Structural comparison to the molybdenumsite of nitrogenase Synthesis and crystal structure of binuclear oxomolybdenum(V)complex with both omercaptophenolate and alkoxide ligands

Complex(n-Bu_4N)[Mo_2O_2(OMe)(mp)_3][1,mp=(o-OC_(?)H_4S)^(2-)]was synthesized by the reaction of MoOCl_3(THF)_2 and Na_2mp in EtOH and crystallized in monoclinic space group P2_(?)/n with crystal data:a=13.910(3),b=23.554(3),c=12.558(2)(?),β=105.20(2)°,Z=4,D_o=1.455g/ cm^3,final R=0.077 for 5325 reflections[I>3σ(I)].The two[Mo(O)mp]^+ moicties are bridged by one 1,2-bidentate ligand mp^(2-) with exceedingly small bite angle(69.0°)and bite distance (2.70(?))and by a methoxy group.The structure can be interpreted as two distorted octahedra around the Mo atoms sharing a face.Attempts have been made to provide structural informa- tions for the syntheses of modelling compounds of FeMoco by comparing the Mo—O and Mo—S bond distances of o-mercaptophenolate ligated compounds to those of the molybdenum site of nitrogenase.

SYNTHESIS OF DIAMMINEPLATINUM(Ⅱ)ASCORBATE AND STRUCTURE COMPARISON WITH ITS DACH DERIVATIVES

An antitumour complex,cis-diammineplatinum(Ⅱ)ascorbate,has been synthesized and its X-ray structure is given.Quantum chemistry calculation compared with its diaminecyclohexane derivatives indicates that they have different electron distribution.

The further crystallographic refinement of trichosanthin at 2.7A resolution and the comparison among the three molecular structures in two crystal forms

The three-dimensional structure of trichosanthin at 2.7A resolution has been improved further, by refitting one of the C-terminal tails, adjusting 16 residues in the molecular surface regions, discarding some water molecules with high B values, and adjusting weights during the further refinement. The R-factor has been reduced to 18.5% and the r.m.s deviations from ideal geometry are also improved. The structures of the two molecules in the monoclinic asymmetric unit and the only molecule in the orthorhombic asymmetric unit are compared with one another. The main-chain structures for most of the residues in the three molecules are substantially the same. However, the courses of the three C-terminal tails are completely different, and the intermolecular interactions resulting from the particular packing of the molecules in the crystals account for the differences. The strand Be-2 and the preceding B-turn in small domain show large r.m.s. deviations among the three molecules and they are also involved in intermolecular interactions.

Comparison of spatial structures of urban agglomerations between the Beijing-Tianjin-Hebei and Boswash based on the subpixel-level impervious surface coverage product

Under the background of China's rapid urbanization, study on comparative analysis of the spatial structure of urban agglomerations between China and the US can provide the policy proposals of space optimization for the Chinese government. Taking the Beijing-Tianjin-Hebei(BTH) and Boswash as study area, we mapped the subpixel-level impervious surface coverage of the BTH and Boswash, respectively, from 1972 to 2011. Further, landscape metrics, gravitational model and spatial analysis were used to analyze the differences of the spatial structures between the BTH and Boswash. The results showed that(1) the area of the impervious surface increased rapidly in the BTH, while those remained stable in the Boswash.(2) The spatial structure of the BTH experienced different periods including isolated cities stage, dual-core cities stage, group cities stage and network-style cities stage, while those of the Boswash was more stable, and its spatial pattern showed a "point-axis" structure.(3) The spatial pattern of high-high assembling regions of the impervious surface exhibited a "standing pancake" feature in the BTH, while those showed a "multi-center, local aggregation and global discrete" feature in the Boswash.(4) All the percentages of the impervious surface of ecological, living, and production land of the BTH were higher than those of the Boswash. At last, from the perspective of space optimization of urban agglomeration, the development proposals for the BTH were proposed.

A new barium-containing alkali metal silicate fluoride NaBa3Si2O7F with deep-UV optical property

A new silicate fluoride,NaBa3 Si207 F,has been successfully synthesized by a high-temperature solution method.It crystallizes in the orthorhombic space group Cmcm(No.63).NaBa3 Si2 O7 F is the first barium-containing alkali metal silicate fluoride with the[NaO6]polyhedra,the[BaO8 F]polyhedra and isolated[Si2 O7]units.The optical characterizations indicate that NaBa3 Si2 O7 F possesses wide transparent window and available luminescence properties.To confirm the coordination surroundings of anionic groups and its thermostability,infrared spectroscopy and thermal behaviors were also analyzed,which proved the existence of tetrahedronly coordinated silicium atoms and the good stability of NaBa3 Si2 O7 F at high temperature.First-principles calculation was also implemented for better understanding the relationship between the structure of NaBa3 Si207 F and its property.Additionally,to further explore the structural novelty of NaBa3 Si2 O7 F,the comparison of the anionic structures was carried out in mixed alkali and alkaline-earth metal silicate fluorides.Interestingly,the result indicates the isolated[Si2 O7]dimer is rare among the above systems,which enriches the structural chemistry of silicate fluorides.