Pyrazine Molecules Research Articles

Equilibrium Structures of Pyrazine, s-Triazine, and s-Tetrazine

In recent years, accurate equilibrium (re) structures have been determined for pyridine, pyridazine, and pyrimidine. Here, we report accurate re structures for the structurally related molecules pyrazine, s-triazine, and s-tetrazine, which were obtained using a composite approach based on explicitly correlated coupled-cluster theory (CCSD(T)-F12b) in conjunction with a large correlation-consistent basis set (cc-pCVQZ-F12) to take core–valence electron correlation into account. Additional terms were included to correct for the effects of iterative triple excitations (CCSDT), noniterative quadruple excitations (CCSDT(Q)), and scalar relativistic contributions (DKH2-CCSD(T)). The performance of this computational procedure was established through test calculations on selected small molecules. For s-triazine, accurate experimental ground-state rotational constants (B0) of the parent molecule and six D3h isotopologues from the literature were used to determine a semiexperimental re structure, which was found to be essentially identical with the best estimate from the current composite approach. The presently recommended equilibrium structural parameters of s-triazine are re(CH) = 108.17 pm, re(CN) = 133.19 pm, and θe(NCN) = 125.95°, with estimated uncertainties of ±0.10 pm and ±0.10°, respectively. The predicted equilibrium geometries for pyrazine and s-tetrazine are expected to be of the same accuracy. We recommend for pyrazine: re(CH) = 108.16 pm, re(CN) = 133.34 pm, re(CC) = 139.07 pm, θe(CNC) = 115.60°, and θe(HCC) = 120.75°; and for s-tetrazine: re(CH) = 107.95 pm, re(CN) = 133.39 pm, re(NN) = 132.01 pm, and θe(NCN) = 126.59°.

Synthesis, structure and effective peroxidase-like activity of a stable polyoxometalate-pillared metal–organic framework with multinuclear cycles

A stable polyoxometalate (POM)-pillared metal–organic framework (MOF) with 6-nuclear Cu-pz and 10-nuclear Cu-pz-Cl cycles, [Cu5(pz)6Cl][SiW12O40] (CuSiW12) (pz = pyrazine), has been hydrothermally synthesized and structurally characterized. Inspired by the reported horseradish peroxidase (HRP) and other enzyme mimics, the peroxidase-like activity of CuSiW12 was investigated in detail to catalyze the oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2, which exhibits excellent peroxidase-like activity than that of pristine silicotungstic acid. Moreover, the detection of H2O2 was also studied in the TMB/CuSiW12/H2O2 system, which exhibits good sensitivity, wide linear range (1–60 μM), the lowest detection limit (0.10 μM) and faster response time towards H2O2 (2 min) to date, to the best our knowledge, maybe due to the maximized synergistic effects of SiW12 clusters, pyrazine molecules, Cu ion and the stable structure.

The time-dependent density matrix renormalisation group method

ABSTRACTSubstantial progress of the time-dependent density matrix renormalisation group (t-DMRG) method in the recent 15 years is reviewed in this paper. By integrating the time evolution with the sweep procedures in density matrix renormalisation group (DMRG), t-DMRG provides an efficient tool for real-time simulations of the quantum dynamics for one-dimensional (1D) or quasi-1D strongly correlated systems with a large number of degrees of freedom. In the illustrative applications, the t-DMRG approach is applied to investigate the nonadiabatic processes in realistic chemical systems, including exciton dissociation and triplet fission in polymers and molecular aggregates as well as internal conversion in pyrazine molecule.

Self-assembly of flexible [2 + 2] ionic metallamacrocycles and their cytotoxicity potency

The syntheses and characterization of two cationic two-dimensional metallamacrocycles are described. Both the macrocycles utilize pyrazine molecule as donor tecton along with two flexible diplatinum(II) organometallic acceptor tectons. Formation of macrocycles was supported by elemental analyses (CHN), multinuclear NMR and electrospray ionization mass spectrometry (ESI-MS). Both the macrocycles are [2 + 2] dimeric metallacycles as evident from mass spectrometry results. Molecular modeling of these macrocycles shows that these macrocycles are nanoscalar and have distorted and circular shaped structure. The cytotoxicity of these PtII-based macrocycles was studied using various cell lines and experimental results confirmed a positive effect of the metallamacrocyle formation on cell growth inhibition.

