Stability Tuning of Vapor-Adsorbed State of Vapochromic Pt(II

May 22, 2019 - New luminescent Pt(II) complexes with chiral ester chains, [PtCl2(R,R-bpybe)] (R-1; bpybe = 2,2′-bipyridine-4,4′-dicarboxylic acid ...
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Article Cite This: Inorg. Chem. 2019, 58, 7385−7392

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Stability Tuning of Vapor-Adsorbed State of Vapochromic Pt(II) Complex by Introduction of Chiral Moiety Yasuhiro Shigeta, Atsushi Kobayashi,* Masaki Yoshida, and Masako Kato* Department of Chemistry, Faculty of Science, Hokkaido University, North-10 West-8, Kita-ku, Sapporo 060-0810, Japan

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ABSTRACT: New luminescent Pt(II) complexes with chiral ester chains, [PtCl2(R,R-bpybe)] (R-1; bpybe = 2,2′-bipyridine-4,4′dicarboxylic acid dibutyl ester) and its racemic mixture (rac-1) with the chiral isomer, S-1, were synthesized, and their vapochromic behavior was investigated. Single-crystal X-ray structural analysis revealed that the rac-1 crystal was composed of only one crystallographically independent column formed by alternating stacking of R-1 and S-1 by the effective intermolecular Pt···Pt interaction. In contrast, three types of columnar structures with different Pt···Pt interactions were found for the R-1 crystal, probably because of the different packing of the chiral ester chains between the columns. Consequently, the estimated molecular volume of R-1 was slightly larger than that in the racemic crystal rac-1, although they have the same chemical formula. The X-ray structure of the toluene-adsorbed rac-1 (rac-1·toluene) also indicated that the intermolecular Pt···Pt interaction, which was effective for unsolvated rac-1, was completely canceled out by adsorption of toluene vapor. Both the rac-1 and R-1 crystals exhibited similar vapochromism driven by toluene vapor adsorption/desorption that switched the emission origin between the strongly emissive 3MMLCT (metal− metal-to-ligand charge transfer) to the weakly emissive 3π−π* phosphorescence. Although both crystals had the same chemical formula, the toluene vapor desorption temperature of R-1·toluene (84 °C) was obviously lower than that of rac-1·toluene (107 °C), suggesting that the binding interaction with toluene molecules was weaker in R-1·toluene than in rac-1·toluene.

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INTRODUCTION Smart materials that change their physical properties under external stimuli have drawn much attention for potential use in devices such as sensors and actuators.1−3 Vapochromic materials, which exhibit a reversible color change induced by vapors, have been studied extensively in recent years because they can be used to detect invisible harmful chemical vapors.4,5 Among the various types of vapochromic materials,6−23 luminescent Pt(II) complexes with metallophilic Pt···Pt interaction are promising candidates for chemical sensing applications because the energy of the electronic transition derived from the metallophilic interaction,24−38 that is, the metal−metal-to-ligand charge transfer (MMLCT) transition, is well-known to depend sensitively on the degree of Pt···Pt interaction.39,40 A key factor for application of vapochromic materials is the stability of the vapor-adsorbed state in the ambient condition, because it dominates the characteristics of the vapochromic material. For example, vapochromic material with a less stable vapor-adsorbed state should be suitable for in situ vapor detectors that can detect chemical vapors in real time and easily release the adsorbed vapors. In contrast, materials with a highly stable vapor-adsorbed state could act as vapor history sensors that can record the history of the presence of chemical vapor.36,37 However, manipulating the stability of the vaporadsorbed state in this way is still challenging, because © 2019 American Chemical Society

molecular modification of the Pt(II) chromophore usually affects not only the vapochromic behavior but also the crystal structure, which dominates the stability of the vapor-adsorbed state according to the host−guest interaction. To overcome this problem, we have recently focused on chiral vapochromic complexes and their racemic mixtures because of their highly similar molecular structures. We previously reported the vapochromic behavior of Pt(II) complexes with a mixture of chiral and racemic hydrogen tartrate counteranions (L-Hta− and DL-Hta−), [PtCl(tpy)](LHta) and [PtCl(tpy)(DL-Hta)] (tpy = 2,2′:6′,2″-terpyridine).38 Although both the dihydrate chiral and racemic crystals formed very similar crystal structures, the chirality of the hydrogen tartrate counteranion certainly affected the vapochromic shift observed in the MeOH-vapor-induced dehydration process. This result suggested that the chirality of the counteranion had little effect on the vapochromic behavior of the Pt(II) complex, but it could enable fine control of the vapochromic shift and the stability of the vapor-adsorption state. In this work, to investigate the positional relationship between the chiral moiety and Pt(II) chromophore, we introduced chirality not into the counteranion, but directly into the ligand framework of the Pt(II) complex. Here, we report the crystal structure and Received: February 23, 2019 Published: May 22, 2019 7385

