Modular crystal structure
From Online Dictionary of Crystallography
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Structure cristalline modulaire (Fr), Struttura cristallina modulare (It), モジュール結晶構造 (Ja)
A modular crystal structure is a structure built by periodically juxtaposing one or more types of modules, which are three-dimensional but less than triperiodic objects that can ideally be described as cuts from a (real or hypothetical) structurally and chemically homogeneous parent structure: the archetype. The symmetry of the modular structure is described by an ordinary space group, whereas the building modules possess only a subperiodic group.
The modules can be obtained from chemically different archetypes: the resulting structures are known as polyarchetypal structures (diarchetypal being the most frequent case) and are evidently also heterochemical (different composition) with respect to each of the archetypes. When instead the modules are obtained from the same archetype, they are known as monoarchetypal structures.
The generation of a series of structures from the periodic juxtaposition of modules is obtained by varying the relative orientation and/or position of adjacent modules. This juxtaposition in monoarchetypal structures may or may not promote a chemical change at the interface between two modules: the resulting structures are thus heterochemical or isochemical respectively.