Heptane-1,7-diaminium sulfate mono­hydrate

Arderne, C.

doi:10.1107/S1600536811030030

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 67| Part 8| August 2011| Page o2183

doi:10.1107/S1600536811030030

Open

access

Heptane-1,7-diaminium sulfate monohydrate

Charmaine Arderne ^a ^*

^aDepartment of Chemistry, University of Johannesburg, PO Box 524, Auckland Park, Johannesburg 2006, South Africa
^*Correspondence e-mail: carderne@uj.ac.za

(Received 14 July 2011; accepted 25 July 2011; online 30 July 2011)

The crystal structure of the title compound, C₇H₂₀N₂²⁺·SO₄²⁻·H₂O, is presented, with particular focus on the packing arrangement in the crystal structure and selected hydrogen-bonding interactions that the compound forms. The crystal structure exhibits parallel stacking of the diammonium dication in its packing arrangement, together with inorganic–organic layering that is typical of these n-alkyldiammonium salts. An intricate three-dimensional hydrogen-bonding network exists in the crystal structure where the hydrogen bonds link the cation and anion layers together through the sulfate anions and the water molecules.

Related literature

For related structural studies of n-alkyl-diammonium sulfate salts, see: van Blerk & Kruger (2008 ). For related literature other n-alkyldiammonium salts, see: Allen (2002 ).

Experimental

Crystal data

C₇H₂₀N₂²⁺·SO₄²⁻·H₂O
M_r = 246.33
Monoclinic, P 2₁ /n
a = 5.7527 (1) Å
b = 22.3459 (4) Å
c = 10.0908 (2) Å
β = 95.180 (1)°
V = 1291.87 (4) Å³
Z = 4
Mo Kα radiation
μ = 0.26 mm⁻¹
T = 295 K
0.48 × 0.44 × 0.14 mm

Data collection

Bruker SMART CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ) T_min = 0.887, T_max = 0.965
33427 measured reflections
3220 independent reflections
2626 reflections with I > 2σ(I)
R_int = 0.029

Refinement

R[F² > 2σ(F²)] = 0.037
wR(F²) = 0.106
S = 1.03
3220 reflections
138 parameters
H-atom parameters constrained
Δρ_max = 0.36 e Å⁻³
Δρ_min = −0.34 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1C⋯O3ⁱ	0.89	1.97	2.8617 (17)	176
N1—H1D⋯O2ⁱⁱ	0.89	1.94	2.8250 (15)	177
N1—H1E⋯O4ⁱⁱⁱ	0.89	1.92	2.8106 (17)	174
N2—H2C⋯O5^iv	0.89	1.89	2.7643 (17)	168
N2—H2D⋯O2^v	0.89	1.91	2.7859 (15)	166
N2—H2E⋯O3	0.89	2.01	2.7770 (16)	144
O1—H1W⋯O4^iv	0.90	1.98	2.880 (2)	180
O1—H2W⋯O3	0.90	2.07	2.971 (2)	180
Symmetry codes: (i) -x+1, -y+1, -z+2; (ii) -x, -y+1, -z+2; (iii) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (iv) x+1, y, z; (v) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ .

Data collection: SMART-NT (Bruker, 1999 ); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009 ) and Mercury (Macrae et al., 2008 ); software used to prepare material for publication: publCIF (Westrip, 2010 ) and PLATON (Spek, 2009 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811030030/zk2015sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811030030/zk2015Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536811030030/zk2015Isup3.mol

Supporting information file. DOI: 10.1107/S1600536811030030/zk2015Isup4.cml

checkCIF report

Comment top

The crystal structure of the title compound (I) adds to our current ongoing studies of long-chained diammonium inorganic mineral acid salts. Colourless crystals of heptane-1,7-diammonium sulfate hydrate were obtained from an attempt to synthesize heptane-1,7-diammonium sulfate. This material forms part of our structural chemistry study of the inorganic mineral acid salts of the n-alkyldiamines. A search of the Cambridge Structural Database (Version 5.32, Allen, 2002) revealed that this compound had not previously been determined.

