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Bridging Ligands

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Bridging Ligands Chapter 9 Coordination Chemistry I: Structure and Isomers 9-1 History 9-2 Nomenclature 9-3 Isomerism 9-4 Coordination Numbers and Structure History What is coordination compound? Coordniantion compounds include compound composed of a metal atom or ion and one or more ligands that formally donate electrons to the metal. More specifically, a transition metal surrounded by neutral molecules or anions with a definite geometry. What is ligand? Ligand can be a atom, ion, and molecules. History Prussian blue (German: Preußischblau or Berliner Blau, in English Berlin blue) is a dark blueWhatpigment is coordinationused in paints and compound? formerly in blueprints. Prussian blue wasCoordination discovered complexesby accident were by pai knownnter Heinrich - although Diesbach not understood in Berlin in 1704-5,in which any sense is why - it since is also the known beginning as Berlin of chemistry, blue. (Diesbach e.g. Prussian was attempting to createblue a paint, Aureolin with ,aand red copperhue.) It vitriolhas several. different chemical names, these being iron(III) ferrocyanide, ferric ferrocyanide, iron(III) hexacyanoferrate(II), and ferricThe hexacyanoferrate. key breakthrough Commonly occurred when and c Alfredonveniently Werner it isproposed, simply called "PB. inter alia, that Co(III) bears six ligands in an octahedral geometry. Aureolin (sometimes called Cobalt Yellow) is a pigment used in oil and watercolor painting. Its color index name is PY40 (40th entry on list of yellow pigments). It was first made in 1851 and its chemical composition is potassium cobaltinitrite. Copper(II) sulfate ("sulphate" in most Commonwealth nations) is the chemical compound with the formula CuSO4. This salt exists as a series of compounds that differ in their degree of hydration. The anhydrous form is a pale green or gray-white powder, while the pentahydrate, the most commonly encountered salt, is bright blue. This hydrated copper sulfate occurs in nature as the mineral called chalcanthite. The archaic name for copper(II) sulfate is "blue vitriol" or "bluestone" Nobel Prize for Chemistry Alfred Werner 1913 For complexes with more than one type of ligand, Werner succeeded in explainingIn 1893, Werner the number was the of firstisomers to proposobserved.e correct For structuresexemple, hefor explained coordination the compounds containing complex ions, in which a central transition metal atom is existence of two isomers of "Co(NH3)4Cl3", one green and one purple. Werner surrounded by neutral or anionic ligands. proposed that these are two geometric isomers of formula [Co(NH3)4Cl2]Cl, with oneFor example,Cl- ion dissociated it was known as confirmed that coba ltby forms conductivity a "complex" measurements. with formula The Co CoCl •6NH , but the nature of the association indicated by the dot was atom 3is surrounded3 by four NH3 and two Cl ligands at the vertices of an 3+ octahedron.mysterious. WernerThe green proposed isomer the is "trans structure" with [Co(NH the two3) 6Cl]Cl ligands3, with the at oppositeCo ion vertices,surrounded and by the six purple NH3 at is the "cis" vertices with the of twoan octahedron.Cl at adjacent The vertices. three Cl- are dissociated as free ions, which he confirmed by measuring the electrical conductivity of the compound in aqueous solution. History What is coordination compound? Coordination complexes were known - although not understood in any sense - since the beginning of chemistry, e.g. Prussian blue, Aureolin, and copper vitriol. The key breakthrough occurred when Alfred Werner proposed, inter alia, that Co(III) bears six ligands in an octahedral geometry. The theory allows one to understand the difference between coordinated and ionic chloride in the cobalt ammine chlorides and to explain many of the previously inexplicable isomers. He resolved the first coordination complex into optical isomers, overthrowing the theory that chirality was necessarily associated with carbon compounds. History What is ligand? In chemistry, a ligand is an atom, ion, or molecule that generally donates one or more of its electrons through a coordinate covalent bond to one or more central atoms or ions (these ligands act as a Lewis base). The ligands that are directly bonded to the metal (that is, share electrons), are called "inner sphere" ligands. If the inner-sphere ligands do not balance the charge of the central atom, this may be done by simple ionic bonding with another set of counter ions (the "outer-sphere" ligands). The complex of the metal with the inner sphere ligands is then called a complex ion (which can be either cationic or anionic). The complex, along with its counter ions, is called a coordination compound. The size of a ligand is