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John C. Kotz Paul M. Treichel John Townsend http://academic.cengage.com/kotz Chapter 22 The Chemistry of the Transition Elements John C. Kotz • State University of New York, College at Oneonta 2 Important – Read Before Using Slides in Class Instructor: This PowerPoint presentation contains photos and figures from the text, as well as selected animations and videos. For animations and videos to run properly, we recommend that you run this PowerPoint presentation from the PowerLecture disc inserted in your computer. Also, for the mathematical symbols to display properly, you must install the supplied font called “Symb_chm,” supplied as a cross-platform TrueType font in the “Font_for_Lectures” folder in the "Media" folder on this disc. If you prefer to customize the presentation or run it without the PowerLecture disc inserted, the animations and videos will only run properly if you also copy the associated animation and video files for each chapter onto your computer. 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Thank you. © 2009 Brooks/Cole - Cengage 3 Transition Metal Chemistry © 2009 Brooks/Cole - Cengage 4 Transition Metal Chemistry © 2009 Brooks/Cole - Cengage 5 Gems & Minerals Citrine and amethyst are quartz (SiO2) with a trace of cationic iron that gives rise to the color. © 2009 Brooks/Cole - Cengage 6 Gems & Minerals © 2009 Brooks/Cole - Cengage Rhodochrosite, MnCO3 Reactions: Transition Metals Fe + Cl2 Fe + O2 © 2009 Brooks/Cole - Cengage Fe + HCl 7 Periodic Trends: Atom Radius © 2009 Brooks/Cole - Cengage 8 Periodic Trends: Density © 2009 Brooks/Cole - Cengage 9 Periodic Trends: Melting Point © 2009 Brooks/Cole - Cengage 10 Periodic Trends: Oxidation Numbers Most common © 2009 Brooks/Cole - Cengage 11 12 Metallurgy: Element Sources © 2009 Brooks/Cole - Cengage 13 Pyrometallurgy • Involves high temperature, such as Fe • C and CO used as reducing agents in a blast furnace • Fe2O3 + 3 C f 2 Fe + 3 CO • Fe2O3 + 3 CO f 2 Fe + 3 CO2 • Lime added to remove impurities, chiefly SiO2 SiO2 + CaO f CaSiO3 • Product is impure cast iron or pig iron © 2009 Brooks/Cole - Cengage 14 Metallurgy: Blast Furnace See Active Figure 22.8 © 2009 Brooks/Cole - Cengage Metallurgy: Blast Furnace Molten iron is poured from a basic oxygen furnace. © 2009 Brooks/Cole - Cengage 15 16 Metallurgy: Copper Ores Azurite, 2CuCO3·Cu(OH)2 Native copper © 2009 Brooks/Cole - Cengage 17 Metallurgy: Hydrometallurgy • Uses aqueous solutions • Add CuCl2(aq) to ore such as CuFeS2 (chalcopyrite) CuFeS2 (s) + 3 CuCl2 (aq) f 4 CuCl(s) + FeCl2 (aq) + 2 S(s) • Dissolve CuCl with xs NaCl CuCl(s) + Cl-(aq) f [CuCl2]• Cu(I) disproportionates to Cu metal 2 [CuCl2]- f Cu(s) + CuCl2 (aq) + 2 Cl- © 2009 Brooks/Cole - Cengage Electrolytic Refining of Cu SeeFigure 22.11 © 2009 Brooks/Cole - Cengage 18 19 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. © 2009 Brooks/Cole - Cengage CH2 CH2 - Cl Pt Cl Cl Coordination Chemistry Pt(NH3)2Cl2 “Cisplatin” - a cancer chemotherapy agent Co(H2O)62+ Cu(NH3)42+ © 2009 Brooks/Cole - Cengage 20 Coordination Chemistry An iron-porphyrin, the basic unit of hemoglobin © 2009 Brooks/Cole - Cengage 21 22 Vitamin B12 A naturally occurring cobalt-based compound Co atom © 2009 Brooks/Cole - Cengage 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 N-fixing 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. © 2009 Brooks/Cole - Cengage 23 24 Coordination Compounds of Ni2+ © 2009 Brooks/Cole - Cengage Nomenclature Ni(NH3)6]2+ A Ni2+ ion surrounded by 6, neutral NH3 ligands Gives coordination complex ion with 2+ charge. © 2009 Brooks/Cole - Cengage 25 26 Nomenclature Inner coordination sphere Ligand: monodentate + Cl- Ligand: bidentate Co3+ + 2 Cl- + 2 neutral ethylenediamine molecules Cis-dichlorobis(ethylenediamine)cobalt(II) chloride © 2009 Brooks/Cole - Cengage 27 Common Bidentate Ligands Bipyridine (bipy) Acetylacetone (acac) Ethylenediamine (en) © 2009 Brooks/Cole - Cengage Oxalate (ox) 28 Acetylacetonate Complexes