5-Carbamoyl-2-methyl-1-(2-methyl­benz­yl)pyridinium bromide

Kim, K.B.; Yu, S.M.; Kim, C.; Kim, Y.

doi:10.1107/S1600536812018958

organic compounds

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ISSN: 2056-9890

Volume 68| Part 6| June 2012| Pages o1609-o1610

doi:10.1107/S1600536812018958

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5-Carbamoyl-2-methyl-1-(2-methylbenzyl)pyridinium bromide

Kyung Beom Kim,^a Seung Man Yu,^a Cheal Kim ^a ^* and Youngmee Kim ^b ^*

^aDepartment of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743, Republic of Korea, and ^bDepartment of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
^*Correspondence e-mail: chealkim@seoultech.ac.kr, ymeekim@ewha.ac.kr

(Received 20 April 2012; accepted 27 April 2012; online 5 May 2012)

In the title molecular salt, C₁₅H₁₇N₂O⁺·Br⁻, the benzene and pyridinium rings form a dihedral angle of 83.0 (1)°. In the crystal, N—H⋯Br and N—H⋯O hydrogen bonds link the components into chains along [010]. These chains are linked by weak C—H⋯O and C—H⋯Br hydrogen bonds, forming a three-dimensional network.

Related literature

The title compound was prepared as an NAD+ (nicotinamide adenine dinucleotide) model. For the role of reduced nicotinamide co-factors (NADH and NADPH) in enzyme-catalysed reactions, see: Hollmann et al. (2001 ); Lee et al. (2011 ); Maenaka et al. (2012 ); Park et al. (2008 ); Ruppert et al. (1988 ); Zhu et al. (2003 , 2006 ). For the generation of NADH, see: Qing et al. (2006 ). For an efficient method of in situ regeneration, see: Song et al. (2008 ). For a related structure, see: Kim et al. (2012 ).

Experimental

Crystal data

C₁₅H₁₇N₂O⁺·Br⁻
M_r = 321.22
Monoclinic, C 2/c
a = 8.4880 (17) Å
b = 10.502 (2) Å
c = 33.450 (7) Å
β = 96.85 (3)°
V = 2960.5 (10) Å³
Z = 8
Mo Kα radiation
μ = 2.77 mm⁻¹
T = 293 K
0.50 × 0.20 × 0.10 mm

Data collection

Bruker SMART CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 1997 ) T_min = 0.338, T_max = 0.769
8103 measured reflections
2879 independent reflections
1857 reflections with I > 2σ(I)
R_int = 0.043

Refinement

R[F² > 2σ(F²)] = 0.042
wR(F²) = 0.096
S = 1.00
2879 reflections
174 parameters
H-atom parameters constrained
Δρ_max = 0.36 e Å⁻³
Δρ_min = −0.31 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯Br1	0.86	2.67	3.477 (3)	157
N1—H1B⋯O1ⁱ	0.86	2.35	3.207 (4)	173
C3—H3⋯O1ⁱ	0.93	2.22	3.149 (5)	174
C4—H4⋯Br1ⁱ	0.93	2.78	3.712 (4)	175
C6—H6C⋯Br1ⁱⁱ	0.96	2.73	3.638 (3)	157
C8—H8B⋯Br1ⁱⁱⁱ	0.97	2.87	3.782 (3)	156
Symmetry codes: (i) $[-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[-x+1, y, -z+{\script{1\over 2}}]$ ; (iii) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999 ); software used to prepare material for publication: SHELXTL (Brandenburg, 1999).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536812018958/lh5461sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812018958/lh5461Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536812018958/lh5461Isup3.cml

checkCIF report

Comment top

Reduced nicotinamide co-factors (NADH and NADPH) play an important role in a variety of enzyme-catalyzed reactions (Hollmann et al., 2001; Lee et al., 2011; Maenaka et al., 2012; Park et al., 2008; Ruppert et al., 1988; Zhu et al., 2003; Zhu et al., 2006). For example, in biocatalytic systems, many enzymes depend on nicotinamide co-factors (NAD and NADP) for their functions (Park et al., 2008).To date, a number of strategies including enzymatic catalysis, whole-cell conversion, chemical method, have been devised to the regeneration of NADH (Qing et al., 2006). The high cost of these co-factors, however, is prohibitive of industrialization of many promising enzymatic processes. An efficient method of their in situ regeneration is the only means for making the processes economically and industrially feasible (Song et al., 2008). Therefore, we and many researchers have given considerable attention to the chemistry of NADH and its models (Hollmann et al., 2001; Kim et al., 2012). In this work, we have synthesized the title compound as a NAD⁺ model and report here the crystal structure.

