Ligand-to-Ligand Interactions That Direct Formation of D2

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Ligand-to-Ligand Interactions Direct Formation of D2-Symmetrical Alternating Circular Helicate Yan Bing Tan, Tsuyoshi Kawai, and Junpei Yuasa J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b12663 • Publication Date (Web): 12 Feb 2018 Downloaded from http://pubs.acs.org on February 12, 2018

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Journal of the American Chemical Society

Ligand-to-Ligand Interactions Direct Formation of D2-Symmetrical Alternating Circular Helicate Tan Yan Bing,† Tsuyoshi Kawai,*† and Junpei Yuasa*‡§ †

Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan

‡

Department of Applied Chemistry, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan

§

Precursory Research for Embryonic Science and Technology (PRESTO), Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan

ABSTRACT: This work demonstrates that ligand-to-ligand interactions between achiral bis-β-diketonate (BTP) and chiral bis(4phenyl-2-oxazolinyl)pyridine [(R)- or (S)-Ph-Pybox] are successfully directed to the fabrication of a D2-symmetrical alternating circular helicate with the general formula [(R)- or (S)-Ph-Pybox]4(LnIII)4(BTP)6. The lanthanide(III) LnIII assemblies (LnIII4-RRRR and LnIII4SSSS) have a nanometer-size square-like grid (interatomic distances > 10 Å). X-ray structure analysis revealed that the circular helicate contains two double helicate LnIII2L2 units, where both show (M)-helicity for LnIII4-RRRR and (P)-helicity for LnIII4-SSSS, where π-π stacking interaction is present between the side arm of (R)-Ph-Pybox (Ph1) and the adjacent BTP ligand around the EuIII metal center (dππ = 3.636 Å: the diketonate plane···Ph1 distance). The newly obtained circular lanthanide(III) helicate exists as single and homochiral diastereomers in solution (LnIII4-RRRR and LnIII4-SSSS), exhibiting circularly dichroism (CD) and circularly polarized luminescence (CPL). Conversely, the circular helicate favors the heterochiral arrangement (e.g., LnIII4-RRRR/LnIII4-SSSS).



Scheme 1

INTRODUCTION

Coordination-driven self-assembly with geometrically intriguing chiral nano-structures (e.g., circular helicates) is promising in view of creating new chiral materials with peculiar chiroptical properties.1 In particular, potential applications of chiral selfassembled lanthanide (LnIII)2–7 structures have attracted great interest because of the unique magnetic dipole transition nature of 4f electrons, affording large circular polarization in luminescence.8–11 Recently, intensive efforts for developing LnIII-based molecular magnetism have been successfully directed to exploiting multinuclear LnIII complexes.12 These systems typically arrange the LnIII ions at short interatomic distances with small rigid linker molecules (e.g., µ-oxo linker), thus providing dense and compact self-assembled structures (Scheme 1a). Large scale selfassembly should contain effective ligands with at least two wellseparated coordination sites,13 which increases the distance between the metal ions (Scheme 1b). In such a case, however, there are inherent difficulties due to the ligand conformational flexibility as well as the low stereochemical preferences of f-block metals. Thus, enantiopure LnIII assembly strategies for nano-scale structures still represent a considerable challenge. We report herein that ligand-to-ligand interactions are successfully directed to the fabrication of D2-symmetrical alternating circular helicates possessing nanometer-size square-like grids (interatomic distances > 10 Å). The self-assembly strategy is summarized in Scheme 1c, where a 1,3-bis(4,4,4-trifluoro-1,3dioxobutyl)phenyl ligand (BTP) with two β-diketonate coordination sites was employed as a bridging ligand. Doubly negatively charged bis-diketonate ligands lead to a neutral monodimensional dinuclear triple helix LnIII2L3 (stoichiometry S = 2/3 = 0.67, global

complexity GC = 2 + 3 = 5).14,15 Each LnIII ion coordinates with six β-diketonate oxygen atoms, which does not satisfy the coordination number of LnIII (n ≥ 8). These LnIII high coordination numbers would make it difficult to control over the self-assembly

