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Chapter 23

Chapter 23. The Transition Elements and Their Coordination Compounds. The Transition Elements and Their Coordination Compounds. 23.1 Properties of the Transition Elements. 23.2 The Inner Transition Elements. 23.3 Highlights of Selected Transition Metals. 23.4 Coordination Compounds.

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Chapter 23

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  1. Chapter 23 The Transition Elements and Their Coordination Compounds

  2. The Transition Elements and Their Coordination Compounds 23.1 Properties of the Transition Elements 23.2 The Inner Transition Elements 23.3 Highlights of Selected Transition Metals 23.4 Coordination Compounds 23.5 Theoretical Basis for the Bonding and Properties of Complexes

  3. The transition elements (d block) and inner transition elements (f block) in the periodic table. Figure 23.1

  4. The transition metals show great similarities within a given period and a group. Their Chemistry does not change as number of valence electron change. They are metals good conductors of heat and electricity: Ex: Ag. More than one oxidation state. General Properties:

  5. Complex ions: Species where transition metal ion is surrounded by a certain number of ligands. Ligand: Molecules or ions that behave as Lewis bases. Paramagnetic-unpaired electrons. General Properties:

  6. Cr: Cu: Mo3+ Ag+ The energy of 3d orbitals in transition metal ions is less than 4s orbitals. Electronic Configurations:

  7. 1. Atomic size decreases from left to right across the period , but then remain fairly constant. 2. Transition elements exhibit a small change in electronegativity. The values are intermediate. 3. First Ionization energies increase little. 4. Lanthanide contraction- 4f orbitals are filled, increases overall charge on nucleus and not the size. Atomic and Physical Properties of Transition Elements:

  8. Horizontal trends in key atomic properties of the Period 4 elements. Figure 23.3

  9. 5.Nuclear charge increases down a group. 6. Heavier transition metals exhibit more covalent character. 7. First I.E increases down a transitional group. 8. Densities increase as atomic mass increases. Atomic and Physical Properties of Transition Elements:

  10. Figure 23.4 Vertical trends in key properties within the transition elements. Electronegativity increases down a group. 2nd and 3rd element nearly same size 1st IE highest at bottom of trans group. Densities increase as mass increases

  11. 1. They have multiple oxidation states. 2. +2 oxi state is most common as ns2 electrons are readily lost. 3. Ionic bonding occurs in lower O.S and covalent in higher O.S. 4. Electrons in a partially filled d sublevels can absorb visible wavelengths and hence their compounds are colored. 5. They are paramagnetic (unpaired d electrons) 6. IE1 increases down a group. Chemical Properties

  12. PROBLEM: The alloy SmCo5 forms a permanent magent because both samarium and cobalt have unpaired electrons. How many unpaired electrons are in the Sm atom (Z = 62)? PLAN: Write the condensed configuration of Sm and, using Hund’s rule and the aufbau principle, place electrons into a partial orbital diagram. 6s 4f 5d Sample Problem 23.2 Finding the Number of Unpaired Electrons SOLUTION: Sm is the eighth element after Xe. Two electrons go into the 6s sublevel and the remaining six electrons into the 4f (which fills before the 5d). Sm is [Xe]6s24f6 There are 6 unpaired e- in Sm.

  13. They contain atleast one Complex ion , bonded to ligands and associated with other counter ions. Coordination compound: Complex transitional metal ion attached to ligands. Two types of valance: 1. secondary Valence- Ability of metal ion to bind to a Lewis base(ligands)-Coordination number. 2. Primary valence-Ability of metal ion to form ionic bonds with oppositely charged ions.-Oxidation state. Coordination compounds:

  14. Complex ions: Species where transition metal ion is surrounded by a certain number of ligands. Ligand: Molecules or ions that behave as Lewis bases. Coordination compounds:

  15. Structures of Complex Ions: Coordination Numbers, Geometries, and Ligands • Coordination Number - the number of ligand atoms that are bonded directly to the central metal ion. The coordination number is specific for a given metal ion in a particular oxidation state and compound. • Geometry - the geometry (shape) of a complex ion depends on the coordination number and nature of the metal ion. • Donor atoms per ligand - molecules and/or anions with one or more donor atoms that each donate a lone pair of electrons to the metal ion to form a covalent bond.

