Fine-Tuning of Luminescence through Changes in Au–S Bond

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Fine-Tuning of Luminescence through Changes in Au−S Bond Lengths as a Function of Temperature or Solvent Chun-Yu Liu,†,‡ Hui-Fang Wang,*,† Zhi-Gang Ren,*,† Pierre Braunstein,§ and Jian-Ping Lang*,†,‡ †

College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P. R. China State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, P. R. China § Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg 4, rue Blaise PascalCS 90032, 67081 Strasbourg, France ‡

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ABSTRACT: The luminescent properties of gold(I)−sulfur compounds have received much attention for their potential applications in the sensing field. The molecular level regulation of luminescence remains a challenge. It is critical to unravel the relationship between the luminescence and the structure. Herein we report a binuclear complex [Au2(dppaptc)2]Cl2 (1, dppaptc = N,N-bis(diphenylphosphanylmethyl)-amino-4-phenyl-thiocarbamide), which exhibits variations at Au−S bond lengths as a function of temperature or solvent. X-ray analysis reveals a linear decrease from 2.900(3) to 2.745(15) Å upon cooling 1· 2CHCl3 from 300 to 80 K combined with a linear correlation with its luminescence intensity at 475 nm, which was confirmed by TD-DFT calculations. Compound 1, if solvated with H2O and alcohol, possesses the shorter Au−S bonds and enhanced luminescence. The close relationship between luminescence intensity and Au−S length serves as a complement to existing luminescent gold(I)−sulfur systems and provides some insight into understanding the thermochromism and solvatochromism of the gold(I)−sulfur compounds.

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bonds and Au···Au interactions and their possible interplay.29 Emphasis is often placed on the energy transfer associated with Au···Au rather than Au−S bonds, whereas longer gold−sulfur bonds (>2.88 Å) are not likely to produce suitable energy transfer,30 and the consequence of their shortening has not been explicitly addressed. Modifying the sulfur environment can lead to the drastic changes in the spectroscopic properties, as demonstrated when the [Au3(μ3-S)]+ unit was used as a precursor to heteronuclear μ4-sulfido complexes, through its binding at extra Ag(I) or Cu(I) centers.31 To investigate the impact of energy transfer associated gold(I)−sulfur bonds on the luminescence properties, we designed the new multifunctional P−S hybrid ligand dppaptc and prepared its binuclear Au complex [Au2(dppaptc)2]Cl2 (1). By combining phosphorus and sulfur donors in a fixed ratio of P and S, we hope to generate a suitable coordination environment for gold atoms that could help us explore the relationship between luminescence and structure, in particular the Au−S distances. We describe below that a linear decrease of the Au−S bond lengths with the temperature results in a linear increase of the luminescence and, furthermore, that the marked solvatochromism observed in solution can be correlated with the Au−S bond lengths observed in the

INTRODUCTION Gold(I) sulfur compounds have attracted growing attention owing to their exciting structural chemistry and rich photophysical properties.1−6 Their luminescent properties are usually caused by charge transfer between the ligand and metal7,8 or by aurophilic interactions.9−11 Understanding the respective influence of these parameters and their fine-tuning represents a fascinating and challenging endeavor.12,13 Furthermore, Au(I) sulfur compounds often exhibit unusual and unanticipated luminescence features due to solvatochromism (emission that is stimulated by interaction with solvent molecules),14−16 mechanochromism (emission that is switched on by grinding and crushing),17,18 or the presence of volatile organic compounds.19−21 The sensitivity of the frequently intense luminescence of such Au(I) complexes to environmental factors suggests that these complexes may find some applications in sensing systems. However, most recent studies have focused on the consequences of variations of Au···Au interactions rather than Au−S bond lengths on luminescence.22,23 Au(I) sulfur complexes usually adopt AunS (n = 1−6) coordination modes,24,25 and complexes with Au−S26,27 or Au2−μ-S bonds28 tend to exhibit enhanced luminescence because of shorter Au−S bonds (∼2.35 Å). With increasing values of n, the luminescence properties in Au(I) sulfur complexes get complicated due to the existence of both Au−S © XXXX American Chemical Society

