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PubMed2006

La2TeI2: a new layered telluride iodide with unusual electrical properties.

A new layered metal-rich telluride halide, La2TeI2, has been synthesized by heating stoichiometric mixtures of LaI3, La, and Te under argon at 900 degrees C, and its structure has been refined from X-ray powder diffraction data. The compound crystallizes in the 3R-Lu2CCl2 structure type (rhombohedral space group R(-)3m with a = 4.5074(4) A, c = 32.528(2) A, and Z = 3). The crystal structure is composed of infinite layers of edge-sharing, Te-centered metal atom octahedra and iodine atoms separating these layers to form three close-packed I-Ln-Te-Ln-I slabs within the unit cell. The title compound is metallic at room temperature and exhibits an anomaly in the resistivity around 140 K which is closely related to changes in the a lattice parameter with temperature. The chemical bonding and metallic properties of La2TeI2 can be plausibly understood in terms of an ionic description (Ln3+)2Te2-(I-)2(e)2 where two electrons are delocalized in the La 5d conduction band.

Journal Article↗
PubMed1996

Ferrimagnetic Mixed-Valency and Mixed-Metal Tris(oxalato)iron(III) Compounds: Synthesis, Structure, and Magnetism.

The synthesis and structural and magnetic characterization of 16 compounds AM(II)Fe(III)(C(2)O(4))(3) (A = N(n-C(3)H(7))(4), N(n-C(4)H(9))(4), N(n-C(5)H(11))(4), P(n-C(4)H(9))(4), P(C(6)H(5))(4), N(n-C(4)H(9))(3)(C(6)H(5)CH(2)), (C(6)H(5))(3)PNP(C(6)H(5))(3), As(C(6)H(5))(4); M(II) = Mn, Fe) are reported. X-ray powder diffraction profiles are indexed in R3c or its subgroup P6(5)22 or P6/mmm to derive unit cell constants. The structures of all the compounds consist of two-dimensional honeycomb networks [M(II)Fe(III)(C(2)O(4))(3)(-)](infinity). The M(II) = Fe compounds behave as ferrimagnets with T(c) between 33 and 48 K, but five exhibit a crossover from positive to negative magnetization near 30 K when cooled in a field of 10 mT. The compounds exhibiting this unusual magnetic behavior are those that have the highest T(c). Within the set N(n-C(n)()H(2)(n)()(+1))(4)Fe(II)Fe(III)(C(2)O(4))(3) (n = 3-5), T(c) increases with interlayer separation and the low-temperature magnetization changes from positive (n = 3) to negative (n = 4, 5). In the M = Mn(II) compounds, the in-plane cell parameter a(0) is approximately 0.03 Å greater than in the corresponding M = Fe(II) ones while the interlayer separation (c(0)/6) is on average 0.08 Å smaller. All members of the M(II) = Mn series have magnetic susceptibilities showing broad maxima at 55 K characteristic of two-dimensional antiferromagnetism, but the magnetization of several of the salts increases sharply below 27 K due to the onset of spin canting, the magnitude of which varies significantly with A.

Journal Article↗
PubMed1996

Unusual 180 degrees P-O-P Bond Angles in ZrP(2)O(7).

The structure of cubic ZrP(2)O(7) at room temperature has been solved and refined using a combination of modeling and high-resolution neutron powder diffraction data. The cell edge is 24.74 Å, the space group is Pa&thremacr;, and Z is 108. For those P(2)O(7) units not on a 3-fold axis, the P-O-P angles range from 134 degrees to 162 degrees. Two crystallographically distinct P(2)O(7) groups are on three fold axes with P-O-P angles thus constrained to be 180 degrees on average. The structure of cubic ZrP(2)O(7) was also refined from data taken at 227, 290, 371, 435, and 610 degrees C. The 3 x 3 x 3 superstructure present at room temperature disappears at about 290 degrees C, and all P-O-P angles of P(2)O(7) are then constrained by symmetry to be 180 degrees on average. The exceptionally low thermal expansion shown by ZrP(2)O(7) above 290 degrees C is likely related to the unusual P-O-P angle.

Journal Article↗
PubMed1996

Synthesis and X-ray Powder Structures of Two Lamellar Copper Arylenebis(phosphonates).

