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Biomedical subjects

Alexander J Blake

Publications and source records attributed to Alexander J Blake.

82 records · Page 5Linked to original sources
PubMed2002

Retroracemization using new forms of Belokon's original ligand: intermediate NiII complexes of N-((2-[N-(S)-alkylprolylamino]phenyl)phenylmethylene)-(S)-phenylalanine (alkyl is 2-picolyl, 3-picolyl or ethyl).

In the title compounds, [N-(phenyl(2-[N-(S)-(2-picolyl)prolylamino]phenyl)methylene)-(S)-phenylalaninato]nickel(II), [Ni(C(33)H(30)N(4)O(3))], (I), [N-(phenyl(2-[N-(S)-(3-picolyl)prolylamino]phenyl)methylene)-(S)-phenylalaninato]nickel(II) hemihydrate, [Ni(C(33)H(30)N(4)O(3))].0.5H(2)O, (II), and [N-((2-[N-(S)-ethylprolylamino]phenyl)phenylmethylene)-(S)-phenylalaninato]nickel(II), [Ni(C(29)H(29)N(3)O(3))], (III), the Ni(II) centres have approximate square-planar coordination geometries from N(3)O donor sets. The picolyl N atoms in (I) and (II) are too remote from the metal centres to interact significantly, but the metal coordination geometries experience tetrahedral distortion and/or displacement of the metal centre from the N(3)O plane. These are linked to conformational differences between the ligands of the symmetry-independent complexes (Z' = 2), which in turn are related to molecular packing. In (III), where a less sterically demanding ethyl group replaces the picolyl substituents, there are none of the distortions or displacements seen in (I) and (II).

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PubMed2002

Studies of a nickel-based single-molecule magnet.

A cyclic complex [Ni(12)(chp)(12)(O(2)CMe)(12)(thf)(6)(H(2)O)(6)] (1) has been synthesised and studied (chp=6-chloro-2-pyridonate). Complex 1 exhibits ferromagnetic exchange between the S=1 centres, giving an S=12 spin ground state. Detailed studies demonstrate that it is a single-molecule magnet with an energy barrier of approximately 10 K for reorientation of magnetisation. Resonant quantum tunnelling is also observed. The field between resonances allows accurate measurement of D, which is 0.067 K. Inelastic neutron scattering studies have allowed exchange parameters to be derived accurately, which was impossible from susceptibility data alone. Three exchange interactions are required: two ferromagnetic nearest neighbour interactions of approximately 11 and 2 cm(-1) and an anti-ferromagnetic next nearest neighbour interaction of -0.9 cm(-1).

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PubMed2002

(Acetonitrile)[2,6-bis(pyrazol-1-yl)pyridine](isonicotinamide)copper(II)-tetrafluoroborate-acetonitrile (1/2/2).

Molecules of the title compound, [Cu(C(2)H(3)N)(C(11)H(9)N(5))(C(6)H(6)N(2)O)](BF(4))(2).2C(2)H(3)N, comprise (acetonitrile)[2,6-bis(pyrazol-1-yl)pyridine](isonicotinamide)copper(II) cations, tetrafluoroborate anions and lattice acetonitrile molecules. The cations have distorted square-pyramidal geometries in which the N(3)-donor, viz. 2,6-bis(pyrazol-1-yl)pyridine, and the N-donor, viz. the isonicotinamide ligand, occupy the four basal positions, with the coordinated acetonitrile N-donor atom occupying the apical position. Pairs of cations are linked by N-H.F hydrogen bonds through tetrafluoroborate anions, forming centrosymmetric dimers, which are further linked by C-H.O hydrogen bonds into two-dimensional undulating sheets, three of which interpenetrate to generate a two-dimensional network.

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PubMed2002

3,6-Di(thiophen-2-yl)pyridazine.

Molecules of the title compound, C(12)H(8)N(2)S(2), which are effectively planar, have all four heteroatoms on the same side but do not have twofold symmetry.

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PubMed2002

Structural isomerism in CuSCN coordination polymers.

CuSCN reacts with the angular ligand 2,4-bis(4-pyridyl)-1,3,5-triazine (dpt) to afford rare examples of coordination polymer structural isomers including a non-centrosymmetric three-dimensional framework with Cd(SO4) topology constructed from tetrahedral metal cations.

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PubMed2002

Aquachlorobis[4,4,5,5-tetramethyl-2-(2-pyridyl)-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide-kappa(2)O(1),N(2)]nickel(II) nitrate methanol disolvate monohydrate.

