Tricarbonyl-Pyrazine-Molybdenum(0) Metal-Organic Frameworks for the Storage and Delivery of Biologically Active Carbon Monoxide

Metal-organic frameworks (MOFs) have high potential as nanoplatforms for the storage and delivery of therapeutic gasotransmitters or gas-releasing molecules. The aim of the present study was to open an investigation into the viability of tricarbonyl-pyrazine-molybdenum(0) MOFs as carbon monoxide-releasing materials (CORMAs). A previous investigation found that the reaction of Mo(CO)₆ with excess pyrazine (pyz) in a sealed ampoule gave a mixture comprising a major triclinic phase with pyz-occupied hexagonal channels, formulated as fac-Mo(CO)₃(pyz)_3/2·1/2pyz (Mo-hex), and a minor dense cubic phase, formulated as fac-Mo(CO)₃(pyz)_3/2 (Mo-cub). In the present work, an open reflux method in toluene has been optimized for the large-scale synthesis of the pure Mo-cub phase. The crystalline solids Mo-hex and Mo-cub were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), FT-IR and FT-Raman spectroscopies, and ¹³C{¹H} cross-polarization (CP) magic-angle spinning (MAS) NMR spectroscopy. The release of CO from the MOFs was studied by the deoxy-myoglobin (deoxy-Mb)/carbonmonoxy-myoglobin (MbCO) UV-vis assay. Mo-hex and Mo-cub release CO upon contact with a physiological buffer in the dark, delivering 0.35 and 0.22 equiv (based on Mo), respectively, after 24 h, with half-lives of 3-4 h. Both materials display high photostability such that the CO-releasing kinetics is not affected by irradiation of the materials with UV light. These materials are attractive as potential CORMAs due to the slow release of a high CO payload. In the solid-state and under open air, Mo-cub underwent almost complete decarbonylation over a period of 4 days, corresponding to a theoretical CO release of 10 mmol per gram of material.

2-(1,2,3-Triazol-4-yl)-imidazoline, -oxazoline, -thiazoline and -tetrahydropyrimidine as ligands in copper(II) and nickel(II) complexes

2-(1-Benzyl-1H-1,2,3-triazol-4-yl)-imidazolines (L1 and L2/L2′), -1,3-oxazoline (L3), -1,3-thiazoline (L4) and -tetrahydropyrimidine (L5) were prepared in one step from a 1,2,3-triazole-4-carboxamidinium tetraphenylborate and studied as novel ligands for copper(II) and nickel(II) ions. The solid-state structures of the following complexes were established: [Cu(L1)2](OTf)2, [CuL2L2′(OTf)2] · 2H2O, [[Cu(L4)2(H2O)2](OTf)2 · [Cu(L4)2(OTf)2], [Cu(L5)2(OTf)2], Cu(L3)2Cl2] · THF, [Ni(L1)2Cl2].

Exploration and characterisation of novel bronze patinas derived from simple coordination complexes

The chemical reactions of aqueous solutions containing simple transition-metal salts and bidentate nitrogen ligands on bronze surfaces results in a series of brightly coloured patinas. Chemically and physically robust patinas involve a chemical oxidation of the copper atoms within the bronze surface, either by an applied ferric salt or atmospheric dioxygen. The combination of Fe(NO(3))(3)·9H(2)O and 2,2'-bipyridine produces a coloured patina that is either red or blue, depending on whether oxygen was present during application, due to the presence of [Fe(bpy)(3)](2+) or [Fe(bpy)(3))](3+), respectively. Application of pyrazine produces a bright orange patina, due to the formation of Cu(i) coordination polymers on the bronze surface. Application of Fe(NO(3))(3)·9H(2)O and tetramethylethylenediamine (TMEDA) yields a forest green coloration, believed to be due to a bimetallic copper-iron complex, while TMEDA alone affords the sapphire blue of [Cu(TMEDA)(2)](2+). These patinas were characterized with ESI-TOF MS, UV-Vis spectrophotometry, and IR spectrophotometry, to determine the molecular basis for the patina chromophores.

Novel pb and zn coordination polymers: synthesis, molecular structures, and third-order nonlinear optical properties

Three novel coordination polymers [Pb(bbbm)(2)(NO(3))(2)](n) (bbbm = 1,1'-(1,4-butanediyl)bis-1H-benzimidazole) 1, [Zn(bbbt)(NCS)(2)](n) (bbbt = 1,1'-(1,4-butanediyl)bis-1H-benzotriazole) 2, and [Zn(pbbt)(NCS)(2)](n) (pbbt = 1,1'-(1,3-propylene)bis-1H-benzotriazole) 3 were synthesized and structurally characterized. Polymer 1 exhibits a two-dimensional rhombohedral grid network structure, the dimensions of the grid are 14.274 x 14.274 A, and the diagonal-to-diagonal distances are 24.809 x 14.125 A. Polymer 2 possesses a concavo-convex chain structure different from those of the known one-dimensional polymers, which are linear chain, zigzag chain, helical chain, double-stranded chain, and ladder chain. Polymer 3 exhibits a one-dimensional zigzag chain structure, and these chains were packed as an.ABAB. layered structure. The third-order nonlinear optical (NLO) properties of polymers1, 2, and 3 were determined with a 7-ns pulsed laser at 532 nm. 1 shows strong third-order NLO absorptive and refractive properties, and its alpha(2) and n(2) values were calculated to be 5.8 x 10(-)(9) m W(-)(1) and 4.67 x 10(-)(18) m(2) W(-)(1) in a 3.4 x 10(-)(4) mol dm(-)(3) DMF solution, respectively. Both 2 and 3 exhibit weaker NLO absorption and strong refractive properties, and their n(2) values are 4.53 x 10(-)(18) m(2) W(-)(1) for 2 in a 5.2 x 10(-)(4) mol dm(-)(3) DMF solution and 3.02 x 10(-)(18) m(2) W(-)(1) for 3 in a 4.35 x 10(-)(4) mol dm(-)(3) DMF solution. The chi((3)) values of 1, 2, and 3 were calculated to be 1.67 x 10(-)(11), 1.62 x 10(-)(11), and 1.08 x 10(-)(11) esu, respectively, and the values are larger than those of the reported coordination polymers. We deduce that the valence shell structures of metal ions may have some influence on the strength of NLO properties, and discuss the relationships between the crystal structures of coordination polymers and the observed NLO properties.

