Dimeric Moieties Research Articles

1-(2,6-dimethylphenyl)-5-allylsulfanyl-1H-tetrazole and its copper(I) tetrafluoroborate n,σ-complex: synthesis, structure and quantum-chemical calculations

1-(2,6-Dimethylphenyl)-5-allylsulfanyl-1 H -tetrazole ( o-dmphast ) and its copper(I) tetrafluoroborate p,σ-complex [Cu 2 ( o-dmphast ) 2 (BF 4 ) 2 ] ( 1 ) were synthesized and X-ray structurally studied. o-Dmphast was prepared in several stages by known protocol, starting from 2,6-dimethyl aniline. The single crystals of 1 were obtained by means of the alternating-current electrochemical technique. The collected diffraction data were processed using CrysAlis RED program. The structures were solved by ShelXT program and refined by least squares method on F 2 by ShelXL program with the following graphical user interface of OLEX 2 . Compound 1 crystallizes in the centrosymmetric space group : a = 7.405(3)), b = 7.786(3), c = 11.625(4) Å, a = 101.90(3) , β = 100.88(3) , g = 104.81(3) , V = 613.0(4) Å 3 , Z = 2. π-Complexe crystallizes in the centrosymmetric space group P 2 1 /n .: a = 9.271(3), b = 14.171(4), c = 11.956(4) Å, β = 91.52(3) , V = 1570.2(9) Å 3 , Z = 2. Allylsulfanyl group of o-dmphast has synclinal conformation relative to the S1—C3 bond and antisynclinal conformation relative to the C2—C3 bond (the corresponding torsion angles C5—S1—C3—C2 and S1—C3—C2—C1 are 76.5(2) and –118.0(3)). In the structure of o-dmphast , the hydrogen atom of the one methyl group (C13) and the hydrogen atom of the methylene group of the allyl substituent form weak С−H···N hydrogen bonds with the nitrogen atoms of the tetrazole ring of neighboring molecules. Tetrazole rings of the nearest molecules are involved in the π···π-stacking interaction at a distance of 3.44 Å. Structure of 1 is built of centrosymmetric dimers which are formed by coordination to two Cu + ions of two chelate-bridging molecules o-dmphast . The dimeric moieties contain a six-membered {Cu 2 N 4 } ring comprised of two pairs of [ - N - N - ] tetrazole fragments. π-Coordinated Cu(I) cation adopts a close to a trigonal pyramidal coordination environment (2N, (C=C) + F). The corresponding four-coordinate geometry indexes τ 4 is 0.78. Copper(I) ion and allylic group (C1, C2 and С3 atoms) in 1 are disordered over two sites with an occupancy ratio of 0.522(4):0.478(4). Fluorine atoms of the anion are also disordered over two sites with an occupancy ratio of 0.737(3):0.263(3). To further analyse the intermolecular interactions in the structures of o-dmphast , Hirshfeld surface analysis and energy framework computational analysis have been performed. Keywords: copper(I), π-complex, allyl derivative of tetrazole, crystal structure, quantum-chemical calculations.

Assessing Cu2L2X4 dimeric moieties as ferromagnetic building blocks in double halide-bridged polymers (X = Cl−, Br− and L = benzamide). An experimental and computational study

Two isostructural double halide-bridged polymers, consisting of stacked Cu2L2X4 dimers, with L = benzamide (BA) and X = Cl− in CuClBA and X = Br− in CuBrBA, were synthesised. The experimental magnetic data of both compounds were recorded and it was found that the χm data fitted a 1D alternating FM/AFM model. A computational First-Principles Bottom-Up computational study was conducted to understand the micro- and bulk magnetic properties. It was determined that a strong ferromagnetic (FM) interaction occurs within the Cu2BA2X4 dimer, with an anti-ferromagnetic (AFM) interaction diagonally connecting Cu2BA2X4 dimeric moieties. For CuClBA, a 1D alternating FM/AFM chain topology was found, whereas CuBrBA shows additional competing interactions within the 1D alternating FM/AFM chain. Strikingly, the magnetic topology for both compounds is different than that expected from crystal packing analyses. Tuning the weaker competing interactions within the double halide-bridged chains might be a good strategy to extend the bulk FM character of the compound.

