The CdSO4, rutile, cooperite and quartz dual nets:: interpenetration and catenation

The CdSO4 and quartz nets are described as tilings of generalized tetrahedra [6(2.)8(2)]. The CdSO4 net shares with the diamond net the property of having the minimum number (2) of vertices in the topological repeat unit of a 4-coordinated net. It is self dual which explains its propensity to occur self-interpenetrating in crystalline frameworks. The rutile (TiO2) and cooperite (PtS) nets are closely related to that of CdSO4 which explains why they also often occur interpenetrating. The dual of the quartz net is a net formerly described as "dense net" and is carried by a tiling [7(4)]. The quartz dual net cannot self-intergrow without degradation of symmetry. Two intergrown quartz nets have half their rings not catenated and the other half doubly catenated. Attention is called to some other simple nets that like that of cooperite have mixed tetrahedral and square coordination. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.