Luminescent Mechanochromic Dinuclear Cu(I) Complexes with

Article pubs.acs.org/IC

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

Luminescent Mechanochromic Dinuclear Cu(I) Complexes with Macrocyclic Diamine-Tetracarbene Ligands Taotao Lu,†,∥ Jin-Yun Wang,‡,∥ Deshuang Tu,† Zhong-Ning Chen,*,‡ Xue-Tai Chen,*,† and Zi-Ling Xue§ †

Downloaded via UNIV OF LOUISIANA AT LAFAYETTE on October 18, 2018 at 19:33:56 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China ‡ State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Fuzhou 350002, P. R. China § Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States S Supporting Information *

ABSTRACT: Dinuclear Cu(I) complexes bearing hexadentate, macrocyclic Nheterocyclic carbene (NHC) ligands, [Cu2(L1)(CH3CN)][PF6]2 (1) and [Cu2(L2)(CH3CN)]2[Cu2(L2)(CH3CN)2][PF6]6 (2), have been synthesized by the reactions of [H4L][PF6]4 (L = L1, L2) with excess Cu2O in acetonitrile. Crystallizations of the heat-treated samples of 1 and 2 from acetone/methanol/ ether or CH3NO2/ether result in [Cu2(L1)][PF6]2 (3) and [Cu2(L2)][PF6]2 (4). Complexes 1−4 are emissive with luminescent maxima at 464, 472, 540, and 488 nm in the solid state, respectively. The origin of the red shift of the emission maximum of 3 relative to the other three complexes has been studied by theoretical calculations, showing the cuprophilic interactions in the excited state of 3. The mechanochromic luminescent properties of 1−4 have been studied. After grinding in a mortar, a significant emission color change is found with a red shift of 98 nm for 1, 82 nm for 2, 20 nm for 3, and 64 nm for 4, respectively. These mechanochromic transformations are found to be a crystalline-to-amorphous conversion, which can be reverted by adding drops of the organic solvent or recrystallization. The possible correlations between the luminescent properties and structural modifications such as Cu···Cu distances are discussed.

■

plexes9 and imidazolate/tetrazolate coordination polymers10 have also been documented. Their reversible luminescent mechanochromic phenomena are attributed to the modification of crystal packing and inter/intramolecular interactions induced by Cu···Cu distances.6−10 Mechanochromism processes have been found to be accompanied by either phase transition3−5,6d−f,7,8a,9,10 or nonphase transition.6a−c,8b,c The former includes the common crystal-to-amorphous state conversion,3,4,5a,6d−f,7,8a,9,10 but rarely one crystalline state to the other crystalline one.6c,d In the cases of crystal-to-amorphous state conversion, the exact origin of the mechanochromism is difficult to identify due to crystallinity damage after being treated with mechanical force. So, the direct structural comparison between original and ground samples is almost impossible. The origin of the mechanochromism has been normally attributed to several structural factors, such as crystal packing, molecular arrangements, and inter/intramolecular interactions, particularly the Cu···Cu interactions in Cu(I) systems.6−10 In order to design new Cu(I)-based mechanochromic materials, the in-depth

INTRODUCTION Stimuli-responsive luminescent materials have attracted much attention because of their broad potential applications in sensing and optical data storage devices.1 There are various stimuli-responsive materials such as thermochromic, vapochromic, and mechanochromic materials, which respond to temperature, volatile organic compounds, and mechanical force, respectively.1−3 In particular, mechanochromic luminescence represents a color change triggered by grinding, compressing, shearing, and other mechanical forces, which has been reported for many organic materials3a−d and to a lesser extent for transition metal complexes containing Pt(II)4 and Au(I) ions.1a,3f,5 More recently, luminescent mechanochromic Cu(I) complexes have been reported.1b,c,6−10 In fact, luminescent Cu(I) complexes are very attractive considering their low cost compared to the noble metal counterparts.2d,11 The majority of luminescent mechanochromic Cu(I) complexes are based on the copper iodide clusters CunIn (n = 4, 6), which have been revealed by Perrachas,6 Hong,7 and others.8 The luminescent mechanochromism is usually associated with the thermochromism, which gives rise to the multi-stimuli responsive materials.6−8 Besides the systems based on Cu-I clusters, a few other Cu(I) complexes with N-heterocyclic ligands including planar trinuclear Cu(I)-pyrazolate com© XXXX American Chemical Society

Received: August 7, 2018

A

DOI: 10.1021/acs.inorgchem.8b02217 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 1. Preparation of 1 and 2

complexes supported by the flexible macrocyclic framework. Herein, we report the synthesis, crystal structures, and luminescent properties of a series of dinuclear Cu(I) complexes [Cu 2 (L 1 )(CH 3 CN)][PF 6 ] 2 (1), [Cu 2 (L 2 )(CH3CN)]2[Cu2(L2)(CH3CN)2][PF6]6 (2), [Cu2(L1)][PF6]2 (3), and [Cu2(L2)][PF6]2 (4). Among them, 3, possessing the shortest Cu···Cu distance, is highly emissive with the highest luminescence quantum yield of 0.93 for Cu(I)-NHC complexes.13 Theoretical calculations have been performed to demonstrate the origin of the red shift of the emission maximum of 3 relative to the other three complexes in the crystalline state. Moreover, all the four complexes exhibit mechanochromic luminescence properties being significantly modified upon mechanical grinding.

understanding of mechanochromism in such materials need to be further studied. Cu(I) complexes bearing N-heterocyclic carbene (NHC) ligands have been extensively studied as catalysts.12 In recent years, luminescent Cu(I)-NHC complexes have garnered a great deal of attention.13,14 Since Tsubomura’s group reported the first example of a luminescent dinuclear Cu(I) complex with a bis(NHC) ligand in 2009,13a a variety of mono-, di-, and trinuclear luminescent Cu(I)-NHC complexes with two-, three-, and four-coordinate Cu(I) ions have been reported.13,14 Thompson, Gaillard, and their co-workers have studied the photoluminescent properties of several three-coordinate trigonal Cu(I)−NHC complexes [(NHC)Cu(N^N)]0/+ bearing a monodentate NHC ligand and a chelating N^N ligand.13b−f More recently, we have reported the threecoordinate luminescent Cu(I) complexes [(NHC)2Cu(N)]+ with an amine-bis(N-heterocyclic carbene) ligand.13g However, only few Cu(I)-NHC complexes have been found to exhibit stimuli-responsive luminescent properties.14 Catalano et al. have showed an example of a vapochromic luminescent switch in a Cu2Au complex with bis(pycolyl)imidazolylidene, which responds to methanol vapor.14a Then, mechanochromic luminescence was found in a similar Cu2Au-NHC complex with an analogous bis(pycolyl)benzimidazolylidene ligand, in which the solvent loss is involved in the crystalline-toamorphous conversion.14b Recently, our groups have designed two tetra-NHC macrocyclic precursors [H 4L 1][PF6] 4 and [H4L 2][PF 6] 4 (Scheme 1) containing four benzimidazoliums and two secondary amines with different length of bridging alkylene groups (ethylene and propylene) between benzimidazolium units. These precursors have been employed to prepare Ag(I), Au(I), Ni(II), Pd(II), and Ir(I) complexes.15 It is reasoned that the macrocyclic NHCs L1 and L2 could be used as dinucleating ligands to construct dinuclear Cu(I) complexes, which allow us to study luminescent properties of Cu(I)

■

RESULTS AND DISCUSSION Synthesis and Characterization. The Cu(I) complexes with coordinated CH3CN molecules, [Cu2(L1)(CH3CN)][PF6]2 (1) and [Cu2(L2)(CH3CN)]2[Cu2(L2)(CH3CN)2][PF6]6 (2 = (2a)2·(2b), 2a = [Cu2(L2)(CH3CN)][PF6]2, 2b = [Cu2(L2)(CH3CN)2][PF6]2) have been prepared by reactions of [H4L1][PF6]415a or [H4L2][PF6]415b with excess Cu2O in acetonitrile, respectively, as shown in Scheme 1. Complexes 1 and 2 have been thoroughly characterized by different spectroscopic techniques including NMR and ESIMS. The 1H NMR spectra of 1 and 2 show the absence of 2Himdazolium proton resonances of [H4L1][PF6]4 and [H4L2][PF6]4, respectively. Moreover, the resonances of acetonitrile molecules in both 1 and 2 are identical with the free acetonitrile in DMSO-d6, suggesting that the coordinated acetonitrile molecules are labile and dissociated from the Cu(I) center in solution.14b ESI-MS spectra show the most intense peaks at m/z 395.25 and 935.17 for 1, 409.25 and 963.33 for 2, corresponding to [Cu2(L)]2+ and [Cu2(L)(PF6)]+ (L = L1, L2) fragments, respectively. B


Article

Inorganic Chemistry

acetonitrile, and acetone, but almost insoluble in alcohols and chlorinated hydrocarbons. They are air-stable in the solid state but noticeably decompose in solution. Structural Characterization. Complexes 1−4 have been characterized by single-crystal X-ray diffraction studies. Crystals of 1·2CH3CN and 2·4CH3CN suitable for X-ray diffraction analysis were obtained by vapor diffusion of diethyl ether into a solution of 1 and 2 in acetonitrile, respectively. Crystals of 3·(CH3)2CO and 4·2CH3NO2 were available from the recrystallization shown in Scheme 2. The structures of the cationic portion of 1−4 are shown in Figures 1−3, and their selected structural parameters are listed in Tables 1−3, respectively.

