Selenium(IV) fluoride and oxofluoride anions

The [((C6H5)3P)2N]+, [(C6H5)4P]+ and [N(CH3)4]+ salts of SeF5−, SeF62− and SeOF3− and CsSeO2F were prepared and characterized. Crystal structures were obtained for [((C6H5)3P)2N][SeF5] and [((C6H5)3P)2N][SeOF3] CH2Cl2. In contrast to oxygen-bridged dimeric TeOF3−, the SeOF3− anion in [((C6H5)3P)2N][SeOF3] CH2Cl2 is monomeric and represents the first experimentally well determined molecular structure of a monomeric trifluoro-chalcogenite anion. Similarly, [((C6H5)3P)2N][SeF5] represents the first example of a structure containing a well-isolated undistorted SeF5− anion. The NMR and the vibrational spectra and their assignments were re-examined and corrected by comparison with high-level theoretical calculations. Whereas the previously published normal coordinate analysis of SeF5− is correct, that for SeOF3− needs major revision.

The three Se(+IV) fluoride and oxofluoride anions, SeF5−, SeOF3− and SeO2F−, have been studied using experimental and theoretical methods. The first crystal structures of a well-isolated undistorted SeF5− and of an oxotrifluoro-chalcogenite anion are reported. The pair-wise substitution of two fluorine atoms by a doubly bonded oxygen atom reduces the CN of Se from 6 to 4, and the presence of a sterically active free valence electron pair on Se has a strong influence on the bonding of the fluorine ligands.Figure optionsDownload as PowerPoint slide