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Coordination Complexes Coordination Complexes Chapter 20 What we learn from Chap 20 • We begin the chapter with what is among the most important coordination complexes of all, iron in hemoglobin (magnesium in chlorophyll might be another). In Section 20.1, we introduce the coordinate covalent bond and reintroduce Lewis acids (central atom) and bases (ligands) as the bonding species in coordination complexes. We also discuss how carbon monoxide can replace oxygen in hemoglobin. Copyright © Houghton Mifflin Company. All rights reserved. 20 | 2 Copyright © Houghton Mifflin Company. All rights reserved. 20 | 3 CHAPTER OUTLINE I. Bonding in Coordination Complexes II. Ligands III. Coordination Number IV. Structure V. Isomers VI. Formulas and Names A. Formulas B. Nomenclature VII. Color and Coordination Compounds A. Transition Metals and Color B. Crystal-Field Theory C. Orbital Occupancy D. The Result of d Orbital Splitting E. Magnetism VIII. Chemical Reactions A. Ligand Exchange Reactions B. Electron Transfer Reactions Copyright © Houghton Mifflin Company. All rights reserved. 20 | 4 20.1 Coordination Complex • Central metal atom – transition metal. • Coordinate covalent bond • Ligand – anion or neutral compound ·· such as H2O: or :NH3. 2+ [Cu(NH3)] 3- [Fe(CN)6] Copyright © Houghton Mifflin Company. All rights reserved. 20 | 5 Complexes Protein Ferrodoxin Plastocyanin Wilkin’s catalysyst Copyright © Houghton Mifflin Company. All rights reserved. 20 | 6 20.2 Ligands • Lewis bases having a lone pair of e- to donate. • Bidentate ligands form two bonds to the metal. • Chelates are polydentate ligands. Copyright © Houghton Mifflin Company. All rights reserved. 20 | 7 Ligand Names Copyright © Houghton Mifflin Company. All rights reserved. 20 | 8 Ligands Copyright © Houghton Mifflin Company. All rights reserved. 20 | 9 Chelate Copyright © Houghton Mifflin Company. All rights reserved. 20 | 10 EDTA Copyright © Houghton Mifflin Company. All rights reserved. 20 | 11 EDTA Copyright © Houghton Mifflin Company. All rights reserved. 20 | 12 20.3 Coordination Number • Coordination number (CN) is the number of donor atoms bonded to central metal atom. • Common coordination numbers are 4 and 6. • May be as low as 2 and as high as 8. • CN determined by – The nature of metal ions : eg. Size – Charge on the ligand & metal – Electron configuration of metal Copyright © Houghton Mifflin Company. All rights reserved. 20 | 13 Coordination Number Copyright © Houghton Mifflin Company. All rights reserved. 20 | 14 Coordination Number Copyright © Houghton Mifflin Company. All rights reserved. 20 | 15 20.4 Structure • CN = 2 – linear complex, 180o bond angles. • CN = 4 – tetrahedral complex, 109o bond angles. – square planar complex (nd8electron configuration), 90o bond angles. • CN = 6 – octahedral complex, 90o bond angles. Copyright © Houghton Mifflin Company. All rights reserved. 20 | 16 Copyright © Houghton Mifflin Company. All rights reserved. 20 | 17 CN = 4 Tetrahedral Square planar 2+ 2+ 2- eg) Cu(NH3)4 , Ni(II), Pd(II), Pt(II) eg) Zn(NH3)4 , CoCl4 cf) VSEPR Model Copyright © Houghton Mifflin Company. All rights reserved. 20 | 18 Sample Problem Predict the geometry of the following complexes: + + [Ni(NH3)6]2 [Pt(NH3)2 Cl2] [Au(CN)] + [Ni(NH3)6]2 CN = 6, octahedral [Pt(NH3)2Cl2] CN = 4, square planar [Au(CN)]+ CN = 2, linear Copyright © Houghton Mifflin Company. All rights reserved. 20 | 19 20.5 Isomers Copyright © Houghton Mifflin Company. All rights reserved. 20 | 20 Linkage Isomer Copyright © Houghton Mifflin Company. All rights reserved. 20 | 21 Ionization Isomers Copyright © Houghton Mifflin Company. All rights reserved. 20 | 22 Coordination (sphere) isomers Copyright © Houghton Mifflin Company. All rights reserved. 20 | 23 Geometric Isomers - SP Cisplatin Copyright © Houghton Mifflin Company. All rights reserved. 20 | 24 Geometric Isomers - Oh Copyright © Houghton Mifflin Company. All rights reserved. 20 | 25 Geometric Isomerism Copyright © Houghton Mifflin Company. All rights reserved. 20 | 26 Optical Isomerism Copyright © Houghton Mifflin Company. All rights reserved. 20 | 27 20.6 Formulas Copyright © Houghton Mifflin Company. All rights reserved. 