The asymmetric unit of compound (I) contains one diammonium dication, one sulfate anion and one water molecule with all atoms occupying general positions. The hydrocarbon chain is also fully extended from N1 to C7 but then distorts from planarity through N2. This is evident in the C5—C6—C7—N2 torsion angle (-70.49°(18)). The molecular structure of (I) is shown in Fig. 1.

Fig. 2 illustrates the packing arrangement of the title compound (I). Single parallel-stacked layers of dications pack together with sulfate anions and water molecules inserted between the dication chains in line with the ammonium groups showing a distinct inorganic–organic layering effect that is a common feature of these long-chained diammonium salts. An extensive three-dimensional hydrogen-bonding network is formed.

A close-up view of selected hydrogen bonding interactions can be viewed in Fig. 3. The three-dimensional hydrogen bonding network is built and linked through hydrogen bonding interactions between the ammonium groups of the dication and the sulfate anions and water molecules. These extensive interactions are seen to contribute to the distortion from planarity of the ω-end of the diammonium cation. The hydrogen bond distances and angles for the title compound (I) can be found in Table 2.

Related literature top

For related structural studies of n-alkyl-diammonium sulfate salts, see: van Blerk & Kruger (2008). For other related literature, see: Allen (2002).

Experimental top

Compound (I) was prepared by adding heptane-1,7-diamine (0.50 g, 3.84 mmol) to 33% sulfuric acid (H₂SO₄, 2 ml, 25.29 mmol, Merck) in a sample vial. The mixture was then refluxed at 363 K for 2 h. The solution was cooled at 2 K h^-1 to room temperature. Colourless crystals of heptane-1,7-diammonium sulfate hydrate were collected and a suitable single-crystal was selected for the X-ray diffraction study.

Computing details top

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010) and PLATON (Spek, 2009).

Figures top

	Fig. 1. Molecular structure of the title compound, with atomic numbering scheme and displacement ellipsoids drawn at the 50% probability level.
	Fig. 2. Packing arrangement of the title compound viewed down the a axis. Hydrogen bonds are indicated by red dashed lines.
	Fig. 3. Close-up view of the title compound clearly showing selected hydrogen-bonding interactions. Hydrogen bonds are indicated by red dashed lines.

Heptane-1,7-diaminium sulfate monohydrate top

Crystal data top

C₇H₂₀N₂²⁺·SO₄²⁻·H₂O	F(000) = 536
M_r = 246.33	D_x = 1.266 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 9981 reflections
a = 5.7527 (1) Å	θ = 2.2–28.2°
b = 22.3459 (4) Å	µ = 0.26 mm⁻¹
c = 10.0908 (2) Å	T = 295 K
β = 95.180 (1)°	Block, colourless
V = 1291.87 (4) Å³	0.48 × 0.44 × 0.14 mm
Z = 4

Data collection top

Bruker SMART CCD diffractometer	3220 independent reflections
Radiation source: fine-focus sealed tube	2626 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.029
ϕ and ω scans	θ_max = 28.3°, θ_min = 1.8°
Absorption correction: multi-scan (APEX2 AXScale; Bruker, 2008)	h = −7→7
T_min = 0.887, T_max = 0.965	k = −29→29
33427 measured reflections	l = −13→13

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)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.106	H-atom parameters constrained
S = 1.03	w = 1/[σ²(F_o²) + (0.0582P)² + 0.3142P] where P = (F_o² + 2F_c²)/3
3220 reflections	(Δ/σ)_max = 0.001
138 parameters	Δρ_max = 0.36 e Å⁻³
0 restraints	Δρ_min = −0.34 e Å⁻³

Crystal data top

C₇H₂₀N₂²⁺·SO₄²⁻·H₂O	V = 1291.87 (4) Å³
M_r = 246.33	Z = 4
Monoclinic, P2₁/n	Mo Kα radiation
a = 5.7527 (1) Å	µ = 0.26 mm⁻¹
b = 22.3459 (4) Å	T = 295 K
c = 10.0908 (2) Å	0.48 × 0.44 × 0.14 mm
β = 95.180 (1)°

