research communications
of bis[4-(dimethylamino)pyridinium] aquabis(oxalato)oxidovanadate(IV) dihydrate
aLaboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Manar II Tunis, Tunisia, and bUniversité de Gabès, Faculté des Sciences de Gabès, Campus Universitaire, Cité Erriadh Zrig, Gabès, 6072, Tunisia
*Correspondence e-mail: faouzi.zid@fst.rnu.tn
The title organic–inorganic hybrid salt, (C7H11N2)2[V(C2O4)2O(H2O)]·2H2O, shows a distorted octahedral coordination environment for the vanadium(IV) atom in the anion (point group symmetry 2), with four O atoms from two symmetry-related chelating oxalate dianions and two O atoms in trans configuration from a coordinating water molecule and a terminal vanadyl O atom. In the crystal, (001) layers of cations and anions alternate along [001]. The anionic layers are built up by intermolecular O—H⋯O hydrogen bonds involving the coordinating and solvent water molecules. The cationic layers are linked to the anionic layers via N—H⋯O hydrogen bonds between the pyridinium group and the non-coordinating O atoms of the oxalate group. The 4-(dimethylamino)pyridinium cations are also engaged in π–π stacking with their antiparallel neighbours [centroid-to-centroid distance = 3.686 (2) Å]. Considering all supramolecular features, a three-dimensional network structure is accomplished.
Keywords: crystal structure; 4-(dimethylamino)pyridine; π–π interactions; vanadium(IV); oxalate ligand.
CCDC reference: 1485722
1. Chemical context
Because of the great importance of vanadium as an effective metal antitumor agent (Evangelou, 2002) and the vanadyl antidiabetic factor via its manifested insulin-mimetic activity (Goc, 2006), the coordination chemistry of this element has received much attention over the past years through the design and synthesis of organic–inorganic hybrid salts and the investigation of their solution chemistry. In addition to that, the use of pyridine and its derivatives in those hybrid materials may also provide biological activity as reported by Markees et al. (1968). Many compounds containing the vanadyl V=O group combined with oxalate ligands have been isolated as mononuclear (Lin et al., 2004; Aghabozorg et al., 2007; Oughtred et al., 1976) or dinuclear (Zheng et al., 1998) compounds.
In this context, we report on the synthesis and 7H11N2)2[V(C2O4)2O(H2O)]·2H2O, (I).
of the title organic–inorganic hybrid salt, (C2. Structural commentary
The vanadium atom V1, the double-bonded oxygen atom O3 of the vanadyl group and the oxygen atom of the coordinating water molecule OW1 lie on a twofold rotation axis. Thus, the of the title compound corresponds to half of the molecular formula which consequently contains one half-anionic complex [V1/2(C2O4)O1/2(HO1/2)]−, one 4-(dimethylamino)pyridinium cation (C7H11N2)+ protonated at the N2 atom of the heterocyclic ring, and one solvent water molecule (Fig. 1). The anionic complex has an overall charge of 2−, requiring a vanadium atom with an of +IV. This formal value is in good agreement with the bond-valence-sum calculation (Brown & Altermatt, 1985), resulting in a value of 4.20 (3) valence units.
