Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download Transition Metal Chemistry
Document related concepts
Transcript
Chemistry and Chemical Reactivity 6th Edition 1 John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 22 The Chemistry of the Transition Elements Lectures written by John Kotz ©2006 2006 Brooks/Cole Thomson © Brooks/Cole - Thomson 2 Transition Metal Chemistry © 2006 Brooks/Cole - Thomson 3 Transition Metal Chemistry © 2006 Brooks/Cole - Thomson 4 Gems & Minerals Citrine and amethyst are quartz (SiO2) with a trace of cationic iron that gives rise to the color. © 2006 Brooks/Cole - Thomson 5 Gems & Minerals © 2006 Brooks/Cole - Thomson Rhodochrosite, MnCO3 Reactions: Transition Metals Fe + Cl2 Fe + O2 © 2006 Brooks/Cole - Thomson Fe + HCl 6 Periodic Trends: Atom Radius © 2006 Brooks/Cole - Thomson 7 Periodic Trends: Density © 2006 Brooks/Cole - Thomson 8 Periodic Trends: Melting Point © 2006 Brooks/Cole - Thomson 9 Periodic Trends: Oxidation Numbers Most common © 2006 Brooks/Cole - Thomson 10 11 Metallurgy: Element Sources © 2006 Brooks/Cole - Thomson 12 Pyrometallurgy • Involves high temperature, such as Fe • C and CO used as reducing agents in a blast furnace • Fe2O3 + 3 C ---> 2 Fe + 3 CO • Fe2O3 + 3 CO ---> 2 Fe + 3 CO2 • Lime added to remove impurities, chiefly SiO2 SiO2 + CaO ---> CaSiO3 • Product is impure cast iron or pig iron © 2006 Brooks/Cole - Thomson 13 Metallurgy: Blast Furnace Active Figure 22.8 © 2006 Brooks/Cole - Thomson Metallurgy: Blast Furnace Molten iron is poured from a basic oxygen furnace. © 2006 Brooks/Cole - Thomson 14 15 Metallurgy: Copper Ores Azurite, 2CuCO3•Cu(OH)2 Native copper © 2006 Brooks/Cole - Thomson 16 Metallurgy: Hydrometallurgy • Uses aqueous solutions • Add CuCl2(aq) to ore such as CuFeS2 (chalcopyrite) CuFeS2 (s) + 3 CuCl2 (aq) --> 4 CuCl(s) + FeCl2 (aq) + 2 S(s) • Dissolve CuCl with xs NaCl CuCl(s) + Cl-(aq) --> [CuCl2]• Cu(I) disproportionates to Cu metal 2 [CuCl2]- --> Cu(s) + CuCl2 (aq) + 2 Cl© 2006 Brooks/Cole - Thomson Electrolytic Refining of Cu Figure 22.11 © 2006 Brooks/Cole - Thomson 17 18 Coordination Chemistry • Coordination compounds – combination of two or more atoms, ions, or molecules where a bond is formed by sharing a pair of electrons originally associated with only one of the compounds. © 2006 Brooks/Cole - Thomson CH2 Pt CH2 - Cl Cl Cl Coordination Chemistry Pt(NH3)2Cl2 “Cisplatin” - a cancer chemotherapy agent Co(H2O)62+ Cu(NH3)42+ © 2006 Brooks/Cole - Thomson 19 Coordination Chemistry An iron-porphyrin, the basic unit of hemoglobin © 2006 Brooks/Cole - Thomson 20 21 Vitamin B12 A naturally occurring cobalt-based compound Co atom © 2006 Brooks/Cole - Thomson Nitrogenase • • • • • Biological nitrogen fixation contributes about half of total nitrogen input to global agriculture, remainder from Haber process. To produce the H2 for the Haber process consumes about 1% of the world’s total energy. A similar process requiring only atmospheric T and P is carried out by Nfixing bacteria, many of which live in symbiotic association with legumes. N-fixing bacteria use the enzyme nitrogenase — transforms N2 into NH3. Nitrogenase consists of 2 metalloproteins: one with Fe and the other with Fe and Mo. © 2006 Brooks/Cole - Thomson 22 23 Coordination Compounds of Ni2+ © 2006 Brooks/Cole - Thomson Nomenclature Ni(NH3)6]2+ A Ni2+ ion surrounded by 6, neutral NH3 ligands Gives coordination complex ion with 2+ charge. © 2006 Brooks/Cole - Thomson 24 25 Nomenclature Inner coordination sphere Ligand: monodentate + Cl- Ligand: bidentate Co3+ + 2 Cl- + 2 neutral ethylenediamine molecules