Data collection top

Bruker SMART CCD diffractometer	3220 independent reflections
Absorption correction: multi-scan (APEX2 AXScale; Bruker, 2008)	2626 reflections with I > 2σ(I)
T_min = 0.887, T_max = 0.965	R_int = 0.029
33427 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.037	0 restraints
wR(F²) = 0.106	H-atom parameters constrained
S = 1.03	Δρ_max = 0.36 e Å⁻³
3220 reflections	Δρ_min = −0.34 e Å⁻³
138 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
C1	0.1381 (3)	0.61468 (7)	0.89575 (17)	0.0465 (4)
H1A	0.0280	0.6095	0.8180	0.056*
H1B	0.0831	0.5915	0.9679	0.056*
C2	0.3751 (3)	0.59183 (7)	0.86564 (17)	0.0452 (3)
H2A	0.4775	0.5908	0.9474	0.054*
H2B	0.4418	0.6194	0.8052	0.054*
C3	0.3639 (3)	0.52966 (7)	0.80374 (18)	0.0485 (4)
H3A	0.3229	0.5009	0.8697	0.058*
H3B	0.2420	0.5289	0.7308	0.058*
C4	0.5934 (3)	0.51120 (7)	0.75228 (18)	0.0491 (4)
H4A	0.7111	0.5080	0.8271	0.059*
H4B	0.6425	0.5424	0.6941	0.059*
C5	0.5826 (3)	0.45218 (7)	0.67668 (17)	0.0459 (4)
H5A	0.5538	0.4199	0.7375	0.055*
H5B	0.4531	0.4534	0.6081	0.055*
C6	0.8066 (3)	0.43935 (6)	0.61273 (17)	0.0459 (4)
H6A	0.8377	0.4726	0.5552	0.055*
H6B	0.9344	0.4372	0.6822	0.055*
C7	0.8037 (3)	0.38213 (7)	0.53201 (15)	0.0447 (3)
H7A	0.6643	0.3812	0.4703	0.054*
H7B	0.9382	0.3813	0.4806	0.054*
N1	0.1483 (2)	0.67881 (5)	0.93356 (12)	0.0375 (3)
H1C	0.2474	0.6836	1.0057	0.056*
H1D	0.0069	0.6911	0.9507	0.056*
H1E	0.1965	0.7002	0.8669	0.056*
N2	0.8078 (2)	0.32888 (5)	0.61913 (12)	0.0374 (3)
H2C	0.9337	0.3302	0.6772	0.056*
H2D	0.8121	0.2959	0.5699	0.056*
H2E	0.6801	0.3284	0.6628	0.056*
O1	0.7918 (3)	0.18441 (8)	0.8741 (2)	0.1013 (6)
H1W	0.9211	0.2015	0.8472	0.152*
H2W	0.7175	0.2197	0.8606	0.152*
O2	0.29797 (18)	0.28426 (5)	1.00281 (10)	0.0408 (2)
O3	0.54854 (19)	0.30097 (6)	0.82996 (12)	0.0561 (3)
O4	0.2061 (2)	0.23929 (6)	0.78875 (13)	0.0647 (4)
O5	0.1673 (2)	0.34542 (6)	0.81662 (12)	0.0595 (3)
S1	0.30421 (5)	0.292599 (15)	0.85790 (3)	0.03274 (11)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0453 (8)	0.0395 (8)	0.0561 (9)	−0.0027 (6)	0.0128 (7)	−0.0056 (7)
C2	0.0444 (8)	0.0367 (8)	0.0553 (9)	0.0023 (6)	0.0080 (7)	−0.0067 (7)
C3	0.0528 (9)	0.0348 (7)	0.0592 (10)	−0.0008 (6)	0.0128 (7)	−0.0063 (7)
C4	0.0505 (9)	0.0341 (7)	0.0632 (10)	0.0009 (6)	0.0083 (7)	−0.0083 (7)
C5	0.0496 (8)	0.0318 (7)	0.0573 (9)	−0.0004 (6)	0.0112 (7)	−0.0050 (6)
C6	0.0507 (9)	0.0313 (7)	0.0571 (9)	−0.0015 (6)	0.0126 (7)	0.0019 (6)
C7	0.0583 (9)	0.0395 (8)	0.0376 (7)	0.0048 (7)	0.0106 (6)	0.0034 (6)
N1	0.0372 (6)	0.0388 (6)	0.0377 (6)	0.0044 (5)	0.0095 (5)	−0.0017 (5)
N2	0.0426 (6)	0.0321 (6)	0.0383 (6)	0.0009 (5)	0.0076 (5)	−0.0027 (5)
O1	0.0804 (11)	0.0641 (10)	0.1661 (19)	0.0094 (8)	0.0479 (12)	0.0226 (11)
O2	0.0442 (6)	0.0449 (6)	0.0343 (5)	0.0026 (4)	0.0096 (4)	0.0039 (4)
O3	0.0337 (6)	0.0865 (9)	0.0501 (7)	−0.0046 (5)	0.0140 (5)	0.0090 (6)
O4	0.0763 (9)	0.0612 (8)	0.0594 (7)	−0.0209 (6)	0.0219 (6)	−0.0252 (6)
O5	0.0583 (7)	0.0599 (7)	0.0583 (7)	0.0159 (6)	−0.0055 (6)	0.0138 (6)
S1	0.02925 (18)	0.03798 (19)	0.03160 (18)	−0.00106 (12)	0.00604 (12)	0.00133 (12)

