Synthese, Eigenschaften und Kristallstruktur von (NH4)NbOBr4/ Synthesis, Properties and Crystal Structure of (NH4)NbOBr4

(NH 4 )NbOBr 4 is obtained as air sensitive, light red crystals from NH 4 Br and NbBr 5 in a sealed glass ampoule at 420 °C, whereby the oxygen presumably originates from the glass surface. The compound crystallizes in the monoclinic space group C2/m with a = 1269.9(1), b = 1384.7(2). c = 773.0(2) pm, β = 114.44(2)° and Z = 6. The structure is built up by NH 4+ cations and polymeric NbOBr 4 anions. Symmetrical linear oxo bridges with Nb-O = 199 pm connect square planar NbBr 4 units to form endless chains arranged in planes parallel (010). Neighbouring NbBr 4 units are in eclipsed as well as staggered orientations. The NH 4 + cations are located between the planes of parallel NbOBr 4 - chains. The vibrational frequencies of the IR and Raman spectrum are assigned.