Crystal structure of piperidinium 4-nitro­phenolate

Sowmya, N.S.; Sampathkrishnan, S.; Sudhahar, S.; Chakkaravarthi, G.; Kumar, R.M.

doi:10.1107/S1600536814025306

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ISSN: 2056-9890

Volume 70| Part 12| December 2014| Pages 559-561

doi:10.1107/S1600536814025306

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Crystal structure of piperidinium 4-nitrophenolate

N. Swarna Sowmya,^a S. Sampathkrishnan,^a S. Sudhahar,^b G. Chakkaravarthi ^c ^* and R. Mohan Kumar ^b

^aDepartment of Applied Physics, Sri Venkateswara College of Engineering, Chennai 602 117, India, ^bDepartment of Physics, Presidency College, Chennai 600 005, India, and ^cDepartment of Physics, CPCL Polytechnic College, Chennai 600 068, India
^*Correspondence e-mail: chakkaravarthi_2005@yahoo.com,mohan66@hotmail.com

Edited by H. Stoeckli-Evans, University of Neuchâtel, Switzerland (Received 13 November 2014; accepted 18 November 2014; online 21 November 2014)

In the title molecular salt, C₅H₁₂N⁺·C₆H₄NO₃⁻, the piperidine ring adopts a chair conformation and the cation is protonated at the N atom. In the anion, the nitro group is twisted at an angle of 10.30 (11)° with respect to the attached benzene ring. In the crystal, N—H⋯O hydrogen bonds link adjacent anions and cations into infinite chains propagating along [100]. The chains are linked by C—H⋯π interactions, forming sheets lying parallel to (001).

Keywords: crystal structure; molecular salt; piperidinium; 4-nitrophenol; hydrogen bonding; C—H⋯π interactions.

CCDC reference: 1034875

1. Chemical context

Piperidine derivatives exhibit a broad-spectrum of biological activities such as anti-bacterial and anti-cancer (Parthiban et al., 2005 ). Nitro-aromatics are widely used either as materials or as intermediates in explosives, dyestuffs, pesticides and organic synthesis (Yan et al., 2006 ). We report herein on the synthesis and crystal structure of the title molecular salt, prepared by mixing piperidine with 4-nitrophenol.

2. Structural commentary

The molecular structure of the title compound is illustrated in Fig. 1. The geometric parameters are close to those reported for similar structures viz. 1-acetyl-c-3,t-3-dimethyl-r-2,c-6-diphenylpiperidin-4-one (Aravindhan et al., 2009 ), 4-nitrophenol-piperazine (2/1) (Nagapandiselvi et al., 2013 ) and 2-carboxylatopyridinium-4-nitrophenol (1/1) (Sankar et al., 2014 ). The piperidine ring (C8–C11/N2/C12) adopts a chair conformation with puckering parameters of Q = 0.5601 (17) Å, θ = 1.80 (17) and φ = 19 (10)°. The nitro group (N1/O2/O3) is twisted at an angle of 10.30 (11)° with respect to the attached benzene ring (C1–C6).

Figure 1
The molecular structure of the title salt, showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

3. Supramolecular features

In the crystal, adjacent cations and anions are linked by the N—H⋯O hydrogen bonds, which generate infinite chains along [100] (see Table 1 and Fig. 2). The chains are linked by C—H⋯π interactions, forming sheets lying parallel to the ab plane (Table 1).

Table 1
Hydrogen-bond geometry (Å, °)

Cg1 is the centroid of the C1–C6 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H2A⋯O1ⁱ	0.90	1.92	2.788 (2)	161
N2—H2B⋯O1ⁱⁱ	0.90	1.80	2.6985 (15)	175
C6—H6⋯Cg1ⁱⁱⁱ	0.93	2.75	3.428 (3)	130
Symmetry codes: (i) $[-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[-x+{\script{1\over 2}}, -y+1, z+{\script{1\over 2}}]$ ; (iii) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z]$ .

Figure 2
The crystal packing of the title salt, viewed along the b axis. Hydrogen bonds are shown as dashed lines (see Table 1

for details; H atoms not involved in hydrogen bonding have been omitted for clarity).