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of LnIII. However, our results reveal that versatile coordination numbers of LnIII provide the opportunity for sequential coordination with chiral co-ligands (R)- and (S)-Ph-Pybox,16 addressing a generation of novel expanded circular lanthanide(III) helicates (LnIII4L6) with a larger global complexity (GC = 4 + 6 = 10) through the ligand-to-ligand interactions.17–19 To the best of our knowledge, the circular lanthanide(III) helicate was first successfully isolated by Senegas et al.20 This contribution theorized the effect of global complexity (GC) on the structure of the LnIII selfassembly, where the isolated LnIII self-assembly (LnIII3L3) with the global complexity GC = 3 + 3 = 6 was the D3-symmetrical trimetallic circular helicate.20 Our strategy is adaptable to various LnIII and rare-earth metals (EuIII, YbIII, SmIII, YIII), expanding the library of circular lanthanide(III) helicates LnIII4-RRRR and LnIII4SSSS with the general formula [(R)- and (S)-PhPybox]4(LnIII)4(BTP)6. The obtained circular helicates are kinetically inert and thus can be isolated and identified by X-ray structure analysis in comparison with NMR spectroscopy. The NMR analysis suggests D2-symmetry for the circular lanthanide(III) helicates (LnIII4L6) with the global complexity GC = 10. Additionally, the present study reveals that the circular lanthanide(III) helicate favors the heterochiral arrangement (Scheme 2). The heterochiral aggregate (EuIII4-RRRR/EuIII4-SSSS) was successfully analyzed by X-ray crystallography, demonstrating that the two enantiomers are packed in an alternating fashion into the crystal form.



RESULTS AND DISCUSSION

X-Ray Crystal Structures of D2-Symmetrical Alternating Circular Helicate. The circular lanthanide(III) and rare-earth metal (EuIII, YbIII, SmIII, YIII) helicates were synthesized by reacting dinuclear tris(BTP) LnIII complexes [(LnIII)2(BTP)3]14 with (R)Ph-Pybox or (S)-Ph-Pybox in 1:2 stoichiometry in methanol (Scheme 1c).21 After removing the solvent by evaporation, the resulting yellow white powder was successfully crystallized by slow diffusion of diethyl ether into a solution of the sample in toluene (for the crystallographic data, refer to Table S1 and S2 in Supporting Information). X-ray crystallography revealed the circular lanthanide(III) helicates with the general formula [PhPybox]4(LnIII)4(BTP)6 (Figure 1a; Figure S1), where each four metal ions possess the nona-coordination geometry with the same chirality (Figure 1b right). The LnIII 4L6 core structure was obtained from the crystal structure of [(R)-Ph-Pybox]4(EuIII)4(BTP)6

Figure 1. (a) X-Ray crystal structures of [(R)-Ph-Pybox]4(EuIII)4(BTP)6 (left: CCDC 1570102) and [(S)-Ph-Pybox]4(EuIII)4(BTP)6 (right: CCDC 1570115). Solvent molecules and hydrogen atoms are omitted for clarity. (b) Left: M4L6 core structure obtained from the crystal structure of [(R)Ph-Pybox]4(EuIII)4(BTP)6; right: coordination geometries around Eu1 and Eu2. (c) Distance and angle between the EuIII ions. (d) Space-filling view of [(R)-Ph-Pybox]4(EuIII)4(BTP)6. Arrows indicate π stacking interactions between the side arm of (R)-Ph-Pybox and the β-diketonate plane. (e) Coordination arrangement around Eu1, where arrows denote coordination direction.

