Chemical Stabilization and Electrochemical Destabilization of the Iron Keggin Ion in Water.

The iron Keggin ion is identified as a structural building block in both magnetite and ferrihydrite, two important iron oxide phases in nature and in technology. Discrete molecular forms of the iron Keggin ion that can be both manipulated in water and chemically converted to the related metal oxides are important for understanding growth mechanisms, in particular, nonclassical nucleation in which cluster building units are preserved in the aggregation and condensation processes. Here we describe two iron Keggin ion structures, formulated as [Bi6FeO4Fe12O12(OH)12(CF3COO)10(H2O)2]3+ (Kegg-1) and [Bi6FeO4Fe12O12(OH)12(CF3COO)12]1+ (Kegg-2). Experimental and simulated X-ray scattering studies show indefinite stability of these clusters in water from pH 1-3. The tridecameric iron Keggin-ion core is protected from hydrolysis by a synergistic effect of the capping Bi3+ cations and the trifluoroacetate ligands that, respectively, bond to the iron and bridge to the bismuth. By introducing electrons to the aqueous solution of clusters, we achieve complete separation of bismuth from the cluster, and the iron Keggin ion rapidly converts to magnetite and/or ferrihydrite, depending on the mechanism of reduction. In this strategy, we take advantage of the easily accessible reduction potential and crystallization energy of bismuth. Reduction was executed in bulk by chemical means, by voltammetry, and by secondary effects of transmission electron microscopy imaging of solutions. Prior, we showed a less stable analogue of the iron Keggin cluster converted to ferrihydrite simply upon dissolution. The prior and currently studied clusters with a range of reactivity provide a chemical system to study molecular cluster to metal oxide conversion processes in detail.

3-(1,3-Di-phenyl-propan-2-yl)-4-methyl-6-phenyl-isoxazolo[3,4-d]pyridazin-7(6H)-one.

In the title compound, C27H23N3O2, the geminal benzyl groups branching out from the methine adjacent to the isoxazole group are both syn-oriented to the methyl group of the pyridazinone moiety, as reflected by C-C distances of 3.812 (2) and 4.369 (2) Šbetween the methyl carbon and the nearest ring carbon of each benzyl group. This kind of conformation is retained in CDCl3 solution, as evidenced by distinct phenyl-shielding effects on the (1)H NMR signals of the methyl H atoms. The isoxazolo[3,4-d]pyridazin ring system is virtually planar (r.m.s. deviation from planarity = 0.031 Å), but the N-bonded phenyl group is inclined to the former by an ring-ring angle of 55.05 (3)°. In the crystal, the T-shaped mol-ecules are arranged in an inter-locked fashion, forming rod-like assemblies along [10-1]. The mol-ecules are held together by unremarkable weak C-H⋯N, C-H⋯O and C-H⋯π inter-actions (C-O,N,C > 3.4 A), while significant π-π-stacking inter-actions are absent.

Semiquinone-bridged bisdithiazolyl radicals as neutral radical conductors.

Semiquinone-bridged bisdithiazolyls 3 represent a new class of resonance-stabilized neutral radical for use in the design of single-component conductive materials. As such, they display electrochemical cell potentials lower than those of related pyridine-bridged bisdithiazolyls, a finding which heralds a reduced on-site Coulomb repulsion U. Crystallographic characterization of the chloro-substituted derivative 3a and its acetonitrile solvate 3a·MeCN, both of which crystallize in the polar orthorhombic space group Pna2(1), revealed the importance of intermolecular oxygen-to-sulfur (CO···SN) interactions in generating rigid, tightly packed radical π-stacks, including the structural motif found for 3a·MeCN in which radicals in neighboring π-stacks are locked into slipped-ribbon-like arrays. This architecture gives rise to strong intra- and interstack overlap and hence a large electronic bandwidth W. Variable-temperature conductivity measurements on 3a and 3a·MeCN indicated high values of σ(300 K) (>10(-3) S cm(-1)) with correspondingly low thermal activation energies E(act), reaching 0.11 eV in the case of 3a·MeCN. Overall, the strong performance of these materials as f = ½ conductors is attributed to a combination of low U and large W. Variable-temperature magnetic susceptibility measurements were performed on both 3a and 3a·MeCN. The unsolvated material 3a orders as a spin-canted antiferromagnet at 8 K, with a canting angle φ = 0.14° and a coercive field H(c) = 80 Oe at 2 K.