20 | 28 Naming Coordination Compounds Copyright © Houghton Mifflin Company. All rights reserved. 20 | 29 Sample Problem Write the formulas for the following: • Sodium hexafluorocobaltate(III) • Bisethylenediaminecopper(II) chloride Sodium hexafluorocobaltate(III) = Na3[CoF6] Bisethylenediaminecopper(II) chloride=[Cu(en)2]Cl2 Copyright © Houghton Mifflin Company. All rights reserved. 20 | 30 Sample Problem Name the following coordination compounds: [Co(H2O)2Cl2]Cl K3[Fe(CN)6] [Co(H2O)2Cl2]Cl diaquodichlorocobalt(III) chloride K3[Fe(CN)6] potassium hexacyanoferrate(III) Copyright © Houghton Mifflin Company. All rights reserved. 20 | 31 •K2[NiCl4] •[Co(NH3)6]Cl3 •[Co(NO2)2(NH3)4]2SO4 • Diamminebis(ethylenediamine) chronium(II) sulfate • Ammonium hexacyanoferrate(III) • Potassium tetrachloronikelate(II) • Hexaamminecobalt(III) Chloride • Diamminedinitrocobalt(IV) sulfate • [Cr(NH3)2(en)2]SO4 •(NH4)3[Fe(CN)3] Copyright © Houghton Mifflin Company. All rights reserved. 20 | 32 20.7 Color and Coordination Compounds • Coordination compounds are usually colored. • The color is due to partially filled d orbitals separated by an energy difference. • A photon causes a lower energy electron to move to a higher energy level. • The color is the results of the light, missing the absorbed photon, being reflected from the metal. Copyright © Houghton Mifflin Company. All rights reserved. 20 | 33 Color and Coordination Compounds Copyright © Houghton Mifflin Company. All rights reserved. 20 | 34 Crystal Field Theory • A free gaseous metal atom or ion does not show an energy level difference among the d orbitals. • In the presence of ligands, the d orbital of the metal are split by a slight energy difference, ∆o Copyright © Houghton Mifflin Company. All rights reserved. 20 | 35 Crystal Field Splitting Copyright © Houghton Mifflin Company. All rights reserved. 20 | 36 결정장모델(Crystal Field Model) Approach of six ligands to transition metal cation splits d orbitals into two sets of different• energy: explain color and magnetic properties eg d 2 2 , d 2 E x −y z △ 3/5 o ∆ ∆o o dxy , dyz , dxz 2/5△o t Free metal ion in Spherical field 2g in Oh field small ∆o large ∆o •Cristal field splitting energy ∆o , Cristal Field Stabilization Energy Copyright © Houghton Mifflin Company. All rights reserved. 20 | 37 Crystal Field Splitting Copyright © Houghton Mifflin Company. All rights reserved. 20 | 38 Crystal Field Splitting Copyright © Houghton Mifflin Company. All rights reserved. 20 | 39 High and Low Spin Copyright © Houghton Mifflin Company. All rights reserved. 20 | 40 Strong Field Ligand vs. Weak Field Ligand 2+ [CoCl ]2- [Co(H2O)6] 4 Copyright © Houghton Mifflin Company. All rights reserved. 20 | 41 2+ 2- [Co(H2O)6] [CoCl4] Copyright © Houghton Mifflin Company. All rights reserved. 20 | 42 Effect of Ligands on the Colors of Coordination Compounds Copyright © Houghton Mifflin Company. All rights reserved. 20 | 43 Spectrochemical Series • The nature of the ligand determines the magnitude of the crystal field splitting, ∆o - - - - - Cl < F < OH < H232 O < NH < NO < CN < CO (small ∆∆) (large ) Copyright © Houghton Mifflin Company. All rights reserved. 20 | 44 Magnetism • Ferromagnetism • Paramagnetism • Diamagnetism • Magnetic moment, µ=[n(n+2)]1/2 n: # unpaired electron 2+ 4- [Mn(H2O)6] µ=5.9 vs. [Mn(CN)6] µ= 2.2 Copyright © Houghton Mifflin Company. All rights reserved. 20 | 45 Strong field Weak field Hund’s Rule strong paramagnetic Copyright © Houghton Mifflin Company. All rights reserved. 20 | 46 Magnetic Properties Paramagnetism illustrated: Copyright © Houghton Mifflin Company. All rights reserved. 20 | 47 20.8 Chemical Reactions • Ligand Exchange 2+ 2+ [Cu(H2O)4] + 4NH3 → [Cu(NH3)4] + 4H2O K=4x108 2+ 2+ [Ni(NH3)6] + 3en → [Ni(en)3] +6NH3 Chelate effect (entropy) K=5x109 Copyright © Houghton Mifflin Company. All rights reserved. 20 | 48 •Labile complexes: exchange ligands rapidly 3 min. 1 day - 2+ [CoCl4] [Co(H2O)6] •Inert complexes: 3 min. 1 day exchange ligands slowly + [Cr(H O) ]3+ [CrCl2(H2O)4] 2 6 Copyright © Houghton Mifflin Company. All rights reserved. 20 | 49 Electron transfer reaction Copyright © Houghton Mifflin Company. All rights reserved. 20 | 50.
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