kompleksiyhdisteet

Kompleksiyhdisteet, also known as coordination compounds, are chemical species composed of a central metal atom or ion bonded to one or more ligands, which donate lone pairs to the metal to form coordinate covalent bonds. The concept originated with Alfred Werenin coordination theory and is now described by ligand field theory and molecular orbital theory. Complexes can be mononuclear or polynuclear and span a wide range of oxidation states. The coordination number, the number of donor atoms bound to the metal, typically ranges from 4 to 6, yielding geometries such as octahedral, tetrahedral, square planar, and trigonal bipyramidal.

Ligands are classified by the number of donor sites: monodentate (one donor atom, e.g., NH3, H2O, Cl−), bidentate (two sites, e.g., en, oxalate), and multidentate ligands that wrap around the metal (chelates). Chelating ligands increase complex stability, a phenomenon known as the chelate effect.

Nomenclature places ligands in alphabetical order, using prefixes di-, tri- as appropriate, followed by the name of the central metal with its oxidation state in parentheses. Example: [Cu(NH3)4]2+ is tetraamminecopper(II).

Properties and applications: many complexes are intensely colored due to d-d transitions or charge-transfer processes. They are important in catalysis, materials science, sensing, imaging, and medicine (notably platinum-based anticancer drugs). Synthesis usually involves combining a metal salt with ligands under suitable solvent and pH, often substituting aqua ligands with incoming ligands.

Historical note: Alfred Werner laid the foundations of coordination chemistry in the early 20th century. Modern understanding employs crystal field theory, ligand field theory, and computational methods.