Synthesis of a xanthene-based macrocyclic imine ligand and two-step planarization by metalation with Ni2+ and Na+

Shigehisa Akine *ab, Masato Nakano b, Yoko Sakata abc and Seiji Tsuzuki d
aNano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. E-mail: akine@se.kanazawa-u.ac.jp
bGraduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
cGraduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
dDepartment of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Received 19th May 2025 , Accepted 7th July 2025

First published on 10th July 2025


Abstract

A xanthene-based macrocyclic π-containing imine ligand, H4L2, was newly designed and synthesized in order to obtain a series of metal-containing planar structures. Due to the xanthene framework with the methylene bridge, the macrocyclic molecule, H4L2, had a more planar structure than the corresponding diaryl-ether-type analogue, H4L1. This macrocyclic molecule, H4L2, was converted into the dinuclear nickel(II) complex, L2Ni2, which was characterized by spectroscopic techniques as well as crystallography. The planarity of the macrocyclic ligand, H4L2, was greatly improved by the introduction of two Ni2+ ions. Furthermore, the L2Ni2 molecule became more planar by incorporation of a Na+ ion in the central O6 binding cavity. Thus, the xanthene-based macrocycle, H4L2, allowed complexation with two different metal ions, Ni2+ and Na+, to demonstrate a two-step improvement in the planarity.


Introduction

Compounds containing π-planes have attracted much attention as functional molecules based on their electronic and optical properties. The planarity of such π-containing molecules has a significant effect on their electronic and photophysical properties derived from the π-conjugation of the molecules. For example, various physicochemical properties, such as optical properties,1 electrochemical properties,2 efficiency of photovoltaics,3etc., are influenced by the molecular planarity, which can be changed by introducing or changing the substituents.4 The dynamic change in the molecular planarity can also cause a significant change in the fluorescent behavior.5

The planarity of some macrocyclic π-containing molecules can be easily controlled by the incorporation of guest species into the cavity, because the macrocyclic compounds generally show a good host–guest binding affinity. For example, the properties of porphyrin derivatives can be altered by protonation6 and metalation7 in the binding pocket, axial functionalization on the metal ions,8etc., although the porphyrin derivatives are generally less flexible to allow a rather smaller conformational change. If a macrocyclic molecule has a larger cavity with two or more binding sites to accommodate multiple guest species, the planarity could be more drastically controlled, perhaps in a multistep manner by using two or more different types of guest species.

In this respect, the macrocyclic imine ligand, H4L1 (Scheme 1a (i)), which we have previously reported, exhibited a unique two-step planarity enhancement, because this molecule has two types of binding sites inside the macrocyclic structure containing six benzene rings, i.e., two H2saloph coordination pockets doubly connected by diaryl ether linkages and one central O6 binding site.9–13 The structure of H4L1 in the absence of metal ions is far from flat, but when Ni2+ ions are introduced into the saloph sites of this molecule, the two square planar [Ni(saloph)] structures are formed to make the L1Ni2 macrocycle relatively more planar (Scheme 1b (i)).9,10 However, this L1Ni2 is still significantly deviated from an ideal planar structure, although the parent [Ni(saloph)] motif is known to be highly planar.14 Particularly, the two [Ni(saloph)] substructures in the L1Ni2 macrocycle are curved in opposite directions to each other mainly due to the steric hindrance of the ortho hydrogen atoms in the diaryl ether moieties (Scheme 1b (i)).


image file: d5dt01183c-s1.tif
Scheme 1 (a) Molecular structures of bis(saloph) macrocycles: (i) diaryl-ether-based macrocycle H4L1 and (ii) xanthene-based macrocycle H4L2, and (b) their nickel(II) complexes (i) L1Ni2 and (ii) L2Ni2. (c) Schematic drawing of two-step planarization of a macrocycle by metalation with two different kinds of metal ions, (i) the first metalation with Ni2+ and (ii) the second metalation with Na+.

If these two neighboring ortho hydrogen atoms are replaced with a bridging methylene group to make a xanthene motif, the resultant macrocycle is expected to be more planar. This structural modification would lead to unique properties originating from the more effective π-conjugation and facilitate the formation of higher-order stacking structures.9–11,15 In this study, we synthesized the macrocyclic imine ligand, H4L2, based on the xanthene motif (Scheme 1a (ii)), which can be converted into a planar dinickel(II) complex, L2Ni2 (Scheme 1b (ii)). We found that the planarity of the macrocyclic ligand, H4L2, was greatly improved by introduction of two Ni2+ ions. Furthermore, the L2Ni2 molecule became more planar by incorporation of Na+ ion into the O6 binding cavity, demonstrating a two-step improvement in the planarity (Scheme 1c).

Results and discussion

Synthesis

For the synthesis of the precursor 4 for the macrocyclic ligand, H4L2 (Scheme 2), we first prepared 9,9-dimethylxanthene-4,5-diol (1) from xanthone according to a literature method.16 The MOM protection of the hydroxy groups in this diol 1 gave the MOM ether 2 (Fig. S1, and S2), which was then converted to dialdehyde 3 (Fig. S3, and S4) by dilithiation followed by the reaction with DMF. Removal of the MOM groups by acid hydrolysis gave the dialdehyde 4 (Fig. S5, and S6).
image file: d5dt01183c-s2.tif
Scheme 2 Synthesis of xanthene-based macrocyclic ligand H4L2 and the corresponding metallohost L2Ni2.

