Crystal Structures of Inorganic Oxoacid Salts Perceived as Cation Arrays: A Periodic-Graph Approach

Abstract

A total of 569 crystal structures of anhydrous simple salts My(LO3)z (L = B, C, N, S, Se, Te, Cl, Br, I) and My(XO4)z (X = Si, Ge, P, As, S, Se, Cl, Br, I) are considered as three-periodic nets of My(L/X)z, where M are cations derived from metal atoms whereas (L/X) are conventional cations derived from nonmetal atoms. Both L and X cations are located in the centers of triangular/trigonal-pyramidal LO3 and tetrahedral XO4 oxoanions, respectively. The cation arrays (M+L/X) are proved to be the elements determining and governing the topology of the respective crystal structures, whereas the oxygens seem to play a secondary role as links between the cations. The preponderant role of cations in determining the crystal structures is founded on a greater uniformity (regularity) of their arrays when compared with those of anions or, even, with mixed cation–anion arrangements. In about three-fourth of the crystal structures analyzed in this work, the cation arrays appear to be topologically equivalent to some binary compounds, such as NaCl, NiAs, FeB, and α-Al2O3. The influence of both charge and size on the resulting array topology is also studied in detail. A quasi-binary representation My[L/X]z is proposed as a general model for the crystal structures of these anhydrous oxoacid salts.