DOI: 10.1021/acs.inorgchem.9b00533 Inorg. Chem. 2019, 58, 7385−7392

Article

Inorganic Chemistry

silica gel column chromatography (eluent: hexane/ethyl acetate = 5:1, Rf = 0.37) to obtain a white solid of R,R- or S,S-bpybe (R,R-bpybe: 504 mg, yield: 69%; S,S-bpybe: 594 mg, 81%). This ligand was used in the next step without further purification. 1H NMR (400 MHz, CDCl3): δ = 8.93 (m, 2H), 8.71 (dd, 2H), 7.92 (dd, 2H), 5.17 (sext, 2H), 1.76 (m, 4H), 1.39 (d, 6H), 1.00 (t, 6H). Synthesis of Chiral [PtCl 2(R,R-bpybe)] and [PtCl2(S,Sbpybe)] Complexes (R-1 and S-1). K2PtCl4 (415 mg, 1.0 mmol) and tetrabutylammonium chloride (555 mg, 2.0 mmol) were dissolved in 20 mL of ultrapure H2O and stirred overnight. The solution was extracted with CH2Cl2 (10 mL × 2), and the organic layer was collected; then R,R-bpybe (356 mg, 1.0 mmol) was added. The mixture was stirred for 1 week in air at room temperature. The reaction mixture was evaporated to dryness under reduced pressure. The obtained reddish-orange solid was suspended in diethyl ether, filtered off, and then washed with H2O and diethyl ether. The resulting orange solid was suspended in a mixture of diethyl ether and CHCl3 (3:4, 140 mL) and filtered off to remove insoluble impurities. The solution was evaporated to dryness to obtain the target complex, R-1, as an orange solid (210 mg, 33%). 1H NMR (400 MHz, CDCl3): δ = 10.02 (d, 2H), 8.59 (d, 2H), 8.12 (d, 2H), 5.22 (sext, 2H), 1.81 (m, 4H), 1.42 (d, 6H), 1.02 (t, 6H). Elemental analysis calcd. for C20H24Cl2N2O4Pt ([PtCl2bpybe)]): C 38.60, H 3.89, N 4.50; found: C 38.57, H 3.79, N 4.38. The chiral isomer S-1 was synthesized in the same manner as R-1 except that S,S-bpybe was used instead of R,R-bpybe (214 mg, 34%). Synthesis of Racemic Complex [PtCl2(bpybe)] (rac-1). The racemic complex rac-1 was obtained by making an equimolar mixture of R-1 and S-1. The anhydrous orange forms of R-1 and S-1 (53 mg each) were dissolved in 4.0 mL of CHCl3. Diethyl ether (50 mL) was added to the mixture, which was left to stand for 30 min. The orange precipitate was collected and washed with diethyl ether to obtain rac1 as an orange solid (93 mg, 88%). Preparation of Single-Crystal R-1 and rac-1. Single crystals of R-1 were obtained by diethyl ether vapor diffusion of an acetone (1 mL) solution of R-1 (2.6 mg). Single crystals of rac-1 were obtained by diethyl ether vapor diffusion of an acetonitrile (1 mL) solution of rac-1 (5.2 mg). Preparation of Single-Crystal Toluene-Included Form, rac1·toluene. Single crystals of rac-1·toluene were obtained by diethyl ether vapor diffusion of a saturated toluene solution (2 mL) of rac-1. Powder X-ray Diffraction. Powder X-ray diffraction (PXRD) studies were conducted using a Rigaku SPD diffractometer at beamline BL-8B of the Photon Factory, KEK, Japan or a Bruker D8 Advance diffractometer equipped with a graphite monochromator using Cu Kα radiation and a one-dimensional LinxEye detector. The wavelength of synchrotron X-ray was 1.5365(1) Å.

vapochromic behavior of two different crystals of the Pt(II) complex [PtCl2(bpybe)] (1) (Scheme 1), which has two chiral Scheme 1. Molecular Structure of 1

butyl ester side-chains in the bpy ligand, namely, the chiral crystal of the R,R-isomer, [PtCl2(R,R-bpybe)] (R-1) and the racemic mixture with [PtCl2(S,S-bpybe)] (S-1; the racemic mixture is denoted as rac-1). We demonstrate that the chiral and racemic crystals, R-1 and rac-1, exhibited similar toluenevapor-induced structural transformations, but the toluene desorption temperature of rac-1·toluene was considerably higher than that of R-1·toluene.

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EXPERIMENTAL SECTION

General Procedures. Caution! Although we did not encounter any diff iculties, most of the chemicals used in this study are potentially harmful and should be used in small quantities and handled with care in a f ume hood. Commercially available starting materials and solvents were used without further purification unless stated. The precursor 2,2′bipyridine-4,4′-dicarboxylic acid was prepared according to a previously published method.41 1H NMR spectra at room temperature were recorded on an ECZ-400S NMR spectrometer. Elemental analysis was conducted at the Analysis Center at Hokkaido University. Synthesis of 2,2′-Bipyridine-4,4′-dicarboxylic Acid Dibutyl Ester (bpybe). 2,2′-Bipyridine-4,4′-dicarboxylic acid (500 mg, 2.1 mmol) was added to a two-neck round-bottom flask and then purged with N2 gas. Thionyl chloride (10 mL, 140 mmol) was subsequently added to the flask, and the mixture was heated to reflux overnight under N2 atmosphere. The reaction mixture was then cooled to 50 °C, and the remaining thionyl chloride was removed by evaporation under vacuum. The obtained solid was cooled to room temperature, and dry CH2Cl2 (20 mL), triethylamine (1.5 mL, 11 mmol), and (R)or (S)-2-BuOH (1.0 mL, 10 mmol) were added. The solvent was stirred overnight at room temperature under N2 atmosphere and then evaporated to dryness under vacuum. The residue was purified by

Figure 1. Crystal structure of rac-1. (a) Stacking structure of the [PtCl2(bpybe)] molecules and (b) packing formation of rac-1 crystal. Hydrogen atoms are omitted for clarity. Displacement parameters are drawn at the 50% probability level. These pictures were drawn using the program VESTA.47 7386

DOI: 10.1021/acs.inorgchem.9b00533 Inorg. Chem. 2019, 58, 7385−7392

Article

Inorganic Chemistry Table 1. Crystal Parameters and Refinement Results of rac-1, R-1, and rac-1·toluene at 150 K complex

rac-1

R-1

rac-1·toluene

formula formula weight crystal system space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 Z Dcal/g·cm−3 reflections collected unique reflections GOF Flack parameter Rint R [I > 2.00σ (I)] Rwa

C20H24Cl2N2O4Pt 622.41 monoclinic P21/n 16.4124(6) 7.1292(2) 18.7817(8) 90 98.203(4) 90 2175.1(1) 4 1.901 12 787 3863 1.071 − 0.0466 0.0430 0.1004