The title complex, [NiCl(C(12)H(16)N(3)O(2))(2)(H(2)O)]NO(3) x 2CH(4)O x -H(2)O, was obtained from a methanolic solution of Ni(NO(3))(2) x 6H(2)O, 2-pyridyl nitronyl nitroxide (2-NITpy) and (NEt(4))(2)[CoCl(4)]. The equatorial coordination sites of the octahedral Ni(II) centre are occupied by two chelating radical ligands, with the axial positions occupied by the Cl(-) and water ligands. The H(2)O[bond]Ni[bond]Cl axis of the complex lies along a crystallographic twofold axis, so that only half the cation is present in the asymmetric unit. The Ni[bond]Cl bond length [2.3614 (17) A] is significantly shorter than distances typical of octahedral Ni(II) centres [2.441 (5) A]. However, with only one nitrate anion per formula unit, the oxidation state of the metal must be assigned as Ni(II). The 2-NITpy ligands bend away from the equatorial plane, forming a hydrophobic region around the Cl atoms. Conversely, the ligated water molecule forms moderately strong hydrogen bonds with the disordered methanol solvent molecules, which in turn form interactions with the water of crystallization and the disordered nitrate anion. These interactions combine to give hydrophilic regions throughout the crystal structure.

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PubMed2002

Constructing terbium co-ordination polymers of 4,4'-bipyridine-N,N'-dioxide by means of diffusion solvent mixtures.

Five different co-ordination polymers of terbium(III) and the bidentate ligand 4,4'-bipyridine-N,N'-dioxide (L), [Tb(L)(CH(3)OH)(NO(3))(3)](infinity) (1), ([Tb(L)(1.5)(NO(3))(3)].CH(2)Cl(2))(infinity) (2), ([Tb(L)(1.5)(NO(3))(3)].CH(3)OH.0.8H(2)O)(infinity) (3), ([Tb(L)(1.5)(NO(3))(3)].0.4C(2)Cl(4).0.8CH(3)OH)(infinity) (4), and [Tb(L)(2)(NO(3))(3)](infinity) (5) have been synthesised by the use of different "diffusion solvent mixtures", and structurally characterised by X-ray crystallography. Compound 1, with a Tb:L stoichiometry of 1:1, adopts a zig-zag chain structure, which forms three-fold interpenetrating diamondoid frameworks through interchain hydrogen bonding between co-ordinated methanol and a nitrate group on an adjacent chain. Polymers 2, 3, and 4 all have a Tb:L stoichiometry of 1:1.5, but adopt different topologies. For 2, a ladder arrangement is found and large channels which accommodate solvent CH(2)Cl(2) molecules are formed by superposition of the ladders. For 3 and 4 4.8(2) net structures are observed. The superposition of the 4.8(2) nets in 3 and 4, by disposing adjacent layers such that every octagon is positioned below a tetragon from the neighbouring layer, allows the formation of two kinds of channel, with that inside the tetragons accommodating methanol molecules. The other kind of channel, between tetragons, accommodates water molecules in the case of 3 and tetrachloroethylene molecules in the case of 4. Compound 5, with a Tb:L stoichiometry of 1:2, has a linear polymeric structure with one bridging and one terminal ligand, and forms (6,3) plane nets by means of intermolecular electrostatic interactions between N-oxide moieties. X-ray powder diffraction studies show that upon desolvation, compound 2 maintains its original ladder framework.

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PubMed2002

Using multimodal ligands to influence network topology in silver(I) coordination polymers.

A range of Ag(I) one- and two-dimensional coordination frameworks has been prepared and structurally characterized by using the multimodal ligand 3,6-di-pyrazin-2-yl-(1,2,4,5)-tetrazine, which offers both monodentate and chelating binding sites. It is demonstrated that multimodal ligands can be used to prepare coordination frameworks with novel and unusual topologies and to influence the precise geometrical arrangement of both ligands and metal centers within such supramolecular arrays.

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PubMed2002

4-Methoxyphenylphosphonic acid: reactivity of Lawesson's reagent.

The title compound, C(7)H(9)O(4)P, obtained as a by-product of the reaction between Lawesson's reagent, (I), and CH(3)I, can be recognized as the final product of the S/O interchange reaction at the P atom of (I). Hydrogen bonds of type P-O-H.O=P link molecules into helical chains and form ten-membered hydrogen-bonded rings with the graph-set notation R(3)(2)(10). Weaker intermolecular contacts between P-O and a phenyl H atom link the chains into a three-dimensional lattice. The parent benzenephosphonic acid [Weakley (1976). Acta Cryst. B32, 2889-2890] does not adopt an analogous structure, but its arsenic analogue [Shimada (1960). Bull. Chem. Soc. Jpn, 33, 301-304] does and can be regarded as isostructural. We rationalize these three structures in terms of their significant intermolecular interactions.

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