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Chapter 21. Transition Metals and Coordination Chemistry The Transition Metals: A Survey General Properties Main Group Elements Main Group Elements similar properties changing properties d-block transtion elecments similar properties f-block transtion elecments Transition Metals Key reason: Last electrons added are inner electrons (d’s, f’s). These electrons d and f electrons cannot participate as easily in bonding as can the valence s and p electrons. But despite their many similarities, the transition metals do vary considerably in many ways. Ex) mp of W = 3422 oC , mp of Hg = -38.83 oC The Transition Metals: A Survey General Properties (Transition Metal Ions) • More than one oxidation state is often found. • Forming complex ions, species where the transition metal ion is surrounded by a certain number of ligands (Lewis bases). L4 L3 L1 L2 • Several coordination numbers, number of ligands attached to a metal ion, and geometries exist. Sc V Cr Mn Fe Co Ni Cu ≤0 o o o o o o o +1 o o o o o o O o O o O O O O O o o O o O O o o O o o O o o o +2 +3 +4 +5 +6 +7 O Ti O o o △ O o o O Zn +2 +3 Ex) Ionic compounds : FeCl2, FeCl3 +2 Complex ions: Co(H2O)62+ +3 Co(NH3)63+ O +2 H2O OH2 Cu o H2O O : most common NH3 OH2 OH2 OH2 H3N Cu NH3 NH3 +2 The Transition Metals: A Survey General Properties (Transition Metal Ions) • Most compounds containing transition metal ions are colored because the ions can absorb visible light of specific wavelength is often found. Wulfenite (PbMoO4) Rhodochrosite (MnCO3) Ruby Pure (Al2O3 : colorless) Impurity (Cr3+, < 1%) absorption : violet and green emission : red Co(H2O)62+ Cr(H2O)63+ Mn(H2O)62+ Ni(H2O)62+ Fe(H2O)63+ • Many compounds containing transition metal ions are paramagnetic (they contain unpaired electrons) EPR Cu2+ Mn2+ The Transition Metals: A Survey Electron Configuration [Ar] = 1s22s22p63s23p6 4s 3d 4s 3d 4s 3d 4s 3d Ti3+ => [Ar]3d1 Mn2+ => [Ar]3d5 Fe3+ => [Ar]3d5 Cu2+ => [Ar]3d9 Zn2+ => [Ar]3d10 The Transition Metals: A Survey Oxidation States, Ionization Energies Sc V Cr Mn Fe Co Ni Cu ≤0 o o o o o o o +1 o o o o o o O o O o O O O O O o o O o O O o o O o o O o o o O o o △ o O o o Oxidation States +2 +3 +4 +5 +6 +7 Ionization Energy O Ti Zn O O : most common O Removing of d-electron M2+(g) → M3+(g) + eMore rapid decrease of energy level of 3d Removing of s or d-electron M(g) → M+(g) + eIncrease of nuclear charge → Decrease of energy level of 3d The Transition Metals: A Survey Reduction Potentials E0 (Mn+ + ne- → M) -2.08 -1.63 -1.2 -1.18 -0.91 -0.76 -0.44 -0.28 -0.23 0.34 E0 (2H+ + 2e- → H2) = 0 In acidic solution, M(s) + 2H+(aq) → H2(g) + M2+(aq) except for Cu The Transition Metals: A Survey The 4d and 5d Transition Series 3d 4d 5d Atomic radii Lanthanide contraction: 4f shielding effect is not big. => 5d contracts. Nuclear charge ↑ The First-Row Transition Metals Scandium (Sc): Ion => only +3 Titanium (Ti): The First-Row Transition Metals Coordination Compounds Coordination coumpounds typically consists of a complex ion and counter ions (anions or cations as needed to produce a neutral compound). Complex ions: species where the transition metal ion is surrounded by a certain number of ligands (Lewis bases). L4 L3 L1 L2 H2O [Co(NH3)5Cl]Cl2(s) → Co(NH3)5Cl2+(aq) + 2Cl-(aq) complex ion counter ion (Cl-) Co3+, Cl- => []2+ Two characteristics of coordination compounds (complex ions): oxidation number of the transition metal and coordination number (and geometry) Coordination Compounds Coordination Number: number of ligands attached to a metal (typically 2 ~8) Coordination Compounds Ligand: A neutral molecule or ion having a lone electron pair that can be used to form a bond to a metal ion (Lewis base). coordinate covalent bond: metal-ligand bond • monodentate ligand: one bond to metal ion • bidentate ligand: two bonds to metal ion • polydentate ligand: can form more than two bonds to a metal ion • chelate ligand: bidentate, polydentate ligands • ambidentate ligand: bonding through different atoms of a same ligand Coordination Compounds Nomenclatures 1. 