Presentation on theme: "Transition Metals and Coordination Compounds"— Presentation transcript:
1 Transition Metals and Coordination Compounds Chapter 24Transition Metals and Coordination Compounds
2 Contents The Colors of Rubies and Emeralds Properties of Transition MetalsCoordination CompoundsStructure and IsomerizationBonding in Coordination CompoundsApplications of Coordination Compounds
3 The Colors of Rubies and Emeralds *****Rubies: About 1% of the Al3+ ions in Al2O3 are replaced by Cr3+.Emeralds: About 1% of the Al3+ ions in Be3Al2(SiO3)6 are replaced by Cr3+.Gemstones: 寶石Rubies: 紅寶石Emeralds: 綠寶石
4 mole compound (conductivity exp) Werner’s Theory of Coordination ChemistryOld formulamole ions/mole compound (conductivity exp)mole AgCl ppt by AgNO3/per mole cpdCorrectWerner formulaCoCl3‧6NH343[Co(NH3)6]Cl3CoCl3‧5NH32[Co(NH3)5Cl]Cl2CoCl3‧4NH31[Co(NH3)4Cl2]ClCoCl3‧3NH3[Co(NH3)3Cl3]The two compounds have very similar formulas but are very different in appearance because of the different chemical structures.
5 Properties of Transition Metals General energy ordering of orbitals for multielectron Atoms:5
6 First-Row Transition Metal Orbital Occupancy *****ns and (n - 1)d sublevels are close in energyCr is 4s13d5, associated with a half-filled stabilityCu is 4s13d10, associated with a completely stability
8 Electron configurations for transition metals [noble gas]ns2(n-1)dx[noble gas]ns2(n-2)f14(n-1)dxx: 1~10Electron configurations for transition metals’ ionlosing electrons from the ns orbital before losing electrons from the (n - 1)d orbitals.
9 Example 24.1Write the ground state electron configuration for Zr.Solution[Kr] 5s24d2Example 24.2*****Write the ground state electron configuration for Co3+.SolutionFor Co [Ar] 3d7 4s2For Co3+ [Ar] 3d6
10 Atomic SizeThe third transition series atoms are about the same size as the second because of the lanthanide contraction.The atomic radii of all the transition metals are very similar.Small increase in size down a column
11 Lanthanide contraction The decrease in expected atomic size for the third transition series atoms that come after the lanthanides.14 between the second and third series go into 4f orbitals.Electrons in f orbitals are not as good at shielding the valence electrons.The result is a greater effective nuclear charge increase and therefore a stronger pull on the valence electrons—the lanthanide contraction.
12 Ionization EnergyThe first IE of the transition metals slowly increases across a series.The first IE of the third transition series is generally higher than the first and second series– lanthanide contraction
13 ElectronegativityThe electronegativity of the transition metals slowly increases across a series. Except for last element in the series.Electronegativity slightly increases between first and second series, but the third transition series atoms are about the same as the second. Trend opposite to main group elements
14 Oxidation StatesUnlike main group metals, transition metals often exhibit multiple oxidation states.
15 Coordination Compounds TerminologyA complex consists of a central atom, which is usually a metal atom or ion, and attached groups (anions or neutral molecule) called ligands.If a complex carries a net electric charge, it is called a complex ion.When a complex ion combines with counterions to make a neutral compound, it is called a coordination compound.The total number of points at which a central atom or ion attaches ligands, called coordination number.
16 Bonding in ComplexCoordinate covalent bond (dative bond): The covalent bonding between two atoms in which both electrons come from only one of the atoms (of the ligand).Central metal atom (ion): Lewis acid, electron pair acceptorLigand: Lewis base, electron pair donorMonodentate : Ligands that donate only one electron pair to the central metal, for example: H2O NH3, Cl−.Chelating agent (chelator): polydentate ligand, for example:Ethylenediamine (en): bidentateOxalato (ox): bidentateEthylenediaminetetraacetato (EDTA): hexadentateChelate: A complex ion that contains either a bidentate or polydentate.
21 ExampleWhat are the coordination number and the oxidation number of the central atom in (a) [CoCl4(NH3)2]– and (b) [Ni(CO)4]?Solution:Co: center atom, 6 ligands attached (4 Cl– and 2 NH3)coordination number: 6.Charge calculation:x – = –1, x = +3central ion is Co3+, oxidation number is +3.(b) coordination number: 4central atom is Ni, oxidation number is 0.Werner’s definition:The primary valence is the oxidation number of the metal.The secondary valence is the number of ligands bonded to the metal (coordination number).
22 Naming Coordination Compounds *****Identify the cation and anion, either may be complex ion or uncomplex ion.Naming complex cation and/or complex anions.Write the compound name as the name of cation followed by the name of the anion.
24 Naming complex cations: Ligand first, metal (with oxidation number written in Roman numerals) after.Name the ligands in alphabetical order (ignoring Greek numeric prefixes).Designate the number of ligands in a complex with a Greek numeric prefix: di = 2, tri = 3, tetra = 4, hexa = 6.
