Coupling d6 Ir(III) and d8 Pt(II) Chromophores - Inorganic Chemistry

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Coupling d6 Ir(III) and d8 Pt(II) Chromophores Van Ha Nguyen,‡ Balamurugan Kandasamy,† and John H. K. Yip*,‡ ‡

Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 Singapore Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR

†

S Supporting Information *

ABSTRACT: Two classes of widely studied luminescent metal complexes are octahedral d6 (i.e., Ir3+) and square planar d8 (i.e., Pt2+) polypyridyl complexes, which have distinctly different photophysics and photoreactivity. In this study we report a series of d6−d8 IrIII−PtII hybrid complexes arising from coordination of metalloligands IrL2(benzene-1-thioether-2-thiolate) or Ir(L)2(benzene-1,2-dithiolate) anion [L = 2-phenylpyridine (ppy), 2-(2,4-difluorophenyl)pyridine (dfppy), or 1-phenylisoquinoline (piq)] to Pt(terpy)2+ (terpy = 2,2′:6′,2″-terpyridine). X-ray crystal structures of the Ir−Pt complexes show the IrL2 and Pt(terpy) chromophores are cofacially oriented with interplanar distances of 3.268−3.442 Å. Density functional theory (DFT) calculations show that the highest occupied molecular orbital and the lowest unoccupied molecular orbital are localized in the IrL2 and the Pt(terpy), respectively. All the complexes display a low-energy absorption band (λmax = 460−534 nm, εmax = (0.75−2.13) × 103 M−1 cm−1), which is attributed to interchromophore-charge-transfer (ICCT) transition, according to time-dependent DFT calculations. The 3ICCT excited state is emissive, giving long-lived phosphorescence that reaches as low as near-infrared (λmax = 668−710 nm, τ = 0.17−0.79 μs).

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INTRODUCTION Luminescent transition-metal complexes that have long-lived triplet excited states in fluids play a key role in important processes such as artificial photosynthesis,1 photocatalysis,2 electroluminescene,3 and bioimaging.4 Two archetypes of phosphorescent emitters of different geometry and excited-state chemistry, namely, octahedral d6 (i.e., RuII, IrIII)5 and square planar d8 (i.e., PtII, AuIII)6 complexes with aromatic α-diimines or related ligands, have been studied extensively because their tunable photophysics and high plasticity due to their modifiable ligands, which allows their incorporation into a variety of molecular settings such as donor−acceptor dyads,7 rotaxanes,8 and metal−organic frameworks (MOFs).9 The d6-α-diimine (e.g., Ru(bipy)32+) and related cyclometalated complexes (e.g., fac-Ir(ppy)3, ppy = 2-phenylpyridine) exhibit dπ→π* metal-to-ligand-charge-transfer (MLCT) emissions.5,10 Depending on the auxiliary ligand, the square planar d8 polypyridiyl complexes display MLCT, ligand-centered ππ* or ligand-to-metal/ligand-charge-transfer emissions.6,10,11 The coordinatively unsaturated d8 complexes would aggregate in solutions or solid state via π−π stacking or metal−metal interactions, which significantly modify the electronic structures of the complexes. For example, dimers or oligomers of PtII-polypyridine complexes and related complexes show a unique low-energy MMLCT absorption and 3MMLCT emission (MMLCT = metal−metal-bond-to-ligand chargetransfer).12 In the reported dyadic molecules containing luminescent d6 RuII or IrIII and PtII or PdII centers, the relatively long, linear separation between the metal ions, which are usually connected by covalent bonds, leading to poor electronic interactions between the chromophores.13 © XXXX American Chemical Society

Our recent studies show that the [Ir(2-phenylpyridine)2(benzene-1,2-dithiolate)] anion ([Ir(ppy)2(S2)]− or 1a, Scheme 1)14 and its methylated derivative Ir(ppy)2(SSMe), 2a15 are metalloligands capable of coordinating to metal ion(s) via its thiolate S atom(s) (Scheme 1). This reactivity is harnessed in the present study to couple a d6 IrIII(L)2 [L = 2-phenylpyridine (ppy), 2-(2,4difluorophenyl)pyridine (dfppy), or 1-phenylisoquinoline (piq)] and a d8 PtII(terpy) (terpy = 2,2′;6′,2″-terpyridine) chromophore. The dithiolate complexes [IrL2(S2)]− (1a−c) react with one or two mole equivalents of [Pt(terpy)(MeCN)]2+ to form binuclear IrIIIPtII complexes 5a−c or trinuclear IrIIIPtII2 complexes 4a−c. Reacting the methylated derivatives [IrL2(SSMe)] (2a−c) with the platinum ions gives monoplatinated complexes 3a−c (Scheme 1). While both IrL2 and Pt(terpy) chromophores are visible emitters (emission maxima = 470−620 nm),5d,f,12,15−17 conjoining them electronically leads to red or even near-infrared (NIR) emission from an IrL2→Pt(terpy) interchromophorecharge-transfer (ICCT) excited state.

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EXPERIMENTAL SECTION

General Methods. All syntheses were performed in an argon atmosphere. All the solvents used for syntheses and spectroscopic measurements were purified according to the literature procedures. Silver trifluoromethanesulfonate (AgOTf), 2,2′:6′,2″-terpyridine (terpy), 2-phenylpyridine (ppy), 2-(2,4-difluorophenyl)pyridine (dfppy), 1-phenylisoquinoline (piq), and benzene-1,2-dithiol were obtained from Aldrich and used without prior purification. Ir2(L)4(μ-Cl)2 Received: February 15, 2018

A

DOI: 10.1021/acs.inorgchem.8b00412 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

30 mL of acetonitrile for 2 h, before the mixture was filtered to give a yellow solution, which was transferred into another Schlenk flask containing benzene-1,2-dithiol (31 mg, 0.2 mmol) and NaOH (35.2 mg, 0.88 mmol) in 30 mL of methanol. The solution turned from yellow to red and was stirred overnight under argon to give a red solution of 1b, which was sensitive to air and was used without being isolated. Na[Ir(piq)2(benzene-1,2-dithiolate)] (1c). Ir2(piq)4(μ-Cl)2 (127 mg, 0.1 mmol) was stirred with AgOTf (57 mg, 0.2 mmol) in 30 mL of acetonitrile for 2 h. The mixture was filtered, and the pale yellow solution was transferred into another Schlenk flask containing benzene1,2-dithiol (31 mg, 0.2 mmol) and NaOH (35.2 mg, 0.88 mmol) in 30 mL of methanol. The solution turned from orange to red and was stirred overnight under argon to give a dark red solution of 1c, which was sensitive to air and was used without being isolated. Ir(ppy)2(benzene-1-thioether-2-thiolate) (2a). Methyl iodide (28 mg, 0.2 mmol) in 20 mL of MeOH was added dropwise to a freshly prepared solution of 1a (0.2 mmol). The color of the solution slowly changed from red to orange, and finally a yellow suspension resulted after it was stirred for 5 h. The solvent was removed by filtration to give yellow solids that were was washed successively with H2O and MeOH. Yield: 89 mg, 68%. 1H NMR (500 MHz, CD3CN) δ 9.75 (d, J = 5.9 Hz, 1H), 8.75 (d, J = 5.9 Hz, 1H), 8.01−8.05 (2H), 7.89 (t, J = 7.8 Hz, 1H), 7.83 (t, J = 7.8 Hz, 1H), 7.76 (d, J = 7.2 Hz, 1H), 7.69 (d, J = 7.7 Hz, 1H), 7.48 (d, J = 7.9 Hz, 1H) 7.28 (dd, J = 7.8, 5.9 Hz, 1H), 7.17 (dd, J = 7.8, 5.9 Hz, 1H), 6.92−6.98 (2H), 6.81−6.89 (3H), 6.75 (t, J = 7.5 Hz, 1H), 6.48 (d, J = 7.6 Hz, 1H), 6.18 (d, J = 7.5 Hz, 1H), 1.57 (s, 3H). ESI-MS: m/z 656.9 [2a+H]+. Ir(dfppy)2(benzene-1-thioether-2-thiolate) (2b). Methyl iodide (28 mg, 0.2 mmol) in 20 mL of MeOH was added dropwise to a freshly prepared solution of 1b (0.2 mmol). The color of the solution slowly changed from red to orange, and finally a yellow suspension resulted after it was stirred for 5 h. Filtration gave yellow solids, which were washed successively with H2O and MeOH. Yield: 93 mg, 64%. 1 H NMR (500 MHz, CD3CN) δ 9.77 (d, J = 6.7 Hz, 1H), 8.75 (d, J = 5.3 Hz, 1H), 8.30−8.34 (2H), 7.96 (t, J = 7.4 Hz, 1H), 7.90 (d, J = 7.4 Hz, 1H), 7.46 (d, J = 8.0 Hz, 1H), 7.41(d, J = 8.0 Hz, 1H), 7.35 (dt, J = 6.6, 1.3 Hz, 1H) 7.23 (dt, J = 6.6, 1.3 Hz, 1H), 6.99 (dt, J = 7.5, 1.3 Hz, 1H), 6.87 (dt, J = 7.5, 1.3 Hz, 1H), 6.50−6.60 (2H), 5.97 (dd, J = 8.3, 2.3 Hz, 1H), 5.63 (dd, J = 8.7, 2.3 Hz, 1H), 1.63 (s, 3H). ESI-MS: m/z 728.9 [2b+H]+. Ir(piq)2(benzene-1-thioether-2-thiolate) (2c). Methyl iodide (28 mg, 0.2 mmol) in 20 mL of MeOH was added dropwise to a freshly prepared solution of 1c (0.2 mmol). A brown suspension was formed after it was stirred for 5 h. The solvent was removed by filtration, and brown precipitates obtained were washed successively with H2O and MeOH. Yield: 105 mg, 70%. 1H NMR (500 MHz, CD3CN) δ 9.79 (d, J = 6.5 Hz, 1H), 8.98 (d, J = 8.2 Hz, 1H), 8.92 (d, J = 8.5 Hz, 1H), 8.64 (d, J = 6.5 Hz, 1H), 8.31 (d, J = 8.0 Hz, 1H), 8.24 (d, J = 8.0 Hz, 1H), 8.06 (d, J = 8.0 Hz, 1H), 8.01 (d, J = 8.0 Hz, 1H), 7.77−7.85 (4H), 7.66 (d, J = 6.7 Hz, 1H), 7.55 (d, J = 6.5 Hz, 1H), 7.45 (d, J = 7.8 Hz, 1H), 7.40 (d, J = 7.8 Hz, 1H), 7.02 (t, J = 7.3 Hz, 1H), 6.93−6.98 (2H), 6.80−6.86 (2H), 6.69 (t, J = 7.3 Hz, 1H), 6.60 (d, J = 7.5 Hz, 1H), 6.18 (d, J = 7.7 Hz, 1H), 1.55 (s, 3H). ESI-MS: m/z 757.0 [2c+H]+. [Ir(ppy)2(benzene-1-thioether-2-((terpy)Pt)thiolate)](OTf)2 (3a). A solution of [Pt(terpy)(MeCN)](OTf)2 (77 mg, 0.10 mmol) in 10 mL of MeCN was added to a solution of 2a (66 mg, 0.10 mmol) in 20 mL of MeOH, and the mixture was stirred for 8 h. The solvent was removed to obtain red solids. Crystals of the compound were obtained by diffusion of Et2O into a MeCN solution of the compound. Yield: 120 mg, 87%. Anal. Calcd (%) for 3a (C46H34IrPtN5S4F6O6): C, 39.97; H, 2.48; N, 5.07. Found: C, 39.55; H, 2.42; N, 4.94. 1H NMR (500 MHz, CD3CN): δ 9.50 (d, J = 5.3 Hz, 1H), 8.89 (d, J = 5.3 Hz, 1H), 8.53 (d, J = 8.1 Hz, 1H), 8.34 (d, J = 5.7 Hz, 1H), 8.29 (d, J = 8.0 Hz, 1H), 8.26 (d, J = 8.2 Hz, 1H), 8.24−8.17 (4H), 8.13 (d, J = 8.0 Hz, 1H), 8.08 (dt, J = 8.0, 1.4 Hz, 1H), 7.99 (d, J = 8.0 Hz, 1H), 7.97 (d, J = 8.0 Hz, 1H), 7.84 (d, J = 7.8 Hz, 1H), 7.47−7.58 (4H), 7.39 (dt, J = 7.6, 1.2 Hz, 1H), 7.31−7.26 (2H), 7.04−7.01 (2H), 6.84 (dt, J = 7.5, 1.2 Hz, 1H), 6.59 (t, J = 7.2, 1.2 Hz, 1H), 6.48−6.44 (m, 2H), 6.38−6.33 (m, 2H), 6.11 (d, J = 7.5 Hz, 1H), 1.86 (s, 3H). ESI-MS: m/z 1233.7 [3a-OTf]+, 541.8 [3a-2OTf]2+. The OTf anions were changed to tetrafluoroborate by

