A/Prof Adam Bridgeman CHEM2402/2912/2916 [Part 2] Ligand-Field Theory and Reaction Kinetics A/Prof Adam Bridgeman Room: 222 Email: A.Bridgeman@chem.usyd.edu.au www.chem.usyd.edu.au/~bridge_a/chem2 Office Hours: Monday 2-4pm, Wednesday 2-4pm Other times by appointment or by chance

Where Are We Going…? Shriver & Atkins, ‘Inorganic Chemistry’, OUP, 4th Edition, 2006 Week 4: Electronic Spectroscopy Jahn-Teller effect Electronic spectra of multi-electron atoms Nephelauxetic effect and the spectrochemical series Selection rules Charge transfer transitions Week 5: Bonding in Complexes, Metalloproteins and Materials π-Donor and π-Acceptor Ligands Metal-metal bonding in clusters and solids Role of ligand-field effects in electrochemistry Week 6: Kinetics and Ligand-Field Effects Differential rate laws Ligand substiution reactions

By the end of week 4… Ligand-field (‘d-d’) spectroscopy be able to predict/explain number of bands for d1-d9 (high-spin) be able to calculate Doct for d1, d3, d4, d6, d7, d8 and d9 be able to explain differences in band intensity (spin forbidden, orbitally forbidden, Laporte forbidden) be able to explain the appearance of charge transfer transitions be able to explain and predict the occurance of the Jahn-Teller effect and its consequences (structural, spectroscopic, reaction rates) Resources Slides for lectures 1-3 Shriver and Atkins “Inorganic Chemistry” Chapter 19 (4th Edition)

Schedule Lecture 1: Electronic absorption spectroscopy Jahn-Teller effect and the spectra of d1, d4, d6 and d9 ions Lecture 2: Interpreting electronic spectra Interelectron repulsion and the nephelauxetic effect Lecture 3: Interpreting electronic spectra Selection rules and charge transfer transitions Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter.

Revision – Ligand-Field Splitting In the absence of any ligands, the five d-orbitals of a Mn+ transition metal ion are degenerate Repulsion between the d-electrons and ligand lone pairs raises the energy of each d-orbital Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. JKB – Lecture 3, S & A 19.1

Revision – Ligand-Field Splitting Two of the d-orbitals point along x, y and z and are more affected than the average Three of the d-orbitals point between x, y and z and are affected less than the average The ligand-field splitting (eg) (t2g) (Doct) eg Doct t2g Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. JKB – Lecture 3, S & A 19.1

Electronic Spectra of d1 Ions A d1 octahedral complex can undergo 1 electronic transition The ground state (t2g)1 comprises three degenerate arrangements The excited state (eg)1 comprises two degenerate arrangements The electronic transition occurs at Doct eg eg Ti3+(aq) Doct t2g t2g Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. ground state excited state JKB – Lecture 3, S & A 19.3

Electronic Spectra of High Spin d4 Ions A high spin d4 octahedral complex can also undergo just 1 transition The ground state (t2g)2(eg)1 comprises two degenerate arrangements The excited state (t2g)2(eg)2 comprises three degenerate arrangements The electronic transition occurs at Doct No other transitions are possible without changing the spin eg eg Cr2+(aq) Doct Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. t2g t2g ground state excited state JKB – Lecture 3, S & A 19.3

Electronic Spectra of High Spin d6 and d9 Ions High spin d6 and d9 octahedral complexes can also undergo just 1 transition The electronic transition occurs at Doct No other transitions are possible changing the spin d6 d9 ground state excited state Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. ground state excited state Cu2+(aq) Fe2+(aq)

Effect of Distortion on the d-Orbitals tetragonal elongation Pulling the ligands away along z splits eg and lowers the energy of dz2 It also produces a much smaller splitting of t2g by lowering the energy of dxz and dyz Doct >>> d1 >> d2 eg d1 Doct t2g d2 Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. tetragonal elongation JKB – Lecture 6, S & A p467