The [2 + 2] macrocyclization of the dialdehyde 4 with o-phenylenediamine readily proceeded in a chloroform/acetonitrile (1[thin space (1/6-em)]:[thin space (1/6-em)]1) mixed solvent (Scheme 2). The macrocyclic ligand, H4L2, was obtained in 89% yield as orange crystals (Fig. S7–S11). The product showed one singlet each for the imine proton at 8.99 ppm and the hydroxy proton at 13.82 ppm, indicative of the formation of a symmetric macrocyclic molecule. The mass spectrum showing m/z = 741.3 for [H4L2 + H]+ confirmed the [2 + 2] macrocyclic structure of H4L2 (Fig. S12). This compound was almost insoluble in pure chloroform or acetonitrile, while slightly soluble in DMSO.

The reaction of H4L2 with nickel(II) acetate in chloroform/methanol then afforded the dinuclear nickel(II) metallohost, L2Ni2, in 56% yield (Scheme 2; Fig. S13). This metallohost showed a very low solubility in common organic solvents, and only very slightly soluble in DMSO.

Crystallography and theoretical studies

The H4L2 macrocycle crystallized in the monoclinic system, space group P21/m, and the crystallographic analysis clearly demonstrated the [2 + 2] macrocyclic structure (Fig. 1a and b). The unit cell contains two crystallographically independent molecules having different conformations, which are referred to as H4L2-A and H4L2-B, hereafter. Both conformations are found to be nonplanar as seen in the diaryl ether analogue, H4L1,9,10 which is presumably due to the repulsion of the oxygen lone pairs. The H4L2-A molecule has a crystallographicaly imposed mirror plane and adopted an approximate C2v symmetry. The two xanthene planes are bent by 39.12(4) deg to the same side with respect to the O6 mean plane of the macrocycle resulting in a V-shaped structure (Fig. 1a). The other molecule, H4L2-B, has a crystallographically imposed inversion center and adopted an approximate C2h symmetry. In contrast to molecule H4L2-A, the two xanthene planes are bent to the opposite side resulting in a step structure (Fig. 1b).
image file: d5dt01183c-f1.tif
Fig. 1 X-ray crystal structures of H4L2 and L2Ni2 showing two crystallographically independent molecules. (a) H4L2-A with a V-shaped conformation; (b) H4L2-B with a step conformation; (c) L2Ni2-A with a shallow V-shaped conformation; (d) L2Ni2-B with a step conformation (ORTEP, 50% probability). Solvent molecules are not shown.

The relative stability of the two conformations of H4L2 was investigated by DFT calculations. The geometry optimizations were performed starting from the crystal structures, H4L2-A and H4L2-B, to obtain the corresponding optimized structures, H4L2-a and H4L2-b, respectively (Fig. S14). The molecule of H4L2-a, which has a V-shaped structure, was more stable by 7.03 kJ mol−1 than H4L2-b having a step conformation.

In contrast to the metal-free macrocycle, H4L2, the corresponding nickel(II) complex has a more planar structure. The nickel(II) complex, L2Ni2, crystallized in the monoclinic system, space group P21/n, and the crystal structural analysis clearly demonstrated a macrocyclic structure containing two square planar nickel(II) ions in the saloph coordination pockets (Fig. 1c and d). The unit cell contains two crystallographically independent molecules, L2Ni2-A and L2Ni2-B hereafter, in a 2[thin space (1/6-em)]:[thin space (1/6-em)]1 ratio. The L2Ni2-A molecule had no crystallographically-imposed symmetry and was slightly bent to form a shallow V-shaped structure (Fig. 1c). The L2Ni2-B molecule had a crystallographically-imposed inversion center (Fig. 1d). The two xanthene moieties are slightly bent in the opposite directions to form a step-like conformation.

The geometry optimizations of L2Ni2 starting from the two structures, L2Ni2-A and L2Ni2-B, gave the corresponding energy-minimized structures, L2Ni2-a and L2Ni2-b, respectively, but both optimized structures were significantly curved unlike the nearly planar structures found in the crystalline state (Fig. S15). L2Ni2-a is more stable than L2Ni2-b by only 2.97 kJ mol−1, suggesting that both conformations as well as those in the crystalline state are present in the solution.

The macrocyclic metallohost, L2Ni2, was expected to show a binding affinity to cationic guest species, because it has a crown ether-like cavity. Indeed, the diaryl ether analog, L1Ni2, and related compounds showed an excellent binding affinity to alkali metal ions, etc., mainly due to the more polarized phenoxo–Ni bonds.9–11,17 In addition, Na+ was the best metal to be accommodated in the binding cavity of L1Ni2 in a monomeric 1[thin space (1/6-em)]:[thin space (1/6-em)]1 stoichiometry. However, the guest binding behavior of L2Ni2 could not be investigated due to its very low solubility. Nevertheless, single crystals of the guest-inclusion complex, [L2Ni2Na(DMSO)2](OTf), was directly obtained by mixing H4L2, Ni(OAc)2, and NaOTf in a methanol/DMSO solution followed by vapor-phase diffusion of diethyl ether.