Thermolysis of both crystalline samples of 1 and 2 is followed by thermal gravimetric analysis (TGA; Figures S1 and S2). At room temperature, 1·2CH3CN begins to lose the acetonitrile molecule. Upon heating to about 119 °C, this complex has lost all three acetonitrile molecules including the coordinated acetonitrile to produce a solvent-free form. The total loss of 9.69% at 119 °C is close to the calculated value of 10.24%. Decomposition occurred when the temperature went up to about 319 °C. Similar thermochemical behavior is also observed in 2, in which all the solvent molecules are released at about 120 °C (Figure S2). X-ray crystallographic studies show that 1 and 2 are dinuclear Cu(I) complexes containing three-coordinate Cu(I) and four-coordinate Cu(I) centers (see below). Considering the easy departure of coordinated CH3CN, we postulated that preparation of new dinuclear Cu(I) complexes 3 and 4, containing two three-coordinate Cu(I) centers without coordinated CH3CN molecules, was feasible. In the preparation process, 1 was first heated at 80 °C under vacuum for 1 h to give a solid sample heated-1, which was then recrystallized by slow vapor diffusion of diethyl ether into a solution in a mixture solvent (CH3OH/acetone = 1/1, volume ratio) to give the crystals of acetonitrile-free complex, which are identified as complex 3 (Scheme 2). Similarly, acetonitrileScheme 2. Synthesis of 3 and 4

Figure 1. Structure of 1. Anions, solvent molecules, and hydrogens are omitted for clarity. Ellipsoids are drawn at 30% probability.

Table 1. Selected Bond Lengths (Å) and Angles (deg) of 1 Cu1−C1 Cu1−N3 Cu2−C32 Cu2−N11 C1−Cu1−C12 C1−Cu1−N3 C21−Cu2−N8 N8−Cu2−N11 C32−Cu2−N11

1.874(14) 2.186(10) 1.931(12) 2.061(10) 155.4(5) 98.9(5) 98.0(4) 92.9(4) 105.5(5)

Cu1−C12 Cu2−C21 Cu2−N8 Cu1···Cu2 C21−Cu2−C32 C12−Cu1−N3 C32−Cu2−N8 C21−Cu2−N11

1.918(13) 1.934(12) 2.243(10) 5.199(24) 134.8(4) 96.2(5) 96.1(4) 116.3(5)

Table 2. Selected Bond Lengths (Å) and Angles (deg) of 2 2a

free crystals of 4 have been obtained by recrystallization of heat-treated complex 2 (heated-2) from noncoordinating mixture solvent CH3NO2/ether (Scheme 2). The 1H NMR spectra of 3 and 4 in DMSO-d6 are identical to those of 1 and 2, respectively, except without the resonances of CH3CN molecules. Such differences are also found in 13C NMR spectra. Besides the 13C resonances for the CH3CN molecules, the same resonances for the coordinated macrocyclic ligands are found in 1 and 3 with a signal at 188.86 ppm for carbene carbon. Similarly, the same resonances at 187.74 ppm are found for the carbene carbon in 2 and 4. These carbene carbon resonances are comparable to those reported for Cu(I)-NHC complexes.13,16 All Cu(I)-NHC complexes 1− 4 are readily soluble in DMSO, DMF, nitromethane,

Cu1−C1 Cu1−N3 Cu2−C32 Cu2−N16 C1−Cu1−C12 C1−Cu1−N3 C21−Cu2−N8 N8−Cu2−N16 C32−Cu2−N16

1.925(4) 2.222(4) 1.910(4) 2.416(6) 168.61(17) 96.04(15) 96.08(15) 92.68(16) 93.28(17)

Cu3−C43 Cu3−N15 C43−Cu3−C53 N15−Cu3−N17 N15−Cu3−C53 N17−Cu3−C53

1.912(4) 2.192(4) 160.61(19) 88.84(17) 95.94(16) 85.23(19)

Cu1−C12 Cu2−C21 Cu2−N8 Cu1···Cu2 C21−Cu2−C32 C12−Cu1−N3 C32−Cu2−N8 C21−Cu2−N16

1.924(4) 1.898(4) 2.227(3) 6.458(12) 158.62(18) 94.18(15) 96.23(15) 103.53(17)

Cu3−C53 Cu3−N17 Cu3···Cu3′ N15−Cu3−C43 N17−Cu3−C43

1.910(5) 2.589(6) 6.168(12) 97.98(17) 108.44(18)

2b

C


Article

Inorganic Chemistry Table 3. Selected Bond Lengths (Å) and Angles (deg) of 3 and 4 Cu1−C1 Cu1−C12 Cu1−N3 Cu2−C21 Cu2−C32 Cu2−N8 Cu1···Cu2 C1−Cu1−C12 C21−Cu2−C32 C1−Cu1−N3 C12−Cu1−N3 C21−Cu2−N8 C32−Cu2−N8

3

4

1.923(3) 1.914(3) 2.229(3) 1.904(3) 1.927(3) 2.256(3) 3.351(5) 162.00(13) 168.93(14) 95.39(11) 96.11(12) 96.49(13) 93.60(13)

1.911(4) 1.910(4) 2.219(3) 1.932(4) 1.922(4) 2.222(4) 6.458(7) 162.45(16) 167.12(17) 96.03(14) 97.44(14) 95.88(15) 96.59(15)

1·2CH3CN crystallizes in monoclinic space group Cc. As shown in Figure 1, two Cu(I) ions are bound with one macrocyclic ligand L1, but adopt different coordination geometries. The Cu1 atom is coordinated by two carbene carbons and one amine nitrogen atom to form a distorted Tshaped coordination geometry, which is similar to the Cu(I) complex bearing a “pincer” type NHC ligand reported previously.17 The benzimidazolylidene planes containing C1 and C12 form a dihedral angle of 58.63°. The Cu1 center lies out of these two benzimidazolylidene planes by a distance of 0.191 and 0.235 Å, respectively. The bond angles of C1−Cu1− N3, C12−Cu1−N3, and C1−Cu1−C12 are 98.9(5)°, 96.2(5)°, and 155.4(5)°, respectively. The sum of the bond angles around the Cu1 atom is 350.5°, which is significantly less than 360°, further testifying to the presence of a distorted plane. The Cu1−C1 and Cu1−C12 distances are 1.874(14) Å and 1.918(13) Å, respectively, and the Cu1−N3 distance is 2.186(10) Å. The Cu2 atom in 1 is coordinated by two carbene carbons, one amine nitrogen atom, and one nitrogen atom of the CH3CN molecule to form a distorted tetrahedral geometry. The bond angles around Cu2 are in the range of 92.9(4)−134.8(4)°. Similarly, the benzimidazolylidene planes containing C21 and C32 form a dihedral angle of about 61.25°. Interestingly, the Cu2 atom lies at a point in the junction of two benzimidazolylidene planes containing C21 and C32, respectively. The Cu2−N8 and Cu2−N11 bonds pull the Cu atom out of the two benzimidazolylidene planes with the C21−Cu2−C32 bond angle of 134.8(4)°. The Cu2−C21 (1.934(12) Å) and Cu2−C32 (1.931(12) Å) distances are slightly larger than those observed around the Cu1 atom. In addition, the Cu2−N8 bond (2.243(10) Å) is also slightly larger than the Cu1−N3 distance. The Cu2−N11 bond is 2.061(10) Å, which is comparable to those in acetonitrilecoordinated Cu(I)-NHC complexes.18 In the crystalline lattice of 1·2CH3CN, CH−π intermolecular interactions are found between the adjacent two molecules (Figure S3). Complex 2 crystallizes as 2·4CH3CN in monoclinic space group C2/c, which is a co-crystal of two molecules of 2a and one molecule of 2b with one and two coordinated acetonitrile molecules, respectively. The structure of 2a is similar to that of 1 (Figure 2), in which one Cu atom is three-coordinated and exhibits a distorted T-shaped coordination geometry while the other is four-coordinated to form a distorted tetrahedral configuration. The sum of the bond angles around the Cu1 atom (358.77°) is close to 360°, suggesting its planar

Figure 2. Structure of 2 ((2a, top) and (2b, bottom)). Anions, solvent molecules, and hydrogens are omitted for clarity. Ellipsoids are drawn at 30% probability.

geometry. The bond angles around Cu2 are in the range of 92.68(16)−158.62(18)°. In 2b, both Cu atoms are fourcoordinated, similar to that of Cu2 in 2a and Cu2 in 1. It is worth noting that the Cu−NCH3CN distances in 2a and 2b are 2.416(6) Å and 2.589(6) Å, respectively, which are significantly longer than that in 1, indicating that the acetonitrile molecules bind weakly to the Cu atoms in 2. The Cu−C and Cu−Namine distances in the range of 1.898(4)−1.925(4) Å and 2.192(4)−2.227(3) Å, respectively, in 2, are comparable to those in 1. The Cu···Cu distances are 5.199(24) Å in 1 and 6.458(12) and 6.168(12) Å in 2, suggesting the absence of Cu···Cu interaction.10d,19 These values are significantly longer than the sum of the van der Waals radii of two Cu(I) ions (the van der Waals radii of Cu(I) ion is 1.4 Å,20 recently re-evaluated to be 1.92 Å21). In addition, the π−π stacking and CH−π interactions between aromatic and aliphatic units are found in the crystal structure of 2 (Figure S4). However, the π−π stacking interactions should be weak because the interacting aromatic units are not oriented parallel to each other. Both 3·(CH3)2CO and 4·2CH3NO2 crystallize in triclinic space group P1̅. As shown in Figure 3, each of two Cu(I) ions in both 3 and 4 are coordinated by two carbene carbons and one amine nitrogen atom to form a distorted T-shaped coordination geometry, similar to Cu1 in 1 and 2a. The sums of the bond angles around the Cu atoms are 353.50° and 359.02° for 3, and 355.92° and 359.59° for 4, respectively. The Cu···Cu distance in 3 is 3.351(5) Å, while that in 4 is 6.458(7) Å. The former is shorter than the sum of the re-evaluated van D