25 ExampleName [CrCl2(NH3)4]+Solution:a complex cation4 NH3: tetraammine, 2 Cl–: dichloroalphabetical order (ignoring Greek numeric prefixes):tetraamminedichlorocomplex cation: unmodified name for central metal.Cr oxidation number (x – = +1)Ans: tetraamminedichlorochromium(III) ion.
26 For metal in complex anion: Replace the ending from –um to –ate. Naming complex anion:Ligand first, metal (with oxidation number written in Roman numerals) after.Name the ligands in alphabetical order (ignoring Greek numeric prefixes).Designate the number of ligands in a complex with a Greek numeric prefix: di = 2, tri = 3, tetra = 4, hexa = 6.For metal in complex anion:Replace the ending from –um to –ate.Certain metals in complex anions, use the Latin-based names: Copper CuprateGold AurateIron FerrateLead PlumbateSilver ArgentateTin Stannate
28 Examples of Naming Coordination Compounds ***** Name [Cr(H2O)5Cl]Cl2Name K3[Fe(CN)6]Identify the cation and anion, and the name of the uncomplex ion.[Cr(H2O)5Cl]2+ is a complex cation;Cl− is chloride.K+ is potassium;[Fe(CN)6]3− is a complex anion.Give each ligand a name and list them in alphabetical order.H2O is aqua;Cl− is chloro.CN− is cyano.Name the metal ion.Cr3+ is chromium(III).Fe3+ is ferrate(III) because the complex ion is anionic.Name the complex ion by adding prefixes to indicate the number of each ligand followed by the name of each ligand followed by the name of the metal ion.[Cr(H2O)5Cl]2+ is pentaquochloro-chromium(III).[Fe(CN)6]3− is hexacyanoferrate(III).Name the compound by writing the name of the cation before the anion. The only space is between ion names.[Cr(H2O)5Cl]Cl2 is pentaquochloro-chromium(III) chloride.K3[Fe(CN)6] is potassium hexacyanoferrate(III).
29 When writing a complex formula from name: Cation first, anion afterFor the complexCenter metal first, ligands afterPlace the ligands in alphabetical order (ignoring Greek numeric prefixes)
30 Example*****Write the formula for sodium hexanitrocobaltate(III).Solution:Coordination compound: made up of Na+ cations and a complex anion.Complex anion charge: –3 (1 Co3+: +3, 6NO2–: –6)Cation first, anion after:Ans: Na3[Co(NO2)6].
32 Structural isomersCoordination isomers: the structural isomers occur when coordinated ligand exchanges places with the uncoordinated counterion, for example:[Co(NH3)5Br]Cl pentaamminebromocobalt(II) chloride[Co(NH3)5Cl]Br pentaamminechlorocobalt(II) bromide*****
33 ii) Linkage isomers: the structural isomers that have ligands attached to the central cation through different ends of the ligand structure, for example:[Co(NH3)5(NO2)]Cl [Co(NH3)5(ONO)]Cl2
37 Example 24.5Drawing Geometric Isomers of [Co(en)2Cl2]+.SolutionMA4B2 type, cis–trans isomers.
38 Optical isomers (enantiomers): Molecules that are nonsuperimposable (not identical) mirror images of one another, like right and left hands.Each enantiomer rotates polarized light in opposite directions.For example:Enantiomer: 鏡像異構物、對掌體異構物Mirror image of each otherTwo nonsuperimposable (not identical) structuresAns: two optical isomers
39 Example 24.7a Determine whether the cis isomer of [Co(en)2Cl2]+ is optically active. Solutionthe two structures are not superimposable, so the cis isomer does exhibit optical activity.
40 Example 24.7b Determine whether the trans isomer of [Co(en)2Cl2]+ is optically active. SolutionIn this case the two are identical, so there is no optical activity.