The molecular structure of the title compound is shown in Fig. 1. The benzene and pyridinium rings form a dihedral angle of 83.0 (1)°. In the crystal, N—H···Br and N—H···O hydrogen bonds link the components into chains along [010]. These chains are linked by weak intermolecular C—H···O and C—H···Br hydrogen bonds to form a three-dimensional network.

Related literature top

The title compound was prepared as an NAD+ (nicotinamide adenine dinucleotide) model. For the role of reduced nicotinamide co-factors (NADH and NADPH) in enzyme-catalysed reactions, see: Hollmann et al. (2001); Lee et al. (2011); Maenaka et al. (2012); Park et al. (2008); Ruppert et al. (1988); Zhu et al. (2003, 2006). For the generation of NADH, see: Qing et al. (2006). For an efficient method of in situ regeneration, see: Song et al. (2008). For a related structure, see: Kim et al. (2012).

Experimental top

6-Methylnicotinamide (136.15 mg, 1 mmol) was dissolved 10 ml dimethylformamide. After stirring for a few minutes, 2-methylbenzyl bromide (185.06 mg, 1 mmol) was carefully added to the reaction solution. The solution was stirred for 3 h at 353K. The precipitate was filtered, washed three times with methylene chloride, and dried under vacuum. 3-Carbamoyl-6-methyl-1-(2-methylbenzyl)pyridinium bromide (16.06 mg, 0.05 mmol) was dissolved in 1 ml methanol and carefully layered by 3 ml isopropyl ether. Suitable crystals of the title compound for X-ray analysis were obtained in a few days.

Computing details top

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Brandenburg, 1999).

Figures top

Fig. 1. The molecular structure of the title compound showing displacement ellipsoids at the 50% probability level.

5-Carbamoyl-2-methyl-1-(2-methylbenzyl)pyridinium bromide top

Crystal data top

C₁₅H₁₇N₂O⁺·Br⁻	F(000) = 1312
M_r = 321.22	D_x = 1.441 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 2248 reflections
a = 8.4880 (17) Å	θ = 2.3–25.2°
b = 10.502 (2) Å	µ = 2.77 mm⁻¹
c = 33.450 (7) Å	T = 293 K
β = 96.85 (3)°	Block, colorless
V = 2960.5 (10) Å³	0.50 × 0.20 × 0.10 mm
Z = 8

Data collection top

Bruker SMART CCD diffractometer	2879 independent reflections
Radiation source: fine-focus sealed tube	1857 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.043
ϕ and ω scans	θ_max = 26.0°, θ_min = 2.5°
Absorption correction: multi-scan (SADABS; Bruker, 1997)	h = −9→10
T_min = 0.338, T_max = 0.769	k = −12→8
8103 measured reflections	l = −41→40

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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.096	H-atom parameters constrained
S = 1.00	w = 1/[σ²(F_o²) + (0.0247P)² + 1.3939P] where P = (F_o² + 2F_c²)/3
2879 reflections	(Δ/σ)_max = 0.001
174 parameters	Δρ_max = 0.36 e Å⁻³
0 restraints	Δρ_min = −0.31 e Å⁻³

Crystal data top

C₁₅H₁₇N₂O⁺·Br⁻	V = 2960.5 (10) Å³
M_r = 321.22	Z = 8
Monoclinic, C2/c	Mo Kα radiation
a = 8.4880 (17) Å	µ = 2.77 mm⁻¹
b = 10.502 (2) Å	T = 293 K
c = 33.450 (7) Å	0.50 × 0.20 × 0.10 mm
β = 96.85 (3)°

