3-(3-Nitro­benz­yl)-4H-chromen-4-one

Gopaul, K.; Koorbanally, N.A.; Shaikh, M.; Su, H.; Ramjugernath, D.

doi:10.1107/S1600536813003589

organic compounds

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ISSN: 2056-9890

Volume 69| Part 3| March 2013| Page o364

doi:10.1107/S1600536813003589

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3-(3-Nitrobenzyl)-4H-chromen-4-one

Kaalin Gopaul,^a Neil Anthony Koorbanally,^a ^* Mahidansha Shaikh,^a Hong Su ^b and Deresh Ramjugernath ^c

^aSchool of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa, ^bChemistry Department, University of Cape Town, Rondebosch 7701, South Africa, and ^cSchool of Chemical Engineering, University of KwaZulu-Natal, Durban 4041, South Africa
^*Correspondence e-mail: koorbanally@ukzn.ac.za

(Received 31 January 2013; accepted 5 February 2013; online 9 February 2013)

In the title compound, C₁₆H₁₁NO₄, the dihedral angle between the 10-membered coplanar chromone ring system and the benzene ring is 77.83 (3)°. In the crystal, weak C—H⋯O hydrogen bonds link the molecules into a three-dimensional network.

Related literature

For the preparation, see: Valkonen et al. (2012 ). For related structures, see: Sievänen et al. (2010 ); Gopaul et al. (2012 ); Valkonen et al. (2012). For general background to homoisoflavoinoids, see: Shaikh et al. (2011 ); du Toit et al. (2010 ).

Experimental

Crystal data

C₁₆H₁₁NO₄
M_r = 281.26
Monoclinic, P 2₁ /c
a = 4.6082 (3) Å
b = 10.4219 (6) Å
c = 26.4468 (17) Å
β = 90.428 (1)°
V = 1270.10 (14) Å³
Z = 4
Mo Kα radiation
μ = 0.11 mm⁻¹
T = 173 K
0.42 × 0.22 × 0.04 mm

Data collection

Bruker Kappa DUO APEXII diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1997 ) T_min = 0.956, T_max = 0.996
16973 measured reflections
4246 independent reflections
3069 reflections with I > 2σ(I)
R_int = 0.030

Refinement

R[F² > 2σ(F²)] = 0.047
wR(F²) = 0.138
S = 1.04
4246 reflections
190 parameters
H-atom parameters constrained
Δρ_max = 0.44 e Å⁻³
Δρ_min = −0.19 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H2⋯O2	0.95	2.32	3.2663 (15)	171
C7—H7⋯O3ⁱ	0.95	2.65	3.5614 (19)	160
C8—H8⋯O3ⁱⁱ	0.95	2.54	3.3071 (18)	138
C14—H14⋯O4ⁱⁱⁱ	0.95	2.50	3.4380 (17)	172
C15—H15⋯O1^iv	0.95	2.62	3.5569 (15)	170
C16—H16⋯O2^v	0.95	2.46	3.3764 (15)	163
Symmetry codes: (i) $[-x, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[x+1, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ ; (iii) -x+1, -y+2, -z+1; (iv) $[-x+2, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (v) x+1, y, z.

Data collection: APEX2 (Bruker, 2006 ); cell refinement: SAINT (Bruker, 2006); 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, 2012 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536813003589/ff2097sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536813003589/ff2097Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536813003589/ff2097Isup3.cml

checkCIF report

Comment top

The title compound, 3-(3-nitrobenzyl)-2-chromen-4-one, belongs to a class of compounds called homoisoflavonoids, which are C-16, α,β unsaturated carbonyl compounds containing two aromatic rings. Homoisoflavonoids may be categorized into four groups depending on the type of structural backbone present. The four groups are 3-benzyl-4-chromanones, of which the title compound belongs to as well as the, 3-benzylidene-4-chromanones, 3-benzyl-3-hydroxy-4-chromanones and scillascillins (du Toit et al., 2010). The most commonly used procedure for the synthesis of homoisoflavoinoids involves the condensation of chroman-4-one with an aromatic aldehyde in the presence of either an acidic or basic catalyst (Shaikh et al., 2011).