2. 3. 4. 5. 6. 7. [Co(NH3)5Cl]Cl2 As with any ionic compound, the cation is named before the anion. 국어이름에서는 반대 [“Chloride” goes last.] In naming a complex ion, the ligands are named before the metal ion. ["NH3, Cl-" named before cobalt] For ligand, an “o” is added to the root name of an anion (Table 21.14). For neutral ligands the name of the molecule is used, with exceptions of Table 21.14. ["Cl- = chloro", "NH3 = ammine"] The prefixes di-, tri-, tetra-, penta-, and hexa- are used to denote the number of simple ligands.The prefix bis-, tris-, tetrakis-, and so on are used for the ligands that already contain di-, tri-, etc. [pentaammine] The oxidation state of the central metal ion is designated by a Roman numeral in parenthesis. [cobalt(III)] When more than one type of ligand is present, they are named alphabetically. [pentaamminechloro] If the complex ion has a negative charge, the suffix “-ate (산)” is added to the name of the metal with exceptions of Table 21.15 [pentaamminechlorocobalt (III) chloride] Ex) K3Fe(CN)6 potassium hexacyanoferrate(III) [Fe(en)2(NO2)2]2SO4 철산 구리산 납산 은산 금산 주석산 bis(ethylenediamine)dinitroiron(III) sulfate triamminebromoplatinum(II) chloride [Pt(NH3)3Br]Cl potassium hexafluorocobaltate(III) K3[CoF6] Isomerism When two or more species have the same formula but different properties, they are said to be isomers. Coordination isomerism: The composition of the complex ion varies. [Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4 Linkage isomerism: Same complex ion structure but point of attachment of at least one of the ligands differs. [Co(NH3)4(NO2)Cl]Cl tetraamminechloronitrocobalt(III) chloride [Co(NH3)4(ONO)Cl]Cl tetraamminechloronitritocobalt(III) chloride Geometrical isomerism (cis-trans): Atoms or groups of atoms can assume different positions around a rigid ring. cis-Pt(NH3)2Cl2 trans-Pt(NH3)2Cl2 trans-Co(NH3)4Cl2+ cis-Co(NH3)4Cl2+ Isomerism Optical isomerism: the isomers have opposite effects on plane-polarized light. early 19C At his age of 26, he first realized that optical activity is exhibited by molecules that have non-superimposable mirro images. said to be chiral, called enantiomers Louis Pateur (1822-95) one of the isomers dextrorotatory (d) the other levorotatory (l) mixture of the two : racemic mixture , when mixed ratio is 1:1, no optical activity Isomerism Optical isomerism: the isomers have opposite effects on plane-polarized light. Co(NH3)Br(en)22+ geometrical NH3 N N N N N N N Br N N N NH3 Br Co(en)2Cl2+ cis N Co Co N cis N N 3+ trans NH3 Br trans optical Co(en)3 N Co Co H3N N Br Bonding In Complex Ions: The Localized Electron Model Bonding Theories of Complex Ions : Valence bond theory (Localized electron bonding model) Crystal field theory Ligand field theory (Delocalized electron bonding model) Review of Chapters 8 amd 9 Covalent Bond Localized electron bonding models •Lewis dot structure •VSEPR (Valence shell electron pair repulsion) •Valence bond theory (hybridization) Delocalized electron bonding model •Molecular orbital (MO) theory Central idea: Formation of hybride atomic orbitals that are used to share electron pairs to form s bond between atoms Bonding In Complex Ions: The Localized Electron Model For complex ions Covalent Bond 1. VSEPR model sometimes works. But it generally does not work Localized electron bonding models •Lewis dot structure •VSEPR (Valence shell electron pair repulsion) •Valence bond theory (hybridization) 2. The interaction between a metal ion and a ligand can be viewed as a Lewis acid-base reaction with the ligand donating a lone pair of electrons to an empty orbital of the metal ion to form a coordinate covalent bond. M empty metal ion hybrid orbital sp3 Co(NH3)6+ d2sp3 L lone pair on the ligand in a hybrid atomic orbital dsp2 M L coordinate covalent bond sp Though the localized electron bonding model improved our understanding of metal-ligand bondings, it does not explain well many important properties of metal ions, such as magnetism and colors. So usually thesedays we do not use it for the complex ions. The Crystal Field Model Crystal field model focuses on the energies of the d orbitals to explain the magnetic properties and color of complex ions. Assumption 1. Ligands are negative point charge. 