Bimetallic iron-iron and iron-zinc complexes of the redox-active ONO pincer ligand.

A new bimetallic platform comprising a six-coordinate Fe(ONO) unit bound to an (ONO)M (M = Fe, Zn) has been discovered ((ONO)H = bis(3,5-di--butyl-2-phenol)amine). Reaction of Fe(ONO) with either (ONO)Fe(py) or with (ONO)FeCl under reducing conditions led to the formation of the bimetallic complex Fe(ONO), which includes unique five- and six-coordinate iron centers. Similarly, the reaction of Fe(ONO) with the new synthon (ONO˙)Zn(py) led to the formation of the heterobimetallic complex FeZn(ONO), with a six-coordinate iron center and a five-coordinate zinc center.

Synthesis and characterization of a redox-active bis(thiophenolato)amide ligand, [SNS]3-, and the homoleptic tungsten complexes, W[SNS]2 and W[ONO]2.

A new tridentate redox-active ligand platform, derived from bis(2-mercapto-p-tolyl)amine, [SNS(cat)]H(3), has been prepared in high yields by a four-step procedure starting from commericially available bis(p-tolyl)amine. The redox-active pincer-type ligand has been coordinated to tungsten to afford the six-coordinate, homoleptic complex W[SNS](2). To benchmark the redox behavior of the [SNS] ligand, the analogous tungsten complex of the well-known redox-active bis(3,5-di-tert-butylphenolato)amide ligand, W[ONO](2), also has been prepared.

Aluminum complexes of the redox-active [ONO] pincer ligand.

A series of aluminum complexes containing the tridentate, redox-active ligand bis(3,5-di-tert-butyl-2-phenol)amine ([ONO]H(3)) in three different oxidation states were synthesized. The aluminum halide salts AlCl(3) and AlBr(3) were reacted with the doubly deprotonated form of the ligand to afford five-coordinate [ONHO(cat)]AlX(solv) complexes (1a, X = Cl, solv = OEt(2); 1b, X = Br, solv = THF), each having a trigonal bipyramidal coordination geometry at the aluminum and containing the [ONHO(cat)](2-) ligand with a protonated, sp(3)-hybridized nitrogen donor. The [ONO] ligand platform may also be added to aluminum through the use of the oxidized ligand salt [ONO(q)]K, which was reacted with AlCl(3) in the presence of either diphenylacetylacetonate (acacPh(2)(-)) or 8-oxyquinoline (quinO(-)) to afford [ONO(q)]Al(acacPh(2))Cl (2) or [ONO(q)]Al(quinO)Cl (3), respectively, with well-defined [ONO(q)](-) ligands.

Coordination effects on electron distributions for rhodium complexes of the redox-active bis(3,5-di-tert-butyl-2-phenolate)amide ligand.

New rhodium complexes of bis(3,5-di-tert-butyl-2-phenol)amine ([ONO(cat)]H(3)) were synthesized, and their electronic properties were investigated. These compounds were prepared by combining [ONO(q)]K and [(cod)Rh(μ-Cl)](2) in the presence of an auxiliary donor ligand to yield complexes of the type [ONO]RhL(n) (n = 3, L = py (1); n = 2, L = PMe(3) (2a), L = PMe(2)Ph (2b), PMePh(2) (2c), PPh(3) (2d)). Single-crystal X-ray diffraction studies on [ONO]Rh(py)(3) (1) revealed a six-coordinate, octahedral rhodium complex.

Hexadentate terephthalamide(bis-hydroxypyridinone) ligands for uranyl chelation: structural and thermodynamic consequences of ligand variation.

Several linear, hexa- and tetradentate ligands incorporating a combination of 2,3-dihydroxy-terephthalamide (TAM) and hydroxypyridinone-amide (HOPO) moieties have been developed as uranyl chelating agents. Crystallographic analysis of several {UO(2)[TAM(HOPO)(2)]}(2-) complexes revealed a variable and crowded coordination geometry about the uranyl center. The TAM moiety dominates the bonding in hexadenate complexes, with linker rigidity dictating the equality of equatorial U-O bonding.

The influence of linker geometry in bis(3-hydroxy-N-methyl-pyridin-2-one) ligands on solution phase uranyl affinity.

Seven water-soluble, tetradentate bis(3-hydroxy-N-methyl-pyridin-2-one) (bis-Me-3,2-HOPO) ligands were synthesized that vary only in linker geometry and rigidity. Solution-phase thermodynamic measurements were conducted between pH 1.6 and pH 9.