Article

--45 9 ---

“---” means not measured. a

τem (μs)

6.8 15.8(75%), 5.5(25%) 14.0(88%), 7.1(12%) --555 488 552 ---

λem (nm) Φem (%)

--93 29 --6.1 18.2(66%), 11.5(34%) 12.8(82%), 4.6(18%) ---

τem (μs) λem (nm)

564 540 560 ----9 9 16

Φem (%) τem (μs)

6.8 12.1(78%), 4.7(22%) 14.2(80%), 6.8(20%) 14.0(82%), 7.1(18%) 555 472 554 488

λem (nm) Φem (%) τem (μs) λem (nm)

--18 2.5 19

2 1

Table 4. Luminescent Data of 1−4 in Degassed Acetonitrile and Solid Statea E

6.1 17.2(97%), 1.3(3%) 12.8(82%), 4.6(18%) 13.6(82%), 5.1(18%)

der Waals radii of two Cu(I) ions (3.84 Å),21 indicating weak Cu···Cu interaction in 3. It is worth noting that the Cu···Cu distance in 3 is significantly shorter than that in 1, while that in 4 is comparable to that in 2. This should be due to the shorter ethylene linker in 3 than the propylene linker in 4. Similar to 1 and 2, π−π stacking and CH−π interactions are formed between the adjacent two molecules in 3 and 4 (Figures S5 and S6). Photoluminescent Properties of 1−4. As presented above, the coordinated CH3CN molecules in 1 and 2 are dissociated from Cu(I) centers in solution. It is thus understandable that the photophysical properties of 1 and 2 are identical to those of 3 and 4, respectively, in acetonitrile solution (Table 4). Therefore, here 3 and 4 are chosen to discuss their photophysical properties in solution. Both 3 and 4 have light yellow-green color in acetonitrile solution and the solid state. UV−visible spectra of 3 and 4 in acetonitrile show intense absorption around 230−280 nm, which can be assigned to the ligand-centered (LC) π−π* transition (Figure S7). There is a weak shoulder at ca. 300−350 nm, which can be assigned to the π−π* transition within the benzimidazolylidene moiety. Moreover, a broad and weak low-energy tail at ca. 350−400 nm was also observed, which can be ascribed to the metal-to-ligand charge transfer (MLCT) absorption. These assignments have been confirmed by the DFT/TD-DFT calculations (see below). 3 and 4 exhibit emission maximum at 564 and 555 nm in acetonitrile solution with the lifetime of 6.1 and 6.8 μs, respectively (Figure S8 and Table 4). Crystalline samples of 1−4 are all emissive at room temperature with the luminescence maximum λem at 464, 472, 540, and 488 nm for 1−4, respectively. Their emission spectra at 298 K are shown in Figure 4, and emission data are summarized in Table 4. Complex 3 shows the emission maximum at 540 nm in comparison to the maximum at 488

564 464 562 564

3

Figure 3. Structures of 3 (top) and 4 (bottom). Anions, solvent molecules, and hydrogens are omitted for clarity. Ellipsoids are drawn at 30% probability.

CH3CN crystalline ground heated

4

Φem (%)

Inorganic Chemistry


Article

Inorganic Chemistry

state.13b,i,19 In addition, 3 with a shorter Cu···Cu distance shows a higher quantum yield of Φem = 0.93 in comparison to that of 4 (Φem = 0.45) with a longer Cu···Cu distance, suggesting that the Cu···Cu distance affects the emission properties of Cu(I) complexes.13i,l,19 To our knowledge, 3 exhibits the highest emission quantum yield for Cu(I)-NHC complexes.13 Mechanochromic Properties. Mechanochromic transformation has been found to be affected by the solvent molecules. For example, Chen and co-workers have reported several Pt(II) complexes and their solvate crystals.4 The solvates lose their lattice solvent molecules to form an amorphous state by grinding, which exhibits a luminescent color change. Catalano et al.14b have revealed luminescent mechanochromism in a AuCu2 complex with a bis(pycolyl)benzimidazolylidene ligand, which is associated with the loss of the coordinated CH3CN. Such solvent-assisted mechanochromism has also been reported in a Cu4I4 cluster by Hong et al.7a Thus, 1 and 2 are expected to exhibit mechanochromic luminescent properties due to the easy loss of the coordinated CH3CN molecules. When the crystalline powder of 1 is thoroughly ground in a mortar, the obtained powder exhibits orange yellow luminescence at λmax = 562 nm (Scheme 3, Figure 5). The grinding-triggered red shift by 98 nm (Figure 5)

Figure 4. Normalized emission spectra of crystalline 1−4 at room temperature.

nm for 4. The distinctness between 3 and 4 could be mainly due to the different Cu···Cu distances of 3.351(5) Å (3) and 6.458(7) Å (4) if the influences of other factors, including molecular arrangements and intermolecular interactions, are not significant considering that they have the same threecoordinate environment. The emission maximum of 3 (540 nm) is also significantly longer than those observed of 1 (464 nm) and 2 (472 nm). It is noted that they have different coordination environments around the Cu(I) centers. The 24 nm difference between emission maximum for 1, 2, and 4 illustrates that the other factors including coordination environment about the Cu(I) center (except the Cu···Cu distances) have only an mild impact on emission energy. The correlation between the luminescent maximum and the Cu··· Cu distance is also revealed by comparison of 1 and 3, which have the same macrocyclic ligand L1, but different Cu···Cu distances (5.199(24) Å and 3.351(5) Å, respectively). With the removal of the acetonitrile molecule from the Cu(I) center in 1 to give 3, the Cu···Cu distance decreases, and the luminescence exhibits a red shift from 464 nm (1) to 540 nm (3). In contrast, with the departure of CH3CN molecules in 2 to form 4, the two Cu(I) ions remain at a similarly long distance from each other (6.458(12) and 6.168(12) Å for 2, and 6.458(7) Å for 4), leading to the similar emission peaks at 472 (2) and 488 nm (4). Emission spectra of 1−4 are broad and featureless, which can be modeled using two biexponential decay times. The two components of excited-state lifetimes of 1−4 are 17.2(97%)/ 1.3(3%), 12.1(78%)/4.7(22%), 18.2(66%)/11.5(34%), and 15.8(75%)/5.5(25%) μs, respectively, indicating that the observed emission originates from the triplet charge transfer

Figure 5. Normalized solid-state emission spectra of 1, ground-1, reverted-1, and heated-1 (λex = 365 nm).

indicates that 1 exhibits a grinding-induced luminescence change. It is found that the CH3CN molecules have been removed upon thorough grinding as determined by NMR (Figure S13). After treating the resulting sample ground-1 with a drop of acetonitrile, the emission is restored immediately to the original blue luminescence of 1 (reverted-1, λmax = 469 nm),

Scheme 3. Luminescent Mechanochromism of 1: Crystals of 1, Powders of Ground-1, and Reverted-1 under 365 nm Illumination

F


Article

Inorganic Chemistry which could be returned to that of ground-1 by grinding. Similar inversion was observed for ground-1 exposed to CH3CN vapor (the resulting sample is named as reverted-1′), which is revealed by PXRD (Figure 7). Recrystallization of ground-1 from CH3CN/ether yields crystals of 1. The color conversion process shown in Scheme 3 is fully reversible as demonstrated through many cycles. Likewise, grinding the crystalline sample of 2 in a mortar exhibiting a red shift by about 82 nm for the luminescence maximum gives the sample ground-2 (λmax = 554 nm, Figure 6, Scheme 4). Similar to the

S18). After grinding, the new band originating from the ground-1 appears at 562 nm, but the band at 464 nm from the original 1 weakens with the increasing of grinding time and disappears after grinding for 5 min. A similar emission trend is observed for the grinding of 2. This suggests that the CH3CN molecules are completely removed after thorough grinding, which has been proved by elemental analysis and NMR spectra (Figures S13 and S17). These observations show that the macrocyclic ligands L1 and L2 remain coordinated to the Cu(I) centers in the same coordination mode after grinding. In other words, during the mechanical treatment, there is no marked structural change, except the loss of CH3CN accompanying with the coordination number changing from four to three. The PXRD of ground-1 and ground-2 show very broad and weak signals, indicating their amorphous nature (Figures 7 and

Figure 6. Normalized solid-state emission spectra of 2, ground-2, reverted-2, and heated-2 (λex = 365 nm). Figure 7. Experimental (1, ground-1, reverted-1, and reverted-1′) and simulated (1) powder diffraction patterns.

case of ground-1, the emission color of ground-2 is reverted to the original blue immediately after adding a small amount of acetonitrile (reverted-2) or exposure to CH3CN vapor. Again, the emission color of reverted-2 could be turned into yellow luminescence after grinding again (Scheme 4). In addition, recrystallization of ground-2 from CH3CN/ether yields crystals of 2. In order to gain insight into the composition and structures of ground-1 and ground-2, their 1H NMR spectra and powder X-ray diffraction (PXRD) patterns have been measured and compared with those of 1 and 2. The 1H NMR spectra for the ground samples with different grinding times show that the identical NMR signals for the coordinated macrocyclic ligand are observed for ground-1 and 1 (Figures S9−S13), ground-2 and 2 (Figures S14−S17). However, the 1H NMR signals of the free CH3CN molecules in ground-1 and ground-2 become gradually weaker with the lengthening of grinding time, suggesting that CH3CN molecules are gradually lost on grinding. The emission spectra of ground-1 and ground-2 obtained with different grinding times are measured (Figure

