(3,5-(CF3)2Pz)3]Sn(CF3SO3) show monomeric structures in the solid state. The In-N and Sn-N bond distances are longer than the corresponding bond distances of nonfluorinated analogues. NMR data of the gallium(I) adduct [HB(3,5-(CF3)2Pz)3]Ga are very similar to those of the indium(I) analogue suggesting similar solution structures.

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PubMed2001

Catalytic growth and characterization of gallium nitride nanowires.

The preparation of high-purity and -quality gallium nitride nanowires is accomplished by a catalytic growth using gallium and ammonium. A series of catalysts and different reaction parameters were applied to systematically optimize and control the vapor-liquid-solid (VLS) growth of the nanowires. The resulting nanowires show predominantly wurtzite phase; they were up to several micrometers in length, typically with diameters of 10-50 nm. A minimum nanowire diameter of 6 nm has been achieved. Temperature dependence of photoluminescence spectra of the nanowires revealed that the emission mainly comes from wurtzite GaN with little contribution from the cubic phase. Moreover, the thermal quenching of photoluminescence was much reduced in the GaN nanowires. The Raman spectra showed five first-order phonon modes. The frequencies of these peaks were close to those of the bulk GaN, but the modes were significantly broadened, which is indicative of the phonon confinement effects associated with the nanoscale dimensions of the system. Additional Raman modes, not observed in the bulk GaN, were found in the nanowires. The field emission study showing notable emission current with low turn-on field suggests potential of the GaN nanowires in field emission applications. This work opens a wide route toward detailed studies of the fundamental properties and potential applications of semiconductor nanowires.

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PubMed2003

Nonaqueous synthesis and selective crystallization of gallium sulfide clusters into three-dimensional photoluminescent superlattices.

A low-temperature, nonaqueous synthesis approach is described that produces a series of gallium sulfide and polysulfide three-dimensional superlattices from binary Ga-S and ternary Zn-Ga-S supertetrahedral clusters. The diversity of superlattices is achieved by modifying the cluster size, the cluster composition, and the inter-cluster linkage mode. Both pure T3 (Ga10S186-) (denoted as UCR-7GaS) and pure T4 (Zn4Ga16S3310-) (denoted as UCR-5ZnGaS) superlattices with ring sizes of 18 and 24 tetrahedral atoms have been made. Of particular interest is the synthesis of the T3-T4 hybrid superlattice (denoted as UCR-19) with an odd ring size of 21 tetrahedral atoms. Another unprecedented feature is the occurrence of the -S-S-S- polysulfide linkage between supertetrahedral clusters in UCR-18. The fluorescent emission wavelength of these materials ranges from 440 to 500 nm and fills the previously observed gap between open-framework oxides and indium sulfides. A comparative study shows that open-framework gallium sulfides are more thermally stable than indium sulfides. They can also undergo ion exchange. It is suggested here that supertetrahedral clusters of different types coexist in a solution and can be selectively crystallized out with a proper choice of structure-directing agents.

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PubMed2003

Analogies between the reactivities of an anionic gallium(I) heterocycle and N-heterocyclic carbenes toward metallocenes.

The synthesis, spectroscopic and structural characterization of the novel nickel-gallium(I) heterocycle complex, [{Ga[N(Ar)C(H)]2}2Ni(mu-Cp)K(tmeda)(mu-Cp)K(mu-C7H8)0.5]infinity, Ar = C6H3Pri2-2,6, are reported. The compound is polymeric in the solid state and reacts with an N-heterocyclic carbene to give the neutral, square planar complex, trans-[Ni{C[N(Me)C(Me)]2}2{Ga[N(Ar)C(H)]2}2]. Analogies between the reactivities of the gallium(I) heterocycle and isoelectronic N-heterocyclic carbenes are discussed.

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PubMed2004

Defect dynamics observed by NMR of quadrupolar nuclei in gallium nitride.

Hexagonal and cubic polytypes of bulk gallium nitride powders are characterized by 69,71Ga and 14N MAS NMR at 11.7 T. The (corrected) 71Ga chemical shifts are 333.0 and 357.5 ppm, respectively; the corresponding 14N chemical shifts are -301.8 and -297.0 ppm (all shifts referenced to 1 M gallium nitrate). The 69,71Ga nuclear quadrupole coupling constants (NQCC) in the hexagonal form are axially symmetric and agree with previous single-crystal determinations. The 71Ga MAS NMR satellite pattern envelope of the cubic form has a large Gaussian half-height width of 297 kHz, due to nonzero NQCC values induced by defects. The 14N MAS NMR spinning sideband pattern of the cubic form has a Lorentzian envelope half-height width of 17.5 kHz for the same reason. A sample containing both phases shows an unexpected marked loss of the 71Ga MAS NMR satellite transition intensity expected for the hexagonal phase. Static 71Ga-selective Hahn spin-echo measurements at the perpendicular edge of the powder pattern for the hexagonal form in this sample show a large reduction in T2, especially at higher temperatures. The partial destruction of both spin-echoes and rotational echoes is due to a chemical-exchange type process involving sites having different NQCC values.

