4,5-Diphen­oxy­benzene-1,2-dicarbo­nitrile

Foo, C.C.; Tan, A.L.; Wimmer, F.L.; Mirza, A.H.; Young, D.J.; Ng, S.W.; Tiekink, E.R.T.

doi:10.1107/S1600536812004060

organic compounds

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ISSN: 2056-9890

Volume 68| Part 3| March 2012| Page o601

doi:10.1107/S1600536812004060

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4,5-Diphenoxybenzene-1,2-dicarbonitrile

Chuan Ching Foo,^a Ai Ling Tan,^a Franz L. Wimmer,^a Aminul Huq Mirza,^a David J. Young,^a ‡ Seik Weng Ng ^b,^c and Edward R. T. Tiekink ^b ^*

^aFaculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link BE 1410, Brunei Darussalam, ^bDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia, and ^cChemistry Department, Faculty of Science, King Abdulaziz University, PO Box 80203 Jeddah, Saudi Arabia
^*Correspondence e-mail: edward.tiekink@gmail.com

(Received 31 January 2012; accepted 31 January 2012; online 4 February 2012)

In the title compound, C₂₀H₁₂N₂O₂, the phenyl and benzene rings are mutually perpendicular, with the dihedral angle between the phenyl rings being 87.92 (16)° and those formed between the phenyl rings and the benzene rings being 73.68 (15) and 84.65 (15)°. Helical supramolecular chains along [010], mediated by C—H⋯N interactions, are found in the crystal structure.

Related literature

For the use of functionalized phthalocyanines as dyes in photodynamic therapy and in dye-sensitized solar cells, see: Li et al. (2008 ); Jiang et al. (2011 ); Zhao et al. (2009 ). For a related structure, see: Yu et al. (2010 ). The present synthesis is based on earlier syntheses; see: Wohrle et al. (1993 ); Li et al. (2008).

Experimental

Crystal data

C₂₀H₁₂N₂O₂
M_r = 312.32
Orthorhombic, P 2₁ 2₁ 2₁
a = 5.6543 (4) Å
b = 13.5163 (9) Å
c = 19.9498 (17) Å
V = 1524.7 (2) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 100 K
0.30 × 0.10 × 0.10 mm

Data collection

Agilent SuperNova Dual diffractometer with an Atlas detector
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010 ) T_min = 0.974, T_max = 0.991
4325 measured reflections
2029 independent reflections
1498 reflections with I > 2σ(I)
R_int = 0.052

Refinement

R[F² > 2σ(F²)] = 0.054
wR(F²) = 0.118
S = 1.01
2029 reflections
217 parameters
H-atom parameters constrained
Δρ_max = 0.26 e Å⁻³
Δρ_min = −0.26 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C13—H13⋯N1ⁱ	0.95	2.52	3.422 (4)	159
Symmetry code: (i) $[-x+3, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Data collection: CrysAlis PRO (Agilent, 2010); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997 ) and DIAMOND (Brandenburg, 2006 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536812004060/hg5172sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812004060/hg5172Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536812004060/hg5172Isup3.cml

checkCIF report

Comment top

Substituted phthalonitriles are precursors for functionalized phthalocyanines used as dyes in, for example, photodynamic therapy (Li et al., 2008; Jiang et al., 2011) and dye-sensitized solar cells (Zhao et al., 2009). Our interest in the latter prompted the synthesis of the title compound, (I).

In (I), Fig. 1, both phenyl rings lie to one side of the benzene ring to which they are connected. The dihedral angles between the (C9–C14) and (C15–C20) rings is 87.92 (16)° indicating an almost orthogonal relationship. The (C9–C14) and (C15–C20) rings form a dihedral angle of 73.68 (15) and 84.65 (15)°, respectively with the (C1–C6) ring. The molecular conformation observed in (I) resembles closely that reported for the p-methoxy derivative (Yu et al., 2010).

The most prominent feature of the crystal packing is the formation of helical supramolecular chains along [010] that are mediated by C—H···N interactions, Table 1 and Fig. 2.

Related literature top

For the use of functionalized phthalocyanines as dyes in photodynamic therapy and in dye-sensitized solar cells, see: Li et al. (2008); Jiang et al. (2011); Zhao et al. (2009). For a related structure, see: Yu et al. (2010). The present synthesis is based on earlier syntheses; see: Wohrle et al. (1993); Li et al. (2008).

