Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ZIRCONIUM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed2000

Clustering of zirconium atoms in Zr5Te6: a novel NiAs-type-related telluride with ordered vacancies.

Zr5Te6 has been synthesized and its structure determined by means of single crystal X-ray diffraction to be trigonal, P3m1, Z=3, Pearson symbol hP33, a = 1172.8(2) pm, c = 707.0(1) pm. Zr5Te6 adopts a metal-deficient, vacancy-ordered 3a x 3a x 1c superstructure of the NiAs type structure. In the Zr atom layers, alternately one and two out of nine Zr atoms are missing. The less densely populated layers (7/9) consist of star-shaped Zr7 clusters with intracluster contacts of 351.1 pm; the shortest Zr-Zr intercluster distance is 470.5 pm. In the more densely populated Zr atom layers (8/9), three quarters of the Zr atoms are arranged to pairs (326.4 pm). The distinctive distribution of the vacancies affords a topologically uniform fivefold Zr coordination (283.5 - 302.6 pm) for all three crystallographically inequivalent Te atoms. They are shifted towards the vacancies in the Zr atom layers. The associated corrugation of the Te atom layers is characterized by an amplitude of 28 pm. The Te-Te contacts are > or =368.1 pm. According to extended Hückel calculations, the defects in the Zr atom layers lead to a reduction in overall Zr-Te bonding interactions relative to ZrTe (NiAs). However, through the clustering the total attractive intralayer Zr-Zr interactions increase considerably, thus providing decisive stabilization of the structure. As revealed by thermal analyses, Zr5Te6 undergoes a reversible phase transition at 1,513 +/- 5 K. On the Zr-rich side, Zr5Te6 coexists with ZrTe (WC), and, above 1,438 +/- 5 K with the hitherto unknown ZrTe (MnP). Zr5Te6 exhibits temperature independent paramagnetic properties (chimol = 0.7 x 10(-3) cm3 mol(-1)) that are typical for a metallic conductor. An abrupt increase in the magnitude of the diamagnetic susceptibility below 2.2 K in a weak magnetic field indicates a superconducting transition.

Journal Article↗
PubMed2003

Formation of dinuclear titanium and zirconium complexes by olefin metathesis--catalytic preparation of organometallic catalyst systems.

The titanium complex [(C(5)H(4)bond;allyl)TiCl(3)] (2) undergoes olefin metathesis coupling when treated with 3 mol % of [Cl(2)(L(1))(L(2))Ru=CHPh] (L(1)=L(2)=PCy(3), 4 a; L(1)=PCy(3), L(2)=(H(2)IMes), 4 b) to yield the dimetallic complex [Cl(3)Ti(C(5)H(4))-CH(2)CH=CHCH(2)-(C(5)H(4))TiCl(3)] (5). The allyl-substituted titanocene complex [Cp(C(5)H(4)bond;allyl)TiCl(2)] (3) analogously yields the dimetallic system 6 when treated with 4. The ansa-zirconocene complex [Me(2)Si(C(5)H(4))(C(5)H(3)bond;allyl)ZrCl(2)] (7) cleanly yields the analogous dimetallic coupling product 8 (>95 % isomerically pure), when treated with catalytic amounts of 4 b in toluene. Complex 8 gives an active homogeneous ethene or propene polymerization catalyst, especially at elevated temperatures, when treated with excess methylalumoxane.

Journal Article↗
PubMed2004

Titanium(IV) and zirconium(IV) sulfato complexes containing the Kläui tripodal ligand: molecular models of sulfated metal oxide surfaces.

