X-ray Diffraction Studies on Some Even-Chain-Length Lead(II) Carboxylates

Abstract X-ray diffraction is used to study structural changes associated with thermotropic phase transitions in a homologous series of even-chain-length lead(II) carboxylates from hexanoate to octadecanoate. For homologues above lead(II) dodecanoate, a lamellar structure with a monolayer molecular organization is indicated at all temperatures up to the melting point. For shorter-chain compounds, the lamellar structure appears to be a bilayer one. In these compounds, the layer spacing decreases markedly with temperature at the crystal-to-mesophase transition point and thereafter remains constant in the temperature range of the mesophase. It is suggested that the layer planes tilt with respect to an axis defined by the hydrocarbon chains on forming a smectic mesophase.