Chapter 2 Physico-chemical properties 2 1 2 2

Chapter 2 Physico-chemical properties 2. 1 2. 2 2. 3 2. 4 E / 103 cm-1 10. 0 2 F 5/2 2 F 0 7/2 Electronic levels Magnetism Electronic absorption spectra Luminescence spectra 2’ 1’ 0’ 3 2 1 0 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 1

Chapter 2 2. 1 Physico-chemical properties Electronic levels 2. 1. 1 Electronic structure of 4 f elements (Summary from the BSc course “Coordination chemistry” Russel-Saunders coupling usually works well (2 S+1) Spectroscopic term Multiplicity = (2 S+1)´(2 L+1) G S P D F G H I J K … 0 1 2 3 4 5 6 7 8 = L spin multiplicity (2 S+1) GJ J = L+S, L+S-1…, |L-S| Spectroscopic level, multiplicity = (2 J+1) MSc: f-Elements, Prof. J. -C. Bünzli, 2008 2

Chapter 2 Physico-chemical properties Hund’s rules for ground state: • Spin multiplicity must be the highest possible (Smax) • If more than one term have the highest multiplicity, the term with the highest value of L is the ground state (Lmax) • The ground level has Jmin if the subshell is less than half filled, Jmax if the subshell is more than half filled Example: Nd 3+, 4 f 3 Smax = 3´½ = 3/2 Lmax = 6 3 2 1 0 -1 -2 -3 ml (l = 3) MSc: f-Elements, Prof. J. -C. Bünzli, 2008 J = 15/2…… 9/2 4 I 9/2 3

Chapter 2 Ln 3+ 4 fn, n Physico-chemical properties Ground Color level Ce 1 2 F Pr 2 3 H Nd 3 4 I Pm 4 5 I Sm 5 6 H Eu 6 7 F Gd 7 8 S Tb 8 7 F Dy 9 6 H Ho 10 5 I Er 11 4 H Tm 12 3 H Yb 13 2 F Magnetic moment exp. calc. colorless 2. 3 -2. 54 green 3. 4 -3. 6 3. 58 9/2 lilac 3. 5 -3. 62 4 pink n. a. 2. 68 5/2 yellow 1. 4 -1. 7 0. 85 0 pale pink 3. 3 -3. 5 0 7/2 colorless 7. 9 -8. 0 7. 94 6 colorless 9. 5 -9. 8 9. 72 yellow 10. 4 -10. 6 yellow 10. 4 -10. 7 10. 6 15/2 rose 9. 4 -9. 6 9. 58 6 pale green 7. 1 -7. 56 7/2 colorless 4. 54 5/2 4 15/2 8 4. 3 -4. 9 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 4

Chapter 2 Physico-chemical properties Spin-orbit coupling constants for aqua-ions Ln. III l 4 f z 4 f Ce 625 Tb -285 1710 Pr 370 740 Dy -483 1932 Nd 295 885 Ho -535 2140 Sm 232 1160 Er -793 2380 Eu 221 1326 Tm -1315 2630 Gd 207 1450 Yb -2940 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 5

Chapter 2 Physico-chemical properties Some electronic levels… MSc: f-Elements, Prof. J. -C. Bünzli, 2008 6

Chapter 2 Physico-chemical properties Ligand field effects They are very weak, a few hundreds cm-1 as compared to a few thousands for spin-orbit coupling, and 104 cm-1 for electron repulsion. Example: Yb 3+ (2 F 7/2 and 2 F 5/2) in D 3 symmetry Since J is half-integer, double group D’ 3 has to be used a) Determine the reducible representation with rotation formula b) Use reduction formula MSc: f-Elements, Prof. J. -C. Bünzli, 2008 7

Chapter 2 C 2 , a = 1800 Physico-chemical properties J = 5/2 sin(1620)/sin(270) = 0 sin(2160)/sin(270) = 0 J = 5/2 sin(360)/sin(60) = 0 J = 7/2 C 32, a = 2400 sin(720)/sin(90) = 0 J = 7/2 C 3 , a = 1200 sin(540)/sin(90) = 0 J = 7/2 C 2 R, a = 5400 J = 5/2 sin(480)/sin(60) = 1 J = 5/2 sin(720)/sin(120) = 0 J = 7/2 sin(960)/sin(120) = -1 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 8

