4′-Formyl­benzo-15-crown-5

Fischer, C.; Helas, S.F.; Seichter, W.; Weber, E.; Ibragimov, B.T.

doi:10.1107/S1600536808022186

organic compounds

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ISSN: 2056-9890

Volume 64| Part 8| August 2008| Page o1556

doi:10.1107/S1600536808022186

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4′-Formylbenzo-15-crown-5

Conrad Fischer,^a Stefanie F. Helas,^a Wilhelm Seichter,^a Edwin Weber ^a and Bakhtiyar T. Ibragimov ^b ^*

^aInstitut für Organische Chemie, TU Bergakademie Freiberg, Leipziger Strasse 29, D-09596 Freiberg/Sachsen, Germany, and ^bInstitute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, H Abdullaev 83, Tashkent 100125, Uzbekistan
^*Correspondence e-mail: bahtier@academy.uzsci.net

(Received 18 April 2008; accepted 15 July 2008; online 19 July 2008)

In the title compound (systematic name: 17-formyl-2,5,8,11,14-pentaoxabicyclo[13.4.0]nonadeca-15,17,19-triene), C₁₅H₂₀O₆, the 15-crown-5 ring adopts a twisted conformation. The formyl group is coplanar with the benzene ring. The crystal packing is stabilized by C—H⋯O interactions involving the C=O group and ether O atoms as acceptors and methylene CH groups as donors.

Related literature

The unsubstituted benzocrown ether was characterized by Pedersen (1967 ) and its structure was described by Hanson (1978 ), while Rogers and co-workers reported 4′-amino- and 4′-nitro-substituted compounds (Rogers, Huggins et al., 1992 ; Rogers, Henry & Rollins, 1992 ). For the synthesis of the title compound, see: Hyde et al. (1978 ).

Experimental

Crystal data

C₁₅H₂₀O₆
M_r = 296.31
Monoclinic, P 2₁ /c
a = 18.0091 (8) Å
b = 9.6678 (4) Å
c = 8.1028 (3) Å
β = 91.262 (2)°
V = 1410.42 (10) Å³
Z = 4
Mo Kα radiation
μ = 0.11 mm⁻¹
T = 90 (2) K
0.60 × 0.39 × 0.05 mm

Data collection

Bruker Kappa APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2004 ) T_min = 0.857, T_max = 0.995
18190 measured reflections
4523 independent reflections
3716 reflections with I > 2σ(I)
R_int = 0.026

Refinement

R[F² > 2σ(F²)] = 0.037
wR(F²) = 0.116
S = 1.00
4523 reflections
190 parameters
H-atom parameters constrained
Δρ_max = 0.28 e Å⁻³
Δρ_min = −0.22 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C13—H13B⋯O4ⁱ	0.99	2.55	3.3351 (10)	137
C14—H14A⋯O5ⁱⁱ	0.99	2.66	3.1700 (12)	112
C8—H8A⋯O1ⁱⁱⁱ	0.99	2.66	3.3775 (13)	130
Symmetry codes: (i) $[-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[x, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ ; (iii) -x, -y+1, -z+1.

Data collection: APEX2 (Bruker, 2004 ); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808022186/gk2144sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536808022186/gk2144Isup2.hkl

checkCIF report

Comment top

The title compound is a derivative of benzo-15-crown-5 (Pedersen, 1967). It was prepared as part of our studies concerning fluorogenic receptor molecules with possible analytical applications. The O-C-C-O torsion angles within the polyether ring are (±)gauche [69.34° (10), -71.10°(8), -65.61°(11)) and anti (168.42°(9)]) resulting in a twisted crown ether conformation. In the title molecule, the dihedral angle between the aromatic ring plane and the mean plane of ether oxygen atoms is 20.67 (5)°. Worth to note, the torsion angle C3—C4—C7—O1 is 179.75 (10)°, indicating only a very small twist of the formyl group relative to the aromatic ring. Thus, in agreement with a previous report (Rogers, Huggins et al., 1992; Rogers, Henry & Rollins, 1992), the substituent on the benzene ring has negligible influence on the conformation of the benzo-15-crown-5 (Hanson, 1978). Owing to the absence of strong hydrogen bond donors, the crystal packing is stabilized by weak C—H···O hydrogen bonds, involving the O atoms of the crown ether and C==O group as acceptors, and the methylene C-H groups as donors (Table 1). In addition, π—π interaction has also been detected, resulting in a stacking of the molecules along the crystallographic c axis with a distance of 4.211 (2) Å between the centroids of two neighboring aromatic rings (Fig.2).