Spacer-Armed Copper(II) Complex Based on Bis(2-pyidyl-1,2,4-triazol-3-yl)butane and 1-Aminoethane-1,1-Diphosphonic Acid

The new complex [Cu4L2(H2AEDP)2(H2O)4] · 34H2O was prepared by the reaction of CuSO4 with bis(2-pyridyl-1,2,4-triazol-3-yl)butane (H2L) and 1-aminoethane-1,1-diphosphonic acid (H4AEDP) and studied by X-ray diffraction (CIF file CCDC no. 1913117). The complex is a spacer-armed dimer in which two dimer subunits formed with participation of diphosphonate dianions are linked to each other via two doubly deprotonated bis(pyridyl)triazoles. The bridging diphosphonate anion exists in the zwitter ion form, bis(triazolyl)butane is coordinated via the nitrogen atoms of the pyridyl moiety and the deprotonated triazole ring. Analysis of the ESR spectrum of the polycrystalline sample attests to weak exchange interactions in the dimeric moieties.

A robust self-healing polyurethane elastomer: From H-bonds and stacking interactions to well-defined microphase morphology

Self-healing materials have attracted considerable attention because of their improved safety, lifetime, energy efficiency and environmental impact. Supramolecular interactions have been extensively considered in the field of self-healing materials due to their excellent reversibility and sensitive responsiveness to environmental stimuli. However, development of a polymeric material with good mechanical performance as well as self-healing capacity is very challenging. In this study, we report a robust self-healing polyurethane (PU) elastomer polypropylene glycol-2-amino-5-(2-hydroxyethyl)-6-methylpyrimidin-4-ol (PPG-mUPy) by integrating ureidopyrimidone (UPy) motifs with a PPG segment with a well-defined architecture and microphase morphology. To balance the self-healing capacity and mechanical performance, a thermal-triggered switch of H-bonding is introduced. The quadruple H-bonded UPy dimeric moieties in the backbone induce phase separation to form a hard domain as well as enable further aggregation into microcrystals by virtue of the stacking interactions, which are stable in ambient temperature. This feature endows the PU with high mechanical strength. Meanwhile, a high healing efficiency can be realized, when the reversibility of the H-bond was unlocked from the stacking at higher temperature. An optimized sample PPG1000-mUPy50% with a good balance of mechanical performance ( 20.62 MPa of tensile strength) and healing efficiency (93% in tensile strength) was achieved. This strategy will provide a new idea for developing robust self-healing polymers.

Cellular protective effect of novel dimeric ferulamide derivatives against UVA and 1 O 2 and its structural mechanism

Abstract N,N′-Diferuloyl-putrescine (DFP) containing ferulamide moiety has skin whitening and antioxidative activities. In this study, we synthesized DFP (n = 4), DFP-1 (n = 3) and DFP-2 (n = 2) with different diamide linkage chain lengths connecting dimeric ferulamide moieties. DFP-1 had higher antioxidative activities and cell penetration ratio than other derivatives for the cellular protective effects against UVA and 1O2. We identified that these oxidative protective effects of DFP-1 were contributed by low steric hindrance on electron donor groups and dipole moment through homogeneous electron density. These results suggest that DFP-1 could be used as potential antioxidative ingredient.

