Introduction to Inorganic Chemistry/Ionic and Covalent Solids - Structures
- 1 Chapter 8: Ionic and Covalent Solids - Structures
- 2 8.1 Close-packing and interstitial sites
- 3 8.2 Structures related to NaCl and NiAs
- 4 8.3 Tetrahedral structures
- 5 8.4 Layered structures and intercalation reactions
- 6 8.5 Bonding in TiS2, MoS2, and pyrite structures
- 7 8.6 Spinel, perovskite, and rutile structures
- 8 8.7 Discussion questions
- 9 8.8 Problems
- 10 8.9 References
Chapter 8: Ionic and Covalent Solids - Structures
8.1 Close-packing and interstitial sites
8.3 Tetrahedral structures
8.4 Layered structures and intercalation reactions
8.5 Bonding in TiS2, MoS2, and pyrite structures
8.6 Spinel, perovskite, and rutile structures
8.7 Discussion questions
- Using the Liverpool 3D visualization website (http://www.chemtube3d.com/solidstate/_table.htm) determine the anion and cation coordination geometries in cadmium chloride and anatase. Describe the arrangement of octahedra (in terms of whether they share edges, faces, etc.) in these structures.
- Count the number of atoms in the Li3Bi and ReO3 unit cells, and determine the coordination environments of each of the ions.
- Silicon, germanium, and many other semiconductors adopt the diamond (or zincblende) structure. Assuming that all the atoms are the same size, calculate the volume fraction of the unit cell that is occupied by the atoms. How does the filling fraction of diamond compare to simple cubic and close-packed structures, and what does this tell us about the relationship between coordination number and density?
- Describe the structural basis of ferroelectricity in barium titanate.
- Explain why ionic compounds rarely have layered crystal structures.
1. The structures of the disulfides (MS2) show an apparently unusual trend, proceeding from left to right across the transition series. On the left side (TiS2, ZrS2, MoS2, etc.), one finds layered structures, whereas in the middle (ReS2, FeS2, RuS2) there are three-dimensional pyrite- and marcasite-type structures. On the right (PtS2, SnS2), there are again layered structures. Briefly explain these trends.
2. The fluorite structure, CaF2, which is generated by filling all the tetrahedral holes in a FCC array, is a common MX2 structure type.
(a) What is the coordination environment of F in a hypothetical relative of CaF2, in which Ca forms a hcp array and F occupies all the tetrahedral sites?
(b) Suggest a reason why the structure described in (a) is very rare.
3. The cuprite (Cu2O) structure is related to zincblende (or diamond) in that oxygen occupies both the Zn and S positions, with copper in between. This is shown schematically at the right. Actually, in cuprite there are two such interpenetrating networks with no bonds between them. Draw the second network in the empty cell. If you put the two halves together and take out the copper, what cubic packing lattice do you get? Is it a closest packing lattice? (Hint #1: start with an O atom at 1/2,1/2,1/2) (Hint #2: try this in pencil first)
4. Draw the rutile structure in sections of the unit cell, and verify that the stoichiometry is MX2. What are the coordination numbers of Ti and O?
5. Stishovite is a high pressure form of SiO2 found in meteorite craters. While normal SiO2 has the quartz structure, in which each Si is coordinated by four O atoms, stishovite has the rutile structure. Would you expect the Si-O bond to be longer in stishovite, or in quartz? What is the bond order in each polymorph?
6. Some MX salts can exist in either the CsCl or NaCl structure. Use the Pauling formula to predict the M-X bond length in the CsCl structure of a compound that has a bond length of 3.5 Å in the NaCl structure. Would applying a high pressure stabilize the CsCl form, or the NaCl form of this compound? (hint: calculate the volume per formula unit)
7. Predict whether each of the following should form a normal or inverse spinel (hint: think about CFSE's): MgV2O4, VMg2O4, NiGa2O4, ZnCr2S4, NiFe2O4, Mn3O4, Fe3O4. Would kind of magnetic ordering (ferro-, ferri-, or antiferromagnetic) would you predict for NiFe2O4?