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Journal of the American Chemical Society (Figure 1b left), where four EuIII ions exist in two different forms (Eu1 and Eu2). This is regarded as the subtle static effects due to the crystal packing that contains solvent molecules (diethyl ether), leading to a reduction in symmetry from D2 to C2 (Figure S1). D2 symmetric solution phase structure is supposed based on 1H NMR discussed below (vide infra). The four EuIII ions are bridged by the six BTP ligands, where the two BTP ligands bridge the two Eu1 ions and the two Eu2 ions, and the other BTP ligands bridge the Eu1 and Eu2 (Figure 1b). Consequently, this facilitates formation of a nanometer-size (1 nm × 1 nm) square-like grid with the four EuIII cores (Figure 1c). The Eu1-Eu1, Eu2-Eu2, and Eu1Eu2 distances are 11.813 Å, 11.621 Å, and 10.014 Å, respectively; Eu1-Eu2-Eu2 (φ) and Eu1-Eu1-Eu2 angles (θ) are close to right angles (90.49° and 89.40°, respectively). Importantly, X-ray crystallography (Figure 1d and e) revealed π-π stacking interaction between the side arm of (R)-Ph-Pybox (Ph1) and the adjacent BTP ligand (BTPA) around Eu2 (dππ = 3.636 Å: the diketonate plane···Ph1 distance). Conversely, the other side arm (Ph2) has no appreciable molecular interaction with the adjacent BTP ligands (BTPB and BTPC), where BTPB and BTPC exist in a helix arrangement (Figure 1e). A similar coordination arrangement can be found around Eu1 (dππ = 3.511 Å). Consequently, the ligand-toligand interactions direct fabrication of the circular helicate structure with a nano-sized square with two helical chains; P-helix for [(S)-Ph-Pybox]4(EuIII)4(BTP)6 and M-helix for [(R)-PhPybox]4(EuIII)4(BTP)6 (Figure S2), showing non-superimposable complete mirror images of each other (Figure 1a). The 1H NMR spectrum of the EuIII self-assembly shows a total of 24 resonances spread over a wide chemical shift range (–3– 18 ppm) according to the paramagnetic properties of EuIII core (Figure 2b). To facilitate the rationalization, we synthesized a chiral self-assembly of yttrium(III) ions (YIII), which exhibit similar coordination modes to EuIII ions but not paramagnetic. The YIII self-assembly [(R)-Ph-Pybox]4(YIII)4(BTP)6 was successfully crystallized by use of the same procedure described above, and chiral self-assembly with the same circular helicate was confirmed by the X-ray structure analysis (Figure S1).22 Hence, the chiral self-assembly of YIII is isomorphous of the EuIII selfassembly. The 1H NMR spectrum of [(R)-Ph-Pybox]4(YIII)4(BTP)6 also exhibits a total of 24 resonances (Figure 2c). In the region for the α-proton (5-7 ppm), three singlets are found with an integration ratio of 1:1:1 (α1–3 in Figure 2c). One of the three singlets corresponds to the α-protons of BTPA with C2 symmetry, and the other two singlets are assignable to the α-protons of BTPB and BTPC without C2-symmetry (Figure 2a). BTPB and BTPC would be identical, assuming D2 symmetry for the self-assembly in solution. This assumption was confirmed by the 19F NMR spectrum, where three 19F NMR signals due to BTP ligands can be observed for the self-assembly (Figure S3). Consequently, the 1H NMR signals of [(R)-Ph-Pybox]4(YIII)4(BTP)6 and [(R)-PhIII Pybox]4(Eu )4(BTP)6 were reasonably assigned sequentially by comparison with 1H NMR signals of free BTP and (R)-Ph-Pybox ligands (Figure 2d and e, respectively) using the COSY and ROESY correlations (Figure S4-S6, for a detailed discussion, see the Supporting Information). Interestingly, no (R)-Ph-second diastereomer was detected in both 1H NMR spectra (Figure 2b and c), a clear indication of a single homochiral conformation in solution. The obtained solution structure of the self-assembly is give in Figure 2a, which possesses D2 symmetry exhibiting the same chirality for each metal ion (Figure 2a).23 In light of these results, we investigated the supramolecular geometry of [(R)-Ph-Pybox]4(EuIII)4(BTP)6 in solution by ESI mass (Figure 3). The ESI mass (positive) spectrum of

Figure 2. (a) Solution structure and NMR signal assignment of [(R)-PhPybox]4(YIII)4(BTP)6. 1H NMR (600 MHz) spectra of (b) [(R)-PhPybox]4(EuIII)4(BTP)6 and (c) [(R)-Ph-Pybox]4(YIII)4(BTP)6 in CDCl3. 1H NMR (400 MHz) spectra of (d) BTP and (e) (R)-Ph-Pybox in CDCl3. Asterisk denotes the solvent NMR peak.

[Ph-Pybox]4(EuIII)4(BTP)6 in chloroform displays two major mass peaks with mass range above m/z 3500 (Figure 3b). Two peaks at m/z = 4201.4 and 4223.4 can be unambiguously assigned to {[PhPybox]4(EuIII)4(BTP)6 + H}+ and {[Ph-Pybox]4(EuIII)4(BTP)6 + Na}+, respectively, by using their calculated isotopic distribution (Figure 3b inset). Conversely, we found mass peak assignable to the LnIII2L3 type complex at m/z = 2101.20, which corresponds to {[Ph-Pybox]2(EuIII)2(BTP)3 + H}+. This can be interpreted as possible thermodynamic equilibria existing in solution at low concentration and possible gas-phase dissociation processes. Alternatively, the simple dinuclear helicate should be considered as the most probable species in solution, because the terminal binding of chiral pybox ligands in LnIII2(BTP)3[Ph-Pybox]2 removes the threefold axis, and one logically expects a C2-point group for LnIII2(BTP)3[Ph-Pybox]2, in agreement with the 24 signals identified by NMR (Figure 2b). Hence, we investigated the photophysical properties of circular helicate in solution phase as well as solid state (vide infra).

