Crystal structure of hexa-μ-chlorido-μ-oxido-tetra-kis-{[1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1-imidazole-κ ]copper(II)} containing short NO⋯NO contacts.

The title tetra-nuclear copper complex, [CuClO(CHNO)] or [CuClO-(MET)] [MET is 1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1-imidazole or metronidazole], contains a tetra-hedral arrangement of copper(II) ions. Each copper atom is also linked to the other three copper atoms in the tetra-hedron bridging chloride ions. A fifth coordination position on each metal atom is occupied by a nitro-gen atom of the monodentate MET ligand.

Coordination of 1-methyl-1,3-dihydro-2-benzimidazole-2-selone to zinc and cadmium: Monotonic and non-monotonic bond length variations for [H(sebenzim)]MCl complexes (M = Zn, Cd, Hg).

The reactions of 1-methyl-1,3-dihydro-2-benzimidazole-2-selone, H(sebenzim), towards the zinc and cadmium halides, MX (M = Zn, Cd; X = Cl, Br, I), afford the adducts, [H(sebenzim)]MX, which have been structurally characterized by X-ray diffraction. The halide ligands of each of these complexes participate in hydrogen bonding interactions with the imidazole N-H moieties, although the nature of the interactions depends on the halide. Specifically, the chloride and bromide derivatives, [H(sebenzim)]ZnX and [H(sebenzim)]CdX (X = Cl, Br), exhibit two intramolecular N-H•••X interactions, whereas the iodide derivatives, [H(sebenzim)]ZnI and [H(sebenzim)]CdI, exhibit only one intramolecular N-H•••I interaction.

Radical Isomerization and Cycloisomerization Initiated by H• Transfer.

Under H2 pressure, Co(II)(dmgBF2)2L2 (L = H2O, THF) generates a low concentration of an H• donor. Transfer of the H• onto an olefin gives a radical that can either (1) transfer an H• back to the metal, generating an isomerized olefin, or (2) add intramolecularly to a double bond, generating a cyclized radical. Transfer of an H• back to the metal from the cyclized radical results in a cycloisomerization.

Crystal structure of bis-[1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazole-κN (3)]silver(I) tetra-fluorido-borate methanol monosolvate.

1-(2-Hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazole (metronidazole, MET) is a medication that is used to treat infections by a variety of anaerobic organisms, but there are relatively few reports of the structures of metal compounds that exhibit coordination of metronidazole. We have demonstrated that MET reacts with AgBF4 to give [Ag(MET)2]BF4·CH3OH, in which the Ag(I) cation is coordinated by two MET ligands with a trans arrangement. The structure of [Ag(MET)2]BF4 exhibits some inter-esting differences from its nitrate counterpart, [Ag(MET)2]NO3 [Fun et al.

Protolytic cleavage of Hg-C bonds induced by 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone: synthesis and structural characterization of mercury complexes.

Multinuclear ((1)H, (77)Se, and (199)Hg) NMR spectroscopy demonstrates that 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzim(Me)), a structural analogue of the selenoamino acid, selenoneine, binds rapidly and reversibly to the mercury centers of HgX2 (X = Cl, Br, I), while X-ray diffraction studies provide evidence for the existence of adducts of composition [H(sebenzim(Me))]xHgX2 (X = Cl, x = 2, 3, 4; X = I, x = 2) in the solid state. H(sebenzim(Me)) also reacts with methylmercury halides, but the reaction is accompanied by elimination of methane resulting from protolytic cleavage of the Hg-C bond, an observation that is of relevance to the report that selenoneine demethylates CysHgMe, thereby providing a mechanism for mercury detoxification. Interestingly, the structures of [H(sebenzim(Me))]xHgX2 exhibit a variety of different hydrogen bonding patterns resulting from the ability of the N-H groups to form hydrogen bonds with chlorine, iodine, and selenium.

Influence of Benzannulation on Metal Coordination Geometries: Synthesis and Structural Characterization of (2-mercapto-1-methylbenzimidazolyl)hydroborato Cadmium Bromide, {[Tm]Cd(μ-Br)}.

The (2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium complex, {[Tm]Cd(μ-Br)}, may be synthesized the reaction of [Tm]K with CdBr. X-ray diffraction demonstrates that {[Tm]Cd(μ-Br)} exists as a dimer, which is in marked contrast to the monomeric structure of the non-benzannulated counterpart, [Tm]CdBr, and thereby demonstrates that benzannulation of (2-mercapto-1-methylbenzimidazolyl)hydroborato ligands can have a distinct impact on the molecular structure of their metal complexes. In accord with this observation, density functional theory calculations indicate that the benzannulated dimers, {[Tm]Cd(μ-X)} (X = Cl, Br, I), are more stable with respect to dissociation than are their non-benzannulated counterparts, {[Tm]Cd(μ-X)}.

Synthesis and Structural Characterization of 1-Arylimidazole-2-thiones and ,'-Aryldiethoxyethylthioureas with Electronically Diverse Substituents: A Manifold of Hydrogen Bonding Networks.

