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PubMed1997

Aqua Complexes of [(2-Methoxyethyl)cyclopentadienyl]zirconium Trichloride.

The behavior of [(eta(5):eta(1)-C(5)H(4)CH(2)CH(2)OMe)ZrCl(2)(&mgr;-Cl)](2) (1) toward a variety of solvents, and especially water, was investigated. The bidentate coordination of the C(5)H(4)CH(2)CH(2)OMe ligand is retained in chloroform, dichloromethane, benzene, acetone, thf, and acetonitrile. No stable adducts of 1 with the last three solvents could be isolated. In methanol and water, coordination of the ether side chain is broken; however, removal of solvent retains this coordination and the stable mono adducts (eta(5):eta(1)-C(5)H(4)CH(2)CH(2)OMe)ZrCl(3)(MeOH) and (eta(5):eta(1)-C(5)H(4)CH(2)CH(2)OMe)ZrCl(3)(H(2)O) were isolated. An X-ray structure of the thf solvate of the latter compound was determined: space group P2(1)/c, a = 11.612(1) Å, b = 10.759(2) Å, c = 14.291(2) Å, beta = 105.50(1) degrees, V = 1720.5(4) Å(3), Z = 4, R = 0.062. The intramolecular coordination of the ether side chain is also broken in DMSO, but in this case it is not retained after removal of solvent. A cationic aqua complex [(eta(5)-C(5)H(4)CH(2)CH(2)OMe)ZrCl(2)(H(2)O)(DMSO)(2)](+)Cl(-) crystallized from the solution: space group P&onemacr;, a = 8.297(1) Å, b = 10.097(1) Å, c = 12.883(1) Å, alpha = 71.12(1) degrees, beta = 86.60(1) degrees, gamma = 87.45(1) degrees, V = 1019.0(2) Å(3), Z = 2, R = 0.049. Compound 1 is a Diels-Alder catalyst even under moist conditions.

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PubMed1997

Structural Novelties in Anionic Cluster Halide Phases. Discrete Tetrahedral A(4)Br(+) Ions in Two New Zirconium Bromide Structures (A = Na-Cs).

Suitable reactions of ABr, Zr, ZrBr(4), and an interstitial Z element in Ta containers at 850 degrees C afford two series of quaternary cluster phases containing A(4)Br(3+) ions. Cubic (A(4)Br)(2)Zr(6)(Z)Br(18) phases occur for various combinations of A = Na-Cs, Z = Be, B, H, Mn. The combination with A = K, Z = B was structurally characterized (inverse fluorite, Fm&thremacr;m, Z = 4, a = 16.191(2) Å). The 15-e cluster exhibits the appropriate magnetic moment, and this decreases toward the diamagnetic 14-electron limit in products with potassium deficiencies, (K(4)(-)(x)())(2)Zr(6)Br(18)B, x </= approximately 0.5. The tetragonal Cs(4)Br[Zr(6)(B)Br(12)]Br(4) (P&fourmacr;2(1)m, Z = 2, a = 12.5482(7) Å, c = 11.5610(9) Å) contains a new type of puckered M(6)Br(16) layers with Cs(4)Br(3+) in tunnels normal to the layers. Both examples of A(4)Br(3+) ions have short central Br-A bonds plus three to nine more distant bromines in neighboring clusters about each A, respectively.

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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.

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PubMed1998

Mechanism of the Topotactic Formation of gamma-Zirconium Phosphate Covalently Pillared with Diphosphonate Groups.

The topotactic reaction of gamma-ZrPO(4)[O(2)P(OH)(2)].2H(2)O (gamma-ZrP) with benzenediphosphonic acid was examined in water and in acetone-water mixtures. This reaction was found to take place in water only on the external surface of the microcrystals, and pillared compounds were never obtained, even after very long reaction times. On the contrary, covalently pillared compounds were quickly obtained in acetone-water mixtures. The mechanism of the latter topotactic reaction was investigated by determining the rate of the phosphate groups released and the rate of the benzenediphosphonates taken up by gamma-ZrP over a long time (50 days). These data showed that pillared derivatives of gamma-ZrP can be obtained because colloidal dispersions of exfoliated lamellae are formed in acetone-water mixtures. The diphosphonate group acts initially as a monovalent species, replacing only one dihydrogen phosphate group on the surface of the exfoliated gamma-lamellae. The colloidal and partially derivatized lamellae thus formed can interact with each other by forming polylamellar pillared systems. When the number of pillared lamellae exceeds a given value (usually 5-6), flocculation of the colloidal gamma-ZrP takes place. Topotactic reactions between packets of pillared lamellae may also continue in the flocculated system. Therefore, the average number of the pillared lamellae slowly increases over time.

