Verfeinerung der Kristallstruktur des Silberperchlorats AgClO4

Abstract

Abstract The crystal structure of anhydrous AgClO4 has been investigated by us recently, using powder diffraction data [1]. Space group is I[unk]2m, the cell dimensions are a = 4.916Å and c= 6.746 Å (25°C), Z = 2. After the isolation of single crystals the structure has now been refined by least squares methods to R = 0.032, using three dimensional X-ray diffraction data. The structure represents a new structure type for perchlorates with Univalent cations. In contrast to the structure of the perchlorates of Na (anhydrite type) and of K, Rb, Cs, Tl, NH+ 4 (baryte type), in silver perchlorate the atoms Ag and Cl are located in fixed positions (2b and 2a) and the ClO4 groups all have equal orientation. The groups are slightly stretched along their [unk] axis (symmetry D 2 d ) and their orientation is such that the two twofold axes point into the direction of the a and b axis of the crystal. After the refinement the interatomic distances within the ClO4 group are Cl – O = 1.440 Å, O – O = 2.327 and 2.364 Å. The shortest O – O distance between neighbouring ClO4 groups is 3.115 Å (mean distance 3.27 Å). The Ag atoms have a 4 + 4 coordination with Ag – O distances of 2.504 and 2.779 Å. The rigid body motion analysis yields r.m.s. amplitudes for the translational motions of the ClO4 group of 0.135 Å (∥ c) and 0.145 Å (∥ a or b) and for the librational motion of 9.5° (about c) and 5.5° (about a or b). The libration causes the apparent Cl – O bond length to be shortened by 0.02 Å.