Experimental top

The title compound was prepared by modification of a literature procedures (Wohrle et al., 1993; Li et al., 2008). 4,5-Dichlorophthalonitrile (1.0 g, 5.0 mmol) and phenol (2.0 g, 21.3 mmol) were dissolved in DMF (20 ml) and heated to 353 K. Potassium carbonate (4.5 g, 32.6 mmol) was added in four portions with stirring over 20 minutes and the temperature maintained for a further three hours. The mixture was then cooled to room temperature and poured into ice-water (100 ml). The resulting precipitate was filtered and recrystallized from acetone / water to provide 0.47 g (35% yield) of colourless crystals, M. pt.: 432–436 K (lit. 422 K (Wohrle et al., 1993)). ¹H NMR (400 MHz, CDCl₃) δ 7.09 (4H, m), 7.16 (2H, s), 7.30 (2H, m), 7.47 (4H, m).

Computing details top

Data collection: CrysAlis PRO (Agilent, 2010); cell refinement: CrysAlis PRO (Agilent, 2010); data reduction: CrysAlis PRO (Agilent, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 1. The molecular of (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.
	Fig. 2. A view of the helical supramolecular chain along [010] in (I). The C—H···N contacts are shown as orange dashed lines.

4,5-Diphenoxybenzene-1,2-dicarbonitrile top

Crystal data top

C₂₀H₁₂N₂O₂	F(000) = 648
M_r = 312.32	D_x = 1.361 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 1267 reflections
a = 5.6543 (4) Å	θ = 2.5–27.5°
b = 13.5163 (9) Å	µ = 0.09 mm⁻¹
c = 19.9498 (17) Å	T = 100 K
V = 1524.7 (2) Å³	Block, colourless
Z = 4	0.30 × 0.10 × 0.10 mm

Data collection top

Agilent SuperNova Dual diffractometer with an Atlas detector	2029 independent reflections
Radiation source: SuperNova (Mo) X-ray Source	1498 reflections with I > 2σ(I)
Mirror monochromator	R_int = 0.052
Detector resolution: 10.4041 pixels mm^-1	θ_max = 27.6°, θ_min = 2.5°
ω scan	h = −7→7
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010)	k = −17→16
T_min = 0.974, T_max = 0.991	l = −25→17
4325 measured reflections

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)] = 0.054	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.118	H-atom parameters constrained
S = 1.01	w = 1/[σ²(F_o²) + (0.0522P)²] where P = (F_o² + 2F_c²)/3
2029 reflections	(Δ/σ)_max < 0.001
217 parameters	Δρ_max = 0.26 e Å⁻³
0 restraints	Δρ_min = −0.26 e Å⁻³

Crystal data top

C₂₀H₁₂N₂O₂	V = 1524.7 (2) Å³
M_r = 312.32	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 5.6543 (4) Å	µ = 0.09 mm⁻¹
b = 13.5163 (9) Å	T = 100 K
c = 19.9498 (17) Å	0.30 × 0.10 × 0.10 mm

Data collection top

Agilent SuperNova Dual diffractometer with an Atlas detector	2029 independent reflections
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010)	1498 reflections with I > 2σ(I)
T_min = 0.974, T_max = 0.991	R_int = 0.052
4325 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.054	0 restraints
wR(F²) = 0.118	H-atom parameters constrained
S = 1.01	Δρ_max = 0.26 e Å⁻³
2029 reflections	Δρ_min = −0.26 e Å⁻³
217 parameters

