A Molecular Approach, 4e - Notes for Chapter (25).doc

Chapter 25. Transition Metals and Coordination Compounds Chapter 25. Transition Metals and Coordination Compounds Chapter 25. Transition Metals and Coordination Compounds Student Objectives 25.1 The Colors of Rubies and Emeralds Know that the colors of gemstones are attributable to electronic transitions between the d-orbitals of transition elements. 25.2 Properties of Transition Metals Recall that the transition metals occupy the d block of the periodic table. Recall how to write electron configurations and determine oxidation states for d-block elements. Recall trends in radius, ionization energy, and electronegativity for d-block elements. 25.3 Coordination Compounds Define complex ion, ligand, coordination compound, and coordinate covalent bond. Recognize monodentate, bidentate, and polydentate ligands. Define chelate and chelating agent. Recognize the common geometries of complex ions. Write names and formulas for coordination compounds. 25.4 Structure and Isomerization Differentiate between structural isomers and stereoisomers. Recognize and identify coordination isomers and linkage isomers. Identify and draw geometric isomers. Recognize and draw optical isomers. 25.5 Bonding in Coordination Compounds State the hybridization of the metal center using valence bond theory for particular geometries. Explain the crystal field theory of d-orbital splitting in octahedral and tetrahedral complexes. Understand the relationship between crystal field splitting and the colors of transition metal complexes. Know the difference between weak-field, moderate-field, and strong-field ligands. Know the relationship between crystal field splitting and the magnetic properties of transition metal complexes. Understand the difference between high-spin and low-spin in transition metal complexes. Predict the number of unpaired electrons in an octahedral complex. 25.6 Applications of Coordination Compounds Know that EDTA is used as a chelating agent to bind toxic heavy metals. Know the role of transition metals in biomolecules such as hemoglobin, cytochrome c, chlorophyll, and carbonic anhydrase. Section Summaries Lecture Outline Terms, Concepts, Relationships, Skills Figures, Tables, and Solved Examples Teaching Tips Suggestions and Examples Misconceptions and Pitfalls Lecture Outline Terms, Concepts, Relationships, Skills Figures, Tables, and Solved Examples 25.1 The Colors of Rubies and Emeralds Crystal field Cr3+ in Al2O3 (ruby, red) in Be3Al2(SiO3)6 (emerald, green) Fe2+ in garnet (red) in peridot (yellow-green) Cu2+ in turquoise Intro figure: illustration of ruby color and the shape of the orbital unnumbered figure: photos of ruby, emerald, garnet, peridot, turquoise 25.2 Properties of Transition Metals Electron configurations Periodic properties atomic radius first ionization energy electronegativity Oxidation states Table 25.1 First-Row Transition Metal Orbital Occupancy Examples 25.1 and 25.2 Writing Electron Configurations for Transition Metals Figure 25.1 Trends in Atomic Radius Figure 25.2 Trends in First Ionization Energy Figure 25.3 Trends in Electronegativity Figure 25.4 First-Row Transition Metal Oxidation States 25.3 Coordination Compounds Coordination complex complex ion plus counterions Common ligands monodentate: water, ammonia, chloride, carbon monoxide, thiocyanate bidentate: oxalate, ethylenediamine polydentate: ethylenediamine tetraacetate Geometries and coordination number linear square planar tetrahedral octahedral Names ligands and prefixes metal center names of metals in anionic complexes unnumbered figure: molecular model of [Co(NH3)6]Cl3 Table 25.2 Common Ligands Figure 25.5 Bidentate and Polydentate Ligands Coordinated to Co(III) Table 25.3 Common Geometries of Complex Ions unnumbered table: Guidelines for Naming Complex Ions Table 25.4 Names and Formulas of Common Ligands Table 25.5 Names of Common Metals when Found in Anionic Complex Ions Examples 25.3 and 