Similar Coordination Spheres Research Articles

Two Bi-MOFs with pyridylmulticarboxylate ligands showing distinct crystal structures and phosphorescence properties

Two Bi-MOFs, [Bi(PDC)(OH)] (Bi-PDC; H2PDC ​= ​2,4-pyridine bicarboxylic acid) and [Bi(PTC)(H2O)2] (Bi-PTC; H3PTC ​= ​2,4,6-pyridine tricarboxylic acid), have been synthesized under almost the same solvothermal condition, respectively. Both Bi-PDC and Bi-PTC were characterized by microanalysis, infrared spectra (IR), thermal gravimetric analyses (TGA), and powder X-ray diffraction (PXRD) techniques. Single-crystal structural analyses indicate that the Bi3+ ions adopt similar coordination sphere of monocapped square antiprism in Bi-PDC and Bi-PTC, while PDC2− and PTC3− ligands display distinct bridging modes through carboxylates and pyridyl groups, leading to Bi-PDC forming three-dimensional (3D) pillared-layer framework and Bi-PTC developing into two-dimensional (2D) layered structure. Two Bi-MOFs emit ligand-centered room temperature phosphorescence due to the heavy atom effect of Bi3+ ion, with lifetime and quantum yield of 0.39 ​ms and 2.49% in Bi-PDC versus 0.57 ​ms and 5.45% in Bi-PTC, and the intense green and orange phosphorescence is visible by naked eyes under ambient condition, and the long-wavelength (orange) phosphorescence Bi-based MOF is seldom reported.

Bis(diphenylphosphinyl)-functionalized dipyrido-annulated NHC towards copper(i) and silver(i).

The coordination chemistry of our recently isolated bis(diphenylphosphinyl)-functionalized dipyrido-annulated NHC (N-heterocyclic carbene), dpaP2-NHC, towards copper(i) and silver(i) has been studied. Based on dpaP2-NHC, two dinuclear silver and copper complexes [2, (Ag2L2) and 3, (Cu2L2)], two tetranuclear copper complexes {4, [Cu4L2(NCMe)2] and 6, (Cu4LBr4)} and a pentanuclear copper complex [5, (Cu5L2Br3)] exhibiting strong intramolecular metal-metal interactions were achieved and characterized. All the complexes exhibited dynamic behavior in solution, in which the NMR coalescence of 2 was well resolved at low temperature (below 208 K) and dissociation for 2 was observed according to the calculated Eyring plot. Ag2L2 (2) shows a similar coordination sphere to that of our previously reported gold complex Au2L2; Cu2L2 (3) features a rare μ2-bridging carbene and a terminal carbene; Cu4LBr4 (6) is neutral and monomeric, in which four copper atoms were rigidly fixed by the tridentate dpaP2-NHC ligand and bromide anions. All the complexes (2-6) were luminescent at room temperature, in which 4-6 provided phosphorescence at 77 K. Based on the comparison of the emission bands with dpaP2-NHC, we conclude that the electronic transitions of 2-6 can be attributed to the ligand-centered (LC) transitions.

Magnetostructural correlations in S = 1 trans-[Ni{(OPPh2)(EPPh2)N}2(dmso)2], E = S, Se, and related complexes

In this work, the structural and spectroscopic characterization of trans-[Ni{(OPPh2)(EPPh2)N)}2(dmso)2], E = S, Se, complexes is described. These Ni(II) complexes contain two chelating (O,E) = [(OPPh2)(EPPh2)N)]− ligands, as well as two dimethyl sulfoxide (dmso) molecules coordinated via their O atoms. X-ray crystallography studies revealed a highly anisotropic pseudo-octahedral trans-NiO4E2 coordination environment, extending the literature dataset of their trans-[Ni(O,E)2(sol)2], sol = dmf, thf, counterparts. Collectively considered, these six complexes contain similar coordination spheres, exhibiting, however, subtle structural differences due to the nature of the donor atom (E) and solvent molecule (sol) coordinated to Ni(II). The spin Hamiltonian parameters of S = 1 trans-[Ni(O,Se)2(dmso)2], E = S, Se, were accurately determined by high-frequency and -field EPR spectroscopy, applying a methodology already used for trans-[Ni(O,E)2(sol)2], sol = dmf, thf. Magnetostructural correlations are explored between all members of this sub-family of Ni(II) complexes.