Special details top

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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	0.7480 (4)	0.46056 (17)	0.21758 (11)	0.0246 (5)
O2	0.8019 (4)	0.49051 (16)	0.08401 (11)	0.0237 (6)
N1	1.6503 (5)	0.2459 (2)	0.05129 (14)	0.0276 (7)
N2	1.5732 (5)	0.1975 (2)	0.24912 (15)	0.0302 (7)
C1	0.9365 (6)	0.4161 (2)	0.18642 (16)	0.0205 (7)
C2	0.9635 (6)	0.4325 (2)	0.11812 (16)	0.0191 (7)
C3	1.1429 (6)	0.3878 (2)	0.08308 (17)	0.0217 (7)
H3	1.1582	0.3992	0.0363	0.026*
C4	1.3028 (6)	0.3257 (2)	0.11572 (16)	0.0215 (8)
C5	1.2763 (6)	0.3093 (2)	0.18456 (16)	0.0197 (7)
C6	1.0916 (6)	0.3539 (2)	0.21997 (17)	0.0196 (7)
H6	1.0724	0.3417	0.2665	0.024*
C7	1.4946 (6)	0.2810 (2)	0.07954 (16)	0.0218 (7)
C8	1.4418 (6)	0.2465 (2)	0.22039 (16)	0.0220 (7)
C9	0.7792 (6)	0.4909 (2)	0.28421 (16)	0.0210 (7)
C10	0.6053 (6)	0.4644 (3)	0.32990 (17)	0.0262 (8)
H10	0.4760	0.4240	0.3168	0.031*
C11	0.6253 (6)	0.4987 (3)	0.39549 (17)	0.0272 (8)
H11	0.5082	0.4813	0.4275	0.033*
C12	0.8137 (6)	0.5579 (2)	0.41466 (18)	0.0288 (8)
H12	0.8254	0.5810	0.4595	0.035*
C13	0.9840 (6)	0.5829 (2)	0.36819 (17)	0.0271 (8)
H13	1.1136	0.6233	0.3812	0.033*
C14	0.9673 (6)	0.5493 (2)	0.30229 (17)	0.0248 (8)
H14	1.0848	0.5665	0.2703	0.030*
C15	0.8279 (5)	0.5936 (2)	0.08943 (16)	0.0200 (7)
C16	1.0254 (6)	0.6379 (2)	0.11785 (16)	0.0220 (8)
H16	1.1490	0.5989	0.1363	0.026*
C17	1.0384 (6)	0.7406 (3)	0.11868 (16)	0.0244 (8)
H17	1.1726	0.7720	0.1378	0.029*
C18	0.8576 (6)	0.7979 (2)	0.09186 (16)	0.0251 (8)
H18	0.8667	0.8681	0.0932	0.030*
C19	0.6632 (6)	0.7514 (3)	0.06305 (16)	0.0253 (8)
H19	0.5397	0.7901	0.0441	0.030*
C20	0.6483 (6)	0.6491 (2)	0.06170 (16)	0.0233 (8)
H20	0.5156	0.6176	0.0419	0.028*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0196 (12)	0.0316 (12)	0.0227 (12)	0.0066 (12)	−0.0010 (10)	−0.0033 (10)
O2	0.0241 (14)	0.0174 (10)	0.0296 (13)	0.0020 (10)	−0.0070 (11)	0.0005 (10)
N1	0.0256 (16)	0.0299 (15)	0.0274 (16)	0.0015 (15)	−0.0001 (14)	−0.0008 (14)
N2	0.0240 (16)	0.0299 (15)	0.0366 (18)	0.0041 (15)	−0.0025 (15)	−0.0008 (14)
C1	0.0182 (16)	0.0166 (14)	0.0267 (19)	−0.0032 (15)	0.0007 (15)	−0.0060 (14)
C2	0.0161 (16)	0.0157 (15)	0.0255 (18)	−0.0002 (14)	−0.0055 (14)	−0.0027 (13)
C3	0.0236 (17)	0.0170 (14)	0.0246 (19)	−0.0017 (14)	−0.0005 (16)	−0.0020 (14)
C4	0.0219 (19)	0.0172 (16)	0.0254 (19)	−0.0014 (15)	0.0000 (15)	−0.0032 (14)
C5	0.0182 (16)	0.0132 (13)	0.0277 (18)	−0.0023 (14)	−0.0042 (15)	−0.0018 (14)
C6	0.0185 (17)	0.0190 (15)	0.0212 (17)	−0.0001 (15)	0.0012 (14)	0.0002 (14)
C7	0.0223 (18)	0.0209 (16)	0.0221 (18)	−0.0042 (16)	−0.0052 (16)	−0.0001 (14)
C8	0.0223 (17)	0.0192 (15)	0.0244 (18)	−0.0013 (16)	0.0030 (15)	−0.0013 (15)
C9	0.0225 (17)	0.0195 (15)	0.0209 (17)	0.0069 (15)	0.0017 (15)	0.0016 (14)
C10	0.0219 (18)	0.0255 (16)	0.031 (2)	−0.0013 (16)	0.0011 (15)	−0.0034 (16)
C11	0.0280 (19)	0.0240 (16)	0.030 (2)	0.0015 (17)	0.0061 (16)	0.0008 (16)
C12	0.035 (2)	0.0262 (18)	0.0253 (19)	0.0079 (17)	−0.0027 (17)	−0.0064 (16)
C13	0.0254 (18)	0.0221 (16)	0.034 (2)	0.0034 (16)	−0.0046 (17)	−0.0058 (15)
C14	0.0188 (16)	0.0203 (16)	0.035 (2)	0.0042 (16)	0.0042 (16)	0.0031 (15)
C15	0.0190 (17)	0.0199 (15)	0.0211 (18)	−0.0016 (15)	0.0027 (15)	−0.0010 (14)
C16	0.0185 (17)	0.0266 (17)	0.0209 (18)	0.0024 (16)	−0.0008 (15)	0.0003 (14)
C17	0.0206 (17)	0.0314 (17)	0.0212 (18)	−0.0053 (17)	0.0007 (15)	−0.0061 (16)
C18	0.0245 (18)	0.0219 (16)	0.0289 (19)	0.0027 (16)	0.0057 (16)	−0.0005 (15)
C19	0.0246 (18)	0.0263 (17)	0.0250 (18)	0.0078 (16)	−0.0004 (15)	0.0026 (16)
C20	0.0172 (16)	0.0293 (17)	0.0232 (18)	0.0014 (16)	0.0004 (15)	0.0002 (15)