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PubMed1999

Chemical Transport Synthesis, Electrochemical Behavior, and Electronic Structure of Superconducting Zirconium and Hafnium Nitride Halides.

The layered nitrides beta-MNX (M = Zr, Hf; X = Cl, Br) crystallize in the space group R&thremacr;m with a hexagonal cell of dimensions a = 3.6031(6) Å, c = 27.672(2) Å for beta-ZrNCl, a = 3.5744(3) Å, c = 27.7075(9) Å for beta-HfNCl, and a = 3.6379(5) Å, c = 29.263(2) Å for beta-ZrNBr. Lithium intercalation using n-buthyllithium in hexane solutions leads to solvent free superconductors of formula Li(0.20)ZrNCl, Li(0.42)HfNCl, Li(0.67)HfNCl, and Li(0.17)ZrNBr showing critical temperatures of 12, 18, 24, and 13.5 K, respectively. Whereas several samples of beta-ZrNBr and beta-ZrNCl showed reproducibility in the lithium uptake and in the corresponding critical temperatures, different samples of beta-HfNCl subjected to the same treatment in n-buthyllithium showed lithium uptakes ranging from 0.07 to 0.67, and corresponding critical temperatures between 0 and 24 K. A linear dependence of T(c) versus the lithium content is observed when all the superconducting samples are considered. The results obtained from electrochemical lithiation are consistent with those obtained with chemical methods, as samples with larger capacity on discharge are also those found to have larger lithium contents after chemical lithiation. Most samples present a reduction step around 1.8 V vs Li(0)-Li(+) whose origin is still unclear. The electrochemical capacity on discharge for beta-HfNCl and beta-ZrNBr depends on the milling time spent in the preparation of the electrodes, with long milling times resulting in lower intercalation degree. Possible causes for this effect are either the creation of structural defects (e.g., stacking faults) or some sample decomposition induced by local heating. The same phenomena are proposed to account for the different behavior of beta-HfNCl samples, although additional aspects such as the presence of hydrogen, oxygen, or extra hafnium atoms in the structure have to be considered. Tight-binding band structure calculations for beta-MNX (M = Zr, X = Cl, Br; M = Hf, X = Cl), ZrCl, and Y(2)C(2)Br(2) are reported. The density of states and Fermi surfaces of the beta-MNX phases as well as the relationship between the electronic structure of the beta-ZrNCl and ZrCl are discussed. Despite the structural relationships, the electronic structures near the Fermi level of the beta-MNX and Y(2)Br(2)C(2) phases are found to be very different.

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PubMed2000

Zirconium and hafnium hydrogen monothiophosphates, H2Zr(PO3S)2 and H2Hf(PO3S)2. Syntheses and selective ion-exchange properties of sulfur-containing analogues of H2M(PO4)2 (M = Zr, Hf).

The reactions between aqueous solutions of M4+ (M = Zr, Hf) and PO3S3- each result in the precipitation of a white gel that can be dried to a powder. Elemental analysis results for the white polycrystalline product yield a stoichiometry of H2M(PO3S)2. These new compounds are characterized by thermal analysis (DSC, TG-MS), vibrational spectroscopy (FT-IR, FT-Raman), 31P MAS NMR spectroscopy, energy-dispersive spectroscopy (EDS), and powder X-ray diffraction (XRD). On the basis of the characterizations and the results of trialkylamine intercalation experiments, we conclude that the H2M(PO3S)2 compounds have a layered structure that is likely similar to that of alpha-H2Zr(PO4)2.H2O. The interlayer spacing for both H2M(PO3S)2 compounds, determined by XRD, is approximately 9.4 A. Our characterization results suggest that the sulfur atom of each PO3S3- group is preferentially pointed into the interlayer region of the compound and is protonated. Two of the many potentially interesting properties of H2Zr(PO3S)2, its ion-exchange capacity and selectivity, are investigated. H2Zr(PO3S)2 is demonstrated to be an effective and recyclable ion-exchange material for both Zn2+(aq) and Cd2+(aq). Mass balance experiments indicate that the removal of Cd2+(aq) and Zn2+(aq) ions by solid H2Zr(PO3S)2 occurs by an ion-exchange process. Ion exchange results in the formation of the new compounds H0.2Cd0.9Zr(PO3S)2 and H0.50Zn0.75Zr(PO3S)2. The extraction of metal ions is monitored by XRD, vibrational spectroscopy, and elemental analysis. H2Zr(PO3S)2 reversibly intercalates Zn2+(aq) ions through three complete cycles of intercalation and deintercalation without any loss of ion-exchange capacity.

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PubMed2000

Reduced zirconium halide clusters in aqueous solution.