The VIV ion is coordinated by four oxygen atoms of two symmetry-related chelating oxalate dianions, defining the equatorial plane, and two axial oxygen atoms from a water molecule and the vanadyl oxygen atom. The resulting octahedral coordination sphere is considerably distorted. The V—Ooxalate bond lengths (Table 1) are in good agreement with structures containing the same [V(C2O4)2O(H2O)]2− anion and diammonium (Oughtred et al., 1976) or piperazinium (Lin et al., 2004) as counter-cations. The short V1=O3 distance of 1.600 (3) Å is typical for a double-bonded vanadyl group and the longest V—O bond involves the aqua ligand, again in agreement with the structures of the related compounds with different cations. The shortest distances between vanadium atoms in the isolated complexes are equal to 7.689 (4) Å along [010] (corresponding to the length of the b axis) and 8.287 (1) Å along [010], while a shorter distance equal to 5.176 (5) Å along the [001] direction is reported by Aghabozorg et al. (2007) for the related piperazinium compound. The oxalate anion is planar (root-mean-deviation of fitted atoms = 0.0343 Å); the two symmetry-related oxalate ligands subtend a dihedral angle of 32.59 (4)° between the least-squares planes. The slightly elongated C—C bond length of 1.552 (3) Å in the oxalate anion is in agreement with the value of 1.539 (2) Å reported for other oxalate complexes (Belaj et al., 2000). Bond lengths and angles of the 4-(dimethylamino)pyridinium cation are consistent with those found in salts with the same cationic entity (Ben Nasr et al., 2015) with C—N distances in the range 1.326 (3)–1.458 (3) Å and C—C distances between 1.343 (3) and 1.413 (3) Å.
3. Supramolecular features
Within the crystal packing, all components are connected by an extensive hydrogen-bonding network (Table 2). The cations and anions are aligned into layers parallel to (001). O—H⋯O hydrogen bonds involving the coordinating OW1 water molecule as donor group and the solvent OW2 molecule as both acceptor and donor groups consolidate the anionic layers parallel to (001), as shown in Fig. 2a. In the structure of the related piperazinium compound (Aghabozorg et al., 2007), a more complex three-dimensional arrangement of the O—H⋯O hydrogen bonds is realized (Fig. 2b). Along the [001] direction, N—H⋯O hydrogen bonds involving the protonated N2 atom of the 4-(dimethylamino)pyridinium cation as double-donor group and non-coordinating O atoms of the oxalate dianion as acceptors ensure the connection between the anionic and cationic layers in the title structure, as shown in Fig. 3. Furthermore, π–π stacking interactions between antiparallel-arranged pyridinium rings [centroid-to-centroid distance = 3.686 (2) Å; Fig. 4] are present and consolidate the three-dimensional network (Fig. 5).
4. Synthesis and crystallization
A solution of 0.5 mmol of vanadium(V) pentoxide dissolved in 10 cm3 of distilled water was added to a solution of 1 mmol of oxalic acid dissolved in 10 cm3 of distilled water. Then, a solution of 1 mmol of 4-(dimethylamino)pyridine dissolved in 10 cm3 of distilled water was poured slowly until pH ≃ 4. The obtained blue solution was placed in a petri dish at room temperature for almost one month until purple crystals suitable for a structural study appeared.
5. Refinement
Crystal data, data collection and structure . H atoms bonded to C and N atoms were placed at geometrically calculated positions using a riding model. C—H distances were fixed at 0.93 Å for aromatic H atoms and 0.96 Å for methyl H atoms, with Uiso(H) = 1.2Ueq(Caromatic) or 1.5Ueq(Cmethyl). The N—H distance was fixed at 0.86 Å. All water H atoms were located from a difference-Fourier map and were refined with restraints [O—H 0.85 (1) Å; H⋯H 1.387 (1) Å].