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Figure 3. (a) Positive ESI mass spectrum of [Ph-Pybox]4(EuIII)4(BTP)6 in chloroform. An intense peak corresponding to {Ph-Pybox + Na}+ was found below m/z 500, which is attributed to dissociated Ph-Pybox during gas-phase dissociation processes. (b) Intensity was enhanced for better visibility of mass peaks corresponding EuIII complexes. Inset: Isotopically resolved signals at m/z = 2101.20, 4210.4, and 4223.4 with the calculated isotopic distributions for {[Ph-Pybox]2(EuIII)2(BTP)3 + H}+, {[PhPybox]4(EuIII)4(BTP)6 + H}+, and {[Ph-Pybox]4(EuIII)4(BTP)6 + Na}+, respectively. (c) Reproducibility for detection of the signals m/z = 4210.4, and 4223.4.

Chiroptical Properties of D2-Symmetrical Alternating Circular Helicate. Figure 4a shows the CD spectra of [(R)- and (S)-PhPybox]4(EuIII)4(BTP)6 in chloroform (red and blue lines, respectively), where they exhibit complete mirror-image CD signals. The assemblies show CD bands in the spectral range of the π-π* transition of the β-diketonate moieties at around λ = 300–370 nm (Figure 4a), suggesting that homochiral assembly formation induces Cotton effects in the absorption band of the β-diketonate ligands. The induced CD spectra show splitting Cotton effects due to excitonic coupling between the BTP ligands,24–26 suggesting the induced chiral configuration of the BTP ligands around the EuIII metal center as can be seen in the X-ray crystal structures (Figure 1a). Similarly, [(S)-Ph-Pybox]4(EuIII)4(BTP)6 shows the CPL signals at the 5D0→7F1 and 5D0→7F2 transitions of EuIII, where each line splits into several crystal-field levels (Figure 4b blue solid lines).27 This CPL signature displayed an almost complete mirror CPL profile for [(R)-Ph-Pybox]4(EuIII)4(BTP)6 in chloroform (Figure 4b red solid line), and is identical to the solid state (KBr pellet) CPL spectrum (Figure 4b blue dashed line). In the same way, there is a nearly quantitative fit between the crystal-field splitting of emission spectrum in solution and that in the solid state (Figure 4b black solid and dashed lines, respectively), showing consistent evidence that the circular EuIII helicate is identical in solution and in the solid state. On the other hand, the dissymmetry factor (glum) of the chiral self-assembly of EuIII assemblies were determined to be +0.22 for the (R)-isomer and –0.24 for the (S)-isomer at the magnetic (5D0→7F1) transition band at λ = 591 nm in chloroform. The glum is defined as glum = 2(IL – IR)/(IL + IR), where IL and IR refer to the intensity of left and right circularly polarized light, respectively. The magnetic dipole transition (5D0 → 7F1) satisfies the magnetic-dipole selection rule, ∆J = 0, ± 1(except 0↔0), which often shows particularly large circular polarization.8-10,28–31 The circular EuIII helicates are luminescent both in the solution and in the solid state. By using a calibrated integrating sphere system upon excitation of the ligand absorption

Figure 4. (a) Top: CD spectra of [(R)-Ph-Pybox]4(EuIII)4(BTP)6 (red) and [(S)-Ph-Pybox]4(EuIII)4(BTP)6 (blue) in chloroform at 298 K (concentrations: 1.7 × 10–7 M). Bottom: Absorption spectrum of [(S)-PhPybox]4(EuIII)4(BTP)6 (1.7 × 10–7 M) in chloroform at 298 K. (b) Top: CPL spectra of [(R)-Ph-Pybox]4(EuIII)4(BTP)6 (red solid line) and [(S)-PhPybox]4(EuIII)4(BTP)6 (blue solid line) in chloroform at 298 K. Blue dashed line shows CPL spectrum of [(S)-Ph-Pybox]4(EuIII)4(BTP)6 in KBr pellet. Bottom: Emission spectra of [(S)-Ph-Pybox]4(EuIII)4(BTP)6 in chloroform (solid line) and in KBr pellet (dashed line) at 298 K. Excitationwavelength: λex = 360 nm. Inset: (b) Emission decay curves at λ = 618 nm of [(R)-Ph-Pybox]4(EuIII)4(BTP)6 (red dots) and [(S)-PhPybox]4(EuIII)4(BTP)6 (blue dots) (A) in chloroform and (B) those in KBr pellet at 298 K.

Figure 5. Photographs of the circular EuIII helicates (initial total concentration: 4.7 × 10-4 M) with different enantiomeric excess (ee) in chloroform under bright conditions (top) and UV/light irradiation (bottom).

band, the emission quantum yield of [(R)-PhPybox]4(EuIII)4(BTP)6 was determined to be Φem = 0.05 in chloroform. The emission decay of the circular EuIII helicate was found to be mono-exponential both in the solution and in the solid state (τ = 0.59 ms in chloroform and 0.48 ms in the solid state, inset of Figure 4b). This again underlines the absence of second diastereomers in solution and solid state.

