SciCombinator

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Concept: Complex

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TONs of copper fun: There is considerable interest in developing catalysts to harness the abundant natural supply of methane for various industrial applications. Two tricopper complexes capable of mediating efficient oxidation of methane to methanol under ambient conditions were tested: a biomimetic tricopper complex and a tricopper-peptide species derived from the particulate methane monooxygenase (pMMO) protein.

Concepts: Complex, Iron, Enzyme, Oxygen, Nitrogen, Methane, Methane monooxygenase, Hydrogen

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Zn(II) complexes of the following new, fluorine-containing, benzothiazole-derived ligands have been synthesized and characterized crystallographically: 2-(3,3,3-trifluoro-2-oxopropyl)benzothiazole (3), 4,5,6,7-tetrafluoro-2-(3,3,3-trifluoro-2-oxopropyl)benzothiazole (4), 4,5,6,7-tetrafluoro-2-(2-hydroxyphenyl)benzothiazole (12), 2-(3,4,5,6-tetrafluoro-2-hydroxyphenyl)-4,5,6,7-tetrafluorobenzothiazole (13), and 2-(3,4,5,6-tetrafluoro-2-hydroxyphenyl)benzothiazole (16); the Cu(II) complex of ligand 4 is also reported. These are analogs of the important photo- and electroluminescent material [Zn(BTZ)(2)](2), where H-BTZ = 2-(2-hydroxyphenyl)benzothiazole. DFT calculations indicate that HOMO and LUMO energy levels in these materials are substantially lowered by fluorination. The fluorinated ZnL(2) complexes are mononuclear (in contrast to the dinuclear, nonfluorinated material [Zn(BTZ)(2)](2)). They easily sublime and show broad visible photoluminescence. A common crystallographic feature is the existence of pairs of fluorinated ZnL(2) molecules related by inversion centers, with their π systems facing one another.

Concepts: Benzene, Following, Material, Complex, Electroluminescence, Luminescence, HOMO/LUMO, Ligand

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Despite the extensive interest in structurally explaining the photophysics of DNA-bound [Ru(phen)(2)dppz](2+) and [Ru(bpy)(2)dppz](2+), the origin of the two distinct emission lifetimes of the pure enantiomers when intercalated into DNA has remained elusive. In this report, we have combined a photophysical characterization with a detailed isothermal titration calorimetry study to investigate the binding of the pure Δ and Λ enantiomers of both complexes with [poly(dAdT)](2). We find that a binding model with two different binding geometries, proposed to be symmetric and canted intercalation from the minor groove, as recently reported in high-resolution X-ray structures, is required to appropriately explain the data. By assigning the long emission lifetime to the canted binding geometry, we can simultaneously fit both calorimetric data and the binding-density-dependent changes in the relative abundance of the two emission lifetimes using the same binding model. We find that all complex-complex interactions are slightly unfavorable for Δ-[Ru(bpy)(2)dppz](2+), whereas interactions involving a complex canted away from a neighbor are favorable for the other three complexes. We also conclude that Δ-[Ru(bpy)(2)dppz](2+) preferably binds isolated, Δ-[Ru(phen)(2)dppz](2+) preferably binds as duplets of canted complexes, and that all complexes are reluctant to form longer consecutive sequences than triplets. We propose that this is due to an interplay of repulsive complex-complex and attractive complex-DNA interactions modulated by allosteric DNA conformation changes that are largely affected by the nature of the ancillary ligands.

Concepts: Explanation, Origin, Intercalation, Complex, Proposal, Geometry, DNA, Structure

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The dynamics of iron tetracarbonyl olefin complexes has been investigated using two-dimensional infrared (2D-IR) spectroscopy. Cross peaks between all CO-stretching bands show that the CO-stretch modes are coupled, and from the cross-peak anisotropies we can confirm previous assignments of the absorption bands. From the pump-probe delay dependence of the diagonal peaks in the 2D-IR spectrum we obtain a correlation time of ∼3 ps for the spectral fluctuations of the CO-stretch modes. We observe a multi-exponential pump-probe delay dependence of the cross-peak intensities, with rate constants ranging from 0.1 ps(-1) to 0.6 ps(-1). To determine whether this delay dependence originates from fluxionality of the complex or from intramolecular vibrational relaxation (IVR), we modulate the free-energy barrier of fluxional rearrangement by varying the pi-backbonding capacities of the olefin ligand in two iron tetracarbonyl olefin complexes: Fe(CO)(4)(cinnamic acid) and Fe(CO)(4)(dimethyl fumarate). Since the pi-backbonding strongly influences the rate of fluxionality, comparing the dynamics in the two complexes allows us to determine to what extent the observed dynamics is caused by fluxionality. We conclude that on the time scale of our experiments (up to 100 ps) the cross-peak dynamics in the iron complexes is determined by intramolecular vibrational energy relaxation. Hence, in contrast to previously investigated irontricarbonyl and ironpentacarbonyl complexes, iron tetracarbonyl olefin complexes exhibit no fluxionality on the picosecond time scale.