Synthesis, crystal structure, and luminescent properties of silver complexes with 2-methylquinoline

The complexes [AgL2(NO3)] (I) and [AgL2(CH3SO3)] · H2O (II) (L is 2-methylquinoline, C10H9N) have been synthesized and structurally characterized by single-crystal X-ray diffraction. Crystals of I are monoclinic, space group P21/n, a = 9.296(1) A, b = 13.495(1) A, c = 14.931(1) A, β = 95.06(1)°, V = 1865.8(3) A3, ρcalc = 1.624 g/cm3, Z = 4. Crystals of II are monoclinic, space group P21/n, a = 13.147(1) A, b = 11.767(1) A, c = 13.814(1) A, β = 96.06(1)°, V = 2124.3(3) A3, ρcalc = 1.599 g/cm3, Z = 4. Compounds I and II are composed of discrete complexes of similar structure but with different orientation of the methyl groups of ligand L (trans and cis arrangement, respectively). Both anions, NO3- and CH3SO3- function as a chelating weakly bound ligand for the Ag+ ion. The presence of water molecules in II is favorable for the formation of dimeric supramolecular moieties between the centrosymmetrically arranged Ag+ complexes with 2-methylquinoline. The luminescence spectra of solid complexes I and II showed a bathochromic shift as compared to the spectrum of L in acetonitrile. Complexes I and II have been characterized by 1H and 13C{H} NMR spectra in CD3CN.

Polyamine derivatives as potential bisintercalators with antiproliferative activity

Bisntercalators are very interesting group of compounds with potential antitumor activity. They interact reversibly with DNA double helix. These agents share common structural features such as the presence of two, planar, polycyclic aromatic or heteroaromatic systems separated by a spacer chain which must be long enough to enable double intercalation between base pairs. The unique chemical structure of these compounds provides numerous modifications within their structure resulting either in higher activity or increased selectivity toward tumor cells. Within the framework of the project, new polyamine derivatives containing dimeric phthalimide, quinoline, cinnoline and chromone moieties were obtained. Three different polyamines: 1,4-bis(3-aminopropyl)piperazine, 4,9-dioxa-1,12-dodecanediamine, 3,3’-diamino-N-methyldipropylamine were used as linkers. The biological activity of compounds was assessed in vitro in a highly aggressive melanoma cell line A375. Quinoline derivatives were found to have a higher antiproliferative activity than cinnoline ones. The lowest IC50 values, below 20 μM, were obtained for quinoline and 2H-chromene-2,4(3H)-dione derivatives. Quinoline diamides were more efficient than cinnoline ones. Polyamine diimides containing phthalimide moieties demonstrated no inhibitory activities against melanoma cells. Preliminary studies of mechanism of action have shown that obtained derivatives were capable of quenching the fluorescence of ethidium bromide-DNA complex, indicating that they bound to ds-DNA in competition with ethidium bromide for binding sites. All the compounds were also subjected to preliminary in silico ADME screening by evaluating their theoretical drug-likeness and physicochemical properties using Discovery Studio 3.0 obtained from Accelrys. Compounds meeting the required ADME and drug-likeness criteria were selected.

Alignment of Palladium Complexes into Columnar Liquid Crystals Driven by Peripheral Triphenylene Substituents

A new triphenylene-imine (ImH) and its ortho-palladated complexes (μ-X)2[Pd2Im2] (X = CH3COO(-), Cl(-), Br(-)), (μ-Cl)(μ-SCnH2n+1)[Pd2Im2] (n = 6, 12), [PdIm(acac)] [PdIm Cl(CNC6H4OC12H25)], [PdImCl(CNC6H3(OC12H25)2)], and [PdImCl(CNC6H2(OC12H25)3)] have been prepared. The free imine ligand is not a liquid crystal, but most ortho-metalated dinuclear palladium complexes and the mononuclear trialkoxyphenyl isocyanide derivative display columnar mesophases at temperatures close to ambient. For the dimeric complexes the mesophase obtained is always columnar rectangular (Colr), with an uncommon structure: the dimeric triphenylene-Pd complex-triphenylene molecules give rise to a triple-column stacking consisting of two columns of stacked triphenylene groups connected to a central column formed by stacking of two ortho-palladated dimeric moieties. For the trialkoxyphenyl isocyanide derivative a related polymer-like arrangement of columns alternating stacking of triphenylenes with stacking of two ortho-palladated dimeric moieties is found. The mesophase structure is columnar oblique (Colob). The free imine and all palladium complexes exhibit fluorescence at room temperature in dichloromethane solution, associated with the triphenylene core.

