4,4′-(Acridine-2,7-di­yl)bis­(2-methyl­but-3-yn-2-ol)

Yamamura, M.; Ikuma, S.; Nabeshima, T.

doi:10.1107/S2414314625009150

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 10| Part 10| October 2025| x250915

https://doi.org/10.1107/S2414314625009150

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4,4′-(Acridine-2,7-diyl)bis(2-methylbut-3-yn-2-ol)

Masaki Yamamura,^a ^* Seira Ikuma ^b and Tatsuya Nabeshima ^b

^aCenter for Liberal Arts and Science, Faculty of Engineering, Toyama Prefectural University, 5180, Kurokawa, Imizu, Toyama 939-0398, Japan, and ^bGraduate School of Pure and Applied Sciences, Tsukuba Research Center for, Interdisciplinary Materials Science (TIMS), University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8571, Japan
^*Correspondence e-mail: [email protected]

Edited by I. Brito, University of Antofagasta, Chile (Received 16 October 2025; accepted 18 October 2025; online 31 October 2025)

The title acridine derivative, C₂₃H₂₁NO₂, which has two 2-methylbut-3-yn-2-ol moieties at the 2,7-positions, was synthesized by Sonogashira coupling reaction. In the crystal, a columnar structure is formed by the π–π stacking of acridine units. The 2-methylbut-3-yn-2-ol moieties form intermolecular hydrogen bonds.

Keywords: acridine; π–π stacking; hydrogen bond; crystal structure.

CCDC reference: 2496569

Structure description

Acridine is often used as a luminophore (Ryan et al., 1997 ) and DNA-intercalator (Lerman, 1963 ). It is known to crystallize in seven polymorphic forms, in which various intermolecular interactions, i.e., π–π, C—H–π, and C—H–N interactions, are observed (Mei & Wolf, 2004 ).

The title compound (Fig. 1) was synthesized by the Sonogashira coupling reaction of 2,7-dibromoacridine with 2-methylbut-3-yn-2-ol. The structure of the core acridine unit of the title compound is very similar to those of other 2,7-substituted acridine (Yamamura et al., 2015 ). All the bond lengths and angles in the acridine unit are in expected ranges. The C12 and C13 atoms in a triple bond are within the least-square plane of the acridine unit (Fig. 2). In contrast, the C16 and C17 atoms in the other triple bond are separated from the plane. The distance of C16 from the plane is 0.179 (3) Å and that of C17 is 0.331 (3) Å.

Figure 1
Molecular structure of the title compound with 50% probability ellipsoids.

Figure 2
Side view of molecular structure. Terminal methyl and hydroxy groups are omitted for clarify.

In the crystal, a columnar structure was observed due to the π–π stacking of acridine units (Fig. 3). The distance between the least-square planes of the acridine units is 3.505 Å. The acridine unit is arranged in anti-fashion toward a neighbor acridine unit. Intermolecular hydrogen bonds also link molecules (Table 1). Two hydroxy groups of 1 form hydrogen bonds with two different molecules, between which another molecule is inserted.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H20⋯O2ⁱ	0.84	2.04	2.794 (4)	149
O2—H21⋯O1ⁱⁱ	0.84	1.94	2.735 (4)	158
Symmetry codes: (i) $[x-1, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (ii) $[-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Figure 3
Packing of the title compound

Synthesis and crystallization

A mixture of 2,7-dibromoacridine (Vlassa et al., 1995 ) (0.158 g, 47.0 mmol), 2-methylbut-3-yn-2-ol (0.15 ml, 1.5 mmol), PdCl₂(PPh₃)₂ (6.7 mg, 2 mol%), and CuI (1.6 mg, 2 mol%) were refluxed for 15 h in diisopropylamine (45 ml). After evaporation, the residue was extracted with CH₂Cl₂ then washed with water. After evaporation, the crude products were separated by silica-gel column chromatography to give the yellow powder of the title compound in 43% yield. Yellow crystals suitable for X-ray analysis were obtained form a CHCl₃/hexane solution.