C20H24Cl2N2O4Pt 622.41 monoclinic P21 23.0967(3) 7.1524(1) 40.3783(5) 90 101.409(1) 90 6538.6(2) 12 1.897 69 940 23 254 1.030 −0.01(1) 0.0576 0.0556 0.1499

C23.5H28Cl2N2O4Pt 668.48 triclinic P1̅ 7.1523(2) 13.4476(3) 13.6723(3) 108.502(2) 94.530(2) 99.213(2) 1219.07(5) 2 1.832 11 820 4263 1.042 − 0.0477 0.0717 0.2117

Rw = {Σ[w(F02 − Fc2)2]/Σw(F02)2}1/2.

a

Luminescence Properties. The luminescence spectra of all the complexes were measured using a JASCO FP-8600 spectrofluorometer at room temperature. Typical slit widths of the excitation and emission light were 5 and 5 nm, respectively. UV−Visible Spectroscopy. The UV−visible (UV−vis) absorption spectra and diffuse reflectance spectra of the prepared complexes were recorded on a Shimadzu UV-2500PC spectrophotometer with an integrated sphere attachment. Thermogravimetric Analysis. Thermogravimetric (TG) analysis was performed using a Rigaku ThermoEvo TG-8120 analyzer. The typical sample mass used for this analysis was 2 mg. Single-Crystal XRD Measurement. All single-crystal XRD measurements were conducted using a Rigaku XtaLAB Synergy diffractometer equipped with Cu Kα (λ = 1.5418 Å) radiation [PhotonJet (Cu)]. Each single crystal was mounted on a MicroMount coated with paraffin oil. The crystal was then cooled using a N2 flowtype temperature controller. The diffraction data were collected and processed using the CrysAlis Pro software.42 The structures were solved by the direct method using SHELXT.43 Structural refinement was conducted by the full-matrix least-squares method with SHELXL.43 Non-hydrogen atoms were refined anisotropically, and all the hydrogen atoms were refined with a riding model. All calculations were conducted using the Olex2 crystallographic software package.44 Full crystallographic data have been deposited with the Cambridge Crystallographic Data Centre (CCDC 1898775− 1898777).

Table 2. Selected Bond Lengths and Angles of the Crystals at 150 K complex

rac-1

R-1

rac-1·toluene

2.02(1) Å 2.03(1) Å 2.293(5) Å 2.290(4) Å 2.02(1) Å 2.01(1) Å 2.292(4) Å 2.296(5) Å −

Pt1···Pt2

2.016(7) Å 2.016(5) Å 2.293(2) Å 2.300(2) Å − − − − 3.3834(5) Å, 4.7035(4) Å −

2.010(9) Å 1.999(7) Å 2.283(3) Å 2.295(2) Å − − − − 4.9739(5) Å, 4.6015(6) Å −

Pt1···Pt1···Pt1 Pt1···Pt2···Pt1

122.83(1)° −

Pt1−N1 Pt1−N2 Pt1−Cl1 Pt1−Cl2 Pt2−N3 Pt2−N4 Pt2−Cl3 Pt2−Cl4 Pt1···Pt1

3.394(1) Å, 4.715(1) Å − 122.96(3)°

96.58(1)° −

was oriented upside-down with respect to its closest neighbors. The two chiral molecules, R-1 and S-1, were stacked alternately along the b axis in an antiparallel orientation to cancel out the dipole moments. Although the Pt···Pt···Pt stacking angle [122.83(1)°] indicated zigzag chain structure, the intermolecular Pt···Pt distances in the zigzag chain were estimated to be 3.3834(5) and 4.7035(4) Å. Thus, the intermolecular Pt···Pt interaction would be effective in adjacent dimers with the shorter Pt···Pt distance. Figure 2 illustrates the crystal structure of the chiral complex R-1. R-1 crystallizes in the monoclinic P21 noncentrosymmetric space group. Although only one crystallographically independent Pt(II) complex molecule was found in rac-1, six crystallographically independent Pt ions were found in R-1. All of the Pt ions were coordinated by two nitrogen atoms of the bpybe ligand and two chloride ligands, taking the typical square planar geometry of the Pt(II) ion. The Pt−N and Pt− Cl bond lengths in all six crystallographically independent [PtCl2(bpybe)] molecules were comparable to those of rac-1

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RESULTS AND DISCUSSION Crystal Structures of rac-1 and R-1. Figure 1 illustrates the crystal structure of the racemic form, rac-1. The crystallographic parameters and selected bond lengths are listed in Tables 1 and 2. This form crystallized in the monoclinic centrosymmetric space group P21/n. This crystal contained only one crystallographically independent Pt(II) complex, that is, one Pt(II) cation, two Cl ligands, and one bpybe ligand with almost the same bond lengths as the isopropyl ester analogue (in the range of 2.003(4)−2.015(4) Å for Pt−N and 2.289(1)−2.298(1) Å for Pt−Cl).45,46 Consequently, the unit cell contained two molecules with different chirality, R-1 and S-1 (Figure 1a). Each ester chain 7387

DOI: 10.1021/acs.inorgchem.9b00533 Inorg. Chem. 2019, 58, 7385−7392

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Figure 2. Crystal structure of R-1. (a) Stacking structures with effective Pt···Pt interaction (column A) and weak Pt···Pt interaction (columns B, C). (b) Crystal packing of R-1 crystal. Hydrogen atoms are omitted for clarity. Displacement parameters are drawn at the 50% probability level. These pictures were drawn using the program VESTA.47

Figure 3. Crystal structure of rac-1·toluene. (a) Stacking structure of the [PtCl2(bpybe)] molecules and (b) packing formation of rac-1· toluene crystal. Red circles indicate toluene molecules. (c) Interactions between toluene and [PtCl2(bpybe)] molecules with C−H···O distances. Hydrogen atoms are omitted for clarity. Displacement parameters are drawn at the 50% probability level. The pictures in (a−c) were drawn using the program VESTA.47