Scheme 1. Synthesis of IrIII−PtII Complexes

(L = ppy, dfppy, or piq)5f,18 and [Pt(terpy)(MeCN)](OTf)219 were prepared according to reported procedures. Physical Methods. The UV−vis absorption and emission spectra were recorded on a PerkinElmer Lambda 750 spectrophotometer and a Horiba FluoroMax-4 fluorescence spectrophotometer, respectively. Emission lifetimes were measured on a Horiba Jobin-Yvon Fluorolog FL-1057 instrument, and cresyl violet was used as a standard for quantum yield measurements. 1H spectra were obtained on a Bruker Avance 500 spectrometer with chemical shifts quoted relative to SiMe4. Electrospray ionization mass spectra (ESI-MS) were obtained using a Finnigan LCQ spectrometer. Cyclic voltammetry measurements were recorded on a CHI 620 electrochemical analyzer (CH Instruments, Inc.), and ferrocene was used as the internal reference. A glassy-carbon working electrode (3 mm diameter, CH Instruments, Inc.), a platinum wire counter electrode, and a Ag/AgNO3 (10 mM in MeCN) reference electrode (CH Instruments, Inc.) were used. All solutions for electrochemical measurements were degassed by argon. For 4a−c, 0.1 M n Bu4NPF6 in MeCN was used, but 0.1 M nBu4NPF6 in CH2Cl2 was used for 3a−c and 5a−c due to their high solubility. Scan rate: 0.05 V s−1 was used for all compounds. Elemental analyses were performed at Elemental Analysis Laboratory, Department of Chemistry, National University of Singapore. Synthesis. Na[Ir(ppy)2(benzene-1,2-dithiolate)] (1a). Ir2(ppy)4 (μ-Cl)2 (107 mg, 0.1 mmol) was stirred with AgOTf (57 mg, 0.2 mmol) in 30 mL of acetonitrile for 2 h, and the mixture was filtered to remove AgCl precipitate to obtain a pale yellow solution, which was transferred into another Schlenk flask containing benzene-1,2-dithiol (31 mg, 0.2 mmol) and NaOH (35.2 mg, 0.9 mmol) in 30 mL of methanol. The solution turned from yellow to red and was stirred overnight under argon to give a deep red solution of 1a, which was sensitive to air and was used without being isolated. Na[Ir(dfppy)2(benzene-1,2-dithiolate)] (1b). Ir2(dfppy)4(μ-Cl)2 (121 mg, 0.1 mmol) was stirred with AgOTf (57 mg, 0.2 mmol) in B


C

no. reflections collected no. independent reflections (R(int)) max, min transmission no. data/restraints/parameters final R indices [I > 2σ(I)] R1 wR2 GOF largest diff. peak and hole (e Å−3)

1.566−27.500 −18 ≤ h ≤ 18 −32 ≤ k ≤ 32 −19 ≤ l ≤ 19 61 959 10 977 (0.0980) 0.7456, 0.5200 10 977/158/687 0.0612 0.1222 1.156 1.753 and −2.381

1.935−28.333 −14 ≤ h ≤ 14 −19 ≤ k ≤ 18 −19 ≤ l ≤ 19 52 545 11 835 (0.0450)

0.7457, 0.4303 11 835/22/653

0.0258 0.0697 1.021 1.648 and −1.179

14.398(3) 24.882(5) 14.757(3) 90 115.396(4) 90 4776.1(16) 4 2.034 5.980 2808 0.360 × 0.260 × 0.200

10.9761(7) 14.7101(9) 14.9142(9) 90.785(2) 93.118(2) 98.018(2) 2380.4(3) 2 1.875 5.891 1298 0.656 × 0.263 × 0.136

θ range for data collection (deg) index ranges

1462.28 monoclinic P21/n

1343.90 triclinic P1̅

formula weight crystal system space group unit cell dimensions a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) volume (Å3) Z density (calcd, g cm−3) abs coefficient (mm−1) F(000) crystal size (mm3)

C46H30F10IrN5O6.5PtS4

3b·0.5H2O

C48H43N6OIrPtS2B2F8

3a·MeCN·0.5Et2O· 0.5H2O

empirical formula

complex

0.0207 0.0427 1.047 0.895 and −0.651

0.7457, 0.6124 11 849/0/684

15.7930(7) 13.8483(6) 21.8968(10) 90 94.1770(16) 90 4776.2(4) 4 1.981 5.975 2768 0.305 × 0.184 × 0.133 2.191−28.282 −21 ≤ h ≤ 21 −18 ≤ k ≤ 18 −29 ≤ l ≤ 29 168 403 11 849 (0.0498)

C54H41Cl2 IrN6O8PtS2 1424.24 monoclinic P21/c

3c·MeCN

0.0283 0.0676 1.037 4.192 and −2.453

0.7457, 0.4680 14 341/108/851

2.072−27.500 −17 ≤ h ≤ 17 −18 ≤ k ≤ 18 −23 ≤ l ≤ 23 93 920 14 341 (0.0309)

13.4216(9) 14.4977(10) 18.2964(12) 76.366(2) 74.941(2) 66.690(2) 3121.6(4) 2 2.032 6.867 1840 0.32 × 0.17 × 0.12


C63H52Cl3IrN10O13Pt2S2

4a·MeOH·2MeCN

0.0266 0.0500 1.028 1.175 and −0.714

0.7457, 0.6364 16 191/21/988

2.122−27.499 −17 ≤ h ≤ 17 −19 ≤ k ≤ 18 −22 ≤ l ≤ 23 100 184 16 191 (0.0525)

13.5395(8) 15.0835(9) 18.0719(11) 91.271(2) 106.920(2) 92.572(2) 3525.0(4) 2 2.043 6.092 2094 0.19 × 0.15 × 0.12


C69H56F13IrN9O10.5Pt2S5

4b·MeCN·1.5Et2O

0.0739 0.1814 1.092 2.543 and −1.280

0.7457, 0.6071 16 672/259/906

2.338−28.333 −19 ≤ h ≤ 19 −44 ≤ k ≤ 37 −19 ≤ l ≤ 16 30 532 16 672 (0.0443)

14.5076(6) 33.6334(14) 14.4633(6) 90 107.4530(10) 90 6732.3(5) 4 1.865 6.263 3608 0.150 × 0.110 × 0.070

1890.04 monoclinic P21/c

C66H46B3F12IrN8O2Pt2S2

4c·2H2O

Table 1. Crystal Data for 3a·MeCN·0.5Et2O·0.5H2O, 3b·0.5H2O, 3c·MeCN, 4a·MeOH·2MeCN, 4b·MeCN·1.5Et2O, 4c·2H2O, and 5a·2.5H2O

0.0885 0.2010 1.322 5.573 and −6.430

0.7457, 0.4628 10 410/246/596

2.092−28.282 −13 ≤ h ≤ 13 −49 ≤ k ≤ 49 −15 ≤ l ≤ 14 74 128 10 410 (0.0457)

9.9072(6) 37.1906(19) 11.5230(6) 90 97.5090(17) 90 4209.3(4) 4 1.907 6.696 2320 0.275 × 0.113 × 0.087

1208.59 monoclinic P21/c

C43H31ClIrN5O6.5PtS2

5a·2.5H2O

Inorganic Chemistry Article


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Inorganic Chemistry

addition of excess aqueous NaBF4 solution to a MeCN solution of the complex. Single crystals qualified for X-ray study were obtained by diffusing Et2O into a MeCN solution of the complex. [Ir(dfppy)2(benzene-1-thioether-2-((terpy)Pt)thiolate)](OTf)2 (3b). A solution of [Pt(terpy)(MeCN)](OTf)2 (77 mg, 0.10 mmol) in 10 mL of MeCN was transferred into a solution of 2b (73 mg, 0.10 mmol) in 20 mL of MeOH, and the mixture was stirred for 8 h. The solvent was removed to obtain orange solids. Crystals of the complex were obtained by diffusing Et2O into its MeOH solution. Yield: 110 mg, 76%. Anal. Calcd (%) for 3b (C46H30IrPtN5S4F10O6): C, 37.99; H, 2.08; N, 4.82. Found: C, 37.50; H, 2.25; N, 4.70. 1H NMR (500 MHz, CD3CN): δ 9.50 (d, J = 5.7 Hz, 1H), 8.90 (d, J = 5.7 Hz, 1H), 8.56 (t, J = 8.1 Hz, 1H), 8.45−8.49 (2H), 8.34−8.37 (2H), 8.29 (d, J = 8.0 Hz, 1H), 8.25 (d, J = 8.0, 1H), 8.19−8.22 (2H), 8.15 (t, J = 8.0 Hz, 1H), 8.01 (d, J = 8.0 Hz, 1H), 7.98 (d, J = 8.0 Hz, 1H), 7.66−7.71 (2H), 7.54−7.59 (2H), 7.43 (t, J = 7.6 Hz, 1H), 7.36 (t, J = 7.8 Hz, 1H), 7.27 (dt, J = 5.7, 3.8 Hz, 1H), 6.65−6.70 (2H), 6.40 (d, J = 5.8 Hz, 1H), 5.99 (ddd, J = 12.0, 9.2, 2.1 Hz, 1H), 5.83 (dd, J = 8.3, 2.1 Hz, 1H), 5.61 (dd, J = 8.3, 2.1 Hz, 1H), 1.90 (s, 3H). ESI-MS: m/z 1304.6 [3b-OTf]+, 578.2 [3b-2OTf]2+. [Ir(piq)2(benzene-1-thioether-2-((terpy)Pt)thiolate)](OTf)2 (3c). A solution of [Pt(terpy)(MeCN)](OTf)2 (77 mg, 0.10 mmol) in 10 mL of MeCN was transferred into a solution of 2c (76 mg, 0.10 mmol) in 20 mL of MeOH, and the mixture was stirred for 8 h. The solvent was removed to obtain dark red solids. Crystals of the complex were obtained by diffusing Et2O into its MeCN solution. Yield: 120 mg, 81%. Anal. Calcd (%) for 3c (C54H38IrPtN5S4F6O6): C, 43.75; H, 2.58; N, 4.72. Found: C, 43.42; H, 2.60; N, 4.70. 1H NMR (500 MHz, CD3CN): δ 9.39 (d, J = 6.4 Hz, 1H), 9.07 (d, J = 8.5 Hz, 1H), 8.89 (d, J = 6.4 Hz, 1H), 8.38−8.43 (2H),

Figure 1. (a) Perspective plot of ΛSS isomer of the cation of 3a. Thermal ellipsoids drawn at 50% probability level. H atoms, BF4−, and solvent molecules are omitted. Color scheme: Pt (purple), Ir (olive green), S (yellow), N (blue), and C (gray). (b) Diagram showing overlap of ppy ligand and Pt(terpy) unit in 3a. (c) Packing of molecules in crystal lattice showing intermolecular and intramolecular π−π interaction (d1 = 3.449, d2 = 3.360, d3 = 3.389, d4 = 3.488 (Å)).

