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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+