2. Metal-ligand bonding is entirely ionic. To derive the energy splittings of the d-orbital in complex ions. Octahedral Complexes eg (dz2, dx2-y2) E t2g (dxy, dyz, dxz) d Free metal ion 3d orbital energies 3d orbital energy splittings in octahedral field 3d orbitals 3d orbitals in octahedral field The Crystal Field Model Octahedral Complexes (magnetic properties) Co3+ (3d6) = ligand field splitting parameter (low-spin, S = 0, diamagnetic) (high-spin, S = 2, paramagnetic) Spectrochemical Series for Ligands CO > CN- > PPh3 > NO2- > phen > bipy > en > NH3 > py > CH3CN > NCS- > H2O > C2O42- > OH- > RCO2- > F- > N3- > NO3- > Cl- > SCN- > S2- > Br- > Iπ acceptor (strong field ligand) π donor (weak field ligand) Spectrochemical Series for Metal Ions (ox # ↑,ᇫ↑), (down a group in periodic table, ᇫ↑) Pt4+ > Ir3+ > Pd4+ > Ru3+ > Rh3+ > Mo3+ > Mn4+> Co3+ > Fe3+ > V2+ > Fe2+ > Co2+ > Ni2+ > Mn2+ The Crystal Field Model Octahedral Complexes (magnetic properties) Ex) Fe(CN)63- has one unpaired electron. CN- is strong-field or weak-field ligand ? Fe3+ (3d5) eg eg t2g t2g weak-field (high-spin, S=5/2, paramagnetic) strong-field (low-spin, S=1/2, paramagnetic) Ex) How many unpaired electrons in Cr(CN)64- ? Cr2+ (3d4) eg eg CN- : strong-field ligand t2g Ex) S of Cu(H2O)62+ ? Cu2+ (3d9) S = 1/2 weak-field (high-spin, S=2, paramagnetic) t2g strong-field (low-spin, S=1, paramagnetic) The Crystal Field Model Octahedral Complexes (colors) The Crystal Field Model Octahedral Complexes (colors) E E = hn = hc/l The Crystal Field Model Other Coordination Geometries Tetrahedral complexes eg (dz2, dx2-y2) t2 (dxy, dyz, dxz) E tet ≈ (4/9)oct t2ge(d(dxyz2, ,ddyzx2-y2 , dxz)) d Free metal ion 3d orbital energies 3d orbital energy splittings in tetrahedral octahedral field All tetrahedral complexes are weak-field cases (high-spin). The Crystal Field Model Other Coordination Geometries Square-planar complexes Linear complexes dx2-y2 b1g eg dz2, dx2-y2 t2 dxy, dyz, dzx d dz2 b1g a1g o t dxy e dz2, dx2-y2 Uniform Field Tetrahedral (Td) dx2-y2 dxy 2 dz2 b2g a1g b2g 3 dxy, dyz, dzx t2g 1 eg dyz, dzx Octahedral (Oh) Tetragonal elongation (D4h) eg dyz, dzx Square-planar (D4h) Bonding In Complex Ions: The Localized Electron Model Bonding Theories of Complex Ions : Valence bond theory (Localized electron bonding model) Crystal field theory Ligand field theory (Delocalized electron bonding model) has not talked about bonding frontier orbitals •electrons from d-orbitals •same splitting pattern and d-orbital configuration as in CFT Higher Class electrons from ligands M ML6 L6 The Biological Importance of Coordination Complexes Roles of metals in biology – electron transport, oxygen storage, oxygen transport, oxidation-reduction catalysis, metal ion storage and transport ....... The Biological Importance of Coordination Complexes How to get energy in our body ? O2 : source of energy - combustion (burning gasoline in automobiles) - oxidation of carbohydrates, proteins, fats through respiratory chain (mammal) heme = Fe + porphyrin Air O2 transport protein O2 storage and transport O2 + nutrients Hemoglobin Hb(aq) + 4O2(g) ← → Hb(O2)4 (aq) Oxyhemoglobin Hemoglobin e- transfer (oxidation of nutrients) cytochromes (Heme proteins) Myoglobin The Biological Importance of Coordination Complexes Others Chlorophyll Nitrogenase Cisplatin Metallurgy and Iron and Steel Production Metallalurgy 1. Mining 2. Pretreatment of the ore 3. Reduction to the free metal 4. Purification of the metal (refining) 5. Alloying removing CO2 FeCO3(s)heat → FeO(s) +CO2(g) 4FeO(s) + O2(g) →2F2O3(s) 3Fe2O3(s) + C(s) →Fe3O4(s)+CO(g)