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Christopher E Anson

Publications and source records attributed to Christopher E Anson.

At least 37 records · Page 2Linked to original sources
PubMed2005

Functionalised trimethylsilyl reagents in cluster synthesis: reactions of Ph2P(S)SSiMe3 with group 11 salts.

A series of complexes, ranging from the small cluster 1/infinity[Ag(Ph2PS2)(dppe)](infinity) [dppe=1,2-bis(diphenylphosphino)ethane] to [Cu48S20(O(t)Bu)2(Ph2PS2)2(dppm-)4(dppm)4][dppm=1,2-bis(diphenylphosphino)methane] (the largest Cu cluster containing phosphinodithioato ligands), has been synthesised. The structural evidence presented here indicates that in these reactions initially small cyclic aggregates or one-dimensional coordination polymers are formed. The growth of these intermediates to larger aggregates can take up to several months and could proceed via cationic intermediates.

Journal Article↗
PubMed2005

Structural characterization of artificial self-assembling porphyrins that mimic the natural chlorosomal bacteriochlorophylls c, d, and e.

We report two crystal structures of a synthetic porphyrin molecule which was programmed for self-assembly. The same groups which ensure that bacteriochlorophylls c, d, and e can self-assemble into the chlorosomal nanorods, the photosynthetic antenna system of some green bacteria, have been engineered into desired positions of the tetrapyrrolic macrocycle. In the case of the 5,15-meso-substituted anchoring groups, depending upon the concentration, by using the same crystallization solvents, either a tetragonal or a layered structure of porphyrin stacks were encountered. Surprisingly, pi-pi interactions combined with extensive dispersive interactions, which also encompass cyclohexane, one of the crystallization solvents, win over putative hydrogen bonding. We are aware that our compounds differ considerably from the natural bacteriochlorophylls, but based upon our findings, we now question the hydrogen-bonding network, previously proposed to organize stacks of bacteriochlorophylls. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS) on various isomeric compounds support our challenge of current models for the chlorosomal antenna as these show structures, astonishingly similar to those of chlorosomes.

Bacterial Proteins↗
PubMed2005

Crystal structure and magnetic properties of a pseudo-cubic close-packed array of oxalate linked {FeII6(mu3-OH)6}6+ clusters.

The ionic hexanuclear cluster aggregate [FeII6(mu3-OH)6]6+ has been synthesised using hydrothermal conditions starting from ferrous oxalate in the presence of barium and bromide or iodide ions. A single crystal X-ray structure on the compound Ba4[FeII6(mu3-OH)6(C2O4)6]Br2.6H2O shows that the [FeII6(mu3-OH)6]6+ units are held together by bridging oxalates in a pseudo-cubic close-packed array. The barium ions in conjunction with oxalate groups provide a barrel-shaped cage between the FeII6 aggregates containing the bromide counterions and lattice waters and corresponding to an 'octahedral hole' in the pseudo-cubic close-packed structure. A magnetic susceptibility study shows that the FeII centres are antiferromagnetically coupled. Below 10 K the system displays a long range antiferromagnetic ordering mediated by the oxalate bridges and a molecular-based description of the magnetism is no longer valid.

Journal Article↗
PubMed2005

Formal encapsulation of [Fe(H2O)6](3+) by {Fe2(hpdta)} units gives a system of S= 13/2 Fe(III)9 oxo clusters showing magnetic hysteresis.

Under solvothermal conditions the unprecedented nonanuclear Fe(III) aggregate [Fe9(mu3-O)4(mu-OH)4(hpdta)4]5- is formed through the formal encapsulation of [Fe(H2O)6]3+ by four [Fe2(hpdta)(H2O)2]+ units: the aggregates have ground state spins of S= 13/2 while the observed hysteresis below 1.8 K results from inter-cluster antiferromagnetic coupling.

Ferric Compounds↗
PubMed2005

Iron(III) activation hits a [4 + 4] macrocycle.

The tetranuclear complex [Fe(III)2(L')(OH)(CH3O)]2, 1, has been synthesised from the reaction of either ferrous [in excess as 4:1 or stoichiometric 2:1 iron(II) : H4L] or ferric ions [4:1 iron(III) : H4L] with the large macrocycle, H4L, using aerobic conditions in methanol in the presence of triethylamine. The structure of 1 was determined by single-crystal X-ray diffraction. These reaction conditions lead to the modification of the original macrocycle through the incorporation of a methylene group between two amine groups to give an imidazolidine ring in (L')4-. The controlled addition of formaldehyde into the reaction system results in a significantly improved yield of 1, suggesting that it is involved in the reaction mechanism. The (L')4- macrocycle binds to two, well-separated, iron(III) centres [Fe(1)...Fe(1a) > 8 A]. Each iron(III) centre is further linked via hydroxy and methoxy bridges to equivalent iron(iii) centres contained in a second macrocycle. Overall this gives a structure containing two {Fe(OH)(CH(3)O)Fe} dimers [Fe(1)...Fe(2)ca. 3.2 A] sandwiched by two (L')4- macrocycles. The complex was further characterised by SQUID magnetic measurements and can be interpreted in terms of two isolated antiferromagnetically coupled Fe(III) dimers (J=-23.75 K).

