Stereochemistry controlled by an asymmetric sulfur atom, and a rare example of a kryptoracemate

Article abstract of DOI:10.1039/c2dt30892d

The ligands 4-methylthio-6-phenyl-2,2′-bipyridine (1) and the corresponding sulfoxide (2) and sulfone (3) have been synthesized and characterized in solution, and in the solid state by single crystal X-ray diffraction. Compounds 2 and 3 crystallize in the same space group (C2/c) with similar unit cell parameters; a small increase in the unit cell volume allows for the presence of the extra oxygen atom in 3. The sulfoxide and sulfone groups adopt conformations that permit intramolecular O...HC_aryl hydrogen bonds. The complexes [Ir(ppy)₂L][PF₆] with L = 1, 2 or 3 have been prepared and characterized. The asymmetric sulfur atom in ligand 2 gives rise to pairs of diastereoisomers of the complex which can be distinguished in the ¹H and ¹³C NMR spectra. In solution, exchange of [PF₆]^- by [Δ-TRISPHAT]^- gives rise to four diastereoisomers and we observed good dispersion of ¹H NMR resonances, especially for those assigned to protons close to the asymmetric sulfur atom. A single crystal X-ray diffraction study of 2{[Ir(ppy) ₂(3)][PF₆]}·CHCl₃·3H ₂O reveals that the complex crystallizes in the chiral space group P2₁2₁2₁, the asymmetric unit containing crystallographically independent Δ- and Λ-[Ir(ppy) ₂(3)]⁺ cations. This provides a rare example of a so-called kryptoracemate in the solid state. In MeCN solution, [Ir(ppy) ₂(1)][PF₆], [Ir(ppy)₂(2)][PF₆] and [Ir(ppy)₂(3)][PF₆] are weakly emissive (λ_em = 600, 647 and 672 nm, respectively) and preliminary studies of the electroluminescent properties of [Ir(ppy)₂(2)][PF ₆] indicate that the complexes are not suitable candidates for LECs.

Full text of DOI:10.1039/c2dt30892d

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 10276
www.rsc.org/dalton
PAPER
Stereochemistry controlled by an asymmetric sulfur atom, and a rare example
of a kryptoracemate†‡
Imenne Bouamaied, Edwin C. Constable,* Catherine E. Housecroft,* Markus Neuburger and
Jennifer A. Zampese
Received 24th April 2012, Accepted 6th June 2012
DOI: 10.1039/c2dt30892d
The ligands 4-methylthio-6-phenyl-2,2′-bipyridine (1) and the corresponding sulfoxide (2) and sulfone
(3) have been synthesized and characterized in solution, and in the solid state by single crystal X-ray
diffraction. Compounds 2 and 3 crystallize in the same space group (C2/c) with similar unit cell
parameters; a small increase in the unit cell volume allows for the presence of the extra oxygen atom in 3.
The sulfoxide and sulfone groups adopt conformations that permit intramolecular O⋯HCaryl hydrogen
bonds. The complexes [Ir(ppy)2L][PF6] with L = 1, 2 or 3 have been prepared and characterized. The
asymmetric sulfur atom in ligand 2 gives rise to pairs of diastereoisomers of the complex which can be
distinguished in the 1H and 13C NMR spectra. In solution, exchange of [PF6]− by [Δ-TRISPHAT]− gives
rise to four diastereoisomers and we observed good dispersion of 1H NMR resonances, especially for
those assigned to protons close to the asymmetric sulfur atom. A single crystal X-ray diffraction study
of 2{[Ir(ppy)2(3)][PF6]}·CHCl3·3H2O reveals that the complex crystallizes in the chiral space group
P212121, the asymmetric unit containing crystallographically independent Δ- and Λ-[Ir(ppy)2(3)]+ cations.
This provides a rare example of a so-called kryptoracemate in the solid state. In MeCN solution,
[Ir(ppy)2(1)][PF6], [Ir(ppy)2(2)][PF6] and [Ir(ppy)2(3)][PF6] are weakly emissive (λem = 600, 647 and
672 nm, respectively) and preliminary studies of the electroluminescent properties of [Ir(ppy)2(2)][PF6]
indicate that the complexes are not suitable candidates for LECs.
well established in [Ru(tpy)2]2+-based systems (tpy = 2,2′:6′,2′′-
terpyridine) that photophysical properties can be fine-tuned by
Introduction
There is much current interest in the preparation of octahedral
iridium(III) complex cations [Ir(C^N)2L]+ in which C^N denotes
a cyclometallated ligand such as the anion derived from Hppy
(2-phenylpyridine) and L is a neutral, chelating ligand. These
luminescent complexes are used in the emissive layer in light-
emitting electrochemical cells (LECs).1 The tuning of the
N,N′-chelating ligands can lead to efficient electroluminescent
behaviour, as was initially observed in [Ir(ppy)2L]+ where L =
4,4′-di-tert-butyl-2,2′-bipyridine.2 Tuning the electroluminescent
properties of [Ir(C^N)2L]+ complexes is at the forefront of syn-
thetic strategy3–5 and there is wide scope for functionalizing
either or both the cyclometallating and the N,N′-ligand.6–8 It is
the introduction of electron-withdrawing or electron-releasing
groups, typically in the 4′-position of tpy.9,10 An attractive series
of synthetically accessible and readily interconverted electron-
withdrawing substituents are SMe, SOMe and SO2Me, the
Hammett parameters for which vary significantly.11,12 For
example, on going from [Ru(tpy)2]2+ (which is non-emissive in
fluid solution) to [Ru(4′-MeO2Stpy)2]2+, the strongly electron-
withdrawing sulfone unit has a dramatic effect on the photophy-
sical properties and results in an emission in MeCN solution at
650 nm with a lifetime of 25 ns.9
Whereas 4′-methylthio-2,2′:6′,2′′-terpyridine, and the corres-
ponding sulfoxide and sulfone derivatives are documented,9,12–16
the analogous 6-phenyl-2,2′-bipyridine compounds have
received negligible attention. Potts has described the synthesis of
4-methylthio-6-phenyl-2,2′-bipyridine (1),17,18 but to the best of
our knowledge, the sulfoxide (2) and sulfone (3) have not been
reported. In this paper, we describe the preparation, characteriz-
ation and photophysical properties of [Ir(ppy)2L]+ (L = 1–3).
The pendant phenyl ring in each of ligands 1–3 is an essential
feature of the N,N′-chelating ligands and is expected to engage
in intra-cation face-to-face π-stacking with a coordinated [ppy]−.
This structural phenomenon has been shown to strongly
influence the photophysical properties of such complexes19 and
Department of Chemistry, University of Basel, Spitalstrasse 51, CH4056
Basel, Switzerland. E-mail: edwin.constable@unibas.ch,
catherine.housecroft@unibas.ch; Fax: +41 61 267 1018;
Tel: +41 61 267 1008
†Dedicated to Professor David Cole-Hamilton on the occasion of his
retirement and for his outstanding contribution to transition metal
catalysis.
‡Electronic supplementary information (ESI) available: Fig. S1. Aro-
1
matic regions of 400 MHz H NMR spectra of [Ir(ppy)2(2)][PF6] and a
1 : 1 mixture of the complex and [Et4N][Δ-TRISPHAT]. CCDC
877474–877477. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt30892d
10276 | Dalton Trans., 2012, 41, 10276–10285
This journal is © The Royal Society of Chemistry 2012

View Article Online
to enhance LEC device lifetimes.20–25 The sulfoxide differs from
the other substituents in possessing a stereogenic sulfur atom26
and we were particularly interested in the consequences of in-
corporating this functionality into the complexes.
10−5 mol dm−3, λex = 264 nm): λem = 362 nm. Found C 72.01,
H 5.12, N 10.07%; C17H14N2S·1/4H2O requires C 72.18, H
5.17, N 9.90.