Two Organic–Inorganic Hybrids Assembled by Carboxylate-Bridging Lanthanide-Substituted Polyoxometalate Dimers with Copper–ethylendiamine Cations

Two new organic–inorganic hybrid carboxylate-bridging copper–lanthanide heterometallic polyoxotungstates K2[Cu(en)2(H2O)]2{[Cu(en)2]3[Ce(GeW11O39)(H2O)2]2(C2O4)}·11H2O (1) and K2 [Cu(en)2(H2O)]2{[Cu(en)2(H2O)]2[Tb(PW11O39)(CH3COO)(H2O)]2}·15H2O (2) (en = 1,2-ethylenediamine) have been prepared under hydrothermal conditions and characterized by elemental analyses, IR spectra, powder X-ray diffraction (PXRD), thermogravimetric (TG) analyses and X-ray single-crystal diffraction. X-ray structural analyses reveal that 1 exhibits the 1D zigzag chain architecture formed by dimeric oxalate-bridging {[Cu(en)2]3[Ce(GeW11O39)(H2O)2]2(C2O4)}6− units and [Cu(en)2]2+ linkers whereas 2 displays a typical hybrid acetate-bridging dimeric structure [(α-PW11O39)Tb(H2O)(η2,μ-1,1)–CH3COO] 2 10− modified by [Cu(en)2(H2O)]2+ fragments. Notably, both contain 2:2-type carboxylate-bridging monolanthanide-substituted Keggin-type dimeric moieties and two types of organic ligands. 1 represents the rare 1D Cu–Ln heterometallic germanotungstate containing mixed ligands of en and oxalate whereas 2 represents the rare dimeric organic–inorganic hybrid Keggin-type phosphotungstate containing both Cu–Ln heterometals and mixed ligands of en and acetate. Two new organic–inorganic hybrid copper–lanthanide heterometallic polyoxotungstates containing mixed organic ligands of en and carboxylate were successfully separated under hydrothermal conditions. 1 exhibits the 1D zigzag chain architecture formed by dimeric oxalate-bridging {[Cu(en)2]3[Ce(GeW11O39)(H2O)2]2(C2O4)}6− units by [Cu(en)2]2+ linkers, whereas 2 displays a typical hybrid acetate-bridging dimeric structure [(α-PW11O39)Tb(H2O)(η2,μ-1,1)–CH3COO] 2 10− modified by [Cu(en)2(H2O)]2+ fragments.

Two 3d–4f heterometallic monovacant Keggin phosphotungstate derivatives

Two 3d–4f heterometallic monovacant Keggin phosphotungstate derivatives [Cu(dap)(H2O)2]0.5[Cu(dap)2]4H2[Pr(α-PW11O39)2] · 3H2O (1) and [Cu(en)2(H2O)]2[Cu(en)2]1.5H4[Pr(α-PW11O39)2] · 10H2O (2) (dap = 1,2-diaminopropane, en = ethylenediamine) have been hydrothermally synthesized by reaction of the trivacant Keggin phosphotungstate precursor Na9[A-α-PW9O34] · 7H2O with CuCl2 · 2H2O and PrCl3 in the presence of dap or en and structurally characterized by elemental analyses, IR spectra, X-ray single-crystal diffraction, and thermogravimetric analyses. Compound 1 crystallizes in the triclinic space group P 1 with a = 17.325(3), b = 18.917(3), c = 19.938(3) Å, α = 104.481(2), β = 98.968(3), γ = 91.306(3)°, V = 6236.4(18) Å3, Z = 2, GOOF = 1.000, R 1 = 0.0806, wR 2 = 0.2016. Compound 2 also belongs to the triclinic space group P 1 with a = 16.005(4), b = 18.053(4), c = 21.127(5) Å, α = 113.894(3), β = 90.745(4), γ = 94.255(4)°, V = 5560(2) Å3, Z = 2, GOOF = 0.999, R 1 = 0.0686, wR 2 = 0.1885. Both 1 and 2 display organic–inorganic hybrid 2-D sheet architectures built by classic mono-PrIII sandwiched dimeric moieties [Pr(α-PW11O39)2]11− through [Cu(L)2]2+ bridges (L = dap, en), which represent rare organic–inorganic hybrid 2-D 3d–4f heterometallic monovacant Keggin polyoxometalates.