indicated by its cone angle. History Organometallic Compound Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Organometallic chemistry combines aspects of inorganic chemistry and organic chemistry. Organometallic compounds find practical use in stoichiometric and catalytically active compounds. Electron counting is key in understanding organometallic chemistry. The 18-electron rule is helpful in predicting the stabilities of organometallic compounds. Organometallic compounds which have 18 electrons (filled s, p, and d orbitals) are relatively stable. This suggests the compound is isolable, but it can result in the compound being inert. Nomenclature – Common Monodentate Ligands Classical (or "Werner Complexes"): Ligands in classical coordination chemistry bind to metals. Organometallic: Ligands are organic (alkenes, alkynes, alkyls) as well as "organic-like" ligands such as phosphines, hydride, and CO. Bioinorganic: Ligands are those provided by nature, especially including the side chains of amino acids, and many cofactors such as porphyrins. Example: hemoglobin Cluster: Ligands are all of the above but also include other metals as ligands. Example Ru3(CO)12 Nomenclature – Common Monodentate Ligands Ambidentate Ligand Nomenclature – Common Chelating Amines Monodentate, bidentate, tri-, tetra-, penta-, hexadentate Nomenclature – Common Multidentate (chelating) Ligands Nomenclature – Bridging Ligands M M N R NN R R N R N N N -O2C CO2- -O2C CO2- Nomenclature – Modern Ligands (Porphyrin) Porphyrin coordinated to magnesium: chlorophyll Porphyrin Photodynamic Therapy(PDT) Porphyrin coordinated to iron: heme Nomenclature – Modern Ligands (Porphyrin) Photodynamic Therapy(PDT) Shown is close up of surgeons' hands in an operating room with a "beam of light" traveling along fiber optics for photodynamic therapy. A patient would be given a photo sensitive drug (photofrin) containing cancer killing substances which are absorbed by cancer cells. 9During the surgery, the light beam is positioned at the tumor site, which then activates the drug that kills the cancer cells, thus photodynamic therapy (PDT). Nomenclature – Modern Ligands Salen nd Grubbs' Catalyst 2 Generation Me Me Me Me Jacobsen epoxidation N N Cl Me Me Ru Cl Ph P(Cy)3 Nomenclature – Modern Ligands (Weak-Link Approach) Mirkin’s Weak-Link Nomenclature – Nomenclature Rules 1. Cation comes first, followed by anion 2. The inner coordination sphere is enclosed in square brackets in the formula. Nomenclature: Ligand → Metal Formula: Metal → Ligand 3. Prefixe Nomenclature – Nomenclature Rules 4. Ligands are named in alphabetical order. (not prefix) 5. Anionic ligands are given an o suffix. Neutral ligands retain their name. Water is called aqua. Ammonia is called amine. 6. Designating charge or oxidation number Stock system: oxidation number of the metal as a Roman nummeral in parentheses. Ewing-Bassett system: charge on the coordination sphere in parentheses Nomenclature – Nomenclature Rules 7. The prefixs cis- and trans- designate adjacent and opposite 8. Bridging ligands between metal ions have the prefix μ. 9. When the complexes is negatively chared. Nomenclature – Nomenclature Rules Na2[NiCl4] sodium tetrachloronickelate(II) Pt(NH3)2Cl4 diamminetetrachloroplatinum(IV) Fe(CO)5 pentacarbonyliron(0) (NH4)2[Ni(C2O4)2(H2O)2] ammonium diaquabis(oxalato)nickelate(II) [Ag(NH3)2][Ag(CN)2] diamminesilver(I) dicyanoargentate(I) Isomerism Isomerism Are the bonds between the same atoms? Yes No Stereo or configurational isomers Structural or Are the molecule has a mirror plane? constitutional isomers Yes No Ionization isomers, Linkage isomers, Coordination isomers, Diastereomers or Enantiommers or Hydrate isomers geometric isomers optical isomers 4 CN ; Square planar Cis and trans Chiral isomers 4 CN ; Tetrahedral Only one structure Isomerism - Stereoisomers 4 CN ; Square planar Cisplatin, cisplatinum or cis- diamminedichloroplatinum(II) (CDDP) is a platinum-based chemotherapy drug used to treat various types of cancers, Cis and It transwas the first member of its class, Antitumor agent: cisplatin which now also includes carboplatin and oxaliplatin. Chelate can induce the cis structure Isomerism - Stereoisomers 4 CN ; Tetrahedral Only one structure With four different ligands or with unsymmetrical chelating ligands Three? Isomerism - Stereoisomers 6 CN ; Octahedron H N H2N NH2 diethylenetriamine facial and meridional Isomerism - Stereoisomers 6 CN ; Octahedron, Triethylentetraamine H N NH2 H2N N H No coplanar rings Two coplanar rings Three coplanar rings Isomerism - Stereoisomers Number of possible Isomers Isomerism - Stereoisomers Number of possible Isomers Ma3bcd a a da ad facial c a a c b b no mirror plane meridional a a a dadaba b c c b d c a a a Isomerism - Stereoisomers Number of possible
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