4-Methyl-1-phenyl­quinolin-2(1H)-one

Petrov, P.Y.; Stoyanova, M.; Shivachev, B.

doi:10.1107/S1600536807061727

organic compounds

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ISSN: 2056-9890

Volume 64| Part 1| January 2008| Page o72

https://doi.org/10.1107/S1600536807061727

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4-Methyl-1-phenylquinolin-2(1H)-one

Petar Yotov Petrov,^a Malinka Stoyanova ^b and Boris Shivachev ^c ^*

^aDepartment of Organic Chemistry, Faculty of Chemistry, University of Sofia, 1126 Sofia, Bulgaria, ^bInstitute of Organic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Building 9, 1113 Sofia, Bulgaria, and ^cBulgarian Academy of Sciences, Central Laboratory of Mineralogy and Crystallography, Acad G. Bonchev Street, Building 107, 1113 Sofia, Bulgaria
^*Correspondence e-mail: bls@clmc.bas.bg

(Received 4 July 2007; accepted 21 November 2007; online 6 December 2007)

In the title compound, C₁₆H₁₃NO, the molecules are connected three-dimensionally through non-classical C—H⋯O and C—H⋯π interactions of 3.272 (3), 3.380 (3) and 3.382 (4) Å. Classical hydrogen bonds are not observed. The dihedral angle between the benzyl and quinolin-2(1H)-one mean planes is 87.15 (7)°

Related literature

For related literature, see: Bondensgaard & Jacobsen (1999 ); Fürstenberg et al. (2006 ); Kovalska et al. (2006 ); Martínez & Chacón-García (2005 ); Perekalin & Lerner (1951 ); Rajnikant et al. (2002 ); Schenkel & Aeberli (1957 ); Shishkina et al. (2005 ); Staerk et al. (1997 ); Vasilev et al. (2005 ); Vincente et al. (2005 ); Zipper et al. (2004 ); Sheldrick & Morr (1981 ).

Experimental

Crystal data

C₁₆H₁₃NO
M_r = 235.27
Monoclinic, P 2₁ /c
a = 8.984 (2) Å
b = 14.194 (4) Å
c = 10.1785 (16) Å
β = 106.631 (15)°
V = 1243.7 (5) Å³
Z = 4
Mo Kα radiation
μ = 0.08 mm⁻¹
T = 290 (2) K
0.31 × 0.31 × 0.31 mm

Data collection

Enraf–Nonius CAD-4 diffractometer
Absorption correction: none
6212 measured reflections
2991 independent reflections
1351 reflections with I > 2σ(I)
R_int = 0.053
3 standard reflections frequency: 120 min intensity decay: none

Refinement

R[F² > 2σ(F²)] = 0.055
wR(F²) = 0.160
S = 0.97
2991 reflections
164 parameters
H-atom parameters constrained
Δρ_max = 0.14 e Å⁻³
Δρ_min = −0.16 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

Cg1 is the centroid of the C11–C16 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C14—H14⋯O1ⁱ	1.13	2.37	3.272 (3)	135
C4—H4⋯O1ⁱⁱ	1.09	2.63	3.380 (3)	125
C8—H8A⋯Cg1ⁱⁱⁱ	1.11	2.73	3.382 (4)	165
Symmetry codes: (i) $[-x+2, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (ii) x-1, y, z; (iii) $[-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994 ); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995 ); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ); Mercury (Bruno et al., 2002 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536807061727/pr2017sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536807061727/pr2017Isup2.hkl

checkCIF report

Comment top

DNA intercalation is one of the interactions of nucleic acids with small organic molecules, through which effective antitumor agents can be designed (Martínez et al., 2005). A relevant area of research is the finding of fluorescent markers for highly sensitive DNA detection (Staerk et al., 1997; Bondensgaard et al., 1999). For the latter application, few cyanine dyes containing quinoline end-groups are established (Zipper et al., 2004), and new representatives with similar and even better efficiency were recently synthesized (Vasilev et al., 2005; Kovalska et al., 2006; Fürstenberg et al., 2006). Herein, we report the structure of (I) which is an oxo-substituted fragment of these dyes – a long known molecule (Perekalin et al., 1951).