Data collection top

Bruker SMART CCD diffractometer	2879 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 1997)	1857 reflections with I > 2σ(I)
T_min = 0.338, T_max = 0.769	R_int = 0.043
8103 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.042	0 restraints
wR(F²) = 0.096	H-atom parameters constrained
S = 1.00	Δρ_max = 0.36 e Å⁻³
2879 reflections	Δρ_min = −0.31 e Å⁻³
174 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
Br1	0.01684 (4)	0.38708 (4)	0.349683 (12)	0.06234 (17)
N1	0.2074 (3)	0.3760 (3)	0.26330 (9)	0.0686 (9)
H1A	0.1599	0.4033	0.2830	0.082*
H1B	0.2111	0.2957	0.2585	0.082*
N2	0.4953 (3)	0.4466 (3)	0.15096 (8)	0.0435 (6)
O1	0.2735 (4)	0.5725 (3)	0.24558 (9)	0.0862 (9)
C1	0.2742 (4)	0.4572 (4)	0.24056 (11)	0.0577 (9)
C2	0.3589 (4)	0.4032 (3)	0.20721 (10)	0.0466 (8)
C3	0.3794 (4)	0.2738 (4)	0.20086 (11)	0.0590 (9)
H3	0.3414	0.2144	0.2180	0.071*
C4	0.4560 (4)	0.2342 (3)	0.16924 (11)	0.0570 (9)
H4	0.4696	0.1475	0.1652	0.068*
C5	0.5131 (4)	0.3198 (3)	0.14343 (10)	0.0468 (8)
C6	0.5919 (4)	0.2774 (3)	0.10809 (10)	0.0599 (10)
H6A	0.5354	0.3112	0.0838	0.090*
H6B	0.5916	0.1861	0.1068	0.090*
H6C	0.6993	0.3078	0.1109	0.090*
C7	0.4195 (3)	0.4868 (3)	0.18186 (9)	0.0452 (8)
H7	0.4083	0.5737	0.1860	0.054*
C8	0.5564 (4)	0.5431 (3)	0.12466 (10)	0.0503 (9)
H8A	0.6635	0.5199	0.1201	0.060*
H8B	0.5617	0.6246	0.1384	0.060*
C9	0.4566 (4)	0.5572 (3)	0.08456 (10)	0.0500 (9)
C10	0.3025 (4)	0.5121 (3)	0.07804 (11)	0.0609 (10)
H10	0.2579	0.4712	0.0986	0.073*
C11	0.2144 (5)	0.5281 (4)	0.04038 (14)	0.0816 (13)
H11	0.1113	0.4971	0.0356	0.098*
C12	0.2825 (7)	0.5909 (4)	0.01029 (14)	0.0939 (17)
H12	0.2248	0.6027	−0.0149	0.113*
C13	0.4333 (7)	0.6351 (4)	0.01754 (14)	0.0880 (14)
H13	0.4773	0.6767	−0.0030	0.106*
C14	0.5231 (5)	0.6206 (3)	0.05406 (12)	0.0664 (11)
C15	0.6904 (6)	0.6707 (5)	0.06056 (15)	0.1029 (16)
H15A	0.7139	0.7144	0.0368	0.154*
H15B	0.7629	0.6010	0.0661	0.154*
H15C	0.7010	0.7286	0.0829	0.154*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.0576 (3)	0.0523 (3)	0.0775 (3)	−0.0027 (2)	0.00950 (18)	0.0134 (2)
N1	0.075 (2)	0.078 (2)	0.0571 (19)	−0.0028 (19)	0.0258 (17)	−0.0019 (17)
N2	0.0468 (15)	0.0348 (15)	0.0494 (16)	0.0015 (13)	0.0076 (13)	−0.0034 (13)
O1	0.118 (2)	0.0592 (18)	0.091 (2)	0.0093 (18)	0.0527 (18)	−0.0127 (16)
C1	0.057 (2)	0.065 (3)	0.052 (2)	0.007 (2)	0.0107 (18)	−0.001 (2)
C2	0.0435 (18)	0.051 (2)	0.0451 (19)	0.0017 (16)	0.0045 (15)	−0.0026 (17)
C3	0.071 (2)	0.045 (2)	0.061 (2)	−0.0051 (19)	0.011 (2)	0.0024 (18)
C4	0.072 (2)	0.035 (2)	0.065 (2)	0.0027 (18)	0.0104 (19)	−0.0033 (18)
C5	0.0427 (19)	0.037 (2)	0.059 (2)	0.0023 (16)	0.0002 (16)	−0.0075 (17)
C6	0.057 (2)	0.053 (2)	0.071 (2)	0.0049 (18)	0.0164 (19)	−0.0177 (19)
C7	0.0461 (19)	0.044 (2)	0.0453 (19)	0.0041 (16)	0.0042 (16)	−0.0068 (16)
C8	0.057 (2)	0.038 (2)	0.058 (2)	−0.0058 (17)	0.0144 (18)	−0.0061 (17)
C9	0.064 (2)	0.0372 (19)	0.050 (2)	0.0100 (18)	0.0107 (18)	−0.0060 (17)
C10	0.065 (2)	0.054 (2)	0.062 (3)	0.018 (2)	0.001 (2)	−0.0070 (19)
C11	0.078 (3)	0.073 (3)	0.090 (3)	0.029 (2)	−0.008 (3)	−0.021 (3)
C12	0.142 (5)	0.079 (4)	0.055 (3)	0.046 (3)	−0.014 (3)	0.002 (2)
C13	0.129 (4)	0.071 (3)	0.064 (3)	0.014 (3)	0.013 (3)	0.004 (2)
C14	0.103 (3)	0.042 (2)	0.055 (2)	0.007 (2)	0.014 (2)	−0.0017 (19)
C15	0.137 (4)	0.088 (3)	0.092 (3)	−0.044 (3)	0.048 (3)	0.005 (3)