One-Dimensional Coordination Polymers of Cobalt with 4,4'-Bipyridine: Syntheses and Structures

Several new one-dimensional coordination polymers were obtained by reactions of different simple cobalt salts with 4,4'-bipyridine. Co(SO(4))(H(2)O)(3)(4,4'-bipy).2H(2)O (1) was obtained by reacting CoSO(4) with 4,4'-bipy in a water/ethanol solvent system: hexagonal, P6(5), a = 11.435(2) Å, c = 20.886(4) Å, Z = 6. CoCl(2)(DMSO)(2)(4,4'-bipy) (2) was crystallized from the reaction of an aqueous solution of CoCl(2) with a DMSO solution of 4,4'-bipy: orthorhombic, Pbcn, a = 11.470(2) Å, b = 11.390(2) Å, c = 14.753(1) Å, Z = 4. Reaction of Co(CH(3)COO)(2) with 4,4'-bipy in water/acetonitrile under hydrothermal conditions yielded Co(CH(3)COO)(2)(4,4'-bipy) (3): triclinic, P&onemacr;, a = 7.996(1) Å, b = 9.128(1) Å, c = 10.676(1) Å, alpha = 109.79(1) degrees, beta = 99.90(1) degrees, gamma = 100.98(1) degrees, Z = 2. 1 and 2 have structures containing linear Co-bipy-Co chains. In 1, the chains are connected by a network of hydrogen bonds. The structure of 3 contains linear double Co-bipy-Co chains bridged by CH(3)COO(-) groups. The reaction chemistry observed in different solvent systems and under hydrothermal conditions is discussed.

A two-dimensional copper(I) polymer containing both molecular rod and anionic bridges: synthesis and crystal structure of (µ-chloro)-(µ-pyrazine)copper(I)

The crystal structure of bright-red crystals of the bidimensional polynuclear diamagnetic (µ-chloro)(µ-pyrazine)copper(I) complex has been analyzed from X-ray diffraction data. The structure was solved by the heavy-atom method. Full-matrix least-squares refinement based on 673 reflections with F > 4σ(F) converged to a final R = 0.043 and Rw = 0.048. Crystals of this complex are monoclinic, space group P2/c, a = 3.814(1), b = 6.356(1) and c = 11.497(5) Å; β = 96.04(2)°, Z = 2. The structure consists of planes of copper(I) atoms linked by pyrazine and Cl− bridges, each Cu(I) being in a distorted tetrahedral environment formed by two chloride ions and two nitrogen atoms belonging to two pyrazine molecules, with bond distances of Cu—Cl = 2.349(1) and Cu—N = 2.038(4) Å. Vibrational and electronic spectroscopy of the title compound is also reported. Keywords: two-dimensional copper(I)–pyrazine complexes.

Antiferromagnetism and metamagnetism in 1,4-diazine and pyridine complexes of nickel(II)

Several nickel(II) complexes containing pyridine (py), pyrazine (pyz) or methylpyrazine (mepyz) have been synthesized and characterized by vibrational and electronic spectroscopy, differential scanning calorimetry, and magnetic susceptibility studies to cryogenic temperatures. A comparison of the magnetic properties of the polymeric diazine-bridged complexes, Ni(pyz)2X2 (X = Cl or NO3), Ni(pyz)(p-CH3C6H4SO3)2, Ni(mepyz)(NO3)2, and Ni(pyz)3(CH3SO3)2•CH3OH with those of the related monometallic systems, Ni(py)4X2 (X = Cl, p-CH3C6H4SO3 or CH3SO3) and Ni(mepyz)4(NO3)2•H2O provides evidence for weak antiferromagnetic coupling between metal centers mediated by bridging diazine ligands in the former group of compounds. The magnetic properties were analyzed employing a model for S = 1 which takes into account zero-field splitting and employs a molecular field term to account for weak magnetic exchange. The compounds Ni(pyz)Cl2 and Ni(py)Cl2 show metamagnetic behaviour with critical fields of 13 and 2 kOe, respectively, at 2 K. In these compounds nickel ions, linked in chains by bridging chlorides, exhibit intrachain ferromagnetic and interchain antiferromagnetic exchange. In Ni(pyz)Cl2 bridging pyrazine ligands are considered to provide the pathway for the antiferromagnetic coupling resulting in a high critical field. Keywords: nickel(II), pyrazine, pyridine, complexes, metamagnetism, antiferromagnetism.