The X-ray crystallographic analysis (Fig. 2) showed that a Na+ ion was situated at the center of the O6 cavity, exactly on the O6 mean plane. The six Na–O distances are almost the same within a range of 2.531–2.665 Å, approximately forming a regular hexagon. This metallohost–guest complex, L2Ni2Na, adopted an almost planar but slightly wavy structure, and two DMSO molecules coordinated to the Na+ ion from above and below the macrocyclic plane. In the packing structure, the planar [Ni(saloph)] substructures in this complex were stacked on top of each other in such a way that they avoided these coordinating DMSO molecules. The counter anion did not directly coordinate to any of the metal centers, Ni2+ or Na+.


image file: d5dt01183c-f2.tif
Fig. 2 X-ray crystal structure of [L2Ni2Na(DMSO)2]+ (ORTEP, 50% probability). Hydrogen atoms are omitted for clarity. Noncoordinating DMSO molecule and the TfO counter anion are not shown.

The DFT calculations gave the optimized structure of the inclusion complex, [L2Ni2Na]+, with the coordinating DMSO molecules omitted (Fig. S16). The calculated host–guest interaction energy between L2Ni2 and Na+ using the optimized geometry was −528.5 kJ mol−1. The destabilization by deformation of the L2Ni2 macrocycle caused by the formation of the Na+ complex was calculated to be only 17.1 kJ mol−1, indicating that the uncomplexed L2Ni2 already has a structure suitable for Na+ binding. As a result, the stabilization energy upon the formation of [L2Ni2Na]+ from L2Ni2 and Na+ was determined to be −528.5 + 17.1 = −511.4 kJ mol−1, which corresponds to the binding energy in the gas phase. In solution, the formation of [L2Ni2Na]+ requires desolvation of Na+; therefore, the binding energy in solution is expected to be much smaller (less negative). From the viewpoint of the small deformation energy associated with complex formation, along with favorable geometrical matching, this L2Ni2 macrocycle appears to be well preorganized for the Na+ binding.

Planarity of the complexes

Since we have obtained the crystal structures of a series of H4L2, L2Ni2, and L2Ni2Na, their structural features, such as the planarity and cavities sizes/shapes, were summarized for comparison with the corresponding diaryl ether analogues (Table 1). Based on the X-ray crystal structures, we defined three parameters in order to discuss the planarity of the macrocyclic molecules; deviation ddev as the average RMS deviation of the 40 skeletal carbon and 4 nitrogen atoms from the O6 mean plane (Fig. 3a); macrocycle bent angle θa as the dihedral angle between the xanthene mean plane and the O6 mean plane (Fig. 3b); and xanthene bent angle θb as the dihedral angle between the two benzene rings in each xanthene unit (Fig. 3c). In addition, the size/shape of the O6 guest binding site is discussed in terms of the diagonal O⋯O distances, dOO(X) and dOO(P), as well as the continuous shape measure (CShM) value,18 which represents the deviation from ideal regular hexagon.
image file: d5dt01183c-f3.tif
Fig. 3 Definition of planarity parameters (a) ddev, (b) θa, and (c) θb. (d) Comparison of the planarity parameters for H4L1, L1Ni2, L1′Ni2Na, H4L2, L2Ni2, and L2Ni2Na.
Table 1 Structural parameters for H4L2, L2Ni2, L2Ni2Na, H4L1, L1Ni2, and L1′Ni2Na
Structure d OO(X)[thin space (1/6-em)]a (Å) d OO(P)[thin space (1/6-em)]b (Å) d dev[thin space (1/6-em)]c (Å) θ a[thin space (1/6-em)]d (°) θ b[thin space (1/6-em)]e (°) CShMf
a The diagonal O⋯O distance between the xanthene oxygen atoms. b The diagonal O⋯O distance between the phenoxo oxygen atoms. c Average RMS deviation of the 40 skeletal carbon and 4 nitrogen atoms from the O6 mean plane (Fig. 3a). d The dihedral angle between the xanthene mean plane and the macrocyclic O6 mean plane (Fig. 3b). e The dihedral angle between the two benzene rings in each xanthene unit (Fig. 3c). f Continuous shape measure (CShM) value for the geometry calculated with the program SHAPE 2.1.18 g [L2Ni2Na(DMSO)2](OTf). h [L1′Ni2Na](OTf).
H4L2-A 6.612(3) 5.683(2) 1.36 39.12(4) 27.28(10) 3.486
H4L2-B 6.597(3) 5.489(3), 5.865(3) 1.67 37.51(5) 30.41(10) 3.226
L2Ni2-A 5.261(12) 5.078(3), 5.151(3) 0.49 7.60(16) 12.64(12) 0.705
L2Ni2-B 5.3048(17) 5.0983(17), 5.0538(17) 0.48 6.38(5), 6.27(4) 23.21(9), 16.41(9) 0.221
L2Ni2Nag 5.319(4) 5.075(4), 5.077(4) 0.25 4.28(13), 5.86(13) 9.8(3), 7.6(3) 0.153
H4L1 [ref. 9 and 10] 6.354(2) 5.270(2), 5.956(2) 1.88 38.12(3), 75.28(4) 72.91(5) 4.624
L1Ni2 [ref. 9 and 10] 5.238(4) 5.167(4), 5.193(4) 0.80 29.29(11), 15.34(16) 42.24(13) 0.027
L1′Ni2Na-A [ref. 11]h 5.091(5) 5.070(5), 5.205(5) 0.82 25.41(11), 21.76(12) 44.46(10) 0.115
L1′Ni2Na-B [ref. 11]h 5.072(5) 5.189(5), 5.079(5) 0.85 22.60(13), 26.00(11) 45.66(10) 0.125


As already mentioned, the metal-free macrocycles, H4L2-A and H4L2-B, have a non-planar conformation in which the two xanthene planes are bent at an angle θa of 37–39 deg with respect to the O6 mean plane. The difference in the bending orientations of the two xanthene planes resulted in two types of conformations, i.e., V-shaped (H4L2-A) and step-shaped (H4L2-B). In addition, each xanthene moiety was also bent at the angle θb of about 27–30 deg. This bending makes the molecular conformation far from planar, with the average deviation ddev of 1.36 and 1.67 Å for H4L2-A and H4L2-B, respectively.