The molecular structure of the title compound is shown in Fig.1. The dihedral angle between the 10-membered co-planar ring O1—C1—C9—C8—C7—C6—C5—C4—C3—C2 and the benzene ring C11—C12—C13—C14—C15—C16 is 77.83 (3)°. In the crystal packing, a number of weak intermolecular C—H···O hydrogen bonds are noted and are listed in Table 1.

Related literature top

For the preparation, see: Valkonen et al. (2012). For related structures, see: Sievänen et al. (2010); Gopaul et al. (2012); Valkonen et al. (2012). For general background to homoisoflavoinoids, see: Shaikh et al. (2011); du Toit et al. (2010).

Experimental top

A mixture of chroman-4-one (1.00 g, 6.75 mmol), 3-nitrobenzaldehyde (1.25 g, 8.10 mmol) and 10–15 drops of piperidine was heated at 80°C for 10 hrs. The reaction mixture was monitored for completion by thin layer chromatography. Upon completion, the reaction mixture was cooled, diluted with water and neutralized using 10% HCl. To the viscous reaction mixture, 15 ml of ethyl acetate was added. The homoisoflavonoid precipitated out upon the addition of hexane to the reaction mixture. The powdered product was filtered, washed with hexane and dried under vacuum. Upon slow evaporation of chloroform, the crystals of the homoisoflavonoid were obtained with a m.p. of 129–130 °C.

Computing details top

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

Fig. 1. A view of the molecule with displacement ellipsoids drawn at the 50% probability level and H atoms drawn as circles of arbitary size.

3-(3-Nitrobenzyl)-4H-chromen-4-one top

Crystal data top

C₁₆H₁₁NO₄	F(000) = 584
M_r = 281.26	D_x = 1.471 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 4.6082 (3) Å	Cell parameters from 16973 reflections
b = 10.4219 (6) Å	θ = 1.5–31.6°
c = 26.4468 (17) Å	µ = 0.11 mm⁻¹
β = 90.428 (1)°	T = 173 K
V = 1270.10 (14) Å³	Plate, colourless
Z = 4	0.42 × 0.22 × 0.04 mm

Data collection top

Bruker Kappa DUO APEXII diffractometer	4246 independent reflections
Radiation source: fine-focus sealed tube	3069 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.030
0.5° ϕ scans and ω scans	θ_max = 31.6°, θ_min = 1.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 1997)	h = −3→6
T_min = 0.956, T_max = 0.996	k = −12→15
16973 measured reflections	l = −38→36

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)] = 0.047	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.138	H-atom parameters constrained
S = 1.04	w = 1/[σ²(F_o²) + (0.0728P)² + 0.2299P] where P = (F_o² + 2F_c²)/3
4246 reflections	(Δ/σ)_max < 0.001
190 parameters	Δρ_max = 0.44 e Å⁻³
0 restraints	Δρ_min = −0.19 e Å⁻³

Crystal data top

C₁₆H₁₁NO₄	V = 1270.10 (14) Å³
M_r = 281.26	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 4.6082 (3) Å	µ = 0.11 mm⁻¹
b = 10.4219 (6) Å	T = 173 K
c = 26.4468 (17) Å	0.42 × 0.22 × 0.04 mm
β = 90.428 (1)°