¹H NMR (300 MHz, CDCl₃): δ 8.62 (s, 1H), 8.14 (d, J = 8.9 Hz, 2H), 8.09 (d, J = 1.7 Hz, 2H), 7.73 (dd, J = 1.7, 8.9 Hz, 2H), 2.08 (s, 2H), 1.70 (s, 12H); ¹³C NMR (100 MHz, CDCl₃): δ 149.1 (CH), 136.2 (C), 133.9 (CH), 132.3 (CH), 130.2 (CH), 127.1 (CH), 121.3 (C), 84.7 (C), 82.6 (C), 66.3 (C), 31.7 (CH₃); Analysis calculated for C₂₃H₂₁NO₂: C, 80.44; H, 6.16; N, 4.08; Found: C, 80.13; H, 5.99; N, 3.89.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	C₂₃H₂₁NO₂
M_r	343.41
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	120
a, b, c (Å)	16.023 (13), 9.496 (7), 12.215 (10)
β (°)	99.646 (10)
V (Å³)	1832 (2)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.08
Crystal size (mm)	0.20 × 0.20 × 0.05

Data collection
Diffractometer	Bruler APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.843, 0.915
No. of measured, independent and observed [I > 2σ(I)] reflections	10340, 3058, 1605
R_int	0.093
(sin θ/λ)_max (Å⁻¹)	0.585

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.056, 0.122, 1.01
No. of reflections	3058
No. of parameters	241
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.32, −0.28
Computer programs: APEX2 and SAINT (Bruker, 2014 ), SHELXT (Sheldrick, 2015a ) , SHELXL2019/1 (Sheldrick, 2015b ) and Mercury (Macrae et al., 2020 ).

Structural data

CCDC reference: 2496569

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314625009150/bx4038sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314625009150/bx4038Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314625009150/bx4038Isup3.cml

checkCIF report

Computing details top

4,4'-(Acridine-2,7-diyl)bis(2-methylbut-3-yn-2-ol) top

Crystal data top

C₂₃H₂₁NO₂	F(000) = 728
M_r = 343.41	D_x = 1.245 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 16.023 (13) Å	Cell parameters from 476 reflections
b = 9.496 (7) Å	θ = 2.5–26.6°
c = 12.215 (10) Å	µ = 0.08 mm⁻¹
β = 99.646 (10)°	T = 120 K
V = 1832 (2) Å³	Prism, colorless
Z = 4	0.20 × 0.20 × 0.05 mm