It was clear that the conversion of H4L2 into L2Ni2 by introducing two Ni2+ ions improved the overall planarity of the macrocyclic molecule; both molecules, L2Ni2-A and L2Ni2-B, showed the average deviations ddev of 0.48–0.49, which are much smaller than those of H4L2. The nickel(II) complex, L2Ni2, also had bent angles θa (6.3–7.6 deg) and θb (12–23 deg) that are significantly smaller than those of H4L2. This planarization also changed the arrangement of the six oxygen atoms; in particular, the diagonal distance between the two xanthene oxygen atoms, dOO(X), was shortened from 6.6 Å to 5.3 Å upon the conversion of H4L2 to L2Ni2. As a result, all the diagonal O⋯O distances within the O6 binding site became almost similar (dOO(P) of 5.05–5.15 Å), approximately making a regular hexagon, which is also evident from the significant decrease in the CShM values (from 3.2–3.5 to 0.2–0.7).

The incorporation of Na+ ion into L2Ni2 further improved the planarity of the macrocycle. The deviation ddev of [L2Ni2Na(DMSO)2](OTf) was 0.25, which was approximately half that for L2Ni2 (ddev = 0.48–0.49). The bent angles θb became smaller (7.6–9.8 deg), which are also smaller than those of L2Ni2. Therefore, the planarity of this host H4L2 was clearly improved in two steps by introducing two different kinds of metals, Ni2+ and Na+. Considering the molecular curvature found in the DFT calculated structures, the crystal packing may also contribute to the observed highly-planar structures of L2Ni2 and L2Ni2Na.

While there is a noticeable difference in the conformational planarity, the geometrical features of the O6 sites of L2Ni2 and L2Ni2Na are quite similar. Whereas the CShM value for L2Ni2Na was slightly smaller than that for L2Ni2, it was particularly noteworthy that there is almost no difference in the diagonal O⋯O distances, dOO(X) and dOO(P), between the inclusion complex L2Ni2Na and the guest-free L2Ni2 macrocycle, indicating that Na+ binding occurs almost without significant deformation of the host framework of L2Ni2. This was also demonstrated from the viewpoint of the deformation energy in the computational investigations as already discussed. Thus, the L2Ni2 metallohost has a well preorganized binding site that is particularly suitable for Na+ binding.

A similar preorganization effect of the O6 binding site was observed for the corresponding diaryl ether analogues, H4L1, L1Ni2,9,10 and L1′Ni2Na.11 However, the xanthene analogues presented here generally exhibit greater planarity than these diaryl ether analogues, particularly in the case of the metal-free H4L2. This enhanced planarity contributes to its stronger binding to Na+ (Ka = 182 M−1; Fig. S17) compared to H4L1 (Ka = 13 M−1),9 owing to its well-preorganized binding site. Moreover, the xanthene analogues showed a more pronounced increase in planarity upon stepwise binding with Ni2+ and Na+, demonstrating the advantage of employing the xanthene motif to construct metal-containing planar structures.

Conclusion

A novel xanthene-based macrocyclic imine ligand, H4L2, was designed and synthesized to make a planar metallohost molecule in which the aromatic organic macrocyclic moiety and the square planar metals are likely to form a coplanar structure. The use of the xanthene motif instead of the diaryl ether in H4L1 lead to a more planar structure of the resultant dinickel(II) metallohost without suffering the steric repulsion between the neighboring hydrogen atoms found in the diaryl ether analogues. From the viewpoint of the structural parameters, we demonstrated that the planarity of the H4L2 macrocycle was improved in a two-step manner by the introduction of Ni2+ into the H2saloph coordination pockets followed by Na+ in the O6 guest binding site. Also, a detailed structural investigation clearly demonstrated that this L2Ni2 is well preorganized for the binding with Na+ in the O6 binding site. However, the present macrocycle, H4L2, and its nickel(II) complex, L2Ni2, showed a significantly low solubility in common organic solvents, which prevented us from investigating their behavior in solution. Nevertheless, the host–guest binding behavior and the possible formation of aggregated species would be of interest due to their highly-planar structures. Further investigations are currently underway to synthesize more soluble analogues by introducing alkyl groups into the phenylenediamine subunit, aiming to facilitate studies in solution chemistry.

Experimental section

General

9,9-Dimethylxanthene-4,5-diol was synthesized according to the literature.16 The reagents and solvents were purchased from commercial sources and used without further purification. The 1H and 13C NMR spectra were recorded on a JEOL JNM-ECS 400 (1H, 400 MHz; 13C, 100 MHz) or a Bruker Avance 600 (1H, 600 MHz). The chemical shifts were referenced with respect to tetramethylsilane (0 ppm) as an internal standard. The ESI-TOF mass spectra were recorded on a Bruker Daltonics micrOTOF II.