Reaction of copper salts with 1,4-phenylenebis(phosphonic acid) yielded a conventional layered compound, Cu(2)[(O(3)PC(6)H(4)PO(3))(H(2)O)(2)], while a similar reaction with 4,4'-biphenylenebis(phosphonic acid) resulted in a new lamellar structure with composition Cu[HO(3)P(C(6)H(4))(2)PO(3)H]. The structures of these compounds were solved ab initio by using X-ray powder diffraction data. The crystals of the phenylenebis(phosphonate) compound are monoclinic, space group C2/c, with a = 18.8892(4) Å, b = 7.6222(2) Å, c = 7.4641(2) Å, beta = 90.402(2) degrees, and Z = 4. The layer structure in this case is similar to that in copper phenylphosphonate, Cu[O(3)PC(6)H(5)]. The metal atoms display a distorted square pyramidal geometry where four of the coordination sites are occupied by the phosphonate oxygens. The remaining site is filled by an oxygen atom of the water molecule. Adjacent metal-O(3)PC layers are covalently pillared by the phenyl group of the phosphonates to create a 3-dimensional structure. Cu[HO(3)P(C(6)H(4))(2)PO(3)H] is triclinic, space group P&onemacr;, with a = 4.856(2) Å, b = 14.225(5) Å, c = 4.788(2) Å, alpha = 97.85(1) degrees, beta = 110.14(1) degrees, gamma = 89.38(1) degrees, and Z = 1. The structure in this case, ideally consists of linear chains of copper atoms. The copper atoms are bridged by centrosymmetrically related phosphonate groups utilizing two of their oxygen atoms. This binding mode leads to square planar geometry for the copper atoms. The third oxygen atom of the phosphonate is protonated and is involved in linking adjacent linear chains through hydrogen bonds. At the same time, these hydroxyl oxygens interact weakly (Cu-O = 3.14 Å) with the copper atoms of the adjacent chain. Considering these long Cu-O interactions, the geometry of the copper atom may be described as distorted square bipyramidal. As in the phenylphosphonate structure, the biphenyl groups covalently link the Cu-O(3)PC networks in the perpendicular direction.

Journal Article↗
PubMed1997

Tungstorhenate Heteropolyanions. 2. Synthesis and Characterization of Enneatungstorhenates(V), -(VI), and -(VII).

The tungstorhenate(V) heteropolyanion [W(9)ReO(32)](5)(-) has been isolated as guanidinium and cesium salts from reaction of [ReO(2)(PPh(3))(py)(3)](+) with sodium tungstate. Crystallographic analysis of black Cs(5)[W(9)ReO(32)].3H(2)O [triclinic, P1 or P&onemacr;; a = 10.194(1), b = 11.503(2), c = 9.682(1) Å; alpha = 100.55(1), beta = 115.81(1), gamma = 99.13(1) degrees; Z = 1], based on 3743 reflections, shows the anion to be isostructural with decatungstate, [W(10)O(32)](4)(-). Refinement in P&onemacr; led to reliability indices R = 0.084, R(w) = 0.046. Electrochemical investigation revealed the existence of Re(VI) and Re(VII) analogues, which were hydrolytically unstable in aqueous solution but which were isolated as crystalline tetra-n-butylammonium and tetra-n-heptylammonium salts, respectively, from nonaqueous solvents. The tetra-n-butylammonium salts of [W(9)Re(VI)O(32)](4)(-) and [W(10)O(32)](4)(-) were shown to be isomorphous by X-ray powder diffraction. Simulation of the Q-band ESR spectrum of [W(9)Re(VI)O(32)](4)(-) (polycrystalline solid solution in [W(10)O(32)](4)(-)) gave g(x)() = 1.69(1), g(y)() = 1.66(1), g(z)() = 1.730(2) and 10(4)A(x)()((185,187)Re, I = (5)/(2)) = (-)252(10), 10(4)A(y)() = (-)398(10), 10(4)A(z)() = (-)653(5) cm(-)(1). The orthorhombic ESR spectrum proves that the Re atom occupies one of the eight equivalent "equatorial" sites in the decatungstate structure.

Journal Article↗
PubMed1997

Syntheses and X-ray Powder Structures of K(2)(ZrSi(3)O(9)).H(2)O and Its Ion-Exchanged Phases with Na and Cs.