4. Synthesis and crystallization

Piperidine (0.85 g) and 4-nitrophenol (1.39) in an equimolar (1:1) ratio were added to methanol as solvent and the mixture was stirred for 2 h, giving a clear solution. The solution was filtered into a beaker and sealed with parafilm and kept at room temperature for one week. Colourless crystals suitable for X-ray diffraction analysis were obtained after one week.

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The N-bound and C-bound H atoms were positioned geometrically and refined using a riding model: N—H = 0.90, C—H = 0.93 and 0.97 Å for CH and CH₂ H atoms, respectively, and with U_iso(H) = 1.2U_eq(N,C).

Table 2
Experimental details

Crystal data
Chemical formula	C₅H₁₂N⁺·C₆H₄NO₃⁻
M_r	224.26
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	295
a, b, c (Å)	6.867 (5), 10.121 (4), 16.497 (6)
V (Å³)	1146.6 (10)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.10
Crystal size (mm)	0.26 × 0.22 × 0.20

Data collection
Diffractometer	Bruker Kappa APEXII CCD
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996 )
T_min, T_max	0.976, 0.981
No. of measured, independent and observed [I > 2σ(I)] reflections	6505, 2908, 2612
R_int	0.017
(sin θ/λ)_max (Å⁻¹)	0.673

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.035, 0.091, 1.04
No. of reflections	2908
No. of parameters	146
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.13, −0.16
Computer programs: APEX2 and SAINT (Bruker, 2004 ), SHELXS97 and SHELXL97 (Sheldrick, 2008 ) and PLATON (Spek, 2009 ).

Supporting information

CCDC reference: 1034875

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536814025306/su5022sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536814025306/su5022Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536814025306/su5022Isup3.cml

checkCIF report

Chemical context top

Piperidine derivatives exhibit a broad-spectrum of biological activities such as anti-bacterial and anti-cancer (Parthiban et al., 2005). Nitro-aromatics are widely used either as materials or as intermediates in explosives, dyestuffs, pesticides and organic synthesis (Yan et al., 2006). We report herein on the synthesis and crystal structure of the title molecular salt, prepared by mixing piperidine with 4-nitrophenol.

Structural commentary top

\ The molecular structure of the title compound is illustrated in Fig. 1. The geometric parameters are close to those reported for similar structures viz. 1-acetyl-c-3,t-3-dimethyl-r-2,c-6-\ diphenylpiperidin-4-one (Aravindhan et al., 2009), 4-nitrophenol-piperazine (2/1) (Nagapandiselvi et al., 2013) and 2-carboxylatopyridinium-4-nitrophenol (1/1) (Sankar et al., 2014). The piperidine ring (C8–C11/N2/C12) adopts a chair conformation with puckering parameters of Q = 0.5601 (17) Å, θ = 1.80 (17) and ϕ = 19 (10)°. The nitro group (N1/O2/O3) is twisted at an angle of 10.30 (11)° with respect to the attached benzene ring (C1–C6).

Supramolecular features top

In the crystal, adjacent cations and anions are linked by the N—H···O hydrogen bonds, which generate infinite chains along [100] (see Table 1 and Fig. 2). The chains are linked by C—H···π interactions, forming sheets lying parallel to the ab plane (Table 1).

Synthesis and crystallization top

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 2. The N-bound and C-bound H-atoms were positioned geometrically and refined using a riding model: N—H = 0.90, C—H = 0.93 and 0.97 Å for CH and CH₂ H atoms, respectively, and with U_iso(H) = 1.2U_eq(N,C).

Related literature top

For related literature, see: Aravindhan et al. (2009); Nagapandiselvi et al. (2013); Parthiban et al. (2005); Sankar et al. (2014); Yan et al. (2006).

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: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top

The molecular structure of the title salt, showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

The crystal packing of the title salt, viewed along the b axis. Hydrogen bonds are shown as dashed lines (see Table 1 for details; H atoms not involved in hydrogen bonding have been omitted for clarity).

