Rhodium(I) Complexes of Tridentate N-Donor Ligands and Their

Article pubs.acs.org/IC

Rhodium(I) Complexes of Tridentate N‑Donor Ligands and Their Supramolecular Assembly Studies Alan Kwun-Wa Chan, Di Wu, Keith Man-Chung Wong,*,† and Vivian Wing-Wah Yam* Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee, Hong Kong) and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China S Supporting Information *

ABSTRACT: New classes of tridentate N-donor rhodium(I) complexes have been synthesized and demonstrated to exhibit interesting induced self-assembly behavior by variation of external stimuli, as a result of extensive Rh(I)···Rh(I) interactions, with the assistance of π−π stacking and hydrophobic−hydrophobic interactions. An isodesmic aggregation mechanism has also been identified in the temperaturedependent process. Upon aggregation in acetone solution, the complex molecules form wire-like nanostructures with their shape dependent on the π-conjugation of the tridentate ligands. On the other hand, crystalline needles of rhodium(I) complexes obtained from recrystallization have also been shown to exhibit conductivity on the order of 10−3 S cm−1.

■

INTRODUCTION Square-planar complexes of second and third row d8 transition metal ions are well-known to exhibit noncovalent metal···metal interactions arising from the close proximity of the metal centers, imparting them with intriguing and unique optical properties. These have been utilized for the development of chemosensors, light-emitting devices, and molecular wires.1 A key factor for the successful development of such functional materials is the utilization of the metal···metal interactions with the rational design and control of the aggregation processes of monomeric complexes in a well-defined manner, especially in an anisotropic fashion2 to give one-dimensional (1D) solidstate materials, that can be readily coassembled through an interplay of different kinds of intermolecular forces and interactions. These may lead to anisotropic behavior such as conductivities, charge transport properties, optical properties, epitaxial growth, and processability in practical applications.3 Besides the well-known examples of the Magnus’s green salt [Pt(NH3)4][PtCl4]4a and the mixed-valence Krogmann’s salt,4b other square-planar platinum(II) systems with an extended linear 1D chain of short Pt(II)···Pt(II) distances1f,4f have been utilized as self-assembled 1D materials.1e,f,2c,3c However, there is relatively less attention on the use of the square-planar rhodium(I) system to provide access to such kinds of molecular functional materials5 even though reports on their rich solidstate polymorphism arising from the extensive Rh(I)···Rh(I) interactions are known in the literature.6,7 In addition, tuning of the aggregation and responsive properties of rhodium(I) complexes by the interplay of different kinds of intermolecular interactions through molecular design has been relatively under-explored.7d,e © XXXX American Chemical Society

By taking advantage of the extensive Rh(I)···Rh(I) interactions, an investigation into new classes of rhodium(I) systems with π-conjugated pincer ligands would represent an important strategy to produce effective and desirable building blocks for the molecular assembly.8,9 Interestingly, there are only two examples of [Rh(terpy)Cl]6f and [Rh(terpy)(NCMe)]+7c in the literature. However, corresponding studies on their self-assembly and aggregation properties have not been reported even though there are extensive studies on the catalytic and mechanistic aspects of other related Rh(I) pincer complexes.7f−i Given the propensity of rhodium(I) complexes with N-donors to undergo oxidative addition reaction to give the octahedral rhodium(III) system, attempts have been made to stabilize the electron-rich rhodium(I) complexes through coordination of good π-acceptor ligands such as carbonyl. In addition, the nonsterically demanding carbonyl ligand is essential to facilitate the self-assembly of the complex molecules to constitute multifunctional materials. Except for a few studies on Rh(I) isocyanides,7d,e the study of aggregation and supramolecular assembly behavior involving the assembly and growth mechanism on systems directed by metal···metal interactions is rare. The strategy of induced self-assembly has been applied to the current system to demonstrate diverse and enhanced aggregation behaviors, given its higher propensity in exhibiting Rh(I)···Rh(I) interactions compared to the isoelectronic platinum(II) system; this is especially true of the Rh(I) system where oligomers other than dimers are observable in the solution state.6,7 In this work, we report the design and Received: February 2, 2016

A

DOI: 10.1021/acs.inorgchem.6b00289 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 1. Molecular structures of complexes 1−3.

synthesis of tridentate N-donor rhodium(I) carbonyl complexes 1−3 (Figure 1) comprising pincer ligands of different πconjugation and hydrophobicity to realize the versatility of molecular structures toward self-assembly and their applications in conductive molecular wires.

