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12_TransitionMetals_1 - Transi'on Metals Chapters 6.8-6.9...

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Unformatted text preview: Transi'on Metals Chapters 6.8-6.9, 23.7, 24 Transi'on Metals 1 Transi'on Metals Occupy the d-block of periodic table Have d-electrons in valence shell Some characteris'cs of Transi'on Metals and their compounds: 1. Exhibit more than one oxida'on state 2. They form an extensive series of compounds known as metal complexes or coordina'on compounds. 3. Transi'on metals exhibit interes'ng magne'c proper'es. 4. Many of their compounds are colored. 5. Transi'on metals play important roles in biological systems and modern technology. Transi'on Metals 2 Periodic trends There are periodic trends in the transition metals, but they are often complex (product of several factors, some working in opposite directions e.g. combining the effects of increasing nuclear charge with the presence of nonbonding d electrons) Lanthanide contraction similarity in size, behavior, properties of 4d and 5d transition elements We won't worry about details of periodic trends in the transition metals or the exact reasons for them Transi'on Metals 3 Electron Configura'ons Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn [Ar] 3d104s2 Transi'on Metals 4 3s23p6 [Ar]4s1 [Ar]4s2 [Ar]3d14s2 [Ar]3d24s2 Transition metal ATOMS Orbital filling in First Row: Sc Zn ELECTRON CONFIGURATIONS Transition Metal IONS Ti Ti2+ Ti3+ Ti4+ Ti5+ Ni4+ Ni2+ [Ar]3d24s2 Ni [Ar]3d84s2 Note: 4s is filled before 3d, but when oxidized, 4s electrons are lost before 3d. Transi'on Metals 5 Transition Metal Oxidation States Oxidation States: Highest oxidation states of Sc, Ti, V, Cr, Mn = number of valence (4s + 3d) electrons. Sc [Ar]3d14s2 Mn [Ar]3d54s2 Trend from Sc Mn: The maximum oxidation state becomes increasingly unstable. Sc3+, Ti4+ Are stable. Sc2O3 & TiO4 are stable oxides. Mn7+ Exists but is easily reduced. MnO4Strong oxidizing agent. Transi'on Metals 6 Electron Configura'ons and Oxida'on States Many transi'on metals form compounds that have fun colors! colors are due to oxida'on state and electron configura'on...more specifics about that later! Transi'on Metals 7 METAL COMPLEXES Transition metal ions are Lewis acids Ligands are Lewis bases Transi'on Metals 8 Complexes Metal complex: metal surrounded by molecules metal is bonded to molecules or ions Complex ion: metal complex that is not neutral Coordina'on compounds: compounds that contain complexes Coordina'on number: # of atoms directly bonded to a metal Transi'on Metals 9 Metal-Ligand Bonds The coordina'on of the ligand with the metal can greatly alter its physical or chemical proper'es EXAMPLE: color Transi'on Metals 10 Reduc'on Poten'al of Metal Complexes Chemical proper'es: Solubility of Transi'on Metal Complexes depends on reduc'on poten'al of the metal complex. Which is easier to reduce, the metal ion or the complex? Ag+(aq) + e- Ag(s) E1/2= +0.80V [Ag(CN)2]-(aq) + e- Ag(s)+ 2CN-(aq) E1/2 = -0.31V Transi'on Metals 11 Oxida'on State and Coordina'on Number Coordina'on Sphere: the central atom + ligands bonded to it Use [ ] to set off components in the coordina'on sphere Oxida'on State: "primary valence" Coordina'on Number: "secondary valence" 12 Transi'on Metals Transi'on Metal Complexes and Oxida'on Numbers Knowing the charge on a complex ion and