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991.
A three-dimensional potential energy surface for the photodissociation of H2O in its lowest excited singlet state 1B1 in C2v or 1A″ in C3 symmetry, respectively, has been calculated with quantum-chemical ab initio methods including electron correlation. The main features of the surface are discussed and qualitative explanations are given for the experimentally observed vibrational and rotational excitations of the product OH(2Π) radicals. The surface will be used in subsequent investigations of the dynamics of the H2O photodissociation process. 相似文献
992.
993.
Dipl. Math. Hans-Wiegand Binzer Prof. Dr. Volker Mammitzsch 《manuscripta mathematica》1979,30(4):383-386
A theorem of W.RUPP [4] on integration of correspondences (set-valued functions) is slightly generalized and a new short proof is given by means of a measurability concept for correspondences which was introduced by H.RICHTER [3]. 相似文献
994.
Complexes have been obtained by the reaction of iron atoms with butadiene or styrene at - 196°C followed by treatment with ligands such as CO or (MeO)3P. 相似文献
995.
996.
997.
2,4-Di-t-butyl-cyclopentadiene-1-carbaldehyde () and 2,4-di-t-butyl-cyclopentadienone oxime () are easily converted into the title compounds and , respectively. The spectroscopic and chemical properties of the new heterocyclic 10π-electron systems are described. 相似文献
998.
Schibli R Marti N Maurer P Spingler B Lehaire ML Gramlich V Barnes CL 《Inorganic chemistry》2005,44(3):683-690
This work describes new synthetic routes to produce mixed carbonyl-nitrosyl complexes of technetium(I) and rhenium(I) in aqueous media. NaNO2, NOHSO4, and NO2(g) have been used to produce in situ nitrous acid as the primary source of NO+. Starting from the organometallic precursor fac-[MX3(CO)3]+, 1 (M = 99Tc, Re; X = Cl, Br), the formation of mixed dicarbonyl-mononitrosyl complexes was observed in aqueous hydrochloric and hydrobromic acid. Time-dependent analyses of the reactions by means of HATR-IR and 99Tc NMR spectroscopy in solution revealed the almost quantitative substitution of one CO ligand by NO+ and, thus, the formation of complexes with facial arrangement of the three pi-acceptor ligands. In the case of technetium, the monomeric complex (NEt4)[TcCl3(CO)2NO] (3a) and the dimeric, chloride-bridged, neutral complex [TcCl(mu-Cl)(CO)2NO]2 (4a) were produced. In the case of rhenium, the monomeric species (NEt4)[ReBr2X(CO)2NO] (X = Br (3b), NO3 (5)) was solely isolated. The X-ray structure of complexes 4a and 5 are discussed. The crystallographic analyses revealed the coordination of the NO+ group trans to the terminal chloride (4a) or the bromide (5), respectively. Crystal data: complex 4a (C4Cl4N2O(6)Tc2), monoclinic, Cc, a = 18.82(3) A, b = 6.103(6) A, c = 12.15(2) A, alpha = 90 degrees , beta = 105.8(2) degrees , gamma = 90 degrees , V = 1343(3) A(3), Z = 4; complex 5 (C10H20N3O(6)Br2Re), orthorhombic, P2(1)2(1)2(1), a = 10.2054(5) A, b = 12.5317(7) A, c = 13.9781(7) A, V = 1787.67(16) A(3), Z = 4. The isolated complexes and their potential facial isomers have been further investigated by density functional theory (DFT) calculations. The energy differences of the isomers are relatively small; however, the calculated energies are consistent with the formation of the observed and isolated compounds. The calculated bond lengths and angles of complex 5 are in good agreement with the data determined by X-ray diffraction. Experiments on the no-carrier-added level starting from fac-[99mTc(H2O)3(CO)3]+ revealed the formation of the complex fac-[99mTcCl(H2O)2(CO)2NO]+ in reasonable good yields. This aqueous-based, synthetic approach will enable the future evaluation of this novel, low-valent metal precursor for potential use in radiopharmacy. 相似文献
999.