41 5. Bonding in Coordination Compounds Valence Bond Theory/Hybridization of Atomic Orbitals
42 electron configuration of Ag: 4d105s1, Ag+: 4d10 for [Ag(NH3)2]+ Continuedelectron configuration of Ag: 4d105s1, Ag+: 4d10for [Ag(NH3)2]+sp hybridization4d5s5pelectron configuration of Zn: 3d104s2 , Zn2+: 3d10for [Zn(NH3)4]2+sp3 hybridization3d4s4p
43 electron configuration of Pd: 4d10, Pd2+: 4d8 for [PdCl4]2- Continuedelectron configuration of Pd: 4d10, Pd2+: 4d8for [PdCl4]2-dsp2 hybridization4d5s5pelectron configuration of Fe: 3d64s2, Fe3+: 3d5for [Fe(H2O)6]3+d2sp3 hybridization3d4s4p
44 Crystal Field Theory ***** Assume the attractions between a central atom (or ion) and its ligands are largely electrostatic.Ligands distort the d-orbitals of the central atom, leading to a splitting of energy levels of those orbitals.Splitting energy (Δ): The splitting of energy levels of d-orbitals which are caused by ligands distoration of those orbitals.The spectrochemical series shows the relative abilities of ligands (Δ) to split the d-orbital energy levels:****** Increases the charge on the metal cation also increases the splitting energy (Δ), for example:Co3+ > Cr3+ > Fe3+ > Fe2+ > Co2+ > Ni2+ > Mn2+
45 Schematic representation of d-level splitting: *****Schematic representation of d-level splitting:ΔΔUsuallyHigh SpinUsingSpectroche-mical seriesUsuallyLow Spin
46 *****Crystal field theory can predict:MagnetismParamagnetic, with spin (unpaired electron)Diamagnetic, without spinMagnetic strengthHigh spin, more unpaired electron (Δ small)Low spin, less unpaired electron, (Δ large)Complex color: According to the energy level transition.
47 *****Example: Predict the magnetism for [Fe(H2O)6]2+ and [Fe(CN)6]4-.Solution:Both are octahedral complexesFe: [Ar]3d64s2, Fe2+: [Ar]3d6 (six 3d electrons)Δ: CN– (large) > H2O (small)DiamagneticLow-spin complexParamagneticHigh-spin complex* From d1 through d10 metal ion in octahedral complexes, only electron d4, d5, d6, or d7 can have low and high spin possibilities.
48 *****ExampleHow many unpaired electrons would you expect for the octahedral complex ion [CoF6]3–?Solution:Electron configuration:Co: [Ar]3d74s2Co3+: [Ar]3d6 (six 3d electrons)F– ligand: Δ smallAns: 4 unpaired electrons
49 How many unpaired electrons would you expect for the octahedral complex ion [Co(NH3)5NO2]2+? Solution:Electron configuration:Co: [Ar]3d74s2Co3+: [Ar]3d6 (six 3d electrons)NH3 and NO2-: Δ largeAns: No unpaired electrons
50 ExampleHow many unpaired electrons would you expect to find in the tetrahedral complex ion [NiCl4]2–?Solution:Electron configuration:Ni: [Ar]3d84s2Ni2+: [Ar]3d8(Tetrahedral, usually Δ small, high spin)Ans: 2 unpaired electrons
51 *****ExampleHow many unpaired electrons would you expect to find in thesquare planar complex ion [PtCl4]2–?Solution:Electron configuration:Pt: [Xe]5d96s1Pt2+: [Xe]5d8(Square planar, usually Δ large, low spin)Ans: no unpaired electronsa diamagnetic species
52 Color In Complex Ions And Coordination Compounds Many complex ions are colored because the energy differences between d orbitals match the energies of components of visible light.Crystal field theory helps to explain the colors of complex ions.Ions having the following electron configurations have no electron transitions in the energy range of visible light (colorless):No electron in d orbital (d0-complex), e.g., Sc3+, Y3+, La3+ (noble-gas electron configuration) are colorless.Electrons completely filled in d orbital (d10-complex), e.g., Zn2+, Cd2+, Hg2+, Cu+, and Ag+ are colorless.
53 The color of the transmitted light is the complementary color of the absorbed light. The Color Wheel: Colors across from one another on the color wheel are said to be complementary.
54 ContinuedLarge ΔHigh νShort λSmall ΔLow νLong λThe Color of [Ti(H2O)6]3+ solutionThe absorption pectrum [Ti(H2O)6]3+ solution
55 Complex Ion Color and Crystal Field Strength The colors of complex ions are due to electronic transitions between the split d sublevel orbitals.The wavelength of maximum absorbance can be used to determine the size of the energy gap between the split d sublevel orbitals.Ephoton = hn = hc/l = D
56 *****Example 24.8The complex ion [Cu(NH3)6]2+ is blue in aqueous solution. Estimate the crystal field splitting energy (in kJ/mol) for this ion.SolutionThe color orange ranges from 580 to 650 nm, so you can estimate the average wavelength as 615 nm. E = hc/λ.Convert J/ion into kJ/mol.
57 6. Applications of Coordination Compounds Extraction of metals from oresSilver and gold as cyanide complexesNickel as Ni(CO)4(g)Use of chelating agents in heavy metal poisoningEDTA for Pb poisoningChemical analysisQualitative analysis for metal ionsBlue = CoSCN+, Red = FeSCN2+Ni2+ and Pd2+ form insoluble colored precipitates with dimethylglyoxime.
59 *****In hemoglobin, the iron complex is octahedral, with the four nitrogen atoms of the porphyrin in a square planar arrangement around the metal. A nitrogen atom from a nearby amino acid of the protein occupies the fifth coordination site, and either O2 or H2O occupies the last coordination site.Hemoglobin: 血紅素蛋白Heme: 血紅素Porphyrin: 紫質