Figure 2. (a) Perspective plot of ΛSS isomer of the cation of 3b. Thermal ellipsoids drawn at 50% probability level. H atoms, OTf−, and solvent molecules are omitted. Color scheme: Pt (purple), Ir (olive green), S (yellow), N (blue), and C (gray). (b) Molecular packing in crystal lattice showing intermolecular and intramolecular π−π interaction (d1 = 3.390, d2 = 3.314, d3 = 3.284, d4 = 3.392 (Å)). D


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Inorganic Chemistry

Figure 4. (a) ORTEP plot of ΛSS isomer of the cation of 4a. Thermal ellipsoids drawn at 50% probability level. H atoms, ClO4−, and solvent molecules are omitted. Color scheme: Pt (purple), Ir (olive green), S (yellow), N (blue), and C (gray). (b) Packing of 4a in crystal lattice showing intramolecular and intermolecular π−π stacking (d1 = 3.360, d2 = 3.292, d3 = 3.280, d4 = 3.438, d5 = 3.372, d6 = 3.353, d7 = 3.606, d8 = 3.576 (Å)). (b) Helical chain of 13a molecules formed by intermolecular π−π stacking. 7.44−7.46 (2H), 7.37 (dt, J = 9.6, 4.8 Hz, 1H), 7.30 (t, J = 8.0 Hz, 1H), 7.23 (t, J = 7.3 Hz, 1H), 7.16 (t, J = 8.0 Hz, 1H), 7.05−7.09 (2H), 6.97 (d, J = 7.7 Hz, 1H), 6.92 (t, J = 7.7 Hz, 1H), 6.54−6.58 (2H), 6.18−6.22 (2H), 1.82 (s, 3H). ESI-MS: m/z 1332.9 [3c-OTf]+, 592.1 [3c-2OTf]2+. The OTf anions were changed to ClO4 by addition of excess aqueous NaClO4 solution to a MeCN solution of the complex. Single crystals qualified for X-ray study were grown by diffusing Et2O into a MeCN solution of the complex. [Ir(ppy)2(benzene-1,2-bis((terpy)Pt)thiolate](OTf)3 (4a). [Pt(terpy)(MeCN)](OTf)2 (170 mg, 0.22 mmol) was added to a freshly prepared solution of 1a (0.1 mmol). The solution slowly turned from deep red to dark red. After it was stirred for 8 h, solvent was removed to obtain red

Figure 3. (a) Perspective plot of ΛSS isomer of the cation of 3c. Thermal ellipsoids drawn at 50% probability level. H atoms, ClO4−, and solvent molecules are omitted. Color scheme: Pt (purple), Ir (olive green), S (yellow), N (blue), and C (gray). (b) Molecular packing in crystal lattice showing intramolecular and possibly intermolecular π−π interaction (d1 = 3.456, d2 = 3.324, d3 = 3.597 (Å)). 8.30 (d, J = 8.1 Hz, 1H), 8.19−8.22 (4H), 8.11 (t, J = 7.9 Hz, 1H), 8.03 (d, J = 8.6 Hz, 1H), 7.90−7.99 (5H), 7.86 (d, J = 6.4 Hz, 1H), 7.78 (d, J = 8.0 Hz, 1H), 7.66 (d, J = 8.0 Hz, 1H), 7.51 (t, J = 8.1 Hz, 1H),

Table 2. Selected Bond Lengths (Å) and Angles (deg) of 3a·MeCN·0.5Et2O·0.5H2O, 3b·0.5H2O, and 3c·MeCN 3a

3b

3c

Ir(1)−C(1) Ir(1)−C(2) Ir(1)−N(1) Ir(1)−N(2) Ir(1)−S(1) Ir(1)−S(2)

2.028(3) 2.021(3) 2.055(3) 2.056(3) 2.4335(8) 2.3963(8)

2.024(8) 2.007(8) 2.071(7) 2.070(7) 2.411(2) 2.395(2)

2.015(3) 2.023(2) 2.061(2) 2.057(2) 2.4607(6) 2.3963(6)

C(1)−Ir(1)−N(1) C(2)−Ir(1)−N(2) S(1)−Ir(1)−S(2) N(1)−Ir(1)−N(2) S(1)−Ir(1)−C(1) S(2)−Ir(1)−C(2) N(3)−Pt(1)−N(4) N(4)−Pt(1)−N(5) N(3)−Pt(1)−N(5)

80.23(12) 80.27(12) 86.33(3) 171.86(10) 175.89(10) 175.12(10) 80.31(11) 80.23(11) 160.27(11)

80.3(3) 80.2(3) 85.81(7) 173.8(3) 174.5(3) 174.8(2) 80.3(4) 80.8(4) 161.2(3)

79.49(9) 79.51(9) 85.18(2) 169.35(8) 170.50(7) 173.71(7) 80.66(9) 79.47(8) 159.98(8)

Pt(1)−N(3) Pt(1)−N(4) Pt(1)−N(5) Pt(1)−S(1) S(1)−C(3) S(2)−C(4) S(2)−C(5) N(4)−Pt(1)−S(1) N(3)−Pt(1)−S(1) N(5)−Pt(1)−S(1) Ir(1)−S(1)−Pt(1) Ir(1)−S(1)−C(3) C(3)−S(1)−Pt(1) Ir(1)−S(2)−C(4) Ir(1)−S(2)−C(5) C(4)−S(2)−C(5) E

3a

3c

3c

2.039(3) 1.963(3) 2.043(3) 2.3201(8) 1.784(3) 1.790(3) 1.815(4) 167.49(8) 93.89(8) 105.83(8) 107.17(3) 103.98(11) 114.00(11) 105.16(11) 111.32(12) 100.60(16)

2.039(8) 1.971(7) 2.043(8) 2.299(2) 1.771(9) 1.787(8) 1.817(9) 172.8(3) 92.9(2) 105.9(2) 111.27(8) 104.9(3) 112.1(3) 105.7(3) 112.2(4) 101.5(5)

2.033(2) 1.972(2) 2.064(2) 2.3287(6) 1.786(3) 1.785(3) 1.815(3) 171.08(6) 92.12(6) 107.89(6) 111.51(2) 102.54(9) 110.57(8) 105.17(8) 108.02(9) 99.91(12)


Article

Inorganic Chemistry

5.64 (dd, J = 8.3, 2.3 Hz, 1H). ESI-MS: m/z 1866.7 [4b-OTf]+, 858.9 [4b-2OTf]2+, 523.4 [4b-3OTf]3+. [Ir(piq)2(benzene-1,2-bis((terpy)Pt)thiolate](OTf)3 (4c). [Pt(terpy)(MeCN)](OTf)2 (170 mg, 0.22 mmol) was added to a freshly prepared solution of 1c (0.1 mmol). After it was stirred for 8 h, the solvent was removed to obtain dark red solids. The solid was washed with water and water/methanol (1/1) several times. Crystals were obtained by diffusing Et2O into its MeOH solution. Yield: 120 mg, 62%. Anal. Calcd (%) for 4c (C69H46IrPt2N8S5F9O9): C, 40.53; H, 2.27; N, 5.48. Found: C, 40.04; H, 2.50; N, 5.39. 1H NMR (500 MHz, CD3CN): δ 9.56 (d, J = 6.4 Hz, 1H), 8.45 (t, J = 8.2 Hz, 1H), 8.35−8.39 (2H), 8.26−8.29 (2H), 8.11−8.14 (2H), 7.98 (dd, J = 6.0, 3.4 Hz, 1H), 7.96 (d, J = 8.2 Hz, 1H), 7.80 (d, J = 8.0 Hz, 1H), 7.72 (dd, J = 6.0, 3.4 Hz, 1H), 7.46−7.52 (3H), 7.25 (t, J = 7.2 Hz, 1H), 7.19 (d, J = 6.4 Hz, 1H), 7.17 (dd, J = 6.0, 3.4 Hz, 1H), 7.08 (dt, J = 8.2, 1.3 Hz, 1H), 6.67 (dd, J = 6.0, 3.2 Hz, 1H), 6.55−6.58 (2H), 6.40 (d, J = 5.4 Hz, 1H). ESI-MS: m/z 1894.8 [4c-OTf]+, 872.9 [4c-2OTf]2+, 532.5 [4c-3OTf]3+. The OTf anions were changed to trifluoroborate by addition of excess aqueous NaBF4 solution to a MeCN solution of the complex. Single crystals were obtained by diffusing Et2O into a MeOH solution of the complex. [Ir(ppy)2(benzene-1-thiolate-2-((terpy)Pt)thiolate)](OTf) (5a). A solution of [Pt(terpy)(MeCN)](OTf)2 (77 mg, 0.10 mmol) in MeCN (30 mL) was added dropwise to a freshly prepared 1a (0.10 mmol) solution. The color turned from deep red to yellowish-green after it was stirred for 8 h. Solvent was then removed under vacuum, and the solids obtained were washed with water and methanol. The dark green product was recrystallized from MeCN and Et2O solvent mixture. Yield: 55 mg,

solids, which were washed with water and water/methanol (1/1) several times and then recrystallized from MeCN/Et2O. Yield: 120 mg, 62%. Anal. Calcd (%) for 4a (C61H42IrPt2N8S5F9O9): C, 37.67; H, 2.18; N, 5.76. Found: C, 37.38; H, 2.42; N, 5.66. 1H NMR (500 MHz, CD3CN): δ 9.55 (d, J = 5.7 Hz, 1H), 8.55 (t, J = 8.2 Hz, 1H), 8.39 (d, J = 5.1 Hz, 1H), 8.31(t, J = 8.5 Hz, 2H), 8.20−8.26 (3H), 8.15 (d, J = 7.2 Hz, 1H), 8.05 (dd, J = 6.0, 3.3 Hz, 1H), 7.49−7.52 (2H), 7.31−7.37 (3H), 7.02 (d, J = 7.7 Hz, 1H), 6.78 (d, J = 5.7 Hz, 1H), 6.71 (dt, J = 6.7, 1.3 Hz, 1H), 6.39 (dt, J = 7.3, 1.2 Hz, 1H), 6.32 (dt, J = 7.3, 1.0 Hz, 1H), 6.13 (d, J = 7.4 Hz, 1H). ESI-MS: m/z 1795.1 [4a-OTf]+, 822.8 [4a-2OTf]2+, 499.1 [4a-3OTf]3+. The OTf anions were changed to perchlorate by addition of excess aqueous NaClO4 solution to a MeCN solution of the complex. Single crystals qualified for X-ray study were grown by diffusing Et2O into a MeCN/MeOH (1/1) solution of the complex. [Ir(dfppy)2(benzene-1,2-bis((terpy)Pt)thiolate](OTf)3 (4b). [Pt(terpy)(MeCN)](OTf)2 (170 mg, 0.22 mmol) was added to a freshly prepared solution of 1b (0.1 mmol). The solution slowly turned from red to orange. After it was stirred for 8 h, solvent was removed to obtain orange solids. The solid was washed with water and water/methanol (1/1) for several times. Crystals were obtained by diffusing Et2O into its MeCN solution. Yield: 120 mg, 62%. Anal. Calcd (%) for 4b (C61H38IrPt2N8S5F13O9): C, 36.33; H, 1.90; N, 5.56. Found: C, 36.14; H, 1.90; N, 5.49. 1H NMR (500 MHz, CD3CN): δ 9.59 (d, J = 5.7 Hz, 1H), 8.58 (t, J = 8.2 Hz, 1H), 8.53 (d, J = 5.7 Hz, 1H), 8.38 (d, J = 8.1 Hz, 1H), 8.33−8.37 (2H), 8.26−8.29 (3H), 8.07 (dd, J = 6.0, 3.4 Hz, 1H), 7.71 (d, J = 8.3 Hz, 1H), 7.66 (ddd, J = 7.4, 5.8, 1.4 Hz, 1H), 7.35−7.41 (3H), 6.79 (dt, J = 7.3, 1.3 Hz, 1H), 6.69 (d, J = 5.8 Hz, 1H), 5.97 (ddd, J = 12.6, 9.1, 2.3 Hz, 1H),

