A structural characterization of two series of ferroelectric low molar mass organosiloxanes is described. X-ray and dilatometry studies have been used to determine the impact of variations in mono- or di-mesogen architecture, halogen substitution and siloxane content on the mesophase structure and thermal behaviour. All of the compounds exhibit smectic C* mesophases with high tilt angles. Bromo substituted compounds are consistently found to exhibit higher tilt angles than their fluoro analogues, and a strong odd-even effect in melting temperature is observed for the dimesogenic bromo series.