The DuPont powder challenge:: The crystal structure of [C5NH6][Al3F10] -: A cautionary tale

A compound previously reported as HAlF4 has been shown to be [pyridinium][Al3F10]. The structure of this phase was solved and refined using a combination of synchrotron X-ray and neutron powder diffraction techniques in association with a number of other analytical techniques. The structure consists of [Al3F10](n)(-) sheets containing both corner-sharing (common) and edge-sharing (unusual) AlF6 octahedra. The sheets are separated by pyridinium cations oriented perpendicular to the sheets. The final crystallographic data are as follows: monoclinic, space group C2/m, a = 8.2706(3), b = 6.1.998(3), c = 10.525(1) Angstrom, beta = 100.38(1)degrees, V = 525.0(1) Angstrom(3), and Z =2,This compound appears to be another example of a layered "clay-like" aluminum fluoride.