Chapter 2 D 3’ Physico-chemical properties E R C 32 R (h=12) C 3 3 C 2 R C 3 R G 1 A 1 +1 +1 +1 G 2 A 2 +1 +1 -1 -1 G 3 E +2 +2 -1 -1 0 0 G 4 +2 -2 +1 -1 0 0 G 5 +1 -1 -1 +1 +i -i G 6 +1 -1 -1 +1 -i +i J=7/2 J=5/2 +8 +6 -8 -6 +1 0 -1 0 0 0 J = 7/2: 3 G 4 + G 5, 6 J = 5/2: 2 G 4 + G 5, 6 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 9

Chapter 2 Physico-chemical properties 3 H 2 L + 2 Yb 3+ ® [Yb 2 L 3] + 6 H+ H 2 L self-assembly process in water yields triple-stranded helicate » D 3 symmetry MSc: f-Elements, Prof. J. -C. Bünzli, 2008 10

Chapter 2 Physico-chemical properties MSc: f-Elements, Prof. J. -C. Bünzli, 2008 11

Chapter 2 D 2 O 2 F 2 F 7/2 Emission 9. 0 5/2 3 0' 2' Physico-chemical properties Excitation * 2 0 1‘ ? 10. 0 10. 5 11. 0 E / 103 cm-1 * vibronic components 5/2 10. 0 x 1010 9. 5 E / 103 cm-1 2 F * 11. 5 269 cm-1 0 F. Gonçalves e Silva, J. -C. G. Bünzli et al. J. Chem. Phys. A 2002, 106, 1670. MSc: f-Elements, Prof. J. -C. Bünzli, 2008 2 F 7/2 2’ 1’ 0’ 3 2 1 0 372 cm-1 » D 3 symmetry 12

Chapter 2 Physico-chemical properties Number of levels Number of f Number of electrons terms levels 2 S+1 L J Number of LF sublevels 2 S+1 G x 1 13 1 2 2 12 7 13 91 3 11 17 41 364 4 10 47 1001 5 9 73 198 2002 6 8 119 295 3003 119 327 3432 7 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 14 13

Chapter 2 Physico-chemical properties 2. 1. 2 Electronic structure of 5 f elements An Atom [Rn]xxx An 3+ An 4+ An Atom An 3+ An 4+ [Rn]xxx Ac 6 d 17 s 2 [Rn] - Bk 5 f 97 s 2 5 f 8 5 f 7 Th 6 d 27 s 2 5 f 1 [Rn] Cf 5 f 107 s 2 5 f 9 5 f 8 Pa 5 f 26 d 17 s 2 5 f 1 Es 5 f 117 s 2 5 f 10 5 f 9 U 5 f 36 d 17 s 2 5 f 3 5 f 2 Fm 5 f 127 s 2 5 f 11 5 f 10 Np 5 f 46 d 17 s 2 5 f 4 5 f 3 Md 5 f 137 s 2 5 f 11 Pu 5 f 67 s 2 5 f 5 5 f 4 No 5 f 147 s 2 5 f 13 5 f 12 Am 5 f 77 s 2 5 f 6 5 f 5 Lr 5 f 13 Cm 5 f 76 d 17 s 2 5 f 7 5 f 6 5 f 146 d 1 5 f 14 7 s 2 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 14

Chapter 2 Physico-chemical properties Deciphering the electronic structure needs the use of an adequate scheme for spin-orbit coupling. The coupling is much greater than for 4 f elements, so that Russel-Saunders scheme does not work. Interpretation of magnetic and optical data is therefore more difficult than for 4 f elements. Sometimes, however, Russell-Saunders coupling scheme is used as a first approach. Example: UIV, 5 f 2 Ground level: 3 H 4 SO levels: 3 H 4, 3 H 5, 3 H 6 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 15

Chapter 2 Physico-chemical properties UIV, 5 f 2 Spin-orbit Note: DE decreases with increasing tetragonal distortion (from Oh) Ligand field Oh D 4 h Electronic repulsion MSc: f-Elements, Prof. J. -C. Bünzli, 2008 16

Chapter 2 Physico-chemical properties 2. 2 Magnetism When Russell-Saunders scheme for spin-orbit coupling is valid and when the ground state is pure and well separated from excited states, the following formulae are well adapted to predict the effective magnetic moment: MSc: f-Elements, Prof. J. -C. Bünzli, 2008 17

