Two members of the tetradentate N-donor ligand families 6,6'-bis(1,2,4-triazin-3-yl)-2,2'-bipyridine (BTBP) and 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen) currently being developed for separating actinides from lanthanides have been studied. It has been confirmed that CyMe4-BTPhen 2 has faster complexation kinetics than CyMe4-BTBP 1. The values for the HOMO-LUMO gap of 2 are comparable with those of CyMe4-BTBP 1 for which the HOMO-LUMO gap was previously calculated to be 2.13 eV. The displacement of BTBP from its bis-lanthanum(III) complex by BTPhen was observed by NMR, and constitutes the only direct evidence for the greater thermodynamic stability of the complexes of BTPhen. NMR competition experiments suggest the following order of bis-complex stability: 1:2 bis-BTPhen complex ≥ heteroleptic BTBP/BTPhen 1:2 bis-complex > 1:2 bis-BTBP complex. Kinetics studies on some bis-triazine N-donor ligands using the stopped-flow technique showed a clear relationship between the rates of metal ion complexation and the degree to which the ligand is preorganized for metal binding. The BTBPs must overcome a significant (ca. 12 kcal mol(-1)) energy barrier to rotation about the central biaryl C-C axis in order to achieve the cis-cis conformation that is required to form a complex, whereas the cis-cis conformation is fixed in the BTPhens. Complexation thermodynamics and kinetics studies in acetonitrile show subtle differences between the thermodynamic stabilities of the complexes formed, with similar stability constants being found for both ligands. The first crystal structure of a 1:1 complex of CyMe4-BTPhen 2 with Y(NO3)3 is also reported. The metal ion is 10-coordinate being bonded to the tetradentate ligand 2 and three bidentate nitrate ions. The tetradentate ligand is nearly planar with angles between consecutive rings of 16.4(2)°, 6.4(2)°, 9.7(2)°, respectively.

A series of novel redox-active and photoactive ruthenium(II) and osmium(II) bipyridyl-, ferrocene-, and cobaltocenium-containing macrocyclic receptors with the dual capability of selectively sensing anionic guest species via electrochemical and optical methodologies have been prepared. Single-crystal X-ray structures of 7·Cl-, 7·2Br-, and 13·2OAc- highlight the importance of hydrogen bonding and respective macrocyclic cavity size to the anion recognition process in the solid state. Proton NMR titration studies in deuterated DMSO solutions reveal these receptors form strong and remarkably selective complexes with Cl-, H2PO4 -, and OAc- anions dependent upon the flexibility, topology, and size of the receptor cavity. Cyclic and square-wave voltammetric investigations have demonstrated these receptors to electrochemically recognize Cl-, H2PO4 -, and OAc- anions. Photophysical studies reveal emission spectral recognition of Cl- in acetonitrile solutions is displayed by 7−12. With the hetero-dinuclear receptors 8, 9, and 12, the rate constants of the energy transfer process responsible for the quenching of the luminescent ruthenium excited state significantly decreased in the presence of chloride anion.

Phenyl-substituted derivatives of 2,2Ј : 6Ј,2Љ-terpyridine and a corresponding bipyridine-pyrazine derivative have been shown to have metal extraction properties and separation factors for americium() over europium() which are comparable to those previously obtained for 2,2Ј : 6Ј,2Љ-terpyridine (L 1 ). The extracting agents in either tertbutylbenzene (TBB) or hydrogenated tetrapropene (TPH) gave D Am /D Eu separation factors (SFs) between 7 and 9 when used to extract the metal ions from 0.01-0.1 M nitric acid solution in synergistic combination with 2-bromodecanoic acid. In contrast to L 1 , the new hydrophobic ligands have little or no solubility in the aqueous phase. In an effort to better understand the nature of the species which may be involved in the extraction process, a series of metal-L 1 complexes which cover the lanthanides have been prepared. Five different structural types have been established for the lanthanide coordination complexes. In type 1,, the metal is 10-coordinate being bonded to one terdentate L 1 ligand, three bidentate nitrates and a water molecule. In type 2,Tb, Dy and Ho), the metal atom in the cation is 10-coordinate, being bonded to two terdentate L 1 ligands and two bidentate nitrates; in the anion the metal is also 10-coordinate, being bonded to one terdentate L 1 ligand and four nitrates, of which three are bidentate and one unidentate. In type 3, [M(NO 3 ) 3 (L 1 )(H 2 O)]ؒL 1 (M = Ho, Er, Tm and Yb), the metal is 10-coordinate, being bonded to three bidentate nitrates, one terdentate L 1 and a water molecule. In addition, an L 1 ligand is found in the asymmetric unit which is hydrogen-bonded to the coordinated water molecule. In type 4, [M(NO 3 ) 3 (L 1 )(H 2 O)] (M = Tm), the metal is 9-coordinate, being bonded to two bidentate nitrates, one unidentate nitrate, one terdentate L 1 ligand and a water molecule. In type 5, [M(NO 3 ) 3 (L 1 )] (M = Yb), the metal is 9-coordinate, being bonded to three bidentate nitrates and one terdentate L 1 ligand. A sixth structural type was observed for M = La in the crystal structureThe metal is not bound to L 1 but instead forms the well-known hexanitrate anion. This complex may give some indication of the type of species which could be formed at higher acid concentrations in the aqueous phase, where protonation of L 1 can occur.