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PubMed2006

Quasi-isomeric gallium amides and imides GaNR2 and RGaNR (R = organic group): reactions of the digallene, Ar'GaGaAr' (Ar' = C6H3-2,6-(C6H3-2,6-Pri2)2) with unsaturated nitrogen compounds.

Reactions of the "digallene" Ar'GaGaAr'(1) (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)), which dissociates to green :GaAr' monomers in solution, with unsaturated N-N-bonded molecules are described. Treatment of solutions of :GaAr' with the bulky azide N(3)Ar(#) (Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,6-Me(2)-4-Bu(t))(2)), afforded the red imide Ar'GaNAr(#) (2). Addition of the azobenzenes, ArylNNAryl (Aryl = C(6)H(4)-4-Me (p-tolyl), mesityl, and C(6)H(3)-2,6-Et(2)) yielded the 1,2-Ga(2)N(2) ring compound Ar'GaN(p-tolyl)N(p-tolyl)GaA' (3) or the products MesN=NC(6)H(2)-2,4-Me(2)-6-Ga(Me)Ar' (4) and 2,6-Et(2)C(6)H(3)N=NC(6)H(3)-2-Et-6-Ga(Et)Ar' (5). Reaction of GaAr' with N(2)CPh(2) yielded the 1,3-Ga(2)N(2) ring compound Ar'Ga(mu:eta(1)-N(2)CPh(2))(2)GaAr' (6), which is quasi-isomeric to 3. Calculations on simple model isomers showed that the Ga(I) amide GaNR(2) (R = Me) is much more stable than the isomeric Ga(III) imide RGaNR. This led to the synthesis of the first stable monomeric Ga(I) amide, GaN(SiMe(3))Ar' ' (8) (Ar' ' = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2) from the reaction of LiN(SiMe(3))Ar' ' (7) and "GaI". Compound 8 is also the first one-coordinate gallium species to be characterized in the solid state. The reaction of 8 with N(3)Ar' ' afforded the amido-imide derivative Ar' 'NGaN(SiMe(3))Ar' ' (9), a gallium nitrogen analogue of an allyl anion. All compounds were spectroscopically and structurally characterized. In addition, DFT calculations were performed on model compounds of the amide, imide, and cyclic 1,2- and 1,3-species to better understand their bonding. The pairs of compounds 2 and 8 as well as 3 and 6 are rare examples of quasi-isomeric heavier main group element compounds.

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PubMed2005

Infrared spectroscopic study on the surface properties of gamma-gallium oxide as compared to those of gamma-alumina.

By hydrolysis of an ethanolic gallium nitrate solution, gamma-Ga2O3 was prepared as a single-phase polymorph having a specific surface area of 160 m2 g(-1). Surface acidity and basicity of this material was studied by IR spectroscopy, using pyridine, 2,6-dimethylpyridine, acetonitrile, and carbon dioxide as spectroscopic probe molecules. For comparison, a gamma-Al2O3 sample having a surface area of 290 m2 g(-1) was also studied. On partially hydroxylated gamma-Ga2O3, the main O-H stretching bands were found at 3693 (sharp) and at 3660-3630 cm(-1) (broad), and the material proved (by adsorbed dimethylpyridine) to have a weak Brønsted acidity. Surface Lewis acidity of gamma-Ga2O3 was revealed (mainly) by adsorbed pyridine, which gave the characteristic IR absorption bands of Lewis-type adducts at 1612, 1579, 1488, and 1449 cm(-1) (values noted under an equilibrium pressure of 1 Torr at room temperature); the corresponding Lewis acid centers (coordinatively unsaturated Ga3+ ions) were found to be weaker, although more abundant, than those present on the surface of gamma-Al2O3 (unsaturated Al3+ ions). Another significant difference between gamma-Ga2O3 and gamma-Al2O3 is the smaller thermal stability of pyridine and 2,6-dimethylpyridine Lewis adducts formed on the gallium oxide. The surface basicity of gamma-Ga2O3 was studied by using carbon dioxide and deuterated acetonitrile as IR probe molecules. Adsorbed CO2 gave carbonate and hydrogen-carbonate surface species similar to those formed by gamma-Al2O3. Adsorbed acetonitrile gave rise to acetamide species, which revealed the basic character of surface O2- ions. These acetamide species were found to be more abundant on gamma-Ga2O3 than on gamma-Al2O3.

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PubMed2006

Theoretical study on the dehydrogenation reaction of alkanes catalyzed by zeolites containing nonframework gallium species.

The dehydrogenation reaction of light alkanes in gallium-containing zeolites was studied by using density functional theory (DFT) and a nonframework gallium species in the dihydridegallium ion form. Two different mechanisms were considered: a 3-step mechanism and a 1-step concerted mechanism. The reactions occurring through the 3-step mechanism showed smaller activation barriers than the ones following the concerted mechanism. However, the energy barrier for the 3-step mechanism seems to be more influenced by the size and type (linear or branched) of the hydrocarbon chain and demands major conformational rearrangement, which could be hampered by the zeolite framework, especially for larger and/or branched hydrocarbons. On the other hand, the concerted mechanism seems to be much less dependent on the substrates geometry. Therefore, the concerted mechanism could be preferential when dealing with larger and/or branched alkanes.

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