1Chapter 19 Coordination Complexes19.1 The Formation of Coordination Complexes19.2 Structures of Coordination Complexes19.3 Crystal-Field Theory and Magnetic Properties19.4 The Colors of Coordination Complexes19.5 Coordination Complexes in BiologyChapter 24 From Petroleum to Pharmaceuticals24.1 Petroleum Refining and the Hydrocarbons24.2 Functional Groups and Organic Synthesis24.3 Pesticides and PharmaceuticalsChapter 25 Synthetic and Biological Polymers25.1 Making Polymers25.2 Biopolymers25.3 Uses for PolymersC1403 Lecture 19 Monday, November 14, 20052The d block metal for coordination complexes withmolecules and ions319.1 Coordination complexesThe electronic basis of the color of metal complexes4Coordination complex: A structure containing a metal(usually a metal ion) bonded (coordinated) to a group ofsurrounding molecules or ions.Ligand (ligare is Latin, to bind): A ligand is a molecule orion that is directly bonded to a metal ion in acoordination complexCoordination sphere: A metal and its surrounding ligandsNote: religare is Latin, to bind tightlyA ligand uses a lone pair of electrons (Lewis base)to bond to the metal ion (Lewis acid)5Complex ions: Three common structural typesOctahedral:Most importantTetrahedralSquare planar6Lewis acid: Co3+Lewis base:NH3Coordination complex:Lewis base coordinatedto a Lewis acidCoordination complex:Ligand (electron donor)coordinated to a metal(electron acceptor)The formation of a coordinate complex is a Lewis acid-base reactionThe number of ligand bonds to the central metal atom istermed the coordination number7The basic idea is that the ligand (Lewis base) isproviding electron density to the metal (Lewis acid)In terms of MO theory we visualize the coordination as thetransfer of electrons from the HO of the Lewis base to the LU ofthe Lewis acidHOLULewis baseLewis acidNH3Co3+The bond from ligand to metal is covalent (shared pair), but bothelectrons come from the ligand (coordinate covanent bond)8Types of Ligands: Monodentate (one tooth) LigandsLatin: “mono” meaning one and “dens” meaning tooth9Types of Ligands: Bidentate (two tooth) LigandsBidentate (chelates):10Types of Ligands: Ethylenediaminetetraacetate ion(EDTA): a polydentate chelating ligandChelate fromGreek chela, “claw”EDTA wraps around the metal ion atall 6 coordination sites producing anexceedingly tight binding to themetal11Alfred WernerSwitzerlandUniversity of ZurichZurich, Switzerlandb. 1866(in Mulhouse, then Germany)d. 1919The Nobel Prize in Chemistry 1913"in recognition of his work on thelinkage of atoms in molecules by whichhe has thrown new light on earlierinvestigations and opened up new fieldsof research especially in inorganicchemistry"Alfred Werner: the father ofthe structure of coordinationcomplexes12Lewis acids and basesA Lewis base is a molecule or ion that donates a lone pairof electrons to make a bondA Lewis acid is a molecule of ion that accepts alone pair of electrons to make a bondExamples:NH3OH2Cl-F-Examples:H+Co3+Co2+Mn+Electrons in the highest occupied orbital (HO) of amolecule or anion are the best Lewis basesMolecules or ions with a low lying unoccupied orbital (LU)of a molecule or cation are the best Lewis acids13Conventions in writing the structure of coordinationcompounds:Brackets [] are used to indicate all of thecomposition of the coordinate complexThe symbol for the central atom metal of thecomplex is first within the bracketsSpecies outside of the [] are not coordinated to themetal but are require to maintain a charge balanceA coordination compounds is a neutral speciesconsisting of a coordinate complex and uncoordinatedions required to maintain the charge balance14Ligand substitution reactionsFor some complex ions, the coordinated ligands maybe substituted for other ligandsComplexes that undergo very rapid substitution ofone ligand for another are termed labileComplexes that undergo very slow substitution ofone ligand for another are termed inert[Ni(H2O)6]2+ + 6 NH3 ! [Ni(NH3)6]2+ + 6 H2O (aqueous)15Werner’s explanation of coordination complexesMetal ions exhibit two kinds of valence: primary andsecondary valencesThe primary valence is the oxidation number (positivecharge) of the metal (usually 2+ or 3+)The secondary valence is the number of atoms thatare directly bonded (coordinated) to the metalThe secondary valence is also termed the “coordinationnumber” of the metal in a coordination complex16Example of a coordination complex: [Co(NH3)6]Cl3[Co(NH3)6]3+What is the atomiccomposition of thecomplex?What is the net chargeof the complex?[Co(NH3)6]How do we know the chargeis 3+ on the metal?3+ is required to balancethe three Cl- ionsThe primary valence of [Co(NH3)6]Cl3 is 3 (charge on Co)The secondary valence of [Co(NH3)6]Cl3 is 6 (ligands)1719.2 Structures of Coordination Complexes: Theammonia complexes of Co(III) = Co3+CoCl3.6NH3CoCl3.5NH3CoCl3.4NH3CoCl3.3NH3In all of these complexes there is no free NH3(No reaction with acid)3 “free” Cl- ionsOrange-Yellow2 “free” Cl- ionsPurple1 “free” Cl- ions Green0 “free” Cl- ions GreenHow did Werner deduce the structure of coordination complexes?Ions releasedComposition Color18Compound 1: CoCl3.6NH3 = [Co(NH3)6]3+(Cl-)3 = [Co(NH3)6](Cl)3Conclude: 3 free Cl- ions, [Co(NH3)6]3+Compound 2: CoCl3.5NH3 = [Co(NH3)5Cl]2+(Cl-)2 = [Co(NH3)5Cl](Cl)2Conclude: 2 free Cl- ions, [Co(NH3)5Cl]2+Compound 3: CoCl3.4NH3 = [Co(NH3)4Cl2]1+(Cl-) = [Co(NH3)4Cl2](Cl)Conclude: 1 free Cl- ion, [Co(NH3)4Cl2]1+Compound 4: CoCl3.3NH3 = [Co(NH3)3Cl3]No free Cl- ions Logic: Cl- is not in coordination sphere; NH3 is in sphere19CoCl3.6NH3CoCl3.5NH3CoCl3.4NH3Isomers!Coordination complexes: Three dimensional structuresCl-Cl-Cl-NH3CoNH3NH3H3NH3NNH3Cl-Cl-ClCoNH3NH3H3NH3NNH3Cl-ClCoClNH3H3NH3NNH3Cl-ClCoNH3NH3H3NH3NClCoH3NCoNH3Bond toward youBond away from you20Coordination complexes: isomersIsomers: same atomic composition, different structuresWe’ll discuss the following typesof isomers:HydrateLinkageCis-transOptical (Enantiomers)21Water in outer sphere (waterthat is part of solvent)Water in the innersphere water (wateris a ligand in thecoordination sphereof the metal)Hydrate isomers:22Linkage isomersBonding to metal may occur atthe S or the N atomExample:C NSBonding occurs from N atom to metal Bonding occurs from S atom to metal23Stereoisomers: geometric isomers (cis and trans)ClCoClNH3H3NH3NNH3Cl-ClCoNH3NH3H3NH3NClCl-24CoCl3.3NH3ClCoClNH3H3NH3NClClCoClClH3NH3NNH3Cis-trans isomers and beyondBeyond cis