SciCombinator

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Concept: Coordination chemistry

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This tutorial review discusses the structural and electronic consequences of the Jahn-Teller effect in transition metal complexes, focussing on copper(ii) compounds which tend to be the most studied. The nature of a Jahn-Teller distortion in molecular complexes and extended lattices can be manipulated by application of pressure or temperature, by doping a molecule into a host lattice, or simply by molecular design. Many of these results have been achieved using compounds with a trans-[CuX(4)Y(2)] coordination sphere, which seems to afford copper centres that are particularly sensitive to their environment. Jahn-Teller distortions lead to some unusual phenomena in molecular magnetism, and are important to the functionality of important classes of conducting and superconducting ceramics.

Concepts: Electron, Oxygen, Chemical bonding, Zinc, Coordination chemistry, Inorganic chemistry, Silver, Jahn–Teller effect

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Metal (II) complexes derived from S-benzyl-N-(1-ferrocenyl-3-(4-methylbenzene)acrylketone) dithiocarbazate; HL(1), S-benzyl-N-(1-ferrocenyl-3-(4-chlorobenzene)acrylketone)dithiocarbazate; HL(2), all the compounds were characterized using various spectroscopic techniques. The molar conductance data revealed that the chelates were non-electrolytes. IR spectra showed that the Schiff bases were coordinated to the metal ions in a bidentate manner with N, S donor sites. The ligands and their metal complexes have been screened for in vitro antibacterial, antifungal properties. The result of these studies have revealed that zinc (II) complexes 6 and 13 of both the ligands and copper (II) complexes 9 of the HL(2) were observed to be the most active against all bacterial strains, antifungal activity was overall enhanced after complexation of the ligands.

Concepts: Spectroscopy, Ligand, Metal, Zinc, Copper, Coordination chemistry, Silver, Schiff base

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The exact structure of the active site of intermediate , the methane-oxidizing species of soluble methane monooxygenase (sMMO), and the reaction mechanism of with methane molecule are still not fully clear. To gain further insights into the structure and reaction mechanism, five diiron models of that differ in shape, oxidation state, spin state, and coordination number of the two iron centers are studied. Different mechanisms in different spin states were explored. Density functional theory (DFT) calculations show that Fe(III)Fe(IV)(μ-O)(μ-OH) is more reactive than Fe(IV)(2)(μ-O)(2) in the oxygen-rich environment and that the reactivity of the active core of sMMO- is not enhanced by converting its oxo bridge into a terminal ligand. A four-coordinated diiron model is the most effective for methane hydroxylation. Both radical and non-radical intermediates are involved in the reactions for the four-coordinated diiron model.

Concepts: Chemical reaction, Redox, Chemistry, Coordination chemistry, Density functional theory, Carbon monoxide, Coordination number, Methane monooxygenase

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In the title complex salt, [Ir(C(5)H(4)O)(C(16)H(22)N(6))(CO)](CF(3)O(3)S), the Ir(III) centre adopts a distorted octahedral geometry with a facial coordination of the tris(3,5-dimethyl-1H-pyrazol-1-yl)methane ligand. The C-C distances of the iridacycle are in agreement with its iridacyclohexa-2,5-dien-4-one nature, which presents a nonsymmetric boat-like conformation with the C-Ir-C vertex more bent than the C-C(=O)-C vertex. The supramolecular architecture is mainly directed by CO…CO and CO…π and Csp(3)-H…O interactions, the arrangement of which depends on the anion.

Concepts: Ammonia, Mathematics, Stereochemistry, Chemistry, Ligand, Coordination chemistry, Director, Octahedral molecular geometry