A zirconium trisilicate compound, with composition K(2)ZrSi(3)O(9).H(2)O (1), was prepared under mild hydrothermal conditions and was structurally characterized by using its X-ray powder diffraction data. The compound crystallizes in the space group P2(1)2(1)2(1) with a = 10.2977(2) Å, b = 13.3207(3) Å, c = 7.1956(1) Å, and Z = 4. The asymmetric unit consists of a metal atom, a trisilicate group, and three lattice positions corresponding to two cations and a water oxygen atom. In the structure, the Zr atom is octahedrally coordinated by the six terminal oxygens of the trisilicate group. The trisilicate groups exist as linear chain polymers connected to each other through the Zr atoms. This arrangement leads to channels and cavities in the structure that are occupied by the cations and water molecules. The K(+) ions in compound 1 were exchanged for Cs(+) ions in two steps. In the first case about 50% of the K(+) ions were exchanged to give a compound with composition K(0.9)Cs(1.1)ZrSi(3)O(9).H(2)O (2). Compound 2 was then loaded with additional Cs(+) ions which resulted in a phase K(0.5)Cs(1.5)ZrSi(3)O(9).H(2)O (3). These exchanged phases retain the crystal symmetry of compound 1, but their unit cell dimensions have expanded as a result of large Cs(+) ions replacing the smaller K(+) ions. Structure analyses of the exchanged phases show that the cations found in the cavities of compound 1 are highly selective for Cs(+) ions. A small amount of Cs ions also go to a site in the large channel that is very close to that occupied by the water oxygen in compound 1. In the absence of Cs, this site is filled with water molecules. The second cation found in the channel of 1 is partially occupied by water and K(+) ions. The K(+) ions in compound 1 were completely exchanged for Na(+) ions, and the compound thus obtained, Na(2)ZrSi(3)O(9).H(2)O (4), was treated with Cs(+) ions in a manner similar to that carried out for compound 1. The low Cs(+) ion phase, Na(0.98)Cs(1.02)ZrSi(3)O(9).H(2)O (5), and the high Cs(+) ion phase, Na(0.6)Cs(1.4)ZrSi(3)O(9).H(2)O (6), show ion distributions very similar to compounds 2 and 3 except for the fact that in the Na phases a small amount Cs(+) ion also goes to the second cation site. Compound 1 on heating releases the lattice water and transforms into a hexagonal phase, K(2)ZrSi(3)O(9), corresponding to the mineral wadeite. In the high-temperature phase the silicate group exists as a condensed cyclic group and the K(+) ions are sandwiched between trisilicate groups. A possible pathway for this conversion is also discussed.

Journal Article↗
PubMed1997

Synthesis and X-ray Powder Structures of Nickel(II) and Copper(II) Coordination Polymers with 2,5-Bis(2-pyridyl)pyrazine.

The reaction of 2,5-bis(2-pyridyl)pyrazine (bppz) with nickel(II) sulfate in aqueous solution yielded a binuclear complex, [Ni(2)(bppz)(H(2)O)(8)](SO(4))(2).2H(2)O (1), whose structure was solved by single-crystal methods. The compound crystallizes in the monoclinic space group P2(1)/n with a = 8.372(2) Å, b = 18.301(2) Å, c = 17.197(2) Å, beta = 97.54(2) degrees, and Z = 4. The bppz ligand chelates the two octahedrally coordinated nickel atoms through its nitrogen donors. The four remaining coordination sites are occupied by water oxygen atoms. The binuclear [Ni(2)(bppz)(H(2)O)(8)](4+) cations are held together by hydrogen bonds involving sulfate anions and water molecules. Similar reactions with nickel(II) or copper(II) chloride in less polar solvents resulted in the formation of two new coordination polymers, {[Ni(2)Cl(2)(bppz)(H(2)O)(2)(CH(3)OH)(2)]Cl(2)}(n)() (2) and [Cu(2)Cl(4)(bppz)](n)() (3). These polymers could be obtained only in microcrystalline form. Their structures were determined ab initio from X-ray powder diffraction data. The complex {[Ni(2)Cl(2)(bppz)(H(2)O)(2)(CH(3)OH)(2)]Cl(2)}(n)() (2) belongs to the triclinic space group P&onemacr; with a = 8.7014(4) Å, b = 10.1465(5) Å, c = 8.0303(3) Å, alpha = 116.095(2) degrees, beta = 112.713(3) degrees, gamma = 64.056(3) degrees, and Z = 1. The octahedral coordination of the nickel atom is achieved by two nitrogens of the ligand bppz, two chloride ions, and two oxygens from the solvent molecules. The bridging nature of the chloride ions and the bis-bidentate ligands (bppz) leads to a one-dimensional polymer. The compound [Cu(2)Cl(4)(bppz)](n)() (3) crystallizes in the monoclinic space group C2/m with a = 13.9124(5) Å, b = 6.1844(2) Å, c = 10.1572(3) Å, beta = 112.952(3) degrees, and Z = 2. The copper atoms display a distorted octahedral geometry where four of the coordination sites are occupied by chloride ions and the remaining two by nitrogen atoms of bppz. The metal atoms are bridged by two chlorine atoms and the bppz ligands, forming a two-dimensional coordination polymer.