Compound 2
Experimental
Compound 1 (500 mg, 1.8 mmol) was dissolved in CH2Cl2
(12 ml) and the solution was cooled in an ice bath. 3-Chloroper-
benzoic acid (400 mg, 2.3 mmol) was added and the solution
was stirred at room temperature for 1.5 h. The mixture was then
diluted by addition of CHCl3 (15 ml), washed twice with
aqueous NaHCO3 and once with H2O, and was dried over
Na2SO4. The crude product was purified by column chromato-
graphy (silica, CH2Cl2 : MeOH 100 : 1) yielding 2 as the second
fraction; the first fraction was 3. Compound 2 was isolated as a
white solid (320 mg, 1.1 mmol, 61%). Compound 3 was isolated
as a yellowish powder (100 mg, 0.32 mmol, 18%). Compound
General
1H and 13C NMR spectra were recorded on a Bruker DRX-400
or DRX-500 NMR spectrometer with chemical shifts referenced
to residual solvent peaks (with respect to TMS = δ 0 ppm). Solu-
tion electronic absorption spectra were recorded on an Agilent
8453 spectrophotometer, and emission spectra on a Shimadzu
RF-5301 PC spectrofluorometer. The wavelengths for the exci-
tation for the fluorescence measurements were selected according
to the absorption measurements. The excitation and emission
slits were kept at 5 units respectively. Electrospray ionisation or
MALDI-TOF mass spectra were measured on a Bruker esquire
3000plus or Microflex BRUKER Daltonics instrument. Electro-
chemical measurements were carried out using a CHI 900B
instrument with glassy carbon working and platinum auxiliary
electrodes; a silver wire was used as a pseudo-reference
electrode. Solvent was dry, purified MeCN and 0.1 mol dm−3
[nBu4N][PF6] was used as supporting electrolyte. Cp2Fe was
used as external reference before each experiment.
1
2: H NMR (500 MHz, CD2Cl2) δ/ppm: 8.70 (ddd, J = 4.7, 1.8,
0.9 Hz, 1H, HE6), 8.66 (dt, J = 7.9, 1.0 Hz, 1H, HE3), 8.53
(d, J = 1.4 Hz, 1H, HF3), 8.24 (m, 2H, HG2), 8.13 (d, J = 1.4 Hz,
1H, HF5), 7.90 (td, J = 7.7, 1.8 Hz, 1H, HE4), 7.55 (m, 2H,
HG3), 7.50 (m, 1H, HG4), 7.39 (ddd, J = 7.5, 4.8, 1.2 Hz, 1H,
HE5), 2.85 (s, 3H, HMe). 13C NMR (126 MHz, CD2Cl2) δ/ppm:
159.2 (CF6), 158.2 (CE2), 157.0 (CF2), 155.5 (CF4), 149.7 (CE6),
138.8 (CG1), 137.7 (CE4), 130.3 (CG4), 129.4 (CG3), 127.7
(CG2), 125.0 (CE5), 121.9 (CE3), 114.4 (CF5), 114.0 (CF3), 44.0
(CMe). MALDI-TOF MS: m/z 294.1 [M]+ (base peak, calc
294.1). UV-Vis λ/nm (MeCN, 1.00 × 10−5 mol dm−3) 248 sh
(ε/dm3 mol−1 cm−1 36 500), 260 (38 500), 281 sh (25 700), 309
The precursor 3,3-bis(methylthio)-1-(2-pyridinyl)-2-propen-
1-one was prepared according to Potts.17,18 The dimer
[Ir2(ppy)4(μ-Cl)2] was prepared by a literature method.27
(13 800). Emission (MeCN, 1.0 × 10−5 mol dm−3, λex
=
Compound 1
263 nm): λem = 358 nm. Found C 69.16, H 4.85, N 9.73%;
C17H14N2OS requires C 69.36, H 4.79, N 9.52.
Anhydrous THF (44 ml) and KOtBu (2.0 g, 16 mmol) were
added to a three-necked round-bottomed flask (250 ml) under
N2. Freshly distilled acetophenone (1.04 g, 8.66 mmol) was
added and the solution was stirred for 45 min after which time
3,3-bis(methylthio)-1-(2-pyridinyl)-2-propen-1-one (2.00 g,
8.88 mmol) was added. The mixture was stirred for 12 h at room
temperature, during which time it turned red and a red solid
precipitated. The mixture was treated with NH4OAc (6.8 g,
0.088 mol) of glacial acetic acid (22.4 ml). THF was removed
by distillation over a 2 h period and then the solution was cooled
to 20 °C. Ice (30 g) was added and the mixture was allowed to
stand for 1 h. Water was added (60 ml) and the precipitate was
collected and recrystallized from petroleum ether to give a black
oil which solidified overnight under high vacuum. Ligand 1 was
isolated as a black solid (1.4 g, 5 mmol, 63%). 1H NMR
(500 MHz, CD2Cl2) δ/ppm: 8.68 (ddd, J = 4.8, 1.8, 0.9 Hz, 1H,
HE6), 8.63 (ddd, J = 8.0, 1.0, 1.0 Hz, 1H, HE3), 8.29 (d, J =
1.7 Hz, 1H, HF3), 8.15 (m, 2H, HG2), 7.88 (td, J = 7.7, 1.8 Hz,
1H, HE4), 7.61 (d, J = 1.7 Hz, 1H, HF5), 7.53 (m, 2H, HG3), 7.47
(m, 1H, HG4), 7.38 (ddd, J = 7.5, 4.8, 1.1 Hz, 1H, HE5), 2.64
(s, 3H, HMe). 13C NMR (126 MHz, CD2Cl2) δ/ppm: 156.5
(CF6), 156.4 (CE2), 155.8 (CF2), 152.5 (CF4), 149.5 (CE6), 139.6
(CG1), 137.4 (CE4), 129.7 (CG4), 129.2 (CG3), 127.5 (CG2),
124.5 (CE5), 121.8 (CE3), 117.0 (CF5), 115.6 (CF3), 14.4 (CMe).
MALDI-TOF MS: m/z 278.1 [M]+ (base peak, calc
278.1). UV-Vis λ/nm (MeCN, 1.00 × 10−5 mol dm−3) 264
Compound 3
Compound 1 (100 mg, 0.36 mmol) was dissolved in CH2Cl2
(2 cm3) and an ice bath was used to cool the solution. 3-Chloro-
perbenzoic acid (142 mg, 0.82 mmol) was added to the solution
and the mixture was stirred for 1.5 h. It was then diluted by the
addition of CHCl3 (5 ml), washed twice with NaHCO3, once
with H2O and finally dried over Na2SO4. The crude product was
purified by column chromatography silica, CH2Cl2 : MeOH
100 : 1) and 3 was isolated as a white solid (73 mg, 0.24 mmol,
67%). 1H NMR (500 MHz, CD2Cl2) δ/ppm: 8.85 (d, J = 1.4 Hz,
1H, HF3), 8.73 (dd, J = 4.7, 0.6 Hz, 1H, HE6), 8.65 (d, J = 8.0
Hz, 1H, HE3), 8.25 (d, J = 1.4 Hz, 1H, HF5), 8.23 (m, 3H, HG2),
7.92 (td, J = 7.7, 1.7 Hz, 1H, HE4), 7.57 (m, 2H, HG3), 7.53
(m, 1H, HG4), 7.43 (ddd, J = 7.4, 4.8, 0.9 Hz, 1H, HE5), 3.18 (s,
3H, HMe). 13C NMR (126 MHz, CD2Cl2) δ/ppm : 158.3 (CF6),
158.3 (CF2), 154.9 (CE2), 151.2 (CF4), 149.8 (CE6), 138.2 (CG1),
137.8 (CE4), 130.7 (CG4), 129.5 (CG3), 127.7 (CG2), 125.4 (CE5),
121.9 (CE3), 117.2 (CF5), 116.6 (CF3), 44.3 (CMe). MALDI-TOF
MS: m/z 310.1 [M]+ (base peak, calc 310.1). UV-Vis λ/nm
(MeCN, 1.00 × 10−5 mol dm−3) 236 (ε/dm3 mol−1 cm−1
23 400), 262 (22 800), 282 sh (16 000), 318 (11 500). Emission
(MeCN, 1.0 × 10−5 mol dm−3, λex = 267 nm): λem = 364 nm.
Found C 65.09, H 4.78, N 8.52%; C17H14N2O2S requires C
65.79, H 4.55, N 9.03.