Dissecting the bond-formation process of d 10-metal–ethene complexes with multireference approaches

The bonding mechanism of ethene to a nickel or palladium center is studied by the density matrix renormalization group algorithm, the complete active space self consistent field method, coupled cluster theory, and density functional theory. Specifically, we focus on the interaction between the metal atom and bis-ethene ligands in perpendicular and parallel orientations. The bonding situation in these structural isomers is further scrutinized using energy decomposition analysis and quantum information theory. Our study highlights the fact that when two ethene ligands are oriented perpendicular to each other, the complex is stabilized by the metal-to-ligand double-back-bonding mechanism. Moreover, we demonstrate that nickel-ethene complexes feature a stronger and more covalent interaction between the ligands and the metal center than palladium-ethene compounds with similar coordination spheres.

Effect of coordination sphere of the copper center and Cu―Cu distance on catechol oxidase and nuclease activities of the copper complexes

To explore the effect of Cu―Cu distance in the structure of copper complexes on their catechol oxidase and nuclease activity, six copper complexes with a similar coordination sphere but different Cu―Cu distances were synthesized and characterized with elemental analysis, single‐crystal X‐ray diffraction, molar conductivity measurements, IR and UV–visible spectroscopy. Complex 1 is a binuclear copper complex and complex 4 is a polynuclear complex with a Z‐chain structure, as evidenced by their crystal structures. Complementary characterizations showed that complexes 2 and 3 have a similar binuclear structure to the complex 1; and complexes 5 and 6 are analogous to complex 4. The catechol oxidase activity of complexes 1, 2, 3 is quite akin to that of 4, 5, 6, suggesting that the catechol oxidase activity of the complexes was determined by the coordination environment of the copper center, when Cu―Cu distance is large. In contrast, DNA cleavage activity of the complexes 1, 2 and 3 are much higher than that of 4, 5 and 6, indicating that the planar ligand structure in the complexes 4, 5 and 6 is more critical than the copper coordination sphere and the Cu―Cu distance for their nuclease activity. Copyright © 2014 John Wiley & Sons, Ltd.

Sugar–metal ion interactions: the coordination behaviors of lanthanum with erythritol

Three novel lanthanum chloride–erythritol complexes (LaCl3·C4H10O4·5H2O (LaE(I)), LaCl3·C4H10O4·3H2O (LaE(II)), and LaCl3·1.5C4H10O4 (LaE(III)) were synthesized and characterized by single crystal X-ray diffraction, FTIR, far-IR, THz, and Raman spectroscopy. The coordination number of La3+ is nine. LaE(I) and LaE(II) have similar coordination spheres, but their hydrogen bond networks are different. Erythritol exhibits two coordination modes: two bidentate ligands and tridentate ligands in LaE(III). Chloride ions and water coordinate with La3+ or participate in the hydrogen-bond networks in the three complexes. Crystal structures, FTIR, FIR, THz, and Raman spectra provide detailed information on the structures and coordination of hydroxyl groups to metal ions in the metal–carbohydrate complexes.

Synthesis, characterization, and polyphenol oxidase activity of CuII, MnII, and FeIII complexes with a N2O2 ligand

To explore the effect of the metal center on catechol oxidase and tyrosinase activities, four complexes, Cu2(μ-Cl)2(hbpg)2 (1), [Cu2(μ-OH2)2(hbpg)2](NO3)2(H2O)2 (2), [Fe2(μ-Cl)2(hbpg)2]Cl2(H2O)2 (3), and [Mn2(μ-Cl)2(hbpg)2](H2O)2 (4) (hbpg = N-(2-hydroxybenzyl)-N-(2-picolyl)glycine), were synthesized and characterized with elemental analysis, single-crystal X-ray diffraction, molar conductivity measurements, mass spectrometry, UV-Visible, and FT-IR spectroscopies. The X-ray crystal structural analysis indicates that 1 has a binuclear copper, coordinated with N2O2 ligands. Complementary characterizations suggested that 2, 3, and 4 have similar coordination sphere. Complex 3 exhibits much higher catechol oxidase and tyrosinase-like activity than 1, 2, and 4. The results suggested that with a similar coordination sphere, the redox potential of the metal center is critical for catalytic activity. This work provides valuable information for improving the polyphenol oxidase activity of metal complexes for phenolic degradation.

