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Abstract: The synthesis and the structure of the new potentially heptadentate ligand 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-methoxybenzene (H5L) is described. The reaction in pyridine or DMF of this ligand with various M(AcO)2 salts (M = NiII, CoII, MnII) leads to very different products depending on the metal. Thus, the dinuclear complexes [M2(H3L)2(py)4] (M = NiII, 1; CoII, 2) or the linear zigzag tetranuclear clusters [Mn4(H2L)2(AcO)2(py)5] (3) and [Mn4(H2L)2(AcO)2(dmf)4] (4) have been synthesized and characterized crystallographically. Slow oxidation of complex 3 leads to the formation of the novel mixed-valence linear complex [Mn3(HL)2(py)6] (5), displaying an unprecedented asymmetric MnIIIMnIIIMnII topology. The coordination geometry of complexes 1 to 5 has been analyzed and discussed by means of continuous shape measures. Magnetic measurements of 3 and 5 demonstrate that the metals within these complexes weakly interact magnetically with coupling constants of J1 = −1.13 cm-1 and J2 = −0.43 cm-1 (S = 0) for complex 3 and J1 = −5.4 cm-1 and J2 = −0.4 cm-1 (S = 5/2) for complex 5 (using the H = −Σ2JijSiSj convention). These results are consistent with X-band EPR measurements on these compounds.
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Feb 2007
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NONE-No attached Diamond beamline
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Abstract: Two high-pressure polymorphs of sulfuric acid monohydrate (oxonium hydrogensulfate) have been obtained at ambient temperature by crystallisation at high pressure from the liquid at 1.3 GPa (form III) and by direct compression of the ambient-pressure form I first to 1.26 GPa (form II) and then to 1.72 GPa (form III). The structure of form III was solved by single crystal X-ray diffraction and this structure was used as the basis for the refinement of hydrogen positions using high-pressure neutron powder diffraction data. Form III crystallises in the orthorhombic crystal system at 1.97 GPa, and features parallel chains of hydrogensulfate ions linked by oxonium ions to form a three-dimensional hydrogen-bonded network. On further compression to 3.05 GPa, the direction of maximum compressibility is found to be along the a-axis and is associated with the shortening of a hydrogen bond between a hydrogensulfate ion and an oxonium ion. The structure of form II remains elusive although at ambient temperature it is stable (or metastable) at pressures as low as 0.42 GPa, perhaps indicating that it could be recoverable to ambient-pressure at low temperature.
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Jan 2008
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Abstract: The polydentate ligand 2,4,6-tris(dipyridin-2-ylamino)-1,3,5-triazine (dpyatriz) in combination with the Cu(ClO4)2/CuX2 salt mixtures (X? = Cl?, Br?, or N3?) leads to the formation of molecular coordination aggregates with formulas [Cu3Cl3(dpyatriz)2](ClO4)3 (2), [Cu3Br3(dpyatriz)2](ClO4)3 (3), and [Cu4(N3)4(dpyatriz)2(DMF)4(ClO4)2](ClO4)2 (4). These complexes consist of two dpyatriz ligands bridged via coordination to CuII and disposed either face-to-face in an eclipsed manner (2 and 3) or parallel and mutually shifted in one direction. The copper ions complete their coordination positions with Cl? (2), Br? (3), or N3?, ClO4?, and N,N-dimethylformamide (DMF) (4) ligands. All complexes crystallize together with noncoordinate ClO4? groups that display anion···? interactions with the triazine rings. These interactions have been studied by means of high level ab initio calculations and the MIPp partition scheme. These calculations have proven the ClO4?···[C3N3] interactions to be favorable and have revealed a synergistic effect from the combined occurrence of ??? stacking of triazine rings and the interaction of these moieties with perchlorate ions, as observed in the experimental systems.
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May 2008
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NONE-No attached Diamond beamline
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Abstract: Hetero-bimetallic complexes of a vanadium(V) and rhenium(VII) combination, connected by a μ-oxido bridge [LVO(μ-O)ReO3]·H2O (L = salen and its derivative) (1, 2), have been synthesized. Compounds undergo a vanadium-based single-electron reduction at E1/2 = 0.59 V (vs. Ag/AgCl reference) to generate catholyte solutions that display characteristic vanadium EPR at room temperature with eight-line pattern (51V, I = 7/2), each line being split into a doublet due to Re-superhyperfine coupling (A (185,187Re) = 20.7 × 10−4 cm−1).
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Oct 2008
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Abstract: The first layered iron borate, Fe5O5(B6O10(OH)(3)] center dot nH(2)O, has been prepared by the boric acid flux method, Its structure, determined by single crystal X-ray diffraction, contains a double FeO6-octahedral layer and an unusual [B6O13] chain. The rigid and cambered [B6O13] Chains bend the octahedral layers, resulting in a wave-like and sandwiched structure. Crystallographic study indicates the structural modulation is mainly from the [B6O13] chains because of the insertion of water molecules in between. Nevertheless, FeO6 layers in the average structure, which are well separated by borate chains, is still a reasonable model to understand the two-dimensional magnetism. The strong antiferromagnetic interactions and the complex Fe3+-net suggest a possible geometrically magnetic frustration, which may be the reason for the second-order temperature-induced magnetic transition at similar to 125 K. The condensed Fe3+ layers and the relatively low redox potential at about 1.25 V versus Li+/Li show its potentials as an anodic material.
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Oct 2009
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I19-Small Molecule Single Crystal Diffraction
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Manuel
Iglesias
,
Dirk J.
Beetstra
,
Kingsley J.
Cavell
,
Athanasia
Dervisi
,
Ian A.
Fallis
,
Benson M.
Kariuki
,
Ross W.