Figure 5. (a) ORTEP plot of ΛSS isomer of the cation of 4b. Thermal ellipsoids drawn at 50% probability level. H atoms, OTf−, and solvent molecules are omitted. Color scheme: Pt (purple), Ir (olive green), S (yellow), F (green), N (blue), and C (gray). (b) Packing of 4b in crystal lattice showing intramolecular and intermolecular π−π stacking (d1 = 3.442, d2 = 3.457, d3 = 3.376, d4 = 3.373, d5 = 3.369, d6 = 3.335, d7 = 3.481 (Å)). (b) Helical chain of 13b molecules formed by intermolecular π−π stacking. F


Article

Inorganic Chemistry

space group determination, structure solution, and least-squares refinements on |F|2. Anisotropic thermal parameters were refined for the rest of the non-hydrogen atoms. The hydrogen atoms were placed in their ideal positions. Solvent molecules were found in crystal structure of 3a·MeCN·0.5Et 2 O·0.5H 2 O, 3b·0.5H 2 O, 3c·MeCN, 4a·MeOH· 2MeCN, 4b·MeCN·1.5Et2O, 4c·2H2O, and 5a·2.5H2O. One of the triflate anion in crystal structure of 3b was disordered into two parts. In the structure of 4b, one of the triflate anions is disordered and was refined with the CF3 split into three parts. Three disordered diethyl ether molecules were located with 0.5 occupancy each. In the structure of 4c, four trifluoroborate anions were located, and two of them have 0.5 occupancy. For 5a structure, the perchlorate anion was disordered into two positions with occupancy ratio of 56:44. Restraints in bond length and thermal parameters were applied to all the disordered atoms and anions during refinement. Crystal data and experimental details are summarized in Table 1

45%. Anal. Calcd (%) for 5a (C44H31IrPtN5S3F3O3): C, 43.38; H, 2.57; N, 5.75. Found: C, 43.07; H, 2.92; N, 5.85. 1H NMR (500 MHz, CD3CN): δ 9.69 (d, J = 5.7 Hz, 1H), 9.42 (d, J = 5.7 Hz, 1H), 8.45 (d, J = 8.1 Hz, 1H), 8.37 (d, J = 5.7 Hz, 1H), 8.24 (d, J = 8.0 Hz, 1H), 8.11−8.19 (4H), 8.07 (d, J = 7.7 Hz, 1H), 8.05 (d, J = 8.2 Hz, 1H), 7.87 (t, J = 7.8 Hz, 1H), 7.69 (d, J = 7.8 Hz, 1H), 7.55 (d, J = 7.6 Hz, 1H), 7.39 (t, J = 6.6 Hz, 1H), 7.25−7.33 (3H), 7.14 (t, J = 7.8 Hz, 1H), 7.03 (d, J = 5.6 Hz, 1H), 6.98 (d, J = 7.6 Hz, 1H), 6.89 (d, J = 7.6 Hz, 1H), 6.83 (t, J = 7.6 Hz, 1H), 6.65−6.69 (2H), 6.48 (t, J = 7.3 Hz, 1H), 6.34−6.38 (2H), 6.27 (t, J = 7.4 Hz, 1H), 6.20 (d, J = 7.7 Hz, 1H). ESI-MS: m/z 1068.9 [5a-OTf]+. The anion was changed to perchlorate by addition of excess aqueous NaClO4 solution to a MeCN solution of the compound. Single crystals qualified for X-ray study were then grown by diffusing Et2O into a CH2Cl2/MeCN (1/1) solution of the complex. [Ir(dfppy)2(benzene-1-thiolate-2-((terpy)Pt)thiolate)](OTf) (5b). A solution of [Pt(terpy)(MeCN)](OTf)2 (77 mg, 0.10 mmol) in MeCN (30 mL) was added dropwise to a freshly prepared 1b (0.10 mmol) solution. The color turned from red to yellowish-green after it was stirred for 8 h. Solvent was then removed under vacuum, and the solids obtained were washed with water and methanol. The dark green product was recrystallized from MeCN/Et2O. Yield: 80 mg, 62%. Anal. Calcd (%) for 5b (C44H27IrPtN5S3F7O3): C, 40.96; H, 2.11; N, 5.43. Found: C, 40.67; H, 2.48; N, 5.38. 1H NMR (500 MHz, CD3CN): δ 9.75 (d, J = 5.6 Hz, 1H), 9.45 (d, J = 6.3 Hz, 1H), 8.53 (d, J = 5.6 Hz, 1H), 8.48 (t, J = 8.2 Hz, 1H), 8.26−8.36 (5H), 8.11−8.22 (5H), 7.95 (t, J = 7.6 Hz, 1H), 7.53−7.58 (4H), 7.36 (t, J = 7.3 Hz, 1H), 7.30 (t, J = 6.5 Hz, 1H), 7.22 (t, J = 7.2 Hz, 1H), 7.02 (t, J = 7.6 Hz, 1H), 6.90 (d, J = 5.8 Hz, 1H), 6.74 (t, J = 7.4 Hz, 1H), 6.44−6.51 (2H), 5.84−5.89 (2H), 5.63 (dd, J = 8.9 Hz, 2.3 Hz, 1H). ESI-MS: m/z 1140.9 [5b-OTf]+. [Ir(piq)2(benzene-1-thiolate-2-((terpy)Pt)thiolate)](OTf) (5c). A solution of [Pt(terpy)(MeCN)](OTf)2 (77 mg, 0.10 mmol) in MeCN (30 mL) was added dropwise to a freshly prepared 1c (0.10 mmol) solution. The color turned from deep red to brown after it was stirred for 8 h. Solvent was then removed under vacuum, and the solids obtained were washed with water and methanol. The product was recrystallized from CH2Cl2/ Et2O. Yield: 62 mg, 47%. Anal. Calcd (%) for 5c (C52H35IrPtN5S3F3O3): C, 47.37; H, 2.68; N, 5.31. Found: C, 46.92; H, 3.04; N, 5.66. 1H NMR (500 MHz, CD3CN) δ 9.75 (d, J = 6.4 Hz, 1H), 9.37 (d, J = 6.4 Hz, 1H), 9.02 (d, J = 8.2 Hz, 1H), 8.28−8.33 (3H), 8.23 (d, J = 8.0 Hz, 1H), 8.16−8.18 (2H), 8.05−8.11 (2H), 7.94 (d, J = 8.6 Hz, 1H), 7.79−7.86 (3H), 7.76 (d, J = 8.0 Hz, 1H), 7.61 (d, J = 6.5 Hz, 1H), 7.59 (d, J = 8.1 Hz, 1H), 7.50 (d, J = 8.0 Hz, 2H), 7.37 (d, J = 7.3 Hz, 1H), 7.30−7.35 (2H), 7.26 (ddd, J = 7.3 Hz, 5.7 Hz, 1.3 Hz, 1H), 6.95−6.99 (2H), 6.90 (dt, J = 8.1 Hz, 1.1 Hz, 1H), 6.87 (d, J = 6.5 Hz, 1H), 6.80 (m, 1H), 6.71 (2H), 6.56−6.59 (3H), 6.50 (ddd, J = 8.2 Hz, 5.6 Hz, 3.0 Hz, 1H). ESI-MS: m/z 1169.0 [5c-OTf]+. Computational Details. Gas-phase structures of all complexes were optimized by the density functional theory (DFT) method using B3PW91 hybrid functional.20 The 6-31G(d)21 basis set was used for all atoms except iridium and platinum, for which Stuttgart−Dresden (SDD)22 relativistic effective core potential and associated basis sets were employed. Unrestricted formalism (UB3PW91) was used with the same basis sets for optimization of the lowest-lying triplet states. Frequency calculation was performed for all optimized geometries to ensure that the stationary point was minimum. Single point and timedependent DFT (TDDFT) calculations were performed at the same functional and basis sets with solvent effect described by polarizable continuum model (PCM). Emission energy was estimated by ΔSCF (SCF = self-consistent field) approach as the difference between energies of the triplet excited state and the ground singlet state at triplet-state optimized geometry.23 Tight SCF convergence criteria were used for all calculations. All DFT calculations were performed using Gaussian 09 software package (Revision A.02).24 X-ray Crystallography. Single-crystal X-ray diffraction was performed on a Bruker AXS SMART CCD three-circle diffractometer with a sealed tube at 223 K using graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å). The software used was as follows: SMART25 for collecting frames of data, indexing reflections, and determining lattice parameters; SAINT25 for integration of intensity of reflections and scaling; SADABS26 for empirical absorption correction; SHELXTL27 for

Figure 6. (a) ORTEP plot of ΛSS isomer of the cation of 4c. Thermal ellipsoids drawn at 50% probability level. H atoms, BF4−, and solvent molecules are omitted. Color scheme: Pt (purple), Ir (olive green), S (yellow), F (green), N (blue), and C (gray). (b) Packing of 4 in crystal lattice showing intramolecular and intermolecular π−π stacking (d1 = 3.313, d2 = 3.414, d3 = 3.268, d4 = 3.430, d5 = 3.192 (Å)). G


Article

Inorganic Chemistry

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RESULTS AND DISCUSSION Synthesis. [Ir(L)2(benzene-1,2-dithiolate)]− [L = ppy (1a), dfppy (1b), and piq (1c)] were synthesized in situ by reacting [Ir(L)2(MeCN)2]+ with sodium benzene-1,2-dithiolate in 1:1 ratio in CH3CN/MeOH.14 The thioether−thiolate complexes 2a−c were produced from nucleophilic substitution MeI by [Ir(L)2(benzene-1,2-dithiolate)]−, the procedure of which was reported in our previous study.15 The reactions are completely diastereoselective, producing only the enantiomers ΛS and ΔR (vide infra). Reacting 2a−c with [Pt(terpy)(MeCN)]2+ in MeOH gave 3a−c, respectively. The orange trimetallic IrPt2 complexes 4a−c were prepared by treating 1a−c with 2 mol equiv of Pt(terpy)(MeCN)2+. Reacting [Ir(L)2(benzene-1,2dithiolate)]− and Pt(terpy)(MeCN)2+ in 1:1 molar ratio led to the greenish thiolate complexes 5a−c, which are nonemissive. Characterizations. Seven (3a−c, 4a−c, 5a) of the nine complexes prepared in this study were characterized by X-ray crystallography. All structures show distorted square planar Pt(terpy)2+ ion coordinated to the S atom(s) of the respective Ir complex. Addition of the Pt ion creates chiral center at the S atom (S or R). Because of the helical chirality centered at the iridium ion (Λ or Δ), the addition of the Pt(terpy) in principle would lead to enantiomers ΔS and ΛR (5a−c) or ΔSS and ΛRR (3a−c and 4a−c) and their diastereomers ΔR and ΛS or ΔRR and ΛSS. Nonetheless, 1H NMR spectra of the platination products show the presence of only one pair of enantiomers, implying that the reactions are completely diastereoselective, producing only ΛS and ΔR for 5a−5c and ΛSS and ΔRR for 3a−c and 4a−c. The absolute configurations are confirmed by the X-ray crystal structures of the complexes. Single crystals of 3a−c were grown by diffusing diethyl ether into its MeCN (3a, 3c) or MeOH (3b) solution at room temperature. ORTEP plots of the complexes are shown in Figures 1−3, and selected bond lengths and bond angles are listed in Table 2. The structures are similar, all showing a distorted octahedral IrL2(SSMe) core bonded to a nearly planar Pt(terpy) group via its coordinated thiolate Ir−S−C atom with Ir(1)−S(1)−Pt(1) angle of 107.17(3)−111.51(2)° and Ir−S(Pt) bonds of 2.411(2)− 2.4607(6) Å. The other sulfur atom exists as coordinated thioether

