N′-[(1E)-2,5-Di­meth­oxy­benzyl­idene]pyridine-2-carbohydrazide

R.Albayati, M.; Mague, J.T.; Akkurt, M.; Mohamed, S.K.; Elgarhy, S.M.I.

doi:10.1107/S2414314618001281

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 3| Part 1| January 2018| x180128

https://doi.org/10.1107/S2414314618001281

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N′-[(1E)-2,5-Dimethoxybenzylidene]pyridine-2-carbohydrazide

Mustafa R.Albayati,^a ^* Joel T. Mague,^b Mehmet Akkurt,^c Shaaban K. Mohamed ^d,^e and Sahar M. I. Elgarhy ^f

^aKirkuk University, College of Education, Department of Chemistry, Kirkuk, Iraq, ^bDepartment of Chemistry, Tulane University, New Orleans, LA 70118, USA, ^cDepartment of Physics, Faculty of Sciences, Erciyes University, 38039 Kayseri, Turkey, ^dChemistry and Environmental Division, Manchester Metropolitan University, Manchester M1 5GD, England, ^eChemistry Department, Faculty of Science, Minia University, 61519 El-Minia, Egypt, and ^fDepartment of Bio-Chemistry, Faculty of Science, University of Beni Suef, Egypt
^*Correspondence e-mail: shaabankamel@yahoo.com

Edited by E. R. T. Tiekink, Sunway University, Malaysia (Received 19 January 2018; accepted 20 January 2018; online 31 January 2018)

The molecule of the title compound, C₁₅H₁₅N₃O₃, is twisted, with the dihedral angle between the pyridyl and benzene rings being 58.34 (6)°. In the crystal, amide-N—H⋯O(amide) and imine-C—H⋯O(amide) hydrogen bonds lead to zigzag (glide symmetry) chains extending along the c axis which are joined into layers parallel to the [100] direction by offset π–π stacking interactions between inversion-related benzene rings [centroid–centroid distance = 3.7468 (7) Å] and by C—H⋯π(pyridyl) interactions. Pyridyl rings protrude from the surfaces of the layers and partially intercalate with those of adjacent layers.

Keywords: crystal structure; pyridine; carbohydrazide; hydrogen bond; π–π stacking; picolinic acid.

CCDC reference: 1818291

Structure description

Picolinic acid (PA) is a naturally occurring product of the degradation of tryptophan which is known to up-regulate host immune responses, especially macrophage cell functions (Shanshan et al., 2006 ). The antimicrobial activity of PA against several strains of microorganisms has been reported (Maria et al., 2008 ). In addition, PA and its derivatives have other biological activities, such as their use as dietary supplements (Komorowski et al., 2008 ) and anti-oxidants (Kırkıl et al., 2008 ), and they are metabolites of fungi (Dowd, 1999 ). Picolinic acid hydrazones have been found to possess significant antifungal activity against a wide range of soil borne pathogens (Aditi & Supradi, 2014 ). As a continuation of our efforts on the synthesis of biologically active compounds containing hydrazones, we report herein the crystal structure of N′-[(1E)-2,5-dimethoxybenzylidene]pyridine-2-carbohydrazide.

In the title compound (Fig. 1), the dihedral angle between the pyridyl and benzene rings is 58.34 (6)°. In the crystal, N2—H2⋯O3 hydrogen bonds, assisted by C9—H9⋯O3 hydrogen bonds, form chains extending along the c axis (Table 1 and Fig. 2). The chains are connected into layers parallel to [100] by offset π–π stacking interactions between inversion-related benzene rings [centroid–centroid = 3.7468 (7) Å; interplanar spacing = 3.3311 (5) Å] and by C4—H4⋯Cg1 interactions (Cg1 is the centroid of the N3/C11–C15 pyridine ring.; Table 1 and Fig. 2). The pyridine rings protrude from the surfaces of the layers and partially intercalate with those of adjacent layers.

Table 1
Hydrogen-bond geometry (Å, °)

Cg1 is the centroid of the N3/C11–C15 pyridine ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H2⋯O3ⁱ	0.879 (18)	2.103 (18)	2.9403 (13)	159.0 (15)
C9—H9⋯O3ⁱ	0.967 (16)	2.525 (15)	3.3202 (14)	139.5 (12)
C4—H4⋯Cg1ⁱⁱ	0.979 (15)	2.839 (16)	3.7240 (13)	150.6 (12)
Symmetry codes: (i) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (ii) $[-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Figure 1
The title molecule of the title compound, with the atom-labelling scheme and 50% probability displacement ellipsoids.