Chapter 2 Physico-chemical properties exceptions MSc: f-Elements, Prof. J. -C. Bünzli, 2008 18

Chapter 2 Physico-chemical properties Actinides § More complicated behavior: large z 5 f (see Table below) and RS coupling scheme for spin-orbit is not applicable. § UVI compounds [Rn]5 f 0 (1 S 0) should be diamagnetic, but they often display temperature-independent paramagnetism (TIP) because of the mixing of excited states with the ground state. § UIV compounds: [Rn]5 f 2 (3 H 4). Predicted g. J = 1 + (4 x 5 + 1 x 2 – 5 x 6)/2 x 4 x 5 = 1 -0. 2 = 0. 8 meff = 0. 8 x(4 x 5)1/2 = 3. 6 measured for [U(NCS)8]4 -: 2. 9 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 19

Chapter 2 Physico-chemical properties Spin-orbit coupling constants for some trivalent ions fn Ln. III z 4 f/cm-1 An. III z 5 f/cm-1 f 3 Nd 885 f 4 Pm f 5 U 1666 1070 Np 2070 Sm 1160 Pu 2292 f 6 Eu 1326 Am 2548 f 7 Gd 1450 Cm 2968 Moreover, interelectronic repulsion is only about 2/3 that of Ln ions, therefore j-j coupling should be used. MSc: f-Elements, Prof. J. -C. Bünzli, 2008 20

Chapter 2 2. 3. 1 Physico-chemical properties Electronic absorption spectra General considerations: selection rules Laporte’s rule: Dl = ± 1 (ed) Dl = ± 0 (md) Spin rule: DS = 0 DS = ± 1 (md) (ed) Rules on L and J: depend on the specific ion Symmetry rule: GopÌ Gix. Gf 2. 3. 2 Spectra of An. III aquo ions They contain f-f transitions (100 -300 M-1 cm-1) and more intense f-d absorptions (1000 -3000 M-1 cm-1), (5 f. N ® 5 f. N-16 d). MSc: f-Elements, Prof. J. -C. Bünzli, 2008 21

Chapter 2 e/ 300 Physico-chemical properties 4 I M-1 cm-1 15/2 4 F 7/2 4 G 5/2 4 S 3/2 5 levels 200 7 levels 4 G 100 4 I 2 H 4 F 7/2 13/2 4 I 9/2 5/2 11/2 0 24 2000 20 e/ 16 M-1 cm-1 12 30 40 4 E / 103 cm-1 f-d transitions 1000 20 8 50 103 cm-1 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 U 3+ 5 f 3, 4 I 9/2 22

Chapter 2 Physico-chemical properties Pu 3+ 5 f 5, 6 H 5/2 28 24 20 16 12 E / 103 cm-1 8 2. 3. 3 Uranyl spectrum UVI: main compounds UF 6, UCl 6, UOF 4, UOMe 6, and UO 22+ compounds MSc: f-Elements, Prof. J. -C. Bünzli, 2008 23

Chapter 2 Uranyl : Physico-chemical properties Linear molecule Vibrational frequencies: 920 -990 cm-1 nas 850 -900 cm-1 ns 240 -260 cm-1 ds z 1. 7 -1. 9 Å very short! Bonding, MO model, symmetry D¥h: UVI: [Rn]5 f 06 d 0, these a. o. can be implied in bonding 6 d sg (dz 2) pg (dxz, dyz) dg (dxy, dx 2 -y 2) 5 f su(fz 3) pu(fxz 2, fyz 2) du(fxyz, fz(x 2 -y 2)) fu(fx(x 2 -3 y 2), fy(3 x 2 -y 2) MSc: f-Elements, Prof. J. -C. Bünzli, 2008 24