Ir−S(Me)−C. There are three chiral centers in the complexes: the two sulfur atoms (S or R) and the iridium center (Δ or Λ). Crystals of 3a−c, which are, respectively, in centrosymmetric space groups of P1̅, P21/n, and P21/c, contain both ΛSS and ΔRR enantiomers. The same diastereoselectivity, which has been observed in the methylation or auration of 1a to form 2a, was attributed to a stereoelectronic effect, which was expounded in detail in our previous paper.15 The Ir(III) centers form three fivemember rings with two cyclometalated ligands L and a thiolato− thioether ligand (SSMe) in a distorted octahedral geometry. The lengths of Ir−C bond (2.007(8)−2.028(3) Å) and Ir−N bond (2.055(3)−2.071(7) Å)) are normal.5f,14,15 The Ir−S(Me) bonds (2.3963(8) Å) are slightly shorter than the Ir−S(Pt) bonds (2.411(2), 2.4335(8), and 2.4607(6) Å), presumably due to the electron-withdrawing Pt(terpy)2+, which renders the S(Pt) atom less donating. Similar distances are found in diaurated (Ir−S(AuPPh3) = 2.423(2) Å) derivatives of 1a.15 The methylated and platinated sulfur atoms display distorted pyramidal geometry with Ir(1)−S(1)−Pt(1) and Ir(1)−S(2)−C(5) angles ranging from 107.17(3) to 111.51(2)° and 108.02(9)−113.32(12)°, respectively. Similar bond angles (109.76(15)−112.83(15)°) are observed in 2a and its AuPPh3 derivative.15 The Pt(terpy) unit and the adjacent cyclometalated ligand L are positioned in a cofacial manner and overlap extensively. They are nearly parallel with small dihedral angles of 2.17° (3a), 13.17° (3b), and 4.31° (3c) and show interplanar distances (360 Å (3a), 3.284 Å (3b), and 3.324 Å (3c)) that fall in the range for stacking separations of planar aromatic molecules, suggesting presence of π−π interactions.12b,17,28 The Pt(II) ions are coordinated to a tridentate terpyridine and a sulfur atom, displaying a distorted square planar geometry. The N(3)−Pt(1)−N(4) and N(4)−Pt(1)−N(5) angles (79.47(8)−80.8(4)°) are similar to that of [Pt(terpy)Cl]Cl (81.1(2)°).12b The Pt(1)−S(1) distances of 2.3201(8) Å (3a), 2.299(2) Å (3b), and 2.3287(6) Å (3c) are comparable with that of reported Pt(terpy)−thiolate complexes such as [Pt2(μ-SMe)(terpy)2](ClO4)3 (2.307(2) and 2.313(3) Å),29a [Pt(trpy)(S-benzo-15-crown-5)] (2.313(2) Å),29b and [{Pt(terpy)}2(μ-SC6H4S-1,3)](PF6)2.29c

Table 3. Selected Bond Lengths (Å) and Angles (deg) of 4a·MeOH·2MeCN, 4b·MeCN·1.5Et2O, and 4c·MeOH·H2O Ir(1)−C(1) Ir(1)−C(2) Ir(1)−N(1) Ir(1)−N(2) Ir(1)−S(1) Ir(1)−S(2) S(1)−C(3) S(2)−C(4) C(1)−Ir(1)−N(1) C(2)−Ir(1)−N(2) S(1)−Ir(1)−S(2) N(1)−Ir(1)−N(2) S(1)−Ir(1)−C(1) S(2)−Ir(1)−C(2) N(3)−Pt(1)−N(4) N(4)−Pt(1)−N(5) N(3)−Pt(1)−N(5) N(4)−Pt(1)−S(1) N(3)−Pt(1)−S(1) N(5)−Pt(1)−S(1)

4a

4b

4c

2.027(4) 2.022(4) 2.057(3) 2.066(3) 2.4327(10) 2.4275(10) 1.776(4) 1.784(4) 80.12(16) 80.19(15) 84.23(3) 172.11(13) 174.11(12) 174.83(11) 80.8(2) 80.4(2) 161.12(18) 173.07(15) 93.80(12) 104.95(14)

2.025(4) 2.011(3) 2.054(3) 2.061(3) 2.4348(9) 2.4206(9) 1.783(3) 1.779(3) 80.21(13) 80.13(13) 84.11(3) 170.91(11) 174.91(10) 176.44(10) 80.68(12) 79.92(12) 160.60(12) 172.95(9) 94.15(9) 105.15(8)

2.020(11) 2.008(12) 2.060(9) 2.061(10) 2.430(3) 2.406(3) 1.801(13) 1.818(13) 79.3(4) 79.0(5) 85.13(10) 173.3(4) 173.1(3) 173.2(4) 80.5(4) 79.8(4) 160.3(4) 173.9(3) 93.5(3) 106.2(3)

Pt(1)−S(1) Pt(1)−N(3) Pt(1)−N(4) Pt(1)−N(5) Pt(2)−S(2) Pt(2)−N(6) Pt(2)−N(7) Pt(2)−N(8) N(6)−Pt(2)−N(7) N(7)−Pt(2)−N(8) N(6)−Pt(2)−N(8) N(7)−Pt(2)−S(2) N(6)−Pt(2)−S(2) N(8)−Pt(2)−S(2) Ir(1)−S(1)−C(3) Ir(1)−S(1)−Pt(1) Pt(1)−S(1)−C(3) Ir(1)−S(2)−C(4) Ir(1)−S(2)−Pt(2) Pt(2)−S(2)−C(4) H

4a

4b

4c

2.3119(10) 2.028(4) 1.965(4) 2.052(5) 2.3024(10) 2.040(4) 1.963(3) 2.040(4) 80.35(14) 80.33(15) 160.66(14) 169.33(10) 92.99(10) 106.24(11) 105.20(14) 110.12(4) 111.33(14) 105.33(14) 108.07(4) 115.15(15)

2.3186(9) 2.030(3) 1.962(3) 2.036(3) 2.3042(9) 2.031(3) 1.962(3) 2.043(3) 80.63(12) 80.36(12) 160.87(11) 165.24(8) 91.02(8) 108.00(8) 104.39(12) 110.02(3) 112.73(12) 104.87(12) 107.43(3) 118.34(12)

2.307(3) 2.027(11) 1.976(9) 2.032(10) 2.307(3) 2.035(10) 1.969(10) 2.035(10) 80.4(5) 80.9(4) 161.2(4) 173.4(3) 93.9(3) 104.8(3) 104.7(4) 114.72(12) 110.3(4) 105.3(4) 113.73(12) 111.8(4)


Article

Inorganic Chemistry Similar to [Pt(terpy)Cl]+ and similar complexes, which stack intermolecularly via metal−metal and/or π−π to form dimeric or polymeric structures in solid state,12a,b,17,30 crystals of 3a−c show dimers that stack via their terpy ligands. The two stacking Pt(terpy) units are parallel with interplanar distance of 3.488 Å (3a), 3.392 Å (3b), and 3.597 Å (3c), but the shortest distance between two Pt ions in two adjacent molecules is much longer (4.560 Å (3a), 6.290 Å (3b), and 5.186 Å (3c)), excluding any possible Pt−Pt interactions. Crystal structures of the cations of 4a−c (Figures 4−6; selected bond lengths and bond angles are listed in Table 3) show trimetallic complexes composed of a cyclometalated IrIII(L)2(SS) moiety coordinated through its two sulfur atoms to two Pt(terpy)2+ ions. All three crystals consist of both ΛSS and ΔRR enantiomers. 1H NMR spectra of the products show one set of signals and thus the presence of only one pair of enantiomers in accord with complete diastereoselectivity of the addition of Pt(terpy). The complexes have an approximate C2 symmetry with the C2 axis bisecting the IrS2C2 chelate ring. The Ir centers display distorted octahedral geometry with N(1)−Ir(1)−N(2), S(1)− Ir(1)−C(1), and S(2)−Ir(1)−C(2) angles of 170.91(11)− 173.3(4)°, 173.1(3)−174.91(11)°, and 173.2(4)−176.44(10)°,

respectively. The Ir−S bond distances of 2.406(3)−2.4348(9) Å are similar to the ones in 3a−c. The S2-phenyl ring is bent from IrS2 plane by an angle of 11.62° (4a) and 16.07° (4b), but they are essentially coplanar in 4c. The platinated sulfur atoms, similar to those in 3a−c, display a pyramidal geometry with Ir−S−Pt, Ir−S−C, and C−S−Pt angles of 107.43(3)−114.72(12)°, 104.39(12)−105.33(14)°, and 110.3(4)−118.34(12)°, respectively. The Pt(terpy)(S) fragments show a distorted square planar geometry with Pt−S bond distances (2.3024(10)−2.3186(9) Å) similar to that of 3a−c. The structure of 4a shows that the Pt(terpy) and an adjacent ppy ligand are nearly parallel with shortest interplanar distance of 3.28 Å (Figure 4a), suggesting the presence of π−π interactions. Examination of solid-state packing reveals alternate aggregation of the ΔRR and ΛSS enantiomers in forming a helical chain (Figure 4b) in which stacking Pt(terpy) units are separated by 3.353 Å. Similarly, crystal structure of 4b shows intramolecular π−π stacking between Pt(terpy) and dfppy (interplanar distance = 3.365 Å) and intermolecular Pt(terpy)−Pt(terpy) stacking (interplanar distance = 3.335 Å) between the enantiomers to form helical chains (Figure 5b). The structure of 4c shows a twisted piq ligand with its isoquinoline ring being bent toward the Pt(terpy) (interplanar distance = 3.268 Å). Instead of stacking with their Pt(terpy) units, the cations of 4c form helices in its crystals via alternate intermolecular and intramolecular Pt(terpy)-isoquinoline (of the piq ligand) stacking with interplanar distances of 3.40 and 3.313 Å, respectively (Figure 6). Crystal structure of 5a (Figure 7 and Table 4) shows one sulfur atom coordinates to a Pt(terpy) group and an Ir ion, while the Table 4. Selected Bond Lengths (Å) and Angles (deg) of 5a· 2.5H2O Ir(1)−C(1)

2.027(15)

Pt(1)−N(3)

2.018(12)

Ir(1)−C(2) Ir(1)−N(1) Ir(1)−N(2) Ir(1)−S(1) Ir(1)−S(2) C(1)−Ir(1)−N(1) C(2)−Ir(1)−N(2) S(1)−Ir(1)−S(2) N(1)−Ir(1)−N(2) S(1)−Ir(1)−C(1) S(2)−Ir(1)−C(2) N(3)−Pt(1)−N(4) N(4)−Pt(1)−N(5)

2.032(13) 2.036(13) 2.058(12) 2.427(4) 2.441(4) 80.3(6) 79.5(5) 84.90(15) 171.2(5) 173.0(4) 176.9(4) 80.3(5) 80.6(5)