In the unit cell of (I), only one independent molecule is present. The bond distances and angles in the benzyl and quinolin-2(1H)-one moieties are comparable to those observed in other quinolinone derivatives (Rajnikant et al., 2002; Vincente et al., 2005; Shishkina et al., 2005). The molecule posses two nearly planar ring systems [r.m.s. deviation of 0.004 (5)Å and 0.021 (4) Å for the benzyl and quinolin-2(1H)-one fragments respectively] which are capable of intercalation, attached to each other in a conformationally fluxional way. The dihedral angle between the benzyl and quinolinone mean planes is 87.15 (7) °.

In the crystal structure of (I), the molecules are connected through non-classical C—H···O hydrogen bonds and CH₃-π interactions between methyl and benzyl fragments C8—H8A···Cg1ⁱ; Cg1 is the centroid of the 1-Phenyl derivative [symmetry code (i): 1 - x, -1/2 + y, 3/2 - z]. The carbonyl O atom forms a bifurcated hydrogen bond. A head-to-tail C4—H4···O1ⁱ [symmetry code (i): x - 1,y,z] interaction between quinolinone fragments build up straight chains along a axis. A side-to-side C14—H14···O1ⁱ [symmetry code (i): 2 - x, 1/2 + y, 3/2 - z] interaction forms zigzag chains along b.

Related literature top

For related literature, see: Bondensgaard & Jacobsen (1999); Fürstenberg et al. (2006); Kovalska et al. (2006); Martínez & Chacón-García (2005); Perekalin & Lerner (1951); Rajnikant et al. (2002); Schenkel & Aeberli (1957); Shishkina et al. (2005); Staerk et al. (1997); Vasilev et al. (2005); Vincente et al. (2005); Zipper et al. (2004); Sheldrick & Morr (1981).

Experimental top

The title compound was synthesized by dehydro-cyclization (Perekalin et al., 1951) of the respective acetoacetamide (Schenkel et al., 1957). Crystals of (I) suitable for X-ray diffraction were obtained by slow evaporation from toluene.

Structure description top

For related literature, see: Bondensgaard & Jacobsen (1999); Fürstenberg et al. (2006); Kovalska et al. (2006); Martínez & Chacón-García (2005); Perekalin & Lerner (1951); Rajnikant et al. (2002); Schenkel & Aeberli (1957); Shishkina et al. (2005); Staerk et al. (1997); Vasilev et al. (2005); Vincente et al. (2005); Zipper et al. (2004); Sheldrick & Morr (1981).

Computing details top

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); Mercury (Bruno et al., 2002); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top

	Fig. 1. View of the structure and the atom-numbering scheme of (I) showing 50% probability displacement ellipsoids. H atoms are shown as small spheres of an arbitrary radii.
	Fig. 2. A view of the molecular packing in (I). All H atoms not involved in the short contact interactions have been omitted for clarity [symmetry codes: (i) 1 + x,y,z; (ii) 2 - x, -1/2 + y, 3/2 - z; (iii) 2 - x, -1/2 + y, 3/2 - z; (iv) 1 - x, 1 - y, 1 - z]. The dotted lines indicate the C—H···O and C—H···π interactions.

4-Methyl-1-phenylquinolin-2(1H)-one top

Crystal data top

C₁₆H₁₃NO	F(000) = 496
M_r = 235.27	D_x = 1.256 Mg m⁻³
Monoclinic, P2₁/c	Melting point: not measured K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 8.984 (2) Å	Cell parameters from 22 reflections
b = 14.194 (4) Å	θ = 18.2–19.3°
c = 10.1785 (16) Å	µ = 0.08 mm⁻¹
β = 106.631 (15)°	T = 290 K
V = 1243.7 (5) Å³	Cubic, pale yellow
Z = 4	0.31 × 0.31 × 0.31 mm

Data collection top

Enraf–Nonius CAD-4 diffractometer	R_int = 0.053
Radiation source: fine-focus sealed tube	θ_max = 28.0°, θ_min = 2.4°
Graphite monochromator	h = 0→11
non–profiled ω/2θ scans	k = −18→18
6212 measured reflections	l = −13→12
2991 independent reflections	3 standard reflections every 120 min
1351 reflections with I > 2σ(I)	intensity decay: none

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)] = 0.055	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.160	H-atom parameters constrained
S = 0.97	w = 1/[σ²(F_o²) + (0.0699P)²] where P = (F_o² + 2F_c²)/3
2991 reflections	(Δ/σ)_max < 0.001
164 parameters	Δρ_max = 0.15 e Å⁻³
0 restraints	Δρ_min = −0.16 e Å⁻³