Chapter 2 Physico-chemical properties D¥h E 2 … ¥sv i 2 … ¥s’v h=¥ S+g 1 1 … +1 +1 1 … +1 x 2+y 2, z 2 S-g 1 1 … -1 +1 1 … -1 Rz Pg 2 2 cosf … 0 +2 -2 cosf … 0 Rx, Ry Dg 2 2 cos 2 f … 0 +2 +2 cos 2 f … 0 Fg 2 2 cos 3 f … 0 +2 0 … … … … … S+u 1 1 … +1 -1 -1 … -1 S-u 1 1 … -1 -1 -1 … + Pu 2 2 cosf … 0 -2 +2 cosf … 0 Du 2 2 cos 2 f … 0 -2 -2 cos 2 f … 0 xyz, x(x 2 -y 2) Fu 2 2 cos 3 f … 0 -2 +2 cos 3 f … 0 x(x 2 -3 y 2), y(3 x 2 -y 2) … … … -2 cos 3 f … … … xy, xz x 2 -y 2, xy z z 3, z(x 2+y 2) x, y xz 2, yz 2 … Symmetry-adapted 2 p(O) orbitals: sg + su + pg + pu Therefore dg, du, fu are non bonding orbitals MSc: f-Elements, Prof. J. -C. Bünzli, 2008 25

Chapter 2 Physico-chemical properties Some m. o. sg 2 pz dz 2 2 pz su fz 3 2 pz pg z 2 px 2 py dxz dyz 2 px 2 py MSc: f-Elements, Prof. J. -C. Bünzli, 2008 fxz 2 fyz 2 pu 2 px 2 py 26

Chapter 2 Physico-chemical properties pg UO 22+ Approximate MO diagram sg 6 d pg dg su dg Ground state: …(pu)4(su)2 1 Sg su p 5 f fu u du pu fu du sg No bonding electron U 6+ su pg sg pu UO 2 2+ 2 Excited states: …(pu)4(su)1(du)1 …(pu)4(su)1(fu)1 2 p …(pu)3(su)2(du)1 …(pu)3(su)2(fu)1 etc. O 2 - MSc: f-Elements, Prof. J. -C. Bünzli, 2008 (Level ordering is somewhat arbitrary) 27

Chapter 2 Physico-chemical properties UVI : typical uranyl spectrum e / M-1 cm-1 [UO 2(Me. CO 2)3 20 ]- av. 670 cm-1 10 0 350 400 450 nm U-O-U stretch Ground state (IR/Raman) 850 cm-1 (symmetric) Excited states: …(pu)4(su)1(du)1 …(pu)4(su)1(fu)1 …(pu)3(su)2(du)1 …(pu)3(su)2(fu)1 etc. …(pu)3(su)2(du)1 gives rise to 1 F , 1 P , 3 F , 3 P u u g g identified as in D¥h 1 P 1 S u g MSc: f-Elements, Prof. J. -C. Bünzli, 2008 28

Chapter 2 Physico-chemical properties 2. 3. 4 Ln. III ions f-f transitions e < 10 M-1 cm-1 - Narrow bands - Barycenters of LF sublevels are not much dependent on the nature of the Ln. III environment therefore energy of the transitions is more or less constant (but not LF splitting!) Electric dipole transitions are forbidden Magnetic dipole transitions are allowed, but very weak The number of components for a given (2 S’+1)L’J’ 2 S+1)LJ transition depends on the site symmetry. Some transitions are hypersensitive, i. e. very sensitive to small changes in the Ln. III environment MSc: f-Elements, Prof. J. -C. Bünzli, 2008 29

Chapter 2 Physico-chemical properties E / 103 cm-1 25 2 1 3 P 0 J 20 1 I 6 1 D 15 2 10 5 0 l/nm Tf 2 N MSc: f-Elements, Prof. J. -C. Bünzli, 2008 2 1 0 3 P 1 I 6 1 D 2 1 G 4 4 3 2 3 F 6 5 3 H 4 Pr. III 4 f 2, 3 H 4 30

Chapter 2 Physico-chemical properties Europium(III), 4 f 6 Special selection rules (also valid for 4 f 8, Tb. III): - ED: DL, DJ = 0, 2, 4, 6 0 -0 - MD: DL = 0, DJ = 0, ± 1 forbidden 2. 8 e / M-1 cm-1 5 L 2. 4 6 Eu. Cl 3 0. 05 M in H 2 O 2. 0 1. 6 1. 2 0. 8 5 G 4 5 G 3 5 K 5 H 6 5 F 4 6 4 0. 4 250 300 (2 S+1)G J 5 G 5 D 4 3 6 5 G 4 5 G 2 5 D 350 400 J 7 F 0, 1 3 5 D 450 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 2 5 D 1 500 nm 31