Journal Article↗
PubMed1997

Structural and Spectroscopic Studies of Two Phases of the Organometallic Chain Polymer [Ru(2){&mgr;(2):&mgr;(2):eta(2)-O(2)PMe(2)}(2)(CO)(4)](n)().

The microcrystalline organometallic coordination polymer [Ru(2){&mgr;(2):&mgr;(2):eta(2)-O(2)PMe(2)}(2)(CO)(4)](n)() which results from the oxidative addition of dimethylphosphinic acid to triruthenium dodecacarbonyl has been structurally characterized by X-ray powder diffraction, lambda = 1.149 49(1) Å, at 295 and 50 K. At room temperature the crystallites have a monoclinic unit cell with the space group C2/c with lattice constants a = 18.0792(3) Å, b = 9.0626(2) Å, c = 10.0372(2) Å, beta = 112.107(1) degrees, and Z = 4; the final refinement of 52 variables converged to R(p)(), R(wp)(), R(F)(), and R(F)()()2 of 8.2, 10.8, 4.6, and 8.3%, respectively, for data collected between 4 and 60 degrees (2theta). At 50 K the phase is described by a triclinic unit cell, space group P&onemacr;, and is characterized by the lattice constants a = 9.8637(6) Å, b = 8.9290(6) Å, c = 9.8870(5) Å, alpha = 115.051(3) degrees, beta = 108.587(5) degrees, gamma = 92.015(5) degrees, and Z= 2; the final refinement of 102 variables converged to and R(p)(), R(wp)(), R(F)(), and R(F)()()2 of 8.3, 11.4, 1.5, and 3.0%, respectively, for data collected between 3 and 74 degrees (2theta). The transition between the two crystalline phases has been determined by differential scanning calorimetry to occur at circa 220 K, and the most pronounced difference in the environment of the chains, as determined by variable-temperature IR spectroscopy, is in the rho(PCH(3)) modes for the bridging dimethylphosphinate ligands.

Journal Article↗
PubMed1998

Simultaneous Antiferromagnetic Order and Spin-Glass-like Behavior in MnAsO(4).

A low-temperature time-of-flight neutron powder diffraction study of a simple new solid, MnAsO(4), in a sample also containing 20% Mn(2)As(2)O(7) has been performed. MnAsO(4) orders magnetically at 14.5(5) K, and the unusual antiferromagnetic structure below this temperature has been determined. Only half of the Mn(3+) spins are ordered, and the remaining "idle" spins show some spin-glass behavior evidenced by susceptibility measurements. The ordered moment is reduced to a value of 2.6 &mgr;(B) by frustration. It is not possible to determine which of the two crystallographically inequivalent Mn sublattices is magnetically ordered and which is idle. The antiferromagnetic structure of the minority phase Mn(2)As(2)O(7) which orders at 10.5(5) K has also been determined.

Journal Article↗
PubMed1998

Syntheses, Structures, and Reactivity of Polynuclear Pyrazolato Copper(I) Complexes, Including an ab-Initio XRPD Study of [Cu(dmnpz)](3) (Hdmnpz = 3,5-Dimethyl-4-nitropyrazole).