Piperidinium 4-nitrophenolate top

Crystal data top

C₅H₁₂N⁺·C₆H₄NO₃⁻	F(000) = 480
M_r = 224.26	D_x = 1.299 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 658 reflections
a = 6.867 (5) Å	θ = 2.4–28.6°
b = 10.121 (4) Å	µ = 0.10 mm⁻¹
c = 16.497 (6) Å	T = 295 K
V = 1146.6 (10) Å³	Block, colourless
Z = 4	0.26 × 0.22 × 0.20 mm

Data collection top

Bruker Kappa APEXII CCD diffractometer	2908 independent reflections
Radiation source: fine-focus sealed tube	2612 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.017
ω and ϕ scan	θ_max = 28.6°, θ_min = 2.4°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −6→9
T_min = 0.976, T_max = 0.981	k = −11→13
6505 measured reflections	l = −22→10

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.035	H-atom parameters constrained
wR(F²) = 0.091	w = 1/[σ²(F_o²) + (0.0452P)² + 0.1138P] where P = (F_o² + 2F_c²)/3
S = 1.04	(Δ/σ)_max < 0.001
2908 reflections	Δρ_max = 0.13 e Å⁻³
146 parameters	Δρ_min = −0.16 e Å⁻³
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.119 (6)

Crystal data top

C₅H₁₂N⁺·C₆H₄NO₃⁻	V = 1146.6 (10) Å³
M_r = 224.26	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 6.867 (5) Å	µ = 0.10 mm⁻¹
b = 10.121 (4) Å	T = 295 K
c = 16.497 (6) Å	0.26 × 0.22 × 0.20 mm

Data collection top

Bruker Kappa APEXII CCD diffractometer	2908 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	2612 reflections with I > 2σ(I)
T_min = 0.976, T_max = 0.981	R_int = 0.017
6505 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.035	0 restraints
wR(F²) = 0.091	H-atom parameters constrained
S = 1.04	Δρ_max = 0.13 e Å⁻³
2908 reflections	Δρ_min = −0.16 e Å⁻³
146 parameters

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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
C1	0.08265 (18)	0.22326 (12)	0.09031 (7)	0.0380 (3)
C2	0.0102 (2)	0.31257 (12)	0.14583 (7)	0.0404 (3)
H2	−0.0220	0.2848	0.1979	0.049*
C3	−0.0144 (2)	0.44223 (12)	0.12419 (7)	0.0403 (3)
H3	−0.0638	0.5014	0.1621	0.048*
C4	0.03355 (18)	0.48874 (11)	0.04556 (7)	0.0373 (3)
C5	0.1115 (2)	0.39408 (13)	−0.00839 (8)	0.0474 (3)
H5	0.1491	0.4211	−0.0600	0.057*
C6	0.1336 (2)	0.26352 (13)	0.01258 (8)	0.0465 (3)
H6	0.1820	0.2029	−0.0247	0.056*
C8	0.6387 (2)	0.21154 (17)	0.33603 (10)	0.0570 (4)
H8A	0.7057	0.2749	0.3702	0.068*
H8B	0.7348	0.1503	0.3149	0.068*
C9	0.5422 (3)	0.28329 (19)	0.26652 (10)	0.0626 (4)
H9A	0.6386	0.3342	0.2371	0.075*
H9B	0.4854	0.2197	0.2294	0.075*
C10	0.3854 (3)	0.37423 (16)	0.29817 (10)	0.0545 (4)
H10A	0.4442	0.4428	0.3312	0.065*
H10B	0.3199	0.4164	0.2530	0.065*
C11	0.2391 (2)	0.29893 (14)	0.34801 (9)	0.0480 (3)
H11A	0.1444	0.3601	0.3703	0.058*
H11B	0.1703	0.2370	0.3135	0.058*
C12	0.4907 (2)	0.13639 (13)	0.38617 (9)	0.0488 (3)
H12A	0.4341	0.0663	0.3537	0.059*
H12B	0.5549	0.0963	0.4324	0.059*
N1	0.10251 (18)	0.08685 (11)	0.11247 (8)	0.0487 (3)
N2	0.33415 (17)	0.22610 (10)	0.41493 (6)	0.0405 (3)
H2A	0.2438	0.1784	0.4415	0.049*
H2B	0.3851	0.2845	0.4502	0.049*
O1	0.00554 (15)	0.61052 (8)	0.02564 (6)	0.0458 (2)
O2	0.1387 (2)	0.00445 (11)	0.06015 (8)	0.0730 (4)
O3	0.0795 (2)	0.05548 (12)	0.18390 (7)	0.0771 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0355 (6)	0.0359 (5)	0.0427 (6)	0.0007 (5)	−0.0004 (5)	0.0057 (5)
C2	0.0423 (6)	0.0453 (6)	0.0337 (5)	−0.0013 (6)	−0.0019 (5)	0.0049 (5)
C3	0.0434 (7)	0.0414 (6)	0.0361 (6)	0.0028 (5)	0.0005 (5)	−0.0033 (5)
C4	0.0324 (6)	0.0364 (6)	0.0431 (6)	−0.0006 (5)	0.0018 (5)	0.0030 (5)
C5	0.0545 (8)	0.0445 (7)	0.0432 (7)	0.0065 (6)	0.0179 (6)	0.0089 (5)
C6	0.0517 (8)	0.0412 (6)	0.0466 (7)	0.0096 (6)	0.0155 (6)	0.0019 (5)
C8	0.0425 (7)	0.0574 (8)	0.0710 (10)	0.0055 (7)	0.0071 (7)	−0.0019 (7)
C9	0.0635 (10)	0.0723 (10)	0.0520 (8)	−0.0044 (9)	0.0162 (8)	0.0073 (8)
C10	0.0568 (9)	0.0489 (8)	0.0577 (8)	−0.0017 (7)	−0.0023 (7)	0.0146 (7)
C11	0.0388 (7)	0.0459 (7)	0.0594 (8)	0.0031 (6)	−0.0029 (6)	0.0053 (6)
C12	0.0495 (8)	0.0408 (6)	0.0559 (7)	0.0053 (6)	−0.0015 (7)	0.0016 (6)
N1	0.0516 (7)	0.0396 (6)	0.0547 (7)	−0.0015 (5)	0.0013 (6)	0.0090 (5)
N2	0.0433 (6)	0.0377 (5)	0.0406 (5)	−0.0053 (4)	0.0014 (4)	−0.0029 (4)
O1	0.0494 (5)	0.0346 (4)	0.0535 (5)	0.0023 (4)	0.0079 (5)	0.0061 (4)
O2	0.1004 (10)	0.0403 (5)	0.0782 (8)	0.0118 (6)	0.0251 (7)	0.0021 (5)
O3	0.1256 (13)	0.0504 (6)	0.0554 (6)	−0.0028 (7)	−0.0012 (7)	0.0188 (5)

Geometric parameters (Å, º) top

C1—C2	1.3798 (18)	C9—C10	1.510 (2)
C1—C6	1.3902 (18)	C9—H9A	0.9700
C1—N1	1.4347 (17)	C9—H9B	0.9700
C2—C3	1.3703 (18)	C10—C11	1.506 (2)
C2—H2	0.9300	C10—H10A	0.9700
C3—C4	1.4187 (17)	C10—H10B	0.9700
C3—H3	0.9300	C11—N2	1.4793 (18)
C4—O1	1.2900 (15)	C11—H11A	0.9700
C4—C5	1.4129 (18)	C11—H11B	0.9700
C5—C6	1.374 (2)	C12—N2	1.4848 (19)
C5—H5	0.9300	C12—H12A	0.9700
C6—H6	0.9300	C12—H12B	0.9700
C8—C9	1.511 (2)	N1—O2	1.2257 (17)
C8—C12	1.516 (2)	N1—O3	1.2306 (16)
C8—H8A	0.9700	N2—H2A	0.9000
C8—H8B	0.9700	N2—H2B	0.9000