Related literature top

The unsubstituted benzocrown ether was characterized by Pedersen (1967) and its structure was described by Hanson (1978), while Rogers and co-workers reported 4'-amino- and 4'-nitro-substituted compounds (Rogers, Huggins et al., 1992; Rogers, Henry & Rollins, 1992). For the synthesis of the title compound, see: Hyde et al. (1978).

Experimental top

The title compound, 4'-formylbenzo-15-crown-5, was synthesized from benzo-15-crown-5 (Pedersen, 1967) which was reacted with N-methylformanilide and phoshoryl chloride (Hyde et al., 1978). Colourless needles of the title compound suitable for X-ray diffraction analysis were obtained by slow cooling and evaporation of a solution of n-heptane. Fast cooling of the solution resulted in the formation of an orthorhombic polymorph of the title compound.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

	Fig. 1. Molecular structure of the title compound with ellipsoids drawn at the 50% probability level.
	Fig. 2. Packing diagram, viewed down the c axis.

17-Formyl-2,5,8,11,14-pentaoxabicyclo[13.4.0]nonadeca-15,17,19-triene top

Crystal data top

C₁₅H₂₀O₆	F(000) = 632
M_r = 296.31	D_x = 1.395 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 9008 reflections
a = 18.0091 (8) Å	θ = 2.4–33.3°
b = 9.6678 (4) Å	µ = 0.11 mm⁻¹
c = 8.1028 (3) Å	T = 90 K
β = 91.262 (2)°	Plate, colourless
V = 1410.42 (10) Å³	0.60 × 0.39 × 0.05 mm
Z = 4

Data collection top

Bruker Kappa APEXII CCD diffractometer	4523 independent reflections
Radiation source: fine-focus sealed tube	3716 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.027
ϕ and ω scans	θ_max = 31.1°, θ_min = 3.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 2004)	h = −26→23
T_min = 0.857, T_max = 0.995	k = −14→12
18190 measured reflections	l = −11→11

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.116	H-atom parameters constrained
S = 1.00	w = 1/[σ²(F_o²) + (0.0681P)² + 0.3911P] where P = (F_o² + 2F_c²)/3
4523 reflections	(Δ/σ)_max < 0.001
190 parameters	Δρ_max = 0.28 e Å⁻³
0 restraints	Δρ_min = −0.22 e Å⁻³

Crystal data top

C₁₅H₂₀O₆	V = 1410.42 (10) Å³
M_r = 296.31	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 18.0091 (8) Å	µ = 0.11 mm⁻¹
b = 9.6678 (4) Å	T = 90 K
c = 8.1028 (3) Å	0.60 × 0.39 × 0.05 mm
β = 91.262 (2)°

Data collection top

Bruker Kappa APEXII CCD diffractometer	4523 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2004)	3716 reflections with I > 2σ(I)
T_min = 0.857, T_max = 0.995	R_int = 0.027
18190 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.037	0 restraints
wR(F²) = 0.116	H-atom parameters constrained
S = 1.00	Δρ_max = 0.28 e Å⁻³
4523 reflections	Δρ_min = −0.22 e Å⁻³
190 parameters