details are summarized in Table 3Supporting information
CCDC reference: 1485722
https://doi.org/10.1107/S2056989016009695/wm5298sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016009695/wm5298Isup2.hkl
Data collection: CAD-4 EXPRESS (Duisenberg, 1992); cell
CAD-4 EXPRESS (Duisenberg, 1992); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).(C7H11N2)2[V(C2O4)2O(H2O)]·2H2O | F(000) = 1132 |
Mr = 543.38 | Dx = 1.514 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
a = 14.682 (2) Å | Cell parameters from 25 reflections |
b = 7.689 (4) Å | θ = 10–15° |
c = 21.280 (3) Å | µ = 0.49 mm−1 |
β = 97.197 (10)° | T = 298 K |
V = 2383.3 (13) Å3 | Prism, purple |
Z = 4 | 0.46 × 0.28 × 0.21 mm |
Enraf–Nonius CAD-4 diffractometer | Rint = 0.028 |
Radiation source: fine-focus sealed tube | θmax = 27.0°, θmin = 2.8° |
ω/2θ scans | h = −18→5 |
Absorption correction: ψ scan (North et al., 1968) | k = −1→9 |
Tmin = 0.841, Tmax = 0.908 | l = −27→27 |
4165 measured reflections | 2 standard reflections every 120 reflections |
2599 independent reflections | intensity decay: 1.4% |
1850 reflections with I > 2σ(I) |
Refinement on F2 | Primary atom site location: heavy-atom method |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.038 | Hydrogen site location: mixed |
wR(F2) = 0.106 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.01 | w = 1/[σ2(Fo2) + (0.0482P)2 + 1.2556P] where P = (Fo2 + 2Fc2)/3 |
2599 reflections | (Δ/σ)max < 0.001 |
174 parameters | Δρmax = 0.25 e Å−3 |
4 restraints | Δρmin = −0.26 e Å−3 |
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. |
x | y | z | Uiso*/Ueq | ||
V1 | 0.0000 | 0.84234 (7) | 0.7500 | 0.03574 (16) | |
O1 | −0.02877 (10) | 0.7977 (2) | 0.65720 (7) | 0.0446 (4) | |
OW1 | 0.0000 | 0.5482 (3) | 0.7500 | 0.0707 (9) | |
O2 | 0.12736 (10) | 0.8022 (2) | 0.73095 (7) | 0.0477 (4) | |
O3 | 0.0000 | 1.0504 (3) | 0.7500 | 0.0583 (7) | |
O4 | 0.03921 (12) | 0.7053 (3) | 0.57518 (8) | 0.0618 (5) | |
O5 | 0.20402 (11) | 0.7168 (3) | 0.65270 (8) | 0.0604 (5) | |
C10 | 0.04062 (15) | 0.7502 (3) | 0.63017 (10) | 0.0424 (5) | |
C11 | 0.13301 (15) | 0.7551 (3) | 0.67444 (11) | 0.0430 (5) | |
HW1A | −0.0389 (16) | 0.480 (3) | 0.7310 (12) | 0.072 (9)* | |
OW2 | 0.88723 (13) | 0.3042 (3) | 0.68686 (11) | 0.0639 (5) | |
HW2A | 0.9136 (14) | 0.216 (2) | 0.7059 (11) | 0.056 (8)* | |
HW2B | 0.8295 (7) | 0.290 (3) | 0.6839 (15) | 0.081 (10)* | |
N1 | 0.34041 (15) | 0.3258 (3) | 0.39759 (9) | 0.0522 (5) | |