■

RESULTS AND DISCUSSION Synthesis and Characterization. 2,2′-(4-Butoxypyridine2,6-diyl)bis(1-butyl-1H-benzo[d]imidazole) (nOBu-Bzimp)8e,f and 2,6-bis(1-alkyl-1H-1,2,3-triazol-4-yl)pyridine (Bu-Triazole)8g tridentate N-donor ligands have been prepared according to the literature procedures. The tridentate N-donor rhodium(I) complexes have been synthesized by reacting [Rh(CO)2Cl]2 with silver trifluoromethanesulfonate (triflate) in the presence of 2 equiv of tridentate N-donor ligands in tetrahydrofuran. The identities of the newly synthesized squareplanar rhodium(I) complexes have been confirmed by 1H NMR, positive FAB mass spectrometry, and satisfactory elemental analysis. One of the rhodium(I) complexes has also been structurally characterized by X-ray crystallography with the illustration of the linearly stacked chainlike structure. Figure 1 shows the chemical structures of cationic rhodium(I) complexes 1−3 with trifluoromethanesulfonate (triflate) as the counteranion. X-ray Crystal Structures. A single crystal of complex 1 has been obtained by slow cooling of a concentrated acetonitrile solution of the complex, and the structure has been determined by X-ray crystallography. Crystal structure determination data are summarized in Table S1a, whereas the selected bond lengths and bond angles are tabulated in Table S1b in the Supporting Information. Similar to the other square-planar rhodium(I) complexes,2,3 complex cations of 1 adopt a slightly distorted square-planar geometry with the rhodium(I) metal centers connected by extensive Rh(I)···Rh(I) interactions (Figure 2 and Figure S1). The crystal packing of the complex shows a head-to-tail stacking between pairs of complex molecules and the N−Rh−N angles (N1−Rh1−N2 79.0°, N1−Rh1−N3 158.4°; N4−Rh2−N5 79.3°, N4−Rh2−N6 158.3°) are found to deviate from the ideal values of 90° and 180°, respectively, due to the bite angle of the terpyridine ligand (Table S1). The bond lengths of Rh1−N1, Rh1−N2, Rh1−N3, and Rh1−C16 are 2.059, 1.983, 2.036 and 1.837 Å, respectively, which are similar to that reported in the related bidentate complexes.7a,8d The rhodium(I) complex molecules are aligned in a zigzag arrangement to constitute an infinite 1D chain with short Rh···Rh distances of 3.323−3.349 Å (Figure 2). The rhodium(I) molecular chain [Rh]n with a Rh−Rh−Rh angle of 160.1° is found to deviate from the ideal 180° of a linear chain. The interplanar distance between the two pyridine rings in the terpyridine ligand in two adjacent molecules is found to be 3.299 Å, indicative of the presence of π−π interaction to facilitate the intermolecular interactions in the

Figure 2. Crystal packing diagrams showing (a) the head-to-tail configuration, (b) the linear chain structure of complex cations of 1 with the dotted line showing the short Rh···Rh contacts.

rhodium chain. It is also observed that the tridentate N-donor ligand, rhodium center, and the carbonyl ligand (N1−N2− N3−Rh1−C16) within each molecule are all lying on the same plane without any distortion to produce the ideal planar molecular structure. Concentration-Dependent Aggregation Studies. Inspired by the extensive Rh(I)···Rh(I) interactions in the wellaligned rhodium chain, concentration-dependent and temperature-dependent UV−vis absorption studies of the rhodium(I) complexes in acetone have, therefore, been performed to explore their self-assembly behavior in solution state. Dilute solutions of 1−3 in acetone at a concentration of 5 × 10−5 M were prepared, and they are found to exhibit intraligand absorptions at 320−370 nm, as well as a moderately intense metal-to-ligand charge transfer (MLCT) [dπ(Rh) → π*(N^N^N)] transition at 430−520 nm (Figure S2 and Table 1), typical of the monomeric species. Emission bands at 542− 665 nm are observed in degassed acetone solutions and are suggested to be originated from the 3MLCT [dπ(Rh) → π*(N^N^N)] excited state. Upon increasing the concentration from 1 × 10−5 to 2 × 10−3 M, the complexes illustrate drastic color changes from yellow to purple or brown. The growth of an absorption shoulder at 560−589 nm and a broad absorption band at 740−880 nm are both found to deviate from Beer’s law (Figure 3). Dimerization plots based on a monomer−dimer equilibrium6d,10a give linear relationships of [Rh]/(A580)1/2 B

DOI: 10.1021/acs.inorgchem.6b00289 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Table 2. Association Constants (log K) of Complexes 1−3

Table 1. Photophysical Data for Rhodium(I) Complexes 1− 3 electronic absorption λmax/nm (ε/dm3 mol−1 cm−1) complex

medium (T/K)

1

acetone (298)a

2

solid (298)b solid (77)b glass (77)c acetone (298)a

3

solid (298)b solid (77)b glass (77)c acetone (298)a solid (298)b solid (77)b glass (77)c

340 (17 660), 354 (18 480), 378 sh (2560), 485 (1220), 516 (1240), 579 sh (360)

366 (21 650), 420 sh (2700), 519 sh (1190), 588 sh (480)

328 (22 310), 358 sh (4280), 435 (2550), 458 (2750), 498 (1250), 580 sh (1110)

emission λem/nm 642d

complex

log Kda,b

log Kta,c

log Kad

1 2 3

4.00 5.11 3.68

2.66 3.79 3.18

2.83 2.77 2.69

a

Association constants are determined in the concentration range of 5 × 10−5 to 2 × 10−3 M in acetone solution from UV−vis absorption studies. bDimerization constant determined from dimerization plot of the monomer−dimer equilibrium. cTrimerization constant determined from trimerization plot of the dimer−trimer equilibrium. dAssociation constant determined from 1H NMR titration studies in the concentration range of 2 × 10−4 to 2 × 10−2 M in CD3CN solution.