Photoelectron spectroscopic study of the anionic transition metalorganic complexes [Fe1,2(COT)]− and [Co(COT)

The gas-phase, iron and cobalt cyclooctatetraene cluster anions, [Fe(1,2)(COT)](-) and [Co(COT)](-), were generated using a laser vaporization source and studied using mass spectrometry and anion photoelectron spectroscopy. Density functional theory was employed to compute the structures and spin multiplicities of these cluster anions as well as those of their corresponding neutrals. Both experimental and theoretically predicted electron affinities and photodetachment transition energies are in good agreement, authenticating the structures and spin multiplicities predicted by theory. The implied spin magnetic moments of these systems suggest that [Fe(COT)], [Fe(2)(COT)], and [Co(COT)] retain the magnetic moments of the Fe atom, the Fe(2) dimer, and the Co atom, respectively. Thus, the interaction of these transition metal, atomic and dimeric moieties with a COT molecule does not quench their magnetic moments, leading to the possibility that these combinations may be useful in forming novel magnetic materials.

Synthesis, Crystal Structures, and Magnetic Properties of Three New Iron Complexes Derived from 3,5‐Bis(pyridin‐2‐yl)‐1,2,4‐triazole

AbstractTwo new iron(III) complexes and one iron(II) complex have been synthesized from the solvothermal reactions of FeCl3·6H2O with 3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole (Hbpt) in methanol or acetonitrile. KSCN acted as the reducing agent in the synthesis of iron(II) complex of 3. [FeCl3(Hbpt)(H2O)]·H2O (1) crystallizes in the triclinic space group $P{\bar 1}$ with a = 7.475(1), b = 9.468(2), c = 12.309(2) Å, α = 73.880(2), β = 74.746(2), γ = 81.849(2)°, V = 805.2(2) Å3, Z = 2. [Fe2(bpt)2Cl4] (2): orthorhombic space group Pnnm with a = 9.895(2), b = 10.632(2), c = 13.195(2) Å, V = 1388.1(4) Å3, Z = 2. [Fe2(bpt)2(MeOH)2Cl2] (3): orthorhombic space group Pbca with a = 14.4204(16), b = 9.8737(11), c = 19.792(2) Å, V = 2818.1(5) Å3, Z = 4. 1 features the first structurally characterized metal complex of the neutral Hbpt ligand in which the Hbpt ligand adopts an unprecedented zwitterionic form. 2 shows a neutral dinuclear iron(III) complex and the [Fe2(bpt)2]4+ unit is ideally planar. The two iron(III) ions separated by a distance of 4.408(2) Å are doubly triazolate‐bridged. Each dimeric unit is connected with six other dimeric ones via the bifurcated C‐H···Cl hydrogen bonds, these connections extend the dimeric moieties into a three‐dimensional molecular architecture. 3 is a neutral centrosymmetric dinuclear FeII complex, in which intermolecular moderate O‐H···N hydrogen bonding interactions between the methanol molecules and 4‐position nitrogen atoms of the triazolato groups extend the dinuclear species into a two‐dimensional supramolecular architecture of (4,4) topology. Magnetic studies indicate there exists an antiferromagnetic spin coupling in FeIII2 and FeII2 units via the double triazolate bridges in 2 and 3.

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.