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Journal of the American Chemical Society tions between them, where LnIII4-RRRR and LnIII4-SSSS show noappreciable ligand exchange in racemic conditions (vide infra).32 Interestingly, the mixing of EuIII4-RRRR and EuIII4-SSSS spontaneously forms a suspension in chloroform.33 Figure 5 presents the photographs of the circular EuIII helicates with different ratios between the EuIII4-RRRR and EuIII4-SSSS in chloroform solutions. Although pure EuIII4-RRRR and EuIII4-SSSS samples are transparent, each racemic mixture forms a suspension (Figure 5). The resulting suspension was diluted (150-fold) to obtain a clear solution for CD spectral measurements of the racemic samples, with no appreciable suspension in the resulting dilute solutions. The CD profile is identical in each case (Figure 6a), but the amplitude (θ) increases almost proportionally with an increase in the initial enantiomeric excess (ee) of the circular EuIII helicate (Figure 6b). The linear relationship suggests that each racemic sample contains mostly the homochiral diastereomers (EuIII4-RRRR and EuIII4-SSSS), where heterochiral diastereomers (e.g., EuIII4-RRSS, EuIII4-RSSS, EuIII4-RRRS) formed by ligand exchange apparently do not extensively coexist. Such ill-defined structures should possess different CD profiles with smaller amplitude than that of the homochiral diastereomers, which should result in a threshold-type non-linear relationship between the CD intensity and the initial enantiomeric excess. The observed linear relationship indicates the resulting precipitate as an insoluble heterochiral aggregate between the EuIII4-RRRR and EuIII4-SSSS isomers (Scheme 2).34 When starting from the racemic Ph-Pybox in the synthesis of the circular EuIII helicates, the self-assemblies crystallized as racemic mixtures, exhibiting the same chirality for each four EuIII/PhPybox site (Figure 7). This empirical observation indicates that the circular EuIII helicate favors the heterochiral arrangement. Perhaps, the heterochiral recognition is due to suitable crystalpacking interaction in the heterochiral aggregates (Figure S7), where the two enantiomers are packed in an alternating fashion into the crystal form.



III

Figure 6. (a) CD spectra of the resulting dilute solutions of Eu 4-RRRR and EuIII4-SSSS mixture with different ratio in chloroform. (b) Plot of θ at λ = 363 nm vs the initial enantiomeric excess (ee) of the circular EuIII helicate.

In conclusion, we have successfully demonstrated a selfassembly strategy for fabrication of nanometer-size circular lanthanide(III) helicates by ligand-to-ligand interactions between the chiral Ph-Pybox and achiral BTP ligands through π-π stacking interactions. The ligand-to-ligand interactions with the tridentate co-ligands (Ph-pybox) should thermodynamically stabilize the circular lanthanide(III) helicates (LnIII4L6) with the large global complexity (GC = 4 + 6 = 10). The obtained circular lanthanide(III) helicate is homochiral (two double helicate M2L2 units in the structure) and no second diastereomer coexists, thus providing circular polarization in the luminescence. In contrast, the circular EuIII helicate favors the heterochiral arrangement, where EuIII4RRRR and EuIII4-SSSS crystallized as racemic mixtures with the same chirality for each four metal ions. The present strategy will be promising for the rational design of self-assembled LnIII showing geometrically intriguing chiral structures.

 III

Figure 7. Molecular packing diagrams of the crystal structures of Eu 4RRRR (red) and EuIII4-SSSS (blue).

The circular lanthanide(III) helicates [(R)- and (S)-PhPybox]4(LnIII)4(BTP)6 (LnIII4-RRRR and LnIII4-SSSS, respectively) are sufficiently rigid for the investigation of heterochiral interac-

SUMMARY AND CONCLUSIONS

ASSOCIATED CONTENT

Supporting Information. Experimental details including 1H NMR assignment of the self-assembled LnIII, crystallographic parameters and refinement details, ORETEP views of the selfassembled LnIII, 19F NMR Spectra, 1H,1H cosy NMR, 2D-ROESY NMR, DOSY NMR, molecular packing diagrams, crystallographic data in CIF format (CCDC 1570102, CCDC 1570113, CCDC 1570116), spectra data for mixture of SmIII-RRRR and EuIII-SSSS,

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Supporting Figures for the Experimental Section. This material is available free of charge via the Internet at http://pubs.acs.org. (8)



AUTHOR INFORMATION

Corresponding Author [email protected]; [email protected]



ACKNOWLEDGMENT

This work was partly supported by JST-PRESTO “Molecular technology and creation of new functions” (14530027), a Grantin-Aid for Scientific Research (C) (JP26410094) and Scientific Research (A) (JP25248019) from the Ministry of Education, Culture, Sports, Science and Technology, Japan and also JSPS KAKENHI Grant Number JP17H05386 (Coordination Asymmetry). This manuscript was improved through the suggestions and comments of Prof. Leigh McDowell (Nara Institute of Science and Technology).



