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Abstract:
The crystal structures of the alkali aluminium thiohypodiphosphates MIAlP2S6 (MI = Li, Na) are reported. NaAlP2S6 crystallizes in the orthorhombic space group Fdd2 (no. 43) with a = 8.0400(2), b = 10.9452(2), c = 20.8801(4) angstrom, and V = 1837.44(7) angstrom 3 (Z = 8). It is isostructural with AgAlP2S6, which is consistent with the similar ionic radii of Na and Ag. In contrast, LiAlP2S6 crystallizes in a different structure type which has not been observed in the large number of thiohypodiphosphates reported so far. It crystallizes in the monoclinic space group C2/c (no. 15) with a = 6.783(3), b = 10.365(4), c = 11.776(4) angstrom, = 94.399(5)degrees, and V = 825.46(5) angstrom 3 (Z = 4).