473 472 476 665d 477 476 494 542d

high tendency toward self-aggregation through the Rh(I)··· Rh(I) interactions, with the assistance of π−π stacking between the π-conjugated pincer ligand and hydrophobic−hydrophobic interactions between the alkyl chains.7e The trimerization plot based on the dimer−trimer equilibrium has also been established for the broad absorption at 740−880 nm. A linear relationship of A850 versus (A550)3/2 has been obtained, supporting its assignment as the absorption of the trimeric species, {[Rh(N^N^N)CO]}33+. Concentration-dependent 1H NMR studies have also been carried out to investigate the aggregation behavior (Figure 4 and Figure S4). By increasing the complex concentration in CD3CN, upfield shifts and broadening of the signals have been observed, indicating the existence of π−π interactions upon aggregation. Although a direct comparison cannot be made, the trend of the dimerization constants of 1−3 (Table 2) is found to be in line with that obtained from the UV−vis absorption studies. The trend is in accordance with the extent of the πconjugation and the hydrophobicity of the complex system, again suggesting that π−π stacking and hydrophobic−hydrophobic interactions would assist the molecular assembly. 2D 1 H−1H NOESY NMR studies have been performed to provide a more thorough understanding of the association mode of the rhodium(I) complexes. Plausible association modes of 1 and 2 in CD3CN solution at the concentration of 10−4 M have been proposed with respect to the NOE cross peaks, again indicating the presence of π−π interactions between pincer ligands (Figures S5 and S6). The diffusion coefficients of the rhodium(I) complexes (Figure S7) are determined from diffusion ordered NMR spectroscopy (DOSY), and the corresponding hydrodynamic radii, Rh, are found to be in the order of 2 (8.0 Å) > 1 (7.8 Å) > 3 (6.5 Å) according to the Stokes−Einstein equation,10b indicating that 2 has a larger propensity toward aggregation. Interestingly, two sets of proton signals with different diffusion coefficients have been observed in the concentrated CD3CN solution of 3 and the one with the more negative log diffusion coefficient can be attributed to oligomers, as revealed from a systematic comparison of the DOSY spectra for the concentrated and dilute sample solutions. Temperature-Dependent Aggregation Studies. Temperature-dependent UV−vis absorption studies have also been performed (Figure 3 and Figure S8). Upon lowering the temperature from 293 to 183 K, a significant increase in the absorption of the trimers (1 at 803 nm, 2 at 740 nm, and 3 at 883 nm) with a decrease in the monomer and dimer absorptions has been observed. The plot of the degree of aggregation at the absorption maximum as a function of temperature displays a well-defined sigmoidal curve. The absorption data have been fitted to the temperature-dependent

470 470 469

a Measured at concentration from 1 × 10−5 to 1 × 10−4 M. bSolid-state emission was recorded after grinding. cIn butyronitrile glass. d Luminescence quantum yield is too weak to be measured with certainty.

Figure 3. UV−vis spectra of 2 (a) from 1 × 10−5 to 2 × 10−3 M in acetone at 298 K. The apparent absorbance values have been obtained by correcting to 1 cm path length equivalence; (b) in 4 × 10−4 M from 343 to 183 K in acetone. Insets: The dimerization plot for monomer− dimer equilibrium and the plot monitored at the absorption wavelength of the trimeric species against temperature and fitted to the isodesmic model.

versus (A580)1/2, suggesting that the absorption shoulders originate from the dimeric [dσ*(Rh2) → π*(N^N^N)] transition of {[Rh(N^N^N)CO]}22+. The dimerization constants are in the order of 2 > 1 > 3 (Table 2) with their magnitudes relatively higher than those reported for other related square-planar rhodium(I)6d,e and platinum(II) complexes.10a These observations suggest that the complexes have a C

DOI: 10.1021/acs.inorgchem.6b00289 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 4. 1H NMR spectra of 2 upon increasing the concentration in CD3CN at 298 K (left). The corresponding plot of chemical shift against the concentration fitted with the self-association model of monomer−dimer equilibrium (right).