(ε/dm3 mol−1 cm−1 41 700). Emission (MeCN, 1.0
×
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 10276–10285 | 10277

View Article Online
(CA1), 150.3 (CE6), 149.7 (CB6/D6), 149.4/149.3 (CB6/D6),
146.55/146.5 (CC1), 143.45/143.43 (CC2/A2), 143.4/143.22 (CC2/A2),
139.9 (CE4), 138.82/138.80 (CB4/CD4), 138.73/138.67 (CB4/CD4),
137.71/137.67 (CG1), 132.06/132.04 (CA6), 131.35/131.27
(CC5), 130.7 (CC6), 130.2 (CA5), 129.92/129.89 (CG4), 128.70/
128.66 (CE5), 128.46/128.47 (CG3), 127.9 (CC2), 126.41/126.36
(CE3), 125.11/125.13 (CC3), 124.5 (CA3), 124.60 (CF5′), 124.54
(CF5), 124.17 (CB5/D5), 124.11 (CB5/D5), 123.41/123.40 (CC4),
123.04/123.01 (CB5/D5), 121.44/121.42 (CA4), 120.44/120.43
(CB3/D3), 120.39/120.36 (CB3/D3), 119.9 (CF5), 119.8 (CD3/B3),
118.59 (CF3′), 118.55 (CF3), 43.3 and 43.4 (CMe, 2 diastereo-
isomers). ESI MS: m/z 795.2 [M − PF6]+ (base peak,
calc 795.1). UV-Vis λ/nm (MeCN, 1.0 × 10−5 mol dm−3) 262
(ε/dm3 mol−1 cm−1 73 200), 310 sh (39 500), 384 sh (9900).
[Ir(ppy)2(1)][PF6]
A
yellow suspension of [Ir2(ppy)4(μ-Cl)2] (180 mg,
0.168 mmol) and compound 1 (93 mg, 0.33 mmol) in a mixture
of MeOH (30 ml) and CH2Cl2 (30 ml) was heated under reflux
in N2 in the dark for 16 h. The orange solution was then cooled
to room temperature, and solid NH4PF6 (277 mg, 1.7 mmol) was
added. The mixture was stirred for 30 min at room temperature
and then evaporated to dryness. The crude product was purified
by column chromatography (silica, CH2Cl2 : MeOH = 100 : 1)
and [Ir(ppy)2(1)][PF6] was isolated as an orange solid (120 mg,
0.13 mmol, 79%). 1H NMR (500 MHz, CD2Cl2) δ/ppm:
8.50 (d, J = 8.3 Hz, 1H, HE3), 8.22 (d, J = 2.1 Hz, 1H, HF3),
8.12 (m, 1H, HE4), 7.85 (m, 4H, HE6+B3+D3+(B4/D4)), 7.77
(m, 1H, HB4/D4), 7.67 (m, 1H, HB6/D6), 7.61 (m, 1H, HB6/D6),
7.52 (m, 1H, HC3), 7.36 (ddd, J = 7.6, 5.5, 1.2 Hz, 1H, HE5),
7.23 (dd, J = 7.8, 1.2 Hz, 1H, HA3), 7.16 (d, J = 2.0 Hz, 1H,
HF5), 7.12 (ddd, J = 7.8, 5.4, 1.6 Hz, 1H, HB5/D5), 7.04 (m, 1H,
HB5/D5), 6.94 (m, 2H, HC4+G4), 6.81 (td, J = 7.5, 1.4 Hz,
1H, HC5), 6.73 (t, J = 7.7 Hz, 2H, HG3), 6.59 (td, J = 7.5,
1.1 Hz, 1H, HA4), 6.52 (br, 1H, HG2), 6.38 (td, J = 7.4, 1.3 Hz,
1H, HA5), 5.96 (d, J = 7.7, 1.2 Hz, 1H, HC6), 5.57 (dd, J = 7.7,
1.2 Hz, 1H, HA6), 2.65 (s, 3H, HMe). 13C NMR (126 MHz,
CD2Cl2) δ/ppm: 169.3 (CB2), 167.7 (CD2), 164.7 (CF6), 157.8
(CE2), 156.7 (CF2), 156.2 (CF4), 151.5 (CA1), 150.8 (CE6), 149.5
(CB6/D6), 149.2 (CB6/D6), 147.4 (CC1), 143.5 (CC2), 143.2 (CA2),
139.7 (CE4), 138.6 (CB4/CD4), 138.4 (CB4/D4), 138.0 (CG1),
131.8 (CA6), 131.2 (CC5), 130.7 (CC6), 130.0 (CA5), 129.5
(CG4), 128.3 (CG3), 128.2 (CE5), 127.3 (CG2), 125.4 (CE3), 125.1
(CC3), 125.0 (CA3), 124.9 (CF5), 123.9 (CB5/D5), 123.2 (CC4),
122.8 (CB5/D5), 121.2 (CA4), 120.4 (CD3/B3), 120.3 (CD3/B3),
119.7 (CF3), 30.2 (CMe). ESI MS: m/z 779.2 [M − PF6]+ (base
Emission (MeCN, 1.0 × 10−5 mol dm−3, λex = 269 nm): λem
=
647 nm. Found C 49.50, H 3.15, N 5.91%; C39H30F6IrN4OPS
requires C 49.84, H 3.22, N 5.96.
[Ir(ppy)2(3)][PF6]
The method was as for [Ir(ppy)2(1)][PF6] starting with
[Ir2(ppy)4(μ-Cl)2] (142 mg, 0.13 mmol) and ligand 3 (77 mg,
0.25 mmol). [Ir(ppy)2(3)][PF6] was isolated as orange
1
solid (80 mg, 0.084 mmol, 67%). H NMR (500 MHz, CD2Cl2)
δ/ppm: 8.86 (d, J = 1.8 Hz, 1H, HF3), 8.66 (d, J = 8.3 Hz, 1H,
HE3), 8.12 (td, J = 8.1, 1.5 Hz, 1H, HE4), 7.88–7.82 (m, 5H,
HB4/D4+D6/B6+B3+D3+E6), 7.81 (d, J = 1.8 Hz, HF5), 7.78 (td, J =
7.9, 1.4 Hz, 1H, HB4/D4), 7.60 (t, J = 8 Hz, 1H, HB6/D6), 7.55
(d, J = 7.8, 1.0 Hz, 1H, HC3), 7.40 (ddd, J = 7.5, 5.5, 1.0 Hz,
1H, HE5), 7.24 (dd, J = 7.8, 0.9 Hz, 1H, HA3), 7.16–7.19
(m, 1H, HB5/D5), 7.00–7.03 (m, 1H, HB5/D5), 6.94–6.98 (m, 2H,
HC4+G4), 6.82–6.77 (m, 3H, HC5+G3), 6.61 (m, 2H, HG2+A4),
6.39 (td, J = 7.5, 1.2 Hz, 1H, HA5), 5.92 (d, J = 7.7 Hz, 1H,
peak, calc 779.2). UV-Vis λ/nm (MeCN, 1.0 × 10−5 mol dm−3
)
258 sh (ε/dm3 mol−1 cm−1 83 100), 268 (88 700). Emission
(MeCN, 1.0 × 10−5 mol dm−3, λex = 270 nm): λem = 600 nm.
Found C 51.34, H 3.58, N 6.27; C39H30F6IrN4PS requires C
50.70, H 3.27, N 6.06.
