Coordination Compounds

Coordination Entity and Coordination Number

A coordination entity consists of a central metal atom or ion bonded to a fixed number of ions or molecules (ligands). The coordination number is the total number of coordinate bonds formed by the ligands with the central metal atom.

Ligands and Denticity

Ligands are neutral molecules or ions that donate a pair of electrons to the central metal atom. Denticity refers to the number of donor atoms a single ligand uses to bind to the metal, classifying them as monodentate, bidentate, or polydentate.

Werner's Coordination Theory

Werner proposed that metals in coordination compounds exhibit two types of valencies: primary valency (ionizable, corresponds to oxidation state) and secondary valency (non-ionizable, corresponds to coordination number and spatial arrangement).

Valence Bond Theory (VBT)

VBT explains the formation of coordination complexes through the overlap of hybridized metal orbitals with ligand orbitals, determining the geometry (such as octahedral or tetrahedral) and magnetic behavior (paramagnetic or diamagnetic).

Crystal Field Theory (CFT)

CFT is an electrostatic model that assumes ligands act as point charges, causing the degeneration of metal d-orbitals to split into different energy levels (like $t_{2g}$ and $e_g$ in octahedral complexes), explaining their characteristic colors and crystal field stabilization energy.