Chapter 2 Physico-chemical properties 5 D 0 7 F 0 (MD) 5 D 5 H 7 F 0 (ED) 1 DJ=1 7 FJ (MD) DJ=0 6 5 L 6 7 F 0 (ED) J=0 DJ=6 5 D 4 0 1 5 G 7 FJ (MD) 5 G 4 5 G 0 1 0 2 J’ 1 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 5 D 2 J=1 7 FJ (ED) J=0, DJ=2 J=1, DJ=1 32

Chapter 2 0. 003 0. 002 A Physico-chemical properties Yb(Tf 2 N)3 10 -2 M in Bumin. Tf 2 N E / 103 cm-1 2 F 5/2 10. 001 0 MD transition 950 960 970 980 990 nm Absorption coefficient: e = 0. 00203/0. 01´ 0. 1 = 2. 03 M-1 cm-1 0 2 F 7/2 Yb. III 4 f 13, 2 F 7/2 Conclusion: RS scheme O. K. for Ln. III ions MSc: f-Elements, Prof. J. -C. Bünzli, 2008 33

Chapter 2 Physico-chemical properties Hypersensitivity Some f-f transitions are particularly sensitive to changes in symmetry and/or in the inner coordination sphere. They display shifts of their maxima, splittings, and intensity variation. Some examples: 3 F 3 H Pr. III 5200 cm-1 2 4 2 H Nd. III , 4 F 5/2 4 I 9/2 17300 cm-1 9/2 5 D 7 F , 5 D 7 F Eu. III 21500, 18700 cm-1 2 0 1 1 5 G 5 I , 5 H 5 I Ho. III 22100, 27700 cm-1 6 8 2 H Er. III 4 I 15/2 19200 cm-1 11/2 1 G 3 H Tm. III 21300 cm-1 4 6 The mechanism has been discussed at length: it arises from the mixing of the 4 f states with ligand states MSc: f-Elements, Prof. J. -C. Bünzli, 2008 34

Chapter 2 Physico-chemical properties Transitions of Nd. III: 4 4 I 3 4 I 2 4 I 1 4 I 420 10 5 9/2 4 F 9/2 4 G , 2 G 7/2 5/2 9/2 2 K , 4 G 500 e/M-1 cm-1 2 1 600 3 5/2, 2 H 103 cm-1 13/2 750 2 K 9/2 20 , 4 S 3/2 7/2 , 2 G 1000 2 G 2 H 9/2 2000 5000 nm 10 4 4 I 0 24 22 20 18 16 14 12 10 8 6 4 4 G 4 S 4 F 15/2 Nd 3+(aq) 0 etc ! 13/2 11/2 9/2 2 103 cm-1 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 35

Chapter 2 Physico-chemical properties Nd. III hypersensitivity 2 H 9/2, CN = 4 F 5/2 4 I 9/2 Nd(Br. O 3)3´ 9 H 2 O (solid) 9 9 [Nd(H 2 O)9]3+ 0. 05 M / H 2 O [Nd(H 2 O)9]3+ 0. 05 M / HCl 11 M CN = 8 8 8 780 Nd. Cl 3´ 6 H 2 O (solid) Nd 2(SO 4)3´ 8 H 2 O (solid) 800 820 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 36

Chapter 2 Physico-chemical properties f-d Transitions Allowed by Laporte’s rule, » 100 -1000 M-1 cm-1 Highly energetic, except for Ce. III, Pr. III, and Tb. III Free ions MSc: f-Elements, Prof. J. -C. Bünzli, 2008 37

Chapter 2 [Ce(H 2 O)9 102 e 8 ]3+, 225 Physico-chemical properties E / 103 cm-1 D 3 h symmetry 250 n. obs. 300 nm 6 2 D 5/2 2 D 3/2 44. 0 4 2 0 48. 0 E / 103 cm-1 48 44 40 36 40. 0 32 Ce 3+ [Xe]5 d 1 generates two levels, 2 D 3/2 and 2 D 5/2 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 2 2 F 7/2 0 2 F 5/2 38