C2—C1—C6	120.73 (12)	H9A—C9—H9B	108.2
C2—C1—N1	119.70 (11)	C11—C10—C9	110.87 (13)
C6—C1—N1	119.55 (12)	C11—C10—H10A	109.5
C3—C2—C1	119.92 (11)	C9—C10—H10A	109.5
C3—C2—H2	120.0	C11—C10—H10B	109.5
C1—C2—H2	120.0	C9—C10—H10B	109.5
C2—C3—C4	121.83 (12)	H10A—C10—H10B	108.1
C2—C3—H3	119.1	N2—C11—C10	111.42 (13)
C4—C3—H3	119.1	N2—C11—H11A	109.3
O1—C4—C5	122.95 (11)	C10—C11—H11A	109.3
O1—C4—C3	121.02 (11)	N2—C11—H11B	109.3
C5—C4—C3	116.03 (11)	C10—C11—H11B	109.3
C6—C5—C4	122.36 (12)	H11A—C11—H11B	108.0
C6—C5—H5	118.8	N2—C12—C8	110.68 (12)
C4—C5—H5	118.8	N2—C12—H12A	109.5
C5—C6—C1	119.09 (12)	C8—C12—H12A	109.5
C5—C6—H6	120.5	N2—C12—H12B	109.5
C1—C6—H6	120.5	C8—C12—H12B	109.5
C9—C8—C12	111.16 (14)	H12A—C12—H12B	108.1
C9—C8—H8A	109.4	O2—N1—O3	121.66 (13)
C12—C8—H8A	109.4	O2—N1—C1	119.64 (12)
C9—C8—H8B	109.4	O3—N1—C1	118.70 (12)
C12—C8—H8B	109.4	C11—N2—C12	112.69 (11)
H8A—C8—H8B	108.0	C11—N2—H2A	109.1
C10—C9—C8	110.09 (13)	C12—N2—H2A	109.1
C10—C9—H9A	109.6	C11—N2—H2B	109.1
C8—C9—H9A	109.6	C12—N2—H2B	109.1
C10—C9—H9B	109.6	H2A—N2—H2B	107.8
C8—C9—H9B	109.6

C6—C1—C2—C3	0.8 (2)	C12—C8—C9—C10	56.35 (18)
N1—C1—C2—C3	−178.12 (12)	C8—C9—C10—C11	−56.27 (19)
C1—C2—C3—C4	−0.2 (2)	C9—C10—C11—N2	55.67 (18)
C2—C3—C4—O1	178.45 (13)	C9—C8—C12—N2	−55.31 (17)
C2—C3—C4—C5	−1.21 (19)	C2—C1—N1—O2	169.09 (14)
O1—C4—C5—C6	−177.44 (14)	C6—C1—N1—O2	−9.8 (2)
C3—C4—C5—C6	2.2 (2)	C2—C1—N1—O3	−9.8 (2)
C4—C5—C6—C1	−1.8 (2)	C6—C1—N1—O3	171.33 (14)
C2—C1—C6—C5	0.2 (2)	C10—C11—N2—C12	−55.30 (16)
N1—C1—C6—C5	179.09 (14)	C8—C12—N2—C11	54.81 (16)

Hydrogen-bond geometry (Å, º) top

Cg1 is the centroid of the C1–C6 ring.

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···O1ⁱ	0.90	1.92	2.788 (2)	161
N2—H2B···O1ⁱⁱ	0.90	1.80	2.6985 (15)	175
C6—H6···Cg1ⁱⁱⁱ	0.93	2.75	3.428 (3)	130

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

Hydrogen-bond geometry (Å, º) top

Cg1 is the centroid of the C1–C6 ring.

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···O1ⁱ	0.90	1.92	2.788 (2)	161
N2—H2B···O1ⁱⁱ	0.90	1.80	2.6985 (15)	175
C6—H6···Cg1ⁱⁱⁱ	0.93	2.75	3.428 (3)	130

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

Experimental details

Crystal data
Chemical formula	C₅H₁₂N⁺·C₆H₄NO₃⁻
M_r	224.26
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	295
a, b, c (Å)	6.867 (5), 10.121 (4), 16.497 (6)
V (Å³)	1146.6 (10)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.10
Crystal size (mm)	0.26 × 0.22 × 0.20

Data collection
Diffractometer	Bruker Kappa APEXII CCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996)
T_min, T_max	0.976, 0.981
No. of measured, independent and observed [I > 2σ(I)] reflections	6505, 2908, 2612
R_int	0.017
(sin θ/λ)_max (Å⁻¹)	0.673

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.035, 0.091, 1.04
No. of reflections	2908
No. of parameters	146
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.13, −0.16

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Acknowledgements

The authors wish to acknowledge the SAIF, IIT, Madras, for the data collection.

References

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Volume 70| Part 12| December 2014| Pages 559-561

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