The 1-arylimidazole-2-thiones, (Hmim) [Ar = 3,4,5-CH(OMe), 2,4-CH(NO)(OMe), 2,4,6-CHCl and 3,5-CH(CF)], which feature electronically diverse substituents, may be obtained acid-catalyzed ring closure of the corresponding ,'-aryldiethoxyethylthiourea derivatives, ArN(H)C(S)N(H)CHCH(OEt), (Hdetu), which in turn are obtained treatment of aminoacetaldehyde diethyl acetal, HNCHCH(OEt), with the respective arylisothiocyanates (ArNCS). The molecular structures of all of the above ,'-aryldiethoxyethylthioureas and 1-arylimidazole-2-thiones have been determined by X-ray diffraction, thereby demonstrating that the substituents have a profound effect on the crystal structures. For example, each of the ,'-aryldiethoxyethylthiourea derivatives adopts a different hydrogen bonding pattern.

Synthesis and structural characterization of tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium halide complexes, {[Tm(MeBenz)]Cd(μ-Cl)}2 and [Tm(MeBenz)]CdI: a rare example of cadmium in a trigonal bipyramidal sulfur-rich coordination environment.

The tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium complexes, {[Tm(MeBenz)]Cd(μ-Cl)}2 and [Tm(MeBenz)]CdI, have been synthesized via the reactions of [Tm(MeBenz)]K with CdCl2 and CdI2, respectively. While X-ray diffraction studies demonstrate that the iodide derivative, [Tm(MeBenz)]CdI, is a monomer, the chloride derivative, {[Tm(MeBenz)]Cd(μ-Cl)}2, exists as a dimer, which is unprecedented for Group 12 [Tm(R)]MX (X = Cl, Br, I) compounds. Furthermore, the cadmium centers of {[Tm(MeBenz)]Cd(μ-Cl)}2 are trigonal bipyramidal, which is an uncommon motif for cadmium complexes with a [S3Cl2] coordination sphere.

Atomic structures and gram scale synthesis of three tetrahedral quantum dots.

Luminescent semiconducting quantum dots (QDs) are central to emerging technologies that range from tissue imaging to solid-state lighting. However, existing samples are heterogeneous, which has prevented atomic-resolution determination of their structures and obscured the relationship between their atomic and electronic structures. Here we report the synthesis, isolation, and structural characterization of three cadmium selenide QDs with uniform compositions (Cd35Se20(X)30(L)30, Cd56Se35(X)42(L)42, Cd84Se56(X)56(L)56; X = O2CPh, L = H2N-C4H9).

Benzannulated tris(2-mercapto-1-imidazolyl)hydroborato ligands: tetradentate κ4-S3H binding and access to monomeric monovalent thallium in an [S3] coordination environment.

The benzannulated tris(mercaptoimidazolyl)borohydride sodium complex, [Tm(Bu(t)Benz)]Na, has been synthesized via the reaction of NaBH4 with 1-tert-butyl-1,3-dihydro-2H-benzimidazole-2-thione, while [Tm(MeBenz)]K has been synthesized via the reaction of KBH4 with 1-methyl-1,3-dihydro-2H-benzimidazole-2-thione. The molecular structures of the solvated adducts, {[Tm(Bu(t)Benz)]Na(THF)}2(μ-THF)2 and [Tm(MeBenz)]K(OCMe2)3, have been determined by X-ray diffraction, which demonstrates that the [Tm(R)] ligands in these complexes adopt different coordination modes to that in {[Tm(MeBenz)]Na}2(μ-THF)3. Specifically, while the [Tm(MeBenz)] ligand of the sodium complex {[Tm(MeBenz)]Na}2(μ-THF)3 adopts a κ(3)-S3 coordination mode, the potassium complex [Tm(MeBenz)]K(OCMe2)3 adopts a most uncommon inverted κ(4)-S3H coordination mode in which the potassium binds to all three sulfur donors and the hydrogen of the B-H group in a linear KH-B manner.

Structural characterization of 1,3-propanedithiols that feature carboxylic acids: Homologues of mercury chelating agents.

The molecular structures of a series of 1,3-propanedithiols that contain carboxylic acid groups, namely - and -2,4-dimercaptoglutaric acid (HDMGA) and 2-carboxy-1,3-propanedithiol (HDMCP), have been determined by X-ray diffraction. Each compound exhibits two centrosymmetric intermolecular hydrogen bonding interactions between pairs of carboxylic acid groups, which result in a dimeric structure for HDMCP and a polymeric tape-like structure for - and -HDMGA. Significantly, the hydrogen bonding motifs observed for - and -HDMGA are very different to those observed for the 1,2-dithiol, -2,3-dimercaptosuccinic acid (-HDMSA), in which the two oxygen atoms of each carboxylic acid group hydrogen bond to two different carboxylic acid groups, thereby resulting in a hydrogen bonded sheet-like structure rather than a tape.

2-Seleno-1-alkylbenzimidazoles and their Diselenides: Synthesis and Structural Characterization of a 2-Seleno-1-methylbenzimidazole Complex of Mercury.