Construction of acetate-bridged dicopper(II) hybrid organic–inorganic networks with calix[4]arene-derived nitrogenous ligands

The reactions of mono-, bis- and tetrapicolyl-p-tert-butylcalix[4]arene derivatives functionalised in the phenolic positions (L 1 –L 4 ) with copper(II) acetate resulted in the formation of discrete complexes or extended coordination polymers. The centrosymmetric dimer [Cu2(μ-O2CCH3)4(L 1 )2] 1, obtained with monodentate L 1 , has square pyramidal coordination around the copper centres and a cone conformer of monopicolyl-calix[4]arene acting as an axial ligand, with a molecule of acetonitrile hosted within its cavity. The potentially bidentate L 2 acts as a monodentate ligand, affording the complex [Cu2(μ-O2CCH3)4(L 2 )2] 2, which based on spectroscopic and combustion analysis data has a similar coordination sphere around Cu(II). Compound L 3 bridges two dicopper units in the coordination polymer [Cu2(μ-O2CCH3)4(μ-L 3 )] n 3, with the calixarene hosting a molecule of tetrahydrofuran. Finally, compound L 4 reacts with 4 equivalents of copper(II) acetate, presumably generating a two-dimensional coordination polymer formulated as [{Cu2(μ-O2CCH3)4}2(L 4 )] 4.

Our variations on iron and cobalt catalysts toward ethylene oligomerization and polymerization

Iron and cobalt complexes are a new family of catalysts for ethylene oligomerization and polymerization. The extensive researches on bis(imino)pyridyl metal complexes have been carried out with the aim of synthesizing their derivatives and finding suitable reaction parameters for the optimum activity. Beyond the modification works of bis(imino)pyridyl metal complexes, several alternative models with similar coordination sphere have been developed in our group. This review article describes our experiences in innovating new models of iron and cobalt complexes as catalysts for ethylene oligomerization and polymerization.

A novel tetranuclear cubic cage, [Tl 4(μ 3-dcp) 4] {Hdcp=2,4-dichlorophenol}, new short Cl⋯Cl interactions, thermal, fluorescence, structural and solution studies

The single crystal X-ray analysis of a novel Tl I complex of 2,4-dichlorophenol (Hdcp) ligand shows that the complex has a tetranuclear cubic cage as a result of bridging ligands dcp − with basic repeating of [Tl(μ 3-dcp)] units. There are four thallium atoms with similar coordination spheres in the cubic cage. These thallium atoms contain irregular coordination sphere with stereo-chemically active lone pair. The thermal stability of [Tl 4(μ 3-dcp) 4] was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The compound [Tl 4(μ 3-dcp) 4] is luminescent in the solution state with emission maxima at 397 nm. The results of studies of the stoichiometry and formation of [Tl 4(μ 3-dcp) 4] complex in DMF solution were found to be in support of their solid state stoichiometry.

C−H Activation by a Mononuclear Manganese(III) Hydroxide Complex: Synthesis and Characterization of a Manganese-Lipoxygenase Mimic?

Lipoxygenases are mononuclear non-heme metalloenzymes that regio- and stereospecifically convert 1,4-pentadiene subunit-containing fatty acids into alkyl peroxides. The rate-determining step is generally accepted to be hydrogen atom abstraction from the pentadiene subunit of the substrate by an active metal(III)-hydroxide species to give a metal(II)-water species and an organic radical. All known plant and animal lipoxygenases contain iron as the active metal; recently, however, manganese was found to be the active metal in a fungal lipoxygenase. Reported here are the synthesis and characterization of a mononuclear Mn(III) complex, [Mn(III)(PY5)(OH)](CF(3)SO(3))(2) (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)pyridine), that reacts with hydrocarbon substrates in a manner most consistent with hydrogen atom abstraction and provides chemical precedence for the proposed reaction mechanism. The neutral penta-pyridyl ligation of PY5 endows a strong Lewis acidic character to the metal center allowing the Mn(III) compound to perform this oxidation chemistry. Thermodynamic analysis of [Mn(III)(PY5)(OH)](2+) and the reduced product, [Mn(II)(PY5)(H(2)O)](2+), estimates the strength of the O-H bond in the metal-bound water in the Mn(II) complex to be 82 (+/-2) kcal mol(-)(1), slightly less than that of the O-H bond in the related reduced iron complex, [Fe(II)(PY5)(MeOH)](2+). [Mn(III)(PY5)(OH)](2+) reacts with hydrocarbon substrates at rates comparable to those of the analogous [Fe(III)(PY5)(OMe)](2+) at 323 K. The crystal structure of [Mn(III)(PY5)(OH)](2+) displays Jahn-Teller distortions that are absent in [Mn(II)(PY5)(H(2)O)](2+), notably a compression along the Mn(III)-OH axis. Consequently, a large internal structural reorganization is anticipated for hydrogen atom transfer, which may be correlated to the lessened dependence of the rate of substrate oxidation on the substrate bond dissociation energy as compared to other metal complexes. The results presented here suggest that manganese is a viable metal for lipoxygenase activity and that, with similar coordination spheres, iron and manganese can oxidize substrates through a similar mechanism.