The Lewis acidic redox-active and photoactive ruthenium(II) bipyridyl moiety in combination with amide (CO−NH) groups has been incorporated into acyclic, macrocyclic, and lower rim calix[4]arene structural frameworks to produce a new class of anion receptor with the dual capability of sensing anionic guest species via electrochemical and optical methodologies. Single-crystal X-ray structures of (1)Cl and (11)H2PO4 reveal the importance of hydrogen bonding to the overall anion complexation process. In the former complex, six hydrogen bonds (two amide and four C−H groups) stabilize the Cl- anion and three hydrogen bonds (two amide and one calix[4]arene hydroxyl) effect H2PO4 - complexation with 11. Proton NMR titration investigations in deuterated DMSO solutions reveal these receptors form strong and, in the case of the macrocyclic 5 and calix[4]arene-containing receptor 11, highly selective complexes with H2PO4 -. Cyclic and square-wave voltammetric studies have demonstrated these receptors to electrochemically recognize Cl-, Br-, H2PO4 -, and HSO4 - anions. The calix[4]arene anion receptor 11 selectively electrochemically senses H2PO4 - in the presence of 10-fold excess amounts of HSO4 - and Cl-. Fluorescence emission spectral recognition of H2PO4 - in DMSO solutions is displayed by 3, 5, and 11.

New hydrophobic, tetradentate nitrogen heterocyclic reagents, 6,6'-bis-(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (BTBPs) have been synthesised. These reagents form complexes with lanthanides and crystal structures with 11 different lanthanides have been determined. The majority of the structures show the lanthanide to be 10-coordinate with stoichiometry [Ln(BTBP)(NO3)3] although Yb and Lu are 9-coordinate in complexes with stoichiometry [Ln(BTBP)(NO3)2(H2O)](NO3). In these complexes the BTBP ligands are tetradentate and planar with donor nitrogens mutually cisi.e. in the cis, cis, cis conformation. Crystal structures of two free molecules, namely C2-BTBP and CyMe4-BTBP have also been determined and show different conformations described as cis, trans, cis and trans, trans, trans respectively. A NMR titration between lanthanum nitrate and C5-BTBP showed that two different complexes are to be found in solution, namely [La(C5-BTBP)2]3+ and [La(C5-BTBP)(NO3)3]. The BTBPs dissolved in octanol were able to extract Am(III) and Eu(III) from 1 M nitric acid with large separation factors.

A wide range of pseudorotaxane assemblies containing positively charged pyridinium, pyridinium nicotinamide, imidazolium, benzimidazolium and guanidinium threading components, and macrocyclic isophthalamide polyether ligands have been prepared using a general anion templation procedure. In noncompetitive solvent media, coupling halide anion recognition by a macrocyclic ligand with ion-pairing between the halide anion and a strongly associated cation provides the driving force for interpenetration. Extensive solution 1H NMR binding studies, thermodynamic investigations, and single-crystal X-ray structure determinations reveal that the nature of the halide anion template, strength of the ion-pairing between the anion template and the cationic threading component, and to a lesser extent favorable second sphere pi-pi aromatic stacking interactions between the positively charged threading component and macrocyclic ligand, together with macrocyclic ring size, affect the efficacy of pseudorotaxane formation.

Computer modelling has been used to investigate the viability of using a non-toxic, water-soluble polymer, polyvinylpyrrolidone (PVP), to inhibit gas hydrate formation. Monte Carlo calculations have been used to study the adsorption of monomer, dimer, tetramer and octamer PVP units on different (001) surfaces of a type I hydrate ; various polymer tacticities have also been considered. Adsorption has been found to occur predominantly through the formation of two hydrogen bonds between the pyrrolidone oxygen and the water surface, and thus the location of adsorption sites depended on the availability of pendant hydrogens on the hydrate surface. PVP chains were generally found to lie flat on the surface, although there was some evidence of loops forming for the octamer. The results indicate that inhibition via adsorption of PVP at hydrate growth sites is viable, but that the main factors influencing the adsorption are inherently statistical.

A new Cu(II) complex of an asymmetrically dicondensed Schiff base (HL = N-(2-hydroxyacetophenylidene)-N'-salicylidene-1,3-propanediamine) derived from 1,3-propanediamine, salicylaldehyde, and o-hydroxyacetophenone has been synthesized. Using this complex, [CuL] (1), as a metalloligand, two new trinuclear Cu-Mn complexes, [(CuL)Mn(N)(HO)](ClO)·HO (2) and [(CuL)Mn(NCS)] (3), have been prepared. Single-crystal structural analyses reveal that complexes 2 and 3 both have the same bent trinuclear {(CuL)Mn} structural unit in which two terminal bidentate square-planar (CuL) units are chelated to the central octahedral Mn(II) ion. This structural similarity is also evident from the variable-temperature magnetic susceptibility measurements, which suggest that compounds 2 and 3 are both antiferromagnetically coupled with comparable exchange coupling constants (-21.8 and -22.3 cm, respectively). The only difference between 2 and 3 lies in the coordination around the central Mn(II) ion; in 3, two SCN groups are coordinated to the Mn(II), leaving a neutral complex, but in 2, one N group and one HO molecule are coordinated to give a positively charged species. The presence of such a labile HO coligand makes 2 catalytically active in mimicking two well-known polynuclear copper proteins, catecholase and phenoxazinone synthase. The turnover numbers (k) for the aerial oxidation of 3,5-di-tert-butylcatechol and o-aminophenol are 1118 and 6581 h, respectively, values which reflect the facility of the heterometallic catalyst in terms of both efficiency and catalytic promiscuity for aerial dioxygen activation. The mechanisms of these biomimetic oxidase reactions are proposed for the first time involving any heterometallic catalyst on the basis of mass spectral analysis, EPR spectroscopy, and cyclic voltammetry. The evidence of the intermediates indicates possible heterometallic cooperative activity where the substrates bind to a Mn(II) center and Cu(II) plays the role of an electron carrier for transformation of the phenolic substrates to their respective products with the reduction of aerial dioxygen.