25.4 Naming Coordination Compounds Teaching Tips Suggestions and Examples Misconceptions and Pitfalls 25.1 The Colors of Rubies and Emeralds The colors of gemstones due to transition metals in different mineral environments are an introduction to crystal field theory, coordination compounds, and complex ions. 25.2 Properties of Transition Metals The electron configurations of transition metals follow the rules and guidelines set forth previously in Section 8.4. Conceptual Connection 25.1 Atomic Size Oxidation states are likely to be somewhat confusing because of the variety of values some elements can assume. In general, the first-row transition metals can have oxidation states of +2 and +3. Elements in the center of the row have more possible states than the ones on the ends. For example, Sc is only +3, Zn is only +2, but Mn can be any state from +2 to +7. Electron configurations of the first-row transition metals fill the 4s before the 3d unless all the 3d orbitals can be filled evenly (e.g., Cr and Cu). When forming cations of transition metals, remove electrons from the 4s before the 3d. 25.3 Coordination Compounds Students may be confused about the organization of metal cations, ligands, and additional properties for complex ions. Table 25.2 lists the common ligands, and Table 25.3 lists the shapes and coordination numbers. Likewise, one can often predict the geometry given the formula of a complex ion. Students may struggle predicting the formulas of complex ions. For example, what does Fe2+ form when reacted with ammonia? Naming complex ions follows some basic guidelines. Often, coordination chemistry relies more on structures than on names. In complexes, all of the valence electrons on the metal are found in the d-orbitals. For this reason, complexes of Ir+ are isoelectronic with complexes of Pt2+ and Au3+. Lecture Outline Terms, Concepts, Relationships, Skills Figures, Tables, and Solved Examples 25.4 Structure and Isomerization Structural isomers coordination isomers linkage isomers Stereoisomers geometric isomers cis-trans fac-mer optical isomers Figure 25.6 Types of Isomers Figure 25.7 Linkage Isomers Table 25.6 Ligands Capable of Linkage Isomerization Figure 25.8 Cis-trans Isomerism Figure 25.9 Fac-Mer Isomerism in Co(NH3)3Cl3 Examples 25.5 and 25.6 Identifying and Drawing Geometric Isomers Figure 25.10 Optical Isomerism in [Co(en)3]3+ Example 25.7 Recognizing and Drawing Optical Isomers 25.5 Bonding in Coordination Compounds Valence bond theory geometry hybridization orbitals Crystal field theory d orbital orientation octahedral field splitting pattern strong field weak field colors and crystal field splitting energy spectrochemical series magnetism high-spin low-spin tetrahedral field splitting pattern square planar field splitting pattern Figure 25.11 Common Hybridization Schemes in Complex Ions Figure 25.12 Relative Positions of d Orbitals and Ligands in an Octahedral Complex Figure 25.13 d Orbital Splitting in an Octahedral Field Figure 25.14 Colors of Complex Ions Figure 25.15 The Color Wheel Figure 25.16 The Color and Absorption Spectrum of [Ti(H2O)6]3+ Example 25.8 Crystal Field Splitting Energy unnumbered figures: orbital diagrams of low- and high-spin Fe2+ complexes Examples 25.9 and 25.10 High- and Low-Spin Octahedral Complexes Figure 25.17 Splitting of d Orbitals by a Tetrahedral Ligand Geometry Figure 25.18 Splitting of d Orbitals by a Square Planar Ligand Geometry Teaching Tips Suggestions and Examples Misconceptions and Pitfalls 25.4 Structure and Isomerization Some ligands can be attached in two distinct ways, giving rise to linkage isomers. Models are likely to be very helpful for seeing or visualizing the arrangement of the ligands in octahedral structures. Fac and mer require three ligands of the same kind in an octahedron. Visualizing optical isomerism in octahedral complexes is much more difficult than in tetrahedral complexes. Models are essential for the beginning student. Tetrahedral complexes cannot exhibit cis-trans isomerism, and square planar complexes cannot exhibit optical isomerism. 