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Bickley, J. F.; Greeves, N.; Kelly, R. V.; Smith, P. M. Organometallics 2005, 24, 3458–3467. Riehl, J. P.; Muller, G. Circularly Polarised Luminescence Spectroscopy from Lanthanide Systems. In Handbook on the Physics and Chemistry of Rare Earths; Gschneidner, K. A., Bünzli, J.-C., Pecharsky, V., Eds,; North Holland Publishing Company: Amsterdam, 2004; Vol. 34, Chapter 220, pp 289–357. Richardson, F. S. Inorg. Chem. 1980, 19, 2806–2812. (a) Carr, R.; Evans, N. H.; Parker, D. Chem. Soc. Rev. 2012, 41, 7673–7686. (b) Muller, G. Dalton Trans. 2009, 0, 9692–9707. (c) Parker, D.; Dickins, R. S.; Puschmann, H.; Crossland, C.; Howard, J. A. K. Chem. Rev. 2002, 102, 1977–2010. (d) dos Santos, C. M. G.; Harte, A. J.; Quinn, S. J.; Gunnlaugsson, T. Coord. Chem. Rev. 2008, 252, 2512– 2527. (e) Bünzli, J.-C. G.; Piguet, C. Chem. Soc. Rev. 2005, 34, 1048–1077. (f) Zinna, F.; Di Bari, L. Chirality 2015, 27, 1–13. Circularly polarized luminescence (CPL) has become one of the hottest research topics due to its intriguing photonic applications, see: (a) Zhang, Y. J.; Oka, T.; Suzuki, R.; Ye, J. T.; Iwasa, Y. Science 2014, 344, 725–728. (b) Zinna, F.; Giovanella, U.; Bari, L. D. Adv. Mater. 2015, 27, 1791– 1795. (a) Li, X.-L.; Wu, J.; Zhao, L.; Shi, W.; Cheng P.; Tang, J. Chem. Commun. 2017, 53, 3026–3029. (b) Vignesh, K. R.; Langley, S. K.; Murray, K. S.; Rajaraman, G. Inorg. Chem. 2017, 56, 2518–2532. (c) Huang, W.; Shen, F.-X.; Wu, S.Q.; Liu, L.; Wu, D.; Zheng, Z.; Xu, J.; Zhang, M.; Huang, X.-C.; Jiang, J.; Pan, F.; Li, Y.; Zhu K.; Sato, O. Inorg. Chem. 2016, 55, 5476–5484. (d) Mukherjee, S.; Lu, J.; Velmurugan, G.; Singh, S.; Rajaraman, G.; Tang, J.; Ghosh, S. K. Inorg. Chem. 2016, 55, 11283–11298. (e) Mondal, A. K.; Jena, H. S.; Malviya, A.; Konar, S. Inorg. Chem. 2016, 55, 5237– 5244 (f) Rinehart, J. D.; Fang, M.; Evans W. J.; Long, J. R. J. Am. Chem. Soc. 2011, 133, 14236–14239. (a) Li, X.-Z.; Zhou, L.-P.; Yan, L.-L.; Yuan, D.-Q.; Lin, C.S.; Sun, Q.-F. J. Am. Chem. Soc. 2017, 139, 8237−8244. (b) Aroussi, B. El; Zebret, S.; Besnard, C.; Perrottet, P.; Hamacek, J. J. Am. Chem. Soc. 2011, 133, 10764–10767. LnIII2L3 type triple-stranded dinuclear helicate structures were found in self-assembly of EuIII with BTP and 2,2’bipyridine or 1,10-phenanthroline that have no possible ligand-to-ligand interaction with BTP. In addition, LnIII2L3 type helicate contains solvent molecules weakly bound to each lanthanide (e.g., (EuIII)2(BTP)3(H2O)4), see: Shi, J.; Hou, Y.; Chu, W.; Shi, X.; Gu, H.; Wang, B.; Sun, Z. Inorg. Chem. 2013, 52, 5013–5022. Bassett, A. P.; Magennis, S. W.; Glover, P. B.; Lewis, D. J.; Spencer, N.; Parsons, S.; Williams, R. M.; De Cola, L.; Pikramenou, Z. J. Am. Chem. Soc. 2004, 126, 9413–9424. (a) Evans, D. A.; Wu, J. J. Am. Chem. Soc. 2003, 125, 10162–10163. (b) Evans, D. A.; Fandrick, K. R.; Song, H.J.; Scheidt, K. A.; Xu, R. J. Am. Chem. Soc. 2007, 129, 10029–10041. (c) Evans, D. A.; Fandrick, K. R.; Song, H.J. J. Am. Chem. Soc. 2005, 127, 8942–8943. In this context, we have previously reported that ligand-toligand interactions between the chiral Pybox and achiral βdiketonate ligands in the mononuclear complex lead to a chiral arrangement of β-diketonate ligands around LnIII, determining the sign of optical chirality, see: Yuasa, J.; Ohno, T.; Miyata, K.; Tsumatori, H.; Hasegawa, Y.; Kawai, T. J. Am. Chem. Soc., 2011, 133, 9892–9902. (a) de Bettencourt-Dias, A.; Barber, P. S.; Bauer, S. J. Am. Chem. Soc. 2012, 134, 6987–6994. (b) de Bettencourt-Dias, A.; Viswanathan, S.; Rollett, A. J. Am. Chem. Soc. 2007, 129, 15436–15437. (c) Chorazy, S.; Nakabayashi, K.; Arczynski, M.; Pełka, R.; Ohkoshi, S.; Sieklucka, B. Chem.– Eur. J. 2014, 20, 7144–7159. (d) Matsumoto, K.; Suzuki,