Chapter 2 Physico-chemical properties Observed f-d transitions for Ln. Br 3 in anhydrous Et. OH: Ce Pr Tb 312 nm ( 800 M-1 cm-1) 228 nm (1500 M-1 cm-1) 231 nm ( 500 M-1 cm-1) 100 e / M-1 cm-1 Ln. III (aq) 300 e / M-1 cm-1 Tb 200 50 0 Pr 100 0 49 47 45 E / 103 cm-1 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 49 47 45 43 E / 103 cm-1 39

Chapter 2 Physico-chemical properties E /103 cm-1 Charge transfer transitions Allowed by Laporte’s rule, » 200 -500 M-1 cm-1 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 40

Chapter 2 Physico-chemical properties Charge transfer in bimetallic complexes with calix[n]arenes p-tert-butylcalix[5]arene (b-L’H 5) wider rim (lipophilic) narrow rim (oxophilic) Cone conformation [Eu 2(b-L’H 2)2(DMSO)4] MSc: f-Elements, Prof. J. -C. Bünzli, 2008 41

Chapter 2 e / M-1 cm-1 3000 Physico-chemical properties [Eu 2(b-L’H 2)2(DMSO)4], 7 x 10 -4 M in thf 2500 2000 24 740 cm-1 1500 M-1 cm-1 719 LMCT transition 1000 500 0 nm 400 500 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 600 42

Chapter 2 Physico-chemical properties p-tert-butylcalix[8]arene “undulated” conformation [Eu 2(b-LH 2)(dmf)5] MSc: f-Elements, Prof. J. -C. Bünzli, 2008 43

Chapter 2 Physico-chemical properties LMCT: 25’ 000 cm-1, MSc: f-Elements, Prof. J. -C. Bünzli, 2008 e = 720 M-1 cm-1 44

Chapter 2 Physico-chemical properties Intensity stealing Overlap between LMCT and f-states leads to f-f transitions with larger intensities, e. g. 5 D 0 7 F 0 Replacing p-tbut by SO 3 H (s-LH 8) and NO 2 (n-LH 8) leads to LMCT states with higher energy and to a reduced intensity stealing Cmpnd MLCT/cm-1 0 -0/cm-1 e / M-1 cm-1 Eu 2(b-LH 2) 24740 17330 5. 0 Eu 2(s-LH 2) 30300 17322 1. 4 Eu 2(n-LH 2) not located 17319 0. 8 [Eu(H 2 O)9]3+ - 0. 001 17212 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 45

Chapter 2 2. 4 Physico-chemical properties Luminescence spectra 2. 4. 1 Basics of luminescence Jablonski’s diagram (organic molecules) energy S 2 S = singlet E 2 T = triplet S 1 E 1 T 1 A F A = absorption 10 -16 s F = fluorescence 10 -12 -10 -6 s P = phosphorescence 10 -6 – 10 s P E 0 S 0 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 non-radiative de-activation intersystem crossing 46

Chapter 2 Physico-chemical properties e(YO. M. ) intersystem one electron changes its spin crossinglet S 1 triplet T 1 Fluorescence : without spin change Phosphorescence : with spin change MSc: f-Elements, Prof. J. -C. Bünzli, 2008 47

Chapter 2 Physico-chemical properties The states involved sp* states s p* pp* states MSc: f-Elements, Prof. J. -C. Bünzli, 2008 48

Chapter 2 Physico-chemical properties np* states n p* Charge transfer states 4 fn ® 4 fn+1 L-1 (reduction of the metal ion) 4 fn ® 4 fn-1 L+1 (oxidation of the metal ion) MSc: f-Elements, Prof. J. -C. Bünzli, 2008 49

Chapter 2 Physico-chemical properties Quantum yield : The quantum yield increases when temperature decreases MSc: f-Elements, Prof. J. -C. Bünzli, 2008 50

Chapter 2 Physico-chemical properties What is the relationship between Iobs and concentration ? The condition on ebc stems from the fact that only the first term of a series development is retained in demonstrating this formula. MSc: f-Elements, Prof. J. -C. Bünzli, 2008 51

Chapter 2 Physico-chemical properties Example of a calibration curve showing the inner-filter effect Iobs NADH in H 2 O c / m. M 0. 001 0. 01 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 0. 1 1. 0 52

Chapter 2 E Physico-chemical properties vibrational levels (rotations not shown) excited state Born-Oppenheimer approximation Vertical absorption Vertical emission Kasha’s rule: emission from relaxed excited state Non-radiative de-activation ground state distance DE = DEel + DEvibr + DErot MSc: f-Elements, Prof. J. -C. Bünzli, 2008 53