Reduced hexazirconium halide cluster compounds have good solubility and stability in strongly acidic and/or halide-rich aqueous solutions. Cyclic voltammetric (CV) measurements in aqueous media established that [(Zr6BCl12)(H2O)6]2+/+ and [(Zr6BBr12)(H2O)6]2+/+ exhibited positive half-wave potentials (E1/2 = 0.059V and 0.160 V, respectively) vs the SHE, indicating that these clusters are only modestly reducing. Several new crystalline cluster compounds have been isolated from cold 12 M HCl solutions; the structures of each contain extended hydrogen-bonding water networks. Crystallographic data for these compounds are reported as follows: [Rb0.44(H3O)4.56][(Zr6BCl12)Cl6].19.44H2O (3), cubic, Im3m, a = 13.8962(3) A, Z = 2; (H3O)5[(Zr6BeCl12)Cl6].19H2O (4), cubic, Im3m, a = 13.8956(4) A, Z = 2; (H3O)5[(Zr6MnCl12)Cl6].19H2O (5), cubic, Im3m, a = 14.029(3) A, Z = 2; (H3O)4[(Zr6BCl12)Cl6].12.97H2O (6), tetragonal, P4(2)/mnm, a = 11.5373(2) A, c = 15.7169(4) A, Z = 2; (H3O)4[(Zr6BCl2)Br6].13.13H2O (7), tetragonal, P4(2)/mnm, a = 11.7288(6) A, c = 15.931(1) A, Z = 2.

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PubMed2001

Reactions of tetrakis(dimethylamide)-titanium, -zirconium and -hafnium with silanes: synthesis of unusual amide hydride complexes and mechanistic studies of titanium-silicon-nitride (Ti-Si-N) formation.

M(NMe(2))(4) (M = Ti, Zr, Hf) were found to react with H(2)SiR'Ph (R' = H, Me, Ph) to yield H(2), aminosilanes, and black solids. Unusual amide hydride complexes [(Me(2)N)(3)M(mu-H)(mu-NMe(2))(2)](2)M (M = Zr, 1; Hf, 2) were observed to be intermediates and characterized by single-crystal X-ray diffraction. [(Me(2)N)(3)M(mu-D)(mu-NMe(2))(2)](2)M (1-d(2), 2-d(2)) were prepared through reactions of M(NMe(2))(4) with D(2)SiPh(2). Reactions of (Me(2)N)(3)ZrSi(SiMe(3))(3) (5) with H(2)SiR'Ph were found to give aminosilanes and (Me(2)N)(2)Zr(H)Si(SiMe(3))(3) (6). These reactions are reversible through unusual equilibria such as (Me(2)N)(3)ZrSi(SiMe(3))(3) (5) + H(2)SiPh(2) right arrow over left arrow (Me(2)N)(2)Zr(H)Si(SiMe(3))(3) (6) + HSi(NMe(2))Ph(2). The deuteride ligand in (Me(2)N)(2)Zr(D)Si(SiMe(3))(3) (6-d(1)) undergoes H-D exchange with H(2)SiR'Ph (R' = Me, H) to give 6 and HDSiR'Ph. The reaction of Ti(NMe(2))(4) with SiH(4) in chemical vapor deposition at 450 degrees C yielded thin Ti-Si-N ternary films containing TiN and Si(3)N(4). Ti(NMe(2))(4) reacts with SiH(4) at 23 degrees C to give H(2), HSi(NMe(2))(3), and a black solid. HNMe(2) was not detected in this reaction. The reaction mixture, upon heating, gave TiN and Si(3)N(4) powders. Analyses and reactivities of the black solid revealed that it contained -H and unreacted -NMe(2) ligands but no silicon-containing ligand. Ab initio quantum chemical calculations of the reactions of Ti(NR(2))(4) (R = Me, H) with SiH(4) indicated that the formation of aminosilanes and HTi(NR(2))(3) was favored. These calculations also showed that HTi(NH(2))(3) (3b) reacted with SiH(4) or H(3)Si-NH(2) in the following step to give H(2)Ti(NH(2))(2) (4b) and aminosilanes. The results in the current studies indicated that the role of SiH(4) in its reaction with Ti(NMe(2))(4) was mainly to remove amide ligands as HSi(NMe(2))(3). The removal of amide ligands is incomplete, and the reaction thus yielded "=Ti(H)(NMe(2))" as the black solid. Subsequent heating of the black solid and HSi(NMe(2))(3) may then yield TiN and Si(3)N(4), respectively, as the Ti-Si-N materials.

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PubMed2002

Phosphorus phenyl-group activation by reduced zirconium and niobium complexes stabilized by the [P2N2] macrocycle.

