Single crystal structural studies at hexagonal fluoride perovskites AM(II)F(3) (M-II = Mg, Mn, Fe, Co, Ni)

At single crystals of nine fluoride phases AMF(3) the hexagonal perovskite structures were refined by X-ray methods, of RbNiF3 below T-C approximate t o 145 K, too. The hexagonal 6L type (P6(3)/mmc, Z = 6) is found at: RbMgF3 (a = 585.7(1); c=1426.0(1) pm), CsMnF3 (624.4(1); 1515.4(4) pm), CsFeF3 (61 5.8(1); 1488.4(6) pm), Rb0.63Cs0.37CoF3 (599.1(1); 1460.3(4)pm), RbNiF3 (12 8 K: 552.6(1); 1426.4(6)pm), Cs2BaLiNi2F9 (593.1(1); 1447.1(4)pm). Of the h exagonal rhombohedral 9 L type (R (3) over bar m, Z = 9) are CsCoF3 (620.1( 1); 2264.0(7) pm) and yellow CsNiF3 (614.7(1); 2235.3(6)pm), prepared at lo wer temperatures resp. under high pressure, whereas light green CsNiF3 (625 .5(1); 524.2(1) pm) belongs to the 2 L type (P6(3)/mmc, Z = 2). The occuren ce of these structures and the interatomic distances observed, comparing al so normal and high pressure phases, are discussed in connection with the to lerance factor.