The reaction of [Cu(CH(3)CN)(4)](BF(4)) with 3,5-dimethyl-4-nitropyrazole (Hdmnpz) in the presence of triethylamine yields the new copper(I) complexes [Cu(dmnpz)](3) (1) and (Et(3)NH)(2)[Cu(4)(dmnpz)(6)] (2), depending on the experimental conditions. The reactivity of 1 and 2 toward neutral ligands such as triphenylphosphine, cyclohexyl isocyanide (RNC), and carbon monoxide has been investigated. In particular, both complexes readily react with RNC, giving the dinuclear complexes [Cu(dmnpz)(RNC)](2) (4) and [Cu(dmnpz)(RNC)(2)](2) (5), depending on the copper/RNC ratio, and with PPh(3), affording the dimeric derivative [Cu(dmnpz)(PPh(3))](2) (6). The crystal and molecular structure of 1 has been determined ab initio using X-ray powder diffraction data from conventional laboratory equipment. Crystals of 1 are monoclinic, C2/c, a = 20.057(2) Å, b = 13.816(2) Å, c = 7.883(1) Å, beta = 95.912(4) degrees; R(F) and R(wp) 0.067 and 0.039, respectively, for Rietveld refinement on 3900 data points collected in the range 17 < 2theta < 95 degrees (Cu Kalpha radiation). Crystals of 1 contain planar trimers, with the copper atoms bridged by exo-bidentate ligands and short intermolecular Cu.Cu contacts (3.329(7) Å). For complexes 2 and 4-6, single-crystal X-ray diffraction studies have been performed. Crystals of 2 are monoclinic, P2(1)/c, a = 11.026(1) Å, b = 13.456(2) Å, c = 18.668(5) Å, beta = 92.91(2) degrees, Z = 2. The ionic packing of 2 contains tetranuclear complexes, with the copper atoms connected by six dmnpz ligands. Crystals of 4 are triclinic, P&onemacr;, a = 7.418(1) Å, b = 9.780(1) Å, c = 11.177(3) Å, alpha = 109.61(2); beta = 101.34(3) degrees, gamma = 105.82(1) degrees, Z = 2. Crystals of 5 are triclinic, P&onemacr;, a = 9.506(4) Å, b = 9.957(2) Å, c = 11.658(4) Å, alpha = 86.73(2) degrees, beta = 79.54(2) degrees, gamma = 82.47(4) degrees, Z = 1. Crystals of 6 are triclinic, P&onemacr;, a = 11.379(2) Å, b = 13.592(2) Å, c = 14.409(3) Å, alpha = 81.22(1) degrees, beta = 85.21(1) degrees, gamma = 87.55(1) degrees, Z = 2. 4, 5, and 6 are binuclear complexes bearing one RNC, two RNC, and one triphenylphosphine ligands on each copper atom, respectively. The steric requirement of the dmnpz ligands, in the presence of RNC or PPh(3), forces the inner [Cu(2)(dmnpz)(2)] core of the three complexes into markedly different conformations.

Journal Article↗
PubMed1998

New Layered Zirconium Tellurides: Zr(0.30)ZrTe(2), Zr(0.29)Zr(2)Te(2)As, and NaZr(2)Te(2)As.

The synthesis and crystal structure determinations of Zr(0.30)ZrTe(2) and M(x)Zr(2)Te(2)As (M = Zr, Na) compounds are reported. The structure of Zr(0.30)ZrTe(2) was refined in the hexagonal space group P6(3)mc (No. 186, Z = 2) with lattice parameters a = 3.9840(3) Å and c = 13.366(3) Å; Zr(0.29)Zr(2)Te(2)As was refined in the rhombohedral space group R&thremacr;m (No. 166, Z = 3) with lattice parameters a = 3.9329(4) Å and c = 29.564(5) Å. Zr(0.30)ZrTe(2) and Zr(0.29)Zr(2)Te(2)As have close structural similarities to Zr(2)Se(3) and Ta(2)S(2)C, respectively, and are built up by stacking hexagonal layers with [Zr(0.30)-Te-Zr-Te] and [Zr(0.29)-Te-Zr-As-Zr-Te] sequences. Four-probe resistivity measurements (77-300 K) show both Zr(0.30)ZrTe(2) and Zr(0.29)Zr(2)Te(2)As to be metallic (Zr(0.29)Zr(2)Te(2)As: 8.9 x 10(-)(5) Omega cm at 273 K). Both compounds exhibit structures wherein Zr atoms are included between layers (ZrTe(2) and Zr(2)Te(2)As) by partially filling trigonal antiprismatic holes. The replacement of the included Zr ions in Zr(0.29)Zr(2)Te(2)As by Na ions has been demonstrated. Powder diffraction data showed that NaZr(2)Te(2)As is isostructural with Zr(0.29)Zr(2)Te(2)As. By use of Rietveld refinements, sodium ions were found to reside in the trigonal antiprismatic sites between the layers. Extended Hückel band calculations on the [Zr(2)Te(2)As](1.16)(-) layer indicate that it should be a metallic conductor and that the [Zr(2)Te(2)As] layer can bear a greater negative charge than has so far been observed. We suggest that the [Zr(2)Te(2)As] layered compounds may offer new opportunities as electron-donating hosts.

