- Title Pages
- Title Pages
- Dedicated to <b>Hartmut Baärnighausen</b> and <b>Hans Wondratschek</b>
- Preface
- List of symbols
- 1 Introduction
- 2 Basics of crystallography, part 1
- 3 Mappings
- 4 Basics of crystallography, part 2
- 5 Group theory
- 6 Basics of crystallography, part 3
- 7 Subgroups and supergroups of point and space groups
- 8 Conjugate subgroups, normalizers and equivalent descriptions of crystal structures
- 9 How to handle space groups
- 10 The group-theoretical presentation of crystal-chemical relationships
- 11 Symmetry relations between related crystal structures
- 12 Pitfalls when setting up group-subgroup relations
- 13 Derivation of crystal structures from closest packings of spheres
- 14 Crystal structures of molecular compounds
- 15 Symmetry relations at phase transitions
- 16 Topotactic reactions
- 17 Group—subgroup relations as an aid for structure determination
- 18 Prediction of possible structure types
- 19 Historical remarks
- Appendices
- A Isomorphic subgroups
- B On the theory of phase transitions
- C Symmetry species
- D Solutions to the exercises
- References
- Glossary
- Index

# Topotactic reactions

# Topotactic reactions

- Chapter:
- (p.216) (p.217) 16 Topotactic reactions
- Source:
- Symmetry Relationships between Crystal Structures
- Author(s):
### Ulrich Müller

- Publisher:
- Oxford University Press

A topotactic reaction is a chemical solid-state reaction such that the orientations of the product crystals are determined by the orientation of the initial crystal. The same symmetry rules apply for the domains as for phase transitions. Crystals of C_{70} (*P*6_{3}/*mcm*) polymerize in the solid state; the space group of poly-C_{70} (*Cmcm*) is a subgroup of *P*6_{3}/*mcm* of index 3 and thus twins with three orientations are the result. Vernier compounds are halides of the lanthanoids with the general formula Ln_{n}X_{2n+1}, e.g., Tm_{7}Cl_{15}. Their structures are hettotypes of the CaF_{2} type. When they crystallize from a melt having some intermediate composition, topotactic textures result consisting of, say, TmCl_{2} and Tm_{7}Cl_{15}. Their domains are intergrown such that the X-ray diffraction pattern is puzzling. However, with group-subgroup relations the puzzle can be solved.

*Keywords:*
topotactic reaction, solid-state reaction, vernier compounds

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- Title Pages
- Title Pages
- Dedicated to <b>Hartmut Baärnighausen</b> and <b>Hans Wondratschek</b>
- Preface
- List of symbols
- 1 Introduction
- 2 Basics of crystallography, part 1
- 3 Mappings
- 4 Basics of crystallography, part 2
- 5 Group theory
- 6 Basics of crystallography, part 3
- 7 Subgroups and supergroups of point and space groups
- 8 Conjugate subgroups, normalizers and equivalent descriptions of crystal structures
- 9 How to handle space groups
- 10 The group-theoretical presentation of crystal-chemical relationships
- 11 Symmetry relations between related crystal structures
- 12 Pitfalls when setting up group-subgroup relations
- 13 Derivation of crystal structures from closest packings of spheres
- 14 Crystal structures of molecular compounds
- 15 Symmetry relations at phase transitions
- 16 Topotactic reactions
- 17 Group—subgroup relations as an aid for structure determination
- 18 Prediction of possible structure types
- 19 Historical remarks
- Appendices
- A Isomorphic subgroups
- B On the theory of phase transitions
- C Symmetry species
- D Solutions to the exercises
- References
- Glossary
- Index