Data collection top

Bruker Kappa DUO APEXII diffractometer	4246 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1997)	3069 reflections with I > 2σ(I)
T_min = 0.956, T_max = 0.996	R_int = 0.030
16973 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.047	0 restraints
wR(F²) = 0.138	H-atom parameters constrained
S = 1.04	Δρ_max = 0.44 e Å⁻³
4246 reflections	Δρ_min = −0.19 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	0.74839 (19)	0.65066 (9)	0.16340 (3)	0.0297 (2)
O2	0.12234 (19)	0.86867 (9)	0.23054 (3)	0.0307 (2)
O3	0.0611 (3)	0.69688 (13)	0.46889 (4)	0.0563 (4)
O4	0.2296 (3)	0.87629 (13)	0.49596 (4)	0.0569 (3)
N1	0.2075 (3)	0.79369 (12)	0.46362 (4)	0.0364 (3)
C1	0.6196 (2)	0.74864 (12)	0.13678 (4)	0.0254 (2)
C2	0.6533 (3)	0.62632 (12)	0.21073 (5)	0.0281 (2)
H2	0.7393	0.5562	0.2282	0.034*
C3	0.4471 (3)	0.69311 (11)	0.23514 (4)	0.0243 (2)
C4	0.3094 (2)	0.80163 (11)	0.21004 (4)	0.0229 (2)
C5	0.4068 (2)	0.82546 (11)	0.15828 (4)	0.0228 (2)
C6	0.2875 (3)	0.92474 (12)	0.12884 (5)	0.0304 (3)
H6	0.1413	0.9783	0.1426	0.037*
C7	0.3805 (3)	0.94494 (15)	0.08021 (5)	0.0380 (3)
H7	0.2999	1.0127	0.0606	0.046*
C8	0.5929 (3)	0.86601 (16)	0.05974 (5)	0.0392 (3)
H8	0.6559	0.8806	0.0261	0.047*
C9	0.7132 (3)	0.76728 (14)	0.08729 (5)	0.0343 (3)
H9	0.8565	0.7131	0.0730	0.041*
C10	0.3523 (3)	0.65438 (12)	0.28725 (5)	0.0303 (3)
H10A	0.4365	0.5691	0.2949	0.036*
H10B	0.1386	0.6446	0.2868	0.036*
C11	0.4334 (2)	0.74495 (11)	0.32985 (4)	0.0238 (2)
C12	0.2953 (3)	0.72947 (12)	0.37618 (4)	0.0265 (2)
H12	0.1554	0.6635	0.3805	0.032*
C13	0.3633 (3)	0.81075 (12)	0.41575 (4)	0.0261 (2)
C14	0.5657 (3)	0.90853 (12)	0.41192 (5)	0.0292 (3)
H14	0.6065	0.9640	0.4396	0.035*
C15	0.7057 (3)	0.92194 (12)	0.36619 (5)	0.0305 (3)
H15	0.8482	0.9871	0.3624	0.037*
C16	0.6411 (3)	0.84133 (12)	0.32557 (5)	0.0265 (2)
H16	0.7402	0.8523	0.2945	0.032*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0335 (4)	0.0285 (4)	0.0271 (4)	0.0059 (3)	0.0036 (3)	−0.0029 (3)
O2	0.0348 (5)	0.0295 (5)	0.0280 (5)	0.0034 (4)	0.0080 (3)	−0.0026 (4)
O3	0.0700 (8)	0.0657 (8)	0.0335 (6)	−0.0301 (6)	0.0160 (5)	−0.0001 (5)
O4	0.0765 (8)	0.0620 (8)	0.0325 (6)	−0.0123 (6)	0.0152 (5)	−0.0182 (5)
N1	0.0398 (6)	0.0462 (7)	0.0233 (5)	−0.0044 (5)	0.0039 (4)	−0.0002 (5)
C1	0.0279 (5)	0.0265 (5)	0.0218 (5)	−0.0018 (4)	0.0010 (4)	−0.0024 (4)
C2	0.0361 (6)	0.0226 (5)	0.0256 (6)	0.0018 (5)	−0.0035 (4)	−0.0009 (4)
C3	0.0329 (6)	0.0202 (5)	0.0198 (5)	−0.0043 (4)	−0.0007 (4)	−0.0008 (4)
C4	0.0267 (5)	0.0210 (5)	0.0212 (5)	−0.0042 (4)	0.0020 (4)	−0.0018 (4)
C5	0.0264 (5)	0.0227 (5)	0.0194 (5)	−0.0023 (4)	0.0010 (4)	−0.0003 (4)
C6	0.0347 (6)	0.0291 (6)	0.0275 (6)	0.0014 (5)	0.0007 (5)	0.0044 (5)
C7	0.0466 (8)	0.0399 (7)	0.0274 (7)	−0.0025 (6)	−0.0010 (5)	0.0105 (6)
C8	0.0419 (7)	0.0533 (9)	0.0224 (6)	−0.0078 (6)	0.0056 (5)	0.0041 (6)
C9	0.0349 (6)	0.0434 (7)	0.0247 (6)	−0.0021 (6)	0.0073 (5)	−0.0057 (5)
C10	0.0455 (7)	0.0238 (5)	0.0215 (6)	−0.0092 (5)	0.0003 (5)	0.0012 (4)
C11	0.0289 (5)	0.0220 (5)	0.0206 (5)	−0.0007 (4)	−0.0010 (4)	0.0018 (4)
C12	0.0298 (5)	0.0269 (5)	0.0230 (6)	−0.0058 (4)	0.0002 (4)	0.0028 (4)
C13	0.0296 (5)	0.0297 (6)	0.0191 (5)	0.0006 (4)	0.0012 (4)	0.0014 (4)
C14	0.0333 (6)	0.0275 (6)	0.0269 (6)	−0.0015 (5)	−0.0029 (5)	−0.0036 (5)
C15	0.0317 (6)	0.0286 (6)	0.0312 (6)	−0.0080 (5)	−0.0001 (5)	−0.0004 (5)
C16	0.0287 (5)	0.0265 (5)	0.0243 (6)	−0.0029 (4)	0.0021 (4)	0.0010 (4)

