Mass spectral fragmentation mechanisms of some dibenzo[c,f][1,2] diazepines

The fragmentation mechanisms of 11H-dibenzo[c,f][1,2]diazepine (I), its 3,8-dichloro derivative (II), 3,8-dichlorodibenzo[c,f] [1,2]diazepin-11-one (III) and 3,8-dichloro-11H-dibenzo-[c,f][1,2]diazepin-N-oxide (IV) are discussed. The initial loss of molecular nitrogen is characteristic of I, II and III. Compound IV has a strong molecular ion, that competitively eliminates cither NO or Cl- and N₂O. The common radical ion, m/166 e present in the mass spectra of I, fluorene, 2-methyl-9,10-anthraquinone and 2-methylbenzo[c]cinnoline, appears to be formed in different states.     

Trinuclear, tetranuclear, and polymeric Cu(II) complexes from the first use of 2-pyridylcyanoxime in transition metal chemistry: synthetic, structural, and magnetic studies

The first use of 2-pyridylcyanoxime, (py)C(CN)NOH, in transition metal chemistry is described. Depending on the nature of the metal starting material and the reaction conditions employed, the Cu(II)/(py)C(CN)NOH system has provided access to complexes [Cu(3)O{(py)C(CN)NO}(3)(NO(3))(H(2)O)(2)(MeOH)] (1), [Cu(4)O{(py)C(CN)NO}(4)(O(2)CMe)(2)] (2), [Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)](2n)·n[Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)] (3), and [Cu{(py)C(CN)NO}(2)](n) (4). The molecule of 1 consists of three Cu(II) atoms in a strictly equilateral arrangement bridged by a central μ(3)-oxide group. The molecule of 2 consists of a tetrahedron of Cu(II) atoms held together by a central μ(4)-oxide ion, four η(1):η(1):η(1):μ-(py)C(CN)NO(-) ligands and two η(1):η(1):μ-MeCO(2)(-) groups. The crystal structure of 3 consists of [Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)](2n) double chains and discrete cluster [Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)] molecules. The crystal structure of 4 consists of neutral polymeric chains based on centrosymmetric mononuclear [Cu{(py)C(CN)NO}(2)] units. The Cu(II) atoms are doubly bridged by the oximate groups of two η(1):η(1):η(1):μ-(py)C(CN)NO(-) ligands. Variable-temperature, solid-state direct current (dc) magnetic susceptibility studies were carried out for 1-4. The data indicate very strong antiferromagnetic exchange interactions for 1-3. The obtained J values are discussed in depth on the basis of the structural parameters of the complexes, literature reports, and existing magnetostructural correlations.     

Low-temperature structural phase transition in SrMo6S8 studied by X-ray powder diffraction

Lattice parameters as a function of temperature for, and atomic coordinates of the low-temperature phase of, SrMo₆S₈ are reported from X-ray powder diffraction. The structure transforms atT ₁=135(3) K from the rhombohedral high-temperature modification (R ,a _rh=6.5630 (3) Å, _rh=88.9982(2)°,V _rh=282.55(5)ų at 298 K) into the triclinic low-temperature modification (P ,a _tr=6.481(1)Å,b _tr=6.572(1)Å,c _tr=6.611(1)Å, _tr=89.246(4)°, _tr=89.304(4)°, _tr=88.169(4)°,V _tr=281.4(2)ų at 20K). The triclinic distortion is larger than in the Ca analogue, and similar to the Ba and Eu analogues.

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Untersuchung des Tieftemperatur-Phasenübergangs von SrMo₆S₈ mittels Röntgenpulverdiffraktometrie (Kurze Mitt.)

