Kristallstrukturen der Samarium-Amido-Komplexe [Sm(l-X){N(SiMe3)2}2(THF)]2 mit X = Cl,Br

Crystal Structures of the Samarium Amido Complexes [Sm(l-X){N(SiMe₃)₂}₂(THF)]₂ with X = Cl, Br The crystal structures of the title compounds have been determined by X-ray methods. [Sm(μ-Cl) · {N(SiMe₃)₂}₂(THF)]₂ ( 1 ): Space group P2₁/n, Z = 2, lattice dimensions at 223 K: a = 1429.5(2), b = 1302.3(3), c = 1658.6(3) pm, β = 114.212(10)°, R = 0.0561. [Sm(μ-Br) · {N(SiMe₃)₂}₂(THF)]₂ ( 2 ): Space group Pbca, Z = 4, lattice dimensions at 223 K: a = 1850.0(7), b = 1611.0(9), c = 1888.1(6) pm, R = 0.0497. 1 and 2 form centrosymmetric dimeric complexes via μ-X-halogeno bridges. The samarium atoms are coordinated in a distorted trigonal-bipyramidal surrounding, the THF molecule and one of the bridging halogen atoms being in axial positions.     

Synthese eines Titana-Oxacyclohexanringes durch kontrollierte Ringöffnung von Tetrahydrofuran. Kristallstrukturen von [Ti(CH2)4O{Me2Si(NBut)2}]2, [TiCl{Me2Si(NBut)2}]3(μ3-O)(μ3-Cl) und [Li2(THF)3{Me2Si(NBut)2}]

Synthesis of a Titana-Oxacyclohexane Ring by Controlled Ring Opening of Tetrahydrofurane. Crystal Structures of [Ti(CH₂)₄O{Me₂Si(NBu^t)₂}]₂, [TiCl{Me₂Si(NBu^t)₂}]₃(μ₃-O)(μ₃-Cl), and [Li₂(THF)₃{Me₂Si(NBu^t)₂}] [TiCl₃(THF)₃] reacts with [(Bu^tNLi)₂SiMe₂]₂ in diethyl ether at –35 °C under redox disproportionation and formation of the yellow titana(IV)-oxacyclohexane complex [Ti(CH₂)₄O{Me₂Si(NBu^t)₂}]₂. According to the crystal structure analysis the titanium atoms are linked to form centrosymmetric dimers via the oxygen atoms of the Ti(CH₂)₄O six-membered rings, which are in chair conformation. Along with the nitrogen atoms of the chelating [Me₂Si(NBu^t)₂]^2– ligands the titanium atoms obtain a distorted trigonal-bipyramidal surrounding. While [TiCl{Me₂Si(NBu^t)₂}]₃(μ₃-O)(μ₃-Cl) with a cluster-like structure is obtained as a by-product. According to the crystal structure analysis of [Li₂(THF)₃ · {Me₂Si(NBu^t)₂}], which is involved in the synthesis reaction, the two lithium atoms are connected with both the nitrogen atoms of the t-butyl amide groups and bridged via an oxygen atom of one of the THF molecules.     

Die Kristallstrukturen der Triarylzinkate [Mg2Br3(THF)6][ZnPh3] und [MgBr(THF)5][ZnMes3]

Crystal Structures of the Triarylzincates [Mg₂Br₃(THF)₆][ZnPh₃] and [MgBr(THF)₅][ZnMes₃] The title compounds were obtained from reactions of the phosphoraneiminato complex [ZnBr(NPMe₃)]₄ with excess Grignard reagents RMgBr (R = C₆H₅, 2,4,6-(CH₃)₃–C₆H₂) in THF solution. According to X-ray structure determinations the [ZnR₃]^– ions contain zinc atoms which are coordinated in a planar fashion with Zn–C distances of 200.7 pm (R = Ph) and 203.4 pm (R = Mes) in average.     

Trans-methyl-azido-bis(triisopropylphosphin)platin(II), [PtN3(CH3)(PiPr3)2]

Trans-methyl-azido-bis(triisopropylphosphine)platinum(II), [PtN₃(CH₃)(PⁱPr₃)₂] [PtN₃(CH₃)(PⁱPr₃)₂] has been prepared by reductive elimination of ethane from [Pt(CH₃)₃N₃]₄ in the presence of triisopropylphosphine at 80 °C. The complex is characterized by IR and NMR spectroscopy and by crystal structure determination, as well as by ab initio calculations. [PtN₃(CH₃)(PⁱPr₃)₂], which is in trans-configuration here, crystallizes in the monoclinic space group P2₁, Z = 2, and with the lattice dimensions a = 806.9(1), b = 1384.3(1), c = 1093.8(1) pm, β = 94.107(10)°.     

Kernel projector matrices for leu1?zervamicin

By performing ab initio calculations on fragments of leu¹(SINGLEBOND)zervamicin, it is demonstrated that accurate wave functions can be obtained for this large structure by combining the results from the fragments. Input information consists of atomic coordinates as obtained, for example, from a crystal structure determination. The fragments are composed of a kernel of atoms surrounded by a chosen neighborhood of atoms. The entire molecule is divided into individual kernels and their neighborhoods are added for the individual fragment calculations on the basis of the distances of other atoms from the atoms in a kernel. The hydrated leu¹(SINGLEBOND)zervamicin is composed of 295 atoms which could be handled in full by Gaussian 94. The results of the fragment calculations were combined to provide an electron density distribution for the molecule. This distribution was compared with one that represents the distribution obtained from a calculation on the entire molecule at once. The clear implication of this study is that it is feasible to perform ab initio calculations on structures by the use of fragments. The time involved increases essentially linearly with complexity. © 1996 John Wiley & Sons, Inc.     

ChemInform Abstract: A New Cu,Al Fluoride Disilicate CuAl2F2(Si2O7) and Its Relations to Topaz.

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