Electrospray Mass Spectrometry of a Series of Mixed Nitrido 99gTc-Heterocomplexes Conjugated with Bio-Active Molecules

Electrospray ionization mass spectrometry (ESI-MS) was successfully employed for the identification of six nitrido technetium mixed ligand complexes with a general formula of [99gTc(N)(O,S-BID)(PNP)], where PNP represents a heterodiphosphine and O,S-BID represents a simple dianionic bidentate ligand (compounds 1-3) or a more sophisticated N-substituted O,S-cysteine framework conjugated with a bio- active molecule (BAM) (compounds 4-6). In spite of similar coordination spheres exhibited by all the complexes investigated, simple co-ordination compounds 1-3 displayed collisionally-induced fragmentation processes (MSn) different from those observed in biomolecule-containing compounds 4-6. In the latter, more decomposition channels were observed. This behavior is likely to be associated with some additional intramolecular contacts of the biomolecule (or part of the biomolecule) with pendant group(s) incorporated in the PNP-co-ligand. This view is further supported by the observations arising from both in vitro binding affinity experiments and nuclear magnetic resonance investigations. The presence of cationized forms for all compounds 1-6 and the practical lack of the [2M + Na]+ species for biomolecule-containing compounds 4-6 provided further evidence of a subtly different structural conformation.

Reaction of bromopentacarbonylrhenium(I) with ferrocenylcarbaldehyde thiosemicarbazones: the first X-ray diffraction studies of metal carbonyl complexes containing bidentate thiosemicarbazone ligands

The reactions of [ReBr(CO) 5] with ferrocenylcarbaldehyde thiosemicarbazones HL with different groups attached to the amide nitrogen (R=H, Me, Ph) yielded complexes [ReBr(CO) 3(HL)] ( 1) in which, according to X-ray studies of 1a·{(CH 3) 2CO} and 1b·1/2{CH 2Cl 2}, the thiosemicarbazone is N, S-bidentate and the geometry around the metal fac-octahedral. Compounds of formula [ReL(CO) 3] 2 ( 2) were then prepared by reaction of the corresponding adduct 1 with NaOMe in acetone. A complex of formula [ReL 2(CO) 3] 2 ( 2b′) was also obtained as a dissolvate by slow concentration of a solution of 1b in acetone. Single crystals of 2a and 2b obtained from the mother liquors are composed of centrosymmetric dimers formed by ReSRe bridges, where S is the thiolic sulfur of an N, S-bidentate thiosemicarbazonato ligand. Although 2b·2{(CH 3) 2CO} and 2b′·2{(CH 3) 2CO} have similar co-ordination spheres, they differ as regards the configuration of the thiosemicarbazonato ligand about the azomethine bond and certain bond lengths (notably ReN); it seems likely that the configuration of L 2− determines how close the rhenium can approach the N atom of the ligand, and hence the delocalization of the π electrons in the CNN fragment of the thiosemicarbazide chain. The mass, IR and UV–vis spectra of the complexes, and their electrochemical behavior, are also discussed.

XAFS study of gadolinium and samarium bisporphyrinate complexes.

The comparative X-ray absorption spectroscopy study of gadolinium and samarium bisporphyrinate complexes represented by the formulas Gd(III)H(oep)(tpp), Gd(III)(oep)(2), Gd(III)H(tpp)(2) and Sm(III)H(oep)(tpp), Sm(III)(oep)(2), Sm(III)H(tpp)(2) is reported. The XAFS spectra are recorded on the LURE-DCI storage ring (Orsay, France) in transmission mode on the microcrystalline samples at the Gd and Sm L(3) edges. The local environment for Ln(3+) ions has been reconstructed applying one-shell and two-shell XAFS analysis procedures. The protonated and nonprotonated bisporphyrinate complexes present different XAFS features. After our analysis on the title derivatives, the gadolinium ion (at 80 K) is found to be bonded: (i) to eight nitrogen atoms at R(Gd-N) 2.50 A, for Gd(III)(oep)(2) [Debye-Waller (DW) factor 0.004 A(2)]; (ii) to seven nitrogen atoms at R(Gd-N) 2.49 A, for Gd(III)H(oep)(tpp) [DW factor 0.005 A(2)] and one nitrogen at long distance; and (iii) to six nitrogen atoms at R(Gd-N) 2.50 A [DW factor 0.006 A(2)] and two nitrogen atoms at long distance for Gd(III)H(tpp)(2). A similar coordination sphere has been detected for the corresponding Sm derivatives. So, the samarium ion (at room temperature) is bonded: (i) to eight nitrogen atoms at R(Sm-N) 2.53 A, for Sm(III)(oep)(2) [DW factor 0.006 A(2)]; (ii) to seven nitrogen atoms at R(Sm-N) 2.53 A, for Sm(III)H(oep)(tpp) [DW factor 0.006 A(2)] and one nitrogen at long distance; and (iii) to six nitrogen atoms at R(Sm-N) 2.50 A, for Sm(III)H(tpp)(2) [DW factor 0.006 A(2)] and two nitrogen atoms at long distance. As far as concerns Ln(III)(oep)(2) complexes, the increase of Ln-N distance in the series Gd(3+) < Eu(3+) < Sm(3+) reflects an increase in the ionic radii, which are in good agreement with previously published XRD data on Eu(III)(oep)(2). Moreover, the protonated Ln(III)H(oep)(tpp) and Ln(III)H(tpp)(2) complexes possess systematically shorter distances of about 0.02 A between the XAFS and XRD data. This difference is attributed to the asymmetry of the distribution concerning Ln-N distances.