Zusammenfassung Die Temperaturabhängigkeit der Gitterparameter und die Atomlagen der Tieftemperaturphase von SrMo₆S₈ wurden mittels Röntgenpulverdiffraktometrie bestimmt. Die rhomboedrische Hochtemperaturmodifikation (R ,a _rh=6.5630(3)Å, _rh=88.9982(2)°,V _rh=282.55(5)ų,T=298 K) wandelt beiT ₁=135(3) K in die trikline Tieftemperaturmodifikation (P ,a _tr=6.481(1)Å,b _tr=6.572(1)Å,c _tr=6.611(1)Å, _tr=89.246(4)°, _tr=89.304(4)°, _tr=88.169(4)°,V _tr=281.4(2)ų,T=20 K) um. Die trikline Deformation ist stärker ausgeprägt als in der Ca-Verbindung und ähnlich jener der Ba- and Eu-Verbindung.

     

Photoionization of liquid benzene: Fluorescence and electron scavenger quenching between 1900 and 1150 Å

In the photoionization region of liquid benzene, the fluorescence yield and quenching constanta increase from 1900 to 1400 Å and level off from 1400 to 1150 Å. Below 1750 Å, the quenching constants of CHCl₃, CH₃Cl, and C₂H₅Cl are proportional to their reactivities with quasi-free electrons and they extrapolate to zero at 7.1 eV, the estimated IP of liquid benzene.     

Synthesis, spectral and structural characterization of two polymeric 1:1 complexes of 2,3-dimethylpyridine and 5-ethyl-2-methylpyridine with copper(II) azide; Cu(2,3-dimethylpyridine) (N3)2 and Cu(2-methyl-5-ethylpyridine) (N3)2

Two new 1:1 ligand complexes of copper(II) azide with disubstituted pyridine ligands, namely catena-di-μ(1,3)-azido-[di-μ(1,1)-azidobis(2,3-lutidine)dicopper(II)] (1) and catena-di-μ(1,1)-azido[di-μ(1,1)-azidobis(2-methyl-5-ethylpyridine)dicopper(II)] (2), have been synthesized and characterized by spectroscopic and X-ray crystallographic methods. The polymeric complex 1 features monodentate 2,3-lut ligands, centrosymmetric di-μ(1,1)-azido-bridged Cu₂N₂ rings, distorted square-pyramidal copper(II) coordination geometry and di-μ(1,3)-azido bridges which link the centrosymmetric binuclear Cu₂(2,3-lut)₂(N₃)₂ moieties to form sheets within the ab plane. In the monoclinic crystals of complex 2, the copper(II) centres are pentacoordinated via N(11), N(21), N(11b) and N(21a) from the azido ligands [Cu---N distances 1.971(5)–2.286(5) Å] and N(1) from the organic molecule at a Cu---N bond length of 2.001(5) Å. Both azido ligands function as μ(1,1) bridges to form chains of polyhedra along the short a-axis of the unit cell. The IR absorption spectra reveal that each of these complexes contains two independent azide ligands. The solid and solution electronic spectra of complexes 1 and 2 show at least three and two strong absorption bands, respectively, associated with N₃⁻ → Cu^II charge transfer transitions. The EPR spectra of powder samples and DMSO solutions at room temperature were recorded and are discussed.     

Präparation und Kristallstrukturanalyse von Ca(N3)2(C5H5N)2

Diazido-dipyridine-calcium was prepared by the reaction of Ca(N₃)₂ with pyridine. The crystals are tetragonal, space group I 2 m (121),N=2,a=699.7 (1),c=1 450.6 (5) pm. The crystal structure was determined by single crystal X-ray diffraction, 415 independent observed Mo-K-counter reflexions,R=0.049. The calcium atoms are sixcoordinated to four nitrogen atoms of azide groups and to two nitrogen atoms of pyridine. The coordination polyhedra are tetragonal bipyramids which are linked together by four azide groups to form sheets of composition Ca(N₃)₂. The pyridine rings are directed perpendicular to the sheets.