H
C6), 5.56 (d, J = 7.6 Hz, 1H, HA6), 3.30 (s, 3H, HMe). 13C
NMR (126 MHz, CD2Cl2) δ/ppm: 169.1 (CB2), 168.0 (CF6),
167.1 (CD2), 159.3 (CF2), 156.3 (CE2), 151.0 (CA1/F4), 150.9
(CB6/D6), 150.8 (CA1/F4), 150.5 (CE6), 149.4 (CB6/D6), 146.3
(CC1), 143.4 (CC2), 143.1 (CA2), 139.8 (CE4), 138.9 (CB4/D4),
138.7 (CB4/D4), 137.4 (CG1), 132.5 (CA6), 131.2 (CC5), 130.7
(CC6), 130.3 (CA5), 130.1 (CG4), 128.8 (CE5), 128.4 (CG3), 127.9
(CG2), 127.4 (CF5), 126.6 (CE3), 125.1 (CC3), 124.8 (CA3),
124.4 (CB5/D5), 123.5 (CC4), 123.2 (CB5/D5), 121.5 (CA4/F3),
121.4 CA4/F3), 120.3 (CF3+D3/B3), 30.2 (CMe). ESI MS: m/z 811.2
[M − PF6]+ (calc. 811.2). UV-Vis λ/nm (MeCN, 1.0 ×
10−5 mol dm−3) 258 (ε/dm3 mol−1 cm−1 75 600), 317 sh (37 400),
[Ir(ppy)2(2)][PF6]
The method was as for [Ir(ppy)2(1)][PF6] starting with
[Ir2(ppy)4(μ-Cl)2] (142 mg, 0.132 mmol) and ligand 2 (78 mg,
0.26 mmol). [Ir(ppy)2(2)][PF6] was isolated as an orange
solid (120 mg, 0.127 mmol, 98%). 1H NMR (500 MHz,
CD2Cl2) δ/ppm: 8.72 (d, J = 1.7 Hz, 0.5H, HF3, see text), 8.68
(overlapping, 1.5H, HF3′+E3, see text), 8.13 (t, J = 7.9 Hz, 1H,
HE4), 7.85 (m, 4H, HE6+B3+D3+(B4/D4)), 7.77 (m, 1H, HB4/D4),
7.72 (d, J = 1.7 Hz, 0.5H, HF5′, see text), 7.64 (m, 2.5H,
HB6+D6+F5, see text), 7.54 (d, J = 7.8 Hz, 1H, HC3), 7.40 (m, 1H,
HE5), 7.28 (d, J = 7.8 Hz, 1H, HA3), 7.13 (m, 1H, HB5/D5), 7.04
(m, 1H, HB5/D5), 6.96 (m, 2H, HC4+G4), 6.82 (td, J = 7.6, 1.3 Hz,
1H, HC5), 6.77 (m, 2H, HG3), 6.64 (t overlapping br, J = 7.5 Hz,
3H, HG2+A4), 6.39 (td, J = 7.5, 1.2 Hz, 1H, HA5), 5.95 (d, J =
7.6 Hz, 1H, HC6), 5.58 (d, J = 7.6 Hz, 1H, HA6), 2.98 (s, 1.5H,
HMe′, see text), 2.97 (s, 1.5H, HMe, see text). 13C NMR
(126 MHz, CD2Cl2) δ/ppm: pairs of signals refer to 1 : 1 mix of
diastereoisomers (see text): 169.3/169.2 (CB2), 167.4 (CD2),
167.0 (CF6), 161.22/161.19 (CF2), 156.0 (CE2), 150.9/150.85
379 sh (11 900). Emission (MeCN, 1.0 × 10−5 mol dm−3, λex
=
263 nm): λem = 672 nm. Found C 48.90, H 3.16, N 5.78%;
C39H30F6IrN4O2PS requires C 49.00, H 3.16, N 5.86.
Crystallography
Data were collected on a Stoe IPDS diffractometer. The data
reduction, solution and refinement used Stoe IPDS28 software
and SHELXL97.29 Structures were analysed using Mercury
v. 2.4.30,31 Crystallographic data are given in Table 1.
10278 | Dalton Trans., 2012, 41, 10276–10285
This journal is © The Royal Society of Chemistry 2012

View Article Online
Table 1 Crystallographic data for compounds 1, 2 and 3, and the complex [Ir(ppy)2(3)][PF6]
Compound
1
2
3
2{[Ir(ppy)2(3)][PF6]}·CHCl3·3H2O
Formula
C
17H14N2S
C17H14N2OS
294.37
Colourless block
Monoclinic
C2/c
C17H14N2O2S
310.37
Colourless plate
Monoclinic
C2/c
C79H67Cl3F12Ir2N8O7P2S2
2085.29
Orange needle
Orthorhombic
P212121
Formula weight
Crystal colour and habit
Crystal system
Space group
278.37
Colourless plate
Triclinic
ˉ
P1
a, b, c (Å)
9.811(4)
9.938(4)
14.981(5)
95.08(3)
95.78(3)
101.52(3)
1415.1(9)
1.307
33.093(6)
6.1290(7)
15.202(3)
90
32.941(7)
6.1326(9)
15.569(3)
90
109.002(16)
90
10.9914(11)
26.259(3)
32.326(4)
90
90
90
α, β, γ (°)
U (Å3)
90
108.672(15)
2921.1(8)
1.339
2973.7(10)
1.386
9329.9(18)
1.480
Dc (Mg m−3
)
Z
4
8
8
4
μ(Mo-Kα) (mm−1
T (K)
)
0.219
173(2)
0.221
173(2)
0.226
173(2)
3.090
173(2)
Refln. collected (Rint
Unique refln.
Refln. for refinement
Parameters
)
14 897 (0.1183)
5026
3639
18 504 (0.0618)
3011
2778
28 003 (0.1010)
3026
2691
94 268 (0.1093)
17 367
16 161
363
191
200
1092
Threshold
2σ(I)
2σ(I)
2σ(I)
2σ(I)
R1 (R1 all data)
wR2 (wR2 all data)
Goodness of fit
Flack parameter
0.0667 (0.0889)
0.1689 (0.1878)
1.039
0.0585 (0.0629)
0.1624 (0.1657)
1.099
0.0382 (0.0441)
0.0943 (0.0981)
1.086
0.0393 (0.0436)
0.1008 (0.1040)
1.058
−0.007(6)
n/a
n/a
n/a
undertaken (see below). Oxidation of 1 to 3 was carried out
using a slight excess of 3-chloroperbenzoic acid (MCPBA) as
previously reported for the conversion of 4′-MeStpy to
4′-MeO2Stpy.9 With 2.3 equivalents of MCPBA, 3 was isolated
in 67% yield. The product was separated from trace amounts of
2 by column chromatography. Conversion of 1 to 2 was achieved
by using 1.3 equivalents of MCPBA; column chromatographic
separation allowed the separation of the resulting mixture of 2
and 3, and the compounds were isolated in 61 and 18% yield,
respectively.
The MALDI-TOF mass spectra of 1, 2 and 3 showed base
peaks at m/z 278.1, 294.1 and 310.1, respectively, arising from
1
[M]+. The H and 13C NMR spectra were assigned using COSY,
HMQC and HMBC techniques. As expected, the largest changes
in the spectra along the series 1 to 2 to 3 are in the signal for
methyl group (δH 2.64, 2.85 and 3.18 ppm in 1, 2 and 3; δC
14.4, 44.0 and 44.3 ppm in 1, 2 and 3) and in the signals for
protons and carbon atoms HF3/CF3, HF4/CF4 and HF5/CF5
(Scheme 1 and see Experimental section).
X-Ray quality single crystals of compounds 1–3 were grown
by diffusion of Et2O into CH2Cl2 solutions of the compound.
The structures are shown in Fig. 1–3. Compound 1 crystallizes
Scheme 1 Ligand synthesis and ring labelling for NMR spectroscopic
assignments in ligands and complexes. Conditions: (i) KOtBu; CS2;
MeI; (ii) PhC(O)Me; KOtBu; NH4OAc/AcOH; (iii) 1.3 equiv. 3-chloro-
perbenzoic acid; (iv) 2.3 equiv. 3-chloroperbenzoic acid.
ˉ
in the triclinic space group P1 with two independent, but structu-
rally similar, molecules in the asymmetric unit. The transoid
conformation of the bpy domain is as expected. The ligand
framework deviates slightly from planarity; in the first molecule,
the angles between the rings containing N1a–N2a and
N2a–C11a are 7.38(13) and 14.80(14)°, and in the second, the
corresponding angles are 11.30(15) and 11.17(16)°. The S–CMe
bond lies in the plane of the pyridine to which it is bonded
(torsion angles C6a–C7a–C8a–S1A = 178.6(2)° and C6b–C7b–
C8b–S1b–179.8(3)°, for the two molecules). Packing of mole-
cules is dominated by CHMe⋯π and CHpyridine⋯π contacts,32,33
and face-to-face π-stacking of bpy units does not play a role.
Results and discussion
Ligand synthesis and characterization
Scheme 1 summarizes the synthetic routes to compounds 1, 2
and 3. Ligand 1 was prepared by Pott’s strategy in which a
ketenedithioacetal (prepared from 2-acetylpyridine, carbon
disulfide and methyl iodide) is condensed with acetophenone in
the presence of ammonium acetate.17,18 Literature data for this
compound are sparse, and therefore full characterization was
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 10276–10285 | 10279

View Article Online
Fig. 1 ORTEP diagram of one of two independent molecules of 1
(ellipsoids plotted at 30% probability level). Important bond parameters:
S1a–C8a = 1.746(3), S1a–C17a = 1.776(4), N1a–C5a = 1.343(3),
N1a–C1a = 1.347(4), N2a–C6a = 1.340(3), N2a–C10a = 1.359(4) Å;
C8a–S1a–C17a = 103.93(16)°. For the second independent molecule:
S1b–C8b = 1.752(3), S1b–C17b = 1.765(4) Å; C8b–S1b–C17b =
103.77(19)°.
Fig. 3 ORTEP diagram of a molecule of 3 (ellipsoids plotted at 30%
probability level). Selected bond parameters: S1–O1 = 1.4388(12),
S1–O2 = 1.4393(12), S1–C17 = 1.7542(18), S1–C8 = 1.7814(15),
N1–C1 = 1.336(2), N1–C5 = 1.342(2), N2–C6 = 1.340(2), N2–C10 =
1.344(2) Å; O1–S1–O2 = 118.18(7), O1–S1–C17 = 109.43(8), O2–S1–
C17 = 108.42(8), O1–S1–C8 = 108.32(7), O2–S1–C8 = 108.89(7),
C17–S1–C8 = 102.45(8)°.