Figure 2
A view in projection along the a axis of the unit-cell contents, showing their association through offset π–π stacking (orange dashed lines) and C—H⋯π(ring) interactions (green dashed lines). The N—N⋯O and C—H⋯O hydrogen bonds are shown, respectively, as blue and black dashed lines.

Synthesis and crystallization

The title compound was synthesized according to our previously reported procedure (Mohamed et al., 2013 ).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	C₁₅H₁₅N₃O₃
M_r	285.30
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	150
a, b, c (Å)	10.7311 (3), 16.4986 (4), 8.2033 (2)
β (°)	110.458 (1)
V (Å³)	1360.78 (6)
Z	4
Radiation type	Cu Kα
μ (mm⁻¹)	0.82
Crystal size (mm)	0.22 × 0.16 × 0.04

Data collection
Diffractometer	Bruker D8 VENTURE PHOTON 100 CMOS
Absorption correction	Multi-scan (SADABS; Bruker, 2016 )
T_min, T_max	0.88, 0.97
No. of measured, independent and observed [I > 2σ(I)] reflections	10229, 2647, 2375
R_int	0.028
(sin θ/λ)_max (Å⁻¹)	0.618

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.035, 0.090, 1.06
No. of reflections	2647
No. of parameters	250
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.14, −0.25
Computer programs: APEX3 and SAINT (Bruker, 2016), SHELXT (Sheldrick, 2015a ), SHELXL2016 (Sheldrick, 2015b ), DIAMOND (Brandenburg & Putz, 2012 ) and SHELXTL (Sheldrick, 2008 ).

Structural data

CCDC reference: 1818291

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2414314618001281/tk4047sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314618001281/tk4047Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314618001281/tk4047Isup3.cml

checkCIF report

Computing details top

Data collection: APEX3 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg & Putz, 2012); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

N'-[(1E)-2,5-Dimethoxybenzylidene]pyridine-2-carbohydrazide top

Crystal data top

C₁₅H₁₅N₃O₃	F(000) = 600
M_r = 285.30	D_x = 1.393 Mg m⁻³
Monoclinic, P2₁/c	Cu Kα radiation, λ = 1.54178 Å
a = 10.7311 (3) Å	Cell parameters from 8226 reflections
b = 16.4986 (4) Å	θ = 4.4–72.4°
c = 8.2033 (2) Å	µ = 0.82 mm⁻¹
β = 110.458 (1)°	T = 150 K
V = 1360.78 (6) Å³	Plate, colourless
Z = 4	0.22 × 0.16 × 0.04 mm

Data collection top

Bruker D8 VENTURE PHOTON 100 CMOS diffractometer	2647 independent reflections
Radiation source: INCOATEC IµS micro-focus source	2375 reflections with I > 2σ(I)
Mirror monochromator	R_int = 0.028
Detector resolution: 10.4167 pixels mm^-1	θ_max = 72.4°, θ_min = 4.4°
ω scans	h = −12→13
Absorption correction: multi-scan (SADABS; Bruker, 2016)	k = −20→19
T_min = 0.88, T_max = 0.97	l = −9→10
10229 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)] = 0.035	Hydrogen site location: difference Fourier map
wR(F²) = 0.090	All H-atom parameters refined
S = 1.06	w = 1/[σ²(F_o²) + (0.0467P)² + 0.3581P] where P = (F_o² + 2F_c²)/3
2647 reflections	(Δ/σ)_max < 0.001
250 parameters	Δρ_max = 0.14 e Å⁻³
0 restraints	Δρ_min = −0.25 e Å⁻³