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K.; Tsukuda, T.; Tsubomura, T. Inorg. Chem. 2010, 49, 4717–4719. (e) Harada, T.; Tokuda, K.; Nishiyama, K. J. Mol. Liq. 2014, 200, 77–80. (a) Scherer, M.; Caulder, D. L.; Johnson, D. W.; Raymond, K. N. Angew. Chem., Int. Ed. 1999, 38, 1587–1592. (b) Hamacek, J.; Blanc, S.; Elhabiri, M.; Leize, E.; Van Dorsselaer, A.; Piguet, C.; Albrecht-Gary, A. M. J. Am. Chem. Soc. 2003, 125, 1541–1550. Senegas, J.-M.; Koeller, S.; Bernardinelli, G.; Piguet, C. Chem. Commun. 2005, 2235–2237. (a) Hasegawa, Y.; Kimura, Y.; Murakoshi, K.; Wada, Y.; Yamanaka, T.; Kim, J.; Nakashima, N.; Yanagida, S. J. Phys. Chem. 1996, 100, 10201–10205. (b) Nakamura, K.; Hasegawa, Y.; Kawai, H.; Yasuda, N.; Kanehisa, N.; Kai, Y.; Nagamura, T.; Yanagida, S.; Wada, Y. J. Phys. Chem. A 2007, 111, 3029–3037. (c) Hasegawa, Y.; Tsuruoka, S.; Yoshida, T.; Kawai, H.; Kawai, T. J. Phys. Chem. A 2008, 112, 803–807. The difference was found in metal-metal distances. The Y1Y1, Y2-Y2, and Y1-Y2 distances are 9.981 Å, 9.911 Å, and 11.591 Å, respectively (Figure S1). This presumably results from crystal packing effects. Total six multiplet signals (P–U) are found in the aliphatic region (4–5.6 ppm, Figure 2c), whereas only three multiplet signals (1:1:1 ratio) were observed in the original ligand in this region (Figure 2e). This observation suggests that [(R)Ph-Pybox] loses the original ligand due to the ligand-toligand interactions, and no ligand exchange occurs in NMR time scale. Telfer, S. G. et al. reported a detailed theoretical studies focusing on Cotton effects in CD spectra result from excitonic couplings between the coordinated ligands, see: (a) Telfer, S. G.; Tajima, N.; Kuroda, R.; Cantuel, M.; Piguet, C. Inorg. Chem. 2004, 43, 5302–5310. (b) Telfer, S. G.; Tajima, N.; Kuroda, R. J. Am. Chem. Soc. 2004, 126, 1408–1418. (c) Telfer, S. G.; Kuroda, R.; Sato, T. Chem. Commun. 2003, 1064–1065. Morcillo, S. P.; Miguel, D.; de Cienfuegos, L. Á.; Justicia, J.; Abbate, S.; Castiglioni, E.; Bour, C.; Ribagorda, M.; Cárdenas, D. J.; Paredes, J. M.; Crovetto, L.; ChoquesilloLazarte, D.; Mota, A. J.; Carreño, M. C.; Longhi, G.; Cuerva, J. M. Chem. Sci. 2016, 7, 5663–5670. Bruhn, T.; Pescitelli, G.; Jurinovich, S.; Schaumlöffel, A.; Witterauf, F.; Ahrens, J.; Bröring, M.; Bringmann, G. Angew. Chem., Int. Ed. 2014, 53, 14592–14595. (a) Yuasa, J.; Ueno, H.; Kawai, T. Chem.–Eur. J. 2014, 20, 8621–8627. (b) Yuasa, J.; Mukai, R.; Hasegawa, Y.; Kawai, T. Chem. Commun. 2014, 50, 7937–7940. (c) Yuasa, J.; Ohno, T.; Tsumatori, H.; Shiba, R.; Kamikubo, H.; Kataoka, M.; Hasegawa, Y.; Kawai, T. Chem. Commun. 2013, 49, 4604–4606. (d) Yuasa, J.; Nakagawa, T.; Kita,