Fig. 2 ORTEP representation of compound 2 (ellipsoids plotted at
30% probability level). Selected bond parameters: S1–O1 = 1.467(2),
S1–C17 = 1.789(3), S1–C8 = 1.797(2), N1–C1 = 1.336(3), N1–C5 =
1.346(3), N2–C6 = 1.339(3), N2–C10 = 1.340(3) Å; O1–S1–C17 =
108.04(14), O1–S1–C8 = 107.77(12), C17–S1–C8 = 96.25(12)°.
Fig. 4 Packing of molecules of (a) 2 and (b) 3 with unit cells viewed
down the b-axis. Hydrogen bonds are shown as hashed black lines. The
unit cell volumes are (a) 2921.1(8) Å3, and (b) 2973.7(10) Å3.
Compounds 2 and 3 both crystallize in the monoclinic space
group C2/c and the unit cell parameters are extremely similar
(Table 1). The volume of cell increases from 2921.1(8) to
2973.7(10) Å3 to accommodate the additional oxygen atom.
Figs. 2 and 3 show the three aromatic rings in each compound
are essentially coplanar. The angles between the least squares
planes of rings containing N1–N2 and N2–C11 in 2 are 4.20(11)
and 8.93(11)°, and corresponding angles in 3 are 3.05(8) and
7.91(8)°. On going from 1 to 2, and from 2 to 3, there is a
noticeable change in the C8–S1–C17 bond angle from 103.93(16)
to 103.77(19)° (two independent molecules) to 96.25(12)° to
102.45(8)° reflecting the changes in repulsions between sulfur
and oxygen lone pairs of electrons. The structures of simple
organic sulfones and sulfoxides have been analysed in detail,34
and the presence of intramolecular O⋯HCaryl hydrogen bonds is
recognized as a ubiquitous structural feature. In 2, the torsion
angle O1–S1–C8–C7 (Fig. 2) is −5.9° and the near planar
arrangement of atoms is consistent with the presence of a hydro-
gen bond between O1 and H7a (C7H7a⋯O1 = 2.53, C7⋯O1 =
2.925(3) Å, C7–H7a⋯O1 = 105°). An analogous interaction is
observed in sulfone 3 in which the torsion angle O1–S1–C8–C7
(Fig. 3) is 6.18(16)° and hydrogen bond parameters are
C7H7a⋯O1 = 2.53, C7⋯O1 = 2.913(2) Å, C7–H7a⋯O1 =
104°.
Molecules of 2 (Fig. 4a) are arranged in the lattice in an ana-
logous manner to those of 3 (Fig. 4b). Packing interactions are
10280 | Dalton Trans., 2012, 41, 10276–10285
This journal is © The Royal Society of Chemistry 2012

View Article Online
Table 2 Intermolecular contacts in 2 and 3. The symmetry code refers
to the atom with the asterisk
D–H⋯A
H⋯A/Å D⋯A/Å D–H⋯A/° Symmetry code
Compound 2
C9H9a⋯O1*
2.54
2.93
3.389(3) 149
3.844(2) 163
3.603(4) 152
3.664(4) 163
1/2 − x, 1/2 + y,
1/2 − z
C9H9a⋯S1*
1/2 − x, 1/2 + y,
1/2 − z
C17*H17a*⋯N1 2.71
C17*H17c*⋯O1 2.72
Compound 3
1/2 − x, 1/2 − y,
1 − z
1/2 − x, 1/2 − y,
1 − z
Scheme 2 Syntheses of [Ir(ppy)2(L)][PF6] (L = 1, 2 or 3): (i) L, (ii)
NH4PF6. Atom labelling in the [ppy]− ligands for NMR spectroscopic
assignments.
C9H9a⋯O2*
2.46
3.353(2) 157
3.644(2) 175
3.529(3) 153
3.398(3) 151
3.534(2) 148
1/2 − x, −1/2 + y,
1/2 − z
C16H16a⋯O2* 2.70
C17*H17a*⋯N1 2.62
C17H17b⋯O2* 2.50
C17*H17a*⋯O1 2.66
1/2 − x, −1/2 + y,
1/2 − z
1/2 − x, 1/2 − y,
1 − z
1/2 − x, −1/2 + y,
1/2 − z
1/2 − x, 1/2 − y,
1 − z
Fig. 6 500 MHz 1H NMR spectrum (aromatic region) of a CD2Cl2 solu-
tion of [Ir(ppy)2(3)][PF6]. Labelling: see Schemes 1 and 2. Signals for
H
B4+D4+D6/B6+B3+D3+F5+E6 overlap; this signal is labelled F5 for clarity.
[Ir(ppy)2(3)][PF6] to 98% for [Ir(ppy)2(2)][PF6]. The dominant
peak in either the MALDI-TOF or ESI mass spectrum of each
complex arises from the [M − PF6]+ ion.
The 1H and 13C NMR spectra of [Ir(ppy)2(1)][PF6] and
[Ir(ppy)2(3)][PF6] were assigned using COSY, HMQC and
HMBC spectra. The absence of a C2 axis running through the
inter-ring C–C bond of the bpy domain in ligand 1 or 3, results
in the two [ppy]− ligands being inequivalent. Signals for the
pairs of protons HA6/HC6, HA5/HC5, HA4/HC4 and HA3/HC3 are
well separated (Fig. 6), but it is more difficult to distinguish
between pairs of signals for protons attached to pyridine rings B
and D. The crystallographic study detailed in the next section
confirms that the pendant phenyl ring of ligand 1 or 3 (ring G,
Scheme 1) lies over one of the cyclometallated rings (defined as
ring C in Scheme 2). The signal for protons HG2 is broad
(Fig. 6) in both complexes, consistent with slow rotation of
phenyl ring G. This mimics the behaviour of the analogous
phenyl ring in a series of related complexes, representative low
temperature spectra for which we have previously reported.35 On
going from [Ir(ppy)2(1)][PF6] to [Ir(ppy)2(3)][PF6], the most
Fig. 5 Electronic absorption spectra of MeCN solutions (1.00 ×
10−5 mol dm−3) of 1 (—), 2 (– –) and 3 (⋯⋯).
dominated by CH⋯O, CH⋯N and CH⋯S hydrogen bonds.
Inspection of Fig. 4a and 4b confirms a comparable pattern of
CH⋯O and CH⋯N hydrogen bonding in the two structures,
with additional CH⋯O contacts reinforcing the network in 3.
Table 2 summarizes the hydrogen-bonded contacts.
The electronic absorption spectra of the three ligands are dis-
played in Fig. 5. The dominant high energy absorptions arise
from π* ← π transitions centred on the 6-phenyl-2,2′-bipyridine
units, while the introduction of the sulfoxide or sulfone group is
accompanied by the appearance of a lower energy band at 309 or
318 nm, respectively. Each ligand is emissive in solution
(MeCN) when irradiated at 265 2 nm, the emission maxima
being similar: 362, 358 and 364 nm for 1, 2 and 3, respectively.
1
noticeable differences in the H NMR spectra are changes in the
chemical shifts for signals arising from the Me group (δ 2.65 to
3.30 ppm), HF3 (δ 8.22 to 8.86 ppm) and HF5 (δ 7.16 to
7.81 ppm).
Complex formation and solution characterization
Each of the [Ir(ppy)2(L)]+ cations is chiral. In contrast to
[Ir(ppy)2(1)]+ and [Ir(ppy)2(3)]+ which are formed as the Δ/Λ
racemate, the asymmetric sulfur atom in ligand 2 leads to the
The complexes [Ir(ppy)2(L)][PF6] (L = 1, 2 or 3) were prepared
as outlined in Scheme 2. Yields ranged from 67% for
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 10276–10285 | 10281

View Article Online
diastereoisomers [Δ-Ir(ppy)2(RS-2)]+ , [Λ-Ir(ppy)2(RS-2)]+, [Δ-Ir-
S
(ppy)2(SS-2)]+ and [Λ-Ir(ppy)2(SS-2)]+. This is evident in the
1H NMR spectrum of [Ir(ppy)2(2)][PF6] which exhibits two
signals of equal intensities at δ 2.97 and 2.98 ppm for the
methyl groups corresponding to the two pairs of enantiomers
([Δ-Ir(ppy)2(RS-2)]+/[Λ-Ir(ppy)2(SS-2)]+,
[Δ-Ir(ppy)2(SS-2)]+/
[Λ-Ir(ppy)2(RS-2)]+. The signals for HF3 and HF5 also split into
two sets, appearing at δ 8.72 and 8.68 ppm (HF3) and δ 7.72 and
7.64 ppm (HF5). The two sets of HMe, HF3 and HF5 protons (dis-
tinguished using labels HMe and HMe′, etc. in the Experimental
section) were correlated from cross peaks in the NOESY spec-
trum. The presence of diastereoisomers is also apparent in the
13C NMR spectrum where most signals are split into 1 : 1 pairs
(see Experimental section). The chiral sulfoxide substituent is
apparently sufficiently remote from the iridium stereogenic
centre that the two enantiomeric pairs are of very similar
energies.