Excitation and deexcitation processes of Eu(III) benzo-15-crown-5 complex studied on comparing with its first coordination sphere

The coordination sphere and the deexcitation mechanism of the Eu(III) benzo-15-crown-5 complex, Eu(B15C5), were studied with references of the Eu(III) complexes with a similar coordination sphere; the dibenzo-18-crown-6 complex, Eu 3(B 218C6) 2, and the cryptand[2.2.1] complex, Eu([2.2.1]). NMR spectroscopy reveals that the Eu(B15C5) complex is quite stable in acetonitrile solution whereas only 40% of the Eu(III) ion forms the complex in the equimolar Eu(NO 3) 3 and B 218C6 acetonitrile solution. The coordination sphere of the Eu(III) complexes in acetonitrile solutions were also discussed by the degenerate 7F 0→ 5D 0 transition energy levels. The Eu(B15C5) have a negative shift compared with the europium(III) nitrate in acetonitrile and it is explained by the coordination of both nitrate ions and the crown ether ligand. Energy transfer from the n–π* excited state located in the catechol structure to the central europium ion was first observed as the sensitized luminescence of 5D 0→ 7F J. The excited state lifetime of the Eu(B15C5) complex was first determined as 201 μs in the present study.

Copper(II) Binding Modes in the Prion Octapeptide PHGGGWGQ: A Spectroscopic and Voltammetric Study

The N-terminal octapeptide repeat region of human prion protein (PrPc) is known to bind Cu(II). To investigate the binding modes of copper in PrPc, an octapeptide Ac-PHGGGWGQ-NH2 (1), which corresponds to an octa-repeat sequence, and a tetrapeptide Ac-HGGG-NH2 (2) have been synthesised. The copper(II) complexes formed with 1 and 2 have been studied by circular dichroism (CD) and electron spin resonance (ESR) spectroscopy. Both peptides form 1:1 complexes with Cu(II) at neutral and basic pH. CD, ESR and visible absorption spectra suggest a similar co-ordination sphere of the metal ion in both peptides, which at neutral pH consists of a square pyramidal geometry with three peptidic nitrogens and the imidazole nitrogen as donor atoms. Cyclic voltammetric measurements were used to confirm the geometrical features of these copper(II) complexes: the observation of negative redox potentials are in good agreement with the inferred geometry. All these results taken together suggest that peptide 1 provides a single metal binding site to which copper(II) binds strongly at neutral and basic pH and that the binding of the metal induces the formation of a stiffened structure in the HGGG peptide fragment.

N-methylation of diamino-substituted macrocyclic complexes: intermolecular reactions

Two N-based isomeric copper(II) complexes of the macrocycle trans-6,13-dimethyl-6,13-bis(dimethylamino)-1,4,8,11-tetraazacyclotetradecane (L3) have been synthesized and characterised spectroscopically and structurally: α-[CuL3(OH2)2]Cl2, monoclinic, space group C2/m, a= 12.908(4), b= 12.433(2), c= 7.330(2)A, β= 105.87(2)°, Z= 2; β-[CuL3(OClO3)2]·2H2O, monoclinic, space group P21/c, a= 9.708(3), b= 9.686(3), c= 14.202(4)A, β= 106.17(1)°, Z= 2. The two isomers exhibit very similar co-ordination spheres but significantly different visible electronic maxima. This difference is attributed to an intramolecular N ⋯ H contact between the pendant dimethylamino group and an adjacent secondary amine H atom.