Ferrocene-based trimethylsilyl chalcogenide reagents for the assembly of functionalized metal-chalcogen architectures.

The ferrocene-based trimethylsilyl chalcogenide reagents [FcC(O)OCH(2)CH(2)ESiMe(3)] (2, E=S, 3 E=Se, Fc=[Fe(η(5)-C(5)H(5))(η(5)-C(5)H(4))]) and [FcC(O)NHCH(2)CH(2) SSiMe(3)] (8b) have been synthesized. The reagents were reacted with solubilized transition-metal acetates to yield functionalized complexes and clusters, including the spherical nanocluster [Ag(14)S{SCH(2)CH(2)O(O)CFc)}(12)(PPh(3))(6)] (11, PPh(3) =triphenylphosphine). The complexes were characterized by NMR spectroscopy and X-ray crystallography. The electrochemical behavior of the complexes was explored by cyclic voltammetry and each displayed a single quasi-reversible redox wave with some adsorption to the electrode surface.

Self-assembly of alkali-uranyl-peroxide clusters.

The hexavalent uranium specie, uranyl triperoxide, UO(2)(O(2))(3)(4-), has been shown recently to behave like high oxidation-state d(0) transition-metals, self-assembling into polyoxometalate-like clusters that contain up to 60 uranyl cations bridged by peroxide ligands. There has been much less focus on synthesis and structural characterization of salts of the monomeric UO(2)(O(2))(3)(4-) building block of these clusters. However, these could serve as water-soluble uranyl precursors for both clusters and materials, and also be used as simple models to study aqueous behavior by experiment and modeling. The countercation is of utmost importance to the assembly of these clusters, and Li(+) has proven useful for the crystallization of many of the known cluster geometries to date. We present in this paper synthesis and structural characterization of two monomeric lithium uranyl-peroxide salts, Li(4)[UO(2)(O(2))(3)] x 10 H(2)O (1) and [UO(2)(O(2))(3)](12)[(UO(2)(OH)(4))Li(16)(H(2)O)(28)](3) x Li(6)[H(2)O](26) (2). They were obtained from aqueous-alcohol solutions rather than the analogous aqueous solutions from which lithium uranyl-peroxide clusters are crystallized. Rapid introduction of the alcohol gives the structure of (1) whereas slow diffusion of alcohol results in crystallization of (2). (2) is an unusual structure featuring uranyl-centered alkali clusters that are linked into ring and spherical arrangements via [UO(2)(O(2))(3)] anions. Furthermore, partial substitution of Rb or Cs into the synthesis results in formation of (2) with substitution of these larger alkalis into the uranyl-centered clusters. We surmise that the slow crystallization allows for direct bonding of alkali metals to the uranyl-peroxide oxygen ligands that is observed in (2), and its Rb and Cs-substituted derivatives. In contrast, the only interaction between UO(2)(O(2))(3)(4-) and Li(+) observed in (1) is through hydrogen bonding of the lithium-bound water. These structures potentially provide some insight to understanding how alkali counterions interact with the UO(2)(O(2))(3)(4-) anions during the self-assembly, crystallization and even redissolution of uranyl-peroxide polyanionic clusters.

Series of comparable dinuclear group 4 neo-pentoxide precursors for production of pH dependent group 4 nanoceramic morphologies.