Table 3. Thermodynamic Parameters for the Temperature-Induced Aggregation Process of Complexes 1−3 complex

ΔH/kJ mol−1

ΔS/J mol−1 K−1

TΔS/kJ mol−1

ΔG/kJ mol−1

melting temp/K

1

−56.52 −44.92b −32.97a −32.32b

−170.98

−50.95

−5.57a

251b

−74.88a

−22.31a

−10.66a

252b

c

c

c

c

c

2 3

a

−45.64

a

a

b

207b

Determined by van’t Hoff plot from UV−vis absorption studies at different temperatures. Determined from curve fitting by applying the temperature-dependent nucleation−elongation model with monitoring of the absorption band of trimers at different temperatures. cA linear plot cannot be obtained. a

b

nucleation−elongation model,11 confirming that the cooling process is isodesmic in nature. The ΔH values (Table 3) are in the trend of 3 (−45.64 kJ mol−1) < 1 (−44.92 kJ mol−1) < 2 (−32.32 kJ mol−1), indicating that a more planar and less sterically bulky framework may render temperature-induced aggregation more favorable, which is different from the observation of the concentration-dependent aggregation process. A linear relationship has been obtained using the van’t Hoff analysis (Figure S9) by plotting the logarithm of the equilibrium constant (Ke) of aggregation against the reciprocal of temperature (1/T) to give the enthalpy (ΔH), the entropy (ΔS), and the Gibbs free energy (ΔG) of 1 and 2, providing further insights into the aggregation affinity (Table 3). The temperature-dependent 1H NMR spectra of complex 2 from 300 to 263 K are obtained and illustrate upfield shifts of proton resonance signals, suggesting the involvement of intermolecular π−π stacking interactions in addition to the Rh(I)···Rh(I) interactions in the aggregation upon cooling (Figure S10). Morphological Studies. Encouraged by the drastic changes in the photophysical properties upon aggregation, attempts have been made to explore the morphology of the assembling architectures. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have been used to probe the supramolecular self-assembly and, more importantly, to rationalize the criteria and principles for such formation. The rhodium(I) complexes are found to exhibit interesting self-assembled wire-like nanostructures when dispersed in acetone solution at the concentration of 2 × 10−4 M. The diameters of the wire-like nanostructures are found to be 100−200 nm with the corresponding lengths in 1− 2 μm (Figure 5 and Figure S11). Interestingly, the linear morphology is in line with the anisotropic linear assembly of the complexes, as revealed by the extensive Rh(I)···Rh(I) interactions in the X-ray crystal structure, similar to that of other square-planar rhodium(I) systems.5a,7a The TEM images

Figure 5. TEM images showing the wire-like nanostructures formation upon dispersion of (a) 1, (b) 2, and (c) 3 in acetone solution.

D

DOI: 10.1021/acs.inorgchem.6b00289 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

isodesmic aggregation mechanism in the temperature-dependent process has been identified upon analyzing the spectroscopic data using the aggregation model. The morphologies of the complexes have also been visualized by TEM and SEM, with the complex molecules found to aggregate to form 1D wire-like nanostructures with their shapes affected by the extent of π−π stacking interactions and hence the substitution patterns of the tridentate ligands. The needle-shaped crystals of the rhodium(I) complexes are also found to be conductive with charge transport via the extensive Rh(I)···Rh(I) interactions. The present studies have provided the fundamental understanding of noncovalent metal···metal interactions and their self-assembly, which may lead to the design of smart and multifunctional molecular materials.

of complexes 1 and 2 with the more conjugated N^N^N ligand display rigid wire-like nanostructures with a more regular shape while that of complex 3 just gives rise to nanostructures that are thinner and with a larger curvature. This may imply that the π−π stacking interactions may play a role in the assembly process to regulate the regular structures. Conductivity Studies. The well-aligned wire-like nanostructures of the complexes have been chosen for electrical conductivity studies. A crystalline needle of the rhodium(I) complexes can be slowly formed by cooling a hot acetonitrile solution of complex 1, and the crystal is oriented across the 200 μm channel of prefabricated gold electrodes. The device shows a current of 15 nA upon applying a + 30 and −30 V bias voltage, respectively. The I−V profile upon scanning the bias voltage exhibits a near linear Ohmic relationship with a very slight deviation (Figure 6). The conductivity of the aligned 1D

■

EXPERIMENTAL SECTION

Materials and Reagents. [Rh(CO)2Cl]2 was purchased from Strem Chemicals. 2,6-Dibromopyridine and chelidamic acid were obtained from AK Scientific. 1-Bromobutane and o-phenylenediamine were obtained from Alfa Aeser. 2,2′:6′,2″-Terpyridine was obtained from GFS Chemicals. All solvents were purified and distilled by using standard procedures before use. All other reagents were of analytical grade and were used as received. The syntheses of the complexes were under inert atmosphere and anhydrous condition. Synthesis. Figure 6. (a) Devices with gold electrodes coated and deposited on the silicon wafer, with aluminum oxide embedded in the silicon wafer (left); a bundle of aligned Rh needles of 1 bridging two gold electrodes with a channel length of 200 μm (right). (b) I−V profiles of the aligned Rh needles.