Journal Article↗
PubMed2004

Structure and magnetic properties of a giant Cu44II aggregate which packs with a zeotypic superstructure.

Reaction of Cu(II) and the aminopolycarboxylate nitrilotripropionic acid (H(3)ntp) in water leads to the formation of [Cu(44)(mu(8)-Br)(2)(mu(3)-OH)(36)(mu-OH)(4)(ntp)(12)Br(8)(OH(2))(28)]Br(2).81H(2)O. The Cu(44) aggregates have a central inorganic core corresponding to [Cu(24)(mu(8)-Br)(2)(mu(3)-OH)(24)(mu-OH)(8)](14+) anchored on two bromide anions, and this is encased in a shell of Cu(II)/ligand units. The aggregates pack into a distorted tetragonal array with a very open structure containing large amounts of water of crystallization. The magnetic properties have been studied and, while complicated by the presence of low-lying excited states, indicate that the individual clusters have nonzero spin ground states.

Journal Article↗
PubMed2004

Electronic interaction in an outer-sphere mixed-valence double salt: a polarized neutron diffraction study of K(3)(MnO(4))(2).

The mixed-valence double salt K(3)(MnO(4))(2) crystallizes in space group P2(1)/m with Z = 2. The manganese centers Mn1 and Mn2 constitute discrete "permanganate", [Mn(VII)O(4)](-), and "manganate", [Mn(VI)O(4)](2-), ions, respectively. There is a spin-ordering transition to an antiferromagnetic state at ca. T = 5 K. The spin-density distribution in the paramagnetic phase at T = 10 K has been determined by polarized neutron diffraction, confirming that unpaired spin is largely confined to the nominal manganate ion Mn2. Through use of both Fourier refinement and maximum entropy methods, the spin on Mn1 is estimated as 1.75 +/- 1% of one unpaired electron with an upper limit of 2.5%.

Journal Article↗
PubMed2004

Intra and intermolecular magnetic interactions in a series of dinuclear Cu(II)/hxta complexes [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: correlation of magnetic properties with geometry.

Nine dinuclear copper(II) complexes with hxta5- ligands [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: [Cu2(MeO-hxtaH)(H2O)2] x 4H2O (1), [Na(micro-H2O)2(H2O)6][Cu2(Cl-hxta)(H2O)3]2 x 6H2O (2), [Cu(H2O)6][Cu2(Me-hxta)(H2O)2](NO3) x 2H2O (3), [Cu2(R-hxtaH)(H2O)3] x 3H2O [R = Cl (4), CH3 (5), and MeO (6)], [Cu2(MeO-hxtaH2)(micro-X)(CH3OH)] x 3CH3OH [X = Cl (7), Br (8)] and K5Na(micro-H2O)10[Cu2(micro-CO3)(Me-hxta)]2 x 4H2O (9), have been synthesized and structurally characterized. In complexes 4-7, the dinuclear units are linked via novel pairwise supramolecular interactions involving the ligand carboxylate groups. The intra- and intermolecular magnetic interactions have been quantified, and the coupling constants have been related to the structural geometries.

Copper↗
PubMed2004

Highly nonplanar, electron deficient, N-substituted tetra-oxocyclohexadienylidene porphyrinogens: structural, computational, and electrochemical investigations.

The structures and electrochemistry of N-benzylated meso-tetrakis (3,5-di-tert-butyl-4-oxo-cyclohexa-2,5-dienylidene) porphyrinogens have been investigated. Structural determinations reveal the isomeric identity of the products obtained from the N-alkylation of the parent meso-tetra (oxo-cyclohexadienylidene) porphyrinogen. The compounds are subject to increased macrocyclic deformations upon increasing N-substitution culminating in the tetra-N-benzyl derivative, which has a buckling superimposed on the already highly puckered macrocycle. The electrochemical analyses emphasize the electron deficiency of the N-benzylated meso-tetra(oxo-cyclohexadienylidene) porphyrinogens and indicate that they can be considered as quinones conjugated via the unsaturated tetrapyrrolic macrocycle. The N-benzylated compounds studied form stable and well-defined pi-cation radical and pi-anion radical species because of their highly conjugated nature. Ab initio molecular orbital calculations at the B3LYP/3-21G() level confirmed the high degree of conjugation between tetrapyrrole and meso substituents and also gave good agreement between calculated and experimentally determined HOMO-LUMO band gap energies.