Commonly called the “acac” ligand. Forms complexes with all transition elements. © 2009 Brooks/Cole - Cengage Multidentate Ligands EDTA4- - ethylenediaminetetraacetate ion Multidentate ligands are sometimes called CHELATING ligands © 2009 Brooks/Cole - Cengage 29 Multidentate Ligands Co2+ complex of EDTA4- © 2009 Brooks/Cole - Cengage 30 31 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 [CuCl4]2- = tetrachlorocuprate 6. Oxidation no. of metal ion indicated © 2009 Brooks/Cole - Cengage Nomenclature [Co(H2O)6]2+ Hexaaquacobalt(II) H2O as a ligand is aqua Pt(NH3)2Cl2 [Cu(NH3)4]2+ Tetraamminecopper(II) diamminedichloroplatinum(II) NH3 as a ligand is ammine © 2009 Brooks/Cole - Cengage 32 Nomenclature Pt( Tris(ethylenediamine)nickel(II) [Ni(NH2C2H4NH2)3]2+ IrCl(CO)(PPh3)2 Vaska’s compound Carbonylchlorobis(triphenylphosphine)iridium(I) © 2009 Brooks/Cole - Cengage 33 Structures of Coordination Compounds © 2009 Brooks/Cole - Cengage 34 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. © 2009 Brooks/Cole - Cengage 35 36 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] © 2009 Brooks/Cole - Cengage 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. © 2009 Brooks/Cole - Cengage 37 38 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. © 2009 Brooks/Cole - Cengage 39 Geometric Isomerism Cis and trans-dichlorobis(ethylenediamine)cobalt(II) chloride © 2009 Brooks/Cole - Cengage Geometric Isomerism Fac isomer © 2009 Brooks/Cole - Cengage Mer isomer 40 41 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 © 2009 Brooks/Cole - Cengage 42 An Enantiomeric Pair [Co(NH2C2H4NH2)3]2+ © 2009 Brooks/Cole - Cengage Stereoisomerism 43 [Co(en)(NH3)2(H2O)Cl]2+ N N Cl Co 2+ NH3 NH3 OH2 NH3 2+ N NH3 Co N Cl OH2 © 2009 Brooks/Cole - Cengage 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. 44 Stereoisomerism These are non-superimposable mirror images [Co(en)(NH3)2(H2O)Cl]2+ © 2009 Brooks/Cole - Cengage 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 f ligand field theory © 2009 Brooks/Cole - Cengage 45 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 © 2009 Brooks/Cole - Cengage 46 Bonding in Coordination Compounds © 2009 Brooks/Cole - Cengage 47 Crystal Field Theory • Consider what happens as 6 ligands approach an Fe3+ ion [Ar] All electrons have the same energy in the free ion five 3d orbitals 4s Orbitals split into two groups as the ligands approach. energy eg t2g © 2009 Brooks/Cole - Cengage d(x2-y2) dxy dxz 2 dz dyz ²E = ² o Value of ∆o depends on ligand: e.g., H2O > Cl- 48 Octahedral Ligand Field © 2009 Brooks/Cole - Cengage 49 Tetrahedral & Square Planar Ligand Field © 2009 Brooks/Cole - Cengage 50 51 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 t2 © 2009 Brooks/Cole - Cengage dxy dxz d(x2-y2) dyz dz2 ²E = ² t 52 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 on size of ∆o and P, the pairing energy. • P = energy required to create e- pair. © 2009 Brooks/Cole - Cengage Magnetic Properties/Fe2+ d(x2-y2) eg dxy energy t2g • High spin dz dxz 2 ² E small dyz Paramagnetic d(x2-y2) dxy dxz t2g eg dz2 dyz Diamagnetic © 2009 Brooks/Cole - Cengage 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? 53 High and Low Spin Octahedral Complexes See Figure 22.25 High or low spin octahedral complexes only possible for d4, d5, d6, and d7 configurations. © 2009 Brooks/Cole - Cengage 54 Crystal Field Theory Why are complexes colored? Fe3+ © 2009 Brooks/Cole - Cengage Co2+ Ni2+ Cu2+ Zn2+ 55 56 Crystal Field Theory Why are complexes colored? – © 2009 Brooks/Cole - Cengage 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 Absorption band © 2009 Brooks/Cole - Cengage 57 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. © 2009 Brooks/Cole - Cengage 58 59 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. © 2009 Brooks/Cole - Cengage 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. © 2009 Brooks/Cole - Cengage 60 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+ © 2009 Brooks/Cole - Cengage 61 Prussian blue contains Fe3+ and Fe2+