In order to study this effect further, we have investigated the
interaction of racemic [Ir(ppy)2(2)]+ with enantiomerically pure
Δ-TRISPHAT anion (TRISPHAT = tris(tetrachlorobenzenedio-
lato)phosphate(V)). The TRISPHAT anion is one of a family of
chiral, hexacoordinate phosphorus(V)-containing anions that are
utilised as NMR chiral solvating, resolving and asymmetry-
inducing reagents for chiral cationic species.36–39 When enantio-
merically pure TRISPHAT (Δ or Λ) is associated with a
configurationally stable cation, its behaves as a general NMR
chiral resolving agent, and can be used quantitatively to separate
stereoisomers such as [Λ,Λ-(ppy)2Ir(μ-L)Ir(ppy)2]2+, [Λ,Λ-
(ppy)2Ir(μ-L)Ir(ppy)2]2+ and [Λ,Λ-(ppy)2Ir(μ-L)Ir(ppy)2]2+
where L = 3,8-di(2-pyridyl)-4,7-phenanthroline.40 This effect is
particularly readily observed with cations containing aromatic
rings, with the resultant π-interactions further amplifying the
energy differences between the diastereoisomeric ion pairs. The
1H NMR spectrum of a 1 : 1 mixture of racemic [Ir(ppy)2(2)]-
[PF6] and [Et4N][Δ-TRISPHAT] in CD2Cl2 was recorded. The
addition of [Et4N][Δ-TRISPHAT] to [Ir(ppy)2(2)][PF6] results in
anion exchange and ion-pairing to give the four diastereoisomers
[Δ-Ir(ppy)2(RS-2)][Δ-TRISPHAT], [Λ-Ir(ppy)2(RS-2)][Δ-TRIS-
PHAT], [Δ-Ir(ppy)2(SS-2)][Δ-TRISPHAT] and [Λ-Ir(ppy)2(SS-2)]-
[Δ-TRISPHAT]. Fig. S1† shows the resultant dispersion of
signals in the aromatic region of the 1H NMR spectrum. The most
well-defined splitting of signals occurs for the methyl resonances,
and for those arising from HF3. As Fig. 7 shows, the signal due to
HE3 is also significantly affected. The results indicate that the
stereogenic sulfur atom does not undergo inversion on the NMR
timescale.41
Fig. 7 Parts of the 400 MHz 1H NMR spectra (CD2Cl2, room tempera-
ture) of (a) and (c) [Ir(ppy)2(2)][PF6], and (b) and (d) a 1 : 1 mixture of
[Ir(ppy)2(2)][PF6] and [Et4N][Δ-TRISPHAT]. The scale under (b) refers
to (a) and (b), and that under (d) refers to (c) and (d).
The solution electronic absorption spectra of [Ir(ppy)2(L)]-
[PF6] (L = 1, 2 or 3) exhibit similar bands, arising from ligand-
based π* ← π transitions. Comparison of Fig. 5 and 8 reveals
that the absorption maxima for the complexes are little shifted
from those in the free ligands 1–3, consistent with the transitions
involving both [ppy]− and bpy-based ligands being of similar
energies. As for the free sulfoxide and sulfone ligands 2 and 3,
the spectra of [Ir(ppy)2(2)][PF6] and [Ir(ppy)2(3)][PF6] show
low energy shoulders.
The three complexes are redox active and cyclic voltammetric
data are presented in Table 3. Each complex exhibits a quasi-
reversible oxidation ca. +0.9 V, and a second oxidation process
(quasi-reversible or irreversible) at more positive potential. The
Fig. 8 Electronic absorption spectra of MeCN solutions (1.00 ×
10−5 mol dm−3) of [Ir(ppy)2(1)][PF6] (—), [Ir(ppy)2(2)][PF6] (– –) and
[Ir(ppy)2(3)][PF6] (⋯).
former process shifts to slightly more positive potential on going
from the SMe to SOMe to SO2Me substituent. Each complex
shows two ligand-based reductions which shift to less negative
potential on going from [Ir(ppy)2(1)][PF6] to [Ir(ppy)2(2)][PF6]
to [Ir(ppy)2(3)][PF6]. The general electrochemical behaviour is
similar to that of related complexes.42
10282 | Dalton Trans., 2012, 41, 10276–10285
This journal is © The Royal Society of Chemistry 2012

View Article Online
Table 3 Cyclic voltammetric data with respect to Fc–Fc+; MeCN
solutions with [tBu4N][PF6] as supporting electrolyte; scan rate =
0.1 V s−1 (r = reversible; irr = irreversible; qr = quasi-reversible)
Complex
Eox (V)
Ered (V)
[Ir(ppy)2(1)][PF6] +0.91/0.75qr, +1.17/+1.09qr −1.50irr, −1.93/−1.81qr
[Ir(ppy)2(2)][PF6] +0.93/+0.76qr, +1.15irr
[Ir(ppy)2(3)][PF6] +0.96/+0.81qr, +1.19irr
−1.32irr, −1.63/−1.53qr
−1.31irr, −1.35/−1.40r
When excited at 266 4 nm, MeCN solutions of [Ir(ppy)2(1)]-
[PF6], [Ir(ppy)2(2)][PF6] or [Ir(ppy)2(3)][PF6] are emissive with
λem of 600, 647 and 672 nm, respectively. This confirms that the
energy of the emission can be successfully tuned by the intro-
duction of the SMe, SOMe or SO2Me substituents. However,
the quantum yields are <3% and, as a representative sample,
[Ir(ppy)2(2)][PF6] did not exhibit electroluminescence in a
device constructed and tested under conditions previously
detailed by us.43
Fig. 9 ORTEP diagram of one of the two independent [Ir(ppy)2(3)]+
cations in 2{[Ir(ppy)2(3)][PF6]}·CHCl3·3H2O (ellipsoids plotted at 30%
probability level). Important bond parameters: Ir1a–C29a = 2.001(7),
Ir1a–C18a = 2.026(7), Ir1a–N4a = 2.038(6), Ir1a–N3a = 2.041(5), Ir1a–
N1a = 2.137(6), Ir1a–N2a = 2.242(5), C8a–S1a = 1.780(7), S1a–O1a =
1.437(6), S1a–O2a = 1.445(5), S1a–C17a = 1.752(8) Å; N1a–Ir1a–N2a
= 76.4(2), C29a–Ir1a–N4a = 80.6(3), C18a–Ir1a–N3a = 79.7(3), N4a–
Ir1a–N3a = 173.4(2), C18a–Ir1a–N1a = 176.2(3), C29a–Ir1a–N2a =
Solid state structure of 2{[Ir(ppy)2(3)][PF6]}·CHCl3·3H2O
Crystals of 2{[Ir(ppy)2(3)][PF6]}·CHCl3·3H2O suitable for
X-ray diffraction were grown by diffusion of Et2O into a CHCl3
solution of racemic [Ir(ppy)2(3)][PF6]. The compound crystal-
lizes in the orthorhombic, chiral space group P212121 with two
independent [Ir(ppy)2(3)]+ cations in the asymmetric unit.