  16. Varies from 2-8. 6 ligands-octahedral arrangement. 4-Tetrahedral/Square planar. 2- Linear. Most common coord. Number is 6. The coordination number

  17. models wedge diagrams chemical formulas Components of a coordination compound. Figure 23.9 6 ligands-octahedral 4 ligands-square planar

  18. Neutral molecule or ion having a lone pair of electron that can be used to form a bond to metal ion. Metal (Lewis acid-e pair acceptor) _______ Nonmetal ( Lewis base- e pair donor) Monodentate/ Unidentate ligand- Ligand forms 1 bond.CN-, H2O, NH3. Ligands:

  19. Chelating ligands/ Chelates: Ligands have more than one atom with a lone pair of electrons that can be used to bond a metal ion. Bidentate ligand- can form 2 bonds.Ex: ethylenediamine(en), oxalate Polydentate ligands- can form more than 2 bonds.Ex: EDTA- 6 bonds. Ligands

  20. Formulas and Names of Coordination Compounds Rules for writing formulas: 1. The cation is written before the anion. 2. The charge of the cation(s) is balanced by the charge of the anion(s). 3. In the complex ion, neutral ligands are written before anionic ligands, and the formula for the whole ion is placed in brackets.

  21. Formulas and Names of Coordination Compounds continued Rules for naming complexes: 1. The cation is named before the anion. 2. Within the complex ion, the ligands are named, in alphabetical order, before the metal ion. 3. Neutral ligands generally have the molecule name, but there are a few exceptions. Anionic ligands drop the -ide and add -o after the root name. 4. A numerical prefix indicates the number of ligands of a particular type. 5. The oxidation state of the central metal ion is given by a Roman numeral (in parentheses). 6. If the complex ion is an anion we drop the ending of the metal name and add -ate.

  22. Name cation before anion. In naming a complex ion, name ligands before the metal ion. In naming ligands, add o to the root name of anion(chloro), Use the full name for a neutral ligand . Exceptions to # 3: aqua, ammine, methylamine, carbonyl, nitrosyl. Nomenclature:

  23. . Use prefix mono, di, tri, tetra , penta and hexa for simple ligands. 6. Use prefix bis,tris,tetrakis for complicated ligands that alreadt have bi,tri. 7. Oxidation state for metal in Roman numerals in () 8. When more than one type of ligand are present name alphabetically. 9. If complex ion has negative charge add the suffix -ate to the name of the metal.(Latin name) Iron copper lead silver gold tin Nomenculature

  24. Sample Problem 23.3 Writing Names and Formulas of Coordination Compounds PROBLEM: (a) What is the systematic name of Na3[AlF6]? (b) What is the systematic name of [Co(en)2Cl2]NO3? (c) What is the formula of tetraaminebromochloroplatinum(IV) chloride? (d) What is the formula of hexaaminecobalt(III) tetrachloro-ferrate(III)? PLAN: Use the rules presented - and . SOLUTION: (a) The complex ion is [AlF6]3-. Six (hexa-) fluorines (fluoro-) are the ligands - hexafluoro Aluminum is the central metal atom - aluminate Aluminum has only the +3 ion so we don’t need Roman numerals. sodium hexafluoroaluminate

  25. (c) tetraaminebromochloroplatinum(IV) chloride (d) hexaaminecobalt(III) tetrachloro-ferrate(III) Sample Problem 23.3 Writing Names and Formulas of Coordination Compounds continued (b) There are two ligands, chlorine and ethylenediamine - dichloro, bis(ethylenediamine) The complex is the cation and we have to use Roman numerals for the cobalt oxidation state since it has more than one - (III) The anion, nitrate, is named last. dichlorobis(ethylenediamine)cobalt(III) nitrate 4 NH3 Br- Cl- Pt4+ Cl- [Pt(NH3)4BrCl]Cl2 6 NH3 Co3+ 4 Cl- Fe3+ [Co(NH3)6][Cl4Fe]3