Received: March 25, 2019

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DOI: 10.1021/acs.inorgchem.9b00845 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

1342 (s), 1264 (s), 1186 (m), 1097 (w), 1026 (w), 854 (w), 758 (s), 693 (s), 511 (w) cm−1. 1·2CH3OH. Anal. Calcd for C68H70Au2Cl2N6O2P4S2: C, 49.27; H, 4.23; N, 5.07%. Found: C, 49.71; H, 4.03; N, 4.86%. IR (KBr disk): 3442 (s), 3052 (w), 1600 (s), 1543 (s), 1496 (s), 1481 (m), 1432 (s), 1344 (s), 1263 (m), 1186 (w), 1099 (w), 1027 (s), 998 (w), 855 (w), 759 (s), 692 (vs), 510 (w) cm−1. 1·CH3OH/C2H5OH. Anal. Calcd for C69H72Au2Cl2N6O2P4S2: C, 49.58; H, 4.31; N, 5.03%. Found: C, 49.74; H, 4.43; N, 4.98%. IR (KBr disk): 3440 (s), 3050 (w), 1599 (s), 1544 (s), 1496 (s), 1482 (s), 1435 (vs), 1344 (s), 1262 (s), 1186 (w), 1098 (w), 1026 (s), 998 (w), 856 (w), 759 (s), 692 (vs), 510 (w) cm−1. 1·2C2H5OH. Anal. Calcd for C70H74Au2Cl2N6O2P4S2: C, 49.88; H, 4.39; N, 4.99%. Found: C, 49.63; H, 4.52; N, 5.07%. IR (KBr disk): 3443 (s), 3051 (w), 1599 (m), 1542 (s), 1495 (m), 1484 (m), 1434 (s), 1344 (m), 1261 (s), 1185 (w), 1098 (s), 1027 (m), 998 (w), 851 (w), 758 (s), 695 (s), 507 (w) cm−1. 1·Acetone. Anal. Calcd for C69H68Au2Cl2N6O2P4S2: C, 50.18; H, 4.12; N, 5.09%. Found: C, 49.89; H, 4.13; N, 4.96%. IR (KBr disk): 3446 (s), 3053 (w), 1597 (s), 1544 (m), 1496 (m), 1482 (s), 1435 (s), 1343 (s), 1262 (m), 1187 (w), 1096 (m), 1025 (m), 998 (w), 854 (w), 757 (s), 694 (s), 512 (w) cm−1. 1·DMF. Anal. Calcd for C69H69Au2Cl2N7OP4S2: C, 49.73; H, 4.14; N, 5.89%. Found: C, 49.55; H, 4.26; N, 5.76%. IR (KBr disk): 3419 (s), 3053 (m), 2930 (w), 2285 (s), 1597 (s), 1544 (s), 1496 (s), 1482 (s), 1435 (s), 1344 (s), 1262 (s), 1186 (w), 1098 (w), 1027 (s), 998 (w), 855 (w), 760 (s), 695 (s), 509 (w) cm−1. 1·CH2Cl2. Anal. Calcd for C66H66Au2Cl2N6O2P4S2: C, 47.23; H, 3.94; N, 5.01%. Found: C, 46.98; H, 3.93; N, 4.96%. IR (KBr disk): 3446 (m), 3051 (w), 1599 (s), 1544 (s), 1496 (s), 1482 (s), 1435 (vs), 1344 (s), 1262 (s), 1186 (w), 1099 (s), 1027 (s), 999 (w), 851 (w), 759 (s), 694 (vs), 512 (w) cm−1. 1·ClCH2CH2Cl. Anal. Calcd for C68H66Au2Cl4N6P4S2: C, 48.26; H, 3.90; N, 4.97%. Found: C, 46.84; H, 3.91; N, 4.92%. IR (KBr disk): 3446 (m), 3052 (m), 1598 (s), 1542 (s), 1495 (m), 1482 (s), 1435 (vs), 1344 (s), 1262 (s), 1186 (w), 1099 (s), 1027 (s), 1000 (w), 851 (w), 759 (s), 692 (s), 510 (w) cm−1. Single-Crystal X-ray Diffraction (SCXRD) Analysis. Singlecrystal X-ray diffraction data for all were collected on a Bruker APEXII diffractometer equipped with a CCD area detector and operated at 50 kV, 1 mA, to generate Mo Kα radiation (λ = 0.71073 Å). A single crystal of 1·2CHCl3 or 1·solvent was coated with Paratone oil on a Cryoloop pin and enveloped in an Oxford Cryosystems cryostream in the range 80−300 K during data collection. Data were processed with the Bruker APEX2 software package,32 integrated using SAINT v8.34A,33 and corrected for the absorption by SADABS 2014/5 routines (no correction was made for extinction or decay).34 The structures were solved by intrinsic phasing (SHELXT) and refined by full-matrix least-squares on F2 (SHELXL-2016).35 All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were geometrically calculated and refined as riding atoms unless otherwise noted. DFT and TD-DFT Calculations. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were carried out by the Gaussian 09 (G09) program package36 to study the UV−vis adsorption and fluorescence properties of crystal 1· 2CHCl3@80 K and crystal 1·2CHCl3@300 K. The stable ground state geometries were optimized using PBEPBE37 as the exchangecorrelation functional together with the Lanl2dz basis set for a Au atom and the 6-31+g(d) basis set for other atoms (P, C, N, S, and H). No symmetry constraints were imposed during optimization, and Au−S distances were fixed according to the measured crystal data. To determine the fluorescence emission properties, the lowest singlet excited state was optimized using a PBEPBE exchange-correlation functional relying on Kasha’s rule. The frontier molecular orbital of the excited states was visualization by Gview 5.0.

