No abstract

N,N,N-butylethylpentylpropylammonium iodide 4 and related molecules have been selectively synthesised from commercially available aldehydes, amines and alkyl iodides using a reductive alkylation procedure. The crystalline texture of 4 obtained on cooling is optically isotropic between crossed polarisers, indicating a cubic structure. Differential scanning calorimetry (DSC, +10 K min-1) reveals a glass phase transition at -59 degrees C and a melting point at 192 degrees C. The melting entropy (23.9 J mol-1 K-1) indicates a first-order transition between a highly disordered mesophase and the isotropic liquid. Powder X-ray diffraction patterns were indexed in the cubic system (a = 14.08A; Pm3n space group). In this cell, the molecular packing with Z = 6 corresponds to a rather low compactness of 65%. Iodine and tetraalkylammonium ions occupy positions with a 4m2 site symmetry. These highly symmetrical states may be generated by stepwise rotation of the ammonium cation. The same structural model for orientationally disordered crystal (ODIC) phases can be applied to a series of tetraalkylammonium bromides and iodides.

Ce travail décrit l'obtention de nouveaux composés bimétalliques à pont oxalate [R 1 R 2 R 3 R 4 N][MnCr(C 2 O 4 ) 3 ], dont les cations assembleurs sont des ammoniums chiraux de formule [R 1 R 2 R 3 R 4 N] + , pour lesquels R représente un groupement n-alkyle variant de méthyle à dodécyle.

The synthesis of a new type of polar membrane having a low glass-transition temperature is described. It is obtained by room-temperature crosslinking between two cyanopropylsiloxane copolymers containing -SiCH=CH, and S S i H reactive groups. Conventional ionophores and electrolytes may be molecularly dissolved in the copolymers. The crosslinked membrane is used as a supporting matrix in ion-selective electrode devices. The best results are obtained when benzo-15-crown-ether-5 is employed as ionophore.

The tribenzosilatrane moiety has been substituted with four long paraffinic chains. The physicochemical properties (optical microscopy, differential scanning calorimetry) of the condensed phases have been determined as a function of the chain length. Several crystalline or mesomorphic phases have been characterized by X-ray diffraction. In some cases, original layered structures have been found with a hexagonal order within the lamellae. However, none of the mesophases can be attributed to the class of plastic crystals. A globularity criterion has been defined which relates the shape of the molecular unit with the type of arrangement in the mesophases.