25.5 Bonding in Coordination Compounds The crystal field model is completely electrostatic and views all ligands as merely point negative charges. This model does not explain the spectrochemical series at all. Strong- and weak-field effects of ligands can be confirmed by the number of unpaired electrons in octahedral complexes. Demonstrations of color (especially cobalt complexes) and magnetism (diamagnetism, paramagnetism, and number of unpaired electrons) are easy and highly illustrative. Conceptual Connection 25.2 Weak- and Strong-Field Ligands Students often will simply memorize the splitting patterns for octahedral, tetrahedral, and square planar complexes. These patterns can be simply deduced by considering the orientation of the d orbitals and the positions of the incoming ligands. Students often confuse the terms weak- and strong-field with high- and low-spin. Lecture Outline Terms, Concepts, Relationships, Skills Figures, Tables, and Solved Examples 25.6 Applications of Coordination Compounds Chelating agents: EDTA Chemical analysis: SCN Coloring agents Biomolecules hemoglobin and cytochrome c: iron in porphyrin ligand chlorophyll: magnesium in porphyrin carbonic anhydrase: zinc Drugs and therapeutic agents cisplatin: cis-[Pt(NH3)2Cl2] Figure 25.19 Chemical Analysis with SCN Table 25.7 Transition Metals and Some of Their Functions in the Human Body unnumbered figure: structures of cytochrome c, heme Figure 25.20 Porphyrin Figure 25.21 Hemoglobin Figure 25.22 Chlorophyll Figure 25.23 Carbonic Anhydrase Figure 25.24 Cisplatin Teaching Tips Suggestions and Examples Misconceptions and Pitfalls 25.6 Applications of Coordination Compounds The use of chelating agents to remove lead and mercury is a documented treatment when a case of heavy metal poisoning is known or strongly suspected. With an unsubstantiated belief that mercury-containing preservatives found in a few antiviral vaccines cause autism, some children are being subjected to EDTA treatment. What are some of the potential dangers or hazards of chelation therapy? Additional Problem for Writing Electron Configurations for Transition Metals (Examples 25.1, 25.2) Write the ground state electron configuration for Nb and Nb3+. Identify noble gas Identify the noble gas that precedes the element and put it in square brackets. Nb is atomic number 41 in period 5 and group 5B. Complete noble gas shell = [Kr] Count the periods Count down the periods to determine the outer principal quantum level—this is the quantum level for the s orbital. Subtract one to obtain the quantum level for the d orbital. Nb is in the 5th period: [Kr] 5s4d Count electrons Count across the row to see how many electrons are in the neutral atom and fill the orbitals accordingly. For an ion, remove the required number of electrons, first from the s and then from the d orbitals. Nb has 5 more electrons than [Kr]: [Kr] 5s24d3 Nb3+ has lost three electrons relative to Nb: [Kr] 5s04d2 or [Kr] 4d2 Additional Problem for High- and Low-Spin Octahedral Complexes (Example 25.9, 25.10) How many unpaired electrons would you expect for the complex ion [Cu(NH3)6]2+? Charge and number of d electrons Begin by determining the charge and number of d electrons on the metal. complex ion = +2 NH3: 6 @ +0 = 0 Cu: 1 @ +2 = +2 Cu2+ Cu: [Ar] 4s13d10 Cu2+: [Ar] 4s03d9 Cu2+ has d9 configuration. Ligands in spectrochemical series Look at the spectrochemical series to determine whether the ligand is a strong-field or weak-field ligand. NH3 is a strong-field ligand, so will be relatively large. High-spin or low-spin? Decide if the complex will be high- or low-spin and draw the electron configuration. Strong-field ligands yield low-spin configurations. Unpaired electrons Count the unpaired electrons. This configuration has one unpaired electron. 328 Copyright © 2017 by Education, Inc. 329 Copyright © 2017 by Education, Inc.