solid-states for the corresponding solvates. Time-dependent density functional theory (TD-DFT) calculation of 1· 2CHCl3@80 K and 1·2CHCl3@300 K confirmed that shorter Au−S bonds are associated with stronger energy transfer. To our knowledge, this is the first report providing a precise relationship between Au−S bond length and luminescence.

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EXPERIMENTAL SECTION

Materials and Methods. All reagents were commercially available and used as received. Elemental analyses (C, H, and N) were performed on a Carlo-Erba CHNO-S microanalyzer. Infrared (IR) spectra were recorded on a Varian 1000 spectrometer using KBr disks (4000−400 cm−1). The 1H NMR and 31P{1H} NMR spectra were recorded at ambient temperatures in DMSO-d6 on a Varian UNITY plus-400/plus-600 spectrometer. Powder X-ray diffraction (PXRD) measurements were acquired on a PANalytical X’Pert PRO MPD system (PW3040/60) with Cu Kα radiation. UV−vis spectra were measured on a Varian Cary-50 UV−vis spectrophotometer. Electrospray ionization mass spectrometry (ESI-MS) spectra were performed on an Agilent 1200/6200 mass spectrometer using CH3CN as the mobile phase. Photoluminescence spectra and quantum yields were obtained on a HORIBA PTI QuantaMaster40 spectrofluorometer. Solid-state emissions at controlled variable temperature (80−300 K) were recorded with Oxford Instruments liquid nitrogen cryostat accessory. Synthesis of dppaptc. A solution containing diphenylphosphine (3.72 g, 20 mmol), 4-phenylthiosemicarbazide (1.67 g, 10 mmol), and formaldehyde (38% solution, 2.06 g, 26 mmol) in MeOH (50 mL) was refluxed for 4 h. The resulting mixture was recrystallized in MeOH and CH2Cl2 to give a white solid of dppaptc (4.86 g, 86%). Anal. Calcd for C33H31N3P2S: C, 70.32; H, 5.51; N, 7.46%. Found: C, 70.28; H, 5.68; N, 7.33%. IR (KBr disk): 3442 (m), 3257 (s), 3139 (w), 2860 (s), 2803 (s), 1593 (s), 1544 (s), 1497 (s), 1481 (s), 1435 (s), 1350 (s), 1308 (s), 1258 (s), 1190 (s), 1026 (m), 998 (w), 866 (w), 843 (w), 759 (s), 741 (s), 695 (s), 515 (w), 503 (w) cm−1. 