Thomas Marti Blake R. Peterson Andreas Fürer Tiziana Mordasini-Denti Jürgen Zarske Bernhard Jaun Franois Diederich Volker Gramlich 《Helvetica chimica acta》1998,81(1):109-144
Three double-decker cyclophane receptors, (±)- 2 , (±)- 3 , and (±)- 4 with 11–13-Å deep hydrophobic cavities were prepared and their steroid-binding properties investigated in aqueous and methanolic solutions. Pd°-Catalyzed cross-coupling reactions were key steps in the construction of these novel macrotricyclic structures. In the synthesis of D2-symmetrical (±)- 2 , the double-decker precursor (±)- 7 was obtained in 14% yield by fourfold Stille coupling of equimolar amounts of bis(tributylstannyl)acetylene with dibromocyclophane 5 (Scheme 1). For the preparation of the macrotricyclic precursor (±)- 15 of D2-symmetrical (±)- 3 , diiodocylophane 12 was dialkynylated with Me3SiC?CH to give 13 using the Sonogashira cross-coupling reaction; subsequent alkyne deprotection yielded the diethynylated cyclophane 14 , which was transformed in 42% yield into (±)- 15 by Glaser-Hay macrocyclization (Scheme 2). The synthesis of the C2-symmetrical conical receptor (±)- 4 was achieved via the macrotricyclic precursor (±)- 25 , which was prepared in 20% yield by the Hiyama cross-coupling reaction between the diiodo[6.1.6.1]paracyclophane 19 and the larger, dialkynylated cyclophane 17 (Scheme 4). Solid cholesterol was efficiently dissolved in water through complexation by (±)- 2 and (±)- 3 , and the association constants of the formed 1:1 inclusion complexes were determined by solid-liquid extraction as Ka = 1.1 × 106 and 1.5 × 105 l mol?1, respectively (295 K) (Table 1). The steroid-binding properties of the three receptors were analyzed in detail by 1H-NMR binding titrations in CD3OD. Observed steroid-binding selectivities between the two structurally closely related cylindrical receptors (±)- 2 and (±)- 3 (Table 2) were explained by differences in cavity width and depth, which were revealed by computer modeling (Fig. 4). Receptor (±)- 2 , with two ethynediyl tethers linking the two cyclophanes, possesses a shallower cavity and, therefore, is specific for flatter steroids with a C(5)?C(6) bond, such as cholesterol. In contrast, receptor (±)- 3 , constructed with longer buta-1,3-diynediyl linkers, has a deeper and wider hydrophobic cavity and prefers fully saturated steroids with an aliphatic side chain, such as 5α-cholestane (Fig. 7). In the 1:1 inclusion complexes formed by the conical receptor (±)- 4 (Table 3), testosterone or progesterone penetrate the binding site from the wider cavity side, and their flat A ring becomes incorporated into the narrower [6.1.6.1]paracyclophane moiety. In contrast, cholesterol penetrates (±)- 4 with its hydrophobic side chain from the wider rim of the binding side. This way, the side chain is included into the narrower cavity section shaped by the smaller [6.1.6.1]paracyclophane, While the A ring protrudes with the OH group at C(3) into the solvent on the wider cavity side (Fig. 8). The molecular-recognition studies with the synthetic receptors (±)- 2 , (±)- 3 , and (±)- 4 complement the X-ray investigations on biological steroid complexes in enhancing the understanding of the principles governing selective molecular recognition of steroids. 相似文献
1000.
Synthesis and Crystal Structure of the Nonaselenide [Sr(15-crown-5)2]Se9 The title compound was prepared by the reaction of excess selenium with strontium diselenide in DMF in the presence of 15-crown-5. [Sr(15-crown-5)2]Se9 forms black crystals, which are soluble in DMF. They were characterized by FIR spectroscopy and by an X-ray structure determination. Space group P21/n, Z = 4, 2 381 observed unique reflections, R = 0.073. Lattice dimensions at 19°C: a = 1 228.7, b = 1 893.4, c = 1 575.7 pm, β = 99.15°. The compound consists of [Sr(15-crown-5)2]2+ ions in which the strontium ion is coordinated by the oxygen atoms of the crown ether molecules in a sandwich-like fashion, and of Se92? ions with a chain structure, which has a topolocical resemblance with the bicyclic ion Se. 相似文献