R. Faggiani

Tricarbonylchromium(0) complexes of 1,3,5-triphenylbenzene: an X-ray crystallographic and high field NMR spectroscopic study

Abstract The reaction of 1,3,5-triphenylbenzene (TPB) with Cr(CO) 6 yields products in which a Cr(CO) 3 moiety is bonded to the central ring or to one, two or all three peripheral phenyl rings. The structure of the TPB · 3Cr(CO) 3 complex has been determined by single crystal X-ray diffraction techniques. The complex crystallizes in the space group P 2 1 / n with unit cell parameters a 8.316(2) A, b 15.498(5) A, c 22.254(4) A, β 92.18(2)°, V 2865.8(11) A 3 and Z = 4. The structure has been solved by direct and Fourier methods and refined by block diagonal matrix least squares to R 1 and R 2 values of 0.053 and 0.053, respectively, for 2830 observed reflections. The structure reveals that the chromium tricarbonyl groups are bonded to the three peripheral phenyls and these aryl rings adopt dihedral angles of 35° −26° and 14° with respect to the central ring; these dihedral angles are remarkably similar to those in the free ligand itself. All three Cr(CO) 3 tripods are oriented to within a few degrees of being perfectly staggered with respect to the aryl carbon atoms. The 500 MHz 1 H and 125 MHz 13 C NMR spectra of these complexes reveal that the peripheral rings do not exhibit restricted rotation even at −90°C. This contrasts with the situation for (hexaphenylbenzene)Cr(CO) 3 the 1 H NMR spectrum of which may indicate slowed rotation of the phenyl rings even at room temperature.

The I42+ cation. X-Ray crystal structures of (I42+)(AsF6–)2 and (I42+)(Sb3F14–)(SbF6–)

The I42+ cation has been fully characterised for the first time by the preparation of the compounds (I42+)(AsF6–)2 and (I42+)(Sb3F14–)(SbF6–) and the determination of their structures by X-ray crystallography; the I42+ cation has a rectangular structure and may be considered to consist of two I2+ cations held together by two rather weak bonds.

Structure, energetics and homoaromaticity

A series of carbenium ion salts have been isolated as crystalline solids and their structures determined using X—ray crystallography. The cations examined include several tropylium and cyclopropenium cations, two different cyclopropyl carbinyl cations, three homotropylium cations, a bicyclo[3.1.O]hexenyl cation and several protonated benzophenones. The structures of these cations are discussed in terms of the nature of the electron delocalization which occurs in them. In particular attention is focused upon the questions of homoaromaticity and antihomoaromaticity in these cations. Conclusions reached on the basis of an analysis of structure are buttressed with some thermochemical measurements. As many of the cations studied here include a protonated carbonyl function, the structure and the charge distribution in this group is explored.

X-Ray diffraction study of Te4S4(AsF6)2·SO2; an electron-rich S4N4-type cage

A single crystal X-ray diffraction study has shown that the compound Te4S4(AsF6)2·SO2 contains the Te4S42+ cation, which has an electron-rich S4N4-type cage structure.

The preparation and structure of [W(CO)4(η3-Te3)][SbF6]2 containing the first three-membered chalcogen ring

The reaction of Te4(SbF6)2 with W(CO)6 in SO2–AsF3 produces [W(CO)4(η3-Te3)][SbF6]2(1), which contains a three-membered tellurium ring co-ordinated in π fashion to the tungsten carbonyl fragment.

Preparation and structure of diphenyl hexaselenium bis(hexafluoroarsenate) sulphur dioxide [Ph2Se6][AsF6]2·SO2

The reaction of Se4(AsF6)2 with Ph2Se2 gives the new compound [Ph2Se6](AsF6)2, which contains a six-membered selenium ring in the boat conformation.

The cadmium(I) ion, Cd22+; X-ray crystal structure of Cd2(AlCl4)2

The structure of Cd2(AlCl4)2 has been determined by X-ray crystallography and the Cd–Cd bond length found to be 2.576 A.

Stopping a chromium carousel: X-ray crystallographic and variable-temperature 13C n. m. r. studies on dicarbonyl(hexaethylbenzene)-thiocarbonylchromium(0) and related complexes

The low temperature 13C n.m.r. spectrum of (C6Et6)Cr(CO)2CS shows the molecule to have Cs symmetry as it does in the solid state; this result provides the first clear evidence of cessation of tripodal rotation in a neutral half-sandwich compound of Cr.

Preparation and partial oxidation of tin(II) trifluoroacetate: spectroscopic properties and X-ray crystal structure of di-µ3-oxo-octakis-µ-trifluoroacetato-tetratin(II)tin(IV)

Pure Sn (O2CCF3)2 has been prepared and characterized by 119Sn Mossbauer and vibrational spectroscopy. A novel mixed-valence compound, SnII4SnIVO2(O2CCF3)8, has been prepared by the partial oxidation of Sn(O2CCF3)2 and characterized spectroscopically and by single-crystal X-ray diffraction (to R′= 0.0722). The crystals are tetragonal, space group I2d, with a=b= 12.448(3), c= 33.300(4)A, and Z= 4. The structure consists of discrete non-centrosymmetric units with point group S4, the central feature of which is a SnII4SnIVO2 unit containing two µ3-oxygen atoms each of which bridge between a tin(IV) atom and two symmetry-related tin(II) atoms. The tin(IV) co-ordination is completed by trifluoroacetate groups which bridge to the tin(II) atoms. The tin(IV) and the two µ3-oxygen atoms lie on the S4 axis and the two SnII2SnIVO planar units are at 90° to one another. Each pair of tin(II) atoms is bridged by two trifluoroacetates.

The structures of some iminium salts. Crystal structures and13C NMR studies of 3-aryl-2-propenylideniminium salts

The X-ray crystal structures ofE-N, N-dimethyl-3-phenyl-2-propenylideniminium perchlorate,1, andE-N, N-dimethyl-3-(p-methoxyphenyl)-2-propenylideniminium perchlorate,2, have been determined.E-N,N-dimethyl-3-phenyl-2-propenylideniminium perchlorate, (C11H14N+)(ClO4−),1, is orthorhombic:Pmcn (No. 62)a=6.595(1),b=18,288(4),c=10.216(2) Å,Z=4.E-N, N-dimethyl-3-(p-methoxyphenyl)-2-propenylideniminium perchlorate, (C12H16NO+)(ClO4−),2, is triclinic:P1 (No. 2) with cell dimensionsa=6.862(1),b=9.830(2),c=13.376(3) Å,α=119.05(1),β=114.99(2), γ=90.79(2)°, andZ=2. Data for both crystals were collected with the use of MoKα radiation and a Syntex P21 diffractometer. The crystal structures were solved by standard methods and refined toR1=0.0688,R2=0.0772 for1 andR1=0.0790 andR2=0.0757 for 2 based on 869 and 1765 independent reflections, respectively. The bond distances are consistent with a highly localized structure with the positive charge situated principally in the iminium moiety. The13C NMR spectra of these salts were obtained on the crystalline solids by CPMAS methods. Since the13C chemical shifts of the salts were very similar, in both solution and solid states, it was concluded that the structures of the salts were comparable in both phases and were analogous.