Transcript Chapter 21
Chapter 21 Transition Metals and Coordination Chemistry Chapter 21 Table of Contents 21.1 21.2 21.3 21.4 21.5 21.6 21.7 21.8 The Transition Metals: A Survey The First-Row Transition Metals Coordination Compounds Isomerism Bonding in Complex Ions: The Localized Electron Model The Crystal Field Model The Biologic Importance of Coordination Complexes Metallurgy and Iron and Steel Production Copyright © Cengage Learning. All rights reserved 2 Section 21.1 The Transition Metals: A Survey Industry : Fe , Cu , Ti , Ag , table 21.1 20.1 The Transition Metals - I Biosystem : transport , storage , catalyst , Return to TOC Section 21.1 The Transition Metals: A Survey Transition Metals • Show great similarities within a given period as well as within a given vertical group. (1) General Properties ( Sc → Cu ) a) Great similarities within a period as well as a group ∵ d subshells incomplerely filled. distinctive coloring formation of paramagnetic compounds catalytic behavior tendency to form complex ions. Return to TOC Copyright © Cengage Learning. All rights reserved 4 Section 21.1 The Transition Metals: A Survey Return to TOC Section 21.1 The Transition Metals: A Survey Cations are often complex ions – species where the transition metal ion is surrounded by a certain number of ligands (Lewis bases). The Complex Ion Co(NH3)63+ : Return to TOC Copyright © Cengage Learning. All rights reserved 6 Section 21.1 The Transition Metals: A Survey b) difference : m.p : W / Hg Hard / soft : Fe , Ti / Cu , Au , Ag Reactivity & oxides : Cu / Fe ; Fe2O3 / CrO3 (2) Electron configurations : 4s before 3d ( Cr / Cu ) Table 21.2 p.931 (3) Oxidation states most common : +2 , +3 ( +2 ～ +7 ) more than one oxidation states Return to TOC Section 21.1 The Transition Metals: A Survey Return to TOC Section 21.1 The Transition Metals: A Survey (4) Ionization energies (5) Reduction Potentials ─────→ period， reducing ability ↓ ( Zn , Cr ) ∵ Zeff ↑ r ↓ ; IE ↑ Return to TOC Section 21.2 Atomic The First-Row MassesTransition Metals • 3d transition metals Scandium – chemistry strongly resembles lanthanides Titanium – excellent structural material (light weight) Vanadium – mostly in alloys with other metals Chromium – important industrial material Manganese – production of hard steel Iron – most abundant heavy metal Cobalt – alloys with other metals Nickel – plating more active metals; alloys Copper – plumbing and electrical applications Zinc – galvanizing steel Return to TOC Copyright © Cengage Learning. All rights reserved 10 Section 21.3 The Mole Coordination Compounds A Coordination Compound • Typically consists of a complex ion and counterions (anions or cations as needed to produce a neutral compound): [Co(NH3)5Cl]Cl2 [Fe(en)2(NO2)2]2SO4 K3Fe(CN)6 Return to TOC Copyright © Cengage Learning. All rights reserved 11 Section 21.3 The Mole Coordination Compounds └→ colored & paramagnetic (often) consists of a complex ion (1) Coordination compounds are neutral species in which a small number of molecules or ions surround a central metal atom or ion. ex. [Co(NH3)5Cl]Cl2 complex ion : [Co(NH3)5Cl]2+ Return to TOC Section 21.3 The Mole Coordination Compounds coordinate covalent bond Complex ion = metal cation + ligands e acceptor e donor center (one) surrounding ( 2 ) .. .. .. transion metal H2O .. , NH3 , :Cl .. － Lewis acid Lewis base ionic force [ Co(NH3)5Cl ]Cl2 central metal ligands counter ions complex ion Return to TOC Section 21.3 The Mole Coordination Compounds (2) Coordination number : The # of donor atoms surrounding the central metal The most common : 4 or 6 Return to TOC Section 21.3 The Mole Coordination Compounds (3) Ligands : A neutral molecule or ion having a line pair that can be used to from a bond to a metal ion. monodentate : H2O, NH3 bidentate : en , ox polydentate : EDTA Chelating agents Return to TOC Section 21.3 The Mole Coordination Compounds Return to TOC p. 939, Table 21-13 Section 21.3 The Mole Coordination Compounds (4) Nomenclature : Rules for naming coordination compounds : p.940 oxidation number : Net charge = charges on (central metal + ligands) [ PtCl6]2－ [Cu(NH3)4]2＋ └→ +4 └→ +2 ex. (a) [Co(NH3)5Cl]Cl2 Pentaammine chloro cobalt(III) chloride cation anion Return to TOC Section 21.3 The Mole Coordination Compounds Return to TOC p. 940, Table 21-14 Section 21.3 The Mole Coordination Compounds (4) Nomenclature : ex. (b) K3[Fe(CN)6] potassium hexacyanoferrate (III) cation ex. (c) anion [Fe(en)2(NO2) 2]2SO4 bis (ethylenediamine) dinitro iron(III) sulfate cation anion Return to TOC Section 21.3 The Mole Coordination Compounds Exercise Name the following coordination compounds. a) [Co(H2O)6]Br3 hexaaquacobalt(III) bromide b) Na2[PtCl4] sodiumtetrachloro-platinate(II) Return to TOC Copyright © Cengage Learning. All rights reserved 20 Section 21.4 Isomerism Return to TOC Copyright © Cengage Learning. All rights reserved 21 Section 21.4 Isomerism Structural Isomerism • Coordination Isomerism: Composition of the complex ion varies. [Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4 • Linkage Isomerism: Composition of the complex ion is the same, but the point of attachment of at least one of the ligands differs. Return to TOC Copyright © Cengage Learning. All rights reserved 22 Section 21.4 Isomerism Linkage Isomerism of NO2– Return to TOC Copyright © Cengage Learning. All rights reserved 23 Section 21.4 Isomerism Stereoisomerism • Geometrical Isomerism (cis-trans): Atoms or groups of atoms can assume different positions around a rigid ring or bond. Cis – same side (next to each other) Trans – opposite sides (across from each other) Return to TOC Copyright © Cengage Learning. All rights reserved 24 Section 21.4 Isomerism Geometrical (cistrans) Isomerism for a Square Planar Compound a) cis isomer b) trans isomer Return to TOC Copyright © Cengage Learning. All rights reserved 25 Section 21.4 Isomerism Geometrical (cis-trans) Isomerism for an Octahedral Complex Ion Return to TOC Copyright © Cengage Learning. All rights reserved 26 Section 21.4 Isomerism Stereoisomerism • Optical Isomerism: Isomers have opposite effects on plane-polarized light. Return to TOC Copyright © Cengage Learning. All rights reserved 27 Section 21.4 Isomerism Optical Activity • • Exhibited by molecules that have nonsuperimposable mirror images (chiral molecules). Enantiomers – isomers of nonsuperimposable mirror images. Return to TOC Copyright © Cengage Learning. All rights reserved 28 Section 21.4 Isomerism Return to TOC p. 947, Fig. 21-17 Section 21.4 Isomerism Return to TOC Section 21.4 Isomerism Ex. 21.3 at p 948 Return to TOC p. 948, Fig. 21-13 Section 21.4 Isomerism Concept Check Does [Co(en)2Cl2]Cl exhibit geometrical isomerism? Yes Does it exhibit optical isomerism? Trans form – No Cis form – Yes Explain. Return to TOC Copyright © Cengage Learning. All rights reserved 32 Section 21.5 Bonding in Complex Ions: The Localized Electron Model Bonding in Complex Ions 1. The VSEPR model for predicting structure generally does not work for complex ions. However, assume a complex ion with a coordination number of 6 : octahedral two ligands : linear. a coordination number of 4 : tetrahedral or square planar. 2. The interaction between a metal ion and a ligand : Lewis acid–base reaction Return to TOC Copyright © Cengage Learning. All rights reserved 33 Section 21.5 Bonding in Complex Ions: The Localized Electron Model Hybrid Orbitals for 6,4, and 2 ligands Return to TOC Copyright © Cengage Learning. All rights reserved 34 Section 21.6 The Crystal Field Model • Focuses on the energies of the d orbitals. Assumptions 1. Ligands are negative point charges. 2. Metal–ligand bonding is entirely ionic: • strong-field (low–spin): large splitting of d orbitals • weak-field (high–spin): small splitting of d orbitals Return to TOC Copyright © Cengage Learning. All rights reserved 35 Section 21.6 The Crystal Field Model (1) Explains the bonding in complex ions solely in terms of electrostatic forces. (2) Two types of electrostatic forces : attraction : ( M＋ ) & ( ligand ion － or ligand ： ) repulsion : ( ligand ： ) & ( metal e in d orbitals ) (3) Consider : octahedral complexes ●● ●●● ●●●●● Return to TOC Section 21.6 The Crystal Field Model An Octahedral Arrangement of Point-Charge Ligands and the Orientation of the 3d Orbitals Return to TOC Copyright © Cengage Learning. All rights reserved 37 Section 21.6 The Crystal Field Model The Energies of the 3d Orbitals for a Metal Ion in an Octahedral Complex Return to TOC Copyright © Cengage Learning. All rights reserved 38 Section 21.6 The Crystal Field Model Possible Electron Arrangements in the Split 3d Orbitals in an Octahedral Complex of Co3+ • Strong–field (low–spin): • Weak–field (high–spin): • Yields the minimum number of unpaired electrons. • Gives the maximum number of unpaired electrons. Return to TOC Copyright © Cengage Learning. All rights reserved 39 Section 21.6 The Crystal Field Model Spectrochemical Series • a list of ligands arranged in order of their abilities to split the d orbital energies • Strong–field ligands to weak–field ligands. (large split) (small split) CN– > NO2– > en > NH3 > H2O > OH– > F– > Cl– > Br– > I– • Magnitude of split for a given ligand increases as the charge on the metal ion increases. Return to TOC Copyright © Cengage Learning. All rights reserved 40 Section 21.6 The Crystal Field Model Color : arise when complexes absorb light in some portion of the visible spectrum. (Table 21.16) ex. [Cu(H2O)6]2+ → blue = E = hn