S19). However, the addition of drops of CH3CN or exposure to CH3CN vapor to them restores the PXRD patterns of 1 and 2, respectively. These observations imply that the crystal lattice has been disrupted after grinding, and thus it is a crystal-toamorphous phase transition. Local heat produced by grinding could promote the CH3CN departure with concomitant disruption of crystalline lattice. The loss of CH3CN molecules and the breaking of the intermolecular interactions would be responsible for the grinding-triggered luminescence change. As presented above, the Cu···Cu distances in 1 and 3 are 5.199(24) Å and 3.351(5) Å, respectively. With the removal of the coordinated acetonitrile molecule from one Cu(I) center in 1, the Cu···Cu distance decreases, and the luminescence exhibits a red shift from 464 nm (1) to 540 nm (3). Such a Cu···Cu distance change could also occur in the grinding process in 1 and 2. When the coordinated CH3CN was removed by grinding, the decrease of coordination number could allow the approach of two Cu(I) ions to give a shorter

Scheme 4. Luminescent Mechanochromism of 2: Crystals of 2, Powders of Ground-2, and Reverted-2 under 365 nm Illumination

G


Article

Inorganic Chemistry Cu···Cu distance as in the crystalline 3, which is responsible for the red shift of emission maximum after grinding 1 and 2. Even though the detailed molecular structures of ground-1 and ground-2 are unknown, we believe that they would adopt the similar molecular structures to 3 with a short Cu···Cu distance. Besides the variation of Cu···Cu distances, the intermolecular interactions have been damaged due to the crystal lattice destruction, which could also adjust the luminescence properties. The removal of CH3CN molecules can also be achieved by heating the crystalline samples of 1 and 2 at 80 °C under vacuum for 1 h, which is proved by elemental analysis and the NMR spectra of the resulting samples heated-1 and heated-2 (Figures S20 and S21). The resulting samples heated-1 and heated-2 exhibit an emission maximum at 564 and 488 nm, respectively. As expected, a large red shift of 100 nm was observed between crystalline 1 and heated-1 in comparison to a 16 nm red shift in the case of crystalline 2 and heated-2. Again, the larger red shift in heating of 1 could be due to the shortening of the Cu···Cu distance accompanying with the loss of CH3CN molecules as in ground-1. It should be noted that the luminescent properties of ground-1 and heated-1 are similar while the emissive maximum of heated-2 is similar to that of 4. However, the properties of ground-2 and heated-2 are different, suggesting that their microstructures should be different. These comparisons indicate that heated-1 and ground-1 could have the same emission origins and probably the same microstructures. Similarly, heated-2 has probably the similar structure to the crystalline 4 since they have the similar luminescent properties (Table 4). Mechanically triggered luminescence changes have also been observed for the CH3CN-free complexes 3 and 4. When a crystalline sample of 3 or 4 is ground in an agate mortar, a clear color change from green-yellow (3) or green (4) to yellow (Figures 8 and 9) is observed. The changes in emission

Figure 9. Normalized solid-state emission spectra of 3, ground-3, 4, and ground-4 (λex = 365 nm).

macrocyclic ligand remains unchanged during the grinding process (Figure S22). The identical NMR patterns are also observed in the 1H NMR spectra of 4 and ground-4 (Figure S23). The PXRD studies show that the diffraction patterns of samples 3 and 4 disappear entirely when they are thoroughly ground, but are restored perfectly to the original PXRD patterns by recrystallization from the corresponding solvents (Figures 10 and S24). In contrast to 1 and 2, the grinding

Figure 10. Experimental (3, ground-3, recrystallized ground-3) and simulated (3) powder diffraction patterns.

process of 3 and 4 does not accompany the removal of CH3CN molecules. The small 20 nm red shift observed in grinding 3 could be attributed to the disruption of the crystal lattice and the resulting change of intermolecular interactions. Since the Cu···Cu distance in 4 is still long, the shortening of the Cu···Cu distance could be triggered by the destruction of the crystal lattice, which could be responsible for the larger red shift of 64 nm observed for grinding 4. Similar to the emission spectra in solution, the samples ground-3 and ground-4 have similar emissive properties with ground-1 and ground-2, respectively. Furthermore, these ground samples exhibit the same emissive maximum as their solutions (Table 4). These observations lead us to believe that the molecular structures of 1−4 would be relaxed to a similar structure as in solution after grinding. DFT/TD-DFT Computational Studies. Considering that the coordinated CH3CN molecules in 1 and 2 are dissociated in solution to give the identical photophysical properties with 3 and 4, the TD-DFT computational studies were only

Figure 8. Photographic images of 3 and 4 taken under 365 nm illumination before and after grinding.

maximum of 3 and 4 before and after grinding are 20 and 64 nm, respectively. Recrystallization of ground-3 and ground-4 yields crystals of 3 and 4, respectively. Interestingly, the emission color of the ground samples (ground-3 and ground-4) can be converted to the color of 1 and 2 upon treating them with drops of acetonitrile, respectively. These suggest that the coordination of CH3CN could occur to change 3 and 4 into 1 and 2, respectively. The color changes in solid-state emission between 3 and 1 and between 4 and 2 can be repeated many times, indicating the reversibility of the processes. Furthermore, the samples ground-3 and ground-4 also exhibit the vapochromic properties. An emission color change from yellow to blue has been observed after exposure of ground-3 or ground-4 to CH3CN or DMF vapor (see Figures S25 and 26). The 1H NMR spectra of 3 and ground-3 in DMSO-d6 are almost identical, indicating that the coordination mode of the H


Article

Inorganic Chemistry

Table 5. Emission (Lowest-Energy Triplet State, T1) Transition for Complexes 3 and 4 in the CH3CN Solution and for 1−4 in the Solid State, Respectively, by TD-DFT Method at the PBE1PBE Level states

E, nm (eV)

f

3 4

622 (1.99) 501 (2.48)

0.0000 0.0000

1

467 (2.66)

0.0000

2 3 4

470 (2.64) 613 (2.02) 476 (2.60)

0.0000 0.0000 0.0000

transition (contri.) CH3CN solution HOMO → LUMO (95%) HOMO → LUMO (88%) solid state HOMO → LUMO (56%) HOMO-1 → LUMO (39%) HOMO-1 → LUMO (95%) HOMO → LUMO (95%) HOMO → LUMO (93%)

assignment 3

MLCT/3LC/3MC/3LLCT MLCT/3LLCT/3MC/3LC

3

3

MLCT/3LC/3MC/3LLCT MLCT/3LC/3MC/3LLCT 3 MLCT/3MC/3LLCT/3LC 3 MLCT/3LC/3MC 3 MLCT/3LLCT/3MC/3LC 3

benzimidazolylidene), mixed with some 3LC (in benzimidazolylidene ligand) and 3 LLCT states (from amines to benzimidazolylidene ligand). Complex 3 is highly emissive in the solid state and exhibits the red shift in luminescence relative to 4 (or 1 and 2). As presented above, 3 possesses a shorter Cu···Cu distance of 3.351(5) Å, which is shorter than the sum of the re-evaluated van der Waals radii of two Cu ions (3.84 Å).21 This might suggest that a possible cuprophilic interaction is responsible for the red shift of emission for 3. It should be noted that only shorter Cu···Cu distances have been experimentally proved to affect the luminescent properties of binuclear or polynuclear Cu(I) complexes.19 Therefore, the distance of 3.351(5) Å in 3 is not probably the major cause of its red shift of the emissive wavelengths. The cuprophilic interactions in the excited states have also been suggested to be responsible for the highly emissive d10 metal complexes in the solid state.22 In order to probe the possible cuprophilic interactions in the excited states for our complexes, we optimize the geometrical structures in the ground (S0) and lowest-energy triplet states (T1). The optimized structures and the Cartesian coordinates of these four complexes in the S0 and T1 states, respectively, are shown in Figure S29 and Tables S9−S16, and the Cu···Cu distances are also listed. It can be seen that the Cu···Cu distance in the T1 state is similar to that in the ground state for 1, 2, and 4. In contrast, the Cu···Cu distance in the T1 state for 3 is 2.58 Å, which is much shorter than that in the ground state (3.90 Å). This Cu···Cu distance, significantly shorter than the sum of previously reported and re-evaluated van der Waals radii of the Cu(I) ion (2.80 Å20 and 3.84 Å21), suggests stronger cuprophilic interaction in the excited state rather than the ground state, which explains the red shift in the emission maximum for 3. By deeply exploring the orbital plots in Figure 11, we can see that the HOMO and LUMO of 2 and 4 only refer to one Cu atom, with the other Cu atom not participating in the orbital distribution. For 1, the orbitals HOMO-1 and HOMO involved in the emission transition are mainly from the contribution of the two Cu atoms, but with scarce overlap of the Cu orbitals, while the LUMO only is typical of one Cu atom. By checking the frontier molecular orbitals of 3, we see that all the HOMO and LUMO refer to the contribution of two Cu atoms, and the overlap between the Cu orbitals is considerable. All of these testify that there are strong cuprophilic interaction in 3.