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
O1	0.58069 (8)	0.51301 (5)	0.21382 (11)	0.0264 (2)
O2	0.21048 (9)	0.35193 (5)	0.42335 (12)	0.0296 (2)
O3	0.81174 (8)	0.15852 (5)	0.53933 (11)	0.0249 (2)
H3	0.3676 (14)	0.5724 (9)	0.2692 (19)	0.027 (4)*
N1	0.65193 (9)	0.27831 (6)	0.34398 (13)	0.0216 (2)
N2	0.75529 (9)	0.24318 (6)	0.30438 (13)	0.0208 (2)
H2	0.7731 (16)	0.2602 (10)	0.213 (2)	0.038 (4)*
N3	0.90627 (10)	0.15664 (6)	0.16736 (13)	0.0223 (2)
C1	0.50657 (11)	0.39155 (7)	0.30184 (14)	0.0194 (2)
C2	0.48793 (11)	0.47459 (7)	0.26627 (14)	0.0204 (2)
C3	0.37985 (11)	0.51426 (7)	0.28827 (15)	0.0228 (2)
C4	0.29014 (11)	0.47126 (7)	0.34139 (15)	0.0234 (2)
H4	0.2133 (15)	0.4986 (9)	0.355 (2)	0.031 (4)*
C5	0.30648 (11)	0.38848 (7)	0.37352 (15)	0.0217 (2)
C6	0.41474 (11)	0.34879 (7)	0.35589 (15)	0.0206 (2)
H6	0.4310 (14)	0.2915 (9)	0.3807 (18)	0.025 (3)*
C7	0.55518 (14)	0.59604 (7)	0.16353 (17)	0.0284 (3)
H7A	0.5597 (16)	0.6316 (10)	0.263 (2)	0.037 (4)*
H7B	0.6227 (16)	0.6116 (10)	0.115 (2)	0.038 (4)*
H7C	0.4644 (17)	0.6035 (10)	0.077 (2)	0.041 (4)*
C8	0.21909 (15)	0.26674 (8)	0.4476 (2)	0.0333 (3)
H8A	0.3058 (18)	0.2514 (10)	0.537 (2)	0.039 (4)*
H8B	0.1455 (19)	0.2525 (11)	0.486 (2)	0.051 (5)*
H8C	0.2072 (17)	0.2381 (10)	0.333 (2)	0.042 (4)*
C9	0.62063 (11)	0.34959 (7)	0.28163 (14)	0.0205 (2)
H9	0.6707 (15)	0.3764 (10)	0.220 (2)	0.031 (4)*
C10	0.82496 (11)	0.18240 (6)	0.40395 (14)	0.0190 (2)
C11	0.92327 (11)	0.14317 (6)	0.33502 (15)	0.0191 (2)
C12	1.02277 (12)	0.09433 (7)	0.44403 (16)	0.0238 (3)
H12	1.0303 (15)	0.0879 (9)	0.566 (2)	0.029 (4)*
C13	1.10766 (12)	0.05531 (7)	0.37400 (18)	0.0287 (3)
H13	1.1779 (17)	0.0204 (11)	0.449 (2)	0.040 (4)*
C14	1.09010 (12)	0.06731 (7)	0.20079 (17)	0.0277 (3)
H14	1.1471 (15)	0.0400 (9)	0.1478 (19)	0.032 (4)*
C15	0.98899 (12)	0.11861 (8)	0.10286 (16)	0.0256 (3)
H15	0.9737 (15)	0.1272 (9)	−0.021 (2)	0.031 (4)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0258 (4)	0.0227 (4)	0.0338 (5)	0.0000 (3)	0.0143 (4)	0.0049 (3)
O2	0.0264 (4)	0.0270 (5)	0.0426 (5)	−0.0011 (3)	0.0209 (4)	−0.0004 (4)
O3	0.0311 (4)	0.0231 (4)	0.0263 (4)	0.0027 (3)	0.0173 (4)	0.0026 (3)
N1	0.0202 (5)	0.0232 (5)	0.0247 (5)	0.0033 (4)	0.0118 (4)	−0.0015 (4)
N2	0.0209 (5)	0.0222 (5)	0.0235 (5)	0.0042 (4)	0.0128 (4)	0.0015 (4)
N3	0.0217 (5)	0.0231 (5)	0.0243 (5)	0.0010 (4)	0.0107 (4)	−0.0001 (4)
C1	0.0191 (5)	0.0215 (5)	0.0172 (5)	0.0013 (4)	0.0058 (4)	−0.0016 (4)
C2	0.0200 (5)	0.0226 (6)	0.0181 (5)	−0.0008 (4)	0.0059 (4)	0.0002 (4)
C3	0.0237 (6)	0.0208 (6)	0.0222 (6)	0.0036 (4)	0.0061 (5)	0.0005 (4)
C4	0.0210 (5)	0.0253 (6)	0.0241 (6)	0.0050 (4)	0.0081 (5)	−0.0010 (4)
C5	0.0200 (5)	0.0252 (6)	0.0212 (6)	−0.0017 (4)	0.0089 (5)	−0.0020 (4)
C6	0.0219 (5)	0.0199 (6)	0.0205 (6)	0.0013 (4)	0.0079 (5)	−0.0015 (4)
C7	0.0331 (7)	0.0223 (6)	0.0299 (7)	−0.0013 (5)	0.0109 (6)	0.0055 (5)
C8	0.0352 (7)	0.0276 (7)	0.0435 (8)	−0.0068 (5)	0.0219 (7)	−0.0019 (5)
C9	0.0197 (5)	0.0239 (6)	0.0187 (5)	0.0007 (4)	0.0077 (4)	0.0001 (4)
C10	0.0191 (5)	0.0167 (5)	0.0225 (5)	−0.0023 (4)	0.0089 (4)	−0.0020 (4)
C11	0.0184 (5)	0.0170 (5)	0.0240 (6)	−0.0022 (4)	0.0101 (4)	−0.0011 (4)
C12	0.0239 (6)	0.0219 (6)	0.0272 (6)	0.0009 (4)	0.0110 (5)	0.0039 (4)
C13	0.0242 (6)	0.0261 (6)	0.0380 (7)	0.0063 (5)	0.0137 (5)	0.0071 (5)
C14	0.0263 (6)	0.0248 (6)	0.0383 (7)	0.0028 (5)	0.0191 (5)	−0.0005 (5)
C15	0.0264 (6)	0.0276 (6)	0.0276 (6)	0.0005 (5)	0.0154 (5)	−0.0017 (5)