Steric and electronic consequences of flexibility in a tetradentate redox-active ligand: Ti(IV) and Zr(IV) complexes.

A redox-active, tetradentate ligand, N,N'-bis-(3-dimethylamino-propyl)-4,5-dimethoxy-benzene-1,2-diamide ([N(2)N(2)(cat)](2-)), was developed, and the six-coordinate metal complexes [N(2)N(2)(cat)]TiCl(2) (3) and [N(2)N(2)(cat)]ZrCl(2) (4) were synthesized. The tetradentate ligand was determined to be fluxional in 3 and 4, enabled by reversible dissociation of the neutral amine groups of the [N(2)N(2)(cat)](2-) ligand. Both amine arms of 3 could be replaced by N,N-dimethylaminopyridine with an overall free energy change of -4.

Encapsulated guest-host dynamics: guest rotational barriers and tumbling as a probe of host interior cavity space.

The supramolecular host assembly [Ga(4)L(6)](12-) (1; L = 1,5-bis[2,3-dihydroxybenzamido]naphthalene) encapsulates cationic guest molecules within its hydrophobic cavity and catalyzes a variety of chemical transformations within its confined interior space. Despite the well-defined structure, the host ligand framework and interior cavity are very flexible and 1 can accommodate a wide range of guest shapes and sizes. These observations raise questions about the steric effects of confinement within 1 and how encapsulation fundamentally changes the motions of guest molecules.

Influence of linker geometry on uranyl complexation by rigidly linked bis(3-hydroxy-N-methyl-pyridin-2-one).

A series of bis(3-hydroxy-N-methyl-pyridin-2-one) ligands was synthesized, and their respective uranyl complexes were characterized by single crystal X-ray diffraction analyses. These structures were inspected for high-energy conformations and evaluated using a series of metrics to measure co-planarity of chelating moieties with each other and the uranyl coordination plane, as well as to measure coordinative crowding about the uranyl dication. Both very short (ethyl, 3,4-thiophene and o-phenylene) and very long (alpha,alpha'-m-xylene and 1,8-fluorene) linkers provide optimal ligand geometries about the uranyl cation, resulting in planar, unstrained molecular arrangements.

Designing the ideal uranyl ligand: a sterically induced speciation change in complexes with thiophene-bridged bis(3-hydroxy-n-methylpyridin-2-one).

Structural characterization of a mononuclear uranyl complex with a tetradentate, thiophene-linked bis(3-hydroxy-N-methylpyridin-2-one) ligand reveals the most planar coordination geometry yet observed with this ligand class. The introduction of ethylsulfanyl groups onto the thiophene linker disrupts this planar, conjugated ligand arrangement, resulting in the formation of dimeric (UO(2))(2)L(2) species in which each ligand spans two uranyl centers. Relative energy calculations reveal that this tendency toward dimer formation is the result of steric interference between ethylsulfanyl substitutents and linking amides.

Aryl bridged 1-hydroxypyridin-2-one: effect of the bridge on the Eu(III) sensitization process.

The efficiency of Eu(3+) luminescence by energy transfer from an antenna ligand can be strongly dependent on the metal ion coordination geometry. The geometric component of the Eu(III) sensitization has been probed using series of tetradentate 1,2-HOPO derivatives that are connected by bridges of varying length and geometry. The ligands are N,N'-(1,2-phenylene)bis(1-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxamide) for the ligand (L(1)), 1-hydroxy-N-(2-(1-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxamido)benzyl)-6-oxo-1,6-dihydropyridine-2-carboxamide (L(2)) and N,N'-(1,2-phenylenebis(methylene))bis(1-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxamide) (L(3)).

Structural consequences of anionic host-cationic guest interactions in a supramolecular assembly.

The molecular structure of the spontaneously assembled supramolecular cluster [M(4)L(6)](n-) has been explored with different metals (M = Ga(III), Fe(III), Ti(IV)) and different encapsulated guests (NEt(4)(+), BnNMe(3)(+), Cp(2)Co(+), Cp*(2)Co(+)) by X-ray crystallography. While the identity of the metal ions at the vertices of the M(4)L(6) structure is found to have little effect on the assembly structure, encapsulated guests significantly distort the size and shape of the interior cavity of the assembly. Cations on the exterior of the assembly are found to interact with the assembly through either pi-pi, cation-pi, or CH-pi interactions.