     

Synthesis, spectral and structural characterization of three zinc(II) azide complexes with aminopyrazine

The reaction between zinc(II) azide, Zn(N₃)₂ and aminopyrazine (ampyz) afforded the complexes: [Zn(N₃)₂(ampyz)₂] (1), [Zn(N₃)₂(ampyz)]_n (2) and [Zn₃(N₃)₆(ampyz)₂]_n (3). These complexes are characterized by spectroscopic and crystallographic methods. The IR spectra of these compounds are measured and discussed. The structure of 1 consists of isolated tetrahedral zinc atom surrounded by two mono-dentate N-ampyz and two terminal azido ligands. Complex 2 features a zigzag chain of zinc centers in which each zinc is surrounded by alternate di-EO (end-on) and di-EE (end-to-end) azide bridges, the chain thus contains alternate four-membered Zn₂N₂ and eight-membered Zn₂(NNN)₂ rings. The two ampyz ligands are located in cis-arrangement and each of them further binds another zinc atom giving rise to a 3D network. Complex 3 contains two structurally different zinc atoms; the six-coordinate Zn(1) center links two di-EO azido bridges and two trans ampyz, thus having ZnN₆ chromophore. The five-coordinate Zn(2) center binds two di-EO bridging azido groups and the fifth position is occupied by an N atom from a bridging ampyz molecule. Both zinc centers, therefore participate in the formation of a 1D chain of cyclic Zn₂N₂ units. Each ampyz ligand binds another zinc atom via the second pyrazinic N atom giving another cross-chain and thus the structure consists of 2D sheets. In these three complexes the azido ligands of all types are asymmetric and linear within the experimental error.     

Shifting the equilibrium of a biocatalytic cascade synthesis to enantiopure epoxides using anion exchangers

Hydroxide-loaded anion exchangers have been successfully employed to shift the equilibrium of a one-pot, two-step, two-enzyme cascade reaction affording enantiopure epoxides starting from prochiral α-chloroketones. The α-chloroketones were asymmetrically reduced employing an alcohol dehydrogenase and then transformed further to the corresponding epoxides employing halohydrin dehalogenases. Each epoxide enantiomer could be obtained with up to 93% conversion in enantiomerically pure form (>99% ee). In contrast to previous studies the amount of hydride donor (2-propanol) could be reduced due to favoured halohydrin formation in the reduction of α-chloroketones.     

Structural characterization of five-coordinate copper(II), nickel(II), and cobalt(II) thiocyanato complexes derived from bis(2-(3,5-dimethyl-1-pyrazolyl)ethyl)amine

The reaction of M(ClO₄)₂·6H₂O with NH₄NCS in presence of the organic sterically hindered bis(2-(di-3,5-dimethyl-1-pyrazolyl)ethyl)amine (bedmpza) afforded the five-coordinate mononuclear dithiocyanato-M(II) complexes [M(bedmpza)(NCS)₂]·xMeOH (1: M = Cu²⁺, x = 0; 2: M = Ni²⁺, x = 0; 3: M = Co²⁺, x = 0.84). The compounds which proved to be non-electrolytes were characterized by IR and UV-Vis spectroscopy and their molecular structures were determined by single-crystal X-ray crystallography. In these complexes, the five-coordinate geometry was achieved by the three N-donors of the ligand bedmpza and two N atoms of the terminal thiocyanato ligands. The Cu(II) complex exists in two polymorphs 1-I and 1-II: an intermediate five-coordinate geometry with the two thiocyanato ligands are arranged as cisoid in 1-I and distorted square pyramidal geometry with the thiocyanato ligands are in transoid orientation in 1-II. Although the later geometry was also observed in the nickel complex 2, distorted trigonal bipyramidal geometry was found in 3. Each complex forms hydrogen bonds of type N-H?S from the secondary amine N(3) donor atoms to the adjacent terminal S(1) acceptor atoms of the thiocyanate group. The thermal behavior of the two polymorphs 1-I and 1-II were similar and no significant differences were observed between the two complexes.