Pt(1)−N(4) Pt(1)−N(5) Pt(1)−S(1) S(1)−C(3) S(2)−C(4) N(3)−Pt(1)−N(5) N(4)−Pt(1)−S(1) N(3)−Pt(1)−S(1) N(5)−Pt(1)−S(1) Ir(1)−S(1)−Pt(1) Ir(1)−S(1)−C(3) C(3)−S(1)−Pt(1) Ir(1)−S(2)−C(4)

1.962(13) 2.032(14) 2.304(4) 1.784(18) 1.770(19) 160.8(5) 170.3(4) 92.6(4) 106.4(4) 107.01(15) 104.6(6) 112.9(6) 103.6(6)

other S atom coordinates to the Ir ion only. Both ΛS and ΔR enantiomers are present in the unit cell. Structural parameters of the complex are comparable to those of 3a−c and 4a−c. The Ir(1)−S(2) distance (2.441(4) Å) is similar to that in 2a (2.4136(11) Å). The S2-phenyl ring is canted from the IrS2 plane in a dihedral angle of 14.11°. The coordination geometry of the Pt(II) ion is similar to that in 3a−c and 4a−c. The terpy ligand is separated from its adjacent ppy ligand by an interplanar distance of 3.360 Å. The compound exists as dimers in its crystal with the stacking Pt(terpy) groups overlap in a head-to-tail manner and are separated by 3.316 Å (Figure 7b). Although we failed to obtain crystals of 5b and 5c, we infer that the structures of the complexes should be similar to that of 5a, as all the complexes show similar 1H NMR and UV−vis absorption spectra (vide infra), and the molecular formulas of the complexes are

Figure 7. (a) Perspective plot of ΛS isomer of the cation of 5a. Thermal ellipsoids drawn at 50% probability level. H atoms, ClO4−, and solvent molecules are omitted. Color scheme: Pt (purple), Ir (olive green), S (yellow), N (blue), C (gray). (b) Packing of two cations of 5a in crystal lattice showing intramolecular and intermolecular π−π stacking (d1 = 3.360, d2 = 3.421, d3 = 3.388, d4 = 3.340, d5 = 3.316 (Å)). I


Article

Inorganic Chemistry confirmed by ESI-MS (Figure S1) and elemental analysis. Their DFT optimized structures are similar to that of 5a (vide infra). For all the complexes, the Pt(terpy) units slightly slant toward the ligands L around the Ir−S bond as the S(1/2)-Pt(1/2)-N(5/8) angle (104.8(3)−108.00(8)°) is invariably larger than the S(1/2)Pt(1/2)-N(3/6) angle (91.02(8)−94.15(9) °) (Figure 1b). The distortion could be taken as evidence for attractive interaction between the Pt(terpy) and the L. 1 H NMR spectra of 4a−c show only one set of signals for cyclometalated ligands L (ppy, dfppy, and piq) and two doublets for benzene-1,2-dithiolate protons in accord with the C2 symmetry of the complexes (see Figure S2 for the two-dimensional (2D) COSY spectra). Spectra of 3a−c and 5a−c have two sets of signals for the protons of L and four signals for benzene-1,2-dithiolate

protons, as the two cyclometalated ligands are nonequivalent as revealed by the crystal structures. The signals of the overlapping L rings in the complexes show diatropic upfield shift. For example the two ppy ligands of 3a give two different sets of signals with the chemical shifts of the protons of the overlapping ppy being 0.4−0.9 ppm lower than that of the nonoverlapping one. Most of the protons of the terpy do not overlap with L, but the H13, which is covered significantly by L, shows an upfieldshifted signal, that is, the H13 signals of 3a (δ 8.34) and 4a (δ 8.39) are lower than that of the corresponding proton in similar complexes such as [Pt2(terpy)2(μ-SMe)](ClO4)3 (δ 9.7),29 and [Pt(terpy)(SCH2CH2OH)](PF6) (δ 9.16).28 The results indicate that the rings remain overlapped in the solutions and probably have the same conformations as depicted in the X-ray crystal structures. Electrochemical data of the complexes are listed in Table 5. All the complexes display a quasi-reversible reduction from −0.80 to −1.02 V and, except 3a and 4a, a quasi-reversible reduction from −1.28 to −1.66 V (vs saturated calomel electrode (SCE)) in their cyclic voltammograms (CVs; Figure S3). The first reduction is assigned one-electron reductions of the Pt(terpy) unit, as reductions at similar potentials have been reported for PtII-terpy complexes.31 The second reduction from −1.42 to −1.62 V could be one-electron reduction of cyclometalated ligands L, as a previous study showed that the ligand-centered reductions of cationic [Ir(ppy)2(bipy)]+ and [Ir(dfppy)2(bipy)]+ occur at similar

Table 5. Electrochemical Data of the Complexes complex 3a 3b 3c 4a 4b 4c 5a 5b 5c

oxidation (V) 1.24 (irr) 1.53 (irr) 1.26 (q) 1.00 (q) 1.43 (irr) 1.05 (q) 0.38 (irr) 0.53 (irr) 0.39 (irr)

1.14 (q) 1.06 (q) 1.15 (irr)

reduction (V) −0.82 (q) −0.69 (q) −0.87 (q) −0.98 (q) −0.80 (q) −1.00 (q) −0.99 (q) −0.93 (q) −1.02 (q)

−1.28 (q) −1.52 (q) −1.39 (q) −1.66 (q) −1.63 (q) −1.61 (q) −1.66 (q)

Figure 8. Frontier molecular orbital surfaces of 3a−c at the ground-state optimized geometries. Surface isovalue 0.03 and hydrogen atoms omitted. J


Article

Inorganic Chemistry

Figure 9. Frontier molecular orbital surfaces of 4a−c at the ground-state optimized geometries. Surface isovalue 0.03 and hydrogen atoms omitted.

potentials of −2.01 and −1.97 V, respectively,32 and an anodic shift of the reduction is expected for the present complexes, which have higher former charges. An irreversible oxidation peak from +1.00 to +1.53 V is assigned to IrIII→IrIV oxidation according to the reported CVs of similar cyclometalated IrIII complexes. That the oxidation is anodic shifted from the corresponding oxidation of neutral fac-IrL3 complexes (+0.77 V for fac-Ir(ppy)3 and facIr(piq)3 and +0.94 V for fac-Ir(dfppy)3) is consistent with the fact that the present complexes are cationic. In addition to the Ir(III)→ Ir(IV) oxidation peak, the CVs of 5a−c exhibit an irreversible oxidation at lower potentials, that is, +0.38 V (5a), +0.53 V (5b), and +0.39 V (5c), which is not found in the CVs of other complexes. It is therefore assigned to the oxidation of the nonplatinated S atom in the complexes. Our DFT calculations show that the highest occupied molecular orbitals (HOMOs) of 5a−c are an antibonding orbital composed mainly of the lone-pair 3p orbital of S (vide infra), and so the oxidation is assigned to oxidation of the thiolate S atom in the complexes. It is noted that the CV of the neutral complex [Ru(bipy)2(SSO2)] (SSO2 = dianion of o-benzene monosulfhydryl monosulfinic acid) shows an oxidation wave of the thiolate S atom at +0.18 V.33

Electronic Structures. The electronic structures of the Ir−Pt complexes were probed by DFT calculations. In general, the DFT optimizations of ground-state structures in solvent (Table S1 for selected structural parameters) are in good agreement with the experimental ones, and the calculated structures of 5b and 5c resemble the crystal structure of 5a. Deviation between experimental and calculated bond distances are less than 0.01 Å for Ir−C bonds and less than 0.03 Å for Ir−N bonds, and the calculated and experimentally determined Pt−N bond lengths are within 0.04 Å. The calculated Ir−S and Pt−S bond lengths are different from the ones in the crystal structures by less than 0.09 Å. The models reproduce coordination geometries of the Ir and Pt centers. The N−Ir−C angles (79.04−83.81°) compare favorably with the experimental values (79.0(3)−80.3(6)°). The S−Ir−S angles (82.72−84.45°) are slightly smaller than the experimental ones (84.11(3)−86.33(3)°). All the calculated structures reproduce the overlap of the Pt(terpy) ring and the ligand L with similar interplanar distance of 3.387−3.578 Å. Plots of lowest unoccupied molecular orbital LUMO+1, LUMO, HOMO, and HOMO−1 are presented in Figures 8−10, and compositions of the orbitals are listed in Tables 6−8. K


Article

Inorganic Chemistry

Figure 10. Frontier molecular orbital surfaces of 5a−c at the ground-state optimized geometries. Surface isovalue 0.03 and hydrogen atoms omitted.

Table 6. DFT-Calculated (B3PW91/(6-31G(d) + SDD)) Energies and Compositions of Frontier Orbitals of 3a−c MO composition (%) orbital

energy (eV)

Ir (s, p)

Ir (d)

L

LUMO+1 LUMO HOMO HOMO−1

−2.92 −3.35 −5.98 −6.43

0.22 0.24 0.21

0.35 33.28 19.36

0.27 24.50 29.39


−2.94 −3.38 −6.25 −6.55

0.03 0.20 0.19 0.19

0.32 30.70 17.96

23.84 31.50 35.53


−2.93 −3.36 −5.96 −6.28

0.03 0.22 0.36 0.31

0.34 30.40 14.07

0.28 28.01 41.61

La

S(Pt)

S(Me)

Pt (s, p)

Pt (d)

terpy

phenyl

0.01 0.47 8.37 15.40

0.36 9.72

3.31 0.25 1.12

1.09 2.69 1.71 4.14

98.82 92.07 0.92 2.15

0.01 0.28 2.59 10.13

0.46 10.36 16.34

0.02 0.33 7.93 1.39

3.39 0.24 1.24

1.07 2.56 2.34 4.52

98.80 92.25 1.11 2.42

0.01 0.31 4.33 12.04

0.47 5.03 3.97

0.01 0.75 2.39

3.34 0.18 0.32

1.08 2.63 1.02 0.95

98.85 91.92 0.62 0.65

0.01 0.29 2.03 1.67

3a

a

0.29 27.60 7.40 3b 0.09 0.23 26.32 4.91 3c 0.03 0.49 31.57 32.76

The cyclometalated ligand L that overlaps with Pt(terpy).