Journal Article↗
PubMed1998

Adducts of Titanium Tetrachloride with Alkylselenium Compounds: Molecular Precursors to Titanium Diselenide Films.

Treatment of titanium tetrachloride (2 equiv) with dimethyl diselenide or diethyl diselenide (1 equiv) in hexane at 0 degrees C, followed by crystallization at -20 degrees C, afforded (TiCl(4))(2)(Se(2)(CH(3))(2)) (78%) and (TiCl(4))(2)(Se(2)(CH(2)CH(3))(2)) (63%), respectively, as red and orange crystalline solids. (TiCl(4))(2)(Se(2)(CH(2)CH(3))(2)) is stable in solution and in the solid state at 23 degrees C, but (TiCl(4))(2)(Se(2)(CH(3))(2)) decomposes to TiCl(4)(Se(CH(3))(2))(2), gray selenium, and other products upon standing in hexane solution, in the solid state, or upon sublimation at 250 degrees C. Treatment of titanium tetrachloride with 2 equiv of dimethyl selenide or diethyl selenide in hexane at ambient temperature afforded a spectroscopically pure brick red solid of TiCl(4)(Se(CH(3))(2))(2) (96%) or TiCl(4)(Se(CH(2)CH(3))(2))(2) (96%), respectively. X-ray crystal structures of (TiCl(4))(2)(Se(2)(CH(2)CH(3))(2)), TiCl(4)(Se(CH(3))(2))(2), and TiCl(4)(Se(CH(2)CH(3))(2))(2) were determined to establish solid state nuclearities. (TiCl(4))(2)(Se(2)(CH(2)CH(3))(2)) crystallizes in the hexagonal space group P3(1)21 with a = 12.106(1) Å, c = 10.786(1) Å, V = 1368.8(4) Å(3), and Z = 3. TiCl(4)(Se(CH(3))(2))(2) crystallizes in the monoclinic space group P2(1)/n with a = 8.175(1) Å, b = 13.051(1) Å, c = 16.871(3) Å, beta = 102.675(8) degrees, V = 1756.3(2) Å(3), and Z = 4. TiCl(4)(Se(CH(2)CH(3))(2))(2) crystallizes in the monoclinic space group P2(1)/n with a = 6.404(4) Å, b = 16.376(7) Å, c = 13.058(8) Å, beta = 101.45(4) degrees, V = 1342(1) Å(3), and Z = 4. TiCl(4)(Se(CH(3))(2))(2) and TiCl(4)(Se(CH(2)CH(3))(2))(2) were evaluated as precursors to titanium diselenide films. TiCl(4)(Se(CH(3))(2))(2) was not a good precursor, but TiCl(4)(Se(CH(2)CH(3))(2))(2) afforded rose-bronze colored titanium diselenide films at substrate temperatures of 500-600 degrees C. The films were characterized by X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Surprisingly, titanium diselenide films prepared from TiCl(4)(Se(CH(2)CH(3))(2))(2) are moisture sensitive and are apparently hydrolyzed by ambient moisture to titanium dioxide and hydrogen selenide. The relevance of the coordination chemistry to the development of precursors to titanium diselenide films is discussed.

Journal Article↗
PubMed1998

Tris(benzylthiolato)bismuth. Efficient Precursor to Phase-Pure Polycrystalline Bi(2)S(3).

Details of the synthesis, physical and spectroscopic characterization, and thermal decomposition of tris(benzylthiolato)bismuth, (BnS)(3)Bi, Bn = CH(2)C(6)H(5), are presented. Results from pyrolysis of (BnS)(3)Bi demonstrate that this compound is a convenient precursor to phase-pure, polycrystalline Bi(2)S(3) with low carbon and hydrogen contamination under mild thermal conditions (ca. 275 degrees C). Flow-tube pyrolysis produces small ( approximately 1 &mgr;m) spherical particles, whereas sealed-tube pyrolysis produces 6-&mgr;m diameter spherical particles composed of radiating acicular crystallites. Bi(2)S(3) was characterized by X-ray powder diffraction and scanning electron microscopy.

Journal Article↗
PubMed1999

Preparation, Characterization, and Luminescence Properties of a 58-Electron Linear Pt(4) Cluster, [Pt(4)(dmb)(4)(PPh(3))(2)](2+) (dmb = 1,8-Diisocyano-p-menthane), and Its Diphosphine Polymers.

