Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 Chemistry 1B Fall 2012 Lectures 13-14 Coordination Chemistry 1 LISTEN UP!!! • WE WILL ONLY COVER LIMITED PARTS OF CHAPTER 19 (pp. 933-937; 946-948; 958-966) [940-944;952-954;963-970]7th 2 Page 1 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 good reasons for studying coordination chemistry •a 4th type of bonding (coordinate covalent) • experimental verification of the shape of atomic orbitals (crystal field theory) • important in biological chemistry • they are pretty !!!! (glazes) 3 remembering • Lewis structures • atomic d-orbitals • electron configurations • paramagnetism and diamagnetism 4 Page 2 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 what is coordination complex? a central metal atom or ion to which ligands are bound by coordinate covalent bonds 5 more • coordinate covalent bond: covalent bond where one atom contributes both electrons (in olden times called ‘dative’ bond) • ligand: ion or molecule which binds to central atom, contributing both electrons to a covalent bond • coordination number: how many coordinate covalent bonds around central atom/ion 6 Page 3 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 simple example (figure on p. 936) [Co(NH3)6] Cl3 (s) salt of complex ion [Co(NH3)6]Cl3 (s) + H2O ö 3+ - [Co(NH3)6] (aq) + 3Cl (aq) 3+ [Co(NH3)6] complex ion denoted by [ ]’s 6 NH3 ligands metal ion 3Cl- counter ions 7 figure 23.9 (Silberberg) 3+ 2- [Co(NH3)6] [Ni(CN)4] octahedral square planar 8 Page 4 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 examples of common ‘simple’ ligands H2O, NH3, Cl , CO, CN . Cl O C≡N H H N C≡O H H H 9 what is common structural feature of ligands lone pairs N . H H C≡O H 10 Page 5 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 Coordinate covalent bond: Lewis acid-Lewis base CHEM 1A nr Lewis acid Lewis base ligand metal L: M+n 11 coordinate covalent bonding 3+ [Co(NH3)6] Octahedral complex coordination number =6 12 Page 6 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 possible geometries of coordination complexes (table 23.6 Silberberg) [see figure 19.6 Zumdahl] 13 ligands (Table 23.7 Silberberg) [Table 19.13 Zumdahl] monodentate 14 Page 7 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 ligands (Table 23.7 Silberberg) [see Table 19.13 Zumdahl] bidentate 15 ethylene diamine bidentate ligand 16 Page 8 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 3+ [Cr(en)3] octahedral complex 17 ligands (Table 23.7 Silberberg) [see Table 19.13 Zumdahl] polydentate 18 Page 9 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 EDTA a chelate (claw!!) hexadentate 19 more EDTA4- 2- for Fe2+ 20 Page 10 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 Table 19.13 , Figure 19.7 21 determining: num ligands charge oxidation state d-electrons given [Co(NH3)n] Cl3 is salt of octahedral complex • coordination number=6 since octahedral • n=6 since NH3 is monodentate ligand • 3+ charge on complex from counterion: 3 Cl • Co3+ oxidation state of metal from charge on complex and zero charge on NH3 ligands • d6 d-electrons from aufbau principle FOR CATIONS 22 Page 11 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 other examples K3[Fe(CN)n] octahedral [Co(en)n]Cl3 octahedral Na2[Ni(CN)n] square planar 23 Sections 19.1-19.2, 19.4 (pp 933-946;948- 958 ) (don’t fret) • General factoids about transition metals • Nomenclature • Isomerism 24 Page 12 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 Section 19.5 Localized Electron model (pp 958-959) (don’t fret) hybridization involving d-orbitals: d2sp3 six octahedrally oriented hybrids dsp3 four square planar hybrids 25 crystal field theory (pp 959-955) • How are the magnetic properties of transition metal complexes related to the shape of d-orbitals? • Why are transition metal complexes colored? 26 Page 13 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 paramagnetism vs diamagnetism (Gouy balance) diamagnetic paramagnetic remember unpaired electron spins ÆÆ: paired electron spins Æ∞ : more [floating frog] later strength of paramagnetism depends on number of unpaired electrons not now 27 crystal field theory and color • most electronic excitations in UV (H 1s → H 2p λ=121 x 10-9 m) •Co3+ [Ar]3d6 → Co3+ [Ar]3d54s1 (λ=75.3 x 10-9 m) UV -9 NH3 → NH3* (excited state) (λ=216 x 10 m) UV 3+ Co and NH3 are colorless !!! but in coordination complex 3+ -9 •[Co(NH3)6] → excited state* (λ=430 x 10 m, absorbs ‘indigo’) 3+ [Co(NH3)6] appears yellow !! 