N2 | 0.21437 (16) | 0.5684 (3) | 0.53481 (11) | 0.0596 (6) | |
H2 | 0.1881 | 0.6207 | 0.5634 | 0.071* | |
C1 | 0.4371 (2) | 0.2774 (4) | 0.40787 (15) | 0.0690 (8) | |
H1A | 0.4496 | 0.2154 | 0.4472 | 0.103* | |
H1B | 0.4743 | 0.3805 | 0.4095 | 0.103* | |
H1C | 0.4512 | 0.2046 | 0.3737 | 0.103* | |
C2 | 0.2904 (3) | 0.2816 (4) | 0.33610 (12) | 0.0774 (10) | |
H2A | 0.2329 | 0.2286 | 0.3420 | 0.116* | |
H2B | 0.3261 | 0.2017 | 0.3146 | 0.116* | |
H2C | 0.2792 | 0.3853 | 0.3112 | 0.116* | |
C3 | 0.29925 (15) | 0.4045 (3) | 0.44227 (10) | 0.0387 (5) | |
C4 | 0.20526 (16) | 0.4499 (4) | 0.43279 (12) | 0.0520 (6) | |
H4 | 0.1699 | 0.4248 | 0.3945 | 0.062* | |
C5 | 0.16691 (18) | 0.5297 (4) | 0.47941 (14) | 0.0609 (7) | |
H5 | 0.1050 | 0.5586 | 0.4725 | 0.073* | |
C6 | 0.30270 (19) | 0.5261 (4) | 0.54591 (12) | 0.0558 (7) | |
H6 | 0.3352 | 0.5526 | 0.5851 | 0.067* | |
C7 | 0.34650 (15) | 0.4462 (3) | 0.50226 (10) | 0.0463 (5) | |
H7 | 0.4083 | 0.4181 | 0.5116 | 0.056* |
U11 | U22 | U33 | U12 | U13 | U23 | |
V1 | 0.0295 (3) | 0.0374 (3) | 0.0388 (3) | 0.000 | −0.0018 (2) | 0.000 |
O1 | 0.0299 (7) | 0.0617 (10) | 0.0400 (8) | 0.0049 (7) | −0.0041 (6) | −0.0010 (7) |
OW1 | 0.0651 (18) | 0.0359 (14) | 0.098 (2) | 0.000 | −0.0396 (16) | 0.000 |
O2 | 0.0287 (7) | 0.0703 (12) | 0.0423 (8) | −0.0025 (7) | −0.0032 (7) | −0.0066 (8) |
O3 | 0.0657 (16) | 0.0377 (13) | 0.0698 (16) | 0.000 | 0.0018 (13) | 0.000 |
O4 | 0.0446 (10) | 0.0979 (15) | 0.0415 (9) | 0.0084 (10) | −0.0004 (8) | −0.0118 (9) |
O5 | 0.0311 (9) | 0.0928 (14) | 0.0571 (10) | 0.0038 (9) | 0.0048 (8) | −0.0131 (10) |
C10 | 0.0340 (12) | 0.0502 (14) | 0.0414 (12) | 0.0018 (10) | −0.0016 (9) | 0.0011 (11) |
C11 | 0.0310 (11) | 0.0501 (14) | 0.0467 (12) | −0.0023 (10) | −0.0003 (9) | −0.0008 (11) |
OW2 | 0.0418 (10) | 0.0568 (12) | 0.0867 (14) | −0.0043 (9) | −0.0175 (10) | 0.0098 (10) |
N1 | 0.0532 (12) | 0.0595 (13) | 0.0433 (10) | 0.0013 (11) | 0.0041 (9) | −0.0075 (9) |
N2 | 0.0658 (15) | 0.0561 (14) | 0.0621 (13) | 0.0034 (12) | 0.0287 (12) | −0.0001 (11) |
C1 | 0.0564 (17) | 0.0740 (19) | 0.0806 (19) | 0.0109 (15) | 0.0245 (15) | −0.0059 (16) |
C2 | 0.105 (3) | 0.081 (2) | 0.0440 (15) | −0.010 (2) | 0.0019 (16) | −0.0155 (14) |
C3 | 0.0365 (11) | 0.0384 (11) | 0.0399 (10) | −0.0019 (9) | −0.0001 (9) | 0.0043 (9) |
C4 | 0.0416 (13) | 0.0595 (16) | 0.0517 (13) | 0.0012 (12) | −0.0068 (11) | 0.0096 (12) |
C5 | 0.0406 (14) | 0.0618 (17) | 0.0824 (19) | 0.0131 (13) | 0.0158 (14) | 0.0190 (15) |
