13TransitionMet - Transition Metals Occupy the d-block of...

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Unformatted text preview: Transition Metals Occupy the d-block of periodic table Have d-electrons in valence shell Some characteristics of Transition Metals and their compounds 1. 2. 3. 4. Exhibit more than one oxidation state Many of their compounds are colored They exhibit interesting magnetic properties. They form an extensive series of compounds known as metal complexes or coordination compounds. ELECTRON CONFIGURATIONS First Row: Sc → Zn Ar 3s23p6 K [Ar]4s1 Ca [Ar]4s2 Sc [Ar]3d14s2 Ti [Ar]3d24s2 . . . . . . Zn [Ar]3d104s2 Note: 4s is filled before 3d, but when oxidized, 4s electrons are lost before 3d. Ti Ti2+ Ti3+ Ti4+ Ti5+ [Ar]3d24s2 [Ar]3d24s0 [Ar]3d14s0 [Ar]3d04s0 does not exist! Transition Metals Magnetic Properties TRANSITION METALS: Sc→Mn Oxidation States: Highest oxidation states of Sc, Ti, V, Cr, Mn = number of valence (4s + 3d) electrons. Sc [Ar]3d14s2 Mn [Ar]3d54s2 Sc3+ [Ar] Mn7+[Ar] maximum maximum Diamagnetic: unaffected by a magnetic field no unpaired electrons Paramagnetic: influenced by a magnetic field unpaired electrons Transition metals and their compounds are often paramagnetic ⇒Have unpaired d-electrons Eg. Ti2+ Mn2+ Trend from Sc → Mn: The maximum oxidation state becomes increasingly unstable. Sc3+, Ti4+ are stable (maximum oxidation states). Sc2O3 Stable oxide. 7+ Mn Exists but is easily reduced. MnO4Strong oxidizing agent. COMPLEX IONS Transition metal ions are Lewis acids ⇒ they accept electron pairs. Ligands are Lewis bases ⇒ molecules or ions which donate electron pairs. Ligands bonded to metal ions ⇒ metal complexes or coordination compounds. Coordination number: number of electron donor atoms attached to the metal. Chelates are ligands possessing two or more donor atoms. TRANSITION METAL COMPLEXES [Cu(NH3)4)]SO4 SO42- + [Cu(NH3)4)]2+ Charge on the complex: Coordination #: Oxidation state of the metal: K2[Ni(CN)4)] 2 K+ + [Ni(CN)4]2Charge on the complex: Coordination #: Oxidation state of the metal: COORDINATION COMPOUNDS • • Metals-Lewis acids Ligands -Lewis bases. Ligand molecules have lone pair electrons. – Anions F−, Cl−, Br−, CN−, SCN−, NO2−, etc. – Neutral ligands-ex. NH3, H2O, CO – mono-dentate -(single claw to hold onto metal d orbital) Ex. :NH3, H-:O:-H , CH3-:O:-H – Bi-dentate -(has 2 claws to hold onto metal d orbitals). Has 2 or more functional groups on ligands that have lone pairs Ex H2N:-CH2-CH2-:NH2 (en or ethylenediammine) – Polydentate-EDTA (ethylenediaminetetraacetic acid) COORDINATION COMPOUNDS Important Chelating Agents Chelate # of Coordination Sites Charge Coordination # = 4 Tetrahedral, e.g. [Zn(NH3)4]2+ Ethylenediamine Porphine EDTA Square Planar, e.g. [Ni(CN)4]2− Oxalate (C2O42-) Carbonate (CO32-) [PtCl2(NH3)2] Cl Pt Cl NH3 NH3 COORDINATION COMPOUNDS Coordination # = 5 Trigonal