Anisotropic Crystals Based on a Main-Group Coordination Polymer with Alignment of Rigid π Skeletons

We succeeded in the alignment of π skeletons, resulting in the formation of anisotropic crystals. The combination of plumbacyclopentadienylidene, which has a divalent lead atom incorporated into the π skeleton, and 1,4-dioxane afforded a coordination polymer, where the π skeletons are completely aligned in the same direction. The resulting plumbylene chains are also aligned in the same direction in the solid state, and therefore the crystals are noncentrosymmetric, showing second-harmonic generation (SHG) properties. Using pyrazine instead of 1,4-dioxane afforded an adduct composed of three plumbole units and two pyrazine molecules, and the crystals are symmetric and exhibit no SHG properties. The solid-state structures and optical properties are highly dependent on the Lewis base utilized. The present findings spotlight the use of group 14 divalent species incorporated into a π skeleton as a novel, useful method for the creation of a π-aligned coordination polymer with NLO properties.

Structures of the adducts urea:pyrazine (1:1), thiourea:pyrazine (2:1) and thiourea:piperazine (2:1)

Abstract The adducts urea:pyrazine (1:1) (1), thiourea:pyrazine (2:1) (2), and thiourea:piperazine (2:1) (3) were prepared and their structures determined. Adduct 1 forms a layer structure, in which urea chains of graph set C(4)[ R 2 1 ${\rm{R}}_{\rm{2}}^{\rm{1}}$ (6)] run parallel to the b axis and are crosslinked by N–H···N hydrogen bonding to the pyrazine residues. Adduct 2 is a variant of the well-known R 2 2 ${\rm{R}}_{\rm{2}}^{\rm{2}}$ (8) ribbon substructure for urea/thiourea adducts, with the pyrazine molecules attached to the remaining thiourea NH groups via bifurcated hydrogen bonds (N–H···)2S; the more distant end of the pyrazine molecules is crosslinked to another symmetry-equivalent but perpendicular ribbon system, thus creating a three-dimensional packing. The packing of adduct 3 involves thiourea layers parallel to the ab plane; the piperazine molecules occupy the regions between these layers and are linked to the thiourea molecules by two hydrogen bonds (one as donor, one as acceptor) at each piperazine nitrogen atom.

Spin Crossover in the {Fe(pz)[Pt(CN)4]} Metal-Organic Framework upon Pyrazine Adsorption.

The spin-crossover behavior of the {Fe(pz)[Pt(CN)4]} metal-organic framework (MOF) upon pyrazine adsorption is investigated through hybrid Monte Carlo/molecular dynamics (MC/MD) simulations. In contrast to previous theoretical studies, which reported a transition temperature of ∼140 K, the present MC/MD simulations predict that the high-spin state is the most stable state at all temperatures, in agreement with the experimental observations. The MC/MD simulations also indicate that the pyrazine molecules adsorbed in the MOF pores lie nearly parallel but staggered by 60° relative to the pyrazine ligands of the framework. The analysis of the magnetization curve as a function of the temperature demonstrates that the staggered configuration assumed by the guest pyrazine molecules within the framework is responsible for the stabilization of the high-spin state. Both the guest pyrazine molecules and the pyrazine ligands of the framework are effectively locked into the minimum-energy configuration and do not display any rotational mobility.

Determination of the number of atoms present in nano contact based on shot noise measurements with highly stable nano-fabricated electrodes

A highly stable experimental setup was developed for the measurement of shot noise in atomic contacts and molecular junctions to determine the number of atoms or molecules present. The use of a nano-fabricated mechanically controllable break junction (MCBJ) electrode improved the overall stability of the experimental setup. The improved stability of the system and optimization of measurement system enabled us to comprehensively investigate the shot noise as well as charge transport properties in Au atomic contacts and molecular junctions. We present a solid proof that the number of atoms (cross sectional atom) in the Au atomic contacts was exactly one. In the atomic contacts, contribution from the additional channels was under the detection limit. Furthermore, the effect of molecular adsorption on the charge transport in the Au atomic contact was investigated. Additional transport channels were opened by exposing pyrazine molecules to the Au contacts, which gave rise to an increase in the Fano factor in the shot noise.