4,5-Bis(methoxymethoxy)-9,9-dimethylxanthene (2)

Under a nitrogen atmosphere, NaH (60% in oil, 5.63 g, 0.141 mol) was washed with petroleum ether to remove the oil and then a solution of 9,9-dimethylxanthene-4,5-diol (1) (8.72 g, 36.0 mmol) in dehydrated DMF (150 mL) was introduced into a flask containing the NaH. The resultant mixture was stirred for 4 h at rt, then chloromethyl methyl ether (8.20 mL, 0.108 mol) was added to the mixture at 0 °C, which was further stirred overnight at rt. After the addition of water, the mixture was extracted several times with chloroform. The combined organic layer was washed with brine, dried over anhydrous sodium sulfate, filtered, and concentrated to dryness under reduced pressure. The crude product was purified by column chromatography on silica gel (hexane/EtOAc, 9[thin space (1/6-em)]:[thin space (1/6-em)]1 → 4[thin space (1/6-em)]:[thin space (1/6-em)]1) to obtain MOM ether 2 (11.7 g, 35.3 mmol, 98%) as a pale yellow oil; 1H NMR (400 MHz, CDCl3) δ 1.62 (s, 6H), 3.57 (s, 6H), 5.30 (s, 4H), 7.00 (t, J = 7.8 Hz, 2H), 7.04 (dd, J = 7.8, 1.9 Hz, 2H), 7.09 (dd, J = 7.8, 1.9 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 31.81, 34.46, 56.30, 96.10, 115.78, 119.35, 122.77, 131.61, 141.49, 145.12. Anal. calcd for C19H22O5: C, 69.07; H, 6.71. Found: C, 68.76; H, 6.69.

4,5-Bis(methoxymethoxy)-9,9-dimethylxanthene-3,6-dicarbaldehyde (3)

Under a nitrogen atmosphere, n-butyllithium (1.6 M in hexane, 6.0 mL, 9.6 mmol) was added to a solution of 2 (0.994 g, 3.01 mmol) in dehydrated THF (20 mL) at 0 °C. After the mixture was stirred for 1 h at 0 °C, dehydrated DMF (1.20 mL, 15.5 mmol) was added at 0 °C to the mixture, which was further stirred overnight at rt. After the addition of diluted hydrochloric acid (1.0 M, 20 mL), the mixture was extracted several times with chloroform. The combined organic layer was washed with brine, dried over anhydrous sodium sulfate, filtered, and concentrated to dryness under reduced pressure. The crude product was purified by column chromatography on silica gel (hexane/EtOAc, 9[thin space (1/6-em)]:[thin space (1/6-em)]1 → 4[thin space (1/6-em)]:[thin space (1/6-em)]1) to obtain dialdehyde 3 (0.692 g, 1.79 mmol, 60%) as pale yellow crystals; 1H NMR (400 MHz, CDCl3) δ 1.67 (s, 6H), 3.64 (s, 6H), 5.41 (s, 4H), 7.29 (dd, J = 8.4, 0.7 Hz, 2H), 7.62 (d, J = 8.4 Hz, 2H), 10.44 (d, J = 0.7 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 31.36, 35.65, 58.20, 100.08, 121.38, 122.27, 128.97, 137.33, 143.02, 147.96, 189.40. Anal. calcd for C21H22O7: C, 65.28; H, 5.74. Found: C, 65.01; H, 5.75.

4,5-Dihydroxy-9,9-dimethylxanthene-3,6-dicarbaldehyde (4)

Hydrochloric acid (4.0 M, 9.0 mL) was added to a solution of 3 (2.25 g, 5.82 mmol) in methanol/chloroform (3[thin space (1/6-em)]:[thin space (1/6-em)]1, 48 mL) and the mixture was stirred overnight at rt. After the addition of water, the mixture was extracted with chloroform, and the combined organic layer was dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to a minimal volume. The addition of hexane to the resultant solution produced precipitates, which were collected on a filter to yield 4 (1.62 g, 5.43 mmol, 93%) as yellow crystals; 1H NMR (400 MHz, CDCl3) δ 1.67 (s, 6H), 7.06 (d, J = 8.4 Hz, 2H), 7.33 (d, J = 8.4 Hz, 2H), 9.91 (s, 2H), 11.21 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 31.38, 35.62, 116.34, 119.52, 126.87, 136.81, 138.56, 150.33, 195.77. Anal. calcd for C17H14O5·0.4H2O: C, 66.84; H, 4.88. Found: C, 66.86; H, 4.70.

Macrocyclic ligand H4L2

A solution of 4 (0.298 g, 1.00 mmol) in dehydrated chloroform (5 mL) was mixed with a solution of o-phenylenediamine (0.108 g, 1.00 mmol) in dehydrated acetonitrile (5 mL) and the resultant solution was allowed to stand for 2 d at rt. The reaction mixture was then filtered using a membrane filter and the filtrate was concentrated under reduced pressure to a minimal volume. The addition of hexane to the resultant solution gave precipitates, which were collected on a filter to yield H4L2 (0.365 g, 0.443 mmol, 89%) as orange crystals; 1H NMR (400 MHz, DMSO-d6) δ 1.64 (s, 12H), 7.17 (d, J = 8.4 Hz, 4H), 7.41 (d, J = 8.4 Hz, 4H), 7.46–7.50 (m, 4H), 7.56–7.60 (m, 4H), 8.99 (s, 4H), 13.82 (s, 4H); 13C NMR (100 MHz, DMSO-d6) δ 31.48, 34.93, 115.76, 117.68, 119.65, 126.74, 128.39, 133.93, 138.03, 141.82, 149.70, 164.56. ESI-TOF MS observed m/z = 741.2737 ([H4L2 + H]+), calcd for C46H36N4O6H m/z = 741.2713. Anal. calcd for C46H36N4O6·0.7CHCl3: C, 68.04; H, 4.49, N, 6.80. Found: C, 67.82; H, 4.78, N, 6.82.

