The excited states of pyrazine: A basis set study

Summary Multiconfigurational second order perturbation theory (CASSCF/CASPT2) has been used to investigate the dependence of computed valence excitation energies and transition moments on the basis sets. Pyrazine has been selected as the test molecule. Atomic normal orbital (ANO) type basis sets are used throughout. Contractions of the structure (4s3p1d/2s) are found to be an optimal compromise between the quality and the size of the calculations and are capable of yielding results virtually identical to more extended basis sets.     

吡嗪衍生物在石墨表面上的自组装单层膜结构

利用扫描隧道显微镜研究了荧光液晶分子2, 5-二-[2-(3, 4-二-十二烷氧基-苯基)-乙烯基]-3, 6-二甲基吡嗪(BPDP12)在石墨表面上自组装单层膜的结构. 实验结果表明, 该化合物在石墨表面形成两种自组装结构：一种是稳定的, 分子的共轭中心相互平行, 烷基链相互交错的密排结构；另一种是不稳定的, 分子的共轭中心彼此为烷基链所分隔的非密排结构. 分子之间较强的π-π作用和分子烷基链之间的范德华作用力对分子组装的取向形成竞争, 是产生两种不同组装结构的根本原因.     

Synthesis,Spectroscopic and EPR Results and Crystal Structure of Copper(II) Formato Derivatives with Pyrazine and Dimethylpyrazines

The complexes of copper formato with pyrazine and dimethylpyrazines: Cu(HCOO)₂(pyrz) ( 1 ), Cu₂(HCOO)₄(pyrz) ( 2 ), Cu₂(HCOO)₄(2,3‐Me₂pyrz) ( 3 ), Cu₂(HCOO)₄(2,5‐Me₂pyrz) ( 4 ), and Cu₂(HCOO)₄(2,6‐Me₂pyrz)₂ ( 5 ) have been synthesized and characterized by chemical analysis and IR and electronic spectro scopies. The three‐dimensional structure of compound 1 consists of –Cu–pyrz–Cu–pyrz– chains joined by bridging formate groups coordinated, in configuration syn‐anti, to two copper atoms. The coordination around the copper atom is orthorhombic with two Cu–O distances of 2.374(1) Å, two Cu–O of 1.952 Å and two Cu–N of 2.080 Å. Compound 5 is formed by molecular dimers with the [Cu₂(μ‐HCOO)₄] unit, two copper atoms and four syn‐syn fomate groups, and two ligands coordinated to the copper atoms in the axial positions. In compounds 2 and 3 chains of [Cu₂(μ‐HCOO)₄] dimers with pyrz or 2,3‐Me₂pyrz as bridging ligands are formed. The EPR signal of 1 is orthorhombic (g = 2.23, 2.20 and 2.06). In the EPR spectra of 2 – 5 compounds the triplet (S = 1) signals are observed. The g_?, g_∥ and D values are been calculated.     

Synthesis of Naturally Occurring Pyrazine and Imidazole Alkaloids from Botryllus LeachiRID=”a”ID=”a”?Dedicated to Prof. G. M?rkl on the occasion of his 75th birthday

The synthesis of the naturally occurring and biologically active alkaloids 1 and 2, first isolated from the red ascidian Botryllus leachi by Duran et al. [1], is described and the structure proposed for Botryllazine B (1) is confirmed. The analytical data for 2-(p-hydroxybenzoyl)-4-(p-hydroxyphenyl)imidazole (2) are discussed and compared with the literature. With special emphasis of ¹H NMR data the tautomerism of aroylimidazolemethanones is described.     

Synthesis, structures and reactivity of triosmium clusters containing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands

Four triosmium carbonyl clusters bearing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands of general formula [Os₃(CO)₉(μ-OH)(μ-OMeCO)L] (1, L = pyrazine; 2, L = 2-methylpyrazine; 3, L = 2,3-dimethylpyrazine; 4, L = 2,3,5-trimethylpyrazine) were synthesized by the reactions of [Os₃(CO)₁₂] with the corresponding pyrazine derivatives and water in the presence of a methanolic solution of Me₃NO in moderate yields. Compounds [Os₃(CO)₉(μ-OH)(μ-OMeCO)L] react with a series of two electron donor ligands, L′ at ambient temperature to give [Os₃(CO)₉(μ-OH)(μ-OMeCO)L′] (5, L′ = PPh₃; 6, L′ = P(OMe)₃; 7, L′ = ^tBuNC; 8, L′ = C₅H₅N) in good yields by the displacement of the pyrazine ligands. This implies that the pyrazine ligands in 1–4 are relatively labile. Compounds 2, 3, 4, and 8 were characterized by single crystal X-ray diffraction analyses. All the four compounds possess two metal–metal bonds and a non-bonded separation of two osmium atoms defined by Os(1)Os(3), which are simultaneously bridged by OH and MeOCO ligands and a heterocyclic ligand is terminally coordinated to one of the two non-bonded osmium atoms.     

