Synthesis How do I make it? Modeling How do I explain it? Chemistry Analysis What is this? Synthesis How do I make it? Three central goals Modeling How do I explain it?

A Chemist’s View- How we think Three different perspectives Macroscopic Microscopic or Particulate Three different perspectives Symbolic NaCl

The Period 4 transition metals

Colors of representative compounds of the Period 4 transition metals nickel(II) nitrate hexahydrate sodium chromate zinc sulfate heptahydrate potassium ferricyanide titanium oxide scandium oxide manganese(II) chloride tetrahydrate copper(II) sulfate pentahydrate vanadyl sulfate dihydrate cobalt(II) chloride hexahydrate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Aqueous oxoanions of transition elements Mn(II) Mn(VI) Mn(VII) One of the most characteristic chemical properties of these elements is the occurrence of multiple oxidation states. V(V) Cr(VI) Mn(VII) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Effects of the metal oxidation state and of ligand identity on color [V(H2O)6]3+ [V(H2O)6]2+ [Cr(NH3)6]3+ [Cr(NH3)5Cl ]2+ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Linkage isomers

An artist’s wheel

Splitting of d-orbital energies by an octahedral field of ligands D is the splitting energy

The effect of ligand on splitting energy

The spectrochemical series 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. I- < Cl- < F- < OH- < H2O < SCN- < NH3 < en < NO2- < CN- < CO WEAKER FIELD STRONGER FIELD LARGER D SMALLER D LONGER  SHORTER  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The color of [Ti(H2O)6]3+ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

High-spin and low-spin complex ions of Mn2+ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

high spin: weak-field ligand low spin: strong-field ligand Orbital occupancy for high- and low-spin complexes of d4 through d7 metal ions high spin: weak-field ligand low spin: strong-field ligand high spin: weak-field ligand low spin: strong-field ligand Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

What is electronic spectroscopy? Absorption of radiation leading to electronic transitions within a molecule or complex Absorption Absorption [Ru(bpy)3]2+ [Ni(H2O)6]2+ 104 10 ~14 000 25 000 50 000 200 400 700 visible UV UV visible n / cm-1 (frequency) - l / nm (wavelength) UV = higher energy transitions - between ligand orbitals visible = lower energy transitions - between d-orbitals of transition metals - between metal and ligand orbitals

Absorption maxima in a visible spectrum have three important characteristics number (how many there are) This depends on the electron configuration of the metal centre 2. position (what wavelength/energy) This depends on the ligand field splitting parameter, Doct or Dtet and on the degree of inter-electron repulsion intensity This depends on the "allowedness" of the transitions which is described by two selection rules

[Ti(OH2)6]3+ lmax = 510 nm Do is  243 kJ mol-1 20 300 cm-1 The energy of the absorption by [Ti(OH2)6]3+ is the ligand-field splitting, Do ES ES eg eg hn Do GS GS t2g t2g d-d transition complex in electronic Ground State (GS) complex in electronic excited state (ES) [Ti(OH2)6]3+ lmax = 510 nm Do is  243 kJ mol-1 20 300 cm-1 An electron changes orbital; the ion changes energy state

Degenerate electronic ground state: T or E The Jahn-Teller Distortion: Any non-linear molecule in a degenerate electronic state will undergo distortion to lower it's symmetry and lift the degeneracy Degenerate electronic ground state: T or E Non-degenerate ground state: A d3 4A2g d5 (high spin) 6A1g d6 (low spin) 1A1g d8 3A2g 2B1g A 2Eg [Ti(H2O)6]3+, d1 2A1g 2T2g n / cm-1 - 10 000 20 000 30 000

Limitations of ligand field theory [Ni(OH2)6]2+ = d8 ion 3 absorption bands 2+ Ni eg A t2g 25 000 15 000 n / cm-1 - LFT assumes there is no inter-electron repulsion Repulsion between electrons in d-orbitals has an effect on the energy of the whole ion

d2 ion Electron-electron repulsion eg eg z2 x2-y2 z2 x2-y2 t2g t2g xy xz yz xy xz yz xy + z2 xz + z2 z z y y x x lobes overlap, large electron repulsion lobes far apart, small electron repulsion These two electron configurations do not have the same energy

The Nephelauxetic Effect cloud expanding some covalency in M-L bonds – M and L share electrons effective size of metal orbitals increases electron-electron repulsion decreases Nephelauxetic series of ligands F- < H2O < NH3 < en < [oxalate]2- < [NCS]- < Cl- < Br- < I- Nephelauxetic series of metal ions Mn(II) < Ni(II) Co(II) < Mo(II) > Re (IV) < Fe(III) < Ir(III) < Co(III) < Mn(IV)

Transition e complexes Selection Rules Transition e complexes Spin forbidden 10-3 – 1 Many d5 Oh cxs Laporte forbidden [Mn(OH2)6]2+ Spin allowed Laporte forbidden 1 – 10 Many Oh cxs [Ni(OH2)6]2+ 10 – 100 Some square planar cxs [PdCl4]2- 100 – 1000 6-coordinate complexes of low symmetry, many square planar cxs particularly with organic ligands Spin allowed 102 – 103 Some MLCT bands in cxs with unsaturated ligands Laporte allowed 102 – 104 Acentric complexes with ligands such as acac, or with P donor atoms 103 – 106 Many CT bands, transitions in organic species