Complex 1. Silver triflate (28 mg, 109 μmol) was added to [Rh(CO)2Cl]2 (20 mg, 51 μmol) in degassed tetrahydrofuran (20 mL). The mixture was allowed to stir for 15 min at room temperature, and then the filtrate was transferred in a dropwise fashion to a solution of 2,2′:6′,2″-terpyridine (24 mg, 103 μmol) in tetrahydrofuran (20 mL). The resulting solution was allowed to stir for 4 h at room temperature, after which, the precipitate was filtered and washed with multiple portions of tetrahydrofuran (20 mL) to give 1 as a deep purple solid (50 mg, 97 μmol, 94%). Subsequent recrystallization by the slow cooling of a concentrated acetonitrile solution of 1 gave 1 as deep purple microcrystals. 1H NMR (400 MHz, CD3CN, 298 K, relative to Me4Si)/ppm: δ 7.41 (t, J = 7.4 Hz, 2 H, Hb), 7.95 (m, 2 H, Hd), 8.00 (m, 2 H, He), 8.08 (t, J = 7.4 Hz, 2 H, Hc), 8.14 (t, J = 7.7 Hz, 1 H, Hf), 8.32 (d, J = 7.4 Hz, 2 H, Ha). IR (KBr disk): v = 1990 cm−1 (v(CO)), v = 1160 cm−1 (v(SO)). MS (positive FAB): m/ z: 364 [M − OTf]+, 336 [M − OTf − CO]+. Elemental analyses calcd for C17H12F3N3O4.5RhS (1·0.5H2O), found (calcd): C, 38.90 (39.10); H, 2.23 (2.32); N, 8.45 (8.05).

rhodium(I) complex has been estimated to be on the order of 10−3 S cm−1 with a cross-sectional area determined to be about 10−8 cm2 from the microscopic studies. The electrical conductivity found in the current system is comparable to that recorded (10−3 S cm−1) in both single crystal forms and solution-processable samples of tetrakis(isocyano)rhodium(I) complexes5c and several orders of magnitude higher than those recorded (10−11 S cm−1) of related systems in the powder form.12 For the other 1D conducting systems, such as those of Fe, Co, Ni, Cu, Zn, and Pt phthalocyanines, the conductivities have been found to range from 10−1 to 10 S cm−1,12c while the Krogmann’s salt has been reported to exhibit a conductivity of about 300 S cm−1 at room temperature.12d It is suggested that the extensive Rh(I)···Rh(I) interactions with staggered molecular conformations that bring the metal centers into close separation (3.3 Å), together with the crystalline ordered structure, could maximize the electronic delocalization and hence the conductivity of the rhodium needles of 1.12 On the contrary, complex 2 exhibits relatively lower conductivity, and the needles are no longer stable and may be broken down when the applied voltage is above ±15 V. Conductivity studies have not been performed for complex 3, which only exists in powder form rather than crystalline needles, precluding its anisotropic I−V measurement.

■

Complex 2. The compound was prepared according to the procedure described for complex 1, except 2,2′-(4-butoxypyridine-2,6diyl)bis(1-butyl-1H-benzo[d]imidazole) (nOBu-Bzimp) (52 mg, 105 μmol) was used in place of 2,2′:6′,2″-terpyridine to give complex 2 as a dark green solid (70 mg, 90 μmol, 88%). 1H NMR (400 MHz, CD3CN, 298 K, relative to Me4Si)/ppm: δ 0.95 (t, J = 7.3 Hz, 6 H, Hi), 1.09 (t, J = 7.3 Hz, 3 H, Hm), 1.41 (m, 4 H, Hh), 1.65 (m, 2 H, Hl), 1.82 (m, 4 H, −Hg), 1.94 (m, 2 H, Hk), 4.37 (t, J = 7.3 Hz, 4 H,

CONCLUSIONS In summary, we have demonstrated the induced self-assembly behavior of a new series of rhodium(I) complexes of tridentate N-donor pincer ligands by variation of concentration and temperature as a result of the extensive Rh(I)···Rh(I), π−π stacking, and hydrophobic−hydrophobic interactions. An E

DOI: 10.1021/acs.inorgchem.6b00289 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

measured by dispersing a sample onto a SiO2 substrate film with Au conductive film as electrodes. The channel length in between the electrodes is 200 μm. A bundle of needles was fished out from the acetone dispersion of complexes and oriented across the gold electrodes. The devices were dried in air for hours. The current− voltage (I−V) characteristics were then measured by an Agilent 4155C Semiconductor Parameter Analyzer at the KEITHLEY Semiconductor Characterization System.

Hf), 4.42 (t, J = 7.3 Hz, 2 H, Hj), 7.09 (d, J = 7.9 Hz, 2 H, He), 7.40 (s, 2 H, Ha), 7.42 (m, 4 H, Hb and Hd), 7.50 (m, 2 H, Hc). IR (KBr disk): v = 1960 cm−1 (v(CO)), v = 1160 cm−1 (v(SO)). MS (positive FAB): m/z: 626 [M − OTf]+, 598 [M − OTf − CO]+. Elemental analyses calcd for C34H39Cl2F3N5O5RhS (2·CH2Cl2), found (calcd): C, 47.86 (47.45); H, 4.39 (4.57); N, 8.34 (8.14).