Geometric parameters (Å, º) top

O1—C1	1.373 (4)	C10—H10	0.9500
O1—C9	1.402 (4)	C11—C12	1.386 (5)
O2—C2	1.383 (4)	C11—H11	0.9500
O2—C15	1.405 (3)	C12—C13	1.379 (5)
N1—C7	1.148 (4)	C12—H12	0.9500
N2—C8	1.148 (4)	C13—C14	1.394 (5)
C1—C6	1.387 (4)	C13—H13	0.9500
C1—C2	1.389 (4)	C14—H14	0.9500
C2—C3	1.372 (4)	C15—C20	1.379 (4)
C3—C4	1.395 (4)	C15—C16	1.388 (4)
C3—H3	0.9500	C16—C17	1.390 (4)
C4—C5	1.399 (4)	C16—H16	0.9500
C4—C7	1.436 (5)	C17—C18	1.390 (5)
C5—C6	1.398 (5)	C17—H17	0.9500
C5—C8	1.452 (5)	C18—C19	1.391 (5)
C6—H6	0.9500	C18—H18	0.9500
C9—C14	1.372 (5)	C19—C20	1.385 (4)
C9—C10	1.388 (5)	C19—H19	0.9500
C10—C11	1.393 (5)	C20—H20	0.9500

C1—O1—C9	117.4 (2)	C12—C11—H11	119.5
C2—O2—C15	117.1 (2)	C10—C11—H11	119.5
O1—C1—C6	122.5 (3)	C13—C12—C11	119.5 (3)
O1—C1—C2	117.4 (3)	C13—C12—H12	120.2
C6—C1—C2	120.1 (3)	C11—C12—H12	120.2
C3—C2—O2	119.2 (3)	C12—C13—C14	120.4 (3)
C3—C2—C1	120.7 (3)	C12—C13—H13	119.8
O2—C2—C1	120.1 (3)	C14—C13—H13	119.8
C2—C3—C4	120.4 (3)	C9—C14—C13	119.2 (3)
C2—C3—H3	119.8	C9—C14—H14	120.4
C4—C3—H3	119.8	C13—C14—H14	120.4
C3—C4—C5	119.0 (3)	C20—C15—C16	121.4 (3)
C3—C4—C7	120.5 (3)	C20—C15—O2	115.6 (3)
C5—C4—C7	120.5 (3)	C16—C15—O2	122.9 (3)
C6—C5—C4	120.5 (3)	C15—C16—C17	118.6 (3)
C6—C5—C8	119.0 (3)	C15—C16—H16	120.7
C4—C5—C8	120.5 (3)	C17—C16—H16	120.7
C1—C6—C5	119.3 (3)	C18—C17—C16	120.9 (3)
C1—C6—H6	120.3	C18—C17—H17	119.6
C5—C6—H6	120.3	C16—C17—H17	119.6
N1—C7—C4	178.9 (3)	C17—C18—C19	119.2 (3)
N2—C8—C5	179.4 (4)	C17—C18—H18	120.4
C14—C9—C10	121.7 (3)	C19—C18—H18	120.4
C14—C9—O1	121.0 (3)	C20—C19—C18	120.5 (3)
C10—C9—O1	117.2 (3)	C20—C19—H19	119.8
C9—C10—C11	118.3 (3)	C18—C19—H19	119.8
C9—C10—H10	120.9	C15—C20—C19	119.4 (3)
C11—C10—H10	120.9	C15—C20—H20	120.3
C12—C11—C10	120.9 (3)	C19—C20—H20	120.3