A series of similarly structured Group 4 alkoxides was used to explore the cation effect on the final ceramic nanomaterials generated under different pH solvothermal (SOLVO) conditions. The synthesis of [Ti(µ-ONep)(ONep)(3)](2) (1, ONep = OCH(2)C(CH(3))(3)) and {[H][(µ-ONep)(3)M(2)(ONep)(5)(OBu(t))]} where M = Zr (2) and Hf (3, OBu(t) = OC(CH(3))(3)) were realized from the reaction of M(OBu(t))(4) (M = Ti, Zr, Hf) and H-ONep. Crystallization of 1 from py led to the isolation of [Ti(µ-ONep)(ONep)(3)](2)(µ-py) (1a) whereas the dissolution of 2 or 3 in py yielded {(µ(3)-O)(µ(3)-OBu(t))[(µ-ONep)M(ONep)(2)](3)} M = Zr (2a) and Hf (3a). The structurally similar congener set of 1-3 was used to investigate variations of their resultant nanomaterials under solvothermal conditions at high (10 M KOH), low (conc. (aq) HI), and neutral (H(2)O) pH conditions. Reproducible nanodots, -squares, and -rods of varied aspect ratios were isolated based on cation and the reaction pH. The hydrolysis products were reasoned to be the "seed" nucleation sites in these processes, and studying the hydrolysis behavior of 1-3 led to the identification of [Ti(6)(µ(3)-O)(7)(µ-O)(µ-ONep)(2)(ONep)(6)](2) (1b) for 1 but yielded 2a and 3a for 2 and 3, respectively. A correlation was found to exist between these products and the final nanomaterials formed for the acidic and neutral processes. The basic route appears to be further influenced by another property, possibly associated with the solubility of the final nanoceramic material.

Comparisons of Pu(IV) and Ce(IV) diphosphonates.

The hydrothermal reaction of PuO(2) with CH(2)(PO(3)H(2))(2) results in the formation of alpha-Pu[CH(2)(PO(3))(2)](H(2)O), beta-Pu[CH(2)(PO(3))(2)](H(2)O) (1), gamma-Pu[CH(2)(PO(3))(2)](H(2)O) (2), and Pu[CH(2)(PO(3))(2)](H(2)O).H(2)O (3) as crystalline compounds with blue, green, red, and very pale peach coloration, respectively. In all cases single crystal X-ray diffraction studies reveals Pu(4+) coordinated by [CH(2)(PO(3))(2)](4-) and water to yield PuO(7) units. The methylenediphosphonate anions bridge between these units to yield three-dimensional networks. Bond-valence parameters of R(o) = 2.068 and b = 0.385 have been derived for Pu(4+) using a combination of the data reported in this work with that available in crystallographic databases. UV-vis-NIR spectroscopic measurements demonstrate that despite the dramatic color differences all of the compounds contain Pu(4+), and that subtle changes in the visible region of the spectra account for different colors.

Homo- and heterometallic complexes of tetra-(di-substituted hydroxybenzyl)-N,N'-ethylenediamine derivatives.

The coordination behavior of a series of group 4 metal alkoxides [M(OR)(4)] modified by a set of novel substituted hydroxybenzyl ethylene diamine (H(4)-ED-L(4)) ligands {[tetra(3,5-di-t-butyl-2-hydroxybenzyl)-N,N'-ethylenediamine] termed H(4)-ED-DBP(4) (1), [tetra(3,5-di-t-amyl-2-hydroxybenzyl)-N,N'-ethylenediamine] termed H(4)-ED-DAP(4) (1a), and [tetra(3,5-dichloro-2-hydroxybenzyl)-N,N'-ethylenediamine] termed H(4)-ED-DCP(4) (2)} was elucidated. The reaction of 1 or 1a with the M(OR)(4) precursor led to the isolation of the structural similar species M(ED-L(4)) where L = DBP, M = Ti (3), Zr (4), Hf (5); L = DAP, M = Zr (4a), Hf (5a). In contrast, the reaction of 2 with the M(OR)(4) precursors yielded Ti(ED-DCP(4)) (6), (py)(2)Zr(ED-DCP(4)) (7), and (HOBu(t))Hf(ED-DCP(4)) (8) where py = pyridine and HOBu(t) = HOC(CH(3))(3). For 3-6, the cations of the monomeric species were completely encapsulated by all available heteroatoms (four O and two N) of the ED-L(4) ligands, yielding an octahedral geometry for each metal center. For 7 and 8, an identical binding by the ED-DCP(4) ligand was observed with the additional coordination of Lewis basic adducts, forming 8- and 7-coordinated metal centers, respectively. Switching to +2 cations led to the isolation of [(THF)Ca](2)(ED-DBP(4)) (9a) where THF = tetrahydrofuran, {[(py)Ca](4)(ED-(mu-DBP-eta(6))(4))(2)}(n) (9b), and [(py)Zn](ED-DBP(4))[Zn(py)(2)] (10) *5py and [(py)Sn](2)(ED-DBP(4)) (11). The structures of these species were significantly different in arrangement compared to the Group 4 derivatives. Further attempts to produce a mixed +4/+2 cationic species yielded [(py)(ONep)(2)Ti(ED-DBP(4))Zn(py)] (12). Reacting the single-source precursor Co[mu-OC(6)H(4)(CHMe(2))(2)-2)(2)Li(py)(2)](2) with 1, led to the isolation of (py)Li[ED-DBP(3)(H-DBP)]Co (13), with one of the phenol protons remaining unreacted. The synthesis and characterization of these compounds are presented in detail.