New mesomorphic organocyclosiloxanes II. Thermal behaviour and mesophase structure of organocyclohexasiloxanes†

Investigations of thermotropic phase transitions performed on organocyclosiloxanes [PhSi(O)OSiR]6, where R is Me3, Me2(CH2Cl) or Me2(CH≃CH2), have revealed that all these hexamers are mesomorphic compounds. The hexamers exhibit uncommon polymesomorphic behaviour forming two quite different mesomorphic structures. The molecular arrangement in the low temperature (LT) modification is characterized by two-dimensional (2D) long-range order with hexagonal packing. The X-ray diffraction pattern and peculiarities of molecular packing in the crystal lead us to suggest that the LT-mesophase is columnar, presumably of the Colhd type. The LT-mesophase is formed by dimeric moieties, which associate with each other in column-like substructures, the ring planes not orthogonal to the stack axis. The high temperature (HT) mesophase is a plastic crystal (3D-order), where molecules take up positions in a face-centred cubic lattice. This is a very uncommon example of thermal behaviour for plastic crystals that provides a unique opportunity to bridge the gap between plastic crystalline and liquid crystalline mesomorphic behaviour. The thermal and structural properties of the mesophases depend upon the type of side groups of the hexamers. The size of the ring also affects the phase behaviour and the mesomorphic structure. This conclusion is consistent with data obtained by us earlier for cyclotetrasiloxanes.

Synthesis and chiral HPLC analysis of the dibenzyltetrahydrofuran lignans, larreatricins, 8'-epi-larreatricins, 3,3'-didemethoxyverrucosins and meso-3,3'-didemethoxynectandrin B in the creosote bush (Larrea tridentata): evidence for regiospecific control of coupling.

The creosote bush (Larrea tridentata) lignans are linked via 8-8' bonds, with the simplest apparently being E-p-anol derived. Of the latter, four of the six theoretically possible diastereoisomers were isolated, namely (-)-larreatricin, (-)-8'-epi-larreatricin, meso-3,3'-didemethoxynectandrin B and the new compounds, (+)- and (-)-3,3'-didemethoxyverrucosins. Following synthesis of each in either racemic or meso form, and chiral HPLC separation of the antipodes of the racemates, it was established that naturally occurring (-)-larreatricin and (-)-8'-epi-larreatricin were present in 92 and 98% enantiomeric excess, respectively, whereas 3,3'-didemethoxyverrucosin was essentially racemic and 3,3'-didemethoxynectandrin B was in the meso-form. The evidence suggests that formation of these lignans occurs under regiospecific, rather than stereoselective, coupling control. This contrasts with laccase-catalyzed "random" coupling of E-p-anol in vitro which generates the corresponding racemic 8-8', 8-3' and 8-O-4' linked dimeric moieties.

A double-decker silver(I) coordination polymer of 1-methylpyrene with columnar aromatic stacks. Effect of substituting groups on structure of silver(I) complexes with polycyclic aromatic hydrocarbons.

A novel silver(I) coordination polymer of 1-methylpyrene (mpyr) with double-decker motifs, {[Ag2(mpyr)2(ClO4)2]0.5benzene}n (1), was synthesized and characterized. Polymer 1 consists of 1-D double-decker chains, which are formed by dimeric double-decker units ([Ag(mpyr)(ClO4)]2) through the linkage of the perchlorate groups. In addition, the dimeric moieties between the adjacent chains are stacked to lead to column π−π stacks. Therefore, complex 1 can also be regarded as a 2-D stacking polymer. The effects of substituting groups, and other factors, on the structure of silver(I) complexes with polycyclic aromatic hydrocarbons are also discussed.

Weakly coordinating anions HA2-generated from oxoanions A- and their conjugate acids. Coordination equilibria, ionic conductivities, and the structures of [Cu2(H(CH3SO3)2)4]n and [Cu(CO)(H(CF3CO2)2)]2.