For 3a−c and 5a−c, their LUMO and LUMO+1 are primarily a π*-orbital of terpy ligand (π*terpy) with small contribution from a dπ orbital of Pt (dPt, 1.07−1.14% for LUMO+1 and 2.56−3.06% for LUMO). Because 4a−c have two Pt(terpy) groups and their structures are slightly distorted from ideal C2 symmetry, the LUMO and LUMO+1 of the complexes have almost the same compositions and energy and are delocalized over the π* orbitals

of both Pt(terpy) groups. In general, the LUMOs of cyclometalated Ir(III) complexes such as fac-IrL3 are composed mainly of the π* orbital of cyclometalated ligands.5d,f,34 However, for the Ir−Pt complexes, the π* orbitals of L lie in higher energy than the terpy-based LUMOs: they are LUMO+3 for 3a and 3b, LUMO +2 for 3c, LUMO+6 for 4a and 4b, LUMO+5 for 4c, LUMO+5 for 5a, LUMO+6 for 5b, and LUMO+2 for 5c. L


Article

Inorganic Chemistry Table 7. DFT-Calculated (B3PW91/(6-31G(d) + SDD)) Energies and Compositions of Frontier Orbitals of 4a−c MO composition (%) orbital

energy (eV)

Ir (s, p)

Ir (d)


−3.37 −3.39 −5.98 −6.15

0.19 0.28 0.19 0

0.35 0.39 35.68 19.11


−3.40 −3.41 −6.23 −6.27

0.16 0.29 0.17 0

0.36 0.40 33.74 16.81


−3.37 −3.39 −5.94 −6.13

0.23 0.29 0.24 0

0.47 0.36 32.28 22.64

C^N 4a 0.53 0.31 53.36 10.70 4b 0.55 0.32 52.38 8.84 4c 0.73 0.55 57.59 22.69

S(Pt)

Pt (s, p)

Pt (d)

terpy

phenyl

0.65 0.42 6.28 38.21

3.07 3.41 0.33 1.97

2.93 2.51 1.27 8.14

92.08 92.14 0.73 4.60

0.20 0.51 2.27 17.37

0.59 0.42 7.59 39.09

3.14 3.41 0 2.13

2.83 2.45 0.26 8.75

92.19 92.20 0.77 4.91

0.19 0.49 3.33 19.61

0.60 0.42 5.78 29.86

3.05 3.41 0.25 1.80

2.90 2.51 1.24 6.49

91.85 91.95 0.81 3.84

0.18 0.47 1.98 12.77

Table 8. DFT-Calculated (B3PW91/(6-31G(d) + SDD)) Energies and Compositions of Frontier Orbitals of 5a−c MO composition (%) orbital

a

energy (eV)

Ir (s, p)

Ir (d)

L


−2.79 −3.19 −5.14 −5.54

0.02 0.22 0.44 0.49

0.01 0.40 17.53 37.42

0 0.3 1.98 25.09


−2.81 −3.22 −5.23 −5.80

0.03 0.20 0.56 0.52

0 0.38 14.71 37.43

0 0.28 1.35 25.01


−2.78 −3.18 −5.14 −5.53

0.02 0.24 0.45 0.45

0.01 0.42 16.36 35.30

0 0.30 2.55 26.55

La 5a 0.07 0.34 3.79 21.89 5b 0.11 0.27 2.75 21.34 5c 0.11 0.76 3.66 24.12

S(Pt)

S

Pt (s, p)

Pt (d)

terpy

phenyl

0.01 0.60 2.70 4.85

0 0.02 46.59 5.03

0 3.07 0.52 0.24

1.13 3.07 1.06 0.90

98.76 91.70 1.14 0.62

0.01 0.27 24.24 3.58

0 0.54 2.52 6.23

0 0.02 49.12 3.58

0.01 3.14 0.50 0.22

1.11 2.93 1.03 1.25

98.74 91.97 1.16 0.71

0.01 0.28 26.30 3.77

0 0.58 2.72 4.54

0 0.01 46.95 4.30

0 3.02 0.27 0.22

1.14 3.07 1.06 0.84

98.71 91.35 1.17 0.68

0.01 0.24 24.54 3.10

The cyclometalated ligand L that overlaps with the Pt(terpy).

The HOMOs of 3a−c are composed of π orbitals of the ligands L (52.1−59.58%) and a dπ orbital of the iridium ion (30.40−33.28%) with small contribution from the 3p orbital of the sulfur atom (5.03−0.36%) and a dπ orbital of the Pt ion (1.02−2.34%). The HOMO−1s have similar dπIr contribution but are slightly more localized on one ligand L. The HOMOs of 4a−c are similar to those of 3a−c, as they mainly comprise of a π orbital of L (52.38−57.59%) and a dπ orbital of the iridium ion (32.28−35.68%) with small contribution from the 3p orbital of the sulfur atom and a dπ orbital of the Pt ion. The HOMOs of 5a−c is an antibonding orbital arising from mixing of the filled dπ orbital of iridium (17.53%, 5a; 14.71%, 5b; and 16.36%, 5c) and the 3p orbital (lone pair) of the thiolate sulfur (46.54% in 5a, 49.08% in 5b, and 46.95% in 5c), the so-called dπ−pπ interactions.14,35 Our previous study showed similar HOMOs for 1a and 2a (Scheme 1).14,15 The HOMO−1 orbitals of 5a−c are mainly composed of a π orbital of the ligands L and an Ir 5d orbital and so correspond to the HOMOs of 3a−c and 4a−c. Energies of the frontier orbitals are shown in Figure 11. The LUMO orbitals of all complexes, which are predominantly localized on Pt(terpy) fragments, are close in energy. The order of LUMO energy, 5a−c > 3a−c ≈ 4a−c, could be explained by

Figure 11. Plot of the energies of the frontier orbitals of the complexes. HOMO−1 (green), HOMO (blue), LUMO (red), and LUMO+1 (magenta).

stabilization of the orbital by Columbic attraction in the higher formal charges of the latter complexes. The LUMO+1 orbitals, M


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Inorganic Chemistry except for those in 4a−c, lie ∼0.4 eV higher in energy than the LUMO. The HOMOs of 5a−c, which are antibonding orbitals arising from dπ(Ir)−pπ(S) interactions, are significantly higher in energy than the HOMOs of 3a−c and 4a−c, which are mainly based on L. The HOMOs of 3a, 3c, 4a, and 4c are very similar in energy, while those of 3b and 4b are ∼0.3 eV lower in energy, because the π-orbtials of dppf are significantly stabilized by the electron-withdrawing fluorine. The HOMO−1s of 5a−c, which correspond to the HOMOs of 3a−c and 4a−c, are higher in energy because of the lower formal charges of the complexes. The calculated HOMO and LUMO energies corroborate with the assignments of the first oxidation and the first reduction in the CVs of the complexes. As mentioned, the HOMOs of 5a−c are significantly higher in energy (−5.14 and −5.23 eV) than the HOMOs of 3a−c and 4a−c, which have similar energies (−5.94 to −6.25 eV). Same trend is observed for the first oxidation of the complexes, as Ir-based oxidation of 3a−c (1.24−1.53 V) and

4a−c (1.00−1.43 V) have similar potentials, but the S-based oxidations of 5a−c occur at significantly lower potentials (0.38, 0.39, 0.51 V). With the exception of 3b, all complexes show similar first reduction potentials (−0.82 to 1.02 V). It is in accord with the similar LUMO energies calculated for all the complexes (−3.18 to −3.41 eV). Electronic Absorption Spectroscopy. UV−Vis absorption spectra of the complexes in MeOH at 298 K are shown in Figure 12, and the spectroscopic and photophysical data are summarized in Table 9. TDDFT calculations were performed to assist Table 9. UV−Vis Absorption and Photophysical Data of the Complexes complex 3a 3b 3c 4a 4b 4c 5a 5b 5c a

λmax, nm (ε, 1 × 103 M−1 cm−1) 520 (0.75); 373 (8.60); 341 (17.20) 460 (1.08); 370 (7.22); 340 (16.30) 525 (0.96); 425 (7.51); 340 (25.59) 534 (1.63); 462 (3.32), 382 (11.74), 342 (25.46) 488 (1.75); 430 (3.46); 340 (24.30) 534 (2.13); 432 (9.54), 342 (36.60) 700 (0.16); 567 (0.60); 380 (7.12) 595 (0.87); 396 (6.42) 700 (0.29); 525 (1.99); 439 (6.79)

λem,a nm

τ,b μs

Φc (%)

λem(s),d nm

692

0.60

0.4

632

668

0.48

1.9

637

690

0.17

1.2

670

710

0.32

0.09

688

0.79

0.1

636

710

0.67

0.2

704

Emission maxima. bEmission lifetime. cEmission quantum yield. Solid-state emission maxima.

d

spectral assignment. Calculated energies, compositions in terms of one-electron excitations, and oscillator strengths of selected spin-allowed electronic transitions are listed in Tables 10−12, and the TDDFT calculated spectra are presented in Figure 13. All the spectra show intense absorption bands in less than 330 nm region (ε ≈ (2−8) × 104 M−1 cm−1) due to intraligand π→π* transition of the ligand L and higher-energy metal(Ir)-toligand(L) charge-transfer transition (MLCT). An intense absorption band at 340 nm (ε ≈ (1−2) × 104 M−1 cm−1) has significant πterpy→π*terpy character, as similar absorption is found in the spectra of the Pt(terpy)2+ complexes such as [Pt(terpy)Cl]Cl.12a,17,36 The spectra of all ppy and dfppy complexes exhibit moderately intense absorption around 380 nm (3a−b and 4a−b, ε = (6.42−11.74) × 103 M−1 cm−1), which is shifted to 425− 439 nm for the piq complexes (3c, 4c, and 5c, ε = (6.79−9.54) × 103 M−1 cm−1). The absorptions are assigned to 1MLCT/π→π* transitions. Similar 1MLCT/π→π* transition absorptions displayed by fac-IrL3 occur at lower energy ( fac-Ir(ppy)3 and fac-Ir(dfppy)35d,10a from 350−450 nm and fac-Ir(piq)3 at 550 nm37). The blue shift of the 1MLCT/π→π* transitions of the Ir−Pt complexes is in accord with the positive formal charges of the complexes. TDDFT calculations also support the assigning of the absorption bands to the 1MLCT/π→π* transitions from metal/ ligand-based HOMOs of 3a−c and 4a−c or HOMO−1s of 5a−c to the L-based π*-orbitals. [Pt(terpy)(X)]+ (X = Cl, Br, I, or SCN) complexes were reported to display dPt→π*terpy MLCT transition in 370−400 nm.12a,17,36 The dPt→π*terpy MLCT transition in the present complexes is expected to be blue-shifted to less than 370 nm because of the weak donation of the coordinated thiolate S atom and the formal charge of +2 of the

Figure 12. UV−Vis absorption spectra of (a) 3a−c, (b) 4a−c, and (c) 5a−c in MeOH at 298 K. (insets) The low-energy absorptions. N


Article

Inorganic Chemistry Table 10. TDDFT (B3PW91/(6-31G(d) + SDD)) Calculated Singlet Excitation Energies of 3a, 3b, and 3c in CH3OHa complex 3a

3b

3c

a

excitation energy, nm

oscillator strength

575 481

0.0196 0.0140

426

0.0141

397

0.0249

383 378

0.0366 0.0129

351

0.053

525

0.0192

465

0.0119

437

0.0086

417

0.0089

401

0.0067

377

0.0343

368

0.0113

361 352

0.0271 0.0166

582

0.0159

483

0.0164

442 412

0.0821 0.0148

391 385

0.0122 0.0147

376

0.0169

363

0.0230

355

0.0696

transition

contribution (%)

λ, nm (expt)

H→L H-1→L H-2→L H-3→L H-4→L H→L+2 H-4→L H→L+3 H-6→L H-4→L H-1→L+2 H-2→L+1 H→L H-1→L H-1→L H-2→L H-2→L H-3→L H-3→L H-2→L H-7→L H-4→L H→L+2 H-1→L+2 H-7→L H-5→L H→L+3 H→L+4 H-1→L+2 H→L H-1→L H-2→L H-3→L H→L+2 H-4→L H-5→L H→L+4 H-1→L+2 H-2→L+2 H-1→L+3 H-2→L+3 H-2→L+2 H-3→L+2 H-2→L+4 H-2→L+3

98 88 9 90 7 69 11 92 79 8 50 10 94 4.6 81 13 62 19 68 14 55 22 73 12 76 7 90 82 5 96 3 74 17 97 65 21 76 75 15 67 13 60 13 24 15

550 520

383

341 500 460

370

340 550 525 425

Figure 13. Theoretically calculated UV−vis spectra of (a) 3a−c, (b) 4a−c, and (c) 5a−c (DFT/B3PW91/(SDD+6-31G(d)), PCM solvent effect of methanol, convolution with full width at half-maxima of 0.25 eV).