the charge on each ligand, one can determine the oxida'on number for the metal. Or, knowing the oxida'on number on the metal and the charges on the ligands, one can calculate the charge on the complex ion. [Cu(NH3)4)]SO4 Charge on the complex: Coordina'on #: Oxida'on state of the metal: Transi'on Metals 13 Transi'on Metal Complexes and Oxida'on Numbers K2[Ni(CN)4)] Charge on the complex: Coordina'on #: Oxida'on state of the metal: Fe3+ surrounded by six water molecules Charge on the complex: Coordina'on number: Pt(II) surrounded by two ammonia molecules and two bromide ions Charge on the complex: Coordina'on number: Transi'on Metals 14 Geometries of Transi'on Metal Complexes Geometry for Coordination # = 4 Tetrahedral Square Planar [Ni(CN)4]2- [Zn(NH3)4]2+ [PtCl2(NH3)2] Transi'on Metals 15 Geometries of Transi'on Metal Complexes Geometry for Coordination # = 5 Trigonal Bipyramidal [Re(SCH2C6H4OCH3-p)3(PPh3)2] ReL3(PR3)2 [Fe(CO)5] Transi'on Metals 16 Geometries of Transi'on Metal Complexes Geometry for Coordination # = 6 Octahedral chromium(III) and cobalt(III) consistently have the same coordina'on number of 6 [CoF6]3- [Co(en)3]3+ Transi'on Metals 17 Special Ligands: Chela'ng Agents Chelates are ligands possessing two or more donor atoms. Mono-dentate Ligands Examples: [Cu(H2O)2(NH3)2]2+ Bi-dentate Ligands Example: ethylenediamine :NH2CH2CH2 :NH2 = en [Cu(H2O)2(en)]2+ Transi'on Metals 18 Bi-dentate Ligands Transi'on Metals 19 Special Ligands: Chela'ng Agents Poly-dentate ligands Example: ethylenediaminetetraace'c acid (EDTA) Applica7ons/Uses: Transi'on Metals 20 Applications: sequestering metal ions ethylenediaminetetraacetic acid (EDTA) Removes trace metals ions that catalyze food decomposi7on Used in poison control Transi'on Metals 21 Uses of Chela7ng Agents to soHen water Used in shampoo to remove trace metals from hard water (Ca2+ and Mg2+): EDTA Na5P3O10 Used in detergents to remove trace amounts of dissolved metals: Transi'on Metals 22 Special Ligands: Chela'ng Agents Other Polydentate Ligands Porphine In complexes: porphyrins Transi'on Metals 23 Biological Applications Myoglobin Protein that stores oxygen in cells Ferrichrome Neutral molecule that can bind iron very strongly (Kf 1030) Transports Fe into cells Transi'on Metals 24 Important Chela7ng Agents Chelate Ethylenediamine (en) Porphine EDTA Oxalate (C2O42-) Carbonate (CO32-) # of Coordination Sites Charge Transi'on Metals 25 METAL COMPLEX STABILITY Cu(OH2)42+ + 4NH3 Cu(NH3)42+ + 4H2O Cu2+(aq) + 4NH3 Cu(NH3)42+ + 4H2O Kf VALUES OF SOME COMPLEXES [Ag(NH3)2] + [Cu(NH3)4] 2+ [Cu(CN)4 ] 2[Ag(CN)2 ] [Ag(S2O3)2 ] 3Transi'on Metals 1.7 x 107 5 x 1012 1 x 1025 1 x 1021 2.9 x 1013 26 THE CHELATE EFFECT Chela7ng ligands form excep%onally stable metal complexes when compared to related monodentate ligands. [Ni(H2O)6]2+ + 6 NH3 [Ni(H2O)6]2+ + 3 en [Ni(NH3)6]2+ + 6H2O [Ni(en)3]2+ + 6H2O Kf = 4x108 Kf = 2x1018 [Ni(NH3)6]2+ + 3 en [Ni(en)3]2+ + 6 NH3 What is the expression for the formation constant for this reaction? Transi'on Metals 27 THE CHELATE EFFECT Chela7ng ligands form excep%onally stable metal complexes when compared to related monodentate ligands. This "chelate effect" is due to : 1) Probability 2) Entropy Effects Probability Effect: Cd+2 NH2CH3 H2 N Cd+2 NH2 NH2CH3 Transi'on Metals 28 Entropy and the Chelate Effect 1) Cd2+ + 4CH3NH2 [Cd(CH3NH2)4]2+ 2) Cd2+ + 2en [Cd(en)2]2+ + 4H2O