Special details top

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	U_iso*/U_eq
O1	−0.03932 (4)	0.76211 (8)	0.74777 (10)	0.02453 (17)
O2	0.18803 (4)	0.54926 (7)	0.45384 (9)	0.01606 (14)
O3	0.25972 (4)	0.29979 (8)	0.55829 (10)	0.02217 (17)
O4	0.42078 (4)	0.40116 (8)	0.32578 (9)	0.01872 (15)
O5	0.41719 (4)	0.72035 (7)	0.34545 (8)	0.01730 (15)
O6	0.26420 (4)	0.75557 (7)	0.36194 (9)	0.01609 (14)
C1	0.15926 (5)	0.67447 (9)	0.49388 (11)	0.01361 (17)
C2	0.09428 (5)	0.69566 (10)	0.57629 (11)	0.01540 (17)
H2	0.0650	0.6190	0.6084	0.018*
C3	0.07132 (5)	0.83094 (10)	0.61289 (11)	0.01618 (18)
C4	0.11385 (6)	0.94299 (10)	0.56708 (12)	0.01868 (19)
H4	0.0984	1.0340	0.5940	0.022*
C5	0.17961 (6)	0.92303 (10)	0.48118 (12)	0.01756 (18)
H5	0.2085	1.0002	0.4487	0.021*
C6	0.20225 (5)	0.78964 (9)	0.44389 (11)	0.01396 (17)
C7	0.00239 (5)	0.85268 (11)	0.70205 (12)	0.02018 (19)
H7	−0.0109	0.9455	0.7262	0.024*
C8	0.14823 (5)	0.43015 (9)	0.50768 (13)	0.01689 (18)
H8A	0.0984	0.4269	0.4539	0.020*
H8B	0.1422	0.4329	0.6288	0.020*
C9	0.19286 (5)	0.30593 (10)	0.46010 (14)	0.0203 (2)
H9A	0.1633	0.2209	0.4769	0.024*
H9B	0.2052	0.3116	0.3418	0.024*
C10	0.32608 (5)	0.28738 (10)	0.46689 (14)	0.0204 (2)
H10A	0.3193	0.2140	0.3827	0.025*
H10B	0.3672	0.2589	0.5425	0.025*
C11	0.34702 (5)	0.42146 (10)	0.38202 (12)	0.01686 (18)
H11A	0.3126	0.4408	0.2879	0.020*
H11B	0.3453	0.4999	0.4604	0.020*
C12	0.44456 (5)	0.49820 (11)	0.20613 (12)	0.01883 (19)
H12A	0.4024	0.5185	0.1295	0.023*
H12B	0.4844	0.4554	0.1410	0.023*
C13	0.47328 (5)	0.63335 (11)	0.27812 (12)	0.01947 (19)
H13A	0.5106	0.6122	0.3662	0.023*
H13B	0.4988	0.6851	0.1905	0.023*
C14	0.37553 (5)	0.79418 (10)	0.22314 (11)	0.01733 (18)
H14A	0.3570	0.7297	0.1367	0.021*
H14B	0.4074	0.8642	0.1705	0.021*
C15	0.31127 (5)	0.86389 (10)	0.30465 (11)	0.01632 (18)
H15A	0.3291	0.9217	0.3982	0.020*
H15B	0.2840	0.9236	0.2247	0.020*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0197 (3)	0.0272 (4)	0.0269 (4)	−0.0004 (3)	0.0049 (3)	−0.0043 (3)
O2	0.0180 (3)	0.0094 (3)	0.0211 (3)	−0.0007 (2)	0.0051 (2)	0.0003 (2)
O3	0.0173 (3)	0.0243 (4)	0.0250 (4)	0.0025 (3)	0.0044 (3)	0.0089 (3)
O4	0.0157 (3)	0.0198 (3)	0.0208 (3)	0.0011 (2)	0.0037 (2)	0.0046 (3)
O5	0.0187 (3)	0.0205 (3)	0.0127 (3)	−0.0001 (3)	0.0001 (2)	0.0022 (2)
O6	0.0177 (3)	0.0122 (3)	0.0186 (3)	−0.0023 (2)	0.0052 (2)	0.0007 (2)
C1	0.0164 (4)	0.0108 (4)	0.0137 (4)	0.0004 (3)	−0.0004 (3)	0.0002 (3)
C2	0.0164 (4)	0.0140 (4)	0.0158 (4)	−0.0003 (3)	0.0005 (3)	0.0001 (3)
C3	0.0175 (4)	0.0163 (4)	0.0148 (4)	0.0023 (3)	−0.0001 (3)	−0.0014 (3)
C4	0.0233 (4)	0.0129 (4)	0.0199 (4)	0.0028 (3)	0.0012 (3)	−0.0017 (3)
C5	0.0222 (4)	0.0119 (4)	0.0186 (4)	−0.0003 (3)	0.0011 (3)	0.0007 (3)
C6	0.0159 (4)	0.0133 (4)	0.0127 (4)	−0.0004 (3)	0.0002 (3)	0.0006 (3)
C7	0.0195 (4)	0.0209 (5)	0.0201 (4)	0.0039 (3)	0.0009 (3)	−0.0053 (4)
C8	0.0161 (4)	0.0112 (4)	0.0235 (5)	−0.0019 (3)	0.0035 (3)	0.0015 (3)
C9	0.0171 (4)	0.0124 (4)	0.0314 (5)	−0.0006 (3)	0.0021 (4)	−0.0001 (4)
C10	0.0169 (4)	0.0171 (4)	0.0274 (5)	0.0023 (3)	0.0044 (3)	0.0054 (4)
C11	0.0162 (4)	0.0154 (4)	0.0191 (4)	−0.0003 (3)	0.0033 (3)	−0.0001 (3)
C12	0.0193 (4)	0.0218 (5)	0.0156 (4)	0.0005 (3)	0.0043 (3)	0.0017 (3)
C13	0.0156 (4)	0.0230 (5)	0.0199 (4)	−0.0019 (3)	0.0023 (3)	0.0025 (4)
C14	0.0185 (4)	0.0208 (4)	0.0127 (4)	−0.0019 (3)	0.0009 (3)	0.0043 (3)
C15	0.0194 (4)	0.0141 (4)	0.0156 (4)	−0.0040 (3)	0.0008 (3)	0.0027 (3)