Reduction of [P2N2]ZrCl2 (where [P2N2] = PhP(CH2SiMe2NSiMe2CH2)2PPh) with KC8 under argon generates the phosphorus phenyl bridged bimetallic complex where the bridging phenyl groups are formally reduced to bis(allyl) dianions. Similar reduction of [P2N2]NbCl caused the one-electron reduction of the phosphorus phenyl group to generate a cyclohexadienyl moiety via a C-C bond formation between the ipso carbons of the two phenyl groups.

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PubMed2004

Pentadienyls vs cyclopentadienyls and reversal of metal-ligand bonding affinity with metal oxidation state: synthesis, molecular structures, and electronic structures of high-valent zirconium pentadienyl complexes.

Molecules of the form Cp(6,6-dmch)ZrX(2) (Cp = eta(5)-cyclopentadienyl, X = Cl, Br, I; 6,6-dmch = eta(5)-6,6-dimethylcyclohexadienyl) have been synthesized, and the molecular and electronic structures have been investigated. These molecules allow direct comparison of the bonding and properties of pentadienyl and cyclopentadienyl ligands in the same high-oxidation-state metal complexes. Unlike the well-known Cp(2)ZrX(2) analogues, these Cp(6,6-dmch)ZrX(2) molecules are intensely colored, indicating significantly different relative energies of the frontier orbitals. Also unusual, the average Zr-C distances to the 6,6-dmch pentadienyl ligand are about 0.1 A longer than the average Zr-C distances to the cyclopentadienyl ligand for these Zr(IV) complexes, opposite of what is observed for the Zr(II) complex Cp(2,6,6-tmch)Zr(PMe(3))(2) (tmch = eta(5)-2,6,6-trimethylcyclohexadienyl), reflecting a dramatic reversal in the favorability of the bonding depending on the metal oxidation state. The experimental and computational results indicate that the color of the Cp(6,6-dmch)ZrX(2) complexes is due to a 6,6-dmch ligand-to-metal charge-transfer band. Compared to the Cp(2)ZrX(2) analogues, the Cp(6,6-dmch)ZrX(2) molecules have a considerably less stable HOMO that is pentadienyl-based and an essentially unchanged metal-based LUMO. Also, the lowest unoccupied orbital of pentadienyl is stabilized relative to cyclopentadienyl and becomes a better potential delta electron acceptor, thus contributing to the differences in structure and reactivity of the low-valent and high-valent metal complexes.

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PubMed2005

The C-H activation of methane by laser-ablated zirconium atoms: CH2=ZrH2, the simplest carbene hydride complex, agostic bonding, and (CH3)2ZrH2.

Reaction of laser-ablated Zr with CH(4) ((13)CH(4), CD(4), and CH(2)D(2)) in excess neon during condensation at 5 K forms CH(2)=ZrH(2), the simplest alkylidene hydride complex, which is identified by infrared absorptions at 1581.0, 1546.2, 757.0, and 634.5 cm(-)(1). Density functional theory electronic structure calculations using a large basis set with polarization functions predict a C(1) symmetry structure with agostic C-H- - -Zr bonding and distance of 2.300 A. Identification of the agostic CH(2)=ZrH(2) methylidene complex is confirmed by an excellent match of calculated and observed isotopic frequencies particularly for the four unique CHD=ZrHD isotopic modifications. The analogous reactions in excess argon give two persistent photoreversible matrix configurations for CH(2)=ZrH(2). Finally, methane activation by CH(2)=ZrH(2) gives the new (CH(3))(2)ZrH(2) molecule.

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PubMed2004

Persistent photo-reversible transition-metal methylidene system generated from reaction of methyl fluoride with laser-ablated zirconium atoms and isolated in a solid argon matrix.

A photoreversible transition-metal methylidene system has been formed for the first time by reaction of methyl fluoride and laser-ablated Zr atoms, isolated in solid argon, and investigated by means of infrared spectroscopy. Four different groups of absorptions are characterized on the basis of behaviors upon broad-band irradiation and sample annealing. Growth of Group I is accompanied by demise of Group II on irradiation with visible light (lambda > 530 nm) and vice versa with UV light (240 < lambda < 380 nm). The methylidene complex CH(2)=ZrHF is responsible for Groups I and II either in different singlet-triplet spin states or argon matrix packing configurations. The ground singlet state is stabilized by an agostic interaction. On the other hand, Group III, which arises from the Grignard type compound CH(3)-ZrF, disappears upon irradiation of UV light (lambda > 380 nm), increasing the concentration of CH(2)=ZrHF by alpha-H elimination. Fragments of methyl fluoride such as the CH(2)F radical comprise Group IV. Theoretical calculations are carried out for the alkylidene complex and other plausible products, and the results are compared with the experimental frequencies.

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