performed for 3 and 4. The details of the theoretical calculations are described in the Supporting Information. The orbital compositions (%) of different energy levels and the absorption transitions of 3 and 4 in CH3CN solution are detailed in Tables S3−S6, and the orbitals involved in the absorption transitions are plotted in Figure S27. The calculated strong absorption from the ground state (S0) to S8 of these two complexes mainly involves HOMO-3/HOMO-2 → LUMO (83% contribution) and HOMO-3/HOMO-2 → LUMO/ LUMO+1 (88% contribution) transitions, respectively. It is found that all of these involved orbitals are mainly populated on benzimidazolylidene (no less than 65%), so these strong absorptions located in 289 and 288 nm, respectively, for 3 and 4, can be predominantly ascribed to the benzimidazolylidene ligand-centered (1LC) π−π* transition. The low-energy absorptions in 350−400 nm, mainly from the transition of HOMO/HOMO-1 → LUMO and HOMO → LUMO+1 for 3 and HOMO-1/HOMO → LUMO/LUMO+1 for 4, are typical of the metal-to-ligand charge transfer (1MLCT) transition from the Cu atom to the benzimidazolylidene moiety, which is combined with some ligand-to-ligand charge transfer (1LLCT) transition from amines to the benzimidazolylidene ligand. The calculated emission transitions at 622 and 501 nm in CH3CN solution (Table 5) for 3 and 4, respectively, coincide well with the experimentally observed values of 564 and 555 nm. These emissions are mainly from the HOMO → LUMO transition (more than 88%). On the basis of the orbital compositions (Table S7 and Figure S28), it can be seen that HOMO is predominantly contributed by Cu atoms (57.62% and 59.61% for 3 and 4, respectively), mixed with some contribution from benzimidazolylidene and amines (21.12% and 20.53% for 3, and 12.70% and 25.49% for 4), while LUMO is mainly located on the benzimidazolylidene ligand (more than 67%), combined with little contribution from Cu atoms. So the emission transitions in CH3CN solution can be ascribed to the 3 MLCT from the Cu atom to the benzimidazolylidene ligand, with some 3LLCT from amines to the benzimidazolylidene ligand and 3LC transition in benzimidazolylidene. To gain insight into the emission transitions in the crystalline states, the characters of lowest-energy triplet excited-states for 1−4 are also detailed in Table 5, and the involved orbitals are plotted in Figure 11. The calculated emission wavelengths of 467, 470, 613, and 476 nm for 1−4 agree well with the experimental values of 464, 472, 540, and 488 nm, respectively. These transitions, mainly from HOMO/ HOMO-1 → LUMO, HOMO-1 → LUMO, HOMO → LUMO, and HOMO → LUMO for 1−4, respectively, are primarily assigned to 3MLCT character (from Cu atom to

■

CONCLUSION In this work, we have prepared four dinuclear Cu(I) complexes 1−4 bearing hexadentate macrocyclic diamine-tetraNHC I


Article

Inorganic Chemistry

Mechanical stimulus promotes the loss of the solvent CH3CN molecules in 1 and 2, and the resulting concomitant disruption of the crystalline lattice and the shortening of the Cu···Cu distance change the luminescent colors. In contrast, the grinding of 3 and 4 does not involve the loss of solvent, but the disruption of the crystalline lattice and probably the Cu···Cu distance change are also responsible for their mechanochromic luminescences. In all of these cases, the emission color changes are reversible and appear to be related to the coordination geometry changes at the Cu(I) center and/or the crystal lattice destruction, resulting in the shortening of the Cu···Cu distance.

■

EXPERIMENTAL SECTION

General Procedures. All manipulations were performed under dry nitrogen, using standard Schlenk techniques unless otherwise stated. Acetonitrile was dried over CaH2 and distilled under nitrogen before use. All other solvents and chemicals are commercially available and were used as received without further purification. The macrocyclic benzimidazolium salts [H4L1][PF6]4 and [H4L2][PF6]4 were prepared according to the literature procedures.15 NMR spectra were recorded on a Bruker Avance 400 MHz (1H, 400 MHz; 13C, 100 MHz) spectrometer at 298 K. Elemental analyses (C, H, and N) were carried out on a PerkinElmer 240C analytic instrument. Mass spectra were measured with an ESI mass spectrometer (LCQ Fleet, Thermo Fisher Scientific). Electronic absorption spectra were recorded with Shimadzu UV-2550 spectrophotometers. Emission and excitation spectra, emission decay lifetimes, and emission quantum yields were measured on a Edinburgh FLS920 spectrofluorometer. General Procedure for the Synthesis of 1 and 2. The ligand precursor [H4L1][PF6]4 or [H4L2][PF6]4 (0.16 mmol) and Cu2O (229 mg, 1.60 mmol) were dissolved in dry and degassed acetonitrile (6 mL). The mixture was heated to reflux for 12 h. Then, the mixture was allowed to cool down to room temperature. Under nitrogen, the mixture was filtered and purified by vapor diffusion of ether to the filtrate to obtain yellow green crystals of 1 or 2. 1 (147 mg, 82% yield): 1H NMR (CD3CN, 400 MHz): δ 7.64 (d, J = 8 Hz, 4 H, bzim), 7.12−7.48 (m, 12 H, bzim), 5.48 (br, 8 H, CH2), 4.36 (br, 8 H, CH2), 2.99 (br, 10 H, CH2 and NH), 1.96 (s, CH3CN). 13 C NMR (DMSO-d6, 100 MHz): δ 188.86 (NCN), 133.99 (bzim), 132.61 (bzim), 123.27 (bzim), 122.96 (bzim), 118.03 (CH3CN), 110.86 (bzim), 110.36 (bzim), 48.84 (CH2), 46.97 (CH2), 44.34 (CH2), 1.07 (CH3CN). ESI-MS: m/z 395.25 [Cu2(L1)]2+, 935.17 [Cu2(L1)(PF6)]+. 2 (112 mg, 63% yield): 1H NMR (DMSO-d6, 400 MHz): δ 7.79 (d, J = 8 Hz, 4 H, bzim), 7.60 (d, J = 8 Hz, 4 H, bzim), 7.42 (t, J = 8 Hz, 4 H, bzim), 7.34 (t, J = 8 Hz, 4 H, bzim), 4.92 (br, 8 H, CH2), 4.46 (br, 8 H, CH2), 3.98 (br, 2 H, NH), 3.25 (br, 8 H, CH2), 2.64 (br, 4 H, CH2), 2.07 (s, CH3CN). 13C NMR (DMSO-d6, 100 MHz): δ 187.74 (NCN), 134.62 (bzim), 131.65 (bzim), 123.53 (123.53) (bzim), 118.01 (CH3CN), 111.43 (bzim), 111.38 (bzim), 49.26 (CH2), 46.62 (CH2), 44.97 (CH2), 29.18 (CH2), 1.06 (CH3CN). ESIMS: m/z 409.25 [Cu2(L2)]2+, 963.33 [Cu2(L2)(PF6)]+. Synthesis of Ground-1. Crystals of 1 (50 mg) were ground for 5 min, and an emission color change under UV light was observed to form ground-1. 1H NMR (CD3CN, 400 MHz): δ 7.65 (d, J = 8 Hz, 4 H, bzim), 7.14−7.48 (m, 12 H, bzim), 5.50 (br, 8 H, CH2), 4.37 (br, 8 H, CH2), 3.00 (br, 10 H, CH2 and NH). Anal. Calcd for C40H42Cu2F12N10P2 ([Cu2(L1)][PF6]2): C, 44.49; H, 3.92; N, 12.97%. Found: C, 44.21; H, 4.23; N, 13.36%. ESI-MS: m/z 395.25 [Cu2(L1)]2+, 935.17 [Cu2(L1)(PF6)]+. Synthesis of Ground-2. Crystals of 2 (50 mg) were ground for 5 min, and an emission color change under UV light was observed to form ground-2. 1H NMR (DMSO-d6, 400 MHz): δ 7.80 (d, J = 8 Hz, 4 H, bzim), 7.60 (d, J = 8 Hz, 4 H, bzim), 7.42 (t, J = 8 Hz, 4 H, bzim), 7.34 (t, J = 8 Hz, 4 H, bzim), 4.92 (br, 8 H, CH2), 4.44 (br, 8 H, CH2), 3.98 (br, 2 H, NH), 3.24 (br, 8 H, CH2), 2.63 (br, 4 H, CH2). Anal. Calcd for C42H46Cu2F12N10P2 ([Cu2(L2)][PF6]2): C,

Figure 11. Plots of the frontier molecular orbitals involved in the emission transitions for complexes 1−4 in the solid state by TD-DFT method at the PBE1PBE level (isovalue = 0.025) based on the lowest triplet structures. For clarity, the H atoms except for those in amines are omitted.

ligands L1 or L2 and studied their interconversion and luminescent properties. Complex 3 with a Cu···Cu distance of 3.351(5) Å is highly emissive with an emission quantum yield of 0.93. The theoretical calculations show that the strong cuprophilic interaction in the triplet excited states contributes significantly to the emissive red shift of 3 relative to that of 1, 2, and 4. It was found that the luminescence colors of these Cu(I) species can be switched by mechanical pressure. Upon grinding, a significant emission color change (with the wavelength change of 20−98 nm) is observed for 1−4. J