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Y.; Kaito, A.; Kawai, T. Chem. Commun. 2017, 53, 6748– 6751. (e) Imai, Y.; Kawai, T.; Yuasa, J. J. Phys. Chem. A 2016, 120, 4131–4138. (f) Okayasu Y.; Yuasa, J. Mol. Syst. Des. Eng. 2017, 10.1039/C7ME00082K. (a) Muller, G.; Riehl, J. P.; Schenk, K. J.; Hopfgartner, G.; Piguet, C.; Bünzli, J.-C. G. Eur. J. Inorg. Chem. 2002, 3101–3110. (b) Muller, G.; Schmidt, B.; Hopfgartner, G.; Riehl, J. P.; Bünzli, J.-C. G.; Piguet, C. J. Chem. Soc., Dalton Trans. 2001, 2655–2662. (c) Bonsall, S. D.; Houcheime, M.; Straus, D. A.; Muller, G. Chem. Commun. 2007, 3676– 3678 (d) Lunkley, J. L.; Shirotani, D.; Yamanari, K.; Kaizaki, S.; Muller, G. J. Am. Chem. Soc. 2008, 130, 13814– 13815. Kitchen, J. A.; Barry, D. E.; Mercs, L.; Albrecht, M.; Peacock, R. D.; Gunnlaugsson, T. Angew. Chem., Int. Ed. 2012, 51, 704–708. Bruce, J. I.; Dickins, R. S.; Govenlock, L. J.; Gunnlaugsson, T.; Lopinski, S.; Lowe, M. P.; Parker, D.; Peacock, R. D.; Perry, J. J. B.; Aime, S.; Botta, M. J. Am. Chem. Soc. 2000, 122, 9674–9684. Wu, T.; Hudecová, J.; You, X.-Z., Urbanová, M.; Bouř, P. Chem.–Eur. J. 2015, 21, 5807–5813. Polynuclear assemblies are suggested to be kinetically much more inert as compared to their mononuclear counterparts, see: (a) Zare, D.; Suffren, Y.; Nozary, H.; Hauser A.; Piguet, C. Angew. Chem., Int. Ed. 2017, 56, 14612– 14617. (b) Charbonnière, L. J.; Williams, A. F.; Frey, U.; Merbach, A. E.; Kamalaprija, P.; Schaad, O. J. Am. Chem. Soc. 1997, 119, 2488–2496. The solid-solution phase behavior of racemates has been often focused on asymmetric amplification originating from solubility differences between the racemic and enantiopure molecules, see: (a) Klussmann, M.; Iwamura, H.; Mathew, S. P.; Wells, D. H., Jr.; Pandya, U.; Armstrong, A.; Blackmond, D. G. Nature 2006, 441, 621–623. (b) Hayashi, Y.; Matsuzawa, M.; Yamaguchi, J.; Yonehara, S.; Matsumoto, Y.; Shoji, M.; Hashizume, D.; Koshino, H. Angew. Chem., Int. Ed. 2006, 45, 4593–4597. (c) Breslow, R.; Levine, M. S. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 12979–12980. (d) Nojiri, A.; Kumagai, N.; Shibasaki, M. Angew. Chem., Int. Ed. 2012, 51, 2137–2141. Similar less soluble suspension was formed when SmIII4RRRR was used instead of EuIII4-RRRR (Figure S8). The resulting precipitate obtained by filtration displays both EuIII emission due to 5D0 → 7F0–3 and Sm emission due to 4G5/2 → 6H5/2, 7/2, 9/2 (Figure S9). There is a possibility that SmIII4RRRR acts as its quasi enantiomer of EuIII4-SSSS, because the structure of SmIII4-RRRR significantly resembles that of EuIII4-RRRR (Figure S10).

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