Macrocyclic metallohost L2Ni2

A solution of H4L2 (21.0 mg, 28.3 μmol) in chloroform/methanol (1[thin space (1/6-em)]:[thin space (1/6-em)]1, 4 mL) was mixed with a solution of nickel(II) acetate tetrahydrate (21.1 mg, 84.8 μmol) in methanol (1.5 mL). After stirring for 6 h at rt, the resultant precipitates were collected on a filter to yield L2Ni2 (14.6 mg, 15.9 μmol, 56%) as brown crystals; 1H NMR (400 MHz, DMSO-d6) δ 1.61 (s, 12H), 6.88 (d, J = 8.6 Hz, 4H), 7.33–7.38 (m, 4H), 7.40 (d, J = 8.6 Hz, 4H), 8.15–8.19 (m, 4H), 8.85 (s, 4H). Anal. calcd for C46H32N4O6Ni2·3.5H2O: C, 60.24; H, 4.29, N, 6.11. Found: C, 60.26; H, 4.14, N, 6.16.

X-ray crystallography

The intensity data were collected at 93 K on a Rigaku Mercury diffractometer (Mo Kα, λ = 0.71073 Å) or a Bruker APEX diffractometer (Cu Kα, λ = 1.54178 Å). The data were corrected for Lorentz and polarization factors, and for absorption by using semiempirical methods based on symmetry-equivalent and repeated reflections. The structures were solved by direct methods (SHELXS 97 or SIR 97)19 and refined by full-matrix least-squares on F2 using SHELXL 2014.20 The crystallographic data are summarized in Table 2.
Table 2 Crystallographic data
  H4L2·0.5CHCl3·2.5MeCN L2Ni2·0.67H2O·0.67MeOH·1.33DMSO [L2Ni2Na(DMSO)2](OTf)·DMSO
Formula C51.5H44Cl1.5N6.5O6 C49.33H44N4Ni2O8.67S1.33 C53H50F3N4NaNi2O12S4
a R 1 = ∑||Fo| − |Fc||/|Fo|; wR2 = {∑w(Fo2Fc2)2/∑[w(Fo2)2]}1/2.
Formula weight 903.10 991.72 1260.62
Crystal system Monoclinic Monoclinic Monoclinic
Space group P21/m P21/n Pn
a (Å) 10.9940(14) 16.3754(5) 10.7194(4)
b (Å) 23.218(3) 21.6479(6) 9.1083(3)
c (Å) 17.421(3) 19.6275(6) 26.4196(9)
α (°) 90 90 90
β (°) 99.151(4) 111.4120(10) 99.796(2)
γ (°) 90 90 90
V3) 4390.2(10) 6477.6(3) 2541.88(15)
Z 4 6 2
D calcd (g cm−3) 1.366 1.525 1.647
μ (mm−1) 0.178 2.217 3.239
Collected/unique reflections 41[thin space (1/6-em)]360/7892 49[thin space (1/6-em)]196/11[thin space (1/6-em)]574 19[thin space (1/6-em)]130/7753
2θmax 50.00 134.24 136.73
R int 0.0460 0.0271 0.0484
Limiting indices −13 ≤ h ≤ 12 −19 ≤ h ≤ 19 −12 ≤ h ≤ 12
−27 ≤ k ≤ 27 −23 ≤ k ≤ 25 −10 ≤ k ≤ 10
−20 ≤ l ≤ 19 −23 ≤ l ≤ 23 −31 ≤ l ≤ 30
Parameters/restraints 660/53 1044/277 796/136
GOF (F2) 1.078 1.014 1.006
R 1 (I > 2σ(I))a 0.0647 0.0334 0.0363
R 1 (all data)a 0.0749 0.0384 0.0472
wR2 (I > 2σ(I))a 0.1650 0.0854 0.0735
wR2 (all data)a 0.1804 0.0886 0.0777
CCDC No. 2448855 2448856 2448857


Computational methods

The Gaussian 16 program21 was used for the DFT calculations. Geometries of the ligand (H4L2) and the metal complexes (L2Ni2 and [L2Ni2Na]+) were optimized at the B3LYP/6-311G**22 level with Grimme's D3 dispersion correction.23 The relative energies of the different conformations were calculated at the same level using the optimized geometries. Interaction energies were calculated by the supermolecule method at the B3LYP/6-311G** level with Grimme's D3 dispersion correction. The basis set superposition error (BSSE)24 was corrected by the counterpoise method.25

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the ESI. Crystallographic data for H4L2·0.5CHCl3·2.5MeCN, L2Ni2·0.67H2O·0.67MeOH·1.33DMSO, and [L2Ni2Na(DMSO)2](OTf)·DMSO have been deposited at the CCDC under 2448855, 2448856, and 2448857 and can be obtained from https://www.ccdc.cam.ac.uk/.