Geometric parameters (Å, º) top

N1—C1	1.315 (5)	C7—H7	0.9300
N1—H1A	0.8600	C8—C9	1.506 (5)
N1—H1B	0.8600	C8—H8A	0.9700
N2—C7	1.348 (4)	C8—H8B	0.9700
N2—C5	1.367 (4)	C9—C10	1.384 (5)
N2—C8	1.476 (4)	C9—C14	1.393 (5)
O1—C1	1.224 (4)	C10—C11	1.397 (5)
C1—C2	1.508 (5)	C10—H10	0.9300
C2—C7	1.363 (4)	C11—C12	1.385 (7)
C2—C3	1.390 (5)	C11—H11	0.9300
C3—C4	1.371 (5)	C12—C13	1.357 (7)
C3—H3	0.9300	C12—H12	0.9300
C4—C5	1.374 (5)	C13—C14	1.369 (6)
C4—H4	0.9300	C13—H13	0.9300
C5—C6	1.494 (4)	C14—C15	1.505 (6)
C6—H6A	0.9600	C15—H15A	0.9600
C6—H6B	0.9600	C15—H15B	0.9600
C6—H6C	0.9600	C15—H15C	0.9600

C1—N1—H1A	120.0	N2—C8—C9	113.5 (3)
C1—N1—H1B	120.0	N2—C8—H8A	108.9
H1A—N1—H1B	120.0	C9—C8—H8A	108.9
C7—N2—C5	121.3 (3)	N2—C8—H8B	108.9
C7—N2—C8	118.4 (3)	C9—C8—H8B	108.9
C5—N2—C8	120.3 (3)	H8A—C8—H8B	107.7
O1—C1—N1	123.6 (4)	C10—C9—C14	120.4 (3)
O1—C1—C2	118.9 (4)	C10—C9—C8	121.8 (3)
N1—C1—C2	117.5 (3)	C14—C9—C8	117.7 (3)
C7—C2—C3	118.1 (3)	C9—C10—C11	119.7 (4)
C7—C2—C1	117.9 (3)	C9—C10—H10	120.2
C3—C2—C1	124.0 (3)	C11—C10—H10	120.2
C4—C3—C2	119.6 (3)	C12—C11—C10	119.2 (4)
C4—C3—H3	120.2	C12—C11—H11	120.4
C2—C3—H3	120.2	C10—C11—H11	120.4
C3—C4—C5	121.4 (3)	C13—C12—C11	120.0 (4)
C3—C4—H4	119.3	C13—C12—H12	120.0
C5—C4—H4	119.3	C11—C12—H12	120.0
N2—C5—C4	117.8 (3)	C12—C13—C14	122.3 (5)
N2—C5—C6	120.4 (3)	C12—C13—H13	118.8
C4—C5—C6	121.8 (3)	C14—C13—H13	118.8
C5—C6—H6A	109.5	C13—C14—C9	118.4 (4)
C5—C6—H6B	109.5	C13—C14—C15	120.3 (4)
H6A—C6—H6B	109.5	C9—C14—C15	121.3 (4)
C5—C6—H6C	109.5	C14—C15—H15A	109.5
H6A—C6—H6C	109.5	C14—C15—H15B	109.5
H6B—C6—H6C	109.5	H15A—C15—H15B	109.5
N2—C7—C2	121.7 (3)	C14—C15—H15C	109.5
N2—C7—H7	119.1	H15A—C15—H15C	109.5
C2—C7—H7	119.1	H15B—C15—H15C	109.5