Geometric parameters (Å, º) top

O1—C7	1.2168 (13)	C7—H7	0.9500
O2—C1	1.3589 (11)	C8—C9	1.5001 (13)
O2—C8	1.4296 (11)	C8—H8A	0.9900
O3—C10	1.4249 (12)	C8—H8B	0.9900
O3—C9	1.4297 (13)	C9—H9A	0.9900
O4—C12	1.4219 (12)	C9—H9B	0.9900
O4—C11	1.4275 (11)	C10—C11	1.5189 (13)
O5—C14	1.4219 (12)	C10—H10A	0.9900
O5—C13	1.4318 (12)	C10—H10B	0.9900
O6—C6	1.3516 (11)	C11—H11A	0.9900
O6—C15	1.4311 (11)	C11—H11B	0.9900
C1—C2	1.3755 (12)	C12—C13	1.5171 (15)
C1—C6	1.4202 (12)	C12—H12A	0.9900
C2—C3	1.4052 (13)	C12—H12B	0.9900
C2—H2	0.9500	C13—H13A	0.9900
C3—C4	1.3822 (13)	C13—H13B	0.9900
C3—C7	1.4651 (13)	C14—C15	1.5044 (13)
C4—C5	1.4003 (13)	C14—H14A	0.9900
C4—H4	0.9500	C14—H14B	0.9900
C5—C6	1.3877 (13)	C15—H15A	0.9900
C5—H5	0.9500	C15—H15B	0.9900

C1—O2—C8	116.64 (7)	H9A—C9—H9B	108.2
C10—O3—C9	114.84 (8)	O3—C10—C11	112.51 (8)
C12—O4—C11	115.04 (7)	O3—C10—H10A	109.1
C14—O5—C13	113.27 (7)	C11—C10—H10A	109.1
C6—O6—C15	118.83 (7)	O3—C10—H10B	109.1
O2—C1—C2	125.56 (8)	C11—C10—H10B	109.1
O2—C1—C6	114.66 (8)	H10A—C10—H10B	107.8
C2—C1—C6	119.78 (8)	O4—C11—C10	105.62 (7)
C1—C2—C3	119.90 (9)	O4—C11—H11A	110.6
C1—C2—H2	120.0	C10—C11—H11A	110.6
C3—C2—H2	120.0	O4—C11—H11B	110.6
C4—C3—C2	120.36 (9)	C10—C11—H11B	110.6
C4—C3—C7	120.03 (9)	H11A—C11—H11B	108.7
C2—C3—C7	119.61 (9)	O4—C12—C13	114.29 (8)
C3—C4—C5	120.35 (9)	O4—C12—H12A	108.7
C3—C4—H4	119.8	C13—C12—H12A	108.7
C5—C4—H4	119.8	O4—C12—H12B	108.7
C6—C5—C4	119.47 (9)	C13—C12—H12B	108.7
C6—C5—H5	120.3	H12A—C12—H12B	107.6
C4—C5—H5	120.3	O5—C13—C12	114.52 (8)
O6—C6—C5	125.67 (8)	O5—C13—H13A	108.6
O6—C6—C1	114.21 (8)	C12—C13—H13A	108.6
C5—C6—C1	120.12 (8)	O5—C13—H13B	108.6
O1—C7—C3	125.61 (10)	C12—C13—H13B	108.6
O1—C7—H7	117.2	H13A—C13—H13B	107.6
C3—C7—H7	117.2	O5—C14—C15	108.54 (7)
O2—C8—C9	106.94 (7)	O5—C14—H14A	110.0
O2—C8—H8A	110.3	C15—C14—H14A	110.0
C9—C8—H8A	110.3	O5—C14—H14B	110.0
O2—C8—H8B	110.3	C15—C14—H14B	110.0
C9—C8—H8B	110.3	H14A—C14—H14B	108.4
H8A—C8—H8B	108.6	O6—C15—C14	106.35 (7)
O3—C9—C8	109.85 (8)	O6—C15—H15A	110.5
O3—C9—H9A	109.7	C14—C15—H15A	110.5
C8—C9—H9A	109.7	O6—C15—H15B	110.5
O3—C9—H9B	109.7	C14—C15—H15B	110.5
C8—C9—H9B	109.7	H15A—C15—H15B	108.7