Concepts: Complex, Fluxional molecule, Spectrum, Observation, Hypothesis, Iron pentacarbonyl, Time, Spectroscopy

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A new synthesis of (8-quinolyl)-5-methoxysalicylaldimine (Hqsal-5-OMe) is reported and its crystal structure is presented. Two Fe(III) complexes, [Fe(qsal-5-OMe)(2) ]Cl⋅solvent (solvent=2 MeOH⋅0.5 H(2) O (1) and MeCN⋅H(2) O (2)) have been prepared and their structural, electronic and magnetic properties studied. [Fe(qsal-5-OMe)(2) ] Cl⋅2 MeOH⋅0.5 H(2) O (1) exhibits rare crystallographically independent high-spin and low-spin Fe(III) centres at 150 K, whereas [Fe(qsal-5-OMe)(2) ]Cl⋅ MeCN⋅H(2) O (2) is low spin at 100 K. In both structures there are extensive π-π and CH⋅⋅⋅π interactions. SQUID magnetometry of 2 reveals an unusual abrupt stepped-spin crossover with T(½) =245 K and 275 K for steps 1 and 2, respectively, with a slight hysteresis of 5 K in the first step and a plateau of 15 K between the steps. In contrast, 1 is found to undergo an abrupt half-spin crossover also with a hysteresis of 10 K. The two compounds are the first Fe(III) complexes of a substituted qsal ligand to exhibit abrupt spin crossover. These conclusions are supported by (57) Fe Mössbauer spectroscopy. Both complexes exhibit reversible reduction to Fe(II) at -0.18 V and irreversible oxidation of the coordinated qsal-5-OMe ligand at +1.10 V.

Concepts: Complexity, Exhibition, Complex, Iron, Redox, Magnetism, Structure, Magnetic field

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The thorium(iv) tetraiodide complex ThI(4)(DME)(2) () (DME = 1,2-dimethoxyethane) has been prepared in high yield by reacting the corresponding chloride complex ThCl(4)(DME)(2) with an excess of trimethylsilyl iodide (Me(3)SiI) in toluene. This new route avoids the use of thorium metal as a reagent. ThI(4)(DME)(2) () exhibits excellent thermal stability compared to ThI(4)(THF)(4) (), which undergoes rapid ring-opening of THF at ambient temperature to yield the iodobutoxide complex ThI(3)[O(CH(2))(4)I](THF)(3) (). Subsequent ligand-exchange between and DME affords ThI(3)[O(CH(2))(4)I](DME)(2) (), which can be converted to with Me(3)SiI. Salt metathesis between and K(L(Me)) (L(Me) = (2,6-(i)Pr(2)C(6)H(3))NC(Me)CHC(Me)N(2,6-(i)Pr(2)C(6)H(3))) cleanly gives (L(Me))ThI(2)[O(CH(2))(4)I](THF) (), which is a rare example of a thorium β-diketiminate complex. Complexes , , and represent the first reported examples of THF ring-opening mediated by thorium. The synthetic utility of ThI(4)(DME)(2) () is demonstrated by preparation of thorium(iv) alkoxide, amide, and organometallic compounds.