Treatment of titanyl sulfate in about 60 mM sulfuric acid with NaL(OEt) (L(OEt) (-)=[(eta(5)-C(5)H(5))Co{P(O)(OEt)(2)}(3)](-)) afforded the mu-sulfato complex [(L(OEt)Ti)(2)(mu-O)(2)(mu-SO(4))] (2). In more concentrated sulfuric acid (>1 M), the same reaction yielded the di-mu-sulfato complex [(L(OEt)Ti)(2)(mu-O)(mu-SO(4))(2)] (3). Reaction of 2 with HOTf (OTf=triflate, CF(3)SO(3)) gave the tris(triflato) complex [L(OEt)Ti(OTf)(3)] (4), whereas treatment of 2 with Ag(OTf) in CH(2)Cl(2) afforded the sulfato-capped trinuclear complex [{(L(OEt))(3)Ti(3)(mu-O)(3)}(mu(3)-SO(4)){Ag(OTf)}][OTf] (5), in which the Ag(OTf) moiety binds to a mu-oxo group in the Ti(3)(mu-O)(3) core. Reaction of 2 in H(2)O with Ba(NO(3))(2) afforded the tetranuclear complex (L(OEt))(4)Ti(4)(mu-O)(6) (6). Treatment of 2 with [{Rh(cod)Cl}(2)] (cod=1,5-cyclooctadiene), [Re(CO)(5)Cl], and [Ru(tBu(2)bpy)(PPh(3))(2)Cl(2)] (tBu(2)bpy=4,4'-di-tert-butyl-2,2'-dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(L(OEt))(2)Ti(2)(O)(2)(SO(4)){Rh(cod)}(2)][OTf](2) (7), [(L(OEt))(2)Ti(O)(2)(SO(4)){Re(CO)(3)}][OTf] (8), and [{(L(OEt))(2)Ti(2)(mu-O)}(mu(3)-SO(4))(mu-O)(2){Ru(PPh(3))(tBu(2)bpy)}][OTf](2) (9), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 mu(B). Treatment of zirconyl nitrate with NaL(OEt) in 3.5 M sulfuric acid afforded [(L(OEt))(2)Zr(NO(3))][L(OEt)Zr(SO(4))(NO(3))] (10). Reaction of ZrCl(4) in 1.8 M sulfuric acid with NaL(OEt) in the presence Na(2)SO(4) gave the mu-sulfato-bridged complex [L(OEt)Zr(SO(4))(H(2)O)](2)(mu-SO(4)) (11). Treatment of 11 with triflic acid afforded [(L(OEt))(2)Zr][OTf](2) (12), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{L(OEt)Zr(SO(4))(H(2)O)}(3)(mu(3)-SO(4))][OTf] (13). The Zr(IV) triflato complex [L(OEt)Zr(OTf)(3)] (14) was prepared by reaction of L(OEt)ZrF(3) with Me(3)SiOTf. Complexes 4 and 14 can catalyze the Diels-Alder reaction of 1,3-cyclohexadiene with acrolein in good selectivity. Complexes 2-5, 9-11, and 13 have been characterized by X-ray crystallography.

Journal Article↗
PubMed2005

Zirconium bis(indenyl) sandwich complexes with an unprecedented indenyl coordination mode and their role in the reactivity of the parent bent-metallocenes: a detailed DFT mechanistic study.

The mechanisms of three closely related reactions were studied in detail by means of DFT/B3 LYP calculations with a VDZP basis set. Those reactions correspond to 1) the reductive elimination of methane from [Zr(eta5-Ind)2(CH3)(H)] (Ind=C9H7-, indenyl), 2) the formation of the THF adduct, [Zr(eta5-Ind)(eta6-Ind)(thf)] and 3) the interconversion between the two indenyl ligands in the Zr sandwich complex, [Zr(eta5-Ind)(eta9-Ind)], which forms the link between the two former reactions. An analysis of the electronic structure of this species indicates a saturated 18-electron complex. A full understanding of the indenyl interchange process required the characterisation of several isomers of the Zr-bis(indenyl) species, corresponding to different spin states (S=0 and S=1), different coordination modes of the two indenyl ligands (eta5/eta9, eta5/eta5 and eta6/eta9), and three conformations for each isomer (syn, anti, and gauche). The fluxionality observed was found to occur in a mechanism involving bis(eta5-Ind) intermediates, and the calculated activation energy (11-14 kcal mol(-1)) compares very well with the experimental values. Two alternative mechanisms were explored for the reductive elimination of methane from the methyl/hydride complex. In the more favourable one, the initial complex, [Zr(eta5-Ind)2(CH3)(H)], yields [Zr(eta5-Ind)2] and methane in one crucial step, followed by a smooth transition of the Zr intermediate to the more stable eta5/eta9-species. The overall activation energy calculated (Ea=29 kcal mol(-1)) compares well with experimental values for related species. The formation of the THF adduct follows a one step mechanism from the appropriate conformer of the [Zr(eta5-Ind)(eta9-Ind)] complex, producing easily (Ea=6.5 kcal mol(-1)) the known product, [Zr(eta5-Ind)(eta6-Ind)(thf)], a species previously characterised by X-ray crystallography. This complex was found to be trapped in a potential well that prevents it from evolving to the 3.4 kcal mol(-1) more stable isomer, [Zr(eta5-Ind)2(thf)], with both indenyl ligands in a eta5-coordination mode and a spin-triplet state (S=1).

Journal Article↗
PubMed2002

Detection of zirconium in organic and aqueous phases using an inductively coupled plasma-mass spectrometer and the same aqueous standards.

Solvent extraction requires measurement of both aqueous and organic phases, and common techniques of such measurements are tedious and time consuming. This paper outlines an inductively coupled plasma-mass spectrometric technique in which both aqueous and organic phases (both contained in a carrier phase, ethanol) can be measured using the same calibration curve. The method has proved to be successful as long as the organic and aqueous content in the carrier phase is kept below 10%. The developed technique is a more convenient tool for solvent extraction chemists who have often used radioactive tracers within their experimental techniques. In addition, this technique may be used in environmental studies involving the analysis of organic fractions, such as metal fingerprinting of petroleum fluids. In such analyses, the ability to use more available and traceable aqueous standards will lead to significantly improved confidence in the analytical results.

Journal Article↗