Structural study of columnar liquid-crystalline phases in homologousseries of tetrapalladium organyls

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Abstract
The molecular organisation within liquid-crystalline columnar phases shown by a series of tetrapalladium organyls has been investigated by varying systematically the number and length of the alkoxy substituents connected to their flat core. Four different columnar phases were observed and studied by polarising microscopy, DSC, X-ray diffraction and dilatometry. In two types of C2mm rectangular centred phases and in an oblique P2 phase, the cores of the columns, formed by the stacking of the roughly rectangular-shaped flat molecular cores, were found to retain the same orientation between neighbouring columns. A transformation of the C2mm lattice into the rectangular P2gg lattice was observed at high temperature for the derivatives with long chains. The succession of columnar phases as well as the evolution of the packing geometry within the organyl series is explained in terms of the relation between the aliphatic chain length and that of the longest side of the flat rectangular columnar cores.