Al 3+ Ion Site Symmetry in (NH 4 ) 2 [AlF 5 · H 2 O] Single Crystals

The production of pure and Cr 3+ doped (NH 4 ) 2 [AlF 5 · H 2 O] single crystals and the crystal structure of this compound are described. The infrared spectra recorded experimentally at room temperature show – using the results of group theory – that the [AlF 5 · H 2 O] 2− complex ion has at most the symmetry of the C 4v group. EPR measurements are carried out for a more exact determination of the site symmetry of Al 3+ ions using the Cr 3+ ion on Al 3+ site as “probe ion”. The determined values of spin‐Hamiltonian parameters suggest that the symmetry of the [AlF 5 · H 2 O] 2− complex ion has at most the symmetry of the C 2v group.