O1—C1—C2—C7	−5.5 (5)	C1—C2—C7—N2	−179.2 (3)
N1—C1—C2—C7	175.8 (3)	C7—N2—C8—C9	−103.9 (3)
O1—C1—C2—C3	174.2 (4)	C5—N2—C8—C9	74.9 (4)
N1—C1—C2—C3	−4.5 (5)	N2—C8—C9—C10	17.3 (4)
C7—C2—C3—C4	−1.4 (5)	N2—C8—C9—C14	−164.3 (3)
C1—C2—C3—C4	178.9 (3)	C14—C9—C10—C11	1.2 (5)
C2—C3—C4—C5	−0.1 (5)	C8—C9—C10—C11	179.6 (3)
C7—N2—C5—C4	−2.2 (4)	C9—C10—C11—C12	−0.9 (6)
C8—N2—C5—C4	179.0 (3)	C10—C11—C12—C13	0.4 (7)
C7—N2—C5—C6	177.6 (3)	C11—C12—C13—C14	−0.2 (7)
C8—N2—C5—C6	−1.1 (4)	C12—C13—C14—C9	0.5 (6)
C3—C4—C5—N2	1.9 (5)	C12—C13—C14—C15	179.6 (4)
C3—C4—C5—C6	−177.9 (3)	C10—C9—C14—C13	−1.0 (5)
C5—N2—C7—C2	0.8 (5)	C8—C9—C14—C13	−179.5 (3)
C8—N2—C7—C2	179.5 (3)	C10—C9—C14—C15	179.9 (4)
C3—C2—C7—N2	1.1 (5)	C8—C9—C14—C15	1.4 (5)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···Br1	0.86	2.67	3.477 (3)	157
N1—H1B···O1ⁱ	0.86	2.35	3.207 (4)	173
C3—H3···O1ⁱ	0.93	2.22	3.149 (5)	174
C4—H4···Br1ⁱ	0.93	2.78	3.712 (4)	175
C6—H6C···Br1ⁱⁱ	0.96	2.73	3.638 (3)	157
C8—H8B···Br1ⁱⁱⁱ	0.97	2.87	3.782 (3)	156

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

Experimental details

Crystal data
Chemical formula	C₁₅H₁₇N₂O⁺·Br⁻
M_r	321.22
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	293
a, b, c (Å)	8.4880 (17), 10.502 (2), 33.450 (7)
β (°)	96.85 (3)
V (Å³)	2960.5 (10)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	2.77
Crystal size (mm)	0.50 × 0.20 × 0.10

Data collection
Diffractometer	Bruker SMART CCD diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 1997)
T_min, T_max	0.338, 0.769
No. of measured, independent and observed [I > 2σ(I)] reflections	8103, 2879, 1857
R_int	0.043
(sin θ/λ)_max (Å⁻¹)	0.617

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.042, 0.096, 1.00
No. of reflections	2879
No. of parameters	174
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.36, −0.31

Computer programs: SMART (Bruker, 1997), SAINT (Bruker, 1997), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 1999), SHELXTL (Brandenburg, 1999).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···Br1	0.86	2.67	3.477 (3)	156.8
N1—H1B···O1ⁱ	0.86	2.35	3.207 (4)	172.7
C3—H3···O1ⁱ	0.93	2.22	3.149 (5)	173.8
C4—H4···Br1ⁱ	0.93	2.78	3.712 (4)	175.1
C6—H6C···Br1ⁱⁱ	0.96	2.73	3.638 (3)	157.0
C8—H8B···Br1ⁱⁱⁱ	0.97	2.87	3.782 (3)	156.0

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

Acknowledgements

Financial support from the Converging Research Center Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2011 K000675), and Seoul National University of Science & Technology is gratefully acknowledged.

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