Infrared spectra of the ammonium ion in crystals. Part XIII. Crystal structure of (NH\\r sub/4sub\\r )\\r sub/2sub\\r [AlF\\r sub/5sub\\r (H\\r sub/2sub\\r O)] and NH\\r sub/3sub\\r D\\r +\\r probe-ion spectra in (NH\\r sub/4sub\\r )\\r sub/2sub\\r [AlF\\r sub/5sub\\r (H\\r sub/2sub\\r O)], NH\\r sub/4sub\\r AlF\\r sub/4sub\\r , and (NH\\r sub/4sub\\r )\\r sub/3sub\\r ZnCl\\r sub/5sub\\r , with remarks on structural filiation of AMF\\r sub/4sub\\r fluorides