  26. ISOMERS Same chemical formula, but different properties Constitutional (structural) isomers Stereoisomers Figure 23.10 Important types of isomerism in coordination compounds. Atoms connected differently Different spatial arrangement Coordination isomers Ligand and counter-ion exchange Linkage isomers Different donor atom Geometric (cis-trans) isomers (diastereomers) Different arrangement around metal ion Optical isomers (enantiomers) Nonsuperimposable mirror images

  27. Same formula but different properties. Structural isomerism: Isomers contain same atoms but different bonds. Coordination isomerism: Composition of complex ion varies. Linkage isomerism: Point of attachment of atleast one of the ligands differs Isomerism:

  28. Stereoisomers: All bonds are same but different spatial arrangements. Geometrical isomerism –cis-trans-Atoms or group of atoms can assume different positions around a rigid ring or bond. Optical Isomerism: Have opposite effects on plane polarized light. Chiral: Objects that have nonsuperimposable mirror images. Enantiomers: Isomers that are nonsuperimposable mirror images of each other. Isomerism

  29. Linkage isomers

  30. Geometric (cis-trans) isomerism. Figure 23.11

  31. Figure 23.12 Optical isomerism in an octahedral complex ion.

  32. PROBLEM: Draw all stereoisomers for each of the following and state the type of isomerism: Sample Problem 23.4 Determining the Type of Stereoisomerism (a) [Pt(NH3)2Br2] (b) [Cr(en)3]3+ (en = H2NCH2CH2NH2) PLAN: Determine the geometry around each metal ion and the nature of the ligands. Place the ligands in as many different positions as possible. Look for cis-trans and optical isomers. SOLUTION: (a) Pt(II) forms a square planar complex and there are two pair of monodentate ligands - NH3 and Br. These are geometric isomers; they are not optical isomers since they are superimposable on their mirror images. trans cis

  33. Sample Problem 23.4 Determining the Type of Stereoisomerism continued (b) Ethylenediamine is a bidentate ligand. Cr3+ is hexacoordinated and will form an octahedral geometry. Since all of the ligands are identical, there will be no geometric isomerism possible. The mirror images are nonsuperimposable and are therefore optical isomers.

  34. Figure 23.13 Hybrid orbitals and bonding in the octahedral [Cr(NH3)6]3+ ion.

  35. Figure 23.14 Hybrid orbitals and bonding in the square planar [Ni(CN)4]2- ion.

  36. Figure 23.15 Hybrid orbitals and bonding in the tetrahedral [Zn(OH)4]2- ion.

  37. It focuses on the energies of d orbitals. Metal –ligand bond is ionic. Ligands are negative point charges. The Crystal Field Model

  38. An artist’s wheel. Figure 23.16

  39. Dz2 and dx2-y2 orbitals have lobes that point directly at the ligands. Dxy, dyz,dxy point their lobes between charges. Electrons fill the d orbitals farthest from the ligands to minimize repulsion. Dxy, dyz,dxy ( t2g set) are at lower energy in octahedral complex first. Dz2 and dx2-y2 (eg set) is at higher energy. Octahedral complexes:

  40. Splitting of 3d orbital energies explains color and magnetism. Strong field case- splitting produced by ligands is very large, electrons will pair in lower t2g orbitals. Diamagnetic (all electrons are paired) Weak field case-splitting produced by ligands is small, electrons will occupy all 5 orbitals before pairing occurs. Paramagnetic( unpaired electrons) Octahedral complexes:

  41. The five d-orbitals in an octahedral field of ligands. Figure 23.17

  42. 1.Fe (CN)63- has one unpaired electron . Does the CN- ligand produce a strong or weak field? 2.Predict the number of unpaired electrons in the complex ion [Cr(CN)6] 4 – Problems:

  43. I- < Cl- < F- < OH- < H2O < SCN- < NH3 < en < NO2- < CN- < CO STRONGER FIELD WEAKER FIELD LARGER D SMALLER D LONGER  SHORTER  The spectrochemical series. Figure 23.22 • For a given ligand, the color depends on the oxidation state of the metal ion. • For a given metal ion, the color depends on the ligand.

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