Geometric parameters (Å, º) top

O1—C2	1.3533 (15)	C7—H7	0.9500
O1—C1	1.3727 (15)	C8—C9	1.375 (2)
O2—C4	1.2377 (14)	C8—H8	0.9500
O3—N1	1.2222 (17)	C9—H9	0.9500
O4—N1	1.2172 (16)	C10—C11	1.5145 (16)
N1—C13	1.4709 (16)	C10—H10A	0.9900
C1—C5	1.3905 (16)	C10—H10B	0.9900
C1—C9	1.3949 (17)	C11—C16	1.3926 (16)
C2—C3	1.3467 (17)	C11—C12	1.3942 (16)
C2—H2	0.9500	C12—C13	1.3804 (17)
C3—C4	1.4546 (16)	C12—H12	0.9500
C3—C10	1.5042 (16)	C13—C14	1.3858 (18)
C4—C5	1.4650 (15)	C14—C15	1.3823 (18)
C5—C6	1.4047 (17)	C14—H14	0.9500
C6—C7	1.3748 (18)	C15—C16	1.3941 (17)
C6—H6	0.9500	C15—H15	0.9500
C7—C8	1.391 (2)	C16—H16	0.9500

C2—O1—C1	118.16 (9)	C8—C9—C1	118.37 (12)
O4—N1—O3	123.17 (12)	C8—C9—H9	120.8
O4—N1—C13	118.71 (12)	C1—C9—H9	120.8
O3—N1—C13	118.12 (12)	C3—C10—C11	116.27 (10)
O1—C1—C5	121.47 (10)	C3—C10—H10A	108.2
O1—C1—C9	116.69 (11)	C11—C10—H10A	108.2
C5—C1—C9	121.83 (12)	C3—C10—H10B	108.2
C3—C2—O1	125.53 (11)	C11—C10—H10B	108.2
C3—C2—H2	117.2	H10A—C10—H10B	107.4
O1—C2—H2	117.2	C16—C11—C12	118.25 (11)
C2—C3—C4	119.35 (11)	C16—C11—C10	123.71 (11)
C2—C3—C10	120.76 (11)	C12—C11—C10	118.03 (10)
C4—C3—C10	119.87 (10)	C13—C12—C11	119.51 (11)
O2—C4—C3	122.81 (10)	C13—C12—H12	120.2
O2—C4—C5	122.20 (11)	C11—C12—H12	120.2
C3—C4—C5	114.98 (10)	C12—C13—C14	123.03 (11)
C1—C5—C6	118.15 (11)	C12—C13—N1	117.96 (11)
C1—C5—C4	120.43 (10)	C14—C13—N1	119.00 (11)
C6—C5—C4	121.42 (11)	C15—C14—C13	117.20 (11)
C7—C6—C5	120.52 (12)	C15—C14—H14	121.4
C7—C6—H6	119.7	C13—C14—H14	121.4
C5—C6—H6	119.7	C14—C15—C16	120.98 (11)
C6—C7—C8	119.91 (13)	C14—C15—H15	119.5
C6—C7—H7	120.0	C16—C15—H15	119.5
C8—C7—H7	120.0	C11—C16—C15	121.00 (11)
C9—C8—C7	121.22 (12)	C11—C16—H16	119.5
C9—C8—H8	119.4	C15—C16—H16	119.5
C7—C8—H8	119.4