Crystal data top

C₁₆H₁₃NO	V = 1243.7 (5) Å³
M_r = 235.27	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 8.984 (2) Å	µ = 0.08 mm⁻¹
b = 14.194 (4) Å	T = 290 K
c = 10.1785 (16) Å	0.31 × 0.31 × 0.31 mm
β = 106.631 (15)°

Data collection top

Enraf–Nonius CAD-4 diffractometer	R_int = 0.053
6212 measured reflections	3 standard reflections every 120 min
2991 independent reflections	intensity decay: none
1351 reflections with I > 2σ(I)

Refinement top

R[F² > 2σ(F²)] = 0.055	0 restraints
wR(F²) = 0.160	H-atom parameters constrained
S = 0.97	Δρ_max = 0.15 e Å⁻³
2991 reflections	Δρ_min = −0.16 e Å⁻³
164 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
N1	0.7036 (2)	0.45463 (12)	0.80663 (18)	0.0468 (5)
C1	0.5505 (2)	0.46557 (16)	0.8116 (2)	0.0443 (5)
C6	0.4822 (3)	0.39507 (15)	0.8725 (2)	0.0448 (5)
O1	0.9282 (2)	0.37000 (13)	0.8539 (2)	0.0763 (6)
C2	0.4652 (3)	0.54564 (16)	0.7571 (2)	0.0500 (6)
H2	0.5194	0.5981	0.7165	0.060*
C11	0.7750 (2)	0.52552 (15)	0.7433 (2)	0.0461 (6)
C5	0.3277 (3)	0.40691 (18)	0.8733 (2)	0.0535 (6)
H5	0.2882	0.3524	0.9123	0.064*
C4	0.2438 (3)	0.48561 (19)	0.8192 (2)	0.0580 (7)
H4	0.1196	0.4968	0.8047	0.070*
C10	0.7938 (3)	0.37699 (17)	0.8615 (3)	0.0554 (6)
C9	0.7218 (3)	0.30818 (17)	0.9274 (2)	0.0580 (7)
H9	0.7825	0.2518	0.9753	0.070*
C3	0.3150 (3)	0.55537 (17)	0.7623 (2)	0.0570 (6)
H3	0.2571	0.6117	0.7295	0.068*
C7	0.5753 (3)	0.31498 (16)	0.9346 (2)	0.0519 (6)
C8	0.5092 (3)	0.24147 (17)	1.0075 (3)	0.0711 (8)
H8B	0.4706	0.2655	1.0736	0.107*
H8C	0.5783	0.1853	1.0437	0.107*
H8A	0.4026	0.2090	0.9385	0.107*
C16	0.7687 (3)	0.51761 (18)	0.6074 (3)	0.0632 (7)
H16	0.7009	0.4576	0.5534	0.076*
C13	0.9139 (3)	0.67027 (18)	0.7559 (3)	0.0639 (7)
H13	0.9747	0.7274	0.8167	0.077*
C14	0.9077 (3)	0.66239 (19)	0.6202 (3)	0.0627 (7)
H14	0.9663	0.7190	0.5738	0.075*
C12	0.8477 (3)	0.60141 (18)	0.8181 (3)	0.0586 (7)
H12	0.8565	0.5980	0.8999	0.070*
C15	0.8372 (3)	0.5863 (2)	0.5463 (3)	0.0730 (8)
H15	0.8372	0.5753	0.4416	0.109 (10)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0390 (10)	0.0453 (11)	0.0582 (12)	0.0007 (9)	0.0173 (9)	0.0040 (9)
C1	0.0376 (12)	0.0499 (13)	0.0448 (13)	−0.0019 (10)	0.0110 (10)	−0.0053 (11)
C6	0.0473 (13)	0.0437 (13)	0.0441 (12)	−0.0056 (11)	0.0144 (10)	−0.0078 (10)
O1	0.0509 (11)	0.0703 (12)	0.1140 (16)	0.0136 (9)	0.0336 (11)	0.0111 (11)
C2	0.0456 (13)	0.0505 (14)	0.0537 (14)	0.0008 (11)	0.0138 (11)	0.0035 (11)
C11	0.0373 (11)	0.0462 (14)	0.0563 (14)	−0.0004 (10)	0.0154 (11)	−0.0018 (11)
C5	0.0496 (14)	0.0584 (15)	0.0568 (15)	−0.0079 (12)	0.0222 (12)	−0.0046 (12)
C4	0.0417 (13)	0.0720 (17)	0.0621 (16)	0.0004 (13)	0.0179 (12)	−0.0039 (14)
C10	0.0476 (14)	0.0510 (14)	0.0680 (16)	0.0056 (12)	0.0173 (12)	−0.0013 (12)
C9	0.0574 (15)	0.0450 (14)	0.0702 (17)	0.0051 (12)	0.0162 (13)	0.0018 (12)
C3	0.0446 (14)	0.0624 (16)	0.0616 (15)	0.0084 (12)	0.0115 (12)	0.0027 (13)
C7	0.0576 (15)	0.0430 (14)	0.0558 (14)	−0.0060 (12)	0.0176 (12)	−0.0063 (11)
C8	0.085 (2)	0.0497 (15)	0.0871 (19)	−0.0027 (14)	0.0388 (17)	0.0077 (14)
C16	0.0760 (18)	0.0561 (15)	0.0619 (17)	−0.0119 (14)	0.0268 (14)	−0.0051 (13)
C13	0.0516 (15)	0.0549 (15)	0.0838 (19)	−0.0149 (12)	0.0171 (14)	−0.0095 (14)
C14	0.0551 (15)	0.0554 (16)	0.084 (2)	−0.0032 (13)	0.0309 (14)	0.0065 (14)
C12	0.0526 (14)	0.0634 (16)	0.0614 (15)	−0.0088 (13)	0.0187 (12)	−0.0081 (13)
C15	0.093 (2)	0.0674 (18)	0.0687 (18)	−0.0083 (17)	0.0392 (17)	−0.0007 (15)