1H NMR (DMSO-d6, 400 MHz, ppm): δ 9.61 (s, 1H, −NH−), 8.12 (s, 1H, −NH−), 7.47−7.29 (m, 20H, −PPh2), 7.08−6.95 (m, 3H, −Ph), 6.74 (d, J = 7.8, 2H, −Ph), 4.23 (d, J = 12.9, 2H, −CH2−), 3.63 (t, J = 12.4, 2H, −CH2−). 31P{1H} NMR (DMSO-d6, 162 MHz, ppm): δ −26.51 (s). Synthesis of [Au2(dppaptc)2]Cl2·2CHCl3 (1·2CHCl3). A mixture containing [Au(tht)Cl] (tht = tetrahydrothiophene) (0.1605 g, 0.5 mmol) and dppaptc (0.2815 g, 0.5 mmol) in CHCl3 (20 mL) was stirred for 2 h at ambient temperature to form a clear colorless solution. Slow diffusion of hexane into the solution afforded colorless block crystals of 1·CHCl3 after 2 days, which were collected by filtration, washed with hexane, and dried in air. Yield: 0.4163 g (91% based on Au). Anal. Calcd for C67H63Au2N6P4S2Cl5: C, 46.99; H, 3.68; N, 4.91%. Found: C, 45.97; H, 3.93; N, 4.87%. IR (KBr disk): 3416 (m), 3051 (w), 1599 (s), 1544 (s), 1496 (s), 1482 (s), 1435 (vs), 1344 (s), 1262 (s), 1099 (s), 1027 (s), 851 (w), 759 (s), 692 (vs), 512 (w) cm−1. 1H NMR (400 MHz, DMSO-d6): δ 8.93 (s, 1H, −NH−), 8.32 (s, 2H, −Ph), 7.93 (s, 1H, −NH−), 7.84−7.82 (d, J = 5.4, 4H, −PPh2), 7.66−7.40 (m, 18H, −PPh2 and CHCl3), 7.10 (s, 3H, −Ph), 5.14 (d, J = 14.5, 2H, −CH2−), 4.25 (d, J = 14.4, 2H, −CH2−). 31P{1H} NMR (400 MHz, DMSO-d6): δ −7.46 (br). Recrystallization Experiments. 1·2CHCl3 (20 mg) was dissolved in 2 mL of solvent, and the mixture was stirred for 2 h in a dark cupboard at room temperature. After filtration, slow diffusion of Et2O into the filtrate afforded yellow crystals in CH3OH, CH3OH/ C2H5OH (v/v = 1), and C2H5OH, while colorless crystals were obtained when it was recrystallized in CH2Cl2, ClCH2CH2Cl, acetone, and DMF. In the case of H2O, the mixture of H2O (2 mL) and 1·2CHCl3 (20 mg) was stirred for 12 h. Then the mixture was filtrated, and yellow crystals of 1·2H2O were afforded after the filtrate was evaporated for 2 weeks. 1·2H2O. Anal. Calcd for C66H66Au2Cl2N6O2P4S2: C, 48.65; H, 4.05; N, 5.16%. Found: C, 48.95; H, 4.13; N, 5.08%. IR (KBr disk): 3441 (s), 3050 (w), 1598 (s), 1544 (s), 1496 (s), 1484 (s), 1433 (s),

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RESULTS AND DISCUSSION Synthesis and Structural Characterization. The ligand dppaptc was synthesized by a typical Mannich reaction,38 in