Cis-dichlorobis(ethylenediamine)cobalt(II) chloride © 2006 Brooks/Cole - Thomson 26 Common Bidentate Ligands Bipyridine (bipy) Acetylacetone (acac) Ethylenediamine (en) © 2006 Brooks/Cole - Thomson Oxalate (ox) 27 Acetylacetonate Complexes Commonly called the “acac” ligand. Forms complexes with all transition elements. © 2006 Brooks/Cole - Thomson Multidentate Ligands EDTA4- - ethylenediaminetetraacetate ion Multidentate ligands are sometimes called CHELATING ligands © 2006 Brooks/Cole - Thomson 28 Multidentate Ligands Co2+ complex of EDTA4- © 2006 Brooks/Cole - Thomson 29 30 Nomenclature Cis-dichlorobis(ethylenediamine)cobalt(III) chloride 1. Positive ions named first 2. Ligand names arranged alphabetically 3. Prefixes -- di, tri, tetra for simple ligands bis, tris, tetrakis for complex ligands 4. If M is in cation, name of metal is used 5. If M is in anion, then use suffix -ate CuCl42- = tetrachlorocuprate 6. Oxidation no. of metal ion indicated © 2006 Brooks/Cole - Thomson Nomenclature Co(H2O)62+ Hexaaquacobalt(II) H2O as a ligand is aqua Pt(NH3)2Cl2 Cu(NH3)42+ Tetraamminecopper(II) diamminedichloroplatinum(II) NH3 as a ligand is ammine © 2006 Brooks/Cole - Thomson 31 Nomenclature Pt( Tris(ethylenediamine)nickel(II) [Ni(NH2C2H4NH2)3]2+ IrCl(CO)(PPh3)2 Vaska’s compound Carbonylchlorobis(triphenylphosphine)iridium(I) © 2006 Brooks/Cole - Thomson 32 Structures of Coordination Compounds © 2006 Brooks/Cole - Thomson 33 Isomerism • Two forms of isomerism – Constitutional – Stereoisomerism • Constitutional – Same empirical formula but different atomto-atom connections • Stereoisomerism – Same atom-to-atom connections but different arrangement in space. © 2006 Brooks/Cole - Thomson 34 35 Constitutional Isomerism Aldehydes & ketones OH2 H2O Cl Cl Cr H2O Cl OH2 green O CH3-CH2-CH O H3C C CH3 OH2 H2O OH2 Cl3 Cr H2O OH2 OH2 violet Peyrone’s chloride: Pt(NH3) 2Cl2 Magnus’s green salt: [Pt(NH3)4][PtCl4] © 2006 Brooks/Cole - Thomson Linkage Isomerism NH3 2+ H3N NO2 sunlight Co H3N NH3 NH3 2+ NH3 H3N ONO Co H3N NH3 NH3 Such a transformation could be used as an energy storage device. © 2006 Brooks/Cole - Thomson 36 37 Stereoisomerism • One form is commonly called geometric isomerism or cis-trans isomerism. Occurs often with square planar complexes. cis trans Note: there are VERY few tetrahedral complexes. Would not have geometric isomers. © 2006 Brooks/Cole - Thomson 38 Geometric Isomerism Cis and trans-dichlorobis(ethylenediamine)cobalt(II) chloride © 2006 Brooks/Cole - Thomson Geometric Isomerism Fac isomer © 2006 Brooks/Cole - Thomson Mer isomer 39 40 Stereoisomerism • Enantiomers: stereoisomers that have a nonsuperimposable mirror image • Diastereoisomers: stereoisomers that do not have a non-superimposable mirror image (cistrans isomers) • Asymmetric: lacking in symmetry—will have a non-superimposable mirror image • Chiral: an asymmetric molecule © 2006 Brooks/Cole - Thomson 41 An Enantiomeric Pair [Co(NH2C2H4NH2)3]2+ © 2006 Brooks/Cole - Thomson Stereoisomerism 42 [Co(en)(NH3)2(H2O)Cl]2+ Cl N N Co 2+ NH3 NH3 OH2 NH3 2+ N NH3 Co N Cl OH2 © 2006 Brooks/Cole - Thomson NH3 2+ These two isomers have N Cl a plane of symmetry. Co N OH2 Not chiral. NH3 NH3 2+ N NH3 Co N OH2 Cl These two are asymmetric. Have non-superimposable mirror images. 