Which Complexes Will Distort? Relative to average: t2g go down by 0.4Doct in octahedral complex Relative to average: eg go up by 0.6Doct in octahedral complex Relative to average dz2 is stablilized by ½d1 and dx2-y2 is destablilized by ½d1 Relative to average dxz and dyz are stablilized by ⅔d2 and dxy is destablilized by ⅓d2 +½d1 eg +0.6 Doct d1 -½d1 Doct +⅔d2 Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. d2 t2g -0.4 Doct -⅓d2 octahedron distorted octahedron

Which Complexes Will Distort? Doct >>> d1 >> d2 dn configuration degeneracy LFSE stabilized? distortion t2g eg 1 1 3 -0.4Doct - 0.33d2 yes small +½d1 eg +0.6 Doct Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. -½d1 +⅔d2 t2g -0.4 Doct -⅓d2

Which Complexes Will Distort? Doct >>> d1 >> d2 dn configuration degeneracy LFSE stabilized? distortion t2g eg 1 2 3 4 5 1 3 -0.4Doct - 0.33d2 yes small 2 3 -0.8Doct - 0.67d2 yes small 3 1 -1.2Doct no no 3 1 2 -0.6Doct - 0.5d1 yes large 3 2 1 no none +½d1 eg +0.6 Doct Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. -½d1 +⅔d2 t2g -0.4 Doct -⅓d2

Which Complexes Will Distort? Doct >>> d1 >> d2 dn configuration degeneracy LFSE stabilized? distortion t2g eg 1 2 3 4 5 6 7 8 9 1 3 -0.4Doct - 0.33d2 yes small 2 3 -0.8Doct - 0.67d2 yes small 3 1 -1.2Doct no no 3 1 2 -0.6Doct - 0.5d1 yes large 3 2 1 no none 4 2 3 -0.4Doct - 0.33d2 yes small 5 Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. 2 3 -0.8Doct - 0.67d2 yes small 6 2 1 -1.2Doct no no 6 3 2 -0.6Doct - 0.5d1 yes large

Which Complexes Will Distort? Doct >>> d1 >> d2 Low spin: dn configuration degeneracy LFSE stabilized? distortion t2g eg 4 5 6 7 1 +½d1 eg +0.6 Doct Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. -½d1 +⅔d2 t2g -0.4 Doct -⅓d2

Which Complexes Will Distort? Large distortions (always seen crystallographically) : high spin d4 low spin d7 d9 Cr2+ Co2+ Cu2+ Small distortions (often not seen crystallographically): d1 d2 low spin d4 low spin d5 high spin d6 high spin d7 Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter.

Any molecule with a degenerate ground state will distort Jahn-Teller Theorem This is a general result known as the Jahn-Teller theorem: Any molecule with a degenerate ground state will distort antibonding bonding Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. +

Effect on Spectroscopy From Slide 6, there is one d-d transition for an octahedral d1 ion From Slide 15, a d1 complex will distort and will not be octahedral There are now 3 possible transitions (A) is in infrared region and is usually hidden under vibrations (B) and (C) are not usually resolved but act to broaden the band eg Ti3+(aq) (B) (C) Demos: charles law (2.3), CO2 density (2.1), star wars (4.3) Brief mention of 3 states of matter. t2g (A) (B) (C)

Summary By now you should be able to.... Show why there is a single band in the visible spectrum for d1, high spin d4, high spin d6 and d9 octahedral complexes Obtain the value of Doct from the spectrum of these ions Show the electronic origin of the (Jahn-Teller) distortion for high spin d4, low spin d7 and d9 octahedral complexes Predict whether any molecule will be susceptible to a Jahn-Teller distortion Explain how the Jahn-Teller effect leads to broadening of bands in the UV/Visible spectrum Next lecture Effects of interelectron repulsion Very important equation - one that you need to remember surely this should depend on the gas ? … No, as we’ll see soon

Practice Very important equation - one that you need to remember surely this should depend on the gas ? … No, as we’ll see soon

Practice Very important equation - one that you need to remember surely this should depend on the gas ? … No, as we’ll see soon