Crystal structure of catena-poly[[(dimethyl sulfoxide-κO)(pyridine-2,6-di-carboxyl-ato-κ(3) O,N,O')nickel(II)]-μ-pyrazine-κ(2) N:N'

The title coordination polymer, [Ni(C7H3NO4)(C4H4N2)(C2H6OS)] n , consists of [010] chains composed of Ni(II) ions linked by bis-monodentate-bridging pyrazine mol-ecules. Each of the two crystallographically distinct Ni(II) ions is located on a mirror plane and is additionally coordinated by a dimethyl sulfoxide (DMSO) ligand through the oxygen atom and by a tridentate 2,6-pyridine-di-carb-oxy-lic acid dianion through one of each of the carboxyl-ate oxygen atoms and the pyridine nitro-gen atom, leading to a distorted octa-hedral coordination environment. The title structure exhibits an inter-esting complementarity between coordinative bonding and π-π stacking where the Ni-Ni distance of 7.0296 (4) Å across bridging pyrazine ligands allows the pyridine moieties on two adjacent chains to inter-digitate at halfway of the Ni-Ni distance, resulting in π-π stacking between pyridine moieties with a centroid-to-plane distance of 3.5148 (2) Å. The double-chain thus formed also exhibits C-H⋯π inter-actions between pyridine C-H groups on one chain and pyrazine mol-ecules on the other chain. As a result, the inter-ior of the double-chain structure is dominated by π-π stacking and C-H⋯ π inter-actions, while the space between the double-chains is occupied by a C-H⋯O hydrogen-bonding network involving DMSO ligands and carboxyl-ate groups located on the exterior of the double-chains. This separation of dissimilar inter-actions in the inter-ior and exterior of the double-chains further stabilizes the crystal structure.

Synthesis, Structure and magnetic properties of a copper (II) complex of 5-nitro-2-hydroxypyridine and pyrazine: [Cu(5-NO2 -2-HOPY)(pz)2(H2O)] (ClO4)2∙H2O

The synthesis, structure, and magnetic properties of [Cu(5-NO 2 -2-HOPY)(pz) 2 (H 2 O)] (ClO 4 ) 2 ∙H 2 O ( pz = pyrazine) (1 )are reported. Crystals were characterized using IR, combustion analysis, X-ray powder diffraction, single crystal X-ray diffraction, and temperature-dependent magnetic susceptibility measurements. Compound 1 crystallizes in the monoclinic space group P2 1 /c. The crystal structure consists of copper/pyrazine chains parallel to the c- axis with terminal pyrazine groups found perpendicular to the bridging pyrazine molecules creating a zig-zag chain structure. The 1D-system exhibits weak antiferromagnetic interactions of J = -7.58 K with no measurable interchain interactions.

An isomer of a POM-based hybrid compound formed through different linkage between CuI ions and pyrazine

One 3D Keggin polyoxometalates-based hybrid compound, [Cu4(pz)6(H2O)2(SiW12O40)] (1) (pz = pyrazine), was hydrothermally synthesized and characterized by an elemental analysis, IR spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction. In compound 1, [Cu4(pz)6(H2O)2] 4+ polymeric cation has 2D network structure including ten-metal rings. The two 2D networks are linked through sharing a coordination water into a double-layer structure. [SiW12O40]4− anions are embedded between two double-layers through the coordination of Ot atoms to Cu atoms. The pyrazine molecule is in situ formed from the decarboxylation of pyrazine-2,3-dicarboxylic acid. The IR data of 1 also proved the correctness of the structure due to no characteristic peak of carbonyl group in IR spectrum. Thermogravimetric analysis and fluorescence of 1 are also analyzed and discussed.