Chapter 2 Physico-chemical properties excited states singlet S 1 triplet T 1 E isc DE < DE , l. P > l. F ground state S 0 Fluorescence and phosphorescence When vibrational levels match, the energy can flow to the triplet state: intersystem crossing isc Phosphorescence occurs distance MSc: f-Elements, Prof. J. -C. Bünzli, 2008 54

Chapter 2 Physico-chemical properties Time dependence of the emitted light If N * is the number of excited molecules at time t: -d. N */dt = kr·N * kr = radiative rate constant (s-1) -d. N */N * = kr·dt Integration between {N 0*; t 0 } and {N *; t } gives N * = N 0*·e-krt I(t) = It=0·e-krt The lifetime of the excited level is given by: t = 1/kobs (s) During this time, a fraction 1/e of the excited molecules return to the ground state (e = 2, 73) MSc: f-Elements, Prof. J. -C. Bünzli, 2008 55

Chapter 2 Physico-chemical properties Photons per s 1000 1/e I 0 800 t = 14 ns 600 7 kobs = 7, 1. 10 s 400 -1 200 t=t 0 0 10 10 9 t / s 20 30 40 Quinine sulfate in water MSc: f-Elements, Prof. J. -C. Bünzli, 2008 56

Chapter 2 Physico-chemical properties In absence of non-radiative de-activation (Q = 1), kobs = kr In presence of non-radiative de-activation (Q < 1), kobs = kr + knr, therefore 2. 4. 2 The special case of 4 f-elements In view of the weak f-f oscillator strengths, direct excitation of Ln. III luminescence is not very efficient, unless powerful lasers are used. Therefore the need for sensitisation (antenna effect). MSc: f-Elements, Prof. J. -C. Bünzli, 2008 57

Chapter 2 Physico-chemical properties Indirect excitation, called sensitisation is achieved through lattice or attached ligands hn hn light harvesting Energy transfer light emision The excited states of Ln. III ions are usually long-lived with lifetimes in the range ms to ms, so that the ligand triplet state plays a major role in the energy transfer process. MSc: f-Elements, Prof. J. -C. Bünzli, 2008 58

Chapter 2 Physico-chemical properties Energy migration paths Ligand E sc i 1 S* Ln. III Complex 4 f* 3 T* Absorption F P LMCT ILCT Absorption Ground state > 20 rate constants ! Non radiative deactivation Energy transfer Quenching or back transfer MSc: f-Elements, Prof. J. -C. Bünzli, 2008 59

Chapter 2 Physico-chemical properties In the special case of Eu. III, tr may be estimated from: intrinsic quantum yield where n is the refractive index, Itot the total emitted light intensity and Imd the intensity of the purely magnetic dipole transition 5 D 0® 7 F 1. MSc: f-Elements, Prof. J. -C. Bünzli, 2008 60

Chapter 2 2. 4. 3 Physico-chemical properties 4 f emission spectra Tb Dy Gd 40 Ho Er Tm Yb 3 P 35 Pr 0 35 Nd Sm Eu 30 40 6 P 30 7/2 25 3 20 3 E / 10 cm -1 5 D 1 D 15 10 2 3 P 1 D 2 1 G 3 F 4 G 4 4 F 5/2 5 D 1 0 0 5 D 4 4 F 1 G 9/2 5 S 4 S 2 5 F 20 4 3/2 15 5 2 F 3/2 4 5 4 I 5/2 10 5 13/2 0 0 3 H 4 4 I 9/2 6 H 5/2 7 F 0, 1 8 S 7/2 7 F 6 6 H 15/2 5 I 8 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 4 I 15/2 3 H 6 2 F 7/2 61

Chapter 2 Physico-chemical properties The smaller the gap between excited and ground state, the larger the contribution of non-radiative de-activation (particularly through vibrations). Tb Gd. III is the best ion, but emits in the UV Eu. III, Tb. III have often large intrinsic quantum yields and are used as luminescent probes. Eu Dy Sm 500 600 700 nm Pr. III (1. 33 mm), Nd. III (1. 06 mm), Er. III (1. 54 mm), and Yb. III (0. 98 mm) have interesting emission bands in the NIR range, some of them are in the telecommunication window (1 – 1. 6 mm) MSc: f-Elements, Prof. J. -C. Bünzli, 2008 62