C9—O1—C1—C6	35.9 (4)	C6—C5—C8—N2	−55 (41)
C9—O1—C1—C2	−146.5 (3)	C4—C5—C8—N2	124 (41)
C15—O2—C2—C3	−103.2 (3)	C1—O1—C9—C14	52.0 (4)
C15—O2—C2—C1	80.0 (4)	C1—O1—C9—C10	−131.6 (3)
O1—C1—C2—C3	−177.7 (3)	C14—C9—C10—C11	0.1 (5)
C6—C1—C2—C3	0.0 (4)	O1—C9—C10—C11	−176.3 (3)
O1—C1—C2—O2	−1.0 (4)	C9—C10—C11—C12	0.1 (5)
C6—C1—C2—O2	176.7 (3)	C10—C11—C12—C13	−0.2 (5)
O2—C2—C3—C4	−177.4 (3)	C11—C12—C13—C14	0.1 (5)
C1—C2—C3—C4	−0.7 (5)	C10—C9—C14—C13	−0.1 (5)
C2—C3—C4—C5	0.5 (5)	O1—C9—C14—C13	176.1 (3)
C2—C3—C4—C7	−178.3 (3)	C12—C13—C14—C9	0.0 (5)
C3—C4—C5—C6	0.4 (5)	C2—O2—C15—C20	−172.5 (3)
C7—C4—C5—C6	179.1 (3)	C2—O2—C15—C16	10.5 (4)
C3—C4—C5—C8	−179.0 (3)	C20—C15—C16—C17	0.8 (5)
C7—C4—C5—C8	−0.2 (5)	O2—C15—C16—C17	177.7 (3)
O1—C1—C6—C5	178.4 (3)	C15—C16—C17—C18	0.2 (5)
C2—C1—C6—C5	0.9 (4)	C16—C17—C18—C19	−0.9 (5)
C4—C5—C6—C1	−1.1 (5)	C17—C18—C19—C20	0.7 (5)
C8—C5—C6—C1	178.3 (3)	C16—C15—C20—C19	−1.0 (5)
C3—C4—C7—N1	123 (21)	O2—C15—C20—C19	−178.1 (3)
C5—C4—C7—N1	−56 (21)	C18—C19—C20—C15	0.2 (5)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C13—H13···N1ⁱ	0.95	2.52	3.422 (4)	159

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

Experimental details

Crystal data
Chemical formula	C₂₀H₁₂N₂O₂
M_r	312.32
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	100
a, b, c (Å)	5.6543 (4), 13.5163 (9), 19.9498 (17)
V (Å³)	1524.7 (2)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.09
Crystal size (mm)	0.30 × 0.10 × 0.10

Data collection
Diffractometer	Agilent SuperNova Dual diffractometer with an Atlas detector
Absorption correction	Multi-scan (CrysAlis PRO; Agilent, 2010)
T_min, T_max	0.974, 0.991
No. of measured, independent and observed [I > 2σ(I)] reflections	4325, 2029, 1498
R_int	0.052
(sin θ/λ)_max (Å⁻¹)	0.651

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.054, 0.118, 1.01
No. of reflections	2029
No. of parameters	217
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.26, −0.26

Computer programs: CrysAlis PRO (Agilent, 2010), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg, 2006), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C13—H13···N1ⁱ	0.95	2.52	3.422 (4)	159

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

Footnotes

‡Additional correspondence author, e-mail: david.young@ubd.edu.bn.

Acknowledgements

We gratefully acknowledge funding from the Brunei Research Council, and thank the Ministry of Higher Education (Malaysia) for funding structural studies through the High-Impact Research scheme (UM.C/HIR/MOHE/SC/12).

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