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Transcript
Unit 23: Coordination Chemistry 23.2 - Transition-Metal Complexes Metal Complexes: Species that are assemblies of a central transition-metal ion bonded to a group of surrounding molecules or ions Ligand - The molecules or ions bonded to the metal ion in a complex Coordination Number - Number of atoms bonded to the metal ion Coordination Sphere - Central metal and the ligands 23.3 - Common Ligands Donor Atom - The ligand atom that binds to the central metal ion Chelating Agents - Bidentate and polydentate ligands Chelate Eect - Formations constants are larger for bidentate and polydentate ligands Porphyrins are important in biomolecules For example, chlorophyll has a porphyrin with magnesium in the center (en) is bidentate EDTA has a coordination number of 6 Larger ligands lower coordination number Ligands that transfer substantial negative charge to the metal ion lower coordination number 23.4 - Nomenclature and Isomerism 1) For ionic complexes, name the cation rst 2) Names of ligands are put in alphabetical order before the name of the metal 3) Names of anionic ligands end with -o, while neutral ligands have a group of special names 4) Use prexes to denote the number of simple ligands (if the name of the ligands already has such a prex, use alternate prexes of bis, tris, tetrakis, etc.) 5) For complex anions, add -ate to the Latin name of the metal 6) Give the oxidation number of the metal *In complex anions (negative charge), copper, gold, iron, and platinum change names to old names *Put parentheses around the complex if there are multiples with an alternate prex: tris(ethylenediamine) Isomers - Same composition but dierent arrangement Structural Isomer - Dierent bonds Linkage Isomerism - If a ligand can bind to the metal with one or another atom as the donor atom Coordination Sphere Isomerism - Dier in which ligands are bonded to the metal and which are outside the coordination sphere 1 Stereoisomer - Same bonds but dierent ways in which the ligands occupy the space Geometric (Diastereoisomers) Isomerism - Arrangement of the atoms is dierent but the same bonds are present Optical Isomerism - These are enantiomers, which are mirror images that cannot be super-imposed on one another Tetrahedrals cannot form geometric isomers since it's the same when viewed from any side Chelating agents can't span across the coordinate sphere, which limits the number of isomers Chiral - Not super-imposable with no plane of symmetry Square planars are not chiral since they are at Tetrahedrals are chiral if all four ligands are dierent Chiral molecules interact the same way as usual except when they interact with other chiral molecules A mixture of equal amounts of L and D isomers is a racemic mixture 23.5 - Color and Magnetism Small molecules and ions that obey the octet rule are colorless Metal ions with completed electronic subshells are usually colorless Large organic molecules with conjugated systems are colored Metal ions with a partially lled d or f level are colored 3d metals with high oxidation numbers are colored If a substance absorbs a certain kind of light, it appears to have its complementary color Diamagnetic - Very weak repulsion from magnetic eld (all electrons paired) Paramagnetic - Weak attraction to magnetic elds (one or several unpaired electrons) Ferromagnetic - Strong attraction to magnetic eld (many unpaired electrons organized in a crystal) High Spin - Many unpaired e− Low Spin - Many paired e− 2