Article

Inorganic Chemistry 45.53; H, 4.19; N, 12.64%. Found: C, 45.68; H, 4.51; N, 12.99%. ESIMS: m/z 409.25 [Cu2(L2)]2+, 963.33 [Cu2(L2)(PF6)]+. Synthesis of Heated-1. Crystals of 1 were heated at 80 °C for 1 h in vacuum to form heated-1. 1H NMR (CD3CN, 400 MHz): δ 7.65 (d, J = 8 Hz, 4 H, bzim), 7.14−7.47 (m, 12 H, bzim), 5.51 (br, 8 H, CH2), 4.38 (br, 8 H, CH2), 3.00 (br, 10 H, CH2 and NH). Anal. Calcd for C40H42Cu2F12N10P2 ([Cu2(L1)][PF6]2): C, 44.49; H, 3.92; N, 12.97%. Found: C, 44.37; H, 4.10; N, 13.30%. ESI-MS: m/z 395.25 [Cu2(L1)]2+, 935.17 [Cu2(L1)(PF6)]+. Synthesis of Heated-2. Crystals of 2 were heated at 80 °C for 1 h in vacuum to form heated-2. 1H NMR (DMSO-d6, 400 MHz): δ 7.80 (d, J = 8 Hz, 4 H, bzim), 7.60 (d, J = 8 Hz, 4 H, bzim), 7.42 (t, J = 8 Hz, 4 H, bzim), 7.34 (t, J = 8 Hz, 4 H, bzim), 4.92 (br, 8 H, CH2), 4.44 (br, 8 H, CH2), 3.98 (br, 2 H, NH), 3.24 (br, 8 H, CH2), 2.63 (br, 4 H, CH2). Anal. Calcd for C42H46Cu2F12N10P2 ([Cu2(L2)][PF6]2): C, 45.53; H, 4.19; N, 12.64%. Found: C, 45.88; H, 3.84; N, 12.47%. ESI-MS: m/z 409.25 [Cu2(L2)]2+, 963.33 [Cu2(L2)(PF6)]+. Synthesis of 3. Heated-1 or ground-1 was recrystallized by slow vapor diffusion of diethyl ether into a methanol/acetone (1/1) solution to form 3. 1H NMR (CD3CN, 400 MHz): δ 7.65 (d, J = 8 Hz, 4 H, bzim), 7.15−7.48 (m, 12 H, bzim), 5.51 (br, 8 H, CH2), 4.38 (br, 8 H, CH2), 3.01 (br, 10 H, CH2 and NH). Anal. Calcd for C40H42Cu2F12N10P2: C, 44.49; H, 3.92; N, 12.97%. Found: C, 44.25; H, 3.78; N, 12.65%. ESI-MS: m/z 395.25 [Cu2(L1)]2+, 935.17 [Cu2(L1)(PF6)]+. Synthesis of Ground-3. Crystals of 3 were ground for 5 min, and an emission color change under UV light was observed to form ground-3. 1H NMR (CD3CN, 400 MHz): δ 7.65 (d, J = 8 Hz, 4 H, bzim), 7.13−7.48 (m, 12 H, bzim), 5.51 (br, 8 H, CH2), 4.38 (br, 8 H, CH2), 3.00 (br, 10 H, CH2 and NH). Anal. Calcd for C40H42Cu2F12N10P2: C, 44.49; H, 3.92; N, 12.97%. Found: C, 44.18; H, 4.09; N, 13.11%. ESI-MS: m/z 395.25 [Cu2(L1)]2+, 935.17 [Cu2(L1)(PF6)]+. Synthesis of 4. Heated-2 or ground-2 was recrystallized by slow vapor diffusion of diethyl ether into a purified CH3NO2 solution to form 4. 1H NMR (DMSO-d6, 400 MHz): δ 7.79 (d, J = 8 Hz, 4 H, bzim), 7.60 (d, J = 8 Hz, 4 H, bzim), 7.42 (t, J = 8 Hz, 4 H, bzim), 7.34 (t, J = 8 Hz, 4 H, bzim), 4.92 (br, 8 H, CH2), 4.45 (br, 8 H, CH2), 3.98 (br, 2 H, NH), 3.25 (br, 8 H, CH2), 2.64 (br, 4 H, CH2). Anal. Calcd for C42H46Cu2F12N10P2: C, 45.53; H, 4.19; N, 12.64%. Found: C, 45.79; H, 4.03; N, 12.38%. ESI-MS: m/z 409.25 [Cu2(L2)]2+, 963.33 [Cu2(L2)(PF6)]+. Synthesis of Ground-4. Crystals of 4 were ground for 5 min, and an emission color change under UV light was observed to form ground-4. 1H NMR (DMSO-d6, 400 MHz): δ 7.80 (d, J = 8 Hz, 4 H, bzim), 7.60 (d, J = 8 Hz, 4 H, bzim), 7.42 (t, J = 8 Hz, 4 H, bzim), 7.34 (t, J = 8 Hz, 4 H, bzim), 4.92 (br, 8 H, CH2), 4.44 (br, 8 H, CH2), 3.98 (br, 2 H, NH), 3.24 (br, 8 H, CH2), 2.63 (br, 4 H, CH2). Anal. Calcd for C42H46Cu2F12N10P2: C, 45.53; H, 4.19; N, 12.64%. Found: C, 45.33; H, 3.95; N, 12.46%. ESI-MS: m/z 409.25 [Cu2(L2)]2+, 963.33 [Cu2(L2)(PF6)]+. X-ray Crystallography. X-ray diffraction data were collected for single crystals of 1−4 on a Bruker APEX DUO diffractometer with a CCD area detector (Mo Kα radiation, λ = 0.71073 Å). The frames of data and lattice parameters were determined by the APEXII program. SAINT was used to integrate the data.23 The absorption corrections were applied using SADABS,24 and the structures were solved using SHELXS-9725 and subsequently completed via Fourier recycling using the SHELXL 97 program.26 All non-hydrogen atoms were refined with anisotropic thermal parameters, and hydrogen atoms were set at the calculated position.

■

Tables for the summary of crystal data and refinement; absorption spectra and emission spectra; powder XRD patterns; NMR spectra (PDF) Accession Codes

CCDC 1561212 and 1587082−1587084 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.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (X.-T.C.). *E-mail: [email protected] (Z.-N.C.). ORCID

Zhong-Ning Chen: 0000-0003-3589-3745 Xue-Tai Chen: 0000-0001-5518-5557 Zi-Ling Xue: 0000-0001-7401-9933 Author Contributions ∥

T.L. and J.-Y.W. contributed equally.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We are grateful for the financial support from the Natural Science Grant of China (No. 21471078 to X.-T.C., 21531008 to Z.-N.C.), and the U.S. National Science Foundation (CHE1633870 to Z.-L.X.).

■

REFERENCES

(1) For reviews: (a) Jobbágy, C.; Deák, A. Stimuli-Responsive Dynamic Gold Complexes. Eur. J. Inorg. Chem. 2014, 2014, 4434− 4449. (b) Cariati, E.; Lucenti, E.; Botta, C.; Giovanella, U.; Marinotto, D.; Righetto, S. Cu(I) Hybrid Inorganic-Organic Materials with Intriguing Stimuli Responsive and Optoelectronic Properties. Coord. Chem. Rev. 2016, 306, 566−614. (c) Kobayashi, A.; Kato, M. Stimuliresponsive Luminescent Copper(I) Complexes for Intelligent Emissive Devices. Chem. Lett. 2017, 46, 154−162. (2) For reviews: (a) Wenger, O. S. Vapochromism in Organometallic and Coordination Complexes: Chemical Sensors for Volatile Organic Compounds. Chem. Rev. 2013, 113, 3686−3733. (b) Kobayashi, A.; Kato, M. Vapochromic Platinum(II) Complexes: Crystal Engineering toward Intelligent Sensing Devices. Eur. J. Inorg. Chem. 2014, 2014, 4469−4483. (c) Zhang, X.; Li, B.; Chen, Z.-H.; Chen, Z.N. Luminescence Vapochromism in Solid Materials Based on Metal Complexes for Detection of Volatile Organic Compounds (VOCs). J. Mater. Chem. 2012, 22, 11427−11441. (d) Ford, P. C.; Cariati, E.; Bourassa, J. Photoluminescence Properties of Multinuclear Copper(I) Compounds. Chem. Rev. 1999, 99, 3625−3648. (3) (a) Sagara, Y.; Kato, T. Mechanically Induced Luminescence Changes in Molecular Assemblies. Nat. Chem. 2009, 1, 605−610. (b) Chi, Z.; Zhang, X.; Xu, B.; Zhou, X.; Ma, C.; Zhang, Y.; Liu, S.; Xu, J. Recent Advances in Organic Mechanofluorochromic Materials. Chem. Soc. Rev. 2012, 41, 3878−3896. (c) Xue, P.; Ding, J.; Wang, P.; Lu, R. Recent Progress in the Mechanochromism of Phosphorescent Organic Molecules and Metal Complexes. J. Mater. Chem. C 2016, 4, 6688−6706. (d) Sagara, Y.; Yamane, S.; Mitani, M.; Weder, C.; Kato, T. Mechanoresponsive Luminescent Molecular Assemblies: An Emerging Class of Materials. Adv. Mater. 2016, 28, 1073−1095. (e) Zhang, X.; Chi, Z.; Zhang, Y.; Liu, S.; Xu, J. Recent advances in mechanochromic luminescent metal Complexes. J. Mater. Chem. C 2013, 1, 3376−3390. (f) Balch, A. L. Dynamic Crystals: Visually Detected Mechanochemical Changes in the Luminescence of Gold

