Pyz Molecules Research Articles

Pyrazine-bridged molybdenum(0) carbonyl and molybdenum(VI) oxide network solids as catalysts for epoxidation and sulfoxidation

The horizons of epoxidation and sulfoxidation processes may be expanded by developing new, efficient, and versatile catalysts. In the present work, three pyrazine-bridged molybdenum(0/VI)-based coordination network solids have been investigated for the epoxidation of olefins and the oxidation of sulfides. The materials studied were the Mo0-based metal-organic framework (MOF) fac-Mo(CO)3(pyz)3/2·1/2pyz (1) with a structure consisting of stacked fac-Mo(CO)3(pyz)3/2 coordination layers, the cubic phase fac-Mo(CO)3(pyz)3/2 (2) with a dense framework consisting of two interpenetrating coordination networks, and the molybdenum oxide-pyrazine hybrid material [Mo2O6(pyz)] (3) with a structure consisting of perovskite-like MoO3 layers pillared by pyz molecules. In the model reaction of cis-cyclooctene with tert-butyl hydroperoxide (TBHP) at 70 °C, quantitative yields of the epoxide were obtained within 2 h for 1, 4 h for 2, and 24 h for 3. Catalysts 1-3 were further examined for the epoxidation of other olefins, including the bio-olefins dl-limonene, methyl oleate and methyl linoleate, and the reaction scope was expanded to include the oxidation of sulfides. In the reactions of the bio-olefins, 3 was highly selective, giving only diepoxide and/or monoepoxide products. While the tricarbonyl-pyrazine-molybdenum(0) compounds displayed higher activity, by-products were obtained in the reactions of dl-limonene and methyl linoleate, namely limonene-1,2-diol and hydroxytetrahydrofuran cyclization products, respectively. Catalysts 1-3 displayed high activity for the selective oxidation of sulfides (methyl phenyl sulfide and diphenyl sulfide) to sulfones under mild conditions (35 °C).

Metal(II) Ion Dependence of the Structures and Properties of Square-Grid Coordination Polymers of Tetrabromobenzenedicarboxylate and Pyrazine as Bridging Ligands

Abstract In this study, we report the synthesis and crystal structures of coordination polymers employing tetrabromobenzenedicarboxylate (Br4bdc2−) and pyrazine (pyz). Uncoordinated pyz molecules are stabilized between the layers by both hydrogen H-bonding and π–π stacking interactions in [M(Br4bdc)(pyz)(H2O)2](pyz), where M = Co(II) and Zn(II). In addition, water molecules are incorporated between the layers in [Cu(Br4bdc)(pyz)(H2O)2](H2O) owing to Jahn–Teller distortion of the Cu(II) ions, which prevents π–π stacking interactions between the pyz and Br4bdc2−. Depending on the metal(II) centers, structural changes that occur during the heating and hydration processes exhibit different behavior. Co(II) compound slowly changes structure by heating and rapidly recovers the crystalline state in air. Conversely, Zn(II) compound assumes the amorphous phase by heating and slowly yields the crystalline phase in ambient conditions. Although the Cu(II) compound also shows structural changes by heating, the dehydrated phase exhibits hydrophobic characteristics. Ion conductivity measurements of the as-synthesized forms show conductivities of 1.9 × 10−6 Scm−1, 4.6 × 10−7 Scm−1, and 1.3 × 10−6 Scm−1, for the Co(II), Zn(II), and Cu(II) complexes at 90 °C and 95% relative humidity (RH), respectively. The relatively low values of the as-synthesized Co(II) and Zn(II) compounds are attributed to the H-bonding interaction and π–π stacking of pyz molecules, which prevent the dynamics of the pyz molecules needed for proton conduction.