(Table S1), suggesting that the coordination environment of Pt(II) was affected very little by the chirality of the butyl ester chains of the bpybe ligand. All the ester chains took only the R configuration, which was consistent with the 1H NMR spectrum of R-1 in the presence of a chiral shift reagent (Figure S1). Interestingly, three types of stacking structures (denoted as A, B, and C in Figure 2b) were found in the unit cell. As shown in Figure 2a, the intermolecular Pt···Pt distances in the A column were estimated to be 3.394(1) and 4.715(1) Å, and the Pt···Pt···Pt stacking angle was 122.96(3)°. These parameters were similar to those of rac-1, indicating that the chiral [PtCl2(R,R-bpybe)] molecules could also be dimerized by the effective intermolecular Pt···Pt interaction. Moreover, the stacking distances estimated at ca. 3.29 and 3.43 Å, suggested π−π stacking is effective. On the other hand, the intermolecular Pt···Pt distances in the stacking structures of the B and C columns were longer than 3.5 Å (Figure 2b and Table 2), suggesting that the intermolecular Pt···Pt interaction would be weaker than that in A column. However, the stacking distances were estimated to be ca. 3.30 Å, 3.42 Å for column B and 3.32 Å, 3.39 Å for column C, suggested that π−π stacking is also effective in the column structure. These column differences between rac-1 and R-1 are probably due to the slight difference in steric hindrance caused by the different orientation of the chiral ester chains, as suggested by the larger anisotropic parameters of the butyl ester side chains in R-1 compared to those in rac-1. In fact, the estimated volume for one R-1 molecule (that is, V/Z = 544.88 Å3) is slightly larger than that of rac-1 (543.78 Å3) even though they have the same chemical formula. Although we have not elucidated the crystal structure of the chiral isomer S-1, the experimental PXRD patterns of R-1 and S-1 were almost identical, suggesting that S-1 formed the same antisymmetric crystal structure as R-1 (Figure S2). Crystal Structures of Toluene-Solvated rac-1. The crystal structure of toluene-solvated rac-1 is presented in Figure 3. This solvated crystal, rac-1·toluene, crystallized in the triclinic centrosymmetric P1̅ space group. Although the

unit cell comprises two molecules of [PtCl2(bpybe)] (R-1 and S-1) and one molecule of toluene, only half of them were crystallographically independent. Consequently, the methyl group of the toluene molecule was disordered at two positions with half occupancy. The bond lengths around the Pt(II) ion were comparable to those of rac-1, suggesting that solvation by toluene did not affect the coordination environment around the Pt(II) ion. As in rac-1, the two molecules R-1 and S-1 were stacked alternately along the a axis, but the Pt···Pt···Pt stacking angle [96.58(1)°] was remarkably smaller than that of rac-1. The estimated intermolecular Pt···Pt distances [4.9739(5) and 4.6015(6) Å] were remarkably longer than those in rac-1, indicating that the intermolecular Pt···Pt interaction was weakened by toluene solvation. The distance between the two adjacent π planes of the bpybe ligands is estimated to be ∼3.5 Å, suggesting that the π−π stacking interaction would be a key factor in the formation of the stacked structure. The solvated toluene molecule was located between the two adjacent [PtCl2(R,R-bpybe)] stacking columns to form a onedimensional solvent channel (Figure 3b). The included toluene molecule did not interact with the planar-shaped {PtCl2(bpy)} moiety via π−π stacking interaction but interacted weakly with the CO moieties of butyl-ester side chains (Figure 3c); the distances between the aromatic C atoms of the toluene molecule and the surrounding O atoms were estimated to be 3.54(1) and 3.55(2) Å (Figure 3d), and the distance between the C atom of the methyl group and the adjacent O atom was 3.38(3) Å. These C−H···O distances suggest a weak hydrogen bonding interaction. Vapochromic Behavior of R-1 and rac-1. As discussed in the crystal structure sections, the racemic complex rac-1 took two different forms, the unsolvated rac-1 and toluenesolvated rac-1·toluene. Next, we examined the reversible transformation between these two forms by toluene vapor adsorption and desorption for both the racemic crystal rac-1 7388

DOI: 10.1021/acs.inorgchem.9b00533 Inorg. Chem. 2019, 58, 7385−7392

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Figure 4. PXRD patterns of (a) R-1 and (b) rac-1 before and after exposure to toluene vapor at 30 °C for 5 days. The toluene-exposed samples were subsequently dried under vacuum for 1 day. Sim.: simulation. (c) TG analysis of toluene-vapor-exposed R-1 and rac-1.

and the chiral crystal R-1. Figure 4 displays the PXRD patterns of R-1 and rac-1 before and after exposure to toluene vapor and subsequent vacuum-drying at 293 K. The patterns of both as-synthesized orange powders, R-1 and rac-1, were almost identical to the simulated patterns calculated from the crystal structures of the unsolvated forms. Slight disagreement of the experimental pattern of as synthesized rac-1 might be due to the anisotropic transformation of the crystal as suggested by the inverse shifts of (002) and (200) diffractions observed at 9.7° and 10.6°, respectively. TG analyses clearly showed that as-synthesized R-1 and rac-1 both exhibited negligible weight loss before decomposition (approximately 230 °C, Figure S3). Thus, these as-synthesized orange powders were identified as the unsolvated forms. After exposure to toluene vapor at 298 K for 5 days, the patterns of both rac-1 and R-1 became similar to the simulated patterns based on the crystal structure of rac1·toluene (for R-1, abbreviated as R-1·toluene). Since the toluene molecule in rac-1·toluene did not form any chemical bonds with the host [PtCl2(bpybe)] molecules (see Figure 3), the toluene vapor adsorption should be classified into physisorption. To confirm the chemical compositions of toluene-vapor-exposed R-1 and rac-1, TG analyses were conducted (Figure 4c). After toluene exposure, both R-1 and rac-1 exhibited comparable weight losses [6.1% and 6.5%, respectively] up to 110 °C, which are similar to the calculated weight for the solvated toluene in rac-1·toluene [0.5 mol per Pt(II) mol, 6.5%]. Notably, the toluene desorption temperature of toluene-exposed rac-1 (107 °C) was remarkably higher than that of R-1 (84 °C) even though they have the same chemical composition. This difference may originate from the slightly different packing structures of rac-1·toluene and R-1·toluene. Considering that unsolvated rac-1 is more dense than R-1 (Table 1), rac-1·toluene could be more densely packed than R-1·toluene to bind the toluene molecules more effectively in the crystal lattice. This discussion is also supported by the similar TG trends for benzene-vaporexposed samples (Figure S4); rac-1 released the adsorbed benzene molecules at a higher temperature (103 °C) than that of R-1 (82 °C). Additionally, the PXRD patterns of benzenevapor-exposed R-1 and rac-1 exhibited similar patterns to each toluene-vapor-exposed ones (Figure S5). These values are