Acknowledgements

We thank Dr Kenji Yoza (Bruker AXS) for the X-ray data collection of L2Ni2·0.67H2O·0.67MeOH·1.33DMSO and [L2Ni2Na(DMSO)2](OTf)·DMSO. The research was partly supported by the Japan Society for the Promotion of Science (KAKENHI Grants JP21H05477 and JP23H04021 [Condensed Conjugation] as well as JP16H06510 [Coordination Asymmetry], JP18H03913, JP20K21206, JP23K17928 and JP23H01972) and the World Premier International Research Initiative, Ministry of Education, Culture, Sports, Science and Technology, Japan.

References

  1. (a) M. Kivala and F. Diederich, Acc. Chem. Res., 2009, 42, 235–248 CrossRef CAS PubMed; (b) J. A. Shelnutt, C. J. Medforth, M. D. Berber, K. M. Barkigia and K. M. Smith, J. Am. Chem. Soc., 1991, 113, 4077–4087 CrossRef CAS; (c) N. I. Nijegorodov and W. S. Downey, J. Phys. Chem., 1994, 98, 5639–5643 CrossRef CAS; (d) M. Kanematsu, P. Naumov, T. Kojima and S. Fukuzumi, Chem. – Eur. J., 2011, 17, 12372–12384 CrossRef CAS PubMed; (e) F. Nifiatis, W. Su, J. E. Haley, J. E. Slagle and T. M. Cooper, J. Phys. Chem. A, 2011, 115, 13764–13772 CrossRef CAS PubMed.
  2. (a) P. Frère and P. J. Skabara, Chem. Soc. Rev., 2005, 34, 69–98 RSC; (b) S. Maji and S. Sarkar, Inorg. Chim. Acta, 2010, 363, 2778–2785 CrossRef CAS.
  3. (a) F. Zhang, R. Wang, Y. Wang, X. Zhanga and B. Liu, Phys. Chem. Chem. Phys., 2019, 21, 6256–6264 RSC; (b) Y. Liu, X. Zhang, C. Li, Y. Tian, F. Zhang, Y. Wang, W. Wu and B. Liu, J. Phys. Chem. C, 2019, 123, 13531–13537 CrossRef CAS.
  4. (a) M. O. Senge, C. J. Medforth, T. P. Forsyth, D. A. Lee, M. M. Olmstead, W. Jentzen, R. K. Pandey, J. A. Shelnutt and K. M. Smith, Inorg. Chem., 1997, 36, 1149–1163 CrossRef CAS PubMed; (b) J. L. Retsek, C. J. Medforth, D. J. Nurco, S. Gentemann, V. S. Chirvony, K. M. Smith and D. Holten, J. Phys. Chem. B, 2001, 105, 6396–6411 CrossRef CAS; (c) T. Chandra, B. J. Kraft, J. C. Huffman and J. M. Zaleski, Inorg. Chem., 2003, 42, 5158–5172 CrossRef CAS PubMed; (d) P. Bhyrappa, M. Sankar and B. Varghese, Inorg. Chem., 2006, 45, 4136–4149 CrossRef CAS PubMed; (e) A. Y. Lebedev, M. A. Filatov, A. V. Cheprakov and S. A. Vinogradov, J. Phys. Chem. A, 2008, 112, 7723–7733 CrossRef CAS PubMed; (f) G. Conboy, H. J. Spencer, E. Angioni, A. L. Kanibolotsky, N. J. Findlay, S. J. Coles, C. Wilson, M. B. Pitak, C. Risko, V. Coropceanu, J.-L. Brédas and P. J. Skabara, Mater. Horiz., 2016, 3, 333–339 RSC; (g) Z. Zhang, M. Li, Y. Liu, J. Zhang, S. Feng, X. Xu, J. Song and Z. Bo, J. Mater. Chem. A, 2017, 5, 7776–7783 RSC; (h) S. Kamiguchi, R. Akasaka, N. Yoshida, T. Imai, Y. Yamaoka, T. Amaya and T. Iwasawa, Tetrahedron Lett., 2022, 92, 153664 CrossRef CAS.
  5. (a) C. Yuan, S. Saito, C. Camacho, S. Irle, I. Hisaki and S. Yamaguchi, J. Am. Chem. Soc., 2013, 135, 8842–8845 CrossRef CAS PubMed; (b) R. Kotani, H. Sotome, H. Okajima, S. Yokoyama, Y. Nakaike, A. Kashiwagi, C. Mori, Y. Nakada, S. Yamaguchi, A. Osuka, A. Sakamoto, H. Miyasaka and S. Saito, J. Mater. Chem. C, 2017, 5, 5248–5256 RSC.
  6. (a) S. Thyagarajan, T. Leiding, S. P. Årsköld, A. V. Cheprakov and S. A. Vinogradov, Inorg. Chem., 2010, 49, 9909–9920 CrossRef CAS PubMed; (b) M. Ballester, L. Ravotto, J. M. E. Quirke, R. L. de la Vega, J. A. Shelnutt, A. V. Cheprakov, S. A. Vinogradov and C. J. Medforth, J. Phys. Chem. A, 2020, 124, 8994–9003 CrossRef CAS PubMed.
  7. (a) Z. Valicsek and O. Horváth, Microchem. J., 2013, 107, 47–62 CrossRef CAS; (b) M. Park, D.-G. Kang, H. Ko, M. Rim, D. T. Tran, S. Park, M. Kang, T.-W. Kim, N. Kim and K.-U. Jeong, Mater. Horiz., 2020, 7, 2635–2642 RSC.
  8. B. A. Hussein, Z. Shakeel, A. T. Turley, A. N. Bismillah, K. M. Wolfstadt, J. E. Pia, M. Pilkington, P. R. McGonigal and M. J. Adler, Inorg. Chem., 2020, 59, 13533–13541 CrossRef CAS PubMed.