B

DOI: 10.1021/acs.inorgchem.9b00845 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry which HPPh2 was refluxed with 4-phenylthiosemicarbazide and formaldehyde in methanol for 4 h to produce a white solid in 86% yield (Figures S1−S3). A mixture of dppaptc and [Au(tht)Cl] (tht = tetrahydrothiophene)39 was stirred in CHCl3 for 2 h at room temperature, and diffusion of hexane into the solution afforded [Au2(dppaptc)2]Cl2·2CHCl3 (1· 2CHCl3) in 91% yield as colorless crystals. This complex was characterized by X-ray diffraction, elemental analysis, electrospray ionization mass spectrometry (ESI-MS) (Figure S4), as well as 1H and 31P{1H} NMR spectroscopy (Figures S5 and S6). The positive-ion ESI-MS spectrum of 1·2CHCl3 is dominated by a peak at m/z 760, which is attributed to [Au2(dppaptc)2]2+. The 31P{1H} NMR spectrum in DMSO-d6 shows a sharp singlet at −26.50 ppm for the equivalent P atoms of the ligand. This complex is stable in solution at ambient temperature. 1·2CHCl3 crystallizes in the orthorhombic space group Pccn, and its asymmetric unit consists of half a [Au2(dppaptc)2]2+ dication and one disordered Cl− anion (occupancy factor = 0.75/0.15/0.1). The ligand dppaptc bridges two Au(I) centers, and each Au(I) is tetrahedrally coordinated by two P atoms and two bridging S atoms from two dppaptc ligands that form the central, centrosymmetric [Au2S2P4] rhombus (Figure 1).

Figure 2. Evolution of Au−S/P bonds as a function of temperature and their fitted curves in 1·2CHCl3. Insert: Photographs of 1·2CHCl3 at 300 and 80 K taken under UV light irradiation (365 nm).

tions.40−42 The relationship between the Au−S bond length and temperature can be fitted as a function of L = 2.691 + (6.73 × 10−4)T, with a correlation coefficient of 0.9892 for Au1−S1, where L is the bond length. Similarly, the relationship between the Au1−S1A bond length and temperature could be fitted to L = 3.031 − (3.87 × 10−4)T. Luminescent Thermochromism Behavior of 1·2CHCl3. The temperature-dependent emissive behavior of 1·2CHCl3 was investigated between 300 and 80 K (Figure 3). Interestingly, 1·2CHCl3 showed luminescent thermochromism in the solid-state with a 368 nm excitation. No luminescence was observed at 300 K, while cooling to 80 K led to a strong emission at 475 nm with a shoulder peak at 420 nm (Figure S9). The emission intensity at 475 nm increases gradually as the temperature decreases, in a linear relationship that can be fitted as a function of I = (1.278 × 107) − (3.58 × 104)T with a correlation coefficient of 0.9988, where I is the intensity and T the temperature, which correlates with the linear relationship between the Au1−S1 distance and the temperature. The emission intensity decreases on average by 0.36% per 1 K with increasing temperature from 80 to 300 K, giving an overall variation of 78.68%. The weak emission at 420 nm progressively decreases as the temperature increases from 80 to 300 K, which could be fitted as a function of I = (4.82 × 106) − (1.15 × 104)T with a correlation coefficient of 0.9717. The emission intensity decreases on average by 0.14% per 1 K with an overall variation of 30.59%, which can be ascribed to thermal activation of the non-radiative-decay pathways.43 TD-DFT Calculations. To further understand the difference between the emissions of 1·2CHCl3@80 K and 1· 2CHCl3@300 K, TD-DFT calculations were performed. The calculated UV−vis adsorption spectra of crystal 1·2CHCl3@80 K is provided in Figure S10. It shows strong absorbance at 350.95, 368.35, and 392.45 nm, which coincides well with the experimental excited wavelength (368 nm). Then, a singlepoint TD-DFT calculation on the optimized singlet excited state was carried out at a modified B3LYP functional comprising a 0.10 Hartree−Fock (HF) exchange interaction. We found that the pure functional PBEPBE gives a red-shifted wavelength (525 nm), while the B3LYP functional 3-4 (with 0.20 HF exchange) offers a blue-shifted wavelength (425 nm) for crystal 1·2CHCl3@80 K as compared to the experimentally

Figure 1. Representation of dppaptc ligand (a) and the [Au2(dppaptc)2]2+ dication in 1·2CHCl3 (b). Dark gray, blue, orange, red, and yellow spheres represent C, N, P, S, and Au atoms, respectively. For clarity, hydrogen atoms have been omitted.