Geometric parameters (Å, º) top

N1—C10	1.387 (3)	C9—C7	1.342 (3)
N1—C1	1.400 (3)	C9—H9	1.0118
N1—C11	1.441 (3)	C3—H3	0.9603
C1—C2	1.394 (3)	C7—C8	1.499 (3)
C1—C6	1.407 (3)	C8—H8B	0.9069
C6—C5	1.401 (3)	C8—H8C	1.0133
C6—C7	1.445 (3)	C8—H8A	1.1127
O1—C10	1.236 (3)	C16—C15	1.391 (4)
C2—C3	1.373 (3)	C16—H16	1.0983
C2—H2	1.0382	C13—C14	1.371 (3)
C11—C12	1.372 (3)	C13—C12	1.387 (3)
C11—C16	1.372 (3)	C13—H13	1.0707
C5—C4	1.372 (3)	C14—C15	1.364 (4)
C5—H5	0.9818	C14—H14	1.1348
C4—C3	1.392 (3)	C12—H12	0.8147
C4—H4	1.0949	C15—H15	1.0773
C10—C9	1.439 (3)

C10—N1—C1	122.73 (19)	C2—C3—C4	121.2 (2)
C10—N1—C11	116.83 (18)	C2—C3—H3	120.7
C1—N1—C11	120.44 (18)	C4—C3—H3	118.0
C2—C1—N1	120.7 (2)	C9—C7—C6	119.1 (2)
C2—C1—C6	119.7 (2)	C9—C7—C8	120.7 (2)
N1—C1—C6	119.6 (2)	C6—C7—C8	120.2 (2)
C5—C6—C1	118.4 (2)	C7—C8—H8B	113.3
C5—C6—C7	122.8 (2)	C7—C8—H8C	116.1
C1—C6—C7	118.8 (2)	H8B—C8—H8C	110.5
C3—C2—C1	120.1 (2)	C7—C8—H8A	111.6
C3—C2—H2	121.5	H8B—C8—H8A	100.4
C1—C2—H2	118.4	H8C—C8—H8A	103.3
C12—C11—C16	120.0 (2)	C11—C16—C15	119.8 (2)
C12—C11—N1	120.1 (2)	C11—C16—H16	115.2
C16—C11—N1	119.9 (2)	C15—C16—H16	124.9
C4—C5—C6	121.8 (2)	C14—C13—C12	120.2 (2)
C4—C5—H5	125.7	C14—C13—H13	120.7
C6—C5—H5	112.4	C12—C13—H13	119.0
C5—C4—C3	118.8 (2)	C15—C14—C13	119.9 (2)
C5—C4—H4	126.5	C15—C14—H14	121.9
C3—C4—H4	114.3	C13—C14—H14	118.2
O1—C10—N1	120.5 (2)	C11—C12—C13	119.9 (2)
O1—C10—C9	123.6 (2)	C11—C12—H12	114.3
N1—C10—C9	116.0 (2)	C13—C12—H12	125.4
C7—C9—C10	123.7 (2)	C14—C15—C16	120.3 (3)
C7—C9—H9	115.6	C14—C15—H15	121.9
C10—C9—H9	120.6	C16—C15—H15	117.8

