Crystal structures of the dihydrogen hexafluorosilicate monohydrates ofp-bromoaniline andp-toluidine

Analysis of X-ray counter data for the dihydrogen hexafluorosilicate monohydrates ofp-bromoaniline, BrC₆H₄NH₂.1/2H₂SiF₆.H₂O, andp-toluidine, CH₃C₆H₄NH₂.1/2H₂SiF₆.H₂O, has shown that the two compounds are isostructural and that the orthorhombic crystals belong to the space groupPbca, witha = 7·80,b = 24·45,c = 9·48 Å anda = 7·89,b = 23·87,c = 9·53 Å, respectively, there being eight molecules in each unitcell. Structure analysis was initiated by the heavy atom method, and subsequent difference syntheses, carried out on thep-bromoaniline compound, then on thep-toluidine analogue, revealed the entire structure apart from the hydrogen atoms. From a difference synthesis on data for thep-toluidine compound refined by full-matrix least-squares procedures, the hydrogen atom sites were located, a reliability index,R = 0·052, being attained. The structures are sheet-like with bi-polar grouping of amino groups on either side of sheets of SiF ₆ ^2? groups and are cross-linked by ionic forces and hydrogen bonds. The SiF ₆ ^2? ion is octahedral, with an average Si-F distance of 1·69 ± 0·02 Å.