The title compounds [Pt(4)(dmb)(4)(PPh(3))(2)]Cl(2) (1) and {[Pt(4)(dmb)(4)(diphos)]Cl(2)}(n)() (diphos = dppb (2), dppp (3), dpph (4)) have been prepared in good yields from the reaction of Pt(2)(dba)(3).CHCl(3) with 2 equiv of dmb and 1 equiv of PPh(3) for 1 (dba = dibenzylideneacetone) and from the reactions of Pt(2)(dba)(3).CHCl(3) with 2 equiv of dmb and 0.5 equiv of diphos for 2-4. The structure for 1 consists of a quasi-linear Pt(4)L(2)(2+) species (L = PPh(3); d(PtPt) = 2.666(2), 2.655(2), 2.641(2) Å), where the dmb ligands bridge the Pt atoms forming a catenate. From Raman spectroscopy, the two nu(PtPt) active modes for 1 are observed at 162 and 84 cm(-)(1) (F(PtPt) = 2.36 mdyn Å(-)(1)). For 2-4, the diphos ligands induce the formation of amorphous polymeric materials (X-ray powder diffraction patterns) with MW ranging from 84 000 to 307 000 according to viscometry. EHMO calculations predict that the HOMO and LUMO are the two dsigma orbitals arising from four interacting Pt atoms via the d(x)()()2(-)(y)()()2, d(z)()()2, s, and p(x)() M atomic orbitals. These are mixed with the ddelta and CNR(pi) MO's. From the examination of the position, absorptivity, and fwhm (full width at half maximum) of the strongly allowed low-energy UV-vis band, a dsigma --> dsigma assignment is made (lambda(max) = 405 nm, epsilon = 35 800 M(-)(1) cm(-)(1); EtOH for 1). The four compounds are luminescent at 77 K in EtOH, where lambda(emi) are 750, 736, 750, and 755 nm and tau(e) are 2.71, 4.78, 5.15, and 5.17 ns for 1-4, respectively. On the basis of the Stokes shifts (10 000-12 000 cm(-)(1)) and the long emission lifetimes, a phosphorescence dsigma --> dsigma assignment is made for the observed emissions. Crystal data for 1: crystal system triclinic; space group P1; a = 12.624(4) Å; b = 14.24(2) Å; c = 27.312(3) Å; alpha = 92.35(3) degrees; beta = 91.655(15) degrees; gamma = 90.28(5) degrees; V = 4903(7) Å(3); Z = 2; D(calc) = 1.528 g cm(-)(3); R(1) = 0.0738; wR(2) = 0.2097; S = 1.018.

Journal Article↗
PubMed1999

Synthesis and X-ray Powder Structure of a New Pillared Layered Cadmium Phosphonate, Giving Evidence that the Intercalation of Alkylamines into Cd(O(3)PR).H(2)O Is Topotactic.

A new pillared layered phosphonate, cadmium 2-aminoethylphosphonate, Cd(O(3)PC(2)H(4)NH(2)) (1), has been synthesized, and its structure was solved ab initio from X-ray powder diffraction data and refined by Rietveld methods. Compound 1 is orthorhombic: space group Pna2(1), a = 15.4643(2) Å, b = 5.16512(7) Å, c = 6.27650(8) Å, and Z = 4. Its layer arrangement is similar to that in Cd(O(3)PR).H(2)O, except that the water molecule coordinated to cadmium in Cd(O(3)PR).H(2)O is replaced by the nitrogen atom from the amino ends of the ethyl chains borne by phosphorus of the upper and lower layers. The strong similarity of the IR, (31)P, and (113)Cd NMR data for Cd(O(3)PC(2)H(4)NH(2)) and Cd(O(3)PCH(3)).n-NH(2)C(4)H(9) clearly shows the topotactic character of the intercalation of n-alkylamines in the dehydrated form of Cd(O(3)PR).H(2)O to yield Cd(O(3)PR).n-NH(2)R'.

Journal Article↗
PubMed1999

Hybrid Organic-Inorganic Frameworks (MIL-n). Hydrothermal Synthesis of a Series of Pillared Lanthanide Carboxyethylphosphonates and X-ray Powder ab Initio Structure Determination of MIL-19, Pr[O(3)P(CH(2))(2)CO(2)].

