Die Kristall- und Molekülstruktur von Bis(trimethylsilyl)diimin

Aqua-tri-fluorido-boron-1,3-dioxolan-2-one (1/2)

The crystal structure of the co-crystal of aqua-tri-fluorido-boron with two ethyl-ene carbonate (systematic name: 1,3-dioxolan-2-one) mol-ecules, BF3H2O·2OC(OCH2)2, was determined by low-temperature single-crystal X-ray diffraction. The co-crystal crystallizes in the ortho-rhom-bic space group P212121 with four formula units per unit cell. The asymmetric unit consists of an aqua-tri-fluorido-boron mol-ecule and two ethyl-ene carbonate mol-ecules, connected by O-H⋯O=C hydrogen bonds. This crystal structure is an inter-esting example of a superacidic BF3H2O species co-crystallized with an organic carbonate.

Low-Temperature Isolation of a Labile Silylated Hydrazinium-yl Radical Cation, [(Me3 Si)2 N-N(H)SiMe3 ]

The oxidation of silylated hydrazine, (Me3 Si)2 N-N(H)SiMe3 , with silver salts led to the formation of a highly labile hydrazinium-yl radical cation, [(Me3 Si)2 N-N(H)SiMe3 ].+ , at very low temperatures (decomposition > -40 °C). EPR, NMR, DFT and Raman studies revealed the formation of a nitrogen-centered radical cation along the N-N unit of the hydrazine. In the presence of the weakly coordinating anion [Al{OCH(CF3 )2 }4 ]- , crystallization and structural characterization in the solid state were achieved. The hydrazinium-yl radical cation has a significantly shortened N-N bond and a nearly planar N2 Si3 framework, in contrast to the starting material. According to DFT calculations, the shortened N-N bond has a total bond order of 1.5 with a π-bond order of 0.5. The π bond can be regarded as a three-π-electron, two-center bond.

μCHILL: a lightweight, modular system for handling crystalline samples at low temperatures under inert conditions

A procedure for preparing and mounting crystals under inert conditions is demonstrated, using a specialized apparatus (μCHILL) to provide a cold gas stream fed from a liquid nitrogen (LN2) reservoir or an open bath heat exchanger. A second, dry gas stream at room temperature enwraps the cold gas, protecting the sample preparation zone from ambient moisture. The technique is extremely flexible, requiring only a single operator, little practice and almost no preparation time. The device enables operation in a wide temperature range (at least 213 K to room temperature), providing temperature control and very stable conditions with no icing for extended time periods. The flexible, modular and low-cost design is based on three-dimensional-printed parts and readily available standard components, potentially making the device available to a wide range of users and applications not limited to single-crystal studies.

Isolation of a labile homoleptic diazenium cation

Following our interest in nitrogen chemistry, we now describe the synthesis, structure, and bonding of labile disilylated diazene, its GaCl3 adduct, and the intriguing trisilylated diazenium ion [(Me3 Si)2 NN-SiMe3 ](+), a dark blue and highly labile (Tdecomp >-30 °C) homoleptic cation of the type [R3 N2 ](+). Although direct silylation of Me3 Si-N=N-SiMe3 failed, the [(Me3 Si)2 N=N-SiMe3](+) ion was generated in a straightforward two-electron oxidation reaction from mercury(II) dihydrazide and Ag[GaCl4]. Moreover, previous structure data of Me3 Si-NN-SiMe3 were revised on the basis of new data.

Solvent-free mesityllithium: solid-state structure and its reactivity towards white phosphorus

The donor-free mesityllithium was prepared from the reaction of MesBr with n-BuLi in diethyl ether at -78 degrees C. The solid-state structure of unsupported mesityllithium consists of C(2)Li(2)-rings composed of two LiMes units, which interact with adjacent dimers [LiMes](2), forming a polymeric infinite chain along the crystallographic c-axis (monoclinic space group, P2(1)/n). The structure of donor-free mesityllithium reveals short contacts between the C atoms of the mesityl rings and the lithium atoms of neighbouring [LiMes](2) units. The structure determination of LiMes was performed by X-ray powder diffraction. In addition we have investigated the reaction of LiMes with Me(3)SnCl and P(4) for our understanding of the reactivity of donor-free mesityllithium. The heterogeneous reaction of donor-free mesityllithium with Me(3)SnCl produces conveniently the stannylated mesitylene Me(3)SnMes (triclinic, space group P1). White phosphorus reacts with three equivalents of unsupported mesityllithium in benzene to give Li(3)P(4)Mes(3). In this context it should be noted that a tetraphosphide with an identical LiP-core as in Li(3)P(4)Mes(3) had been formed in the 1:3 reaction of P(4) with the silanide Li[SitBu(3)]. The tetraphosphide Li(3)P(4)Mes(3) was analyzed using X-ray crystallography (monoclinic, space group C2/c).

