Dr. Anthony Haynes

An FCC lattice of Cl^- anions with Na⁺ cations in all the octahedral holes (or vice versa).
Both Na⁺ and Cl^- have coordination number 6.

Also adopted by a wide variety of ionic compounds.

A simple cubic lattice of Cl^- anions with Cs⁺ cations in all the cubic holes (or vice versa).
Both Cs⁺ and Cl^- have coordination number 8.

An FCC lattice of S^2- anions with Zn²⁺ cations in half of the tetrahedral holes or vice versa.
Both Zn²⁺ and S^2- have coordination number 4.

Also adopted by CuCl, CdS, HgS, GaP and InAs.

An FCC lattice of Ca²⁺ cations with F^- anions in all of the tetrahedral holes.
Coordination numbers are 8 for Ca²⁺ and 4 for F^-.

Also adopted by BaCl₂, PbO₂, HgF₂, and UO₂.

The antifluorite structure is analogous but with the positions of cations and anions reversed.  This structure is adopted by K₂O, K₂S, Li₂O, Na₂O and Na₂S.

An HCP lattice of S^2- anions with Zn²⁺ cations in half of the tetrahedral holes  or vice versa.
Both Zn²⁺ and S^2- have coordination number 4.

Also adopted by ZnO, BeO, AgI, and one polymorph of SiC.

An HCP lattice of O^2- anions with Ti⁴⁺ cations in half of the octahedral holes.
Coordination numbers are 6 for Ti⁴⁺ and 3 for O^2-.

Also adopted by SnO₂, MgF₂, and MnO₂.

Due to the small, highly polarising naure of the Be²⁺ cation, some covalent character is present and BeCl₂ doesn't have a regular ionic lattice. Instead it is composed of polymeric chains with Be atoms linked by bridging chlorides. At a certain orientation you can look directly down the chains, which are arranged parallel to each other. A single chain from this stucture is shown below.

A single (BeCl₂)_n chain

Each Be is linked to four Cl arranged tetrahedrally.

A similar polymeric structure is adopted by BeH₂