Zur Kenntnis von Ammoniumchrom(III)-fluorid NH4CrF4

T h . H i n r i c h s e n Fachbereich Geowissenschaften der Universität Marburg, Lahnberge, D-3550 Marburg Z. Naturforsch. 84b , 934-938 (1979); eingegangen a m 28. März 1979 Tetrafluorochromates(III) , Powder X r a y Data, Magnetic Susceptibilities, Thermolysis of NH4CrF4 The hitherto unreported c o m p o u n d NH4CrF4 could be prepared b y applying hydrothermal high pressure techniques. X r a y powder data show NÜ4CrF4 to crystallize tetragonally with a = 743.2, c = 650.4 pm, similar to CsFeF4 and other TIAIF4-related structures. The magnetic behaviour was studied below room temperature and proved NH4CrF4 to become antiferromagnetic (TN = 34 K ) within the range known from other AJCrF4 compounds. The thermolysis of NH4CrF4, as investigated b y X-rays and T G / D T A , begins at about 400 °C and yields CrF3 and also Cr2F5 , if extended to 1000 °C.