Data collection top

Bruler APEXII CCD diffractometer	1605 reflections with I > 2σ(I)
Radiation source: fine-focus seald tube	R_int = 0.093
φ and ω scan	θ_max = 24.6°, θ_min = 1.3°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −18→18
T_min = 0.843, T_max = 0.915	k = −11→11
10340 measured reflections	l = −14→11
3058 independent reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.056	H-atom parameters constrained
wR(F²) = 0.122	w = 1/[σ²(F_o²) + (0.030P)² + 1.P] where P = (F_o² + 2F_c²)/3
S = 1.01	(Δ/σ)_max < 0.001
3058 reflections	Δρ_max = 0.32 e Å⁻³
241 parameters	Δρ_min = −0.28 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O1	0.05976 (13)	0.6608 (2)	0.54622 (18)	0.0336 (6)
H20	0.046205	0.632400	0.480520	0.050*
O2	0.95459 (13)	−0.0895 (2)	0.8478 (2)	0.0391 (7)
H21	0.936554	−0.016649	0.875071	0.059*
N1	0.49494 (16)	0.2007 (3)	0.3889 (2)	0.0259 (7)
C1	0.57022 (19)	0.1892 (3)	0.5807 (3)	0.0222 (8)
C2	0.51585 (19)	0.2890 (3)	0.6130 (3)	0.0236 (8)
H1	0.523062	0.319641	0.688064	0.028*
C3	0.44299 (19)	0.2968 (3)	0.4223 (3)	0.0221 (8)
C4	0.45037 (19)	0.3441 (3)	0.5345 (3)	0.0201 (8)
C5	0.55663 (19)	0.1465 (3)	0.4664 (3)	0.0227 (8)
C6	0.39012 (19)	0.4417 (3)	0.5630 (3)	0.0238 (8)
H2	0.394231	0.472234	0.637781	0.029*
C7	0.1346 (2)	0.7473 (3)	0.5551 (3)	0.0269 (8)
C8	0.60864 (19)	0.0387 (3)	0.4338 (3)	0.0246 (8)
H3	0.600074	0.008741	0.358542	0.030*
C9	0.68701 (19)	0.0220 (3)	0.6217 (3)	0.0246 (8)
C10	0.3259 (2)	0.4925 (3)	0.4836 (3)	0.0263 (9)
C11	0.3759 (2)	0.3515 (3)	0.3423 (3)	0.0275 (9)
H4	0.370215	0.321267	0.267231	0.033*
C12	0.8143 (2)	−0.1025 (3)	0.7458 (3)	0.0286 (9)
C13	0.7548 (2)	−0.0444 (3)	0.6939 (3)	0.0257 (8)
C14	0.88472 (19)	−0.1841 (3)	0.8114 (3)	0.0277 (8)
C15	0.63762 (19)	0.1265 (3)	0.6553 (3)	0.0251 (8)
H5	0.648782	0.157535	0.730252	0.030*
C16	0.2620 (2)	0.5886 (3)	0.5099 (3)	0.0274 (9)
C17	0.2065 (2)	0.6609 (3)	0.5275 (3)	0.0256 (8)
C18	0.6699 (2)	−0.0219 (3)	0.5076 (3)	0.0274 (9)
H6	0.702629	−0.095674	0.483679	0.033*
C19	0.3198 (2)	0.4463 (3)	0.3715 (3)	0.0293 (9)
H7	0.276038	0.482228	0.316502	0.035*
C20	0.1141 (2)	0.8677 (3)	0.4733 (3)	0.0307 (9)
H8	0.102475	0.830157	0.397582	0.046*
H9	0.162315	0.932392	0.480441	0.046*
H10	0.064129	0.918263	0.489222	0.046*
C21	0.1557 (2)	0.7998 (3)	0.6747 (3)	0.0335 (9)
H11	0.108256	0.855329	0.692606	0.050*
H12	0.206642	0.858645	0.683083	0.050*
H13	0.165849	0.719074	0.725186	0.050*
C22	0.8534 (2)	−0.2498 (3)	0.9101 (3)	0.0352 (9)
H14	0.899577	−0.302739	0.954676	0.053*
H15	0.806286	−0.313714	0.883803	0.053*
H16	0.834173	−0.175585	0.955753	0.053*
C23	0.9165 (2)	−0.2961 (3)	0.7380 (3)	0.0382 (10)
H17	0.941707	−0.249937	0.679546	0.057*
H18	0.868982	−0.355098	0.704005	0.057*
H19	0.959236	−0.354900	0.783358	0.057*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0267 (13)	0.0324 (14)	0.0409 (18)	−0.0101 (11)	0.0031 (12)	−0.0138 (12)
O2	0.0330 (15)	0.0263 (14)	0.0553 (19)	−0.0053 (12)	−0.0010 (13)	−0.0019 (13)
N1	0.0270 (16)	0.0263 (15)	0.0247 (19)	0.0009 (14)	0.0048 (14)	0.0022 (13)
C1	0.0202 (18)	0.0209 (17)	0.026 (2)	−0.0004 (15)	0.0052 (16)	0.0019 (16)
C2	0.0246 (19)	0.0260 (18)	0.020 (2)	−0.0046 (16)	0.0036 (16)	−0.0035 (16)
C3	0.0223 (19)	0.0203 (18)	0.024 (2)	0.0011 (15)	0.0054 (16)	0.0012 (16)
C4	0.0214 (18)	0.0194 (17)	0.021 (2)	−0.0019 (15)	0.0069 (16)	−0.0002 (15)
C5	0.0240 (19)	0.0218 (18)	0.023 (2)	−0.0006 (16)	0.0048 (17)	0.0032 (16)
C6	0.025 (2)	0.0231 (18)	0.025 (2)	−0.0008 (16)	0.0082 (17)	−0.0020 (16)
C7	0.0214 (19)	0.0197 (17)	0.039 (2)	−0.0002 (15)	0.0037 (16)	−0.0033 (16)
C8	0.025 (2)	0.0248 (18)	0.025 (2)	0.0012 (16)	0.0070 (17)	0.0004 (16)
C9	0.0196 (19)	0.0246 (19)	0.030 (3)	−0.0018 (16)	0.0048 (17)	0.0004 (17)
C10	0.025 (2)	0.0237 (18)	0.031 (3)	0.0000 (16)	0.0081 (18)	0.0005 (17)
C11	0.030 (2)	0.0279 (19)	0.023 (2)	−0.0008 (17)	−0.0002 (17)	0.0030 (16)
C12	0.033 (2)	0.0233 (18)	0.031 (2)	0.0005 (17)	0.0073 (18)	0.0015 (17)
C13	0.025 (2)	0.0222 (18)	0.030 (2)	−0.0017 (17)	0.0034 (17)	−0.0004 (16)
C14	0.0227 (19)	0.0238 (18)	0.035 (2)	−0.0020 (16)	0.0001 (16)	−0.0005 (17)
C15	0.026 (2)	0.0258 (19)	0.023 (2)	−0.0051 (16)	0.0016 (16)	0.0018 (16)
C16	0.023 (2)	0.0285 (19)	0.032 (2)	0.0013 (17)	0.0071 (17)	0.0038 (17)
C17	0.027 (2)	0.0202 (18)	0.029 (2)	−0.0016 (16)	0.0020 (16)	0.0013 (15)
C18	0.026 (2)	0.0225 (19)	0.036 (3)	0.0017 (16)	0.0114 (18)	−0.0033 (17)
C19	0.024 (2)	0.030 (2)	0.034 (3)	0.0030 (16)	0.0052 (17)	0.0085 (18)
C20	0.0251 (19)	0.0263 (19)	0.040 (2)	0.0039 (15)	0.0053 (17)	0.0047 (17)
C21	0.039 (2)	0.0278 (19)	0.034 (2)	−0.0010 (17)	0.0065 (18)	−0.0082 (17)
C22	0.040 (2)	0.035 (2)	0.032 (2)	0.0013 (18)	0.0117 (18)	0.0105 (18)
C23	0.029 (2)	0.045 (2)	0.040 (3)	0.0041 (18)	0.0023 (18)	−0.0062 (19)