Journal Article↗
PubMed2004

Synthesis and magnetism of oxygen-bridged tetranuclear defect dicubane Co(II) and Ni(II) clusters.

Reaction of aqueous/ethanolic solutions of CoCl2.6H2O and nitrilotripropionic acid (H3ntp=N(CH2CH2COOH)3) in the presence of potassium hydroxide affords the hydroxy-bridged tetranuclear cluster [Co4mu3-OH)2(H2O)6(ntp)2].2H2O (1). The Ni(II) analogue [Ni4(mu3-OH)2(H2O)6(ntp)2].2H2O (2) can also be isolated using aqueous solutions and Ni(SO4).7H2O as metal salt. With small changes in reaction conditions the methoxy-bridged analogue, [Ni4(mu3-OMe)2(H2O)6(ntp)2](3), can also be isolated. In these tetramers the M(II) ions are oxygen-bridged and exhibit a defect dicubane-like core with two missing vertices. The magnetic properties have been studied for all three clusters and reveal competing antiferromagnetic and ferromagnetic interactions between the four Co(II) ions in 1 and ferromagnetic coupling between the four Ni(II) ions in 2 and 3. In all three compounds the individual clusters order antiferromagnetically at Neel temperatures below 1 K.

Journal Article↗
PubMed2004

Syntheses of the 47 electron clusters [(Cp*Fe)3(mu3-X)2] (X = S, Se) and the First Fe/Sn/Se Heterocubane Cluster [(CpFe)3(SnCl3)(mu3-Se)4] x DME by the use of chalcogenostannate salts.

By reacting 1-aminoethylammonium (H2NCH2CH2NH3+ = enH+) salts of [Sn2E6]4- anions (E = S, Se), [enH]4[Sn2S6] (1) and [enH]4[Sn2Se6] x en (2), with FeCl2/LiCp, three novel (partly) oxidized, Cp* ligated iron chalcogenide clusters were synthesized. Two of them, [(CpFe)3(mu3-S)2] (3) and [(Cp*Fe)3(mu3-Se)2] (4), contain formally 47 valence electrons. [(Cp*Fe)3(SnCl3)(mu3-Se)4] x DME (5) represents the first known mixed metal Fe/Sn/Se heterocubane type cluster. Compounds 3-5 were structurally characterized by single-crystal X-ray diffraction, and the odd valence electron number of the [Fe3E2] clusters (E = S, Se) was confirmed by density functional (DFT) investigations, mass spectrometry, cyclic voltammetry and a susceptibility measurement of 3.

Journal Article↗
PubMed2004

A novel mixed-ligand antimycobacterial dimeric copper complex of ciprofloxacin and phenanthroline.

A novel mixed-ligand Cu(II) complex of ciprofloxacin (cfH) and phenanthroline, is found to crystallize as a dimeric moiety containing monocationic and dicationic species. Two such dimeric moieties are found in the same unit cell leading to a dicationic cluster. The higher negative redox potential for this cluster dampens its antimycobacterial activity against M. smegmatis.

Anti-Bacterial Agents↗
PubMed2004

The building block approach to extended solids: 3,5-pyrazoledicarboxylate coordination compounds of increasing dimensionality.

A series of M(II) complexes with the ligand 3,5-pyrazoledicarboxylic acid (H3dcp) has been synthesised mainly via hydrothermal reactions and their structures have been characterised. Simple mononuclear [Ni(Hdcp)(H2O)4] (1), Na2(mu-H2O)2(H2O)8[Ni(Hdcp)2(H2O)2] (2), [M(H2dcp)2(H2O)2] x 2H2O [M = Co (3), Zn (4) and Cu (5)] and dinuclear (Et3NH)2[Cu2(dcp)2(H2O)2] (9) building blocks have been isolated and subsequently linked into 1-D chains [Mn(Hdcp)(H2O)2]infinity (6), [[Mn(H2O)4][Mn(Hdcp)2(H2O)2] x 4H2O]infinity (7), [Ni2(Hdcp)2(mu-H2O)2(H2O)2]infinity (8), [[Ni(H2O)4][Ni2(dcp)2(H2O)4]]infinity (11), or 3-D arrays [[Na2(mu-H2O)2][Cu2(dcp)2]]infinity (10), [Cu3(dcp)2(H2O)4]infinity (12), utilising novel bridging modes of the H3dcp ligand. In the unprecedented 1-D Ni(II) chain 8, rarely reported double aqua-bridges link the Ni(II) ions to form an inter-linked double stranded chain. The magnetic properties of these compounds have been measured and reveal a variety of antiferromagnetic coupling behaviours induced by the ligand bridging modes.

Journal Article↗