Topic overview

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Isomerism in coordination compounds is organized into two broad categories. Structural isomers differ in connectivity and include ionization, hydrate or solvate, linkage, coordination, coordination-position, and polymerization isomerism. Stereoisomers have the same connectivity but differ in spatial arrangement; these include geometric and optical forms. Geometric isomerism is illustrated by cis/trans arrangements in square-planar and octahedral complexes, and fac/mer arrangements in octahedral complexes. Optical isomerism involves non-superimposable mirror-image forms, such as the Δ and Λ forms of [Co(en)₃]³⁺. Comparing the coordination sphere, counter-ions, ligand attachment, and three-dimensional arrangement provides a practical way to identify the isomerism involved.