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Robert T Paine

Publications and source records attributed to Robert T Paine.

11 recordsLinked to original sources
PubMed2006

Synthesis and lanthanide coordination properties of new 2,6-bis(N-tert-butylacetamide)pyridine and 2,6-bis(N-tert-butylacetamide)pyridine-N-oxide ligands.

The compound 2,6-bis(N-tert-butylacetamide)pyridine (2) was obtained via a Ritter synthesis, and oxidation with oxone provided the title pyridine-N-oxide (3). The compounds were characterized by spectroscopic methods, and the molecular structure of the N-oxide was determined by single-crystal X-ray diffraction methods. The coordination chemistry with Eu(NO3)3 was examined by using 1:1 and 2:1 ligand/Eu ratios, and a single-crystal X-ray analysis for Eu(3)(NO3)3(H2O) was completed. The ligand 3 is found to chelate in a tridentate fashion on the Eu(III).

Journal Article↗
PubMed2006

Formation of a layered framework structure based upon 4-methyl-2,6-bis(methylphosphonic acid) phenol.

The trifunctional ligands, [(HO)2P(O)CH2]2C6H2(R)OH, (5-H4)(R = CH3, Br) were prepared in good yield via an Arbusov reaction between P(OEt)3 and the respective 4-R-2,6-bis(chloromethyl)phenols followed by acidic aqueous hydrolysis and they were spectroscopically characterized by IR and NMR techniques. The ligand 5-H4-CH3 readily dissolves lanthanide hydroxide residues and it forms a crystalline complex from aqueous LaCl3 solutions. This complex was characterized by single crystal X-ray diffraction methods and found to adopt a complex 2-D lamellar network in the bc plane. The La(III) inner coordination sphere is seven coordinate formed by oxygen atoms from two water molecules and five phosphonate oxygen atoms from three different ligands. The phenolic oxygen atom is not involved in the ligand binding to La(III).

Journal Article↗
PubMed2006

A three-dimensional framework structure constructed from 2-(2-pyridyl-N-oxide) ethylphosphonic acid and Nd(III).

A multistep synthesis for 2-(2-pyridyl-N-oxide) ethylphosphonic acid 6-H2 is described along with its spectroscopic (IR, NMR) data and a single-crystal X-ray diffraction structure analysis. Combination of the ligand with Nd(OH)3 results in the formation of a complex Nd(6-H)3. Single-crystal X-ray diffraction analysis reveals a three-dimensional crystal network generated by hydrogen-bonded chains along the crystallographic c axis. The hydrogen bonds are formed between phosphonic acid anion (6-H)(-1) protons on one chain and pyridyl N-oxide oxygen atoms in neighboring chains. The asymmetric unit contains 1/3[Nd(6-H)3] and there are two unique Nd(III) atoms, each with point symmetry. As a result, each Nd(III) ion is bound to six (6-H)(-1) ligands and the symmetry about the Nd(III) ion is octahedral with each vertex occupied by a phosphonate oxygen atom. The Nd-O bond lengths are essentially identical: Nd(1)-O(3), 2.336 (1) A; Nd(2)-O(4), 2.340 (1) A. The monoanionic ligand (6-H)(-1), therefore, serves to bridge the unique Nd(III) centers.

Journal Article↗
PubMed2004

Hydrogen bonded framework structures constructed from 2-(pyridyl N-oxide) methylphosphonic acid ligands and erbium(III).

Syntheses for 2-(pyridyl N-oxide) methylphosphonic acid, 1-H, and 2-(pyridyl N-oxide) hydroxymethylphosphonic acid, 4-H, are described, and the crystal structures of both ligands are presented. Combination of these ligands with freshly prepared erbium hydroxide results in the formation of the isostructural complexes Er(L(-))(3)(LH).8H(2)O. The crystal structure determinations of the complexes show that extensive hydrogen bonding links the individual eight coordinate Er(L(-))(3)(LH) molecular units into a 3-D structure.

Journal Article↗
PubMed2002

Features of the thermodynamics of two-phase distribution reactions of americium(III) and europium(III) nitrates into solutions of 2,6-bis[(bis(2-ethylhexyl)phosphino)methyl]pyridine N,P,P'-trioxide.