C2—O1—C1—C5	3.07 (16)	C7—C8—C9—C1	−0.7 (2)
C2—O1—C1—C9	−177.07 (11)	O1—C1—C9—C8	−178.84 (12)
C1—O1—C2—C3	−2.33 (18)	C5—C1—C9—C8	1.02 (19)
O1—C2—C3—C4	−0.18 (19)	C2—C3—C10—C11	111.41 (14)
O1—C2—C3—C10	178.04 (11)	C4—C3—C10—C11	−70.37 (15)
C2—C3—C4—O2	−178.62 (11)	C3—C10—C11—C16	−15.66 (18)
C10—C3—C4—O2	3.14 (17)	C3—C10—C11—C12	165.39 (11)
C2—C3—C4—C5	1.83 (16)	C16—C11—C12—C13	1.26 (17)
C10—C3—C4—C5	−176.41 (10)	C10—C11—C12—C13	−179.73 (11)
O1—C1—C5—C6	179.30 (11)	C11—C12—C13—C14	−0.19 (19)
C9—C1—C5—C6	−0.55 (18)	C11—C12—C13—N1	178.39 (11)
O1—C1—C5—C4	−1.39 (17)	O4—N1—C13—C12	−168.33 (13)
C9—C1—C5—C4	178.76 (11)	O3—N1—C13—C12	11.53 (19)
O2—C4—C5—C1	179.38 (11)	O4—N1—C13—C14	10.31 (19)
C3—C4—C5—C1	−1.07 (15)	O3—N1—C13—C14	−169.83 (13)
O2—C4—C5—C6	−1.33 (18)	C12—C13—C14—C15	−0.96 (19)
C3—C4—C5—C6	178.22 (11)	N1—C13—C14—C15	−179.52 (12)
C1—C5—C6—C7	−0.23 (19)	C13—C14—C15—C16	1.02 (19)
C4—C5—C6—C7	−179.53 (12)	C12—C11—C16—C15	−1.20 (18)
C5—C6—C7—C8	0.5 (2)	C10—C11—C16—C15	179.86 (12)
C6—C7—C8—C9	0.0 (2)	C14—C15—C16—C11	0.0 (2)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2···O2	0.95	2.32	3.2663 (15)	171
C7—H7···O3ⁱ	0.95	2.65	3.5614 (19)	160
C8—H8···O3ⁱⁱ	0.95	2.54	3.3071 (18)	138
C14—H14···O4ⁱⁱⁱ	0.95	2.50	3.4380 (17)	172
C15—H15···O1^iv	0.95	2.62	3.5569 (15)	170
C16—H16···O2^v	0.95	2.46	3.3764 (15)	163

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

Experimental details

Crystal data
Chemical formula	C₁₆H₁₁NO₄
M_r	281.26
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	173
a, b, c (Å)	4.6082 (3), 10.4219 (6), 26.4468 (17)
β (°)	90.428 (1)
V (Å³)	1270.10 (14)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.11
Crystal size (mm)	0.42 × 0.22 × 0.04

Data collection
Diffractometer	Bruker Kappa DUO APEXII diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1997)
T_min, T_max	0.956, 0.996
No. of measured, independent and observed [I > 2σ(I)] reflections	16973, 4246, 3069
R_int	0.030
(sin θ/λ)_max (Å⁻¹)	0.736

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.047, 0.138, 1.04
No. of reflections	4246
No. of parameters	190
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.44, −0.19

Computer programs: APEX2 (Bruker, 2006), SAINT (Bruker, 2006), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 2012).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2···O2	0.95	2.32	3.2663 (15)	170.8
C7—H7···O3ⁱ	0.95	2.65	3.5614 (19)	160.0
C8—H8···O3ⁱⁱ	0.95	2.54	3.3071 (18)	137.5
C14—H14···O4ⁱⁱⁱ	0.95	2.50	3.4380 (17)	171.5
C15—H15···O1^iv	0.95	2.62	3.5569 (15)	170.4
C16—H16···O2^v	0.95	2.46	3.3764 (15)	162.9

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

Acknowledgements

We thank the University of KwaZulu-Natal and the South Africa Research Chairs initiative of the Department of Science and Technology for financial support and the National Research Foundation of South Africa for a bursary for KG.

References

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