A series of lanthanide and yttrium carboxyethylphosphonates has been hydrothermally prepared (200 degrees C, 4 days) from the 1:1 mixture of carboxyethylphosphonic acid and the metal chlorides. The crystal structure of the praesodymium compound Pr(III)[O(3)P(CH(2))(2)CO(2)] has been determined ab initio from X-ray powder diffraction data and refined by the Rietveld method. The compound crystallizes in the monoclinic space group P2(1)/m (No. 11) with cell parameters at 20 degrees C a = 8.3617(2) Å, b = 7.1899(2) Å, c = 5.4586(2) Å, beta = 103.784(2) degrees, and Z = 2. The final agreement factors converged to the values R(p) = 0.139, R(wp) = 0.177, Bragg R = 0.123, R(F) = 0.055, and chi(2) = 3.50. The hybrid framework consists of inorganic Pr/O/P/C layers connected by organic groups, with an interlayer spacing of approximately 8.36 Å. The praesodymium atoms are 7-fold coordinated in this pillared layered structure. Isostructural compounds were prepared for yttrium and the entire series of the lanthanide elements.

Journal Article↗
PubMed1999

Nanoporous, Interpenetrated Metal-Organic Diamondoid Networks.

Reactions of Cd(NO(3))(2).4H(2)O with 4-cyanopyridine in the presence of ethanol or pyrazine guest molecules under hydro(solvo)thermal conditions afford two new cadmium coordination polymers, [Cd(isonicotinate)(2)(EtOH)][EtOH], 1, and [Cd(isonicotinate)(2)(H(2)O)][pyrazine], 2. The Cd centers in both 1 and 2 are seven-coordinate with distorted pentagonal bipyrimidal structures via coordination to two pyridyl nitrogen atoms, one oxygen atom from a solvent molecule, one chelating carboxylate, and one semichelating carboxylate group. The bridging isonicotinate groups link each Cd center to four adjacent Cd centers, resulting in three-dimensional polymeric networks based on doubly interpenetrated diamondoid structures. One molecule of ethanol or pyrazine is also included in 1 or 2, respectively, to fill the void space left within the solid after the twofold interpenetration. Thermogravimetric analyses (TGA) showed that the included and coordinated ethanol molecules in 1 could be removed stepwise at 100 and 160 degrees C, respectively. After the removal of the guest ethanol molecules, the resulting nanoporous solid exhibits the same X-ray powder diffraction (XRPD) pattern as 1. Guest ethanol molecules can be reintroduced into the evacuated sample of 1 via exposure to ethanol vapor at room temperature. Further heating results in the loss of coordinated ethanol molecules and the collapse of the polymeric network structure. On the other hand, XRPD shows that removal of pyrazine in 2 is accompanied by the loss of the coordinated water molecules and, consequently, the collapse of the polymeric network structure. These results demonstrate that nanopores can be designed based on interpenetrated coordinated networks. Crystal data for 1: orthorhombic space group Pbca, a = 12.691(1) Å, b = 15.545(1) Å, c = 18.342(1) Å, and Z = 8. Crystal data for 2: orthorhombic space group Pbca, a = 12.081(1) Å, b = 15.323(2) Å, c = 19.705(3) Å, and Z = 8.

Journal Article↗
PubMed1999

First Tin Pnictide Halides Sn(24)P(19.3)I(8) and Sn(24)As(19.3)I(8): Synthesis and the Clathrate-I Type of the Crystal Structure.

Sn(24)P(19.3)I(8) (I) and Sn(24)As(19.3)I(8) (II) have been prepared by a standard ampule synthesis. I crystallizes in a cubic space group Pm&thremacr;n, a = 10.9540(10) Å, z = 1. The crystal structure of I is built of the 3D net composed of tin and phosphorus atoms, while iodine atoms occupy large polyhedral holes of two different types, pentagonal dodecahedral and tetrakaidodecahedral. An arrangement of such polyhedra follows that of the clathrate-I type. The 3D net has vacancies at one of the phosphorus atoms positions. The vacancies cause the split of the tin atomic position into two, having different coordination, which is reflected in the (119)Sn Mössbauer spectrum. The vacancy concentration correlates well with the occupancy factors of the split tin atomic positions, and in accordance with the Zintl-Klemm formalism for valence compounds, I is a narrow-gap semiconductor. Powder diffraction data shows that II belongs to the same clathrate family, but has an 8 times larger face-centered cubic unit cell.

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