almost the same as those of toluene-adsorbed rac-1 and R-1, suggesting that the benzene molecule would be bound similarly to the toluene molecule in rac-1·toluene. This result also suggests that the disordered orientation of the toluene molecule in rac-1·toluene would not be important for stabilization of the solvated toluene molecule. Next, to confirm the reversibility of these processes, both toluene-exposed samples were dried in vacuum at 293 K to desorb the toluene molecules. After drying, the PXRD pattern of R-1·toluene became almost identical to that of the original R-1. This result indicates that the structural transformation between R-1 and R-1·toluene is reversible. On the other hand, the PXRD pattern of rac-1·toluene also changed after drying under vacuum at 293 K, but the observed pattern was different from that of the original rac-1 and appeared to be composed of the diffraction patterns of rac-1·toluene and rac-1. These differences clearly show that rac-1·toluene should be more stable in vacuum than R-1·toluene. These findings are consistent with the TG result discussed above. In other words, a higher temperature is required to remove the solvating toluene molecules from rac-1·toluene than from R1·toluene. In fact, the PXRD pattern of rac-1·toluene became almost identical to that of the original rac-1 form after heating at 393 K for 2 h (Figure S6). Therefore, we conclude that the toluene-vapor-induced structural transformation of the racemic form between rac-1 and rac-1·toluene is also reversible. Although we have investigated about the structural transformation triggered by chiral vapors, no change was observed in PXRD measurements (Figure S7). To examine the vapochromic luminescent behavior, the emission spectra of each form were measured. As shown in Figure 5, the as-synthesized R-1 and rac-1 exhibited almost the same broad emission spectra, with emission maxima centered at 660 and 663 nm, respectively, and a relatively high emission quantum yield (Φ = 0.58 and 0.60, respectively). To clarify the origin of the emission, excitation and absorption spectra were measured (Figures 5 and S8). An obvious excitation band was clearly observed up to 570 nm for both as-synthesized R-1 and rac-1. In addition, a broad absorption band was also observed in the solid-state UV−vis diffuse reflectance spectra of both forms in the same wavelength region. In contrast, in acetone 7389

DOI: 10.1021/acs.inorgchem.9b00533 Inorg. Chem. 2019, 58, 7385−7392

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Inorganic Chemistry

was also confirmed by emission spectroscopy as well as the PXRD measurements described above.

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CONCLUSION We synthesized a Pt(II) complex with a 2-butyl-estersubstituted chiral bipyridine ligand, [PtCl2(bpybe)] (1), and its racemic mixture. Single-crystal X-ray structural analysis of the racemic crystal, rac-1, revealed that the single crystallographically independent stacking column was composed of two chiral R and S isomers, whereas three different stacking structures were formed in the chiral crystal R-1. The intermolecular Pt···Pt interaction was effective in the stacking column of rac-1 and in one of the three columns of R-1. In contrast, it was negligible in the other two columns of R-1, probably because of the difference in the steric hindrance of the chiral butyl ester chains of R-1 molecules. X-ray structural analysis of the toluene-solvated form, rac-1·toluene, clearly revealed that intermolecular Pt···Pt interaction was completely canceled out because of the solvating toluene, which was weakly bound by the C−H···O-type hydrogen bonding interaction. Both rac-1 and R-1 exhibited vapochromic behavior driven by adsorption/desorption of toluene vapor. In the vapochromic process, the emission origin switched from the strongly emissive 3MMLCT state to the weakly emissive 3 π−π* state because the intermolecular Pt···Pt interaction was canceled out by toluene adsorption. An interesting difference between R-1 and rac-1 was observed during toluene release; a higher temperature was required for rac-1·toluene than for R1. This was attributed to the stronger binding of toluene molecules in rac-1·toluene. This finding suggested that the vapor adsorption and desorption behavior can be manipulated by introducing chirality.

Figure 5. Changes in emission spectra (λex = 400 nm, solid lines) and excitation spectra (dotted lines) of (a) R-1 and (b) rac-1 upon exposure to toluene vapor and subsequent drying at 293 K under vacuum. The rac-1 sample was further heated at 393 K for 2 h to remove the toluene vapor completely.