Geometric parameters (Å, º) top

C1—N1	1.4829 (19)	C6—H6A	0.9700
C1—C2	1.512 (2)	C6—H6B	0.9700
C1—H1A	0.9700	C7—N2	1.4782 (18)
C1—H1B	0.9700	C7—H7A	0.9700
C2—C3	1.522 (2)	C7—H7B	0.9700
C2—H2A	0.9700	N1—H1C	0.8900
C2—H2B	0.9700	N1—H1D	0.8900
C3—C4	1.519 (2)	N1—H1E	0.8900
C3—H3A	0.9700	N2—H2C	0.8900
C3—H3B	0.9700	N2—H2D	0.8900
C4—C5	1.522 (2)	N2—H2E	0.8900
C4—H4A	0.9700	O1—H1W	0.9003
C4—H4B	0.9700	O1—H2W	0.9022
C5—C6	1.520 (2)	O2—S1	1.4777 (10)
C5—H5A	0.9700	O3—S1	1.4703 (11)
C5—H5B	0.9700	O4—S1	1.4674 (12)
C6—C7	1.515 (2)	O5—S1	1.4586 (12)

N1—C1—C2	111.28 (12)	C7—C6—H6A	108.6
N1—C1—H1A	109.4	C5—C6—H6A	108.6
C2—C1—H1A	109.4	C7—C6—H6B	108.6
N1—C1—H1B	109.4	C5—C6—H6B	108.6
C2—C1—H1B	109.4	H6A—C6—H6B	107.6
H1A—C1—H1B	108.0	N2—C7—C6	111.14 (12)
C1—C2—C3	112.65 (13)	N2—C7—H7A	109.4
C1—C2—H2A	109.1	C6—C7—H7A	109.4
C3—C2—H2A	109.1	N2—C7—H7B	109.4
C1—C2—H2B	109.1	C6—C7—H7B	109.4
C3—C2—H2B	109.1	H7A—C7—H7B	108.0
H2A—C2—H2B	107.8	C1—N1—H1C	109.5
C4—C3—C2	112.46 (13)	C1—N1—H1D	109.5
C4—C3—H3A	109.1	H1C—N1—H1D	109.5
C2—C3—H3A	109.1	C1—N1—H1E	109.5
C4—C3—H3B	109.1	H1C—N1—H1E	109.5
C2—C3—H3B	109.1	H1D—N1—H1E	109.5
H3A—C3—H3B	107.8	C7—N2—H2C	109.5
C3—C4—C5	114.14 (13)	C7—N2—H2D	109.5
C3—C4—H4A	108.7	H2C—N2—H2D	109.5
C5—C4—H4A	108.7	C7—N2—H2E	109.5
C3—C4—H4B	108.7	H2C—N2—H2E	109.5
C5—C4—H4B	108.7	H2D—N2—H2E	109.5
H4A—C4—H4B	107.6	H1W—O1—H2W	88.6
C6—C5—C4	112.23 (13)	O5—S1—O4	110.28 (8)
C6—C5—H5A	109.2	O5—S1—O3	110.06 (8)
C4—C5—H5A	109.2	O4—S1—O3	110.21 (8)
C6—C5—H5B	109.2	O5—S1—O2	108.90 (7)
C4—C5—H5B	109.2	O4—S1—O2	109.00 (7)
H5A—C5—H5B	107.9	O3—S1—O2	108.35 (6)
C7—C6—C5	114.75 (13)