Construction of hydrogen-bonded networks of 1′,1‴-diboronic acids of biferrocene and biferrocenium cation

The solid-state structures of 1′,1‴-biferrocenediboronic acid (1) were elucidated by X-ray crystallography, to obtain insight into controlling the structures of hydrogen-bonded (H-bonded) assemblies from a functional organobimetallic building block. Four solvated crystal forms of 1 were newly obtained by recrystallization under different solvent conditions. The dioxane-, pyridine-, and pyrimidine-solvated crystals (Forms III to V) involved chain-like 1D H-bonded networks of 1. The 1D chains of 1 were capped with solvent molecules with lateral H-bonds. The pyrazine-solvated crystals (Form VI) involved 1D chains of 1, which were connected by pyrazine molecules with lateral H-bonds to afford sheet-like 2D networks. The suitable bidentate H-bond acceptor was found to transform 1D chains into 2D networks. Two crystal forms of 1′,1‴-biferroceniumdiboronic acid (1+) were also prepared and investigated the geometry of the H-bonded assemblies and the valence states of 1+. The mixed-valence (MV) cation 1+ forms 1D chains (Form VII) and discrete dimers (Form VIII) with triiodide anions in the valence-detrapped and trapped states, respectively. This study demonstrates the usefulness of the boronic acid-based method to obtain MV supramolecular structures in the solid state.

Crystal structure of catena-poly[[[trans-bis(aceto-nitrile-κN)diaquacobalt(II)]-μ-pyrazine-κ(2) N:N'] dinitrate

The central structural motif of the title coordination polymer, [Co(NO3)2(C4H4N2)(CH3CN)2(H2O)2] n , is a chain composed of Co(II) ions linked by bis-monodentate bridging pyrazine ligands through their N atoms. The Co(II) ion is located on an inversion center and is additionally coordinated by two O atoms of water mol-ecules and two N atoms of aceto-nitrile mol-ecules. The resultant N4O2 coordination sphere is distorted octa-hedral. The linear cationic chains extend parallel to the a axis and are aligned into layers parallel to the ac plane. Nitrate anions are situated in the space between the Co(II) chains and form O-H⋯O hydrogen bonds with the coordinating water mol-ecules, leading to a three-dimensional network structure. Weak C-H⋯O hydrogen bonds are also present between pyrazine or aceto-nitrile mol-ecules and the nitrate anions.

Discrete CH···N Bonded Patterns Modified by Temperature and Pressure in Four Pyrazine Polymorphs

Pyrazine molecules aggregate by remarkably similar CH···N hydrogen bonds into four polymorphs. Of eight CH···N bonds to each molecule, six H-bonds are very similar for all pyrazine structures. A diagram of four crystalline phases has been outlined and their low-temperature and high-pressure structures determined. Phase I is metastable and occurs only within the ambient-pressure region of phase II.

Copper inorganic-organic hybrid coordination compound as a novel L-cysteine electrochemical sensor: Synthesis, characterization, spectroscopy and crystal structure

Dinuclear coordination compound of Cu(II), namely, [Cu2(pydc)2(pz)(H2O)2] ⋅2H2O, where pydc = pyridine-2,6-dicarboxylic acid (dipicolinic acid) and pz = pyrazine has been synthesized and characterized by elemental analysis, spectra (IR, UV-Vis), thermal (TG/DTG) analysis, magnetic measurements and single crystal X-ray diffraction. In the dimeric structure, the planar tridentate pyridine-2,6-dicarboxylic acid dianion coordinates to a Cu(II) ion in a meridional fashion and defines the basal plane of the complex. The fourth equatorial coordination site is then occupied by a pyrazine molecule that functions as a linear bidentate ligand bridging two Cu(II) complexes to form a dimer. The axial positions of each Cu(II) complex are occupied by one water molecule to form a distorted square pyramidal geometry. The complicated hydrogen bonding network accompanied with C–O ⋯π and C–H ⋯π stacking interactions assemble the crystal structure of 1 into a fascinating supramolecular architecture. Electrochemical behavior of [Cu2(pydc)2(pz)(H2O)2] (Cu-PDAP) on the surface of carbon nanotube (CNTs) glassy carbon electrode (GCE) is described. Oxidation of cysteine on the surface of modified electrode was investigated with cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results show that the Cu-PDAP/CNTs film displays excellent electrochemical catalytic activities towards L-cysteine oxidation. Dinuclear coordination compound of Cu(II), namely, [Cu2(pydc)2(pz)(H2O)2].2H2O, has been synthesized and characterized by elemental analysis, spectral (IR, UV-Vis), thermal (TG/DTG) analysis as well as single crystal X-ray diffraction. Electrochemical behavior of [Cu2(pydc)2(pz)(H2O)2] on the surface of carbon nanotube (CNTs) glassy carbon electrode (GCE) was described and oxidation of cysteine on the surface of modified electrode was investigated.

Gossypol inclusion compound with pyrazine: crystal structure and thermal behavior

Single crystals of gossypol complex with pyrazine (1:4) have been obtained in two ways: (I) in the pyrazine solution of gossypol (T = 56 °C) and (II) in the dichloromethane solution of dianhydrogossypol/pyrazine mixture (room temperature). The crystals were characterized by X-ray crystallography. Crystal data: (I), C30H30O8·4(C4H4N2), M = 838.91, T = 130 (2) K, MoKα = 0.71073 A, a = 7.5230 (3), b = 13.9185 (6), c = 19.8328 (8) A, α = 88.789 (4), β = 87.255 (3), γ = 86.683 (4)°, V = 2070.46 (15) A3, Z = 2, Dcalc = 1.346 g/cm3, crystal system: triclinic, space group: P−1, R = 0.0393 for 7218 observed reflections; (II), C30H29,56O7,85·4(C4H4N2), M = 836.11, T = 100 (2) K, CuKα, 1.54184 A, a = 7.5010 (4), b = 13.9425 (6), c = 19.7848 (9) A, α = 88.618 (4), β = 87.442 (4), γ = 86.898 (4)°, V = 2063.57 (17) A3, Z = 2, Dcalc = 1.345 g/cm3, crystal system: triclinic, space group: P−1, R = 0.0509 for 7215 observed reflections. Pair of gossypol and pyrazine molecules are formed the centrosymmetric tetramers untypical for gossypol type structures. Crystal structures are characterized with the presence of wide channels for guest molecules. TG-DSC curves of gossypol with pyrazine complex (1:4) showed that decomposition of crystals occurs in four steps. Formation of new gossypol:pyrazine host:guest complexes with ratios of 2:3 and 1:1 were observed in TG-DSC curves.

Crystal structure of catena-poly[[aqua-bis-(4-formyl-benzoato)-κ(2) O (1),O (1');κO (1)-zinc]-μ-pyrazine-κ(2) N:N'

The asymmetric unit of the title polymeric compound, [Zn(C8H5O3)2(C4H4N2)(H2O)] n , contains two mol-ecular units. Each unit comprises two 4-formyl-benzoate (FB) anions, one pyrazine mol-ecule and one coordinating water mol-ecule; the FB anions act either as bidentate or as monodentate ligands. The O atoms of the bidentately coordinating FB anions are disordered over two positions, and they were refined with fixed occupancy ratios of 0.75:0.25 and 0.70:0.30, respectively. In the ordered monodentately coordinating FB anions, the carboxyl-ate groups are twisted away from the attached benzene rings (B and E) by 12.1 (2) and 9.2 (2)°, respectively. In the disordered FB anions, the corresponding angles are 14.1 (1) and 4.0 (2)° for benzene rings A and D, respectively. Benzene rings A and B are oriented at a dihedral angle of 45.7 (1)°, D and E at 23.2 (1)°. Pyrazine ring C makes dihedral angles of 85.6 (1) and 72.7 (1)°, respectively, with benzene rings A and B, and pyrazine ring F makes dihedral angles of 87.0 (1) and 81.3 (1)° with benzene rings D and E, respectively. The pyrazine ligands bridge the Zn(II) cations, forming polymeric chains running parallel to the b-axis direction. Medium-strength intra-molecular O-H⋯O hydrogen bonds link the water mol-ecules to the carboxyl-ate O atoms. In the crystal, water-carboxyl-ate O-H⋯O hydrogen bonds link adjacent chains into layers parallel to the bc plane. The layers are linked via weak pyrazine-formyl C-H⋯O and form-yl-carboxyl-ate C-H⋯O hydrogen bonds. π-π contacts between the benzene rings, with centroid-to-centroid distances of 3.7765 (16), 3.7905 (15) and 3.8231 (16) Å, may further stabilize the structure. There are also weak C-H⋯π inter-actions present.

