The crystal and molecular structure of 1,1,4,4-tetraethyl-2,5-dimethyl-1,4-diphosphoniacyclohexadiene-1,4-dibromide

The structure of the title compound has been determined by a single-crystal, x-ray diffraction study. The compound crystallizes in a monoclinic unit cell (P2₁/c) with two molecules per unit cell. Least-squared lattice parameters are: a = 7.164 ± 0.001Å, b = 14.770 ± 0.001Å, c = 10.562 ± 0.001Å, and β = 124.95 ± 0.01°. The structure parameters refined to a value of R=0.06₂, excluding hydrogens, for the 1475 statistically significant reflections. The structure determination confirmed that the compound is indeed a diene and not a delocalized structure. The ring is planar but the ethyl groups extend over the ring in an unusual crab-like fashion.     

The crystal and molecular structure of 1,1,4,4-tetraphenyl-1,4-diphosphoniacyclohexane dibromide

The crystal and molecular structure of 1,1,4,4-tetraphenyl-1,4-diphosphoniacyclohexane dibromide has been determined by a single-crystal, x-ray diffraction study using diffractometer data. The compound crystallizes in the monoclinic space group P2₁/c with unit cell constants of a = 12.777(1), b = 26.180 (2), c = 16.283 (1) Å, and β = 91.18(1)°. The structure was solved by the heavy atom method with the 4176 independent and statistically significant structure factors refining to a value of R = 0.07. The diphosphonium ring is in the chair conformation with each phosphorus ion having an axial and equatorial phenyl ring attached. P-C and C-C bond lengths of 1.78 ± .03 Å and 1.53 ± .03 Å respectively agree well with the literature value for these distances.     

The crystals and molecular structure of 1,1,4,4-Tetraphenyl-2,5-di-(t-butyl)-1,4-diphosphoniacyclohexadiene-2,5-dichloride

The crystal and molecular structure of the title compound has been determined by single crystal, x-ray diffraction techniques. The compound crystallizes in a monoclinic space group of C2/c symmetry with four molecules in a unit cell of dimensions a = 24.578(1), b = 10.503(1), c = 17.579(1) Å and (3 = 1.30.93 ± .01°. The unit cell also contains two waters of crystallization which are involved in hydrogen bonds to the chloride ions. The central ring has been shown to be a diene which resides in a boat conformation defined by dihedral angles of 157°. The structure has been refined to a value of R = 0.08 using the 1535 statistically significant reflections measured out ot a 2θ value of 140°.     

The crystal and molecular structure of 1,1,1,3,3,3-hexaphenyl-1,3-disilapropane

Crystals of the title compound H₂C(SiPh₃)₂ are triclinic, space group P$\text{1}$, with a = 9.290(2), b = 12.128(4), c = 16.882(4) Å, α = 62.08(1), β = 106.88(1), γ = 117.28(2)° and Z = 2. The central skeletal angle SiCSi is 128.8(7)°. The structures of the molecules H₂C(SiR₃)₂ (R = H, CH₃, and Ph) are compared and discussed: a simple model for the skeletal geometry of species H₂C(MR₃)₂ is proposed, and tested against experimental data and theoretical calculations.     

The crystal and molecular structure of 2,5-dichloro-3-methoxypyrazine

A three-dimensional X-ray structure determination of 2,5-dichloro-3-methoxypyrazine has been completed with diffractometer data. The crystals are monoclinic, space group P2₁/_c, with lattice constants a = 4.059, b = 15.773, c = 11.123Å and β = 90.96° (Z = 4). The structure was solved by Sayre's equation and all hydrogen atoms were located by difference synthesis. Full-matrix least-squares refinement of all position parameters, hydrogen isotropic temperature factors, and anisotropic temperature factors for all other atoms converged at R = 5.7% for the 1397 reflections above background. Bond distances and angles are consistent with literature values.     

Synthesis and crystal structure of cyclopentadienyl(1,4-dimethyl-1,4-dibora-2,5-cyclohexadiene)cobalt

The synthesis of the organometallic derivative cyclopentadienyl(1,4-dimethyl-1,4-diboracyclohexa-2,5-diene)cobalt is described. This complex, [(CH₃BC₄H₄BCH₃)Co(η-C₅H₅)], forms red-oranged monoclinic crystals, space group P2₁/a with Z = 4 in a unit cell of dimensions a 11.362(7), b, 7.467(7), c 13.290(12) Å, β 103.76(6)°. The structure has been elucidated by heavy-atom methods from 1732 reflections (I > 2σ(I)) measured on a Syntex P2₁ four-circle diffractometer and refined to R = 0.055. In the coordination complex all six atoms of the cyclohexadiene ring are within bonding distance of the metal atom, but the two boron atoms bend away from the metal atom, and the ring elongates slightly in the B---B direction. As a standard of comparison the known geometry of the free ligand [1,4-difluoro-1,4-dibora-2,3,5,6-tetramethylcyclohexa-2,5-diene] is used. The terminal methyl groups on the boron atoms, by contrast, bend slightly back towards the metal atom. The cyclopentadienyl ring remains planar but is positionally disordered.     

Synthesis and crystal structure of hexaaquamagnesium 18-crown-6 dibromide dihydrate

A new complex compound [Mg(H₂O)₆]Br₂ · 18-crown-6 · 2H₂O(I) is synthesized, and its structure is studied by X-ray diffraction analysis. The crystals are monoclinic: space group P2₁/c, a = 7.128 Å, b = 18.584 Å, c = 9.598 Å, Å = 103.01°, Z = 2; R = 0.039 for 2180 independent reflections (CAD-4 automated diffractometer, λMoK _α radiation). The coordination polyhedron of the Mg²⁺ cation is a slightly distorted octahedron. The 18-crown-6 molecule has the conformation of a distorted crown with the approximate D _3d symmetry. The crystal contains a branched three-dimensional network of intermolecular (interionic) hydrogen bonds.     

大叶香茶菜庚素的晶体结构和分子结构研究

大叶庚(Rabdophyllin G)是从中草药中提取得到的抗癌有效药物.其晶体属正交晶系,空间群为P2_12_12_1;晶胞参数为:α=6.820(5),b=9.076(1),c=33.525(7)A;Z=4.用X射线衍射法测定该化合物的晶体结构和分子结构.R因子最终修正到0.0584.不久前借其他实验手段得出的分子结构式,本文对它作出一些订正.文中还讨论了分子中的某些结构和化学活性问题.     

The molecular and crystal structure of psi-retroprogesterone

The crystal structure of synthetic, racemic ψ-retroprogesterone (9α-methyl-19-nor-progesterone) has been determined by X-ray analysis and refined to R = 0.050. The analysis was carried out to establish the relative configuration at positions 9, 10 and 17 in connection with the biological activity of the compound.     

溪黄草甲素的晶体和分子结构

溪黄草甲素,C_(20)H_(26)O_5,M_r=346.43,是从中草药溪黄草(Radosia serra [Maxim] Hara)中提取得到的一种具有抗癌活性的化合物,它的结构式已由化学分析和光谱数据确定为1,14-二羟基-7,20;19,20-二桥氧-(1α,4α,7α,14R,20R)-贝壳杉烯-16-烯-15-酮(1),和它的同系物kamebakaurene(2)的结构式大体相似.