Harrington
,
William
Clegg
,
Peter
Horton
,
Simon
Coles
,
Michael B.
Hursthouse
Diamond Proposal Number(s):
[987]
Abstract: An unsaturated seven-membered amidinium salt 7 decomposes in the presence of metal salts under basic conditions. However, 7 readily forms a Diels–Alder cycloadduct with CpH from which the RhI complexes may be prepared. Thus, structurally elaborate, sterically crowded carbene ligand complexes bearing peripheral unsaturated functionality are available in a short versatile synthesis.
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Jun 2010
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[987]
Abstract: Six new layered lanthanide molybdate and tungstate phases pillared by either naphthalenedisulfonate (NDS) or fumarate anions have been synthesized hydrothermally and structurally characterized. Five of these materials, [Nd(H2O)MoO4]2[2,6-NDS] (1), [Nd(H2O)MoO4]2[1,5-NDS] (2), [La(H2O)WO4]2[1,5-NDS] (3), [La(H2O)WO4]2[2,6-NDS] (4), and [Ce(H2O)MoO4]2[fumarate] (6), have a closely related cationic inorganic layer structure which comprises a bilayer of polyhedra leading to the formation of a framework layer containing small, inaccessible pores. These layers are pillared by the organic anions which also bridge between the lanthanide cations within the layers. In the La/WO4/2,6-NDS system, a second polymorph, [La2(H2O)2W2O8][2,6-NDS] (5), is observed. In this compound, the tungstate anions have dimerized, forming W2O84?. This dimer is unique and comprises two square-based pyramidal tungsten centers which are opposed to each other.
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Sep 2010
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Abstract: New CoII members of the family of multifunctional materials of general formula [DAMS]4[M2Co(C2O4)6]·2DAMBA·2H2O (MIII = Rh, Fe, Cr; DAMBA = para-dimethylaminobenzaldehyde and [DAMS+] = trans-4-(4-dimethylaminostyryl)-1-methylpyridinium) have been isolated and characterized. Such new hybrid mixed metal oxalates are isostructural with the previously investigated containing ZnII, MnII, and NiII. This allows to preserve the exceptional second harmonic generation (SHG) activity, due to both the large molecular quadratic hyperpolarizability of [DAMS+] and the efficiency of the crystalline network which organizes [DAMS+] into head-to-tail arranged J-type aggregates, and to further tune the magnetic properties. In particular, the magnetic data of the RhIII derivative demonstrate that high spin octacoordinated CoII centers behave very similarly to the hexacoordinated CoII ones, being dominated by a large orbital contribution. The CrIII derivative is characterized by ferromagnetic CrIII−CoII interactions. Most relevantly, the FeIII compound is characterized by a moderate antiferromagnetic interaction between FeIII and CoII, resulting in a ferrimagnetic like structure. Its low temperature dynamic magnetic properties were found to follow a thermally activated behavior (τ0 = 8.6 × 10−11 s and ΔE = 21.4 K) and make this a candidate for the second oxalate-based single chain magnet (SCM) reported up to date, a property which in this case is coupled to the second order non linear optical (NLO) ones.
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Nov 2010
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6447]
Abstract: The systematic exploration of the phase diagram of the GeO2-1,6-diaminohexane-water-pyridine-HF system has allowed the identification of specific roles of the HF, H2O contents, and HF/H2O ratio in the formation of Ge7X19 (Ge7), Ge9X25?26 (Ge9), and Ge10X28 (Ge10) clusters (X = O, OH, F). This work has led to the discovery of two novel structures with extra-large 18-membered rings accommodating 1,6-diaminohexane (DAH): SU-63, |1.5H2DAH|[Ge7O14X3]·2H2O, a layered germanate constructed from Ge7 clusters with the Kagomé topology, and SU-64, |11H2DAH|[Ge9O18X4][Ge7O14X3]6·16H2O, a germanate built of two-dimensional slabs containing both Ge7 and Ge9 clusters (X = OH or F). We also put SU-64 in context with previously reported cluster germanate compounds with related topologies by means of a simple crystal deconstruction study.
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Nov 2010
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I04-Macromolecular Crystallography
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Abstract: Methanobactins (mbs) are a class of copper-binding peptides produced by aerobic methane oxidizing bacteria (methanotrophs) that have been linked to the substantial copper needs of these environmentally important microorganisms. The only characterized mbs are those from Methylosinus trichosporium OB3b and Methylocystis strain SB2. M. trichosporium OB3b produces a second mb (mb-Met), which is missing the C-terminal Met residue from the full-length form (FL-mb). The as-isolated copper-loaded mbs bind Cu(I). The absence of the Met has little influence on the structure of the Cu(I) site, and both molecules mediate switchover from the soluble iron methane mono-oxygenase to the particulate copper-containing enzyme in M. trichosporium OB3b cells. Cu(II) is reduced in the presence of the mbs under our experimental conditions, and the disulfide plays no role in this process. The Cu(I) affinities of these molecules are extremely high with values of (6?7) × 1020 M?1 determined at pH ? 8.0. The affinity for Cu(I) is 1 order of magnitude lower at pH 6.0. The reduction potentials of copper-loaded FL-mb and mb-Met are 640 and 590 mV respectively, highlighting the strong preference for Cu(I) and indicating different Cu(II) affinities for the two forms. Cleavage of the disulfide bridge results in a decrease in the Cu(I) affinity to ?9 × 1018 M?1 at pH 7.5. The two thiolates can also bind Cu(I), albeit with much lower affinity (? 3 × 1015 M?1 at pH 7.5). The high affinity of mbs for Cu(I) is consistent with a physiological role in copper uptake and protection.
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Jan 2011
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