CHM 116 Ch 24-Coordination Compounds

CHM 116 Ch 24-Coordination Compounds - Chapter 24 Chemistry...

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1 1 1 Chapter 24 Chemistry of Coordination Compounds z Transition metal compounds z Variable oxidation number z Unusual composition z Coordinate covalent bonds z Ligands z Colored z Unusual magnetic properties 2 Chapter 24 Chemistry of Coordination Compounds Topics z Structure z Geometry z Ligands vs Counter ions z Nomenclature z Isomerism z Color and Magnetism z Crystal Field Theory (Bonding Theory) 3 24.1 The Structure of Complexes z Contain coordinate covalent bonds z Called complex ion if charged z [Cu(NH 3 ) 4 ]SO 4 . H 2 O hydrate anion ligands central metal ion 4 Coordination Compounds z Complex ion: [Cu(NH 3 ) 4 ] 2 + z Coordination compound: K 2 CuCl 4 z Complex ion: [CuCl 4 ] 2 - z Exist in aqueous equilibria z Examples in nature: z heme z chlorophyll z enzymes 5 Coordination Sphere z Nature of coordination compounds is determined by both the oxidation number of the central ion and its coordination number. z Coordination number z # of coordinate covalent bonds to transition metal z The coordination number is (mostly) constant for a metal with a given oxidation number. 6 First Coordination Sphere
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2 2 7 First Coordination Sphere z Mostly predictable geometry: z Coordination number = 2, linear z Coordination number = 4, square planar or tetrahedral z Coordination number = 6, octahedral 8 Complex Ion Geometry z Tetrahedral, square planar, octahedral 9 Ligands z Molecules or anions (rarely cations) z Anions are named with the anion name, but with an ending of -o z (eg. chloro) z Molecules have special names z (eg. H 2 O is aqua and NH 3 is ammine) 10 Formula and Names of Some Ligands H 2 O aqua NH 3 ammine CO carbonyl NO nitrosyl OH - hydroxo O 2 - oxo F - fluoro Cl - chloro Br - bromo I - iodo -CN - cyano -NC - isocyano -NCS - isothiocyanato -SCN - thiocyanato SO 4 2 - sulfato NO 3 - nitrato -NO 2 - nitro -ONO - nitrito CO 3 2 - carbonato H 2 NCH 2 CH 2 NH 2 ethylenediamine 11 24.2 Chelates z Types of Ligands z Monodentate: attach at only one atom (:NH 3 ) z Polydentate: attach at two or more separated atoms (called chelates) z ethylenediamine (en): NH 2 CH 2 CH 2 NH 2 (bidentate) z ethylenediaminetetraacetic acid (EDTA): (HOOCCH 2 ) 2 NCH 2 CH 2 N(CH 2 COOH) 2 attaches at up to six positions - at 2 Ns and 4 Os 12 Chelates z Co(en) 3 3+ z en = H 2 NCH 2 CH 2 NH 2 z What is the C.N.?
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3 3 13 Chelating Ligands 14 Chelate Effect z Chelating ligands give much larger values of formation constants (K f ) [Ni(H 2 O) 6 ] 2+ + 6NH 3 U [Ni(NH 3 ) 6 ] 2+ + 6H 2 O K f = 4 × 10 8 [Ni(H 2 O) 6 ] 2+ + 3en U [Ni(en) 3 ] 2+ + 6H 2 O K f = 2 × 10 18 z Sequestering agents are chelating agents that are used to remove unwanted metal ions. z In medicine sequestering agents are used to selectively remove toxic metal ions (e.g. Hg 2+ and Pb 2+ ) while leaving biologically important metals. 15 Chelating Ligands z One very important chelating agent is ethylenediaminetetraacetate (EDTA 4- ).
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This note was uploaded on 06/09/2008 for the course CHM 116 taught by Professor Unknown during the Spring '08 term at ASU.

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CHM 116 Ch 24-Coordination Compounds - Chapter 24 Chemistry...

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