Ligand 1 2 Methyl amine CH3NH2 H(kJ) -57.3 -56.5 S(J/K) G -37.2kJ -60.7kJ H = -57.3 kJ H = -56.5 kJ Why is S so much larger? [Cd(H2O)4]2+ + 4 CH3NH2 [Cd(H2O)4]2+ + 2 en Transi'on Metals [Cd(CH3NH2)4]2+ + 4H2O [Cd(en)2]2+ + 4H2O 29 Magne'c Proper'es of Transi'on Metals Many transition metal compounds are colored (diverse range of colors), and many have interesting magnetic properties. Diamagnetic Paramagnetic Ferromagnetic MAGNETIC PROPERTIES Diamagne7c: unaffected by a magne'c field Paramagne7c: influenced by a magne'c field Ferromagne7c: permanent magne'c field Transi'on Metals 30 Magnetism The magnetic properties of a complex depend on the number of unpaired electrons Na+ Mn2+ Ti2+ Co3+ Experiment shows: [Co(CN)6]3 has no unpaired electrons [CoF6]3 has four unpaired electrons WHY do they have different numbers of unpaired electrons? Transi'on Metals 31 CRYSTAL FIELD THEORY M in spherical Oh Field - - - - - - E d orbitals in free metal ion (all degenerate) d orbitals in uniform, "spherical" field of negative charge; all orbitals raised in energy equally Presence of ligand electrons raises energy of metal d orbitals due to electrostatic repulsion Transi'on Metals 32 Crystal Field Theory Which metal d orbitals are most affected by the metal-ligand bonding electrons? Depends on geometry of the complex: (where are the electrons?) For an octahedral complex: Transi'on Metals 33 Crystal Field Splinng Crystal Field Splitting of d orbitals in octahedral ligand field Transi'on Metals 34 Transi'on metals in an octahedral field (6 ligands) Sc+3 e- config # unpaired e Ti+3 V+3 Cr+3 Mn+3 P = spin pairing energy = energy needed to pair electrons in the same orbital. Transi'on Metals 35 Crystal field splitting energy Which one will be high spin (more unpaired e-)? Low spin (fewer unpaired e-)? Transi'on Metals 36 Crystal field splitting energy = Crystal Field Splitting Energy How big is ? How does effect properties of complexes? The magnitude of depends on: Transi'on Metals 37 MAGNETIC PROPERTIES OCTAHEDRAL COMPLEXES Which of the diagrams below corresponds to [CoF6]3 and which corresponds to [Co(CN)6]3? WHY? What properties of these complexes would be different? Transi'on Metals 38 Spectrochemical Series: Ability of L to increase the energy gap Cl- < F- < H2O < NH3 < en < NO2- < CN- Increasing Transi'on Metals 39 Many transition metal complexes are colored The color of a complex depends on: 1. The element 2. Its oxidation state 3. Identity of ligands Example: V(H2O)63+ V(H2O)62+ green violet Op'cal Proper'es of TM Complexes Transi'on Metals 40 Thinking about COLOR When light of a certain wavelength is absorbed by a complex, the complex will appear the complementary color of the wavelength absorbed (you see the light that is RELFLECTED!) Transi'on Metals 41 Colors of metal complexes Visible absorption spectrum of [Ti(H2O)6]3+ : what color is it? Transi'on Metals 42 Color also depends on iden7ty of the ligands Ni2+ (aq) Op'cal Proper'es of TM Complexes [Ni(H2O)6]2+ + 6 NH3 [Ni(NH3)6]3+ + 6 H2O Transi'on Metals 43 OPTICAL PROPERTIES of TM Observed color is related to the amount of energy required to promote an electron. Compare to energy absorbed. Transi'on Metals 44 COMPLEXES: COLOR Which of these complexes absorbs light at the shorter wavelength? Which complex has the larger o? Transi'on Metals 45 ...
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