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b02217. K


Article

Inorganic Chemistry and Other Transition-Metal Complexes. Angew. Chem., Int. Ed. 2009, 48, 2641−2644. (4) (a) Zhang, X.; Wang, J.-Y.; Ni, J.; Zhang, L.-Y.; Chen, Z.-N. Vapochromic and Mechanochromic Phosphorescence Materials Based on a Platinum(II) Complex with 4-Trifluoromethylphenylacetylide. Inorg. Chem. 2012, 51, 5569−5579. (b) Ni, J.; Wang, Y.-G.; Wang, H.-H.; Xu, L.; Zhao, Y.-Q.; Pan, Y.-Z.; Zhang, J.-J. Thermoand Mechanical-Grinding-Triggered Color and Luminescence Switches of the Diimineplatinum(II) Complex with 4-Bromo-2,2’bipyridine. Dalton Trans. 2014, 43, 352−360. (5) (a) Ito, H.; Saito, T.; Oshima, N.; Kitamura, N.; Ishizaka, S.; Hinatsu, Y.; Wakeshima, M.; Kato, M.; Tsuge, K.; Sawamura, M. Reversible Mechanochromic Luminescence of [(C6F5Au)2(μ-1,4Diisocyanobenzene)]. J. Am. Chem. Soc. 2008, 130, 10044−10045. (b) Ito, H.; Muromoto, M.; Kurenuma, S.; Ishizaka, S.; Kitamura, N.; Sato, H.; Seki, T. Mechanical Stimulation and Solid Seeding Trigger Single-Crystal-to-Single-Crystal Molecular Domino Transformations. Nat. Commun. 2013, 4, 3009. (c) Jin, M.; Seki, T.; Ito, H. MechanoResponsive Luminescence via Crystal-to-Crystal Phase Transitions between Chiral and Non-Chiral Space Groups. J. Am. Chem. Soc. 2017, 139, 7452−7455. (6) (a) Perruchas, S.; Le Goff, X. F.; Maron, S.; Maurin, I.; Guillen, F. O.; Garcia, A.; Gacoin, T.; Boilot, J.-P. Mechanochromic and Thermochromic Luminescence of a Copper Iodide Cluster. J. Am. Chem. Soc. 2010, 132, 10967−10969. (b) Benito, Q.; Maurin, I.; Poggi, M.; Martineau-Corcos, C.; Gacoin, T.; Boilot, J.-P.; Perruchas, S. Impact of Crystalline Packing on the Mechanochromic Luminescence Properties of Copper Based Compounds: Towards Functional Coatings. J. Mater. Chem. C 2016, 4, 11231−11237. (c) Benito, Q.; Baptiste, B.; Polian, A.; Delbes, L.; Martinelli, L.; Gacoin, T.; Boilot, J.-P.; Perruchas, S. Pressure Control of Cuprophilic Interactions in a Luminescent Mechanochromic Copper Cluster. Inorg. Chem. 2015, 54, 9821−9925. (d) Benito, Q.; Le Goff, X. F.; Maron, S.; Fargues, A.; Garcia, A.; Martineau, C.; Taulelle, F.; Kahlal, S.; Gacoin, T.; Boilot, J.-P.; Perruchas, S. Polymorphic Copper Iodide Clusters: Insights into the Mechanochromic Luminescence Properties. J. Am. Chem. Soc. 2014, 136, 11311−11320. (e) Benito, Q.; Maurin, I.; Cheisson, T.; Nocton, G.; Fargues, A.; Garcia, A.; Martineau, C.; Gacoin, T.; Boilot, J.-P.; Perruchas, S. Mechanochromic Luminescence of Copper Iodide Clusters. Chem. - Eur. J. 2015, 21, 5892−5897. (f) Huitorel, B.; El Moll, H.; Cordier, M.; Fargues, A.; Garcia, A.; Massuyeau, F.; Martineau-Corcos, C.; Gacoin, T.; Perruchas, S. Luminescence Mechanochromism Induced by Cluster Isomerization. Inorg. Chem. 2017, 56, 12379−12388. (7) (a) Shan, X.-C.; Jiang, F.-L.; Zhang, H.-B.; Qian, X.-Y.; Chen, L.; Wu, M.-Y.; AL-Thabaiti, S. A.; Hong, M.-C. A Solid and Logic Stimuli-Responsive Material with Bright Nondestructive Performance Designed by Sensitive Cuprophilicity. Chem. Commun. 2013, 49, 10227−10229. (b) Shan, X.-C.; Zhang, H.-B.; Chen, L.; Wu, M.-Y.; Jiang, F.-L.; Hong, M.-C. Multistimuli-Responsive Luminescent Material Reversible Switching Colors via Temperature and Mechanical Force. Cryst. Growth Des. 2013, 13, 1377−1381. (c) Shan, X.-C.; Jiang, F.-L.; Chen, L.; Wu, M.-Y.; Pan, J.; Wan, X.-Y.; Hong, M.-C. Using Cuprophilicity as a Multi-Responsive Chromophore Switching Color in Response to Temperature. Mechanical Force and Solvent Vapors. J. Mater. Chem. C 2013, 1, 4339−4349. (8) (a) Deshmukh, M. S.; Yadav, A.; Pant, R.; Boomishankar, R. Thermochromic and Mechanochromic Luminescence Umpolung in Isostructural Metal−Organic Frameworks Based on Cu6I6 Clusters. Inorg. Chem. 2015, 54, 1337−1345. (b) Kwon, E.; Kim, J.; Lee, K. Y.; Kim, T. H. Non-Phase-Transition Luminescence Mechanochromism of a Copper(I) Coordination Polymer. Inorg. Chem. 2017, 56, 943− 949. (c) Yang, K.; Li, S.-L.; Zhang, F.-Q.; Zhang, X.-M. Simultaneous Luminescent Thermochromism, Vapochromism, Solvatochromism, and Mechanochromism in a C3-Symmetric Cubane [Cu4I4P4] Cluster without Cu−Cu Interaction. Inorg. Chem. 2016, 55, 7323−7325. (9) (a) Gong, F.; Wang, Q.; Chen, J.; Yang, Z.; Liu, M.; Li, S.; Yang, G.; Bai, L.; Liu, J.; Dong, Y. Exploring Intertrimer Cu···Cu Interactions and Further Phosphorescent Properties of Aryl Trimer

Copper(I) Pyrazolates via Substituent Changing and External Pressure. Inorg. Chem. 2010, 49, 1658−1666. (b) Xiao, Q.; Zheng, J.; Li, M.; Zhan, S.-Z.; Wang, J.-H.; Li, D. Mechanically Triggered Fluorescence/Phosphorescence Switching in the Excimers of Planar Trinuclear Copper(I) Pyrazolate Complexes. Inorg. Chem. 2014, 53, 11604−11615. (10) (a) Wen, T.; Zhang, D.-X.; Liu, J.; Lin, R.; Zhang, J. A Multifunctional Helical Cu(I) Coordination Polymer with Mechanochromic, Sensing and Photocatalytic Properties. Chem. Commun. 2013, 49, 5660−5662. (b) Wen, T.; Zhang, D.-X.; Zhang, H.-X.; Zhang, H.-B.; Zhang, J.; Li, D.-S. Redox-Active Cu(I) Boron Imidazolate Framework for Mechanochromic and Catalytic Applications. Chem. Commun. 2014, 50, 8754−8756. (c) Zhang, D.-X.; Zhang, H.-X.; Wen, T.; Li, D.-S.; Zhang, J. Mechanochromic Cu(I) Boron Imidazolate Frameworks with Low-Dimensional Structures and Reducing Function. Inorg. Chem. Front. 2016, 3, 263−267. (d) Wen, T.; Zhou, X.-P.; Zhang, D.-X.; Li, D. Luminescent Mechanochromic Porous Coordination Polymers. Chem. - Eur. J. 2014, 20, 644−648. (e) Hu, L.-X.; Gao, M.; Wen, T.; Kang, Y.; Chen, S. Synthesis of Halide-Modulated Cuprous(I) Coordination Polymers with Mechanochromic and Photocatalytic Properties. Inorg. Chem. 2017, 56, 6507−6511. (11) (a) Armaroli, N.; Accorsi, G.; Cardinali, F.; Listorti, A. Photochemistry and Photophysics of Coordination Compounds: Copper. Top. Curr. Chem. 2007, 280, 69−115. (b) Barbieri, A.; Accorsi, G.; Armaroli, N. Luminescent Complexes beyond the Platinum Group: the d10 Avenue. Chem. Commun. 2008, 2185− 2193. (c) McMillin, D. R.; McNett, K. M. Photoprocesses of Copper Complexes that Bind to DNA. Chem. Rev. 1998, 98, 1201−1220. (12) (a) Lazreg, F.; Nahra, F.; Cazin, C. S. J. Copper-NHC Complexes in Catalysis. Coord. Chem. Rev. 2015, 293−294, 48−79. (b) Egbert, J. D.; Cazin, C. S. J.; Nolan, S. P. Copper N-Heterocyclic Carbene Complexes in Catalysis. Catal. Sci. Technol. 2013, 3, 912− 926. (13) (a) Matsumoto, K.; Matsumoto, N.; Ishii, A.; Tsukuda, T.; Hasegawa, M.; Tsubomura, T. Structural and Spectroscopic Properties of a Copper(I)−Bis(N-heterocyclic)carbene Complex. Dalton Trans. 2009, 6795−6801. (b) Krylova, V. A.; Djurovich, P. I.; Whited, M. T.; Thompson, M. E. Synthesis and Characterization of Phosphorescent Three-Coordinate Cu(I)−NHC Complexes. Chem. Commun. 2010, 46, 6696−6698. (c) Krylova, V. A.; Djurovich, P. I.; Aronson, J. W.; Haiges, R.; Whited, M. T.; Thompson, M. E. Structural and Photophysical Studies of Phosphorescent ThreeCoordinate Copper(I) Complexes Supported by an N-Heterocyclic Carbene Ligand. Organometallics 2012, 31, 7983−7993. (d) Krylova, V. A.; Djurovich, P. I.; Conley, B. L.; Haiges, R.; Whited, M. T.; Williams, T. J.; Thompson, M. E. Control of Emission Colour with Nheterocyclic Carbene (NHC) Ligands in Phosphorescent Threecoordinate Cu(I) Complexes. Chem. Commun. 2014, 50, 7176−7179. (e) Leitl, M. J.; Krylova, V. A.; Djurovich, P. I.; Thompson, M. E.; Yersin, H. Phosphorescence versus Thermally Activated Delayed Fluorescence. Controlling Singlet−Triplet Splitting in Brightly Emitting and Sublimable Cu(I) Compounds. J. Am. Chem. Soc. 2014, 136, 16032−16038. (f) Marion, R.; Sguerra, F.; Di Meo, F.; Sauvageot, E.; Lohier, J.-F.; Daniellou, R.; Renaud, J.-L.; Linares, M.; Hamel, M.; Gaillard, S. NHC Copper(I) Complexes Bearing Dipyridylamine Ligands: Synthesis, Structural and Photoluminescent Studies. Inorg. Chem. 2014, 53, 9181−9191. (g) Lu, T.; Wang, J.-Y.; Shi, L.-X.; Chen, Z.-N.; Chen, X.-T.; Xue, Z.-L. Synthesis, Structures and Luminescence Properties of Amine-bis-(N-heterocyclic Carbene) Copper(I) and Silver(I) Complexes. Dalton Trans. 2018, 47, 6742− 6753. (h) Wang, Z.; Zheng, C.; Wang, W.; Xu, C.; Ji, B.; Zhang, X. Synthesis, Structure, and Photophysical Properties of Two FourCoordinate Cu(I)-NHC Complexes with Efficient Delayed Fluorescence. Inorg. Chem. 2016, 55, 2157−2164. (i) Nitsch, J.; Lacemon, F.; Lorbach, A.; Eichhorn, A.; Cisnetti, F.; Steffen, A. Cuprophilic Interactions in Highly Luminescent Dicopper(I)−NHC−Picolyl Complexes−Fast Phosphorescence or TADF? Chem. Commun. 2016, 52, 2932−2935. (j) Zhong, R.; Pöthig, A.; Mayer, D. C.; L