C6 | 0.0608 (17) | 0.0625 (17) | 0.0440 (12) | −0.0085 (14) | 0.0067 (12) | −0.0042 (12) |
C7 | 0.0353 (12) | 0.0585 (15) | 0.0435 (11) | −0.0018 (11) | −0.0011 (9) | −0.0017 (11) |
V1—O3 | 1.600 (3) | N2—C5 | 1.326 (3) |
V1—O2i | 1.986 (2) | N2—C6 | 1.329 (3) |
V1—O2 | 1.986 (2) | N2—H2 | 0.8600 |
V1—O1 | 1.997 (1) | C1—H1A | 0.9600 |
V1—O1i | 1.997 (1) | C1—H1B | 0.9600 |
V1—OW1 | 2.262 (3) | C1—H1C | 0.9600 |
O1—C10 | 1.284 (3) | C2—H2A | 0.9600 |
OW1—HW1A | 0.842 (10) | C2—H2B | 0.9600 |
O2—C11 | 1.268 (3) | C2—H2C | 0.9600 |
O4—C10 | 1.218 (3) | C3—C7 | 1.411 (3) |
O5—C11 | 1.228 (3) | C3—C4 | 1.413 (3) |
C10—C11 | 1.552 (3) | C4—C5 | 1.348 (4) |
OW2—HW2A | 0.855 (9) | C4—H4 | 0.9300 |
OW2—HW2B | 0.848 (10) | C5—H5 | 0.9300 |
N1—C3 | 1.334 (3) | C6—C7 | 1.343 (3) |
N1—C1 | 1.458 (3) | C6—H6 | 0.9300 |
N1—C2 | 1.458 (3) | C7—H7 | 0.9300 |
O3—V1—O2i | 98.94 (6) | C5—N2—H2 | 120.2 |
O3—V1—O2 | 98.94 (6) | C6—N2—H2 | 120.2 |
O2i—V1—O2 | 162.13 (11) | N1—C1—H1A | 109.5 |
O3—V1—O1 | 99.90 (5) | N1—C1—H1B | 109.5 |
O2i—V1—O1 | 95.01 (6) | H1A—C1—H1B | 109.5 |
O2—V1—O1 | 81.91 (6) | N1—C1—H1C | 109.5 |
O3—V1—O1i | 99.90 (5) | H1A—C1—H1C | 109.5 |
O2i—V1—O1i | 81.91 (6) | H1B—C1—H1C | 109.5 |
O2—V1—O1i | 95.01 (6) | N1—C2—H2A | 109.5 |
O1—V1—O1i | 160.21 (10) | N1—C2—H2B | 109.5 |
O3—V1—OW1 | 180.0 | H2A—C2—H2B | 109.5 |
O2i—V1—OW1 | 81.06 (6) | N1—C2—H2C | 109.5 |
O2—V1—OW1 | 81.06 (6) | H2A—C2—H2C | 109.5 |
O1—V1—OW1 | 80.10 (5) | H2B—C2—H2C | 109.5 |
O1i—V1—OW1 | 80.10 (5) | N1—C3—C7 | 122.2 (2) |
C10—O1—V1 | 114.24 (13) | N1—C3—C4 | 122.1 (2) |
V1—OW1—HW1A | 128.7 (19) | C7—C3—C4 | 115.7 (2) |
C11—O2—V1 | 114.38 (14) | C5—C4—C3 | 119.8 (2) |
O4—C10—O1 | 126.3 (2) | C5—C4—H4 | 120.1 |
O4—C10—C11 | 119.9 (2) | C3—C4—H4 | 120.1 |
O1—C10—C11 | 113.77 (19) | N2—C5—C4 | 122.4 (2) |
O5—C11—O2 | 125.8 (2) | N2—C5—H5 | 118.8 |
O5—C11—C10 | 118.9 (2) | C4—C5—H5 | 118.8 |
O2—C11—C10 | 115.2 (2) | N2—C6—C7 | 122.0 (2) |
HW2A—OW2—HW2B | 108.9 (15) | N2—C6—H6 | 119.0 |
C3—N1—C1 | 121.9 (2) | C7—C6—H6 | 119.0 |
C3—N1—C2 | 121.5 (2) | C6—C7—C3 | 120.4 (2) |
C1—N1—C2 | 116.5 (2) | C6—C7—H7 | 119.8 |
C5—N2—C6 | 119.7 (2) | C3—C7—H7 | 119.8 |
V1—O1—C10—O4 | 175.1 (2) | C1—N1—C3—C4 | −179.3 (2) |
V1—O1—C10—C11 | −5.5 (2) | C2—N1—C3—C4 | −0.2 (4) |
V1—O2—C11—O5 | −177.1 (2) | N1—C3—C4—C5 | −179.8 (2) |
V1—O2—C11—C10 | 4.0 (3) | C7—C3—C4—C5 | 0.8 (4) |
O4—C10—C11—O5 | 1.5 (4) | C6—N2—C5—C4 | −0.9 (4) |
O1—C10—C11—O5 | −178.0 (2) | C3—C4—C5—N2 | 0.1 (4) |
O4—C10—C11—O2 | −179.5 (2) | C5—N2—C6—C7 | 0.8 (4) |