Bipyramidal, e.g. [Fe(CO)5] COORDINATION COMPOUNDS Coordination # = 6 Octahedral e.g. [CoF6]3F F F Co F F F OC OC O C Fe C O CO e.g. [Co(en)3]3+ N N Co N N N N IMPORTANT CHELATING LIGANDS Porphine IMPORTANT CHELATING LIGANDS EDTA O HOCCH2 O NCH2CH2N : CH2COH CH2COH O N HN HOCCH2 O : NH N METAL COMPLEX STABILITY Uses of Chelating Agents • Used to “sequester” metal ions • Used in detergents to remove trace amounts of dissolved metals: Na5P3O10 • Complex trace metals ions that catalyze food decomposition: EDTA • Used in poison control: EDTA • Used in shampoo to remove trace metals from hard water (Ca2+ and Mg2+): EDTA Ag(NH3)2+ Cu(NH3)42+ Cu(CN)42− Ag(CN)2− Ag(S2O3)23− 1.7 x 107 5 x 1012 1 x 1025 1 x 1021 2.9 x 1013 Cu(OH2)42+ + 4NH3 ↔ Cu(NH3)42+ + 4H2O Cu2+(aq) + 4NH3 ↔ Cu(NH3)42+ + 4H2O [H2O] = constant KF = [Cu(NH ) ] [Cu ][NH ] 2+ 3 4 2+ 4 3 Formation constant Kf VALUES OF SOME COMPLEXES CHELATING EFFECT Chelating ligands (> 1 points of attachment) form more stable compounds. [Ni(H2O)6]2+ + 6NH3 ↔ [Ni(NH3)6]2+ + 6H2O Kf = 4x108 [Ni(H2O)6]2+ + 3en ↔ [Ni(en)3]2+ + 6H2O Kf = 2x1018 DUE TO PROBABILITY AND ENTROPY EFFECTS Cd2+ + 4CH3NH2 ↔ [Cd(CH3NH2)4]2+ ∆G° = −37.2kJ ∆H° = −57.3kJ ∆S° = 67.3J/K Cd2+ + 2en ↔ [Cd(en)2]2+ ∆G° = −60.7kJ ∆H° = −56.5kJ ∆S° = +14.1J/K CRYSTAL FIELD THEORY CRYSTAL FIELD THEORY Presence of ligand electrons raises energy of metal d orbitals due to electrostatic repulsion CRYSTAL FIELD SPLITTING Crystal Field Splitting of d orbitals in octahedral ligand field E E d orbitals in uniform, “spherical” field of negative charge d orbitals in free metal ion (all degenerate) e (dz2, dx2–y2) ∆ “delta octahedral” t (dxy, dxz, dyz) d orbitals in uniform, “spherical” field of negative charge d orbitals in octahedral field electrostatic repulsion raises the energies of all the orbitals ∆ = Crystal field splitting energy Spectrochemical series CN− >NO2−> en > NH3 > H2O> F− >Cl− Increasing ∆ SPECTROCHEMICAL SERIES CRYSTAL FIELD SPLITTING ENERGY ∆ depends on 1. Metal 2. Oxidation state 3. Ligands P spin pairing energy P does not depend on the ligands CNCO NO2- Strong field ligands en NH3 H2 O Oxalate OHFSCN- Weak field ligands ClBrI- P < ∆ ⇒ Low Spin Complexes. P > ∆ ⇒ High Spin Complexes. absorbs observed MAGNETIC PROPERTIES OCTAHEDRAL COMPLEXES OPTICAL PROPERTIES COLOR Color depends on identity of the ligands E [Ni(H2O)6]2+ + 6 NH3 → [Ni(NH3)6]3+ + 6 H2O CoF63QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. High spin Paramagnetic Co(CN)63Low spin (spin paired) diamagnetic COLOR When light of a certain wavelength is absorbed by a complex, the complex will appear the complementary color of the wavelength absorbed OPTICAL PROPERTIES COLOR COMPLEXES: COLOR Which of these complexes absorbs light at the shorter wavelength? Which complex has the larger ∆o? Compare ∆ to energy absorbed. ...
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