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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

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

[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

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 & Hellner, Erwin
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

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

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

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

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

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

Platinum Group Thiophenoxyimine Complexes: Syntheses,Crystallographic and Computational Studies of Structural Properties

Description: Monomeric thiosalicylaldiminate complexes of rhodium(I) and iridium(I) were prepared by ligand transfer from the homoleptic zinc(II) species. In the presence of strongly donating ligands, the iridium complexes undergo insertion of the metal into the imine carbon-hydrogen bond. Thiophenoxyketimines were prepared by non-templated reaction of o-mercaptoacetophenone with anilines, and were complexed with rhodium(I), iridium(I), nickel(II) and platinum(II). X-ray crystallographic studies showed that while the thiosalicylaldiminate complexes display planar ligand conformations, those of the thiophenoxyketiminates are strongly distorted. Results of a computational study were consistent with a steric-strain interpretation of the difference in preferred ligand geometries.
Date: October 3, 2006
Creator: Krinsky, Jamin L.; Arnold, John & Bergman, Robert G.
Partner: UNT Libraries Government Documents Department

Uranium (VI)Bis(imido) chalcogenate complexes:synthesis and density functional theory analysis

Description: Bis(imido) uranium(VI) trans- and cis-dichalcogenate complexes with the general formula U(NtBu)2(EAr)2(OPPh3)2 (EAr = O-2-tBuC6H4, SPh, SePh, TePh) and U(NtBu)2(EAr)2(R2bpy) (EAr = SPh, SePh, TePh) (R2bpy = 4,4'-disubstituted-2,2'-bipyridyl, R = Me, tBu) have been prepared. This family of complexes includes the first reported monodentate selenolate and tellurolate complexes of uranium(VI). Density functional theory calculations show that covalent interactions in the U-E bond increase in the trans-dichalcogenate series U(NtBu)2(EAr)2(OPPh3)2 as the size of the chalcogenate donor increases and that both 5f and 6d orbital participation is important in the M-E bonds of U-S, U-Se, and U-Te complexes.
Date: January 1, 2009
Creator: Spencer, Liam P; Batista, Enrique R; Boncella, James M; Yang, Ping & Scott, Brian L
Partner: UNT Libraries Government Documents Department

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

Vancouver Library Square

Description: The view shows a detail of the colonnaded elliptical wall that resembles Rome's Colosseum.
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

Vancouver Library Square

Description: The upward raking view shows the facade detail of engaged columns and square insets.
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

Vancouver Library Square

Description: The close detail view shows the separation of the free standing outer wall and the rest of the building.
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