Synthesis and Biological Activity of Some New Pyrazolo[3,4‐b]Pyrazines

New derivatives of pyrazolo[3,4‐b]pyrazine and related heterocycles were prepared starting from 6‐amino‐3‐methyl‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyrazine‐5‐carbonitrile ( 2 ) and using the key intermediates 4 , 5 , 6 , 14 , 15 and 16 . Some of the prepared compounds were evaluated for their antifungal and antibacterial activities.     

Indium(III) one-dimensional polymers with pyrazine and pyrazine, 2-carboxylic acid as the spacer molecules

The reactions of indium(III) chloride tetrahydrate with pyrazine (C₄H₄N₂) and pyrazine, 2-carboxylic acid afford two polymeric frameworks, the structures of which were characterized in the solid state by single crystal analysis. The former is a one-dimensional infinite structure interlinked by the pyrazine spacer, while the latter is a one-dimensional ‘zigzag’ polymeric structure. A dimeric indium(III) pyrazine complex is also reported.     

A stable carbonyl-pyrazine-metal(0) complex: Synthesis and characterization of cis-tetracarbonylpyrazinetrimethylphosphitetungsten(0)

Pentacarbonylpyrazinetungsten(0), (CO)₅W(pyz), is not stable in solution in polar solvents such as acetone or dichloromethane and undergoes conversion to a bimetallic complex, (CO)₅W(pyz)W(CO)₅ plus free pyrazine. These three species exist at equilibrium. Using the quantitative ¹H NMR spectroscopy, the equilibrium constant could be determined to be K_eq = (5.9 ± 0.8) × 10⁻² at 25 °C. Introducing a second pyrazine ligand into the molecule does not stabilize the complex, as cis-W(CO)₄(pyz)₂ was found to be less stable than W(CO)₅(pyz) and, therefore, could not be isolated. However, introducing trimethylphosphite as a donor ligand into the complex leads to the stabilization of the carbonyl-pyrazine-metal(0) complexes, as shown by the synthesis of cis-W(CO)₄[P(OCH₃)₃](pyz). This complex could be isolated from the reaction of the photogenerated W(CO)₄[P(OCH₃)₃](tetrahydrofuran) with trimethylphosphite upon mixing for 2 h at 10 °C in tetrahydrofuran and characterized by elemental analysis, IR, MS, ¹H, ¹³C, and ³¹P NMR spectroscopy.     

Über die Schichtstruktur von Cu2(H2O)4[C4H4N2][C6H2(COO)4]·2H2O

The Layered Structure of Cu₂(H₂O)₄[C₄H₄N₂][C₆H₂(COO)₄]·2H₂O Triclinic single crystals of Cu₂(H₂O)₄[C₄H₄N₂][C₆H₂(COO)₄]·2H₂O have been grown in an aqueous silica gel. Space group (Nr. 2), a = 723.94(7) pm, b = 813.38(14) pm, c = 931.0(2) pm, α = 74.24(2)°, β = 79.24(2)°, γ = 65.451(10)°, V = 0.47819(14) nm³, Z = 1. Cu²⁺ is coordinated in a distorted, octahedral manner by two water molecules, three oxygen atoms of the pyromellitate anions and one nitrogen atom of pyrazine (Cu—O 194.1(2)–229.3(3) pm; Cu–N 202.0(2) pm). The connection of Cu²⁺ and [C₆H₂(COO)₄)]^4? yields infinite strands, which are linked by pyrazine molecules to form a two‐dimensional coordination polymer. Thermogravimetric analysis in air showed that the dehydrated compound was stable between 175 and 248 °C. Further heating yielded CuO.     

Synthesis and Complexation Studies of a Convex Bis-porphyrin Tweezer—A Molecular Capsule Precursor

The synthesis and spectroscopic studies of a convex bis-porphyrin based molecular tweezer are reported. The complexation of small bidentate ligands by metallated derivatives of the bis-porphyrin host were monitored through UV–visible and ¹H NMR spectroscopy and yielded large association constants.