Abstract Trimesityltin hydroxide and fluoride have been prepared and have been studied by single crystal X-ray diffraction and IR spectroscopy. In both compounds the tin atoms are tetrahedrally coordinated, and the oxygen and fluorine atoms twofold and singly coordinated, respectively. The observed bond lengths are 199.9 pm for Sn O and 195.7/196.5 pm (av. 196.1 pm) for Sn F.