A DFT study of pyrazine derivatives and their Fe complexes in corrosion inhibition process

The DFT/B3LYP calculations were applied to investigate the relationship between electronic properties and corrosion inhibition efficiency of three pyrazine derivatives, 2-methylpyrazine (MP), 2-aminopyrazine (AP) and 2-amino-5-bromopyrazine (ABP). To take into account the solution acidity in experimental conditions, all possible mono-protonated forms, that is protonation at N1, N4 and NH2 sites, as well as the non-protonated form were considered. The molecular orbital analysis showed a good correlation between EHOMO, ELUMO and ΔE (EHOMO−ELUMO) with inhibition efficiency of the three pyrazine derivatives. Four types of interactions between iron and pyrazine molecules, i.e. Fe–π, Fe–N1, Fe–N4 and Fe–NH2 were included in the calculations. As a new approach to this system, inhibition mechanism of the three pyrazine molecules has been discussed in detail based on these four types of interactions. It was found that all four interactions are energetically important. The flat pyrazine ring was substantially deformed followed by a Fe–π interaction. The calculated binding energy of ABP in all forms was found to be higher than two other pyrazines, which is consistent with experimentally observed highest corrosion inhibition efficiency. The lack of Fe–NH2 interaction for MP molecule seems to be the reason for its lower corrosion inhibition efficiency.

Photoconductive and nonlinear optical properties of composites based on metallophthalocyanines

AbstractThe photoconductive, photorefractive and nonlinear optical properties of composites from polyvinylcarbazole or aromatic polyimide containing supramolecular ensembles of (tetra-15-crown-5) - phthalocyaninato gallium, indium, - phthalocyaninateacetato yttrium, - phthalocyaninato ruthenium with axially coordinated pyrazine molecules were investigated at 633, 1030 and 1064nmusing continuous and pulsed lasers. Supramolecular ensembles (SE) were prepared through dissolution of molecular metallophthalocyanines in tetrachloroethane (TCE) and subsequent treatment via three cycles of heating to 90∘C and slow cooling to room temperature. The zscan method in femtosecond and nanosecond regimeswas used for measuring nonlinear optical properties phthalocyaninato indium and yttrium in TCE solutions and polymer films. It was established that effect of heavy metallic atom is basic factor which determines the quantum yield, photorefractive amplification of laser object beam, dielectric susceptibility of third order and nonlinear optical properties of metallophthalocyanines.

Synthesis, structure, solution and DFT studies of a pyrazine-bridged binuclear Cu(II) complex: On the importance of noncovalent interactions in the formation of crystalline network

A pyrazine-bridged binuclear Cu(II) complexes with formulae of [Cu2(chel)2(pyz)(H2O)4], (1, pyz=pyrazine, H2chel=chelidamic acid), has been synthesized and characterized by elemental analyses, IR spectroscopy and solution studies. The crystal structure of the binuclear Cu(II) complex has been determined by X-ray single-crystal diffraction technique. Both copper(II) metal centers are bridged by pyrazine. The coordination environment around each copper(II) atom can be described as a distorted octahedral geometry. The axial positions of each Cu(II) complex are occupied by two water molecules and equatorial positions are occupied by a tridentate chelidamic acid dianion and a pyrazine molecule that functions as a linear bidentate ligand bridging two Cu(II) complexes to form a dimer. Hydrogen bonding and CO⋯π interactions link the binuclear Cu(II) complex generating the 3D infinite network. These assemblies are described and analyzed by means of density functional theory (DFT) calculations since they play an important role in the construction of three-dimensional supramolecular frameworks. The protonation constants of pyrazine and chelidamic acid as the building blocks of the proton transfer systems (H2chel-pyz) and their corresponding stability constants were determined by potentiometric studies. The stoichiometry and stability constants of H2chel-pyz complex with Cu2+ was investigated by potentiometric technique in aqueous solution. The results from solution studies were compared with the solid state data, in details.