The Au···Au distance of 4.170 Å is too long to include any significant metal−metal interaction. The phase purity of the bulk sample of 1·2CHCl3 was confirmed by powder X-ray diffraction (PXRD) (Figure S7). Temperature-Dependent Structure Changes of 1· 2CHCl3. A set of the temperature-dependent structures were determined by using the same single crystal of 1·2CHCl3 at a variety of temperatures, and the selected crystallographic data are listed in Table S1. Upon cooling a single crystal of 1· 2CHCl3 from 300 to 80 K, its unit cell volume got decreased by 3.26% (from 7453.6(10) to 7218.3(9) Å3) while the overall connectivity within the cluster was retained. Whereas the Au−P bonds remain almost unchanged as a function of temperature (within ca. 0.009 Å, Table S2), a dramatic change of the Au−S bond length occurs, with a variation from 2.901(3) to 2.745(15) Å (0.156 Å) for Au1−S1, and from 2.912(3) to 3.002 Å (0.089 Å) for Au1−S1A (300 to 80 K), indicating the high sensitivity of the Au−S interaction to temperature (Figure 2). Upon the decrease of temperature, the Au2S2 core is gradually distorted from a rhombus to a parallelogram with the shortening of Au1−S1 and the elongation of Au1−S1A (Figure S8). This is fully reversible and resembles single-crystal-to-single-crystal transformaC

DOI: 10.1021/acs.inorgchem.9b00845 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

S4). The LUMO state of 1·2CHCl3@80 K was mainly delocalized around the Au−S σ orbital and the phenyl groups of the dppaptc ligand, while the HOMO state was largely delocalized over the central fragment and mostly resulted from the gold and sulfur atoms. Thus, the emission of 1·2CHCl3@ 80 K was assumed to be metal-to-ligand charge transfer (MLCT) and intraligand charge transfer (ILCT). The emission of 1·2CHCl3@300 K was calculated to be at 420.79 nm with the greatest contribution of the energy transition from the HOMO−1 state to the LUMO state (88%). The LUMO state of 1·2CHCl3@300 K was similar to that of 1·2CHCl3@80 K, but there is a remarkable difference in their HOMO−1 states because the Au atom contributes less to the HOMO−1 state of 1·2CHCl3@300 K (Figure 4). Considering the emission of free dppaptc (λem = 420 nm, λex = 350 nm, Figure S11), which is attributed to ILCT, the MLCT contributes little to the emission of 1·2CHCl3@300 K at 420 nm. Thus, the significant difference in the energy transition between 1·2CHCl3@80 K and 1·2CHCl3@300 K is caused by the different Au−S bond lengths as a function of temperature. When the Au−S bond gets shortened, the bonding character increases and the energy transfer is enhanced, which results in an increased emission intensity. The luminescent thermochromism of 1·2CHCl3 at 475 nm is ascribed to the slight contraction of the Au−S bond length at low temperatures. Moreover, the Au−S vibrational frequency could also exert some impact on the emission intensity,46 and vibrational energy loss usually decreases with the strengthening of the Au−S bond and temperature lowering. An emission increase at ∼420 nm also appeared, which may be caused by the smaller vibrational energy loss of dppaptc ligand. The large emission enhancement at 475 nm at 80 K was three times larger than that at 420 nm (Figure 3b), which is caused by the smaller vibrational energy loss of Au−S bond and the shorter Au−S bond length. Luminescent Solvatochromism Behaviors of 1· 2CHCl3. Thermochromic luminescence is often accompanied by solvatochromism, since both temperature and solvent can slightly alter the structure of a complex.47 Thus, we measured the luminescence properties of 1·2CHCl3 in different solvents.

Figure 3. (a) Temperature-dependent emission spectrum of 1· 2CHCl3 from 80 to 300 K with an interval of 10 K excited at 368 nm. (b) Temperature-dependent emission intensity at 420 nm (red) and 475 nm (black) and their fitted curves at different temperatures from 80 to 300 K.

observed emission maximum at ∼475 nm (Table S3).44,45 To include the solvent effect, optimization of excited states was also executed by the modified B3LYP functional using the PCM method with chloroform as a solvent. The emission of 1·2CHCl3@80 K was calculated to be at 482.34 nm with the greatest contribution of the energy transition from the HOMO to LUMO states (87%) (Table

Figure 4. TD-DFT calculations of 1·2CHCl3. The LUMO, HOMO, HOMO−1, and HOMO−2 states of 1·2CHCl3@80 K and 1·2CHCl3@300 K were given. D