■

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00289. Crystal and structure determination data (CCDC 1437971); photophysical data; concentration-dependent UV−vis absorption data and their corresponding dimerization plot for monomer−dimer equilibrium; temperature-dependent UV−vis absorption data and curve-fitting by the temperature-dependent supramolecular aggregation model and van’t Hoff analysis; temperature-dependent 1H NMR data; and diffusion order NMR data (PDF) Crystallographic data for 1 (CIF)

Complex 3. The compound was prepared according to the procedure described for complex 1, except 2,6-bis(1-alkyl-1H-1,2,3triazol-4-yl)pyridine (34 mg, 104 μmol) (Bu-Triazole) was used in place of 2,2′:6′,2″-terpyridine to give complex 3 as a greenish yellow solid (60 mg, 98 μmol, 96%). 1H NMR (400 MHz, CD3CN, 298 K, relative to Me4Si)/ppm: δ 0.97 (t, J = 7.2 Hz, 6 H, Hg), 1.39 (m, 4 H, Hf), 1.92 (m, 4 H, He), 4.46 (t, J = 7.2 Hz, 4 H, Hd), 7.76 (d, J = 7.6 Hz, 2 H, Hb), 8.15 (t, J = 7.6 Hz, 1 H, Hc), 8.45 (s, 2 H, Ha). IR (KBr disk): v = 2030 cm−1 (v(CO)), v = 1150 cm−1 (v(SO)). MS (positive FAB): m/z: 456 [M − OTf]+, 428 [M − OTf − CO]+. Elemental analyses calcd for C20H25Cl2F3N7O4RhS (2·CH2Cl2), found (calcd): C, 34.24 (34.80); H, 3.65 (3.65); N, 14.49 (14.20). Physical Measurements and Instrumentation. 1H NMR spectra were recorded on a Bruker DPX-300 (300 MHz) or Bruker DPX-400 (400 MHz) Fourier transform NMR spectrometer with chemical shifts recorded relative to tetramethylsilane (Me4Si). Positive FAB mass spectra were recorded on a Thermo Scientific DFS high resolution magnetic sector mass spectrometer. IR spectra were obtained as KBr disks on a Bio-Rad FTS-7 FTIR spectrometer (4000−400 cm−1). Elemental analyses of the newly synthesized complexes were performed on a Flash EA 1112 elemental analyzer at the Institute of Chemistry, Chinese Academy of Sciences. The electronic absorption spectra were obtained by using a Varian Cary 50 UV−vis spectrophotometer. The concentrations of solution samples for electronic absorption measurements were typically in the range of 1 × 10−6 to 2 × 10−4 mol dm−3. Steady-state excitation and emission spectra were recorded at room temperature and at 77 K on a Spex Fluorolog-3 model FL3-211 fluorescence spectrofluorometer equipped with an R2658P PMT detector. Solid-state photophysical studies were carried out with solid samples contained in a quartz tube inside a quartz-walled Dewar flask. Measurements of the butyronitrile glass or solid-state sample at 77 K were similarly conducted with liquid nitrogen filled into the optical Dewar flask. The concentrations of complex solutions in butyronitrile for glass emission measurements were usually in the range of 10−6 mol dm−3. All solutions for photophysical studies were degassed on a high-vacuum line in a twocompartment cell consisting of a 10 mL Pyrex bulb and a 1 cm path length quartz cuvette and sealed from the atmosphere by a Bibby Rotaflo HP6 Teflon stopper. The solutions were rigorously degassed with at least four successive freeze−pump−thaw cycles. Emission lifetime measurements were performed by using a conventional laser system. The concentrations of the complexes in solution for lifetime measurements were usually about 2 × 10−5 mol dm−3. The excitation source used was a 355 nm output (third harmonic) of a SpectraPhysics Quanta-Ray Q-switched GCR-150-10 pulsed Nd-YAG laser. Luminescence decay signals were detected by a Hamamatsu R928 PMT and recorded on a Tektronix Model TDS-620A (500 MHz, 2GS/s) digital oscilloscope and analyzed by using a program for exponential fits. TEM experiments were performed on a Philips CM100 transmission electron microscope. They were conducted at the Electron Microscope Unit of The University of Hong Kong. The samples were prepared by dropping a few drops of solutions onto a carbon-coated copper grid. Slow evaporation of solvents in air for 10 min was allowed before placing the samples into the instrument. The charge-transporting property of the crystalline rhodium(I) needles was

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Present Address †

Department of Chemistry, South University of Science and Technology of China, No. 1088, Tangchang Boulevard, Nanshan District, Shenzhen, Guangdong, P. R. China. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS V.W.-W.Y. acknowledges support from The University of Hong Kong and the URC Strategic Research Theme on New Materials. This work has been supported by the University Grants Committee Areas of Excellence Scheme (AoE/P-03/ 08) and a General Research Fund (GRF) grant from the Research Grants Council of Hong Kong Special Adminstrative Region, P. R. China (HKU 17304715). A.K.-W.C. acknowledges the receipt of a Hong Kong Ph.D. Fellowship and a Hung Hing Ying Scholarship, administered by the Research Grants Council and The University of Hong Kong, respectively. Dr. Vonika Ka-Man Au is gratefully acknowledged for her helpful discussions. Mr. Liaoyuan Yao is sincerely acknowledged for mounting the crystals for structural determination and solving the X-ray crystal structure.