Geometric parameters (Å, º) top

O1—C7	1.442 (4)	C10—C19	1.425 (5)
O1—H20	0.8400	C10—C16	1.448 (4)
O2—C14	1.446 (4)	C11—C19	1.362 (4)
O2—H21	0.8400	C11—H4	0.9500
N1—C3	1.344 (4)	C12—C13	1.189 (4)
N1—C5	1.351 (4)	C12—C14	1.487 (5)
C1—C2	1.388 (4)	C14—C22	1.516 (4)
C1—C15	1.422 (4)	C14—C23	1.533 (4)
C1—C5	1.435 (4)	C15—H5	0.9500
C2—C4	1.400 (4)	C16—C17	1.171 (4)
C2—H1	0.9500	C18—H6	0.9500
C3—C11	1.424 (4)	C19—H7	0.9500
C3—C4	1.427 (4)	C20—H8	0.9800
C4—C6	1.423 (4)	C20—H9	0.9800
C5—C8	1.419 (4)	C20—H10	0.9800
C6—C10	1.377 (4)	C21—H11	0.9800
C6—H2	0.9500	C21—H12	0.9800
C7—C17	1.498 (4)	C21—H13	0.9800
C7—C20	1.518 (4)	C22—H14	0.9800
C7—C21	1.527 (4)	C22—H15	0.9800
C8—C18	1.346 (4)	C22—H16	0.9800
C8—H3	0.9500	C23—H17	0.9800
C9—C15	1.374 (4)	C23—H18	0.9800
C9—C13	1.427 (4)	C23—H19	0.9800
C9—C18	1.436 (4)

C7—O1—H20	109.5	O2—C14—C12	108.7 (3)
C14—O2—H21	109.5	O2—C14—C22	110.7 (3)
C3—N1—C5	117.6 (3)	C12—C14—C22	108.7 (3)
C2—C1—C15	123.3 (3)	O2—C14—C23	107.1 (2)
C2—C1—C5	118.0 (3)	C12—C14—C23	110.0 (3)
C15—C1—C5	118.7 (3)	C22—C14—C23	111.5 (3)
C1—C2—C4	119.6 (3)	C9—C15—C1	121.6 (3)
C1—C2—H1	120.2	C9—C15—H5	119.2
C4—C2—H1	120.2	C1—C15—H5	119.2
N1—C3—C11	118.2 (3)	C17—C16—C10	175.8 (4)
N1—C3—C4	123.3 (3)	C16—C17—C7	176.7 (3)
C11—C3—C4	118.4 (3)	C8—C18—C9	121.7 (3)
C2—C4—C6	122.5 (3)	C8—C18—H6	119.2
C2—C4—C3	118.2 (3)	C9—C18—H6	119.2
C6—C4—C3	119.3 (3)	C11—C19—C10	120.9 (3)
N1—C5—C8	118.3 (3)	C11—C19—H7	119.5
N1—C5—C1	123.3 (3)	C10—C19—H7	119.5
C8—C5—C1	118.4 (3)	C7—C20—H8	109.5
C10—C6—C4	120.9 (3)	C7—C20—H9	109.5
C10—C6—H2	119.6	H8—C20—H9	109.5
C4—C6—H2	119.6	C7—C20—H10	109.5
O1—C7—C17	109.4 (2)	H8—C20—H10	109.5
O1—C7—C20	107.1 (3)	H9—C20—H10	109.5
C17—C7—C20	110.8 (3)	C7—C21—H11	109.5
O1—C7—C21	107.8 (3)	C7—C21—H12	109.5
C17—C7—C21	109.8 (3)	H11—C21—H12	109.5
C20—C7—C21	111.9 (3)	C7—C21—H13	109.5
C18—C8—C5	121.2 (3)	H11—C21—H13	109.5
C18—C8—H3	119.4	H12—C21—H13	109.5
C5—C8—H3	119.4	C14—C22—H14	109.5
C15—C9—C13	123.5 (3)	C14—C22—H15	109.5
C15—C9—C18	118.3 (3)	H14—C22—H15	109.5
C13—C9—C18	118.3 (3)	C14—C22—H16	109.5
C6—C10—C19	119.4 (3)	H14—C22—H16	109.5
C6—C10—C16	122.5 (3)	H15—C22—H16	109.5
C19—C10—C16	118.0 (3)	C14—C23—H17	109.5
C19—C11—C3	121.0 (3)	C14—C23—H18	109.5
C19—C11—H4	119.5	H17—C23—H18	109.5
C3—C11—H4	119.5	C14—C23—H19	109.5
C13—C12—C14	175.9 (3)	H17—C23—H19	109.5
C12—C13—C9	174.1 (4)	H18—C23—H19	109.5