C8—O2—C1—C2	−2.33 (13)	C2—C1—C6—C5	1.40 (14)
C8—O2—C1—C6	177.50 (8)	C4—C3—C7—O1	179.75 (10)
O2—C1—C2—C3	178.83 (9)	C2—C3—C7—O1	−1.06 (16)
C6—C1—C2—C3	−0.99 (14)	C1—O2—C8—C9	−176.14 (8)
C1—C2—C3—C4	−0.25 (14)	C10—O3—C9—C8	−127.42 (9)
C1—C2—C3—C7	−179.43 (9)	O2—C8—C9—O3	69.34 (10)
C2—C3—C4—C5	1.12 (15)	C9—O3—C10—C11	73.81 (11)
C7—C3—C4—C5	−179.71 (9)	C12—O4—C11—C10	164.16 (8)
C3—C4—C5—C6	−0.71 (15)	O3—C10—C11—O4	168.42 (8)
C15—O6—C6—C5	−1.01 (14)	C11—O4—C12—C13	82.80 (10)
C15—O6—C6—C1	179.48 (8)	C14—O5—C13—C12	−78.28 (10)
C4—C5—C6—O6	179.97 (9)	O4—C12—C13—O5	−71.10 (11)
C4—C5—C6—C1	−0.54 (14)	C13—O5—C14—C15	171.27 (8)
O2—C1—C6—O6	1.10 (12)	C6—O6—C15—C14	178.69 (8)
C2—C1—C6—O6	−179.06 (8)	O5—C14—C15—O6	−65.61 (9)
O2—C1—C6—C5	−178.45 (8)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C13—H13B···O4ⁱ	0.99	2.55	3.3351 (10)	137
C14—H14A···O5ⁱⁱ	0.99	2.66	3.1700 (12)	112
C8—H8A···O1ⁱⁱⁱ	0.99	2.66	3.3775 (13)	130

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

Experimental details

Crystal data
Chemical formula	C₁₅H₂₀O₆
M_r	296.31
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	90
a, b, c (Å)	18.0091 (8), 9.6678 (4), 8.1028 (3)
β (°)	91.262 (2)
V (Å³)	1410.42 (10)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.11
Crystal size (mm)	0.60 × 0.39 × 0.05

Data collection
Diffractometer	Bruker Kappa APEXII CCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 2004)
T_min, T_max	0.857, 0.995
No. of measured, independent and observed [I > 2σ(I)] reflections	18190, 4523, 3716
R_int	0.027
(sin θ/λ)_max (Å⁻¹)	0.727

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.037, 0.116, 1.00
No. of reflections	4523
No. of parameters	190
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.28, −0.22

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C13—H13B···O4ⁱ	0.99	2.55	3.3351 (10)	137
C14—H14A···O5ⁱⁱ	0.99	2.66	3.1700 (12)	112
C8—H8A···O1ⁱⁱⁱ	0.99	2.66	3.3775 (13)	130

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

Acknowledgements

Financial support from the German Federal Ministry of Economics and Technology (BMWi) under grant No. 16IN0218 `ChemoChips' is gratefully acknowledged. We thank Dr Tobias Gruber for fruitful discussions.

References

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