■

REFERENCES

(1) (a) Liu, I. P.-C.; Wang, W.-Z.; Peng, S.-M. Chem. Commun. 2009, 4323. (b) Pyykkö, P. Chem. Rev. 1997, 97, 597. (c) Hui, J. K. H.; MacLachlan, M. J. Coord. Chem. Rev. 2010, 254, 2363. (d) Guo, Y.; Xu, L.; Liu, H.; Li, Y.; Che, C.-M.; Li, Y. Adv. Mater. 2015, 27, 985. (e) Lanigan, N.; Wang, X. Chem. Commun. 2013, 49, 8133. (f) Yuen, M.-Y.; Roy, V. A. L.; Lu, W.; Kui, S. C. F.; Tong, G. S. M.; So, M.-H.; Chui, S. S.-Y.; Muccini, M.; Ning, J. Q.; Xu, S. J.; Che, C.-M. Angew. Chem., Int. Ed. 2008, 47, 9895. (g) Xiao, J.; Yin, Z.; Wu, Y.; Guo, J.; Cheng, Y.; Li, H.; Huang, Y.; Zhang, Q.; Ma, J.; Boey, F.; Zhang, H.; F

DOI: 10.1021/acs.inorgchem.6b00289 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Zhang, Q. Small 2011, 7, 1242. (h) He, X.; Yam, V. W.-W. Coord. Chem. Rev. 2011, 255, 2111. (2) (a) Takezawa, Y.; Shionoya, M. Acc. Chem. Res. 2012, 45, 2066. (b) Lu, X.; Yavuz, M. S.; Tuan, H.-Y.; Korgel, B. A.; Xia, Y. J. Am. Chem. Soc. 2008, 130, 8900. (c) Sun, Y.; Ye, K.; Zhang, H.; Zhang, J.; Zhao, L.; Li, B.; Yang, G.; Yang, B.; Wang, Y.; Lai, S.-W.; Che, C.-M. Angew. Chem., Int. Ed. 2006, 45, 5610. (d) Li, Y.; Li, X.; Li, Y.; Liu, H.; Wang, S.; Gan, H.; Li, J.; Wang, N.; He, X.; Zhu, D. Angew. Chem., Int. Ed. 2006, 45, 3639. (e) Tsuda, A.; Nagamine, Y.; Watanabe, R.; Nagatani, Y.; Ishii, N.; Aida, T. Nat. Chem. 2010, 2, 977. (f) Lu, W.; Chui, S. S.-Y.; Ng, K.-M.; Che, C.-M. Angew. Chem. 2008, 120, 4644. (3) (a) Okamoto, H.; Yamashita, M. Bull. Chem. Soc. Jpn. 1998, 71, 2023. (b) Palmer, L. C.; Stupp, S. I. Acc. Chem. Res. 2008, 41, 1674. (c) Lu, W.; Chen, Y.; Roy, V. A.-L.; Chui, S. S.-Y.; Che, C.-M. Angew. Chem., Int. Ed. 2009, 48, 7621. (d) Rawashdeh-Omary, M. A.; Lopezde-Luzuriaga, J. M.; Rashdan, M. D.; Elbjeirami, O.; Monge, M.; Rodriguez-Castillo, M.; Laguna, A. J. Am. Chem. Soc. 2009, 131, 3824. (e) Liu, H.; Zhao, Q.; Li, Y.; Liu, Y.; Lu, F.; Zhuang, J.; Wang, S.; Jiang, L.; Zhu, D.; Yu, D.; Chi, L. J. Am. Chem. Soc. 2005, 127, 1120. (4) (a) Magnus, G. Poggendorff's Ann. Phys. 1828, 14, 239. (b) Krogmann, K. Angew. Chem., Int. Ed. Engl. 1969, 8, 35. (c) Chan, C.-W.; Lai, T.-F.; Che, C.-M.; Peng, S.-M. J. Am. Chem. Soc. 1993, 115, 11245. (d) Bailey, J. A.; Hill, M. G.; Marsh, R. E.; Miskowski, V. M.; Schaefer, W. P.; Gray, H. B. Inorg. Chem. 1995, 34, 4591. (e) Yam, V. W.-W.; Wong, K. M.-C.; Zhu, N. J. Am. Chem. Soc. 2002, 124, 6506. (f) Wong, K. M.-C.; Yam, V. W.-W. Acc. Chem. Res. 2011, 44, 424. (5) (a) Jang, K.; Jung, G. I.; Nam, H. J.; Jung, D.-Y.; Son, S. U. J. Am. Chem. Soc. 2009, 131, 12046. (b) Prater, M. E.; Pence, L. E.; Clerac, R.; Finniss, G. M.; Campana, C.; Auban-Senzier, P.; Jerome, D.; Canadell, E.; Dunbar, K. R. J. Am. Chem. Soc. 1999, 121, 8005. (c) Chen, Y.; Li, K.; Lloyd, H. O.; Lu, W.; Chui, S. S.-Y.; Che, C.-M. Angew. Chem., Int. Ed. 2010, 49, 9968. (6) (a) Mann, K. R.; Thich, J. A.; Bell, R. A.; Coyle, C. L.; Gray, H. B. Inorg. Chem. 1980, 19, 2462. (b) Balch, A. L. J. Am. Chem. Soc. 1976, 98, 8049. (c) Stace, J. J.; Lambert, K. D.; Krause, J. A.; Connick, W. B. Inorg. Chem. 2006, 45, 9123. (d) Mann, K. R.; Lewis, N. S.; Williams, R. M.; Gray, H. B.; Gordon, J. G. Inorg. Chem. 1978, 17, 828. (e) Mann, K. R.; Gordon, J. C.; Gray, H. B. J. Am. Chem. Soc. 1975, 97, 3553. (f) De Pater, B. C.; Fruhauf, H.-W.; Vrieze, K.; De Gelder, R.; Baerends, E. J.; McCormack, D.; Lutz, M.; Spek, A. L.; Hartl, F. Eur. J. Inorg. Chem. 2004, 2004, 1675. (7) (a) Jakonen, M.; Oresmaa, L.; Haukka, M. Cryst. Growth Des. 2007, 7, 2620. (b) Lo, L. T.-L.; Chu, W.-K.; Tam, C.-Y.; Yiu, S.-M.; Ko, C.-C.; Chiu, S.-K. Organometallics 2011, 30, 5873. (c) Inoki, D.; Matsumoto, T.; Nakai, H.; Ogo, S. Organometallics 2012, 31, 2996. (d) Wong, K. M.-C.; Au, V. K. M.; Yam, V. W.-W. Comprehensive Inorganic Chemistry II: From Elements to Applications 2013, 8, 59. (e) Chan, A. K.-W.; Wong, K. M.-C.; Yam, V. W.-W. J. Am. Chem. Soc. 2015, 137, 6920. (f) Wilson, J. M.; Sunley, G. J.; Adams, H.; Haynes, A. J. Organomet. Chem. 2005, 690, 6089. (g) Konrad, F.; Fillol, J. L.; Wadepohl, H.; Gade, L. H. Inorg. Chem. 2009, 48, 8523. (h) Barthes, C.; Lepetit, C.; Canac, Y.; Duhayon, C.; Zargarian, D.; Chauvin, R. Inorg. Chem. 2013, 52, 48. (i) Huang, K.-W.; Grills, D. C.; Han, J. H.; Szalda, D. J.; Fujita, E. Inorg. Chim. Acta 2008, 361, 3327. (8) (a) Constable, E. C. Adv. Inorg. Chem. 1986, 30, 69. (b) Constable, E. C. Prog. Inorg. Chem. 1994, 42, 67. (c) Marcec, R. React. Kinet. Catal. Lett. 1986, 31, 337. (d) Guisado-Barrios, G.; Bouffard, J.; Donnadieu, B.; Bertrand, G. Organometallics 2011, 30, 6017. (e) Froidevaux, P.; Harrowfield, J. M.; Sobolev, A. N. Inorg. Chem. 2000, 39, 4678. (f) Wang, K.; Haga, M. A.; Monjushiro, H.; Akiba, M.; Sasaki, Y. Inorg. Chem. 2000, 39, 4022. (g) Li, Y.; Huffman, J. C.; Flood, A. H. Chem. Commun. 2007, 2692. (9) (a) Yu, S. C.; Hou, S.; Chan, W. K. Macromolecules 1999, 32, 5251. (b) Haga, M. A.; Hong, H. G.; Shiozawa, Y.; Kawata, Y.; Monjushiro, H.; Fukuo, T.; Arakawa, R. Inorg. Chem. 2000, 39, 4566. (10) (a) Wong, K. M.-C.; Zhu, N.; Yam, V. W.-W. Chem. Commun. 2006, 3441. (b) Edward, J. T. J. Chem. Educ. 1970, 47, 261.

