CHEM 1312H 1st Edition Lecture 11 LECTURE MATERIAL Coordination compounds a compound composed of a central atom metal directly bonded to a number of groups ligands Monodentate ligands binds to a metal through one atom Polydentate ligands binds through 2 atoms Sequestering agents bind to metal and make it less reactive ASSIGNED READING MATERIAL 23 4 NOMENCLATURE AND ISOMERISM IN COORDINATION CHEMISTRY Naming Rules when naming complexes that are salts the cation name comes before the anion when naming complex ions or molecules the ligands come before the metal ligands are listed in alphabetical order disregard charges prefixes that denote the number of ligands are not considered anionic ligand names end in the letter o but electronically neutral ligands use the molecule names Greek prefixes di tri tetra penta hexa are used to indicate the number of each ligand when there s more than one present if the complex is an anion its name ends in ate oxidation number of the metal is given by the Roman numeral in parentheticals following the name of the metal Isomerism Isomers when two ore more compounds have the same composition but a different arrangement of atoms structural isomers isomers with different bonds stereoisomers isomers with the same bonds whose ligands are arranged differently around the metal center aka different spatial arrangements Structural Isomers linkage isomerism arises when a ligand is capable of coordinating to a metal in two ways o for ex NO2 can coordinate to a metal ion either through its nitrogen or one of its oxygens coordination sphere isomers isomers that differ in which species in the complex are ligands and which are outside the coordination sphere in the solid Stereoisomerism geometric isomerism when the arrangement of atoms is different but the same bonds are present o cis isomer when ligands are adjacent to each other These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o trans isomer when ligands are on opposite sides of the central atom o see Figure 23 21 for illustration optical isomerism otherwise known as o enantiomers mirror images that cannot be superimposed on each other no way to rotate one of the enantiomers to make it identical to another this inability to be superimposed upon something else makes them chiral molecules or ions o properties of optical isomers only differ if they are in a chiral environment o when a polarized light is passed through a solution containing an optical isomer an isomer that rotates the plan of polarization to the right is dextrorotatory its mirror image rotates the plan of polarization to the left and is called levorotatory if a mixture is racemic this means it does not rotate polarized light because when equal amounts of the two isomers are obtained their effects cancel each other out 23 5 COLOUR AND MAGNETISM IN COORDINATION CHEMISTRY the colour of a complex depends on the identity of its metal ion its oxidation state and the ligands bound to it for a substance to have colour it has to absorb some portion of the visible light spectrum absorption takes place when there s enough energy to move an electron from the substance in the ground state to an excited state Magnetism of Coordination Compounds recall that a lot of transition metal complexes exhibit paramagnetism
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