Cation A has the Δ-configuration and cation B Λ. The occurrence
of a chiral structure containing both enantiomers (as opposed to
the partial or complete formation of crystals containing only one
of the two enantiomers) upon crystallization of a racemate is not
common and was initially described by Dalhus and Görbitz.44 In
2003, Flack estimated that there were only ≈50 such cases
arising in the 250 000 entries present in the Cambridge Structural
Database (CSD) at that time.45 Seven years later and utilising
enhanced methods of searching the CSD, Fábián and Brock
revealed 181 organic so-called ‘kryptoracemates’, 151 of which
could, in principle, have produced ordered crystal lattices in
achiral space groups.46 These authors point out that: “pairs of
enantiomers in the true kryptoracemates usually have very
similar conformations; often the match is near-perfect”.46 Fig. 9
shows the structure of one of the independent [Ir(ppy)2(3)]+
cations (cation A). Fig. 10 illustrates an overlay of cations A and
B, after inversion of one of the cations and superimposition of
pairs of atoms Ir1a/Ir1b, S1a/S1b and C17a/C17b. The results
of this analysis confirm that the independent cations possess
opposite handednesses and exhibit very similar conformations to
one another (see later).
The octahedral coordination sphere of Ir1a (or Ir1b) consists
of two cyclometallated [ppy]− ligands arranged with their
N-donor atoms mutually trans. This mimics the arrangement of
[ppy]− ligands in all related structures with {Ir(ppy)2(N^N)}
coordination spheres in the CSD (Conquest version 5.33 with
February 2012 updates).30 The bond lengths and angles within
the coordination sphere of the iridium(III) centre in both indepen-
dent cations are unexceptional; those for cation A are listed in
the caption to Fig. 9. The structural parameters of the sulfone
group (see Fig. 9) are also as anticipated. In keeping with pre-
vious observations for aryl sulfones34 including ligand 3, the
169.7(2), O1a–S1a–O2a
= 118.2(3), O1a–S1a–C17a = 108.6(4),
O2a–S1a–C17a = 110.0(4), O1a–S1a–C8a = 109.4(3), O2a–S1a–C8a =
106.1(3)°.
Fig. 10 Overlay of cations A and B of [Ir(ppy)2(3)]+, after inversion
of one of the cations and superimposition of pairs of atoms Ir1a/Ir1b,
S1a/S1b and C17a/C17b (see Fig. 9 for numbering).
sulfone unit is twisted so that one S–O bond (S1a–O2a in Fig. 9)
lies in the plane of the aromatic ring to which it is attached,
thereby allowing an intra-cation CH⋯O hydrogen bond to form.
Hydrogen bond parameters for these interactions are, in
cation A, C9aH9aa⋯O2a = 2.47, C9a⋯O2a = 2.867(8) Å,
C9aH9aa⋯O2a = 105°, and in cation B, C9bH9ba⋯O2b =
2.55, C9b⋯O2b = 2.930(8) Å, C9bH9ba⋯O2b = 104°. These
parameters correspond to torsion angles O2a–S1a–C8a–C9a
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 10276–10285 | 10283

View Article Online
[Ir2(ppy)4(μ-Cl)2] leads, after anion exchange, to [Ir(ppy)2L]-
[PF6] with L = 1, 2 or 3. The asymmetric sulfur atom in ligand 2
results in the formation of diastereoisomeric pairs of enantio-
mers, i.e. [Δ-Ir(ppy)2(RS-2)]+/[Λ-Ir(ppy)2(SS-2)]+ and [Δ-Ir-
(ppy)2(SS-2)]+/[Λ-Ir(ppy)2(RS-2)]+) which can be distinguished
1
in the H and 13C NMR spectra. Exchange of the [PF6]− anion
for [Δ-TRISPHAT]− produces four diastereoisomers in solution
with especially good dispersion in the 1H NMR spectrum of
signals arising from protons closest to the asymmetric sulfur
atom. Unexpectedly, the complex rac-[Ir(ppy)2(3)][PF6] crystal-
lizes in the chiral space group P212121 with crystallographically
independent Δ- and Λ-[Ir(ppy)2(3)]+ cations in the asymmetric
unit of 2{[Ir(ppy)2(3)][PF6]}·CHCl3·3H2O; this provides an
unusual example of a so-called kryptoracemate in the solid
state. The solution photoluminescence of [Ir(ppy)2(1)][PF6],
[Ir(ppy)2(2)][PF6] and [Ir(ppy)2(3)][PF6] illustrates the effects of
Fig. 11 O⋯π and CH⋯O interactions between the two independent
cations in 2{[Ir(ppy)2(3)][PF6]}·CHCl3·3H2O; cation A (right) and
cation B (left). See text for inter-cation distances.
going from the SMe substituent (λem = 600 nm) to SOMe (λem
=
(Fig. 9) and O2b–S1b–C8b–C9b of 6.96(64) and −3.64(71)°,
respectively. In cation A, the phenyl ring containing atom C11a
is rotated 80.61(26)° out of the plane of the pyridine ring to
which it is bonded; the corresponding angle in cation B is
67.66(24)°. The origin of these twists is the face-to-face π-stack-
ing of the pendant phenyl ring and the cyclometallated ring of
one of the [ppy]− ligands. This structural feature is anticipated,
being ubiquitous among complexes of this type (see introduc-
tion). In cation A, the centroid–centroid distance between the
rings containing atoms C11a and C18a is 3.53 Å (3.48 Å in
cation B), but the efficiency of the stacking inter-cation is
reduced by the non-zero angle between the planes of the rings
(8.9 and 10.8° in cations A and B, respectively).
The two independent cations A and B associate together
through O⋯π and CH⋯O interactions (Fig. 11). Atom O1b in
the sulfone group of cation B sits in a V-shaped cleft formed
between two pyridine rings in cation A, the closest contacts
being O1b⋯C27a = 3.37(1), O1b⋯C8a = 3.404(9), O1b⋯C9a
= 3.274(9) Å (right side of Fig. 9). Oxygen atom O2a of the
sulfone group in cation A points towards the π-system of the pyr-
idine ring containing N3b (in cation B) with O2a⋯C distances
ranging from 3.12(1) to 3.39(1) Å and O2a⋯N3b = 3.193(8) Å.
Examples of O⋯π interactions (both intra- and inter-molecular)
have been documented,47 with attention paid to their role in
hosting oxoanions in molecular cavities.48 The left-hand side of
Fig. 11 illustrates that both sulfone O atoms of cation A are
involved in weak hydrogen bonds (C16H16b⋯O2a = 2.52 Å
and C9H9Ba⋯O1a = 2.81 Å). The two independent [PF6]− ions
are ordered and are involved in extensive CH⋯F packing inter-
actions. Solvent molecules in the lattice of 2{[Ir(ppy)2(3)]-
[PF6]}·CHCl3·3H2O are disordered. The CHCl3 molecule has
been modelled over two sites, each of half-occupancy. The
remaining electron density has been modelled as the O atoms of
three water molecules (one full occupancy and four half-occu-
pancy). These disorders make discussion of packing involving
contacts to the solvent molecules meaningless.
647 nm) to SO2Me (λem = 672 nm) in the 4-substituted-
6-phenyl-2,2′-bipyridine ligand. However, preliminary studies of
the electroluminescent properties of these complexes did not
reveal them to be promising candidates for LECs.
Acknowledgements
We acknowledge the financial support of the European Union
(CELLO, STRP248043), the Swiss National Science Foun-
dation, the European Research Council (Advanced Grant 267816
LiLo) and the University of Basel. PD Dr Daniel Häussinger is
thanked for assistance with NMR spectroscopic experiments,
and Professor Howard Flack for helpful discussion. Dr Henk
J. Bolink and Antonio Pertegas, Instituto de Ciencia Molecular,
Universidad de Valencia are acknowledged for the solid state
photoluminescence measurements.
Notes and references
1 Q. B. Pei, G. Yu, C. Zhang, Y. Yang and A. J. Heeger, Science, 1995,
269, 1086.
2 See for example: J. D. Slinker, A. A. Gorodetsky, M. S. Lowry, J. Wang,
S. Parker, R. Rohl, S. Bernhard and G. G. Malliaras, J. Am. Chem. Soc.,
2004, 126, 2763.
3 R. D. Costa, F. Monti, G. Accorsi, A. Barbieri, H. J. Bolink, E. Ortí and
N. Armaroli, Inorg. Chem., 2011, 50, 7229 and references therein.
4 Q. Zhao, S. Liu, M. Shi, C. Wang, M. Yu, L. Li, F. Li, T. Yi and
C. Huang, Inorg. Chem., 2006, 45, 6152.
5 H. J. Bolink, L. Cappelli, E. Coronado, M. Grätzel, E. Ortí, R. D. Costa,
P. M. Viruela and Md. K. Nazeeruddin, J. Am. Chem. Soc., 2006, 128,
14786.