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Platinum(ii) complexes comprising abnormal diimidazolylidene ligands were synthesized from cis-PtMe(2)(DMSO)(2) using microwave-assisted double C-H bond activation. NMR analysis revealed an unusual solvolysis process, induced by coordinating solvents such as DMSO and MeCN, which has not been observed in related normal dicarbene complexes. NMR and IR spectroscopy and crystallographic analysis of the mono-substituted DMSO complex indicate a sulfur-bonding of the DMSO ligand to the platinum(ii) center. Analysis of the DMSO exchange kinetics provided for the first time a quantitative measure of the trans effect of abnormal carbene ligands. The kinetic exchange rate in these bidentate abnormal dicarbene complexes is 0.050(±2) s(-1) and thus similar to analogous platinum(ii) complexes containing phenylpyridine, yet significantly slower than that induced by pyridylidene pyridine. Reaction of the dicarbene platinum(ii) complexes with PhICl(2), Br(2) and I(2) afforded the corresponding platinum(iv) complexes. Linkage isomerism of the Pt(IV)-bound DMSO was observed when the bromination reaction was performed in DMSO solution. Moreover, solvolysis was less pronounced in the platinum(iv) complexes than in the corresponding platinum(ii) analogues.

Concepts: Ligand, Denticity, EDTA, Chemical bonding, Coordination chemistry, Solvent, C-H bond activation, Acetonitrile

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Eleven mononuclear copper(II), nickel(II), zinc(II) and cobalt(II) complexes of Schiff base ligands derived from 3,5-dibromosalicylaldehyde/3,5-dichlorosalicylaldehyde were synthesized and determined by single crystal X-ray analysis. The crystal structures of complexes 1, 2, 4, 5, 6, 8 and 11 present the square-planar coordination geometry at the metal center and complexes 7, 9 and 10 show the distorted tetrahedral geometry. While one copper center in 3 has a square-planar geometry, the other copper is slightly distorted square-planar. The inhibitory activities of all the obtained complexes were tested in vitro against jack bean urease. It was found that Schiff base copper(II) complexes 1, 3, 5, 8 and 11 showed strong urease inhibitory activities (IC(50) = 1.51-3.52 μM) compared with acetohydroxamic acid (IC(50) = 62.52 μM), which was a positive reference. Their structure-activity relationships were further discussed.

Concepts: Acid, Coordination complex, Ligand, Metal, Zinc, Coordination chemistry, Solid, Schiff base

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The complexation of Cm(iii) and Eu(iii) with 2,6-bis(5,6-di(sulfophenyl)-1,2,4-triazin-3-yl)pyridine (aq-BTP) is studied in water at pH 3.0 applying time-resolved laser fluorescence spectroscopy. With increasing ligand concentration [M(H(2)O)(9-3n)(aq-BTP)(n)] (M = Cm(iii)/Eu(iii), n = 1, 2, 3) complex species are spectroscopically identified. The conditional stability constants of the M(iii) 1 : 3 complex species with aq-BTP are log β(03) = 12.2 for Cm(iii) and log β(03) = 10.2 for Eu(iii). The complexation reaction is enthalpy- and entropy-driven for both metal ions, while the enthalpy change ΔH(03) is 9.7 kJ mol(-1) more negative for Cm(iii); changes in ΔS(03) are marginal. The difference in ΔG(03) of -12.7 kJ mol(-1) between the formation of the [M(aq-BTP)(3)] complexes agrees with aq-BTP’s selectivity in liquid-liquid extraction studies.

Concepts: Spectroscopy, Ligand, Lone pair, Coordination chemistry, Inorganic chemistry, Enthalpy, Logarithm, Standard enthalpy change of formation

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The interaction of trivalent lanthanide and actinide cations with polyaminopolycarboxylic acid complexing agents in lactic acid buffer systems is an important feature of the chemistry of the TALSPEAK process for the separation of trivalent actinides from lanthanides. To improve understanding of metal ion coordination chemistry in this process, the results of an investigation of the kinetics of lanthanide complexation by ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) and diethylenetriamine-N,N,N',N'‘,N’‘-pentaacetic acid (DTPA) in 0.3 M lactic acid/0.3 M ionic strength solution are reported. Progress of the reaction was monitored using the distinctive visible spectral changes attendant to lanthanide complexation by the colorimetric indicator ligand Arsenazo III, which enables the experiment but plays no mechanistic role. Under the conditions of these experiments, the reactions occur in a time regime suitable for study by stopped-flow spectrophotometric techniques. Experiments have been conducted as a function of EDTA/DTPA ligand concentration, total lactic acid concentration, and pH. The equilibrium perturbation reaction proceeds as a first order approach to equilibrium over a wide range of conditions, allowing the simultaneous determination of complex formation and dissociation rate constants. The rate of the complexation reaction has been determined for the entire lanthanide series (except Pm(3+)). The predominant pathway for lanthanide-EDTA and lanthanide-DTPA dissociation is inversely dependent on the total lactate concentration; the complex formation reaction demonstrates a direct dependence on [H(+)]. Unexpectedly, the rate of the complex formation reaction is seen in both ligand systems to be fastest for Gd(3+). Correlation of these results indicates that in 0.3 M lactate solutions the exchange of lanthanide ions between lactate complexes and the polyaminopolycarboxylate govern the process.