Iron and Cobalt Complexes of 2,6-Diacetylpyridine-bis(R-thiosemicarbazone) (R=H, phenyl) Showing Unprecedented Ligand Deviation from Planarity.

The syntheses, characterization, and single-crystal X-ray crystal structures are reported for four complexes of iron and cobalt with the pentadentate ligands, 2,6-diacetylpyridinebis(thiosemicarbazone) (H(2)L(1)) and 2,6-diacetylpyridinebis-(phenylthiosemicarbazone) (H(2)L(2)), including a cobalt dimer displaying a deviation from planarity which is unprecedented for this class of ligands and allows the ligand to occupy five positions of a pseudo-octahedral coordination sphere. This dimer reacts with KCN to produce a mononuclear complex of relevance to the active site of cobalt nitrile hydratase.

A 3,5-dinitro-benzoyl derivative of a stereoisomer of glycerol menthonide.

The title compound, [(2S,5R,6S,9R)-6-isopropyl-9-methyl-1,4-dioxaspiro-[4.5]dec-2-yl]methyl 3,5-dinitro-benzoate, C(20)H(26)N(2)O(8), was synthesized as part of a study of three-carbon stereochemical systems. The crystallographic assignment of the absolute stereochemistry is consistent with having started with (-)-menthone, the acetal carbon is R and the secondary alcohol is S. This brings the dinitro-benzoate into approximately the same plane as the menthyl ring and anti to the isopropyl group. Close inter-molecular C=O⋯NO(2) contacts between neighboring mol-ecules [2.8341 (16) Å] contribute to the packing arrangement. The structure was refined as a pseudo-merohedral twin (monoclinic space group P2(1) emulating the ortho-rhom-bic space group C222(1)). Application of the twin law 100, 00, 0 gave a 2:1 ratio of twin moieties [refined BASF value = 0.3790 (7)].

Antimony oxide hydroxide ethanedisulfonate: a cationic layered metal oxide for Lewis acid applications.

We have discovered a rare example of a cationically charged inorganic material. The layered structure is an example outside the extensively studied isostructural set of anionic clays/layered double hydroxides and our previously reported lead fluoride nitrate. For the present compound, the antimony oxide hydroxide layers are positively charged and are templated by anionic alkylenedisulfonate. The organic molecules are only bonded electrostatically to the layers with sulfonate oxygen to antimony distances beyond the covalent range. The material catalyzes a ketal formation reaction as a Lewis acid without the need for drying the solvent before the reaction or a nonaqueous medium such as toluene. The catalyst is heterogeneous and is completely recovered after the catalysis for reapplication.

A unique heterobimetallic benzyl calciate--an organometallic mixed-metal species involving a heavy alkaline-earth metal.

A co-complexation reaction utilizing homometallic benzylcalcium and benzyllithium affords a rare example of a heterobimetallic benzyl calciate.

Implications of bond disorder in a S=1 kagome lattice.

Strong hydrogen bonds such as F···H···F offer new strategies to fabricate molecular architectures exhibiting novel structures and properties. Along these lines and, to potentially realize hydrogen-bond mediated superexchange interactions in a frustrated material, we synthesized [H2F]2[Ni3F6(Fpy)12][SbF6]2 (Fpy = 3-fluoropyridine). It was found that positionally-disordered H2F+ ions link neutral NiF2(Fpy)4 moieties into a kagome lattice with perfect 3-fold rotational symmetry. Detailed magnetic investigations combined with density-functional theory (DFT) revealed weak antiferromagnetic interactions (J ~ 0.4 K) and a large positive-D of 8.3 K with ms = 0 lying below ms = ±1. The observed weak magnetic coupling is attributed to bond-disorder of the H2F+ ions which leads to disrupted Ni-F···H-F-H···F-Ni exchange pathways. Despite this result, we argue that networks such as this may be a way forward in designing tunable materials with varying degrees of frustration.