Expanded Porous Metal–Organic Frameworks by SCSC: Organic Building Units Modifying and Enhanced Gas-Adsorption Properties

Two amino-functional copper metal-organic frameworks of formula [Cu3(ATTCA)2(H2O)3]·2DMF·11H2O·12EtOH (1) (H3ATTCA = 2-amino-[1,1:3,1-terphenyl]-4,4,5-tricarboxylic acid, pyz = pyrazine, DMF = dimethylformamide) and [Cu3(ATTCA)2(pyz)(H2O)]·2DMF·12H2O·8EtOH (2) were synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, infrared spectroscopy, elemental analyses, thermogravimetric analyses, and powder X-ray diffraction. Single-crystal X-ray diffraction analysis revealed that both complexes 1 and 2 are built of the Cu2(COO)4 paddlewheel secondary building units with an fmj topology. Importantly, complex 1 can be transformed into complex 2 by the single-crystal to single-crystal transformation of which the coordinated water molecules are replaced with pyz molecules. However, the adsorption abilities of 2 are obviously lower than those of 1, as its pores are partially blocked by pyz molecules. Moreover, gas-adsorption analysis showed that the amino-functional 1 possesses higher gas-adsorption capacity than UMCM-151 for N2, H2, CH4, and C2H2, especially for CO2.

Structural and thermodynamic properties of molecular complexes of aluminum and gallium trihalides with bifunctional donor pyrazine: decisive role of Lewis acidity in 1D polymer formation

Solid state structures of group 13 metal halide complexes with pyrazine (pyz) of 2:1 and 1:1 composition have been established by X-ray structural analysis. Complexes of 2:1 composition adopt molecular structures MX3·pyz·MX3 with tetrahedral geometry of group 13 metals. Complexes of AlBr3 and GaCl3 of 1:1 composition are 1D polymers (MX3·pyz)∞ with trigonal bipyramidal geometry of the group 13 metal, while the weaker Lewis acid GaI3 forms the monomeric molecular complex GaI3·pyz, which is isostructural to its pyridine analog GaI3·py. Tensimetry studies of vaporization and thermal dissociation of AlBr3·pyz and AlBr3·pyz·AlBr3 complexes have been carried out using the static method with a glass membrane null-manometer. Thermodynamic characteristics of vaporization and equilibrium gas phase dissociation of the AlBr3·pyz complex have been determined. Comprehensive theoretical studies of (MX3)n·(pyz)m complexes (M = Al, Ga; X = Cl, Br, I; n = 1, 2; m = 1-3) have been carried out at the B3LYP/TZVP level of theory. Donor-acceptor bond energies were obtained taking into account reorganization energies of the fragments. Computational data indicate that the formation of (MX3·pyz)∞ polymers with coordination number 5 is only slightly more energetically favorable than the formation of molecular complexes of type MX3·pyz for X = Cl, Br. It is expected that on melting (MX3·pyz)∞ polymers dissociate into individual MX3·pyz molecules. This dovetails with low melting enthalpies of the (MX3·pyz)∞ complexes. Polymer stability decreases in the order AlCl3 > AlBr3 > GaCl3 > AlI3 > GaBr3 > GaI3. For MI3·pyz complexes computations predict that the monomeric structure motif is more energetically favorable compared to the catena polymer. These theoretical predictions agree well with the experimentally observed monomeric complex GaI3·pyz in the solid state. Thus, the Lewis acidity of the group 13 halides may play a decisive role in the formation of 1D polymeric networks.

Antiferromagnetic Porous Metal–Organic Framework Containing Mixed-Valence [MnII4MnIII2(μ4-O)2]10+ Units with Catecholase Activity and Selective Gas Adsorption

A multifunctional porous metal organic framework based on mixed-valence hexa-nuclear [Mn(III)(2)Mn(II)(4)O(2)(pyz)(2)(C(6)H(5)CH(2)COO)(10)] (pyz = pyrazine) units has been synthesized. The complex has been characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction analysis, and variable-temperature magnetic measurements. The structural analysis reveals that the bidentate pyz molecules connect each [Mn(6)] unit to its four [Mn(6)] neighbors through the peripheral Mn(II) centers, giving rise to a three-dimensional (3D) distorted diamond-like porous framework. Variable-temperature (2-300 K) magnetic susceptibility measurements show the presence of dominant antiferromagnetic interactions within the discrete [Mn(6)] cluster that have been fitted with a model containing three exchange constants developed for the complex (J(1) = -8.6 cm(-1), J(2) = -3.9 cm(-1), and J(3) = -100.0 cm(-1)). Using 3,5-di-tert-butyl catechol (3,5-DTBC) as the substrate, catecholase activity of the complex has been studied; the turn over number is determined to be of 2547 h(-1) in acetonitrile. This porous compound shows remarkable selectivity for adsorption of CO(2) over N(2) that may be correlated with the effect of window flexibility of the pore to the corresponding adsorbate molecules.

P4S3 and P,P′ or N,N′ Donors as Competitive Building Blocks in Copper(I) Coordination Polymers

AbstractThe synthesis and characterization of hybrid polymers combining organic P,P′ (dppe) or N,N′ (pyrazine) ligands and inorganic donors (P4S3) as cross‐linkers between copper(I) halide aggregates is described. As a simple model system the reaction of a mixture of P4S3, PEt3, and CuX (X = Cl, Br, I) was studied. According to X‐ray diffraction analysis, pseudotetrahedral monomers [CuX(PEt3)2(P4S3)] (1–3) were formed, in which P4S3 coordinates through the apical phosphorus atom. Layering a mixture of P4S3, Ph2PCH2CH2PPh2 (dppe), and toluene with CuCl in MeCN under diffusion conditions gives 1D‐[CuCl(dppe)(MeCN)] (6), which contains (Cu2Cl2)2(μ‐dppe)2 clusters linked by another dppe ligand. The analogous reaction with CuI gives 1D‐[CuI(P4S3)(dppe)] (7), which is built up of alternating trans‐(Cu2I2)(P4S3)2 units and dppe linkers. Hybrid polymers 2D‐[CuX(P4S3)(dppe)] [X = Br (8), I (9)] are formed if CH2Cl2 is used instead of toluene. The 2D structures of 8 and 9 may be derived from that of 7 by connecting neighboring (CuX)(dppe) strands with pairs of inversely coordinated P4S3 cages. Replacement of dppe by pyrazine (pyz) yields 3D‐[(CuCl)4(P4S3)2(pyz)] (10) and 3D‐[(CuBr)3(P4S3)(pyz)] (12), respectively. The structure of 10 comprises a 3D network composed of alternating, linked 2D‐[(CuCl)2(P4S3)] and 2D‐[CuCl(pyz)] layers. The structure of 12 contains cradles built from opposing (CuBr)6 rings and pairwise pyz and P4S3 bridges. These cradles are organized into a 3D framework by condensation of the (CuBr)6 rings, and the layers formed are linked by additional pyz molecules. The resulting voids are occupied by toluene molecules. The behavior of P4S3 and P,P′ or N,N′ ligands as competitive building blocks is also expressed by the formation of binary P4S3/CuX or pyz/CuX polymers.

Magnetic Investigation of a Double-Helix Chain Framework Based on Dinuclear Cobalt(II) SBUs

A coordination polymer [Co(dpa)pyz0.5] n (1) with double-helix chains has been constructed hydrothermally using H2dpa (H2dpa = diphenic acid), pyz (pyz = pyrazine) and Co(NO3)2· 6H2O. Its structure and magnetic properties were investigated. The compound crystallizes in the triclinic space group P -1. Each Co atom is five-coordinated and takes a distorted tetragonal pyramid geometry. Two carboxylates of the H2dpa ligands bridge four Co(II) ions to form infinite right-handed or left-handed helical ─C─O─Co─ chains. The two types of helical chains are interconnected to each other through the Co(II) centers to produce double-helix chains. The chains form a 2D sheet through the coordination interaction of pyz molecules between adjacent chains. Magnetic studies for complex 1 show stronger antiferromagnetic coupling between the Co(II) ions.

New types of the flexible self-assembled metal–organic coordination polymers constructed by aliphatic dicarboxylates and rigid bidentate nitrogen ligands

The reaction of metal ions, flexible aliphatic dicarboxylates and rigid bidentate linear ligands under mild conditions in water afford four novel metal-organic coordination polymers, [Cd(mu-mal)(mu-pyz)(0.5)(H(2)O)](n) 1 (mal = malonate dianion, pyz = pyrazine), [Cd(2)(mu-suc)(2)(mu-pyz)(H(2)O)(2)](n) 2 (suc = succinate dianion), and ([M(mu-bipy)(H(2)O)4][suc].4H(2)O)(n)(M = Co, 3, M = Zn, 4, bipy = 4,4'-bipyridine). The molecular structures of 1-4 have been established by single-crystal X-ray crystallography. 1 is a 3D network being composed of layers of octahedrally coordinated Cd atoms bridged by malonate anions in syn-anti configurations within the layers and pyz molecules between layers. Unlike that in 1, each Cd atom in 2 displays uncommon pentagonal-bipyramidal geometry to form 2D infinite grid sheets with square grid dimensions of ca. 7.936 x 7.936 [Angstrom]. Both 3 and 4 exhibit 1D linear -M-bipy-M-bipy- chain polymers, and these chains were packed as ...ABCABC... layered structures. The bridging succinate ligands in 2 adopt the syn-anti mode with a torsion angle of 60.8(7) degrees, while the solvated succinate ligands in 3 and 4 adopt the anti-anti mode with a torsion angle of 180.0 degrees. To our knowledge, compound 2 represents the first example of flexible self-assembled succinate-pyrazine mixed bridging ligand coordination network. 3 and 4 are the first two cases of succinate-bipy polymers with non-coordinated succinate. The magnetic behavior for 3 was studied in the temperature range of 5-300 K. The result indicates the occurrence of a weak antiferromagnetic coupling between the cobalt(II) ions.

Fabrication of infinite two-dimensional sheets of tetragonal metal(II) lattices: X-ray crystal structures and magnetic properties of [M(CA)(pyz)]n (M2+=Mn2+ and Co2+; H2CA=chloranilic acid; pyz=pyrazine)

New cobalt(II) and manganese(II) co-ordination polymers containing tetragonal lattices [M(CA)(pyz)]n (M2+=Mn2+ (1) and Co2+ (2); H2CA=chloranilic acid; pyz=pyrazine) have been synthesized and characterized. Both compounds 1 and 2 are isomorphous. Each metal atom for 1 and 2 displays a six-coordinate geometry with the two bis-chelating CA2− anions and pyz molecules, providing an infinite square grid sheet. The temperature dependence of magnetic susceptibilities revealed the presence of antiferromagnetic interaction with J=−0.32 cm−1, zJ′=−0.34 cm−1, g=2.00 for 1 and J=−1.09 cm−1, J′=−0.55 cm−1, g=2.27 for 2, respectively.

Synthesis and Crystal Structure of New Salicylate-Bridged Coordination Polymer, [Cu2(sal)2(pyz)(MeOH)2

Abstract The title compound, {[Cu2(sal)2(pyz)]·2MeOH}n (H2sal = salicylic acid, pyz = pyrazine) (1), has been synthesized, and structurally characterized. Each sal ligand connects the three copper centers to afford a novel 2-D network structure. The CuII-sal framework forms a rhombus type two-dimensional coordination framework. The pyz molecules, which fill the voids of the network, bind to the Cu site to afford zigzag chain.

Hydrothermal assembly and crystal structures of three novel open frameworks based on molybdenum(vi) oxides

The hydrothermal syntheses, crystal structures and thermal behaviours of three new 3-D framework molybdenum(VI) oxide hybrid materials, [MoO 3 (pyz) 0.5 ] 1 (pyz=pyrazine), [{Cu(pip) 0.5 }MoO 4 ] (pip=piperazine) 2 and [H 2 Mo 2 Cu 3 O 10 ] 3, are presented. 1 and 2 that are hybrids of inorganic oxide layers and bridging organodiamine ligands exhibit a covalent/coordination framework connectivity. 3 represents a novel open framework example of bimetallic oxides based on Mo VI and Cu II . These new materials are synthesized by a judicious selection of organodiamines accompanied by the concurrent alteration of initial reaction conditions. The choice of organodiamines is found to be critical to the framework composition and construction of solid architectures. The chiral framework of 1 and the 3-D structure of 2 are characterised by one-dimensional channels along the orthorhombic and triclinic b axis respectively circumscribed by six {MoO 5 N} octahedra and two pyz molecules in 1, and by two {MoO 4 } tetrahedra, four {CuO 4 N} square pyramids and two pip molecules in 2. The 3-D open framework of 3 has six-ring channels along the triclinic b axis. The thermal behaviours of the three solids are similar, undergoing a phase transition in the range 260-420 °C upon the removal of organic ligands in 1 and 2 and dehydration in 3.

The structural characterization of the novel ribbon sheet, [Cu 2Cl 2(pyz)] n (pyz = pyrazine)

The new copper(I) sheet compound [Cu 2Cl 2(pyz)] n (pyz = pyrazine) ( 1) has been synthesized and characterized. 1 crystallizes in the triclinic, space group P 1 with a = 6.885(2) A ̊ , b = 7.5719(6) A ̊ , c = 3.752(1) A ̊ , α = 98.84(1)°, β = 92.27(2)°, γ = 106.55(2)°, U = 184.55(7) A ̊ 3, and Z = 1 . Crystal structure consists of one-dimensional CuCl n ladders and stacked pyz columns. Infinite, zigzag ribbons are formed by Cu(I) ions and chlorides. The ladders extend along the c-direction, and are linked by pyz molecules which coordinate to adjacent copper atoms, forming a two-dimensional sheet. The pyz molecules are stacked in the sheet and make a column along the c-axis.

Oxidation of the pyrazine(pyz)-bridged polymeric copper(I) cation [Cu(cnge)(MeCN)(pyz)]+ by NOBF4 and formation of the corresponding copper(II) cation [Cu(MeCN)4(pyz)]2+(cnge = 2-cyanoguanidine)

The complex [Cu(cnge)(MeCN)(pyz)]BF4·0.5pyz 1(pyz = pyrazine, cnge = 2-cyanoguanidine) resulted from treatment of [Cu(MeCN)4]BF4 with mixtures of pyz and cnge in MeCN. Oxidation of compound 1 with NOBF4 in CH2Cl2 yielded Cu(pyz)(cnge)(BF4)22. Recrystallisation from MeCN resulted in loss of cnge and formation of [Cu(MeCN)4(pyz)][BF4]23. Reaction of 1 with NBut4NO2 in MeCN led to Cu(pyz)(cnge)(MeCN)(NO2)24. Single-crystal X-ray structural analysis has shown compound 1 to contain a one-dimensional zigzag cationic chain based on four-co-ordinate tetrahedral copper(I); each metal atom is ligated by two bridging pyz molecules and terminal MeCN and cnge molecules. The unco-ordinated pyz molecule, which is located at an inversion centre, connects parallel copper(I) chains via N ⋯ H–N bonds involving the amino moieties of ligating cnge molecules. The crystal structure of compound 3 contains a one-dimensional linear cationic chain based on six-co-ordinate copper(II), the tetragonally distorted octahedral co-ordination geometry of which comprises two bridging pyz molecules (equatorial) and four terminal MeCN molecules (two equatorial, two axial).