Concepts: Acid, Chemistry, Coordination complex, Ligand, Lone pair, Coordination chemistry, Ion, Lactic acid

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The reactivity of the complexes [PtCl(2){Ph(2)PN®PPh(2)-P,P}] (R = -H, 3; R = -(CH(2))(9)CH(3), 8) toward group 6 carbonylmetalates Na[MCp(CO)(3)] (M = W or Mo, Cp = cyclopentadienyl) was explored. When R = H, the triangular clusters [PtM(2)Cp(2)(CO)(5)(μ-dppa)] (M = W, 4; M = Mo, 5), in which the diphosphane ligand bridges a Pt-M bond, were obtained as the only products. When R = -(CH(2))(9)CH(3), isomeric mixtures of the triangular clusters [PtM(2)Cp(2)(CO)(5){Ph(2)PN®PPh(2)-P,P}], in which the diphosphane ligand chelates the Pt center (M = W, 11; M = Mo, 13) or bridges a Pt-M bond (M = W, 12; M = Mo, 14), were obtained. Irrespective of the M/Pt ratio used when R = -(CH(2))(9)CH(3), the reaction of [PtCl(2){Ph(2)PN®PPh(2)-P,P}] with Na[MCp(CO)(3)] in acetonitrile stopped at the monosubstitution stage with the formation of [PtCl{MCp(CO)(3)}{Ph(2)PN®PPh(2)-P,P}] (R = -(CH(2))(9)CH(3), M = W, 9; M = Mo, 10), which are the precursors to the trinuclear clusters formed in THF when excess carbonylmetalate was used. The dynamic behavior of the dppa derivatives 4 and 5 in solution as well as that of their carbonylation products 6 and 7, respectively, is discussed. Density functional calculations were performed to study the thermodynamics of formation of 4 and 5 and 11-14, to evaluate the relative stabilities of the chelated and bridged forms and to trace a possible pathway for the formation of the trinuclear clusters.

Concepts: Ligand, Chemical bonding, Hapticity, Coordination chemistry, Chelation, Acetonitrile, Ethylenediamine, Cyclopentadienyl complex

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Two new dinuclear dysprosium compounds, [Dy2(HL1)2(PhCOO)2(CH3OH)2] (1) and [Dy2(L2)2(NO3)2(CH3OH)2]·2CH3OH·4H2O (2), have been assembled through applying two ligands with different coordination pockets. The different features of ligands H3L1 and H2L2 result in the distinct coordination geometry of the metal ions in their respective structures. The Dy ions of complexes 1 and 2 were linked by the alkoxide- and hydrazone-O, and display the hula hoop-like and the broken hula hoop-like coordination geometry, respectively. Consequently, these two compounds show distinct magnetic properties. Complex 1 behaves as a single molecule magnet (SMM) with rather slow quantum tunneling rate (τ > 274 ms), while no SMM behavior was observed for complex 2. In addition, the comparison of the structural parameters among the similar Dy2 SMMs with hula hoop-like geometry reveals the significant role played by coordination geometry and magnetic interaction in modulating the relaxation dynamics of SMMs.

Concepts: Chemistry, Magnetism, Ligand, Coordination chemistry, Inorganic chemistry, Terbium, Dysprosium, Dysprosium(III) oxide