43 Stereoisomerism These are non-superimposable mirror images [Co(en)(NH3)2(H2O)Cl]2+ © 2006 Brooks/Cole - Thomson Bonding in Coordination Compounds • Model must explain – – – – Basic bonding between M and ligand Color and color changes Magnetic behavior Structure • Two models available – Molecular orbital – Electrostatic crystal field theory – Combination of the two ---> ligand field theory © 2006 Brooks/Cole - Thomson 44 Bonding in Coordination Compounds • As ligands L approach the metal ion M+, – L/M+ orbital overlap occurs – L/M+ electron repulsion occurs • Crystal field theory focuses on the latter, while MO theory takes both into account © 2006 Brooks/Cole - Thomson 45 Bonding in Coordination Compounds © 2006 Brooks/Cole - Thomson 46 Crystal Field Theory • Consider what happens as 6 ligands approach an Fe3+ ion All electrons have the same energy in the free ion five 3d orbitals [Ar] 4s Orbitals split into two groups as the ligands approach. energy eg t2g © 2006 Brooks/Cole - Thomson d(x2-y2) dxy dxz 2 dz dyz ²E = ² o Value of ∆o depends on L: e.g., H2O > Cl- 47 Octahedral Ligand Field © 2006 Brooks/Cole - Thomson 48 Tetrahedral & Square Planar Ligand Field © 2006 Brooks/Cole - Thomson 49 50 Crystal Field Theory •Tetrahedral ligand field •Note that ∆t = 4/9 ∆o and so ∆t is small •Therefore, tetrahedral complexes tend to blue end of spectrum energy e dxy dxz dyz ²E = ² t2 © 2006 Brooks/Cole - Thomson d(x2-y2) dz2 t 51 Ways to Distribute Electrons • For 4 to 7 d electrons in octahedral complexes, there are two ways to distribute the electrons. – High spin — maximum number of unpaired e– Low spin — minimum number of unpaired e- • Depends size of ∆o and P, the pairing energy. • P = energy required to create e- pair. © 2006 Brooks/Cole - Thomson Magnetic Properties/Fe2+ energy d(x2-y2) eg • High spin dz 2 ² E small dxy t2g dxz dyz Paramagnetic d(x2-y2) dxy dxz t2g eg dz2 dyz Diamagnetic © 2006 Brooks/Cole - Thomson ² E large energy • Weak ligand field strength and/or lower Mn+ charge • Higher P possible? • Low spin • Stronger ligand field strength and/or higher Mn+ charge • Lower P possible? 52 High and Low Spin Octahedral Complexes Figure 22.25 High or low spin octahedral complexes only possible for d4, d5, d6, and d7 configurations. © 2006 Brooks/Cole - Thomson 53 Crystal Field Theory • Why are complexes colored? Fe3+ © 2006 Brooks/Cole - Thomson Co2+ Ni2+ Cu2+ Zn2+ 54 Crystal Field Theory • Why are complexes colored? – Note that color observed is transmitted light Absorption band © 2006 Brooks/Cole - Thomson 55 56 Crystal Field Theory Why are complexes colored? – © 2006 Brooks/Cole - Thomson Note that color observed for Ni2+ in water is transmitted light Crystal Field Theory • Why are complexes colored? – Note that color observed is transmitted light – Color arises from electron transitions between d orbitals – Color often not very intense • Spectra can be complex – d1, d4, d6, and d9 --> 1 absorption band – d2, d3, d7, and d8 --> 3 absorption bands • Spectrochemical series — ligand dependence of light absorbed. © 2006 Brooks/Cole - Thomson 57 58 Light Absorption by Octahedral Co3+ Complex d(x -y ) dxz dxy dz2 Ground state + energy (= ² o) dyz 2 (light absorbed) t2g eg d(x2-y2) dxy t2g 2 dz2 dxz eg energy energy Excited state Usually excited complex returns to ground state by losing energy, which is observed as heat. © 2006 Brooks/Cole - Thomson dyz Spectrochemical Series • d orbital splitting (value of ∆o) is in the order I- < Cl- < F- < H2O < NH3 < en < phen < CN- < CO As ∆ increases, the absorbed light tends to blue, and so the transmitted light tends to red. © 2006 Brooks/Cole - Thomson 59 Other Ways to Induce Color • Intervalent transfer bands (IT) between ion of adjacent oxidation number. – Aquamarine and kyanite are examples – Prussian blue • Color centers – Amethyst has Fe4+ – When amethyst is heated, it forms citrine as Fe4+ is reduced to Fe3+ © 2006 Brooks/Cole - Thomson 60 Prussian blue contains Fe3+ and Fe2+