C15—C1—C2—C4	−179.2 (3)	C3—C4—C6—C10	−1.1 (4)
C5—C1—C2—C4	0.0 (4)	N1—C5—C8—C18	−178.4 (3)
C5—N1—C3—C11	−178.0 (3)	C1—C5—C8—C18	−0.5 (4)
C5—N1—C3—C4	0.4 (4)	C4—C6—C10—C19	0.1 (4)
C1—C2—C4—C6	177.0 (3)	C4—C6—C10—C16	178.1 (3)
C1—C2—C4—C3	−1.1 (4)	N1—C3—C11—C19	178.3 (3)
N1—C3—C4—C2	1.0 (4)	C4—C3—C11—C19	−0.2 (4)
C11—C3—C4—C2	179.3 (3)	C13—C9—C15—C1	−179.6 (3)
N1—C3—C4—C6	−177.3 (3)	C18—C9—C15—C1	0.9 (4)
C11—C3—C4—C6	1.1 (4)	C2—C1—C15—C9	176.1 (3)
C3—N1—C5—C8	176.1 (3)	C5—C1—C15—C9	−3.1 (4)
C3—N1—C5—C1	−1.6 (4)	C5—C8—C18—C9	−1.7 (5)
C2—C1—C5—N1	1.4 (4)	C15—C9—C18—C8	1.6 (5)
C15—C1—C5—N1	−179.3 (3)	C13—C9—C18—C8	−178.0 (3)
C2—C1—C5—C8	−176.3 (3)	C3—C11—C19—C10	−0.8 (5)
C15—C1—C5—C8	2.9 (4)	C6—C10—C19—C11	0.8 (5)
C2—C4—C6—C10	−179.2 (3)	C16—C10—C19—C11	−177.3 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H20···O2ⁱ	0.84	2.04	2.794 (4)	149
O2—H21···O1ⁱⁱ	0.84	1.94	2.735 (4)	158

Symmetry codes: (i) x−1, −y+1/2, z−1/2; (ii) −x+1, y−1/2, −z+3/2.

Funding information

Funding for this research was provided by: MEXT, Japan (grant No. 15H00985).

References

Bruker (2014). APEX2 and SAINT. Bruker AXS Inc.,Madison, Wisconsin, USA. Google Scholar
Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3–10. Web of Science CSD CrossRef ICSD CAS IUCr Journals Google Scholar
Lerman, L. S. (1963). Proc. Natl Acad. Sci. USA 49, 94–102. CrossRef PubMed CAS Google Scholar
Macrae, C. F., Sovago, I., Cottrell, S. J., Galek, P. T. A., McCabe, P., Pidcock, E., Platings, M., Shields, G. P., Stevens, J. S., Towler, M. & Wood, P. A. (2020). J. Appl. Cryst. 53, 226–235. Web of Science CrossRef CAS IUCr Journals Google Scholar
Mei, X. & Wolf, C. (2004). Cryst. Growth Des. 4, 1099–1103. Web of Science CSD CrossRef CAS Google Scholar
Ryan, E. T., Xiang, T., Johnston, K. P. & Fox, M. A. (1997). J. Phys. Chem. A 101, 1827–1835. CrossRef CAS Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Vlassa, M., Silberg, I. A., Custelceanu, R. & Culea, M. (1995). Synth. Commun. 25, 3493–3501. CrossRef CAS Google Scholar
Yamamura, M., Ikuma, S. & Nabeshima, T. (2015). J. Mol. Struct. 1093, 59–64. CrossRef CAS Google Scholar

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