Article

Inorganic Chemistry Jandl, C.; Altmann, P. J.; Herrmann, W. A.; Kühn, F. E. Spectroscopic and Structural Properties of Bridge-Functionalized Dinuclear Coinage-Metal (Cu, Ag, and Au) NHC Complexes: A Comparative Study. Organometallics 2015, 34, 2573−2579. (k) Catalano, V. J.; Munro, L. B.; Strasser, C. E.; Samin, A. F. Modulation of Metal Separations in a Series of Ag(I) and Intensely Blue Photoluminescent Cu(I) NHCBridged Triangular Clusters. Inorg. Chem. 2011, 50, 8465−8476. (l) Nishikawa, M.; Sano, T.; Washimi, M.; Takao, K.; Tsubomura, T. Emission Properties and Cu(I)−Cu(I) Interaction in 2-Coordinate Dicopper(I)-Bis(N-heterocyclic) Carbene Complexes. Dalton Trans. 2016, 45, 12127−12136. (14) (a) Strasser, C. E.; Catalano, V. J. On-Off” Au(I)—Cu(I) Interactions in a Au(NHC)2 Luminescent Vapochromic Sensor. J. Am. Chem. Soc. 2010, 132, 10009−10011. (b) Chen, K.; Nenzel, M. M.; Brown, T. M.; Catalano, V. J. Luminescent Mechanochromism in a Gold(I)−Copper(I) N-Heterocyclic Carbene Complex. Inorg. Chem. 2015, 54, 6900−6909. (15) (a) Lu, T.; Yang, C.-F.; Zhang, L.-Y.; Fei, F.; Chen, X.-T.; Xue, Z.-L. Metal Complexes with a Hexadentate Macrocyclic DiamineTetracarbene Ligand. Inorg. Chem. 2017, 56, 11917−11928. (b) Lu, T.; Yang, C.-F.; Steren, C. A.; Fei, F.; Chen, X.-T.; Xue, Z.-L. Synthesis and Characterization of Ag(I) and Au(I) Complexes with Macrocyclic Hybrid Amine N-Heterocyclic Carbene Ligands. New J. Chem. 2018, 42, 4700−4713. (c) Fei, F.; Lu, T.; Yang, C.-F.; Chen, X.-T.; Xue, Z.-L. Synthesis, Structures, and Catalytic Properties of Dinuclear Iridium(I) Complexes with a Hexadentate Macrocyclic Diamine-Tetracarbene Ligand. Eur. J. Inorg. Chem. 2018, 2018, 1595− 1602. (16) (a) McKie, R.; Murphy, J. A.; Park, S. R.; Spicer, M. D.; Zhou, S.-Z. Homoleptic Crown N-Heterocyclic Carbene Complexes. Angew. Chem., Int. Ed. 2007, 46, 6525−6528. (b) Andrew, R. E.; Storey, C. M.; Chaplin, A. B. Well-Defined Coinage Metal Transfer Agents for the Synthesis of NHC-Based Nickel, Rhodium and Palladium Macrocycles. Dalton Trans. 2016, 45, 8937−8944. (17) Bezuidenhout, D. I.; Kleinhans, G.; Guisado-Barrios, G.; Liles, D. C.; Ung, G.; Bertrand, G. Isolation of a Potassium Bis(1,2,3-triazol5-ylidene)Carbazolide: a Stabilizing Pincer Ligand for Reactive Late Transition Metal Complexes. Chem. Commun. 2014, 50, 2431−2433. (18) (a) Liu, B.; Pan, S.; Liu, B.; Chen, W. Di, Tri, and Tetranuclear Copper(I) Complexes of Phenanthroline-Linked Dicarbene Ligands. Inorg. Chem. 2014, 53, 10485−10497. (b) Smith, J. M.; Long, J. R. First-Row Transition Metal Complexes of the Strongly Donating Pentadentate Ligand PY4Im. Inorg. Chem. 2010, 49, 11223−11230. (19) (a) Che, C.-M.; Lai, S.-W. Structural and Spectroscopic Evidence for Weak Metal−Metal Interactions and Metal−Substrate Exciplex Formations in d10 Metal Complexes. Coord. Chem. Rev. 2005, 249, 1296−1309. (b) Yam, V. W.-W.; Au, V. K.-M.; Leung, S. Y.-L. Light-Emitting Self-Assembled Materials Based on d8 and d10 Transition Metal Complexes. Chem. Rev. 2015, 115, 7589−7728. (20) Bondi, A. Van der Waals Volumes and Radii. J. Phys. Chem. 1964, 68, 441−451. (21) (a) Batsanov, S. S. Van der Waals Radii of Elements. Inorg. Mater. 2001, 37, 871−885. (b) Nag, S.; Banerjee, K.; Datta, D. Estimation of the Van der Waals Radii of the D-block Elements Using the Concept of Bond Valence. New J. Chem. 2007, 31, 832−834. (22) (a) El Sayed Moussa, M.; Evariste, S.; Wong, H.-L.; Le Bras, L.; Roiland, C.; LePolles, L.; Le Guennic, B.; Costuas, K.; Yam, V. W.-W.; Lescop, C. A Solid State Highly Emissive Cu(I) Metallacycle: Promotion of Cuprophilic Interactions at the Excited States. Chem. Commun. 2016, 52, 11370−11373. (b) Belyaev, A.; Eskelinen, T.; Dau, T. M.; Ershova, Y. Y.; Tunik, S. P.; Melnikov, A. S.; Hirva, P.; Koshevoy, I. O. Cyanide−Assembled d10 Coordination Polymers and Cycles: Excited State Metallophilic Modulation of Solid−State Luminescence. Chem. - Eur. J. 2018, 24, 1404−1415. (c) Rawashdeh-Omary, M. A.; Omary, M. A.; Patterson, H. H.; Fackler, J. P. Excited-State Interactions for [Au(CN)2−]n and [Ag(CN)2−]n Oligomers in Solution. Formation of Luminescent Gold−Gold Bonded Excimers and Exciplexes. J. Am. Chem. Soc. 2001, 123, 11237−11247. (d) Omary, M. A.; Patterson, H. H. Luminescent

Homoatomic Exciplexes in Dicyanoargentate(I) Ions Doped in Alkali Halide Crystals. 1. “Exciplex Tuning” by Site-Selective Excitation. J. Am. Chem. Soc. 1998, 120, 7696−7705. (23) SMART & SAINT Software Reference Manuals, version 6.45; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 2003. (24) Sheldrick, G. M. SADABS: Software for Empirical Absorption Correction, version 2.05; University of Gö ttingen: Gö ttingen, Germany, 2002. (25) Sheldrick, G. M. SHELXS-1997: Program for Crystal Structure Solution; University of Göttingen: Göttingen, Germany, 1997. (26) Sheldrick, G. M. SHELXL-2014: Program for Crystal Structure Refinement; University of Göttingen: Göttingen, Germany, 2014.

M


Luminescent Mechanochromic Dinuclear Cu(I) Complexes with

Recommend Documents