Valence Bond Theory (VBT), Crystal Field Theory (CFT), Ligand Field Theory (LFT), and Molecular Orbital Theory (MOT) are among the approaches suggested to elucidate the nature of bonding in coordination compounds.

Metal atoms or ions, influenced by ligands, undergo hybridization of their (n-1)d, ns, np orbitals to produce a set of equivalent orbitals with defined geometries (e.g., octahedral, tetrahedral). These hybridized orbitals then overlap with ligand orbitals to facilitate bonding.

Linkage isomerism occurs in complexes with ambidentate ligands. For instance, thiocyanate ligand (NCS⁻) can bind through nitrogen (M–NCS) or sulphur (M–SCN), illustrated by complexes like [Co(NH₃)₅(NO₂)]Cl₂.

Coordination isomerism involves the interchange of ligands between cationic and anionic entities. In [Co(NH₃)₆][Cr(CN)₆], NH₃ binds to Co³⁺ and CN⁻ to Cr³⁺. In its coordination isomer [Cr(NH₃)₆][Co(CN)₆], the ligand binding arrangement switches.

Ionisation isomerism occurs when the counter ion in a complex salt becomes a ligand. In [Co(NH₃)₅(SO₄)]Br, SO₄ displaces a ligand, while in [Co(NH₃)₅Br]SO₄, Br⁻ becomes the ligand. This is similar to ‘hydrate isomerism’ when water is involved as a solvent.