The coordination or ion pairing of the hydrogen-bonded anions H(CF3CO2)2- and H(CH3SO3)2- to NEt4+, Li+, Cu+, and/or Cu2+ was investigated. The structure of [Cu2(H(CH3SO3)2)4]n consists of centrosymmetric dimeric moieties that contain two homoconjugated (CH3SO2O-H...OSO2CH3)- anions per Cu2+ ion, forming typical Jahn-Teller tetragonally elongated CuO6 coordination spheres. The oxygen atoms involved in the nearly linear O-H...O hydrogen bonds (O...O approximately 2.62 A) are not coordinated to the Cu2+ ions. The structure of Cu2(CO)2(H(CF3-CO2)2)2 consists of pseudo-C2-symmetric dimers that contain one homoconjugated (CF3COO-H...OCOCF3)- anion per Cu+ ion, forming highly distorted tetrahedral Cu(CO)O3 coordination spheres. Three of the four oxygen atoms in each hydrogen-bonded H(CF3CO2)2- anion are coordinated to the Cu+ ions, including one of the oxygen atoms in each O-H...O hydrogen bond (O...O approximately 2.62 A). Infrared spectra (v(CO) values) of Cu(CO)(CF3CO2) or Cu(CO)(CH3SO3) dissolved in acetonitrile or benzene, with and without added CF3COOH or CH3SO3H, respectively, demonstrate that HA2- anions involving carboxylates or sulfonates are more weakly coordinating than the parent anions RCO2- and RSO3-. Direct current conductivities of THF solutions of Li(CF3CO2) containing varying concentrations of added CF3COOH further demonstrate that Li+ and NEt4+ ion pair much more weakly with H(CF3CO2)2- than with CF3CO2-.

(Imidazole-N3)(N-salicylidene-α-aminoisobutyrato-O,N,O')copper(II) Dimer

The title compound, [Cu(C11H11NO3)(C3H4N2)], adopts a square-pyramidal CuII coordination with a tridentate N-salicylidene-α-aminoisobutyrato Schiff-base dianion and the imidazole ligand bound in the basal plane. The apex of the pyramid is occupied by a phenolic O atom from the neighbouring chelate at an apical distance of 2.623 (2) Å, building a dimeric structural unit in which the copper(II) ions are magnetically equivalent. The dimeric moieties in the crystal packing are tilted with respect to each other leading to a distorted antiferrodistortive ordering.

Location, catalytic activity, and subunit composition of NAD-reducing hydrogenases of some Alcaligenes strains and Rhodococcus opacus MR22

Six new strains of Alcaligenes enriched for and isolated as nickel-resistant bacteria resemble Alcaligenes eutrophus H16 and contain both an NAD-reducing, tetrameric soluble hydrogenase and a membrane-bound hydrogenase. None of the soluble hydrogenases share with the Rhodococcus opacus MR11 enzyme tetramer the property of being cleaved easily into two dimeric moieties [a hydrogenase (betadelta) and an NADH:acceptor oxidoreductase (alphagamma)], in the absence of nickel or at low ionic strength. The soluble hydrogenase of the newly isolated strain MR22 of R. opacus equalled that of strain MR11. The absence of a membrane-bound hydrogenase in Alcaligenes denitrificans strain 4a-2 and in Alcaligenes ruhlandii was confirmed.

Network hydrogen bonding: the crystal and molecular structure of cubane-1,3,5,7-tetracarboxylic acid dihydrate

The structure of cubane-1,3,5,7-tetracarboxylic acid dihydrate (1) has been determined. It crystallizes in the space groupP21/c with cell dimensionsa=6.503(1),b=19.173(1),c=10.527(1) A, β=101.60(1). The details of this structure have reaffirmed the fact that the cubane skeleton is a flexible entity which reflects its steric and electronic environment. Of the four carboxylic acid groups three adopt asyn conformation while the fourth adopts ananti conformation. The orientation of these groups with respect to the cubane skeleton is reflected in the C−C bond lengths. Those C−C bonds which are perpendicular to the carboxylic acid groups are the longest and those which are most nearly eclipsed are the shortest in the cubane skeleton. In all cases it is the C=O rather than the C−O bond which is most nearly eclipsed with a C−C bond. The tetrahedral orientation of the substitutents does not express itself in a three dimensional supramolecular assembly; however, all four carboxylic acid groups are involved in very strong donor hydrogen bonds which result in a two dimensional array parallel to (100). An additional surprising results is the fact that none of the four substituents participate in traditional hydrogen bonded carboxylic acid dimeric moieties.