Concepts: Complexity, Tetrahydrofuran, Complex, Organometallic chemistry, Thorium, Olefin metathesis, Chloride, Solvent

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The synthesis of mixed tethered alkyl uranium metallocenes has been investigated by examining the reactivity of the bis(tethered alkyl) metallocene [(η(5) -C(5) Me(4) SiMe(2) CH(2) -κC)(2) U] (1) with substrates that react with only one of the UC linkages. The effect of these mixed tether coordination environments on the reactivity of the remaining UC bond has been studied by using CO insertion chemistry. One equivalent of azidoadamantane (AdN(3) ) reacts with 1 to yield the mixed tethered alkyl triazenido complex [(η(5) -C(5) Me(4) SiMe(2) CH(2) -κC)U(η(5) -C(5) Me(4) SiMe(2) -CH(2) NNN-Ad-κ(2) N(1,3) )]. Similarly, a single equivalent of CS(2) reacts with 1 to form the mixed tethered alkyl dithiocarboxylate complex [(η(5) -C(5) Me(4) SiMe(2) CH(2) -κC)U(η(5) -C(5) Me(4) SiMe(2) - CH(2) C(S)(2) -κ(2) S,S')], a reaction that constitutes the first example of CS(2) insertion into a U(4+) C bond. Complex 1 reacts with one equivalent of pyridine N-oxide by CH bond activation of the pyridine ring to form a mixed tethered alkyl cyclometalated pyridine N-oxide complex [(η(5) -C(5) Me(4) SiMe(2) CH(2) -κC)(η(5) -C(5) Me(4) SiMe(3) )U(C(6) H(4) NO-κ(2) C,O)]. The remaining (η(5) -C(5) Me(4) SiMe(2) CH(2) -κC)(2-) ligand in each of these mixed tethered species show reactivity towards CO and tethered enolate ligands form by insertion. Subsequent rearrangement have been identified in [(η(5) -C(5) Me(4) SiMe(3) )U(C(5) H(4) NO-κ(2) C,O)(η(5) -C(5) Me(4) SiMe(2) C(CH(2) )O-κO)] and [(η(5) -C(5) Me(4) SiMe(2) CH(2) NNN-Ad-κ(2) N(1,3) )U(η(5) -C(5) Me(4) SiMe(2) C(CH(2) )O-κO)].

Concepts: Tether propulsion, Coordination number, Complexity, Complex, Tether, Ligand

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Now even terminal: The 2,4,6-trimethylbenzylidyne complexes [MesCM{OC(CF(3) )(2) Me}(3) ] (M=Mo, W) were synthesized from [Mo(CO)(6) ] and [W(CO)(6) ], respectively. The molybdenum complex is an efficient catalyst for the metathesis of internal and terminal alkynes and also for the ring-closing metathesis of internal and terminal α,ω-diynes at room temperature and low catalyst concentrations.

Concepts: Complexity, Alkyne, Complex, Olefin metathesis

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Biomimetic complexes are artificially engineered molecules that aim to reduce the structural complexity of biological systems in order to unveil the key electronic and structural factors relevant to a protein’s function. In this work, a novel coordination compound () which mimics non-heme binuclear proteins was synthesized from the Schiff-base ligand HL = (E)-N'-(phenyl(pyridin-2-yl)methylene)isonicotinohydrazide. The crystal structure of showed that the intramolecular Fe-Fe distances (3.1-3.2 Å) were analogous to those found in non-heme binuclear ferric proteins. However, in , two methoxide groups act as bridging units for oxidized iron (Fe(3+)). Such a bridging motif is unprecedented in the biological realm. Magnetic susceptibility measurements demonstrated that is characterized by a singlet (S = 0) ground state and a very small magnetic coupling constant J (≪ -1 cm(-1)). The J value featured by differs considerably from the values observed in non-heme binuclear proteins in the oxidized form (-100 cm(-1) < J < -10 cm(-1)), which encompass oxo/hydroxo and carboxylate bridging residues. The singlet ground state of as well as the weak magnetic interaction between the two ferric cations was successfully predicted by density functional theory (DFT).

Concepts: Complex, Ligand, Oxygen, Magnetism, Density functional theory, Scientific method, Magnetic susceptibility, Iron

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Zipper injuries are highly distressing to patients and often difficult to manage. Several management techniques are described in the literature. Many are complex and laborious, requiring sophisticated instruments in skilled hands, or even rely on a formal operation. This new technique involves the release of entrapped penile skin from a zipper by cutting the zipper tape and teeth immediately superior and inferior to the zipper connector and using a needle holder to pull the zipper apparatus apart following the application of lubrication and appropriate use of local analgesia. This novel technique is quick, nontraumatic and requires readily available equipment. It has been used successfully in two patients who were ineligible for a circumcision.

Concepts: Skin bridge, Creativity techniques, Leadership, Complex, Superiority complex, Penis, Inferiority complex, Management