Geometric parameters (Å, º) top

O1—C2	1.3702 (13)	C5—C6	1.3845 (16)
O1—C7	1.4293 (14)	C6—H6	0.969 (15)
O2—C5	1.3734 (14)	C7—H7A	0.994 (17)
O2—C8	1.4180 (16)	C7—H7B	0.977 (17)
O3—C10	1.2324 (14)	C7—H7C	0.993 (17)
N1—C9	1.2795 (15)	C8—H8A	0.997 (18)
N1—N2	1.3869 (13)	C8—H8B	0.975 (19)
N2—C10	1.3435 (15)	C8—H8C	1.019 (18)
N2—H2	0.879 (18)	C9—H9	0.967 (16)
N3—C15	1.3380 (15)	C10—C11	1.5062 (14)
N3—C11	1.3412 (15)	C11—C12	1.3862 (16)
C1—C2	1.4005 (16)	C12—C13	1.3929 (17)
C1—C6	1.4039 (15)	C12—H12	0.984 (15)
C1—C9	1.4652 (15)	C13—C14	1.3807 (19)
C2—C3	1.3973 (16)	C13—H13	0.977 (17)
C3—C4	1.3831 (17)	C14—C15	1.3891 (18)
C3—H3	0.973 (15)	C14—H14	0.976 (16)
C4—C5	1.3905 (17)	C15—H15	0.983 (16)
C4—H4	0.979 (15)

C2—O1—C7	116.56 (9)	H7A—C7—H7C	105.6 (14)
C5—O2—C8	117.26 (9)	H7B—C7—H7C	111.0 (13)
C9—N1—N2	114.22 (9)	O2—C8—H8A	110.7 (9)
C10—N2—N1	119.36 (9)	O2—C8—H8B	105.3 (11)
C10—N2—H2	121.0 (11)	H8A—C8—H8B	110.7 (14)
N1—N2—H2	119.6 (11)	O2—C8—H8C	110.4 (9)
C15—N3—C11	117.17 (10)	H8A—C8—H8C	110.4 (13)
C2—C1—C6	119.51 (10)	H8B—C8—H8C	109.3 (14)
C2—C1—C9	120.18 (10)	N1—C9—C1	120.13 (10)
C6—C1—C9	120.31 (10)	N1—C9—H9	121.0 (9)
O1—C2—C3	123.43 (10)	C1—C9—H9	118.9 (9)
O1—C2—C1	116.83 (10)	O3—C10—N2	124.86 (10)
C3—C2—C1	119.73 (10)	O3—C10—C11	121.15 (10)
C4—C3—C2	120.07 (11)	N2—C10—C11	113.98 (9)
C4—C3—H3	119.1 (9)	N3—C11—C12	123.77 (10)
C2—C3—H3	120.9 (9)	N3—C11—C10	116.85 (10)
C3—C4—C5	120.52 (10)	C12—C11—C10	119.36 (10)
C3—C4—H4	120.3 (9)	C11—C12—C13	118.03 (11)
C5—C4—H4	119.1 (9)	C11—C12—H12	119.4 (9)
O2—C5—C6	124.57 (11)	C13—C12—H12	122.6 (9)
O2—C5—C4	115.44 (10)	C14—C13—C12	118.98 (11)
C6—C5—C4	119.98 (10)	C14—C13—H13	122.0 (10)
C5—C6—C1	120.17 (10)	C12—C13—H13	119.1 (10)
C5—C6—H6	122.3 (8)	C13—C14—C15	118.72 (11)
C1—C6—H6	117.5 (8)	C13—C14—H14	120.7 (9)
O1—C7—H7A	112.3 (9)	C15—C14—H14	120.5 (9)
O1—C7—H7B	106.0 (10)	N3—C15—C14	123.31 (11)
H7A—C7—H7B	110.6 (14)	N3—C15—H15	116.6 (9)
O1—C7—H7C	111.5 (10)	C14—C15—H15	120.0 (9)