{1,1'-Bis[(pyridin-2-yl)meth-yl]-2,2'-bipiperid-yl}(perchlorato)copper(II) perchlorate.

The title complex, [CuII(ClO4)(mesoPYBP)](ClO4) {PYBP = 1,1'-bis-[(pyridin-2-yl)meth-yl]-2,2'-bipiperidyl, C22H30N4}, was prepared and found to crystallize with two crystallographically independent complex salt moieties. The metal atoms of the cations adopt a pseudo-square-pyramidal coordination geometry, where the tetra-dentate amino-pyridine ligands (PYBP) are wrapped around the Cu atoms in the equatorial plane. The Cu-O bonds involving an O atom of the coordinating perchlorate anion are approximately perpendicular to the plane. The two remaining non-coordinating perchlorate anions are involved in several C-H⋯O hydrogen bonds with the PYBP ligand and balance the total charge of the complex salt. The two crystallographically independent moieties are related to each other via a pseudo-translation along the a-axis direction. Exact translational symmetry is broken by (i) a difference in the conformation of one of the piperidine rings, featuring a chair conformation in one of the cations, and a sterically disfavored boat conformation in the other; and (ii) by modulation of the non-coordinating perchlorate anions.

A chiral, heterometallic metal-organic framework derived from a tris(chelate) coordination complex.

A novel tris(chelate) metalloligand has been used to synthesize a chiral, heterometallic metal-organic framework that is robust to solvent removal and shows selective uptake of nitroaromatic compounds.

Nickel (II) complexes of naphthaquinone thiosemicarbazone and semicarbazone: synthesis, structure, spectroscopy, and biological activity.

Ni(II) complexes of ortho-naphthaquinone thiosemicarbazone and semicarbazone were synthesized and spectroscopically characterized. The X-ray crystal structure of both the complexes describe a distorted octahedral coordination with two tridentate mono-deprotonated ligands. In vitro anticancer studies on MCF-7 human breast cancer cells reveal that the semicarbazone derivative along with its nickel complex is more active in the inhibition of cell proliferation than the thiosemicarbazone analogue.

Crystal structure of poly[[[µ4-5-(9H-carbazol-9-yl)isophthalato][µ3-5-(9H-carbazol-9-yl)isophthalato]bis-(di-methyl-formamide)(methanol)dizinc] di-methyl-formamide monosolvate].

The structure of the polymeric title compound, {[Zn2(C20H11NO4)2(C3H7NO)2(CH3OH)]·C3H7NO} n , comprises carbazolylisophthalate moieties connecting dimetallic tetra-carboxyl-ate zinc secondary building units (SBUs) parallel to [100] and [010], leading to a layer-like arrangement parallel to (001). Each SBU consists of two Zn atoms in slightly distorted tetra-hedral and octa-hedral coordination environments [Zn⋯Zn = 3.5953 (6) Å]. Three carboxyl-ate groups bridge the two Zn atoms in a µ2-O:O' mode, whereas the fourth coordinates through a single carboxyl-ate O atom (µ1-O). The O atoms of two di-methyl-formamide (DMF) and one methanol mol-ecule complete the Zn coordination spheres. The methanol ligand inter-acts with the noncoordinating DMF mol-ecule via an O-H⋯O hydrogen bond of medium strength. Carbazoles between the layers inter-digitate through weak C-H⋯.π inter-actions to form a laminar solid stacked along [010]. Two kinds of C-H⋯π inter-actions are present, both with a distance of 2.64 Å, between the H atoms and the centroids, and a third C-H⋯π inter-action, where the aromatic H atom is located above the carbazole N-atom lone pair (H⋯N = 2.89 Å). Several C-H⋯O inter-actions occur between the coordinating DMF mol-ecule, the DMF solvent mol-ecule, and ligating carboxyl-ate O atoms.