solution, both R-1 and rac-1 exhibited the 1MLCT absorption band at approximately 420 nm, and negligible absorption appeared above 520 nm. The difference between the excitation spectra in the solid state and the absorption spectra in the solution state suggests that the extension of the excitation band edge to 570 nm in the solid state originates from the effective intermolecular Pt···Pt interaction, as suggested by the crystal structures. Thus, we assigned the red luminescence of both R-1 and rac-1 to 3MMLCT emission. The slightly longer wavelength (∼3 nm) of 3MMLCT emission from rac-1 compared to that from R-1 would be reasonable because of the slightly shorter intermolecular Pt···Pt distances in rac-1 than in R-1. On the other hand, R-1·toluene and rac-1· toluene, which were obtained by exposing the unsolvated samples to toluene vapor, exhibited completely different emission spectra, with vibronic progression around 521 nm. Notably, the emission quantum yields of R-1 and rac-1 were remarkably decreased by exposure to toluene vapor (Φ = 0.02 for both complexes). These significant changes indicate a change in the origin of the emission. Considering that the excitation band edges of both R-1·toluene and rac-1·toluene agreed qualitatively with the absorption band edge in the acetone solution state, the intermolecular Pt···Pt interaction should be negligible in the toluene-solvated forms, as suggested by the crystal structure of rac-1·toluene. Therefore, the emission of R-1·toluene and rac-1·toluene can be identified as 3 π−π* emission from the bpybe ligand. In the previous section, the PXRD patterns of rac-1·toluene after vacuum treatment for 1 day indicated the existence of both rac-1 and rac-1· toluene. In this vacuum-dried state, the emission spectrum would mainly contain the nonsolvated rac-1 because of the large emission quantum yield differences between rac-1 and rac-1·toluene (0.60 and 0.02). However, the color of rac-1 is retained at least 4 h under vacuum condition (Figure S9.). Therefore, this system can be useful not only for the toluene vapor detection (under UV-light irradiation), but also for the vapor-history sensor based on the color under ambient condition. After desorption of toluene vapor, the original broad emission of R-1 and rac-1 centered at approximately 660 nm was recovered. Thus, the reversibility of the toluenevapor-induced vapochromic luminescence of R-1 and rac-1

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b00533. 1 H NMR signals of R-1, S-1, and rac-1 obtained using a chiral shift reagent; comparison of PXRD patterns of the as-synthesized R-1 and S-1; TG analysis of R-1 and rac1; TG analysis of benzene-vapor-exposed R-1 and rac-1; PXRD patterns of rac-1 before and after toluene vapor exposure and drying; UV−vis absorption spectra and diffuse reflectance spectra of R-1 and rac-1 (PDF) Accession Codes

CCDC 1898775−1898777 contain the supplementary crystallographic data for this paper. These data can be obtained free of 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 Authors

*E-mail: [email protected] (A.K.). *E-mail: [email protected] (M.K.). ORCID

Yasuhiro Shigeta: 0000-0003-1240-5796 Atsushi Kobayashi: 0000-0002-1937-7698 Masako Kato: 0000-0002-6932-9758 7390

DOI: 10.1021/acs.inorgchem.9b00533 Inorg. Chem. 2019, 58, 7385−7392

Article

Inorganic Chemistry Notes

(16) Hariharan, P. S.; Moon, D.; Anthony, S. P. Reversible Fluorescence Switching and Topochemical Conversion in an Organic AEE Material: Polymorphism, Defection and Nanofabrication Mediated Fluorescence Tuning. J. Mater. Chem. C 2015, 3, 8381− 8388. (17) Martinez-Abadia, M.; Varghese, S.; Giménez, R.; Ros, M. B. Multiresponsive Luminescent Dicyanodistyrylbenzenes and Their Photochemistry in Solution and in Bulk. J. Mater. Chem. C 2016, 4, 2886−2893. (18) He, Y.-G.; Shi, S.-Y.; Liu, N.; Ding, Y.-S.; Yin, J.; Wu, Z.-Q. Tetraphenylethene-Functionalized Conjugated Helical Poly(phenyl isocyanide) with Tunable Light Emission, Assembly Morphology, and Specific Applications. Macromolecules 2016, 49, 48−58. (19) Sakon, A.; Sekine, A.; Uekusa, H. Powder Structure Analysis of Vapochromic Quinolone Antibacterial Agent Crystals. Cryst. Growth Des. 2016, 16, 4635−4645. (20) Drache, F.; Bon, V.; Senkovska, I.; Adam, M.; Eychmüller, A.; Kaskel, S. Vapochromic Luminescence of a Zirconium-Based Metal− Organic Framework for Sensing Applications. Eur. J. Inorg. Chem. 2016, 2016, 4483−4489. (21) Kar, P.; Yoshida, M.; Shigeta, Y.; Usui, A.; Kobayashi, A.; Minamidate, T.; Matsunaga, N.; Kato, M. Methanol-Triggered Vapochromism Coupled with Solid-State Spin Switching in a Nickel(II)-Quinonoid Complex. Angew. Chem., Int. Ed. 2017, 56, 2345−2349. (22) Ogoshi, T.; Shimada, Y.; Sakata, Y.; Akine, S.; Yamagishi, T. Alkane-Shape-Selective Vapochromic Behavior Based on Crystal-State Host−Guest Complexation of Pillar[5]arene Containing One Benzoquinone Unit. J. Am. Chem. Soc. 2017, 139, 5664−5667. (23) Sergeenko, A. S.; Ovens, J. S.; Leznoff, D. B. Copper(II) Dihalotetracyanoplatinate(IV) Coordination Polymers and Their Vapochromic Behavior. Inorg. Chem. 2017, 56, 7870−7881. (24) Kumpfer, J. R.; Taylor, S. D.; Connick, W. B.; Rowan, S. J. Vapochromic and Mechanochromic Films from Square-Planar Platinum Complexes in Polymethacrylates. J. Mater. Chem. 2012, 22, 14196−14204. (25) Ni, J.; Wang, Y.-G.; Wang, J.-Y.; Zhao, Y.-Q.; Pan, Y.-Z.; Wang, H.-H.; Zhang, X.; Zhang, J.-J.; Chen, Z.-N. A New Sensor for Detection of CH3CN and ClCH2CN Vapors Based on Vapoluminescent Platinum(II) Complex. Dalton Trans. 2013, 42, 13092− 13100. (26) Taylor, S. D.; Norton, A. E.; Hart, R. T., Jr.; Abdolmaleki, M. K.; Krause, J. A.; Connick, W. B. Between Red and Yellow: Evidence of Intermediates in a Vapochromic Pt(II) Salt. Chem. Commun. 2013, 49, 9161−9163. (27) Zhang, X.-P.; Wu, T.; Liu, J.; Zhang, J.-X.; Li, C.-H.; You, X.-Z. Vapor-Induced Chiroptical Switching in Chiral Cyclometalated Platinum(II) Complexes with Pinene Functionalized C^N^N Ligands. J. Mater. Chem. C 2014, 2, 184−194. (28) Kitani, N.; Kuwamura, N.; Tsuji, T.; Tsuge, K.; Konno, T. Water-Molecule-Driven Vapochromic Behavior of a Mononuclear Platinum(II) System with Mixed Bipyridine and Thioglucose. Inorg. Chem. 2014, 53, 1949−1951. (29) Han, A.; Du, P.; Sun, Z.; Wu, H.; Jia, H.; Zhang, R.; Liang, Z.; Cao, R.; Eisenberg, R. Reversible Mechanochromic Luminescence at Room Temperature in Cationic Platinum(II) Terpyridyl Complexes. Inorg. Chem. 2014, 53, 3338−3344. (30) Zhang, R.; Liang, Z.; Han, A.; Wu, H.; Du, P.; Lai, W.; Cao, R. Structural, Spectroscopic and Theoretical Studies of a Vapochromic Platinum(II) Terpyridyl Complex. CrystEngComm 2014, 16, 5531− 5542. (31) Yamashita, Y.; Tateishi, T.; Sawaguchi, K.; Kobayashi, A.; Kato, M.; Nakajima, K. Tribo-, Thermo-, and Vapochromic Behavior of Hydrazone−Pt(II) Complexes Induced by Protonation−Deprotonation in the Solid State, and Their Luminescence Properties in Solution. Chem. Lett. 2014, 43, 1912−1914. (32) Naziruddin, A. R.; Lee, C.-S.; Lin, W.-J.; Sun, B.-J.; Chao, K.H.; Chang, A. H. H.; Hwang, W.-S. Platinum Complexes Bearing Normal and Mesoionic N-Heterocyclic Carbene Based Pincer