Chapter 2 Physico-chemical properties Cerium(III) in Oh symmetry Cs 2 Na(Y: Ce)Cl 6 Double group O’h Emission spectrum at 10 K, exc. 50 x 103 cm-1 2 T 2 2 g(G 8 g) ® F 7/2 G 6 u E / 103 cm-1 24 25 G 7 u 2 T 26 2 g(G 8 g) 48. 0 30. 0 ® 2 F 5/2 27 G 8 g 2 E g 44. 0 G 8 u E / 103 cm-1 28 (E. P. Tanner et al. JACS 2003 125, 13225) MSc: f-Elements, Prof. J. -C. Bünzli, 2008 2 0 G 7 g G 8 g G 6 u G 8 u G 7 u 2 T 2 g 2 F 7/2 2 F 5/2 63

Chapter 2 Physico-chemical properties Cs 2 Na(Y: Ce)Cl 6 Double group O’h Emission spectrum at 10 K, exc. 50 x 103 cm-1 2 E ( g G 8 g) ® 2 F 5/2 G 8 u G 7 u 48. 0 G 8 g 2 E g 44. 0 ® 2 F 7/2 G 8 u G 7 u 44 E / 103 cm-1 30. 0 45 46 E / 103 cm-1 47 (E. P. Tanner et al. JACS 2003 125, 13225) MSc: f-Elements, Prof. J. -C. Bünzli, 2008 2 0 G 7 g G 8 g G 6 u G 8 u G 7 u 2 T 2 g 2 F 7/2 2 F 5/2 64

Chapter 2 Physico-chemical properties Neodymium(III): Nd(NTf 2)3 in Bumim. NTf 2 E / 103 cm-1 4 I 4 I 800 2 G 20 11/2 laser line 4 I 9/2 1000 4 G 10 13/2 1200 4 F nm Tf 2 N MSc: f-Elements, Prof. J. -C. Bünzli, 2008 7/2 5/2 3/2 15/2 5 13/2 11/2 0 9/2 4 I 65

Chapter 2 N N OH Physico-chemical properties N N O H 2 L O OH • logb 23 = 51 for Eu • p. Eu = 21 (dota : 25) Samarium emission spectrum: MSc: f-Elements, Prof. J. -C. Bünzli, 2008 66

Chapter 2 Physico-chemical properties Samarium(III): Sm 2 L 3 in H 2 O E / 103 cm-1 4 I 20 15 J 4 F 4 G J J 7/2 5/2 160 11/2 6 F J 5 6 H 0 1/2 15/2 4 G 5/2 ® 6 HJ 120 80 10 7/2 9/2 5/2 11/2 40 nm 0 550 600 650 700 750 J 5/2 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 67

Chapter 2 Physico-chemical properties Europium(III): tris(dipicolinate) Cs 3[Eu(dpa)3] Solid state Emission spectrum dpa 250 300 lexc = 280 nm (L) Excitation spectrum 5 L 6 5 D 350 400 450 395 nm (f-f) 5 D 2 500 1 550 l / nm 580 600 620 MSc: f-Elements, Prof. J. -C. Bünzli, 2008 640 660 l / nm 680 700 720 68

Chapter 2 Physico-chemical properties Europium(III): tris(dipicolinate) Q LEu = 56 ± 2 % tobs = 1. 8 ± 0. 1 ms Q Eu. Eu = 66 ± 4 % hsens = 56/66 = 85 % Itot / IMD = 7. 4 n = 1. 517 trad = 2. 74 ms Q Eu. Eu = 1. 8/2. 74 = 66 % Perfect match! MSc: f-Elements, Prof. J. -C. Bünzli, 2008 69

Chapter 2 Physico-chemical properties Terbium(III): Tb(NO 3)3 in DMSO E / 103 cm-1 5 5 D 0 1 4 ® 7 F J 5 D 25 3 J=6 4 3 5 D 20 2 x 6 30 4 15 10 5 650 600 550 500 nm MSc: f-Elements, Prof. J. -C. Bünzli, 2008 0 0 6 7 F 70

MSc: f-Elements, Prof. J. -C. Bünzli, 2008 71