Chem 1120 1st Edition Lecture 23 Outline of Last Lecture I Transition Metal Properties and Trends II Magnetism III Coordination Complexes and Ligands Outline of Current Lecture I Coordination Numbers and Geometry II Chelates and Kinetic Lability III Nomenclature IV Isomerism Current Lecture I Coordination Number number of ligands bonded directly to central metal ion or atom Coordination number is specific for a given metal in a particular oxidation state governed by metal size ligand size ligand type ligand charge For example while iron III can bind to 6 fluorides it can only gain 4 chlorides because the chlorides are larger than the fluorides Geometry shape of a complex depends on coordination number and metal ion Most common coordination numbers are 4 and 6 Coordination number of 4 tetrahedral and square planar Coordination number of 6 octahedral What are the coordination numbers for the metal ions in the pictures to the right 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 Answer 4 for both theres 4 things attached II Many organic molecules have multiple donor atoms chelate a ligand bonded to a central metal atom at two or more points for example ethylenediamine en is a bidentate ligand meaning it is bonded to the metal atom in two points More than two donor atoms make the ligand polydentate for example EDTA supplies at most 6 donors Bidentate and polydentate ligands are chelating agents where the metal ion is geld tightly by ligand Chelate Effect increased stability and rate of formation for a metal complex because of polydentate ligands Coordination complexes can exchange inner sphere ligands however in determining reactivity we must consider both thermodynamic stability and kinetic lability Thermodynamic Stability property of a compound with a large formation constant and thus a large negative G Kinetic Lability the tendency to exchange ligands very quickly in solution whether or not the compound is stable depends on how fast they exchange the faster they exchange ligands the less stable and vice versa In biological systems carbon monoxide CO and cyanide CN are poisonous because they will bind more tightly to the iron than will oxygen III Square brackets enclose the complex ion and counterions ions are outside the brackets 1 the cation is named before the anion NaCl sodium chloride K3 Fe CN 6 Potassium hexacyanoferrate III 2 Ligands are named first metals last 3 Ligands are named in alphabetical order 4 Ligand names anions end in o most neutral ligands are named as the molecule exceptions water aqua CO carbonyl ammonia ammine 5 Number of each ligand is indicated by Greek prefixes 6 Metal oxidation state is indicated by Roman numerals determining oxidation state Net charge M charge L charge 7 Anionic metal complex names end in ate basically if the net charge on the complex is negative add ate to the end of the metal name Answer A IV It s possible to assemble a coordination complex in several different ways which results in the formation of isomers Isomers compounds with the same formulas but different arrangements of atoms 1 Structural Isomers molecules have the same molecular formula but are bonded together in different orders 2 kinds 2 Coordination Sphere Isomers composition within the brackets is arranged differently 3 Linkage Isomers ligand is bound to the metal by a different atom 4 Stereoisomers have the same molecular formula and sequence of bonded atoms but differ only in 3D orientation 5 Geometric Isomers have a restricted rotation somewhere in a molecule usually just involve the carbon carbon double bond trans atoms locked on opposite sides of the double bond cis atoms locked on the same side of the double bond 6 Optical Isomers molecules that are the mirror image but cannot be superimposed Square planar and octahedral complexes can have cis or trans isomers tetrahedral cannot Stereoisomers enantiomers d dextrorotatory right handed l levorotatory left handed