Isostructural

Isostructural describes a relationship between two or more compounds that share the same crystal structure or network topology. When compounds are isostructural, they typically crystallize in the same space group and exhibit the same connectivity between atoms or ions, even though their chemical compositions may differ. The term emphasizes structural similarity rather than exact chemical identity.

Criteria and implications

Two compounds are considered isostructural if their atomic arrangements form the same overall framework or motif. This often means the same coordination geometry around centers (such as metal ions), the same linkage pattern between building units, and a comparable topology. Lattice parameters may differ due to the substitution of atoms with different sizes, but the fundamental network remains the same. Isostructural relationships are common in crystallography, inorganic chemistry, and materials science, including metal–organic frameworks and coordination polymers.

Examples

A classic example is the rock-salt family, where NaCl and KCl are isostructural, sharing the same rock-salt arrangement despite differing cation sizes. In crystals of isostructural series, researchers can substitute one metal or ligand for another while preserving the network, allowing systematic studies of how composition influences properties within a fixed topology.

Applications and caveats

Isostructural analysis aids materials design, enabling prediction of structural motifs and guiding synthesis of related compounds with tailored properties. However, isostructural does not guarantee identical physical properties; differences in bond lengths, angles, and electronic effects can lead to distinct behaviors. Distortions or disorder can also obscure true isostructurality in some cases.