Return to TOC Section 21.6 The Crystal Field Model ex. [Ti(H2O)6]3+ max absorption at 498 nm (6.631034 Js)(3.00108 m / s) hn h 498nm109 m / nm 3.991019 J c 240kJ / m ol Return to TOC Section 21.6 The Crystal Field Model color of gems Return to TOC p. 954, Table 21-17 Section 21.6 The Crystal Field Model Concept Check Which of the following are expected to form colorless octahedral compounds? Zn2+ Cu+ Fe3+ Fe2+ Cr3+ Cu2+ Mn2+ Ti4+ Ni2+ Ag+ Return to TOC Copyright © Cengage Learning. All rights reserved 44 Section 21.6 The Crystal Field Model Tetrahedral Arrangement • None of the 3d orbitals “point at the ligands”. Difference in energy between the split d orbitals is significantly less. • d–orbital splitting will be opposite to that for the octahedral arrangement. Weak–field case (high–spin) always applies. Return to TOC Copyright © Cengage Learning. All rights reserved 45 Section 21.6 The Crystal Field Model The d Orbitals in a Tetrahedral Arrangement of Point Charges Return to TOC Copyright © Cengage Learning. All rights reserved 46 Section 21.6 The Crystal Field Model The Crystal Field Diagrams for Octahedral and Tetrahedral Complexes Tetrahedral Complexes: Difference in energy between the split d orbitals is significantly less, Weak–field case (high–spin) always applies for. Return to TOC Copyright © Cengage Learning. All rights reserved 47 Section 21.6 The Crystal Field Model Concept Check Consider the Crystal Field Model (CFM). a) Which is lower in energy, d–orbital lobes pointing toward ligands or between? Why? b) The electrons in the d–orbitals – are they from the metal or the ligands? Return to TOC Copyright © Cengage Learning. All rights reserved 48 Section 21.6 The Crystal Field Model Concept Check Using the Crystal Field Model, sketch possible electron arrangements for the following. Label one sketch as strong field and one sketch as weak field. a) Ni(NH3)62+ b) Fe(CN)63– c) Co(NH3)63+ Return to TOC Copyright © Cengage Learning. All rights reserved 49 Section 21.6 The Crystal Field Model Concept Check A metal ion in a high–spin octahedral complex has 2 more unpaired electrons than the same ion does in a low–spin octahedral complex. What are some possible metal ions for which this would be true? Metal ions would need to be d4 or d7 ions. Examples include Mn3+, Co2+, and Cr2+. Return to TOC Copyright © Cengage Learning. All rights reserved 50 Section 21.6 The Crystal Field Model Concept Check Between [Mn(CN)6]3– and [Mn(CN)6]4– which is more likely to be high spin? Why? Return to TOC Copyright © Cengage Learning. All rights reserved 51 Section 21.6 The Crystal Field Model The d Energy Diagrams for Square Planar Complexes Return to TOC Copyright © Cengage Learning. All rights reserved 52 Section 21.6 The Crystal Field Model The d Energy Diagrams for Linear Complexes Where the Ligands Lie Along the z Axis Return to TOC Copyright © Cengage Learning. All rights reserved 53 Section 21.7 The Biologic Importance of Coordination Complexes • Metal ion complexes are used in humans for the transport and storage of oxygen, as electrontransfer agents, as catalysts, and as drugs. Return to TOC Copyright © Cengage Learning. All rights reserved 54 Section 21.7 The Biologic Importance of Coordination Complexes First-Row Transition Metals and Their Biological Significance Return to TOC Copyright © Cengage Learning. All rights reserved 55 Section 21.7 The Biologic Importance of Coordination Complexes Biological Importance of Iron • Plays a central role in almost all living cells. • Component of hemoglobin and myoglobin. • Involved in the electron-transport chain. Return to TOC Copyright © Cengage Learning. All rights reserved 56 Section 21.7 The Biologic Importance of Coordination Complexes The Heme Complex Return to TOC Copyright © Cengage Learning. All rights reserved 57 Section 21.7 The Biologic Importance of Coordination Complexes Myoglobin • • The Fe2+ ion is coordinated to four nitrogen atoms in the porphyrin of the heme (the disk in the figure) and on nitrogen from the protein chain. This leaves a 6th coordination position (the W) available for an oxygen molecule. Return to TOC Copyright © Cengage Learning. All rights reserved 58 Section 21.7 The Biologic Importance of Coordination Complexes Hemoglobin • • two α chains and two β chains complex with four O2 molecules. Return to TOC Copyright © Cengage Learning. All rights reserved 59 Section 21.7 The Biologic Importance of Coordination Complexes About high altitude sickness Hb(aq) + 4O2(g) Hb(O2)4(aq) Return to TOC p. 959, Fig. 21-22 Section 21.7 The Biologic Importance of Coordination Complexes About Supercharge Blood: EPO at page 960. 1964 Winter Olympics Gold medal’s winner The 2009 Tour de France Return to TOC p. 960, Fig. 21-24