DOI: 10.1021/acs.inorgchem.9b00845 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry When dissolved in acetone, N,N′-dimethylformamide (DMF), CHCl 3 , CH 2 Cl 2 , or ClCH 2 CH 2 Cl, complex 1·2CHCl 3 produced colorless solutions that are nonluminescent at 300 K. However, when dissolved in CH3OH, C2H5OH, or the mixture of CH3OH/H2O (v/v = 1:1, considering the poor solubility of 1·2CHCl3 in water), complex 1·2CHCl3 produced yellow solutions that are luminescent at ∼475 nm (Figure 5). In the mixture of CH3OH/H2O (v/v = 1:1), a weak shoulder at ∼420 nm belonging to the ILCT appears, which is caused by the weak interaction between water and compound 1.14,16

view of the [Au2S2P4] unit), emission wavelengths, and quantum yields of various 1·solvent are listed in Table 1. The Au1−S1 bond was found to be shorter when crystallization solvents are H2O, CH3OH, and C2H5OH. The uniform Au1−S1 bond lengths in 1·2H2O, 1·2CH3OH, 1· CH3OH/C2H5OH, and 1·2C2H5OH are 2.662(12), 2.744(2), 2.736(3), and 2.730(4) Å, respectively (Table S6). These OHcontaining solvent mo lecules interact with the [Au2(dppaptc)2]2+ and the Cl− ions via strong hydrogenbonding interactions (N−H···O, O−H···Cl, N−H···Cl, C−H··· Cl) (Figure 6 and Figure S14). All of these interactions result

Figure 5. Emission spectra of 1·2CHCl3 in different solvents at 300 K. All emission spectra were scanned with λex = 368 nm. Inset: the photographs of 1·2CHCl3 dissolved in different solvents without UV irradiation (top) or under UV irradiation (bottom) at 300 K. Figure 6. Hydrogen-bonding interactions among various solvent molecules and 1·H2O (a), 1·CH3OH (b), 1·CH3OH/C2H5OH (c), or 1·2C2H5OH (d). Pink spheres, [Au2(dppaptc)2]2+ unit; blue spheres, N atoms; green spheres, Cl− ions. Red and black spheres represent O and C atoms of solvent, respectively.

In an attempt to correlate these solution properties with solid-state phenomena, 1·2CHCl3 was recrystallized from different solvents. In the cases of acetone, DMF, CH2Cl2, CHCl3, ClCH2CH2Cl, H2O, CH3OH, CH3OH/C2H5OH (v/v = 1:1), and C2H5OH, it was clear from SCXRD analysis that solvent molecules were included in the structure of 1·solvent (Table S5). The phase purity of each bulk sample of 1·solvent was established by comparison of their experimental and simulated PXRD patterns (Figures S12 and S13). Pertinent structural parameters (Au1−S1 bond length, Au···Au contact,

in the formation of the shorter Au−S bonds.48,49 The shorter Au−S bonds are associated with yellow crystals, while the longer Au1−S1 bonds are found in colorless crystals, which is fully consistent with the colors observed in different solvents.

Table 1. Summary of the Structural Parameters, Emission Wavelengths, and Quantum Yields of Various 1·Solvent Speciesa

a Asterisk indicates that there are two asymmetric units in 1·2C2H5OH, and the Au−S bond length and the Au···Au separation given here represent average values.

E

DOI: 10.1021/acs.inorgchem.9b00845 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry *E-mail: [email protected].

Solid-state luminescence at 300 K was examined for all solvated complexes 1·solvent listed in Table 1. When solvent molecules are acetone, DMF, CH 2 Cl 2 , CHCl 3 , or ClCH2CH2Cl, no luminescence was observed under 368 nm excitation (Figure S15). The crystal structures of these solvates show that the Au1−S1 bond lengths are >2.85 Å, which is too long to allow significant energy transfer. However, luminescence at ∼475 nm was observed for H2O, CH3OH, CH3OH/ C2H5OH, and C2H5OH, which corresponds to the structures with shorter Au1−S1 bonds (