(11) (a) Smulders, M. M. J.; Nieuwenhuizen, M. M. L.; de Greef, T. F. A.; van der Schoot, P.; Schenning, A. P. H. J.; Meijer, E. W. Chem. Eur. J. 2010, 16, 362. (b) Korevaar, P. A.; Schaefer, C.; de Greef, T. F. A.; Meijer, E. W. J. Am. Chem. Soc. 2012, 134, 13482. (12) (a) Gordon, J. G., II; Williams, R.; Hsu, C.-H.; Cuellar, E.; Samson, S.; Mann, K.; Gray, H. B.; Hadek, V.; Somoano, R. Ann. N. Y. Acad. Sci. 1978, 313, 580. (b) Mitsumi, M.; Goto, H.; Umebayashi, S.; Ozawa, Y.; Kobayashi, M.; Yokoyama, T.; Tanaka, H.; Kuroda, S.; Toriumi, K. Angew. Chem., Int. Ed. 2005, 44, 4164. (c) Pelletier, S. W.; Mody, N. V. J. Am. Chem. Soc. 1977, 99, 284. (d) Zeller, H. R.; Beck, A. J. Phys. Chem. Solids 1974, 35, 77.

G

DOI: 10.1021/acs.inorgchem.6b00289 Inorg. Chem. XXXX, XXX, XXX−XXX