O1—C10—C11—O2 | 1.1 (3) | N2—C6—C7—C3 | 0.1 (4) |
C1—N1—C3—C7 | 0.1 (4) | N1—C3—C7—C6 | 179.7 (2) |
C2—N1—C3—C7 | 179.2 (2) | C4—C3—C7—C6 | −0.9 (4) |
Symmetry code: (i) −x, y, −z+3/2. |
D—H···A | D—H | H···A | D···A | D—H···A |
OW1—HW1A···OW2ii | 0.84 (1) | 1.90 (1) | 2.740 (3) | 172 (3) |
OW2—HW2A···O3iii | 0.86 (1) | 1.95 (1) | 2.792 (3) | 166 (2) |
OW2—HW2B···O5iv | 0.85 (1) | 1.96 (1) | 2.779 (2) | 161 (3) |
N2—H2···O4 | 0.86 | 2.32 | 3.002 (3) | 136 |
N2—H2···O5 | 0.86 | 2.02 | 2.777 (3) | 146 |
Symmetry codes: (ii) x−1, y, z; (iii) x+1, y−1, z; (iv) x+1/2, y−1/2, z. |
Acknowledgements
Financial support from the Ministry of Higher Education and Scientific Research of Tunisia is gratefully acknowledged.
References
Aghabozorg, H., Motyeian, E., Aghajani, Z., Ghadermazi, M. & Attar Gharamaleki, J. (2007). Acta Cryst. E63, m1754–m1755. Web of Science CSD CrossRef IUCr Journals Google Scholar
Belaj, F., Basch, A. & Muster, U. (2000). Acta Cryst. C56, 921–922. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Ben Nasr, M., Lefebvre, F. & Ben Nasr, C. (2015). Am. J. Anal. Chem. 6, 446–456. CSD CrossRef CAS Google Scholar
Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Brown, I. D. & Altermatt, D. (1985). Acta Cryst. B41, 244–247. CrossRef CAS Web of Science IUCr Journals Google Scholar
Duisenberg, A. J. M. (1992). J. Appl. Cryst. 25, 92–96. CrossRef CAS Web of Science IUCr Journals Google Scholar
Evangelou, A. M. (2002). Crit. Rev. Oncol. Hematol. 42, 249–265. Web of Science CrossRef PubMed Google Scholar
Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854. Web of Science CrossRef CAS IUCr Journals Google Scholar
Goc, A. (2006). Cent. Eur. J. Biol. 1(3), 314–332. Google Scholar
Harms, K. & Wocadlo, S. (1995). XCAD4. University of Marburg, Germany. Google Scholar
Lin, L., Wu, S.-F., Huang, C.-C., Zhang, H.-H., Huang, X.-H. & Lian, Z.-X. (2004). Acta Cryst. E60, m631–m633. Web of Science CSD CrossRef IUCr Journals Google Scholar
Markees, D. G., Dewey, V. C. & Kidder, G. W. (1968). J. Med. Chem. 11, 126–129. CrossRef CAS PubMed Google Scholar
North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351–359. CrossRef IUCr Journals Web of Science Google Scholar
Oughtred, R. E., Raper, E. S. & Shearer, H. M. M. (1976). Acta Cryst. B32, 82–87. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar
Zheng, L.-M., Schmalle, H. W., Ferlay, S. & Decurtins, S. (1998). Acta Cryst. C54, 1435–1438. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.