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by a Grant-in-Aid for JSPS Research Fellows (Grant Number 17J01139) and JSPS KAKENHI (Grant Numbers JP18K19086, JP17H06367). The PXRD measurements were performed under the approval of the Photon Factory Program Advisory Committee (Proposal No. 2017G528).

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REFERENCES

(1) Yoshida, R. Self-Oscillating Gels Driven by the Belousov− Zhabotinsky Reaction as Novel Smart Materials. Adv. Mater. 2010, 22, 3463−3483. (2) Song, Y.; Weili, W.; Xiaogang, Q. Colorimetric Biosensing Using Smart Materials. Adv. Mater. 2011, 23, 4215−4236. (3) Coudert, F.-X. Responsive Metal−Organic Frameworks and Framework Materials: Under Pressure, Taking the Heat, in the Spotlight, with Friends. Chem. Mater. 2015, 27, 1905−1916. (4) Wenger, O. S. Vapochromism in Organometallic and Coordination Complexes: Chemical Sensors for Volatile Organic Compounds. Chem. Rev. 2013, 113, 3686−3733. (5) Kobayashi, A.; Kato, M. Vapochromic Platinum(II) Complexes: Crystal Engineering toward Intelligent Sensing Devices. Eur. J. Inorg. Chem. 2014, 2014, 4469−4483. (6) Yamaguchi, S.; Yoshikawa, I.; Mutai, T.; Araki, K. Solid-State Luminescence of Tetraphenylpyrene Derivatives: Mechano/Vapochromic Luminescence of 1,3,6,8-tetra(40-carboxyphenyl)pyrene. J. Mater. Chem. 2012, 22, 20065−20070. (7) Zeng, M.-H.; Tan, Y.-X.; He, Y.-P.; Yin, Z.; Chen, Q.; Kurmoo, M. A Porous 4-Fold-Interpenetrated Chiral Framework Exhibiting Vapochromism, Single-Crystal-to-Single-Crystal Solvent Exchange, Gas Sorption, and a Poisoning Effect. Inorg. Chem. 2013, 52, 2353−2360. (8) Nishiuchi, T.; Tanaka, K.; Kuwatani, Y.; Sung, J.; Nishinaga, T.; Kim, D.; Iyoda, M. Solvent-Induced Crystalline-State Emission and Multichromism of a Bent π-Surface System Composed of Dibenzocyclooctatetraene Units. Chem. - Eur. J. 2013, 19, 4110− 4116. (9) Shakirova, K. R.; Grachova, E. V.; Melnikov, A. S.; Gurzhiy, V. V.; Tunik, S. P.; Haukka, M.; Pakkanen, T. A.; Koshevoy, I. O. Toward Luminescence Vapochromism of Tetranuclear AuI−CuI Clusters. Organometallics 2013, 32, 4061−4069. (10) Hettiarachchi, C. V.; Rawashdeh-Omary, M. A.; Korir, D.; Kohistani, J.; Yousufuddin, M.; Dias, H. V. R. Trinuclear Copper(I) and Silver(I) Adducts of 4-Chloro-3,5-bis(trifluoromethyl)pyrazolate and 4-Bromo-3,5-bis(trifluoromethyl)pyrazolate. Inorg. Chem. 2013, 52, 13576−13583. (11) Sun, H.; Liu, S.; Lin, W.; Zhang, K. Y.; Lv, W.; Huang, X.; Huo, F.; Yang, H.; Jenkins, G.; Zhao, Q.; Huang, W. Smart Responsive Phosphorescent Materials for Data Recording and Security Protection. Nat. Commun. 2014, 5, 3061. (12) Oliveri, I. P.; Malandrino, G.; Di Bella, S. Phase Transition and Vapochromism in Molecular Assemblies of a Polymorphic Zinc(II) Schiff-Base Complex. Inorg. Chem. 2014, 53, 9771−9777. (13) Minei, P.; Koenig, M.; Battisti, A.; Ahmad, M.; Barone, V.; Torres, T.; Guldi, D. M.; Brancato, G.; Bottari, G.; Pucci, A. Reversible Vapochromic Response of Polymer Films Doped with a Highly Emissive Molecular Rotor. J. Mater. Chem. C 2014, 2, 9224− 9232. (14) Li, W.; Wang, L.; Zhang, J.-P.; Wang, H. Bis-pyrene-Based Supramolecular Aggregates with Reversibly Mechanochromic and Vapochromic Responsiveness. J. Mater. Chem. C 2014, 2, 1887−1892. (15) Naito, H.; Morisaki, Y.; Chujo, Y. o-Carborane-Based Anthracene: A Variety of Emission Behaviors. Angew. Chem., Int. Ed. 2015, 54, 5084−5087. 7391

DOI: 10.1021/acs.inorgchem.9b00533 Inorg. Chem. 2019, 58, 7385−7392

Article

Inorganic Chemistry Ligands: Syntheses, Structures, and Photo-Functional Attributes. Dalton Trans. 2016, 45, 5848−5859. (33) Lin, C.-J.; Liu, Y.-H.; Peng, S.-M.; Shinmyozu, T.; Yang, J.-S. Excimer−Monomer Photoluminescence Mechanochromism and Vapochromism of Pentiptycene-Containing Cyclometalated Platinum(II) Complexes. Inorg. Chem. 2017, 56, 4978−4989. (34) Li, Y.; Chen, L.; Ai, Y.; Hong, E. Y.-H.; Chang, A. K.-W.; Yam, V. W.-W. Supramolecular Self-Assembly and Dual-Switch Vapochromic, Vapoluminescent, and Resistive Memory Behaviors of Amphiphilic Platinum(II) Complexes. J. Am. Chem. Soc. 2017, 139, 13858−13866. (35) Bryant, M. J.; Skelton, J. M.; Hatcher, L. E.; Stubbs, C.; Madrid, E.; Pallipurath, A. R.; Thomas, L. H.; Woodall, C. H.; Christensen, J.; Fuertes, S.; Robinson, T. P.; Beavers, C. M.; Teat, S. J.; Warren, M. R.; Pradaux-Caggiano, F.; Walsh, A.; Marken, F.; Carbery, D. R.; Parker, S. C.; McKeown, N. B.; Malpass-Evans, R.; Carta, M.; Raithby, P. R. A Rapidly-Reversible Absorptive and Emissive Vapochromic Pt(II) Pincer-Based Chemical Sensor. Nat. Commun. 2017, 8, 1800. (36) Jiang, B.; Zhang, K.; Ma, J.-Q.; Zheng, W.; Chen, L.-J.; Sun, B.; Chao, L.; Hun, B.-W.; Tan, H.; Li, X.; Yang, H.-B. Vapochromic Behavior of a Chair-Shaped Supramolecular Metallacycle with Ultrastability. J. Am. Chem. Soc. 2016, 138, 738−741. (37) Shigeta, Y.; Kobayashi, A.; Ohba, T.; Yoshida, M.; Matsumoto, T.; Chang, H.-C.; Kato, M. Shape-Memory Platinum(II) Complexes: Intelligent Vapor-History Sensor with ON-OFF Switching Function. Chem. - Eur. J. 2016, 22, 2682−2690. (38) Shigeta, Y.; Kobayashi, A.; Yoshida, M.; Kato, M. Effect of the Chirality of Counter Anions on the Vapochromic Behavior of Luminescent PtII Complexes. Eur. J. Inorg. Chem. 2019, 2019, 1011− 1017. (39) Connick, W. B.; Henling, L. M.; Marsh, R. E.; Gray, H. B. Emission Spectroscopic Properties of the Red Form of Dichloro(2,2′bipyridine)platinum(II). Role of Intermolecular Stacking Interactions. Inorg. Chem. 1996, 35, 6261−6265. (40) Kato, M.; Kosuge, C.; Morii, K.; Ahn, J. S.; Kitagawa, H.; Mitani, T.; Matsushita, M.; Kato, T.; Yano, S.; Kimura, M. Luminescence Properties and Crystal Structures of Dicyano(diimine)platinum(II) Complexes Controlled by Pt···Pt and π-π Interactions. Inorg. Chem. 1999, 38, 1638−1641. (41) Chadwick, N.; Kumar, D. K.; Ivaturi, A.; Grew, B. A.; Upadhyaya, H. M.; Yellowlees, L. J.; Robertson, N. Isomer Dependence of Efficiency and Charge Recombination in DyeSensitized Solar Cells Using Ru Complex Dyes Bearing Halogen Substituents. Eur. J. Inorg. Chem. 2015, 2015, 4878−4884. (42) CrysAlisPro, version 1.171.39.45h; Rigaku Corporation: Oxford, UK, 2018. (43) Sheldrick, G. M. A Short History of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (44) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Pushmann, H. OLEX2: A Complete Structure Solution, Refinement and Analysis Program. J. Appl. Crystallogr. 2009, 42, 339−341. (45) Browning, C.; Nesterov, V. N.; Wang, X.; Omary, M. A. Synthesis and Structural Features of [4, 4’- Diisopropoxyester- 2, 2’bipyridine], [Dichloro(4, 4’- diisopropoxyester- 2, 2’- bi- pyridine) platinum(ii) ] and Its Dichloromethane Solvated Pseudo- Polymorph: Versatile Supramolecular Interactions. J. Chem. Crystallogr. 2015, 45, 277−283. (46) Scattergood, P. A.; Jesus, P.; Adams, H.; Delor, M.; Sazanovich, I. V.; Burrows, H. D.; Serpa, C.; Weinstein, J. A. Exploring excited states of Pt(II) diimine catecholates for photoinduced charge separation. Dalton Trans. 2015, 44, 11705−11716. (47) Momma, K.; Izumi, F. VESTA 3 for Three-Dimensional Visualization of Crystal, Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44, 1272−1276.

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