Question
Sat May 31, 2008 By:

What is the difference between a normal compound and a coordination compound?

Expert Reply
Sat May 31, 2008

Metal complexes, also known as coordination compounds, include all metal compounds, aside from metal vapors, plasmas, and alloys. The study of "coordination chemistry" is the study of "inorganic chemistry" of all alkali and alkaline earth metals, transition metals, lanthanides, actinides, and metalloids. Thus, coordination chemistry is the chemistry of the majority of the periodic table. Metals and metal ions only exist, in the condensed phases at least, surrounded by ligands.The ions or molecules surrounding the metal are called ligands. Ligands are generally bound to a metal ion by a coordinate covalent bond (donating electrons from a lone electron pair into an empty metal orbital), and are thus said to be coordinated to the ion. The areas of coordination chemistry can be classified according to the nature of the ligands, broadly speaking:

  • Classical (or "Werner Complexes"): Ligands in classical coordination chemistry bind to metals, almost exclusively, via their "lone pairs" of electrons residing on the main group atoms of the ligand. Typical ligands are H2O, NH3, Cl, CN, enExamples: [Co(EDTA)], [Co(NH3)6]Cl3, [Fe(C2O4)3]K3
  • Organometallic Chemistry: Ligands are organic (alkenes, alkynes, alkyls) as well as "organic-like" ligands such as phosphines, hydride, and CO.Example: (C5H5)Fe(CO)2CH3
  • Bioinorganic Chemistry: Ligands are those provided by nature, especially including the side chains of amino acids, and many cofactors such as porphyrins.Example: hemoglobin
  • A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by massNot all molecules are compounds. A diatomic molecule of hydrogen, represented by H2, is homonuclear — made of atoms of only one element, so is not regarded as a compound. Compounds are pure substances that contain two or more elements combined in a definite fixed proportion.
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