28 Page 14 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 crystal field theory and magnetic properties 3+ [Co(NH3)6] is diamagnetic but 3 [Co(F)6] is paramagnetic 29 remember atomic d-orbitals (figure 12.21) 30 Page 15 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 metal ion d-obitals in octahedral complex (Silberberg fig. 23.17; Zumdahl fig. 19.21 ) http://switkes.chemistry.ucsc.edu/teaching/CHEM1B/Jmol/CrystalField/CFT_OrbsOctahedral.html 31 what happens to energies of d-orbitals when ligands bind to metal ion? (fig 23.18) average ligand repulsion for metal d-electrons would each d-electron be repelled the same? 32 Page 16 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 what happens to energies of d-orbitals when ligands bind to metal ion? (fig 23.18) greater repulsion of d22 and d 2 x-y z electrons by octahedral ligands smaller repulsion of dxy, dxz, and dyz electrons by octahedral ligands average ligand repulsion would each d-electron for metal d-electrons be repelled the same? 33 filling of d-orbitals in octahedral complex: d1 → d3 ground state 4 [V(CN)6] V2+ d3 _____ _____ eg ↑ ↑ ↑ _____ ______ ______ t2g 3 configuration: (t2g) ↑↑ ↑ paramagnetic: three unpaired electrons 34 Page 17 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 filling of d-orbitals in octahedral complex: d4 → d10 ground state 2+ 4 [Cr(H2O)6] vs [Cr(CN)6] Cr2+ Cr2+ d4 d4 ? _____ _____ eg ↑? ↑ ↑ _____ ______ ______ t2g where does electron 4th go ? 35 strong and weak field ligands: lowest orbitals vs unpaired spins Δ vs (Epairing) (Silberberg fig 23.18) d4 d4 ↑ ↑ ↑ ↑ ↑↓↑ ↑ ↑ Δ > (Epairing) (Epairing) > Δ small Δ favors filling large Δ favors filling maximum unpaired spins lowest orbitals first 36 Page 18 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 2+ 4 [Cr(H2O)6] vs [Cr(CN)6] 2+ 4 • [Cr(H2O)6] ,d, weak-field ≡ high spin, 4 unpaired electrons, paramagnetic 4 4 • [Cr(CN)6] , d , strong-field ≡ low spin, 2 unpaired electrons, paramagnetic 37 high-spin vs low-spin complexes: d4 → d7 (Silberberg fig. 23.24) small D large D d6 paramagnetic diamagnetic 38 Page 19 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 other examples (do in section) 2+ 6 [Fe(H2O)6] , d , weak field, 4 unpaired e’s, paramagnetic 4 6 [Fe(CN)6] ,d , strong field, 0 unpaired e’s, diamagnetic 39 spectrochemical series (fig. 23.22 Silberberg; Zumdahl p. 961) know: CN, CO strong (high) field F ,Cl, I (halogen anions) weak (low) field in using others you would be told which 40 Page 20 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 crystal field theory (pp 959-955) • How are the magnetic properties of transition metal complexes related to the shape of d-orbitals? • Why are transition metal complexes colored? 41 why are some molecules colored ? (spectroscopy lectures later) human vision and chemistry LATER in spectroscopy not now • light in 400-700 nm range interacts with a molecule (rhodopsin) in the rods and cones at the back of the eye (the retina) • substances that absorb light in this region will appear colored 42 Page 21 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 transition metal complex ions octahedral complex t2g →eg not now (lone-pair) n → * → * in molecules with conjugated pi-systems not now rhodopsin, the molecule most important to seeing color not now 43 color and absorption of light • The color of an object arises from the wavelengths reflected by the object • If the object is viewed in white light (as is usual) the color seen is the complement of the wavelengths absorbed 44 Page 22 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 color and absorption of light, white light (R+G+B) incident (table 19.16) (R,G,B) primaries white=R+G+B Y (yellow)=R+G Cyan=G+B (blue-green) Purple=R+B know: absorbs appears nothing White B Yellow (R+G) Cyan (G+B) Red reflects G Purple (R+B) Y (R+G) Blue R + G + B R Green-Blue (cyan) R+G+B Black 45 color Color in octahedral complex ions arises from t2g → eg electronic transitions (excitations) that have energies corresponding to photons in the visible wavelengths. 46 Page 23 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 color and absorption of light (Zumdahl fig 19.25, Silberberg fig. 23.20) 3+ 1 [Ti(H2O)6] d absorbs green-yellow appears purple 47 so …… λ= 11.4 10-9 m λ510 10-9 m colorless appears purple ↑ 3d ↑ } 3d 3+ 1 Ti3+ (g) d1 [Ti(H2O)6] d 48 Page 24 Lectures 13-14 Coordination Complexes Lectures Chemistry 1B, Fall 2012 d-orbital energies for tetrahedral and square planar geometries (fig.