New bifunctional and trifunctional organophosphorus ligands, 2-[(bis(2-ethylhexyl)phosphino)methyl]pyridine N,P-dioxide, DEH(MNOPO), and 2,6-bis[(bis(2-ethylhexyl)phosphino)methyl]pyridine N,P,P'-trioxide, TEH(NOPOPO), have been synthesized. In contrast with previously reported phenyl derivatives, the increased solubility of these ligands in normal paraffinic hydrocarbon solvents make them attractive reagents for actinide partitioning. While the bifunctional reagent DEH(MNOPO) interacts with Eu(3+) and Am(3+) comparatively weakly, the trifunctional TEH(NOPOPO) exhibits moderate to high ability to transfer the trisnitrato complexes of these ions into n-dodecane from acidic aqueous solutions. We report here the details of TEH(NOPOPO) and DEH(MNOPO) preparation and of their ability to extract HNO(3), Am(NO(3))(3), and Eu(NO(3))(3) into paraffinic hydrocarbons. The trifunctional TEH(NOPOPO) can extract up to two molecules of HNO(3). The dominant extracted species for both Am(NO(3))(3) and Eu(NO(3))(3) has two TEH(NOPOPO) ligands associated over the range of temperatures 10-40 degrees C. From the variation in the equilibrium coefficients for the phase transfer reactions as a function of temperature, we have calculated the enthalpies and entropies for extraction of HNO(3), Am(NO(3))(3), and Eu(NO(3))(3) into n-dodecane. Each metal nitrate is transferred into the organic phase in an exothermic process but opposed by an unfavorable (negative) entropy. The thermodynamic data are interpreted to indicate that the pyridine N-oxide is apparently a significantly weaker donor group for these metal ions than the phosphine oxides.

Journal Article↗
PubMed2002

Steric control of substituted phenoxide ligands on product structures of uranyl aryloxide complexes.

A series of uranyl aryloxide complexes has been prepared via metathesis reactions between [UO(2)Cl(2)(THF)(2)](2) and di-ortho-substituted phenoxides. Reaction of 4 equiv of KO-2,6-(t)()Bu(2)C(6)H(3) with [UO(2)Cl(2)(THF)(2)](2) in THF produces the dark red uranyl compound, UO(2)(O-2,6-(t)()Bu(2)C(6)H(3))(2)(THF)(2).THF, 1. Single-crystal X-ray diffraction analysis of 1 reveals a monomer in which the uranium is coordinated in a pseudooctahedral fashion by two apical oxo groups, two cis-aryloxides, and two THF ligands. A similar product is prepared by reaction of KO-2,6-Ph(2)C(6)H(3) with [UO(2)Cl(2)(THF)(2)](2) in THF. Single-crystal X-ray diffraction analysis of this compound reveals it to be the trans-monomer UO(2)(O-2,6-Ph(2)C(6)H(3))(2)(THF)(2), 2. Dimeric structures result from the reactions of [UO(2)Cl(2)(THF)(2)](2) with less sterically imposing aryloxide salts, KO-2,6-Cl(2)C(6)H(3) or KO-2,6-Me(2)C(6)H(3). Single-crystal X-ray diffraction analyses of [UO(2)(O-2,6-Cl(2)C(6)H(3))(2)(THF)(2)](2), 3, and [UO(2)Cl(O-2,6-Me(2)C(6)H(3))(THF)(2)](2), 4, reveal similar structures in which each U atom is coordinated by seven ligands in a pseudopentagonal bipyramidal fashion. Coordinated to each uranium are two apical oxo groups and five equatorial ligands (3, one terminal phenoxide, two bridging phenoxides, and two nonadjacent terminal THF ligands; 4, one terminal chloride, two bridging phenoxides, and two nonadjacent terminal THF ligands). Apparently, the phenoxide ligand steric features exert a greater influence on the solid-state structures than the electronic properties of the substituents. Emission spectroscopy has been utilized to investigate the molecularity and electronic structure of these compounds. For example, luminescence spectra taken at liquid nitrogen temperature allow for a determination of the dependence of the molecular aggregation of 3 on the molecular concentration. Electronic and vibrational spectroscopic measurements have been analyzed to examine trends in emission energies and stretching frequencies. However, comparison of the data for compounds 1-4 reveals that the innate electron-donating capacity of phenoxide ligands is only subtly manifest in either the electronic or vibrational energy distributions within these molecules.

Journal Article↗
PubMed2002

Trophic control of production in a rocky intertidal community.

In the low intertidal zone at Tatoosh Island, Washington, United States, minimal estimates of primary production can vary from 0 to an average of 86 kilograms of wet mass per square meter per year when the grazing assemblage is manipulated. Highly productive annual kelps (Laminariales) replace less productive perennial species when macroscopic grazers are reduced or absent, resulting in monodominant assemblages of Alaria marginata. Experiments were repeated in seven consecutive years. Increased species richness makes no significant additional contribution to annual production. Rather, a competitively superior species is favored when its enemies are reduced, suggesting that terrestrial perspectives on the role of biodiversity that are developed without considering consumers may not be general.

Animals↗