εmax= 230−870 M−1 cm−1) in the spectra of 5a−c, which show an additional weak tail in 700−800 nm (εmax= 100−200 M−1 cm−1), which causes the peculiar green color of the complexes. TDDFT calculations show that, for 3a−c and 4a−c, the spinallowed HOMO→LUMO transitions from dπIr/πL (HOMO) to π*Pt(terpy) (LUMO) [1(dπIr/πL→π*Pt(terpy))] have energies close to the 450−600 nm absorptions (Tables 10 and 11). The calculated transition energies are consistently higher than the experimental values by 700−900 cm−1 for 3a−c and 200−400 cm−1 for 4a−c but follow the same order of the experimental ones: 3a ≈ 3c > 3b and 4a ≈ 4c > 4b. In fact the experimental absorption energies follow the order of the calculated energies of the HOMO (Figure 11), which are mainly IrL2-centered. In view of the fact that the HOMO and the LUMO are localized mainly in the Ir and Pt chromophores, respectively, the dπIr/πL→π*Pt(terpy) transition can be labeled interchromophoric-charge-transfer transition (ICCT). Because of their strongly donating thiolate ligands, the HOMO−1 (dπIr/πL) of 5a−c is destabilized, and accordingly the ICCT transitions of the complexes are red-shifted (experimental: 595−660 nm, calculated: 590−659 nm (Table 12).

375

Only major transitions are shown.

Pt(terpy) unit, and so it could be covered by the intense highenergy absorptions. Notably, the spectra of 3a−c and 4a−c display moderately intense absorptions in 450−600 nm (insets in Figure 11, λmax = 460−534 nm; εmax = (750−2.13) × 103 M−1 cm−1), which are absent in the spectra of the parental Ir and Pt complexes 2a and Pt(terpy)Cl,12a,17,36 suggesting that the absorptions are derived from interactions between the Ir and Pt chromophores. The high absorptivity and the low energy of the 450−600 nm absorption argue against any possible spin-forbidden components of Ir→L π* and Pt→terpy π* 3MLCT transitions. The absorption is redshifted to 590−660 nm (insets in Figure 11, λmax = 700−730 nm; O


Article

Inorganic Chemistry Table 11. TDDFT (B3PW91/(6-31G(d) + SDD)) Calculated Singlet Excitation Energies of 4a, 4b, and 4c in CH3OHa complex 4a

4b

4c

a


oscillator strength

581 578

0.0027 0.0330

548

0.0420

422

0.0412

403 398

0.0155 0.0329

388

0.0193

387

0.0406

370

0.0392

536

0.0719

533

0.0013

442

0.0121

395 391 383

0.0383 0.1084 0.0115

374

0.0222

368

0.0228

346

0.0768

590

0.0043

587

0.0286

552 491 438 423 400 394

0.0344 0.0147 0.0688 0.0154 0.0189 0.0952

375

0.0531

Table 12. TDDFT (B3PW91/(6-31G(d) + SDD)) Calculated Singlet Excitation Energies of 5a, 5b, and 5c in CH3OHa

transition

contribution (%)

λ, nm (expt)

complex

H→L H-1→L+1 H-2→L H-1→L H→L+1 H-5→L H-4→L+1 H→L+4 H-8→L H-9→L+1 H→L+5 H→L+6 H-6→L+1 H-7→L H→L+6 H→L+5 H-1→L H→L+1 H→L H-1→L+1 H-3→L H-4→L+1 H-5→L H-1→L+4 H→L+4 H-1→L+5 H-6→L+1 H-7→L H→L+5 H→L+6 H-1→L+7 H→L+6 H→L H-1→L+1 H→L+1 H-1→L H-1→L H-2→L H→L+5 H-5→L H→L+6 H-1→L+6 H→L+7 H→L+7 H-1→L+6

95 90 9 90 9 59 33 81 33 30 41 26 40 36 55 20 67 32 58 40 64 19 73 75 64 20 48 26 65 19 58 26 92 3 92 6 89 81 91 92 72 52 18 62 16

573

5a


oscillator strength

845 659

0.0039 0.0107

521 476

0.0164 0.0112

462

0.0503

440 434

0.0146 0.0287

403

0.0116

398

0.0190

488

809 590 499 447

0.0036 0.0121 0.0141 0.0143

430

438

0.0208

431

0.0205

399

0.0104

385

0.0129

376

0.0112

837 659

0.0046 0.0139

542

516 482

0.0371 0.0139

437

466 455

0.0139 0.0419

454 431

0.0651 0.0157

380

0.0320

534

382

5b 527

376

340

5c

575

a


transition

contribution (%)

λ, nm (expt)

H→L H-1→L H→L+1 H-2→L H-3→L H-4→L H→L+2 H-4→L H-5→L H→L+6 H→L+4 H-6→L H-9→L H-1→L+5 H-1→L+4 H→L H-1→L H-2→L H-5→L H-4→L H→L+4 H→L+3 H→L+6 H→L+5 H-6→L H-9→L H-1→L+2 H-6→L+1 H-1→L+4 H-1→L+5 H→L H-1→L H→L+1 H→L+3 H-4→L H-2→L H-3→L H-1→L+2 H-1→L+3 H→L+4 H→L+4 H→L+6 H→L+5 H-3→L+3 H-2→L+3

99 84 14 95 78 17 85 9 72 54 29 50 14 43 20 99 97 95 73 17 47 24 86 8 64 17 64 14 40 21 99 92 6 96 71 13 11 95 90 7 88 48 46 47 22

730 660 567

425

380 700 595

423 396

375 730 650 503

439

376


bands of the Ir−Pt complexes obey Beer’s Law in the concentration range (1 × 10−5 M to 1 × 10−3 M), in which the absorption and emission spectra were recorded (Figure S4), indicating no dimerization in solution, and thus the low-energy absorptions should come from individual Ir−Pt molecules. Emissions. While 5a−c are not emissive in solids or solutions, degassed CH2Cl2 solutions of 3a−c and 4a−c display broad, unstructured emission bands at 692 nm (3a), 668 nm (3b), 690 nm (3c), 710 nm (4a), 688 nm (4b), and 710 nm (4c) (Figure 14 and Table 9). The emissions are much lower in energy than the 3MLCT/ππ* phosphorescence of fac-IrL3 ( fac-Ir(ppy)3 λmax = 514 nm, fac-Ir(dfppy)3 λmax = 450 nm, fac-Ir(piq)3

The calculated HOMO→LUMO excitations of 5a−c, which correspond to charge-transfer transition from the antibonding orbital composed the sulfur π-orbital (pS) and an Ir dπ orbital (dπIr) to the π* orbital of Pt(terpy), have low oscillator strengths and energies (5a, 845 nm; 5b, 809 nm; 5c, 837 nm) similar to the 700−800 nm absorption tail displayed by 5a−c, which is accordingly assigned to [(pS/dπIr)→π*Pt(terpy)] charge transfer. Pt(terpy)Cl+ and related complexes are known to aggregate in solution at high concentration via metal−metal and/or π−π interactions, which leads to a low-energy absorption (e.g., 470 nm for [Pt(terpy)Cl]+) arising from metal−metal-bond-toligand-charge-transfer transition.12a However, all the absorption P


Article

Inorganic Chemistry

ICCT transitions. The ICCT nature of the lowest-energy triplet excited states T1 of the complexes is supported by the calculated spin density (Figure S6), electron density difference map (Figure S7), and natural transition orbitals of the excited state (Figure S8). The spin distribution of the T1 excited states of 3a and 4a (Figure 15) shows spin density in the IrL2 and the two Pt(terpy) parts of the molecules, indicating that electron is transferred from the IrL2 chromophore to the Pt(terpy) chromophore upon excitation. The calculated spin density of the T1 excited states of the rest of the complexes shows similar spin distributions (Figure S6) The calculated energies of the T1 states (e.g., 1.57 eV (3a), 1.69 eV (3b), and 1.60 eV (3c)) are consistently lower than the emission maxima (1.79 eV (3a), 1.86 eV (3b), and 1.80 eV (3c)) but follow the same order. No 3MLCT emission from the Ir(L)2 moiety is observed when the solutions are excited at MLCT absorption (350−400 nm), indicating a very facile internal conversion from the MLCT excited states (singlet and triplet) to the ICCT excited state. The low emission quantum yields (0.1− 1.9%) are probably due to fast nonradiative decay intrinsic for low-energy emissions38 and/or internal conversion to low-lying ligand field excited state of the Pt2+ ion, a major excited-state deactivation pathway for the d8 complexes.39

■

CONCLUSION In this study, we have demonstrated by harnessing the metalligating propensity of the cyclometalated Ir3+-dithiolate, a d6 Ir(III) and a d8 Pt(II) chromophore can be assembled in close proximity and in a cofacial configuration. Nine Ir−Pt complexes were synthesized, and their electronic structures were probed by spectroscopy and DFT calculation. For all the complexes, their LUMOs are mainly composed of a π* orbital of the Pt(terpy) fragment. While the HOMOs of 3a−c and 4a−c are localized in the IrL2 fragment, the HOMOs of 5a−c are predominantly the 3p orbital of the thiolate S atom. The spectroscopy of the complexes show ground-state electronic interactions between the two chromophores as evidenced by the presence of low-energy (dπIr/πL)→π*Pt(terpy) interchromophoric charge-transfer transition. On the one hand, the interactions between the chromophores give rise to excited-state manifolds and photophysics different from that of the parental complexes with interchromophoric charge-transfer excited-state 3[(π*Pt(terpy))1(dπIr/πL)1] being the emissive excited state of 3a−c and 4a−c. On the other hand, 5a−c are not emissive, and their lowest-energy electronic transition is the charge transfer from the lone pair of the thiolate S to a π* orbital of the Pt(terpy) [(pS/dπIr)→π*Pt(terpy) charge transfer].

Figure 14. Normalized emission spectra of (a) 3a−c and (b) 4a−c.

Figure 15. Spin density distribution of the lowest-energy triplet excited state of 3a (left) and 4a (right).

λmax = 620 nm), which have vibronic structures, implying that the emissive excited states of the present complexes are not the 3 MLCT/ππ*. Notably, despite the two chromophores being visible-light emitters, a significant portion of the emissions lies in the near-infrared region (>700 nm). Solids of the complexes display slightly blue-shifted emissions, but the order of the emission energies is the same as the solution spectra. All the excitation spectra (Figure S5) resemble the corresponding absorption spectra. The emission energies follow the same order of the ICCT absorption bands (3a ≈ 3c < 3b and 4a ≈ 4c < 4b), suggesting that the emissions are derived from the same electronic transitions. The relatively long emission lifetimes of 0.17−0.79 μs (Table 9) indicate that the luminescence is derived from triplet excited states as would be expected from the strong spin−orbit coupling of the Ir and Pt ions. The emissions are attributed to the radiative decay from the triplet ICCT or 3[(π*Pt(terpy))1(dπIr/πL)1] excited states as the energy of the emission parallel to the (dπIr/πL)→π*Pt(terpy)

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00412. 2D-COSY NMR, CVs of the complexes, ESI-MS cluster peaks of 5a and 5b, Lambert−Beer plots, excitation spectra of 3a−c and 4a−c, ground state optimized structural parameters, spin density distribution of the lowest triplet excited state, electron density difference map and natural transition orbitals of the lowest energy triplet transition of 3a−c and 4a−c (PDF) Accession Codes

CCDC 1536432, 1536434, 1536437, 1536439, 1536441, 1536443, and 1824896 contain the supplementary crystallographic data for this paper. These data can be obtained free of Q


Article

Inorganic Chemistry

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charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Van Ha Nguyen: 0000-0002-6426-4385 John H. K. Yip: 0000-0002-0955-4873 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work is dedicated to Professor Chi-Ming Che on the occasion of his 60th birthday. The Ministry of Education (R-143000-640-112) Singapore and the National Univ. of Singapore are thanked for financial support. We are grateful to Ms. G. K. Tan (X-ray crystallography lab, NUS Chemistry) for solving the crystal structures.

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