  9. S. Akine, F. Utsuno and T. Nabeshima, Chem. Commun., 2010, 46, 1029–1031 RSC.
  10. S. Akine, F. Utsuno, S. Piao, H. Orita, S. Tsuzuki and T. Nabeshima, Inorg. Chem., 2016, 55, 810–821 CrossRef CAS PubMed.
  11. S. Akine, M. Nakano, Y. Sakata and S. Yano, Chem. – Eur. J., 2024, 30, e202403071 CrossRef CAS PubMed.
  12. (a) Y. Sakata, C. Murata and S. Akine, Nat. Commun., 2017, 8, 16005 CrossRef CAS PubMed; (b) Y. Sakata, M. Tamiya, M. Okada and S. Akine, J. Am. Chem. Soc., 2019, 141, 15597–15604 CrossRef CAS PubMed; (c) M. Cametti, Y. Sakata, J. Martí-Rujas and S. Akine, Inorg. Chem., 2019, 58, 14871–14875 CrossRef CAS PubMed; (d) Y. Sakata, M. Okada, M. Tamiya and S. Akine, Chem. – Eur. J., 2020, 26, 7595–7601 CrossRef CAS PubMed; (e) Y. Sakata, M. Okada and S. Akine, Chem. – Eur. J., 2021, 27, 2284–2288 CrossRef CAS PubMed; (f) M. T. Chaudhry, B. O. Patrick, S. Akine and M. J. MacLachlan, Org. Biomol. Chem., 2022, 20, 8259–8268 RSC; (g) D. Walter, Y. Sakata and S. Akine, Chem. – Asian J., 2025, 20, e202401876 CrossRef CAS PubMed.
  13. Related macrocyclic bis(saloph) structures, see: (a) S. Akine, Z. Varadi and T. Nabeshima, Eur. J. Inorg. Chem., 2013, 5987–5998 CrossRef CAS; (b) Y. Sakata, S. Kobayashi and S. Akine, Chem. Commun., 2017, 53, 6363–6366 RSC; (c) Y. Sakata, S. Kobayashi, M. Yamamoto, K. Doken, M. Kamezawa, S. Yamaki and S. Akine, Commun. Chem., 2024, 7, 166 CrossRef CAS PubMed.
  14. (a) A. Radha, M. Seshasayee, K. Ramalingam and G. Aravamudan, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 1985, 41, 1169–1171 CrossRef; (b) J. Wang, F.-L. Bei, X.-Y. Xu, X.-J. Yang and X. Wang, J. Chem. Crystallogr., 2003, 33, 845–849 CrossRef CAS.
  15. (a) A. J. Gallant and M. J. MacLachlan, Angew. Chem., Int. Ed., 2003, 42, 5307–5310 CrossRef CAS PubMed; (b) S.-i. Kawano, Y. Ishida and K. Tanaka, J. Am. Chem. Soc., 2015, 137, 2295–2302 CrossRef CAS PubMed.
  16. Y. Sato, R. Yamasaki and S. Saito, Angew. Chem., Int. Ed., 2009, 48, 504–507 CrossRef CAS PubMed.
  17. (a) S. Akine and T. Nabeshima, Dalton Trans., 2009, 10395–10408 RSC; (b) S. Akine, J. Inclusion Phenom. Macrocyclic Chem., 2012, 72, 25–54 CrossRef CAS; (c) S. Akine, Metal Complexes with Oligo(salen)-Type Ligands, in The Chemistry of Metal Phenolates, Volume 2, ed. J. Zabicky, Patai's Chemistry of Functional Groups, John Wiley and Sons Ltd, Chichester, 2018, ch. 4, pp. 153–194 Search PubMed.
  18. M. Llunell, D. Casanova, J. Cirera, P. Alemany and S. Alvarez, SHAPE 2.1, University of Barcelona, Barcelona, Spain, 2013 Search PubMed.
  19. (a) G. M. Sheldrick, SHELXS 97. Program for Crystal Structure Solution, University of Göttingen, Göttingen (Germany), 1997; (b) A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori and R. Spagna, J. Appl. Crystallogr., 1999, 32, 115–119 CrossRef CAS.
  20. G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem., 2015, 71, 3–8 Search PubMed.
  21. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B. Foresman and D. J. Fox, Gaussian 16, Revision C.01, Gaussian, Inc., Wallingford CT, 2016 Search PubMed.
  22. A. D. Becke, J. Chem. Phys., 1993, 98, 5648–5652 CrossRef CAS.
  23. S. Grimme, J. Antony, S. Ehrlich and H. Krieg, J. Chem. Phys., 2010, 132, 154104 CrossRef PubMed.
  24. B. J. Ransil, J. Chem. Phys., 1961, 34, 2109–2118 CrossRef CAS.
  25. S. F. Boys and F. Bernardi, Mol. Phys., 1970, 19, 553–566 CrossRef CAS.

Footnotes

Electronic supplementary information (ESI) available. CCDC 2448855–2448857. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d5dt01183c
H2saloph = N,N′-disalicylidene-o-phenylenediamine.

This journal is © The Royal Society of Chemistry 2025
Click here to see how this site uses Cookies. View our privacy policy here.