C10—N1—C1—C2	178.9 (2)	C11—N1—C10—C9	178.5 (2)
C11—N1—C1—C2	−0.8 (3)	O1—C10—C9—C7	−179.2 (2)
C10—N1—C1—C6	−1.0 (3)	N1—C10—C9—C7	1.6 (4)
C11—N1—C1—C6	179.3 (2)	C1—C2—C3—C4	−1.2 (4)
C2—C1—C6—C5	1.5 (3)	C5—C4—C3—C2	1.4 (4)
N1—C1—C6—C5	−178.6 (2)	C10—C9—C7—C6	0.5 (4)
C2—C1—C6—C7	−176.9 (2)	C10—C9—C7—C8	−178.7 (2)
N1—C1—C6—C7	3.0 (3)	C5—C6—C7—C9	178.9 (2)
N1—C1—C2—C3	179.8 (2)	C1—C6—C7—C9	−2.8 (3)
C6—C1—C2—C3	−0.3 (3)	C5—C6—C7—C8	−1.9 (3)
C10—N1—C11—C12	−93.2 (2)	C1—C6—C7—C8	176.4 (2)
C1—N1—C11—C12	86.6 (3)	C12—C11—C16—C15	0.5 (4)
C10—N1—C11—C16	87.5 (3)	N1—C11—C16—C15	179.7 (2)
C1—N1—C11—C16	−92.7 (3)	C12—C13—C14—C15	−0.4 (4)
C1—C6—C5—C4	−1.3 (3)	C16—C11—C12—C13	0.4 (4)
C7—C6—C5—C4	177.0 (2)	N1—C11—C12—C13	−178.9 (2)
C6—C5—C4—C3	−0.1 (4)	C14—C13—C12—C11	−0.4 (4)
C1—N1—C10—O1	179.5 (2)	C13—C14—C15—C16	1.3 (4)
C11—N1—C10—O1	−0.7 (3)	C11—C16—C15—C14	−1.3 (4)
C1—N1—C10—C9	−1.3 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C14—H14···O1ⁱ	1.13	2.37	3.272 (3)	135
C4—H4···O1ⁱⁱ	1.09	2.63	3.380 (3)	125
C8—H8A···Cg1ⁱⁱⁱ	1.11	2.73	3.382 (4)	165

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

Experimental details

Crystal data
Chemical formula	C₁₆H₁₃NO
M_r	235.27
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	290
a, b, c (Å)	8.984 (2), 14.194 (4), 10.1785 (16)
β (°)	106.631 (15)
V (Å³)	1243.7 (5)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.08
Crystal size (mm)	0.31 × 0.31 × 0.31

Data collection
Diffractometer	Enraf–Nonius CAD-4
Absorption correction	–
No. of measured, independent and observed [I > 2σ(I)] reflections	6212, 2991, 1351
R_int	0.053
(sin θ/λ)_max (Å⁻¹)	0.660

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.055, 0.160, 0.97
No. of reflections	2991
No. of parameters	164
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.15, −0.16

Computer programs: CAD-4 EXPRESS (Enraf–Nonius, 1994), CAD-4 EXPRESS, XCAD4 (Harms & Wocadlo, 1995), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997); Mercury (Bruno et al., 2002), WinGX (Farrugia, 1999).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C14—H14···O1ⁱ	1.13	2.37	3.272 (3)	134.5
C4—H4···O1ⁱⁱ	1.09	2.63	3.380 (3)	124.8
C8—H8A···Cg1ⁱⁱⁱ	1.11	2.73	3.382 (4)	165.4

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

Acknowledgements

The authors thank the National Research Fund of Bulgaria for financial support (grant No. BYX 03.05).

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