Synthese und Kristallstruktur von Iodmethyltriphenylphosphonium-iodid (C6H5)3PCH2I+I- / Synthesis and Crystal Structure of Iodomethyltriphenylphosphonium Iodide (C6H5)3PCH2I+I-

Iodomethyltriphenylphosphonium iodide, (C6H5)3PCH2I+I-, has been prepared by the reaction of (C6H5)3P with CH2I2 in dichloromethane forming colourless needle like crystals. The crystal and molecular structures have been determined by an X-ray structure analysis. The crystals are orthorhombic, space group Pca21, Z = 8; a = 1478,8(3) pm, b = 1249,3(3) pm, c = 2053,2(3) pm. R = 0.050 for 3219 observed reflections with I ≥ 2 σ(Ι). In the solid state the title compound exists as two discrete monomeric units, (C6H5)3PCH2I+I-. In both symmetry independent units the I-I distances are surprisingly short with 346,5(1) pm and 356,3(1) pm. For the title compound the results of AM 1, PM 3, and MNDO calculations are in good agreement with corresponding values determined by the X-ray analysis.

The crystal and electron structure of 3-benzylbenzothiazolium bromide

3-Benzylbenzothiazolium bromide forms colourless needle-like crystals of monoclinic system, space group P21/c, with cell parameters a = 8.315(6), b = 12.323(9), c = 13.140(11) . 10-10 m, β = 103.79(6)0, and Z = 4. The phase problem was solved by heavy atom method and structure was refined by full matrix least-squares method with anisotropic thermal parameters to final R = 0.105 and wR = 0.113. The crystal structure is formed by monomer non-centrosymmetric units, among them weak non-bonding interactions of type Br...S, Br...N and also intermolecular interactions of van der Waals type C...S, C...N, C...C, and C...H-C are observed. Values of angles C6N1C8 122.2(6)°, C7N1C8 122.5(7)°, and C6N1C7 115.4(7)° correspond to sp2 type of nitrogen hybridization and they support its trigonal planar configuration. The CNDO/2 quantum chemistry method for electron structure calculation was used. Calculations were concentrated to partial optimization of two dihedral angles and to evaluation of indices describing the electron density distribution in the molecule of the title compound. The torsion angles for the most stable conformation are in a good agreement with the X-ray structure analysis results.

A note on the supposed dehydration of hydrated platin-cyanides on cooling

In the ‘Proceedings of the Royal Society’ for 1909, Prof. J. Emerson Reynolds describes some results on the cooling of hydrated platin-cyanides in liquid air. From a solution of a salt of ascribed formula Li 2 Pt (CN) 5 . 2H 2 O saturated at 40°C. and then quickly cooled to 15°C., a colourless needle-like crystalline solid exhibiting a slight fluorescence was obtained. This colourless salt was found to contain three molecules of water. By heating or cooling this trihydrate a molecule of water was said to have been lost, giving rise to the red dihydrate, i. e. , Li 2 Pt (CN) 5 3H 2 O heating ⇆ cooling Li 2 Pt (CN) 5 2H 2 O + H 2 O. This example of the loss of water on cooling, although not impossible from phase rule considerations, is the only one known to the author. Observations by Dr. C. H. Stubbs on other coloured hydrated salts did not indicate any such change on cooling. Through the kindness of the late Prof. Reynolds a specimen of the trihydrate exhibiting the phenomenon was given to the author. The crystals were sealed in a flask in a moist state. To bring about the change it was found to be unnecessary to employ so low a temperature as that obtained by the use of liquid air. At about -14°C. the crystals assumed a distinct red colour, the colour disappearing when the temperature was allowed to rise. A red colour was obtained when the crystals were warmed over the flame. Close examination of the cooled crystals showed, however, that they were covered with a slight overgrowth.