Structural and conformational properties of fluoroformic acid anhydride, FC(O)OC(O)F

The conformational properties and geometric structures of fluoroformic acid anhydride, FC(O)OC(O)F, have been studied by vibrational spectroscopy, gas electron diffraction (GED), single-crystal X-ray diffraction, and quantum chemical calculations (HF, MP2, and B3LYP methods with 6-31G* and B3LYP/6-311+G* basis sets). Satellite bands in the IR matrix spectra, which increase in intensity when the matrix gas mixture is heated prior to deposition as a matrix, indicate the presence of two conformers at room temperature. According to the electron diffraction analysis, the prevailing conformer is of C(2) symmetry with both C=O bonds synperiplanar with respect to the opposite C-O bond ([sp, sp] conformer). The minor conformer [15(5)% from IR matrix and 6(11)% from GED] is predicted by quantum chemical calculations to possess an [sp, ac] structure. FC(O)OC(O)F crystallizes in the orthorhombic system in the space group P2(1)2(1)2(1) with a = 6.527(1) angstroms, b = 7.027(1) angstroms, and c = 16.191(1) angstroms and four formula units per unit cell. In the crystal, only the [sp, sp] conformer is present, and the structural parameters are very similar to those determined by GED.

Tris(trifluoromethyl)borane carbonyl, (CF3)3BCO-synthesis, physical, chemical and spectroscopic properties, gas phase, and solid state structure

Tris(trifluoromethyl)borane carbonyl, (CF(3))(3)BCO, is obtained in high yield by the solvolysis of K[B(CF(3))(4)] in concentrated sulfuric acid. The in situ hydrolysis of a single bonded CF(3) group is found to be a simple, unprecedented route to a new borane carbonyl. The related, thermally unstable borane carbonyl, (C(6)F(5))(3)BCO, is synthesized for comparison purposes by the isolation of (C(6)F(5))(3)B in a matrix of solid CO at 16 K and subsequent evaporation of excess CO at 40 K. The colorless liquid and vapor of (CF(3))(3)BCO decomposes slowly at room temperature. In the gas phase t(1/2) is found to be 45 min. In the presence of a large excess of (13)CO, the carbonyl substituent at boron undergoes exchange, which follows a first-order rate law. Its temperature dependence yields an activation energy (E(A)) of 112 kJ mol(-)(1). Low-pressure flash thermolysis of (CF(3))(3)BCO with subsequent isolation of the products in low-temperature matrixes, indicates a lower thermal stability of the (CF(3))(3)B fragment, than is found for (CF(3))(3)BCO. Toward nucleophiles (CF(3))(3)BCO reacts in two different ways: Depending on the nucleophilicity of the reagent and the stability of the adducts formed, nucleophilic substitution of CO or nucleophilic addition to the C atom of the carbonyl group are observed. A number of examples for both reaction types are presented in an overview. The molecular structure of (CF(3))(3)BCO in the gas phase is obtained by a combined microwave-electron diffraction analysis and in the solid state by single-crystal X-ray diffraction. The molecule possesses C(3) symmetry, since the three CF(3) groups are rotated off the two possible positions required for C(3)(v)() symmetry. All bond parameters, determined in the gas phase or in the solid state, are within their standard deviations in fair agreement, except for internuclear distances most noticeably the B-CO bond lengths, which is 1.69(2) A in the solid state and 1.617(12) A in the gas phase. A corresponding shift of nu(CO) from 2267 cm(-)(1) in the solid state to 2251 cm(-)(1) in the gas phase is noted in the vibrational spectra. The structural and vibrational study is supported by DFT calculations, which provide, in addition to the equilibrium structure, confirmation of experimental vibrational wavenumbers, IR-band intensities, atomic charge distribution, the dipole moment, the B-CO bond energy, and energies for the elimination of CF(2) from (CF(3))(x)()BF(3)(-)(x)(), x = 1-3. In the vibrational analysis 21 of the expected 26 fundamentals are observed experimentally. The (11)B-, (13)C-, and (19)F-NMR data, as well as the structural parameters of (CF(3))(3)BCO, are compared with those of related compounds.

The Chemistry of 1,3,5-Triazacyclohexane Complexes. 6.(1) Synthesis and Characterization of the Cobalt(II) Methoxide Core {Co(3)(OMe)(4)}(2+)

We report the synthesis and characterization of the first eta(3)-1,3,5-trimethyl-1,3,5-triazacyclohexane (Me(3)TAC) alkoxo complexes. Dehydration of [Co(H(2)O)(6)](X)(2) with 2,2-dimethoxypropane or HC(OMe)(3) and subsequent treatment with Me(3)TAC results in the formation of the methoxo cube fragment clusters [{(Me(3)TAC)Co}(3)(OMe)(4)](X)(2) (X = B(C(6)F(5))(4) (2a) and B(m-C(6)H(3)(CF(3))(2))(4) (2b)). 2a crystallizes in the triclinic space group P&onemacr; (a = 13.857(2) Å, b = 16.843(3) Å, c = 19.318(2) Å, alpha = 79.23(2) degrees, beta = 76.855(13) degrees, gamma = 70.10(2) degrees, Z = 2) and 2b in the monoclinic space group P2(1) (a = 12.710(3) Å, b = 23.251(3) Å, c = 18.702(4) Å, beta = 101.16(2) degrees, Z = 2). The cations contain a {Co(3)(OMe)(4)} cube fragment core with an eta(3)-Me(3)TAC bonded to each cobalt atom. Me(3)TAC is bonded unsymmetrically due to hydrogen-bonding interactions with the anions. This broken symmetry can also be observed as solvent-, anion-, and H/D isotope-dependent splitting of the signals in (1)H and (2)H NMR. A byproduct of the reaction is the protonated Me(3)TAC. The analogous monoacid adduct Me(3)TAC.HCl has been characterized by X-ray crystallography (orthorhombic space group Pbca, a = 11.0366(9) Å, b = 12.2986(6) Å, c = 13.9949(7) Å, Z = 8).

The OC(2)F(5)(-), OCF(CF(3))(2)(-), and OCFCF(2)O(-) Anions: Preparation and Structure

The compounds pip(+)CF(3)O(-), pip(+)CF(3)CF(2)O(-), pip(+)(CF(3))(2)CFO(-), and (CH(3))(4)N(+)OCFCF(2)O(-) (pip(+) = 1,1,3,3,5,5-hexamethylpiperidinium) are obtained from pip(+)F(-) or (CH(3))(4)N(+)F(-) and COF(2), CF(3)COF, (CF(3))(2)CO, and (COF)(2). The structures of pip(+)CF(3)CF(2)O(-), pip(+)(CF(3))(2)CFO(-), and (CH(3))(4)N(+)OCFCF(2)O(-) have been investigated by single-crystal X-ray crystallography. Crystal data are as follows: for pip(+)CF(3)CF(2)O(-), monoclinic P2(1)/c, a = 1300.7(1) pm, b = 828.0(1) pm, c = 1513.3(2) pm, beta = 110.13(1) degrees, Z = 4; for pip(+)(CF(3))(2)CFO(-), monoclinic P2(1)/c, a = 1182.2(1) pm, b = 1032.9(2) pm, c = 1459.1(1) pm, beta = 107.45(1) degrees, Z = 4; for (CH(3))(4)N(+)OCFCF(2)O(-), tetragonal P&fourmacr;2(1)/c, a = 1115.9(1) pm, c = 1377.1(1) pm, Z = 8. All anion structures are indicative of a negative hyperconjugation effect. The structure of FCOCF(2)O(-) is clearly nonsymmetric and resembles a close to planar cis oxygen configuration with one additional fluorine bound to one carbon atom. This fluorine atom is positioned slightly toward the second carbon atom, which corresponds to a movement from the asymmetric to the symmetric fluorine-bridged structure. Interionic forces seem to be responsible for this peculiar structure. These findings are compared with structures predicted by ab initio calculations.