2-Seleno-1-methylbenzimidazole, H(sebenzim), can be synthesized from 1-methylbenzimidazole by sequential treatment with BuLi, elemental selenium and HCl(aq). This method is also applicable to the synthesis of 2-seleno-1-t-butylbenzimidazole, H(sebenzim ). Single crystal X-ray diffraction and NMR spectroscopic data demonstrate that H(sebenzim) and H(sebenzim ) exist as the selone rather than the selenol tautomers, which is in accord with the results of density functional theory (B3LYP) calculations.

Molecular redox: revisiting the electronic structures of the group 9 metallocorroles.

The electronic structures of monocationic tris[(5,10,15-pentafluorophenyl)-corrolato]iridium compounds, [Ir(tpfc)L2](+), where L = 4-cyanopyridine [1](+), pyridine [2](+), 4-methoxypyridine [3](+), or 4-(N,N'-dimethylamino)pyridine [4](+), have been probed by electron paramagnetic resonance (EPR) spectroscopy, Ir L3,2-edge X-ray absorption spectroscopy (XAS), UV/visible (UV-vis) spectroelectrochemistry, and density functional theoretical (DFT) calculations. The data demonstrate that these complexes, which have been previously formulated as either of the limiting cases [Ir(III)(tpfc(•))L2](+) or [Ir(IV)(tpfc)L2](+), are best described as possessing a singly occupied molecular orbital (SOMO) dominated by tpfc with small but significant Ir admixture. EPR g-values and electronic absorption spectra are reproduced well using a simple DFT approach.

Electron transfer triggered by optical excitation of phenothiazine-tris(meta-phenylene-ethynylene)-(tricarbonyl)(bpy)(py)rhenium(I).

We have investigated excited-state electron transfer in a donor-bridge-acceptor complex containing phenothiazine (PTZ) linked via tris(meta-phenylene-ethynylene) to a tricarbonyl(bipyridine)(pyridine)Re(I) unit. Time-resolved luminescence experiments reveal two excited-state (*Re) decay regimes, a multiexponential component with a mean lifetime of 2.7 ns and a longer monoexponential component of 530 ns in dichloromethane solution.

Iodinated aluminum(III) corroles with long-lived triplet excited states.

The first reported iodination of a corrole leads to selective functionalization of the four C-H bonds on one pole of the macrocycle. An aluminum(III) complex of the tetraiodinated corrole, which exhibits red fluorescence, possesses a long-lived triplet excited state.

Electronic structures of Group 9 metallocorroles with axial ammines.

The electronic structures of metallocorroles (tpfc)M(NH(3))(2) and (tfc)M(NH(3))(2) (tpfc is the trianion of 5,10,15-(tris)pentafluorophenylcorrole, tfc is the trianion of 5,10,15-trifluorocorrole, and M = Co, Rh, Ir) have been computed using first principles quantum mechanics [B3LYP flavor of Density Functional Theory (DFT) with Poisson-Boltzmann continuum solvation]. The geometry was optimized for both the neutral systems (formal M(III) oxidation state) and the one-electron oxidized systems (formally M(IV)). As expected, the M(III) systems have a closed shell d(6) configuration; for all three metals, the one-electron oxidation was calculated to occur from a ligand-based orbital (highest occupied molecular orbital (HOMO) of B(1) symmetry).

Outer-sphere effects on reduction potentials of copper sites in proteins: the curious case of high potential type 2 C112D/M121E Pseudomonas aeruginosa azurin.

Redox and spectroscopic (electronic absorption, multifrequency electron paramagnetic resonance (EPR), and X-ray absorption) properties together with X-ray crystal structures are reported for the type 2 Cu(II) C112D/M121E variant of Pseudomonas aeruginosa azurin. The results suggest that Cu(II) is constrained from interaction with the proximal glutamate; this structural frustration implies a "rack" mechanism for the 290 mV (vs NHE) reduction potential measured at neutral pH. At high pH (∼9), hydrogen bonding in the outer coordination sphere is perturbed to allow axial glutamate ligation to Cu(II), with a decrease in potential to 119 mV.

Near-IR phosphorescence of iridium(III) corroles at ambient temperature.

The photophysical properties of Ir(III) corroles differ from those of phosphorescent porphyrin complexes, cyclometalated and polyimine Ir(III) compounds, and other luminescent metallocorroles. Ir(III) corrole phosphorescence is observed at ambient temperature at wavelengths much longer (>800 nm) than those of most Ir(III) phosphors. The solvatochromic behavior of Ir(III)-corrole Soret and Q absorption bands suggests that the lowest singlet excited states (S(2) and S(1)) are substantially more polar than the ground state.

Structures and reactivity patterns of group 9 metallocorroles.

Group 9 metallocorroles 1-M(PPh(3)) and 1-M(py)(2) [M = Co(III), Rh(III), Ir(III); 1 denotes the trianion of 5,10,15-tris-pentafluorophenylcorrole] have been fully characterized by structural, spectroscopic, and electrochemical methods. Crystal structure analyses reveal that average metal-N(pyrrole) bond lengths of the bis-pyridine metal(III) complexes increase from Co (1.886 A) to Rh (1.