N1—C1—C2—C3	−170.09 (14)	C3—C4—C5—C6	172.97 (15)
C1—C2—C3—C4	170.28 (15)	C4—C5—C6—C7	−178.04 (14)
C2—C3—C4—C5	−173.90 (15)	C5—C6—C7—N2	−70.49 (18)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1C···O3ⁱ	0.89	1.97	2.8617 (17)	176
N1—H1D···O2ⁱⁱ	0.89	1.94	2.8250 (15)	177
N1—H1E···O4ⁱⁱⁱ	0.89	1.92	2.8106 (17)	174
N2—H2C···O5^iv	0.89	1.89	2.7643 (17)	168
N2—H2D···O2^v	0.89	1.91	2.7859 (15)	166
N2—H2E···O3	0.89	2.01	2.7770 (16)	144
O1—H1W···O4^iv	0.90	1.98	2.880 (2)	180
O1—H2W···O3	0.90	2.07	2.971 (2)	180

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

Experimental details

Crystal data
Chemical formula	C₇H₂₀N₂²⁺·SO₄²⁻·H₂O
M_r	246.33
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	295
a, b, c (Å)	5.7527 (1), 22.3459 (4), 10.0908 (2)
β (°)	95.180 (1)
V (Å³)	1291.87 (4)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.26
Crystal size (mm)	0.48 × 0.44 × 0.14

Data collection
Diffractometer	Bruker SMART CCD diffractometer
Absorption correction	Multi-scan (APEX2 AXScale; Bruker, 2008)
T_min, T_max	0.887, 0.965
No. of measured, independent and observed [I > 2σ(I)] reflections	33427, 3220, 2626
R_int	0.029
(sin θ/λ)_max (Å⁻¹)	0.667

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.037, 0.106, 1.03
No. of reflections	3220
No. of parameters	138
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.36, −0.34

Computer programs: SMART (Bruker, 1999), SAINT (Bruker, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), OLEX2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2008), publCIF (Westrip, 2010) and PLATON (Spek, 2009).

Selected torsion angles (º) top

C5—C6—C7—N2

−70.49 (18)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1C···O3ⁱ	0.89	1.97	2.8617 (17)	176
N1—H1D···O2ⁱⁱ	0.89	1.94	2.8250 (15)	177
N1—H1E···O4ⁱⁱⁱ	0.89	1.92	2.8106 (17)	174
N2—H2C···O5^iv	0.89	1.89	2.7643 (17)	168
N2—H2D···O2^v	0.89	1.91	2.7859 (15)	166
N2—H2E···O3	0.89	2.01	2.7770 (16)	144
O1—H1W···O4^iv	0.90	1.98	2.880 (2)	180
O1—H2W···O3	0.90	2.07	2.971 (2)	180

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

Acknowledgements

The author acknowledges the National Research Foundation Thuthuka programme (GUN 66314) and the University of Johannesburg for funding for this study. The University of the Witwatersrand is thanked for the use of their facilities and the use of the diffractometer in the Jan Boeyens Structural Chemistry Laboratory.

References

Allen, F. H. (2002). Acta Cryst. B58, 380–388. Web of Science CrossRef CAS IUCr Journals Google Scholar
Blerk, C. van & Kruger, G. J. (2008). J. Chem. Crystallogr. 38, 175–179. Web of Science CSD CrossRef Google Scholar
Bruker (1999). SMART-NT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2008). SADABS and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341. Web of Science CrossRef CAS IUCr Journals Google Scholar
Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466–470. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar