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Actinide complexation kinetics: rate and mechanism of dioxoneptunium (V) reaction with chlorophosphonazo III

Description: Rates of complex formation and dissociation in NpO{sub 2}{sup +}- Chlorophosphonazo III (2,7-bis(4-chloro-2-phosphonobenzeneazo)-1,8- dihydroxynapthalene-3,6-disulfonic acid)(CLIII) were investigated by stopped-flow spectrophotometry. Also, limited studies were made of the rates of reaction of La{sup 3+}, Eu{sup 3+}, Dy{sup 3+}, and Fe{sup 3+} with CLIII. Rate determining step in each system is an intramolecular process, the NpO{sub 2}{sup +}-CLIII reaction proceeding by a first order approach to equilibrium in the acid range from 0.1 to 1.0 M. Complex formation occurs independent of acidity, while both acid dependent and independent dissociation pathways are observed. Activation parameters for the complex formation reaction are {Delta}H=46.2{+-}0.3 kJ/m and {Delta}S=7{+-} J/mK (I=1.0 M); these for the acid dependent and independent dissociation pathways are {Delta}H=38.8{+-}0.6 kJ/m, {Delta}S=-96{+-}18 J/mK, {Delta}H=70.0{+-} kJ/m, and {Delta}S=17{+-}1 J/mK, respectively. An isokinetic relationship is observed between the activation parameters for CLIII complex formation with NpO{sub 2}{sup +}, UO{sub 2}{sup 2+}, Th{sup 4+}, and Zr{sup 4+}. Rates of CLIII complex formation reactions for Fe{sup 3+}, Zr{sup 4+}, NpO{sub 2}{sup +}, UO{sub 2}{sup 2+}, Th{sup 4+}, La{sup 3+}, Eu{sup 3+}, and Dy{sup 3+} correlate with cation radius rather than charge/radius ratio.
Date: December 1, 1996
Creator: Fugate, G.; Feil-Jenkins, J.F.; Sullivan, J.C. & Nash, K.L.
Partner: UNT Libraries Government Documents Department

Thermodynamics, Kinetics, and Mechanism of (silox)3M(olefin) to (silox)3M(alkylidene) Rearrangements (silox = tBu3SiO; M = Nb, Ta)

Description: Article discussing the thermodynamic, kinetic, and mechanism of (silox)3M(olefin) to (silox)3M(alkylidene) rearrangements (silox = tBu3SiO; M = Nb, Ta).
Date: March 10, 2005
Creator: Hirsekorn, Kurt F.; Veige, Adam S.; Marshak, Michael P.; Koldobskaya, Yelena; Wolczanski, Peter T.; Cundari, Thomas R., 1964- et al.
Partner: UNT College of Arts and Sciences

[White Buildings]

Description: Photograph of three adjoining white buildings in Mexico. The buildings are visible in the center of the frame. Each building has an open arched passageway in the front of the building. Some trees intersect the buildings in the foreground. Behind the white buildings, other complexes are visible amongst the surrounding greenery.
Date: unknown
Creator: Gough, Ray
Partner: UNT College of Visual Arts + Design

THE CRYSTAL STRUCTURE OF RbU$sub 6$F$sub 2$$sub 5$

Description: The compound RbU/sub 6/F/sub 25/ has a hexagonal crystal structure with the parameters a/sub o/ = 8.195 plus or minus 0.002 A and c/sub o/ = 16.437 plus or minus 0.002 A. This compound is believed to be isomorphous to KU/sub 6/F/sub 25/ and KTh/sub 6/F/sub 25/. (auth) uranium hexafluoride -chlorine trifluoride -hydrogen fluoride from a knowledge of the behavior of the three binary systems. The conditions under which chlorine trifluoride and hydrogen fluoride could be removed from uranium hexafluoride by fractional distillation are discussed. (auth)
Date: May 15, 1958
Creator: Harris, L.A.
Partner: UNT Libraries Government Documents Department

Space Groups and Lattice Complexes

Description: From Abstract: "The lattice complex is to the space group what the site is to the point group - an assemblage of symmetry-related equivalent points. The Tables list site sets and lattice complexes in standard and alternate representation. The higher the symmetry of the crystal structures is, the more useful the lattice-complex approach should be on the road to the ultimate goal their classification."
Date: May 1973
Creator: Fisher, Werner; Burzlaff, Hans; Hellner, Erwin & Donnay, J. D. H.
Partner: UNT Libraries Government Documents Department

Vancouver Library Square

Description: The street side retail elevation of the curved portion of the elliptical wall is visible in this view.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: 1992/1995
Creator: Safdie, Moshe
Location Info:
Partner: UNT College of Visual Arts + Design

Photochemical activation and reactivity of polynuclear transition metal complex molecules. Progress report, June 1979-May 31, 1980

Description: During this contract year several new ligands and binuclear metal complexes have been prepared including many that can be expected to exhibit long-lived excited states. The metal ions represented are Cu(II), Ni(II), Co(II), Mn(II), Cr(III), Ti(IV), V(IV), U(VI), and Pd(II). In addition, many mononuclear complexes that are precursors in the formation of heterobinuclear complexes were prepared. These include complexes of Cu(II), Ni(II), Pd(II), and Ru(II). Many of these compounds will be used in photochemical and electron transfer studies. Polarographic, cyclic voltammetric and coulometric studies have been carried out on a number of binuclear Cu(II) triketonates and their Schiff-base derivatives. Most of these compounds undergo reversible or quasi-reversible two electron transfer reactions which makes them potetially useful electron transfer reagents. Much of the electrochemical data can be rationalized by the formation of dimers which are new electroactive species. The importance of such species in multi-electron transfer processes is being investigated.
Date: February 1, 1980
Creator: Endicott, J.F. & Lintvedt, R.L.
Partner: UNT Libraries Government Documents Department

[Group transfer and electron transfer reactions of organometallic complexes]: Summary of research accomplished in 1993

Description: In the past year the research on mechanisms of electron transfer processes between organometallic complexes has continued to progress with emphasis on two electron processes and on reactions of organometallic radicals. This summary will highlight the research on: (1) halide transfer reactions, (2) alkyl and acyl transfer reactions and (3) reactions of seventeen-electron organometallic complexes. At this point some conclusions on the transfer of hydrogen, halogen and methyl as the cation, radical and anion can be made. For each group, transfer as the cation is more facile. For hydrogen, transfer as the hydride is considerably slower, but H{center_dot} transfers nearly as rapidly as H{sup +}. Methyl could be transferred as CH{sub 3}{sup +} or CH{sub 3}{sup {minus}}, but not as the radical. Halogens transfer readily as X{sup +}, more slowly as X{center_dot} and not at all as X{sup {minus}}.
Date: December 31, 1993
Partner: UNT Libraries Government Documents Department

Base- and Precious-Metal Concentrations of Early Proterozoic Massive Sulfide Deposits in Arizona- Crustal and Thermochemical Controls of Ore Deposition

Description: A report about early proterozoic massive sulfide deposits associated with submarine mafic to felsic metavolcano rocks are present throughout central, west-central, and northwestern Arizona. Also, production data for copper, lead, zinc, gold, and silver for most of the known deposits and prospects in 13 metallic mineral districts are summarized.
Date: 1995
Creator: DeWitt, Ed
Partner: UNT Libraries Government Documents Department

Solvent and Ionic Complexes of the Calix[6]arenes

Description: One of the more attractive attributes of calixarenes is their wide variety of possible conformations and hence cavity shapes. However, the flexibility that allows this long-range benefit gives rise to major synthetic challenges when working with the larger members of the family. O-alkylations have proven to be the most widely employed synthetic routes to "functionalization" of the calixarenes, and these have shown a dependence upon both solvent and the metal ions present. Surprisingly, there have been no structural data presented concerning the complexes between the simple unsubstituted calix[6]arenes and the metal ions of groups 1 and 2. The structures of four complexes, containing cesium, rubidium, and calcium are reported as determined by X-ray crystallography. The solution behavior of the complexes for both representative groups is also discussed, in particular with regard to conformational stabilization of the calix[6]arenes and the role of solvent upon this stabilization. These complexes are also investigated as starting materials for the selective functionalization of the calix[6]arenes.
Date: December 1997
Creator: Wolfgong, William J.
Partner: UNT Libraries

Interplay of metal-allyl and metal-metal bonding in dimolybdenum allyl complexes

Description: Addition of PMe{sub 3} to Mo{sub 2}(allyl){sub 4} afforded Mo{sub 2}(allyl){sub 4}(PMe{sub 3}){sub 2}, in which two of the allyl groups adopt an unprecedented {mu}{sub 2{sup -}}{eta}{sup 1}, {eta}{sup 3} bonding mode; theoretical studies elucidate the role sof the {sigma}- and {pi}-donor ligands in the interplay of metal-allyl and metal-metal bonding.
Date: January 1, 2008
Creator: John, Kevin D; Martin, Richard L; Obrey, Steven J & Scott, Brian L
Partner: UNT Libraries Government Documents Department

Reactions of a Ru(II) Phenyl Complex with Substrates that Possess C-N or C-O Multiple Bonds: C-C Bond Formation, N-H Bond Cleavage, and Decarbonylation Reactions

Description: Article on the reactions of an Ru(II) phenyl complex with substrates that possess C-N or C-O multiple bonds and C-C bond formation, N-H bond cleavage, and decarbonylation reactions.
Date: February 8, 2006
Creator: Lee, John P.; Pittard, Karl A.; DeYonker, Nathan J.; Cundari, Thomas R., 1964-; Gunnoe, T. Brent & Petersen, Jeffrey L.
Partner: UNT College of Arts and Sciences

Low-Coordinate Chromium Siloxides: The "Box" [Cr(μ-OSitBu3)]4, Distorted Trigonal [(tBu3SiO)3Cr] [Na(benzene)] and [(tBu3SiO)3Cr] [Na(dibenzo-18-c-6)], and Trigonal (tBu3SiO)3Cr

Description: Article discussing low-coordinate chromium siloxides and the "box" [Cr(μ-Cl)(μ-OSiᵗBu₃)]₄, distorted trigonal [(ᵗBu₃SiO)₃Cr][Na(benzene)] and [(ᵗBu₃SiO)₃Cr][Na(dibenzo-18-c-6)], and trigonal (ᵗBu₃SiO)₃Cr.
Date: March 24, 2005
Creator: Sydora, Orson L.; Wolczanski, Peter T.; Lobkovsky, Emil B.; Buda, Corneliu & Cundari, Thomas R., 1964-
Partner: UNT College of Arts and Sciences

Studies of Low-Coordinate Iron Dinitrogen Complexes

Description: This article discusses low-coordinate iron dinitrogen complexes. Understanding the interaction of N₂ with iron is relevant to the iron catalyst used in the Haber process and to possible roles of the FeMoco active site of nitrogenase.
Date: December 31, 2005
Creator: Smith, Jeremy M.; Sadique, Azwana R.; Cundari, Thomas R., 1964-; Rodgers, Kenton R.; Lukat-Rodgers, Gudrun; Lachicotte, Rene J. et al.
Partner: UNT College of Arts and Sciences

Small Molecule Elimination from Group IVB (Ti, Zr, Hf) Amido Complexes

Description: This article discusses small molecule elimination from group IVB (Ti, Zr, Hf) amido complexes. An ab initio quantum chemical analysis of HX (X = H, CH₃, Cl, NH₂, SiH₃) elimination by group IVB (Ti, Zr, Hf) amidos (H₂(X)M - NH₂ → H₂M = NH + HX), of interest in the context of CVD precursor design, is reported.
Date: May 1993
Creator: Cundari, Thomas R., 1964- & Gordon, Mark S.
Partner: UNT College of Arts and Sciences