6 C. Dragonetti, L. Falciola, P. Mussini, S. Righetto, D. Roberto, R. Ugo,
A. Valore, F. De Angelis, S. Fantacci, A. Sgamellotti, M. Ramon and
M. Muccini, Inorg. Chem., 2007, 46, 8533 and references therein.
7 M. Lepeltier, T. K.-M. Lee, K. K.-W. Lo, L. Toupet, H. Le Bozec and
V. Guerchais, Eur. J. Inorg. Chem., 2005, 110.
8 M. S. Lowry, W. R. Hudson, R. A. Pascal Jr. and S. Bernhard, J. Am.
Chem. Soc., 2004, 126, 14129.
9 E. C. Constable, A. M. W. Cargill Thompson, N. Armaroli, V. Balzani
and M. Maestri, Polyhedron, 1992, 11, 2707.
10 See for example: M. Duati, S. Tasca, F. C. Lynch, H. Bohlen, J. G. Vos,
S. Stagni and M. D. Ward, Inorg. Chem., 2003, 42, 8377; J. Wang,
Y.-Q. Fang, G. S. Hanan, F. Loiseau and S. Campagna, Inorg. Chem.,
2005, 44, 5; A. C. Benniston, G. Chapman, A. Harriman, M. Mehrabi
and C. A. Sams, Inorg. Chem., 2004, 43, 4227; C. Bhaumik, S. Saha,
S. Das and S. Baitalik, Inorg. Chem., 2011, 50, 12586 and references
therein.
Conclusions
We have prepared and characterized both in solution and the
solid state, 4-methylthio-6-phenyl-2,2′-bipyridine (1) and the
corresponding sulfoxide (2) and sulfone (3). Reaction with
10284 | Dalton Trans., 2012, 41, 10276–10285
This journal is © The Royal Society of Chemistry 2012

View Article Online
11 C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165.
12 J. Chambers, B. Eaves, D. Parker, R. Claxton, P. S. Ray and S. J. Slattery,
Inorg. Chim. Acta, 2006, 359, 2400.
30 I. J. Bruno, J. C. Cole, P. R. Edgington, M. K. Kessler, C. F. Macrae,
P. McCabe, J. Pearson and R. Taylor, Acta Crystallogr., Sect. B: Struct.
Sci., 2002, 58, 389.
13 U. S. Sampath, W. C. Putnam, T. A. Osiek, S. Touami, J. Xie, D. Cohen,
A. Cagnolini, P. Droege, D. Klug, C. L. Barnes, A. Modak,
J. K. Bashkin and S. S. Jurisson, J. Chem. Soc., Dalton Trans., 1999,
2049.
31 C. F. Macrae, I. J. Bruno, J. A. Chisholm, P. R. Edgington, P. McCabe,
E. Pidcock, L. Rodriguez-Monge, R. Taylor, J. van de Streek and
P. A. Wood, J. Appl. Crystallogr., 2008, 41, 466.
32 M. Nishio, CrystEngComm, 2004, 6, 130.
14 J. R. Jeitler, M. M. Turnbull and J. L. Wikaira, Inorg. Chim. Acta, 2003,
351, 331.
15 M. J. Hannon, C. L. Painting, E. A. Plummer, L. J. Childs and
N. W. Alcock, Chem.–Eur. J., 2002, 8, 2225.
16 K. Stippich, D. Weiss, A. Guether, H. Görls and R. Beckert, J. Sulfur
Chem., 2009, 30, 109.
17 K. T. Potts, M. J. Cipullo, P. Ralli and G. Theodoridis, J. Org. Chem.,
1982, 47, 3027.
33 S. Tsuzuki and A. Fujii, Phys. Chem. Chem. Phys., 2008, 10, 2584.
34 C. Glidewell, W. T. A. Harrison, J. N. Low, J. G. Sime and J. L. Wardell,
Acta Crystallogr., Sect. B: Struct. Sci., 2001, 57, 190; F. A. M. Rudolph,
A. L. Fuller, A. M. Z. Slawin, M. Bühl, R. A. Aitken and J. D. Woollins,
J. Chem. Crystallogr., 2010, 40, 253 and references therein.
35 A. M. Bünzli, H. J. Bolink, E. C. Constable, C. E. Housecroft,
M. Neuburger, A. Pertegás and J. A. Zampese, Eur. J. Inorg. Chem.,
2012, DOI: 10.1002/ejic.201200394.
18 K. T. Potts, M. J. Cipullo, P. Ralli and G. Theodoridis, J. Am. Chem.
Soc., 1981, 103, 3585.
36 J. Lacour and R. Frantz, Org. Biomol. Chem., 2005, 3, 15.
37 J. Lacour and D. Linder, Chem. Rec., 2007, 7, 275.
19 F. Neve, A. Crispini, S. Campagna and S. Serroni, Inorg. Chem., 1999,
38, 2250.
38 J. Lacour and V. Hebbe-Viton, Chem. Soc. Rev., 2003, 32, 373.
39 J. Lacour, C. R. Chim., 2010, 13, 985.
20 H. J. Bolink, E. Coronado, R. D. Costa, E. Ortí, M. Sessolo, S. Graber,
K. Doyle, M. Neuburger, C. E. Housecroft and E. C. Constable, Adv.
Mater., 2008, 20, 3910.
40 A. Auffrant, A. Barbieri, F. Barigelletti, J. Lacour, P. Mobian, J.-P. Collin,
J.-P. Sauvage and B. Ventura, Inorg. Chem., 2007, 46, 6911.
41 S. Toyota, Rev. Heteroat. Chem., 1999, 21, 139.
21 R. D. Costa, E. Ortí, H. J. Bolink, S. Graber, C. E. Housecroft,
M. Neuburger, S. Schaffner and E. C. Constable, Chem. Commun., 2009,
2029.
22 R. D. Costa, E. Ortí, H. J. Bolink, S. Graber, S. Schaffner, M. Neuburger,
C. E. Housecroft and E. C. Constable, Adv. Funct. Mater., 2009, 19,
3456.
42 See for example: R. D. Costa, E. Ortí, D. Tordera, A. Pertegás,
H. J. Bolink, S. Graber, C. E. Housecroft, L. Sachno, M. Neuburger and
E. C. Constable, Adv. Energy Mater., 2011, 1, 282 and references therein.
43 R. D. Costa, D. Tordera, E. Ortí, H. J. Bolink, J. Schönle, S. Graber,
C. E. Housecroft, E. C. Constable and J. A. Zampese, J. Mater. Chem.,
2011, 21, 16108.
23 R. D. Costa, E. Ortí, H. J. Bolink, S. Graber, C. E. Housecroft and
E. C. Constable, Adv. Funct. Mater., 2010, 20, 1511.
24 R. D. Costa, E. Ortí, H. J. Bolink, S. Graber, C. E. Housecroft and
E. C. Constable, J. Am. Chem. Soc., 2010, 132, 5978.
25 R. D. Costa, E. Ortí, H. J. Bolink, S. Graber, C. E. Housecroft and
E. C. Constable, Chem. Commun., 2011, 47, 3207.
26 E. L. Eliel, S. H. Wilen and L. N. Mander, Stereochemistry of Organic
Compounds, Wiley-Interscience, New York, 1994.
27 S. Sprouse, K. A. King, P. J. Spellane and R. J. Watts, J. Am. Chem. Soc.,
1984, 106, 6647.
44 B. Dalhaus and C. H. Görbitz, Acta Crystallogr., Sect. B: Struct. Sci.,
2000, 56, 715.
45 H. Flack, Helv. Chim. Acta, 2003, 86, 905.
46 L. Fábián and C. P. Brock, Acta Crystallogr., Sect. B: Struct. Sci., 2010,
66, 94.
47 See for example: C.-Q. Wan, X.-D. Chen and T. C. W. Mak, CrystEng-
Comm, 2008, 10, 475; X.-L. Gao, L.-P. Lu and M.-L. Miao, Acta Crystal-
logr., Sect. C: Cryst. Struct. Commun., 2009, 65, o123; Z. Zhang, Y. Wu
and G. Zhang, CrystEngComm, 2011, 13, 4496; M. G. B. Drew, S. De,
S. Nag and D. Datta, Inorg. Chim. Acta, 2009, 362, 610; J. E. Gautrot,
P. Hodge, D. Cupertino and M. Helliwell, New J. Chem., 2006, 30, 1801
and references therein.
28 Stoe & Cie, IPDS software v 1.26, Stoe & Cie, Darmstadt, Germany,
1996.
29 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112.
48 See for example: M. Wenzel, J. R. Hiscock and P. A. Gale, Chem. Soc.
Rev., 2012, 41, 480 and references therein.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 10276–10285 | 10285