A coordination polyhedron is the spatial arrangement of ligand atoms directly attached to the central atom/ion. Common polyhedra include octahedral (e.g., [Co(NH₃)₆]³⁺), tetrahedral (e.g., [Ni(CO)₄]), and square planar (e.g., [PtCl₄]²⁻).
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The coordination sphere is the central atom/ion and the ligands enclosed in square brackets, such as [Fe(CN)₆]⁴⁻ in K₄[Fe(CN)₆]. Counter ions, like K⁺, are written outside the brackets.
The coordination number is determined by the number of sigma bonds formed by ligand donor atoms directly with the central metal atom/ion. Pi bonds, if present, are not considered when determining the coordination number.
Numerical prefixes like mono, di, tri indicate the number of ligands. Terms like bis, tris, tetrakis are used when ligand names include numerical prefixes, placed in parentheses. For example, [NiCl₂(PPh₃)₂] is named dichloridobis(triphenylphosphine)nickel(II).
Anionic ligands end in “-o,” neutral and cationic ligands have the same name, except for aqua (H₂O), ammine (NH₃), carbonyl (CO), and nitrosyl (NO). These ligands are enclosed in brackets while writing the formula of the coordination entity.
Coordination compounds are named following additive nomenclature. The cation is named first, followed by ligands in alphabetical order, regardless of their charge.
The charge of a coordination entity is indicated as a right superscript outside the square brackets, such as [Co(CN)₆]³⁻ or [Cr(H₂O)₆]³⁺. The charge of the cation(s) is balanced by the charge of the anion(s) in the overall compound.
The rules include listing the central atom first, followed by ligands in alphabetical order, regardless of their charge. Polydentate ligands are alphabetically listed, and ligand abbreviations are ordered based on the first letter. The entire coordination entity’s formula, whether charged ...
Nomenclature is crucial in Coordination Chemistry to provide an unambiguous method for describing formulas and names, especially for isomers. The recommendations of the International Union of Pure and Applied Chemistry (IUPAC) are followed for naming coordination entities.
The oxidation number of copper is +1 in [Cu(CN)₄]³⁻, represented as Cu(I). It signifies the charge the central atom would carry if ligands and shared electron pairs were removed.