C9—N1—N2—C10	158.68 (11)	N2—N1—C9—C1	175.33 (10)
C7—O1—C2—C3	−6.40 (16)	C2—C1—C9—N1	166.98 (11)
C7—O1—C2—C1	174.85 (10)	C6—C1—C9—N1	−13.43 (17)
C6—C1—C2—O1	−179.91 (10)	N1—N2—C10—O3	−6.16 (17)
C9—C1—C2—O1	−0.31 (15)	N1—N2—C10—C11	173.16 (9)
C6—C1—C2—C3	1.28 (16)	C15—N3—C11—C12	1.74 (16)
C9—C1—C2—C3	−179.12 (10)	C15—N3—C11—C10	−176.62 (10)
O1—C2—C3—C4	179.90 (10)	O3—C10—C11—N3	162.00 (10)
C1—C2—C3—C4	−1.38 (17)	N2—C10—C11—N3	−17.34 (14)
C2—C3—C4—C5	0.06 (17)	O3—C10—C11—C12	−16.44 (16)
C8—O2—C5—C6	−4.14 (17)	N2—C10—C11—C12	164.22 (10)
C8—O2—C5—C4	176.43 (11)	N3—C11—C12—C13	−1.80 (17)
C3—C4—C5—O2	−179.18 (10)	C10—C11—C12—C13	176.52 (10)
C3—C4—C5—C6	1.35 (17)	C11—C12—C13—C14	0.54 (18)
O2—C5—C6—C1	179.15 (10)	C12—C13—C14—C15	0.63 (18)
C4—C5—C6—C1	−1.43 (17)	C11—N3—C15—C14	−0.44 (17)
C2—C1—C6—C5	0.12 (16)	C13—C14—C15—N3	−0.71 (19)
C9—C1—C6—C5	−179.48 (10)

Hydrogen-bond geometry (Å, º) top

Cg1 is the centroid of the N3/C11–C15 pyridine ring.

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···O3ⁱ	0.879 (18)	2.103 (18)	2.9403 (13)	159.0 (15)
C9—H9···O3ⁱ	0.967 (16)	2.525 (15)	3.3202 (14)	139.5 (12)
C4—H4···Cg1ⁱⁱ	0.979 (15)	2.839 (16)	3.7240 (13)	150.6 (12)

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

Acknowledgements

The support of NSF–MRI for the purchase of the diffractometer and of Tulane University for support of the Tulane Crystallography Laboratory are gratefully acknowledged.

Funding information

Funding for this research was provided by: NSF–MRI (grant No. 1228232).

References

Aditi, K. & Supradi, S. (2014). Plant Path. J, 13, 152–159. Google Scholar
Brandenburg, K. & Putz, H. (2012). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Bruker (2016). APEX3, SAINT, SADABS, and SHELXTL. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Dowd, P. F. (1999). Nat. Toxins, 7, 337–341. CrossRef PubMed CAS Google Scholar
Kırkıl, G., Hamdi Muz, M., Seçkin, D., Şahin, K., Küçük, O. & Ömer, (2008). Respir. Med. 102, 840–844. Google Scholar
Komorowski, J. R., Greenberg, D. & Juturu, V. (2008). Toxicol. In Vitro, 22, 819–826. CrossRef PubMed CAS Google Scholar
Maria, H. B., Sylwia, K. C., Renata, M., Jerzy, P., Renata, S. & Wtodzimierz, L. (2008). Pol. J. Food Nutr. Sci. 58, 415–418. Google Scholar
Mohamed, S. K., Albayati, M. R., Sabry HH Younes, S. H. H. & Abed-Alkareem, M. G. (2013). Chem. Sci. J., Article No. CSJ-97. Google Scholar
Shanshan, C., Katsumasa, S., Toshiaki, S., Seiko, Y., Miho, H., Chiaki, S. & Haruaki, T. (2006). J. Antimicrob. Chemother. 57, 85–93. PubMed Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar