Structure types with different properties

Abstract

Abstract The crystal structures of elements A or organic molecules like CH4 can be characterized by the self-coordination numbers T1 T2 T3 of nearest, next-nearest and third A–A or C–C neighbors (with C atoms as centers of gravity of CH4 molecules). The sphere, layer or rod packings have different densities and can be correlated to the sphere, layer or rod-like habit of single crystals. There are about 500 sets T1 T2 T3 with increased Ti values (aristotypes), which can be derived from the 402 characteristic lattice complexes. Structure types are approximated to the list of lattice complexes. Non-spherical molecules, covalent bonding or electronic effects of atoms like lone electron pairs or Jahn-Teller distortion give rise to deviations. The different atoms of binary and ternary compounds can form a single packing like the bcc sphere packing of different atoms in CsCl and AlMnCu2. The interactions between atoms like the repulsive Cs–Cs or Cl–Cl interactions in CsCl can be derived from structure maps with T1 T2 T3 coordinates. NiAs and Pb(CO3) with layer packings of As or Pb atoms and rod packings of Ni or C atoms are examples with different plate- or rod-like habit of crystals depending on the dominance of A–A or B–B interactions.