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Organic vs Inorganic What is inorganic chemistry? Inorganic Chemistry Organimetallic Bioinorganic Introduction to Inorganic Chemistry Organic vs Inorganic Introduction to Inorganic Chemistry Organic vs Inorganic Introduction to Inorganic Chemistry 8.11 Ligand chirality 8.10 Octahedral complexes 8.9 Trigonal-bipyramidal and square-pyramidal complexes 8.8 Tetrahedral complexes 8.7 Square-planar complexes Isomerism and chirality 8.6 Nomenclature 8.5 Representative ligands Ligands and nomenclature 8.4 Polymetallic complexes 8.1 High coordination numbers 8.2 Intermediate coordination numbers 8.1 Low coordination numbers Constitution and geometry Chapter 8 An Introduction to Coordination Compounds Ligand can be a atom, ion, and molecules. What is ligand? More specifically, a transition metal surrounded by neutral molecules or anions with a definite geometry. What is coordination compound? Coordination compounds include compound composed of a metal atom or ion and one or more ligands that formally donate electrons to the metal. History 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" The key breakthrough occurred when Alfred Werner proposed, Aureolin (sometimes called Cobalt Yellow) pigment used in oil and inter alia, that Co(III) bears six ligands inisana octahedral geometry. 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. Prussian blue (German: Preußischblau or Berliner Blau, in English Berlin History blue) is a dark blue pigment used in paints and formerly in blueprints. Prussian blue was discovered by accident by painter Heinrich Diesbach in What compound? Berlin in 1704-5, whichisiscoordination why it is also known as Berlin blue. (Diesbach was Coordination attempting to complexes create a paint with a red- hue.) It has different were known although notseveral understood chemical iron(III) ferrocyanide, in anynames, sense these - sincebeing the beginning of chemistry,ferric e.g. ferrocyanide, Prussian iron(III) hexacyanoferrate(II), and ferric hexacyanoferrate. Commonly and blue, Aureolin, and copper vitriol. conveniently it is simply called "PB. For complexes with more than one type of ligand, Werner succeeded in explaining the number of first isomers observed. For structures exemple, he the In 1893, Werner was the to propose correct forexplained coordination existence of containing two isomers of "Co(NH Clwhich and one purple. 3)4in 3", oneagreen compounds complex ions, central transition metal Werner proposed that are geometric isomers of formula atom is surrounded by these neutral ortwo anionic ligands. - ion dissociated as confirmed by conductivity [Co(NH withknown one Clthat 3)4Cl2]Cl, For example, it was cobalt forms a "complex" with formula measurements. The Co atom is surrounded by four NH and two Cl ligands CoCl 3•6NH3, but the nature of the association indicated3by the dot was at the vertices of an proposed octahedron. green [Co(NH isomer is) ]Cl "trans" with the two mysterious. Werner theThe structure 3 6 3, with the Co3+ Cl at opposite vertices, and the purple is "cis" with the two Cl at ionligands surrounded by six NH 3 at the vertices of an octahedron. The three Cladjacent vertices. are dissociated as free ions, which he confirmed by measuring the electrical conductivity of the compound in aqueous solution. Alfred Werner Nobel Prize for Chemistry 1913 He resolved the first coordination complex into optical isomers, overthrowing the theory that chirality was necessarily associated with carbon compounds. 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. The key breakthrough occurred when Alfred Werner proposed, inter alia, that Co(III) bears six ligands in an octahedral geometry. Coordination complexes were known - although not understood in any sense - since the beginning of chemistry, e.g. Prussian blue, Aureolin, and copper vitriol. What is coordination compound? History What is ligand? 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. 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). 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). History 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. Organometallic compounds find practical use in stoichiometric and catalytically active compounds. Organometallic chemistry combines aspects of inorganic chemistry and organic chemistry. Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Organometallic Compound History Cluster: Ligands are all of the above but also include other metals as ligands. Example Ru3(CO)12 Bioinorganic: Ligands are those provided by nature, especially including the side chains of amino acids, and many cofactors such as porphyrins. Example: hemoglobin Organometallic: Ligands are organic (alkenes, alkynes, alkyls) as well as "organic-like" ligands such as phosphines, hydride, and CO. Classical (or "Werner Complexes"): Ligands in classical coordination chemistry bind to metals. Nomenclature – Common Monodentate Ligands Size: ligand, central atom or ion Electron density Multiple bond {[Mn(H2O)6]2+SO42-} vs [Mn(H2O)5SO4] In an inner-sphere complex, the ligands are attached directly to a central metal ion: the number of ligands depends on the size of the metal, the identity of the ligands, and the electronic interactions. Constitution and geometry Position of these complexes in periodic table. Coordination number 3: with bulky ligands Coordination number 2; Cu+, Ag+, Au+, they often gain additional ligands to form three- or four- coordinate complexes. Constitution and geometry 8.1 Low coordination numbers Square-planar complexes are typically observed for metals with d8 configurations (Rh+, Ir+, Pd2+, Pt2+, Au3+). Tetrahedral complexes are favoured over higher coordinate complexes if the central atom is small or the ligands large. - ligand-ligand repulsions override the energy advantage of forming more metal-ligand bonds Four-coordination: Coordination number 4, 5, 6. They include the vast majority of complexes. Constitution and geometry 8.2 Intermediate coordination numbers Geometric isomerism Constitution and geometry 8.2 Intermediate coordination numbers Distortions from these ideal geometries are common. Square pyramidal or trigonal bipyramidal. The energies of the various geometries of five-coordinate complexes differ little from one another and such complexes are often fluxional. Five-coordination: Constitution and geometry 8.2 Intermediate coordination numbers [Fe(CO)5]; crystal, NMR, IR Berry pseudorotation Constitution and geometry 8.2 Intermediate coordination numbers