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Glycinium hydrogen fumarate glycine solvate monohydrate

aDepartment of Physics, Madurai Kamaraj University, Madurai 625 021, India, bDepartment of Physics, The Madura College, Madurai 625 011, India, and cDepartment of Food Science and Technology, Faculty of Agriculture, University of Ruhuna, Mapalana, Kamburupitiya (81100), Sri Lanka
*Correspondence e-mail: nilanthalakshman@yahoo.co.uk

(Received 7 December 2008; accepted 15 January 2009; online 4 February 2009)

In the title compound, C2H6NO2+·C4H3O4·C2H5NO2·H2O, the asymmetric unit contains two glycine residues, one protonated and one in the zwitterionic form, a hydrogen fumarate anion and a water mol­ecule. Through N—H⋯O and O—H⋯O hydrogen bonds, mol­ecules assemble in layers parallel to the (10[\overline{1}]) plane, one layer of hydrogen fumarate anions alternating with two layers of glycine mol­ecules. In each glycine layer, hydrogen bonds generate an R44(19) graph-set motif. Further hydrogen bonds involving the water mol­ecule and the hydrogen fumarate anions result in the formation of a three-dimensional network.

Related literature

For related structures and general background, see: Alagar et al. (2003a[Alagar, M., Krishnakumar, R. V., Subha Nandhini, M. & Natarajan, S. (2003a). Acta Cryst. E59, o857-o859.],b[Alagar, M., Krishnakumar, R. V., Rajagopal, K., Subha Nandhini, M. & Natarajan, S. (2003b). Acta Cryst. E59, o952-o954.]); Kvick et al. (1980[Kvick, Å., Canning, W. M., Koetzle, T. F. & Williams, G. J. B. (1980). Acta Cryst. B36, 115-120.]). For hydrogen-bonding motifs, see: Etter (1990[Etter, M. C. (1990). Acc. Chem. Res. 23, 120-126.]); Bernstein et al. (1994[Bernstein, J., Etter, M. C. & Leiserowitz, L. (1994). Structure Correlation, Vol. 2, edited by H.-B. Bürgi & J. D. Dunitz, pp. 431-507. New York: VCH.]).

[Scheme 1]

Experimental

Crystal data
  • C2H6NO2+·C4H3O4·C2H5NO2·H2O

  • Mr = 284.23

  • Monoclinic, P 21 /n

  • a = 13.0580 (12) Å

  • b = 6.8251 (7) Å

  • c = 15.3263 (14) Å

  • β = 112.65 (2)°

  • V = 1260.6 (3) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.14 mm−1

  • T = 293 (2) K

  • 0.18 × 0.16 × 0.11 mm

Data collection
  • Nonius MACH3 diffractometer

  • Absorption correction: ψ scan (North et al., 1968[North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351-359.]) Tmin = 0.923, Tmax = 0.953

  • 2742 measured reflections

  • 2219 independent reflections

  • 1922 reflections with I > 2σ(I)

  • Rint = 0.020

  • 2 standard reflections frequency: 60 min intensity decay: none

Refinement
  • R[F2 > 2σ(F2)] = 0.033

  • wR(F2) = 0.095

  • S = 1.04

  • 2219 reflections

  • 182 parameters

  • 3 restraints

  • H atoms treated by a mixture of independent and constrained refinement

  • Δρmax = 0.18 e Å−3

  • Δρmin = −0.21 e Å−3

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994[Enraf-Nonius (1994). CAD-4 EXPRESS. Enraf-Nonius, Delft, The Netherlands.]); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1996[Harms, K. & Wocadlo, S. (1996). XCAD4. University of Marburg, Germany.]); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: ORTEPIII (Burnett & Johnson, 1996[Burnett, M. N. & Johnson, C. K. (1996). ORTEPIII. Report ORNL-6895. Oak Ridge National Laboratory, Tennessee, USA.]), ORTEP-32 for Windows (Farrugia, 1997[Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.]) and PLATON (Spek, 2003[Spek, A. L. (2003). J. Appl. Cryst. 36, 7-13.]); software used to prepare material for publication: SHELXL97.

Supporting information


Comment top

Glycine is the simplest amino acid and is the only amino acid that is not optically active. This amino acid is essential for the biosynthesis of nucleic acids, as well as the biosynthesis of bile acids, porphyrins, creatine phosphate and other amino acids. Fumaric acid is among the organic compounds widely found in nature, and is key intermediate in the biosynthesis of organic acids. Our main interest in glycine compounds relates to their geometric features of non-covalent interactions at atomic resolution that are important in the structural assembly and function of proteins. X-ray investigations of amino acid complexes with fumaric acid seem to have been first initiated in our laboratory (Alagar et al., (2003a), (2003b)).

The asymmetric unit is built up from two glycine residues, a ionized fumaric acid and a water molecule linked by hydrogen bonds (Fig. 1). One of the glycine residue has been protonated, and the other one is in the zwitterionic form. The fumaric acid molecule is in the ionized state, as expected from the strength of the acid and the required charge neutrality of the salt.

The glycine carboxyl skeletons including atoms O5, O6, C5, C6 and O7, O8, C7, C8 are both planar with rms deviations of 0.0025 (6) Å and 0.0002 (6) Å respectively. The N2 and N1 atoms are slightly displaced out of these planes, by 0.138 (3)Å and 0.139 (3)Å respectively, corresponding to a small rotation around C5—C6 and C7—C8 atoms respectively. The relevant torsion angles are O5—C6—C5—N2 of 6.3 (2)°, O6—C6—C5—N2 of -174.47 (13)° and O7—C7—C8—N1 of 174.13 (13)°, O8—C7—C8—N2 of -5.8 (2)°. These can be compared with the corresponding values in pure γ-glycine 167.1 (1)° and -15.4 (1)°, respectively (Kvick et al., (1980)), which is more distorted from planarity. The fumaric acid molecule has a non crystallographic centre of symmetry, and is planar with trans configuration about the central C=C bond.

Through N-H···O and O-H···O hydrogen bondings, the molecules assemble in layers parallel to the (1 0 -1) plane, one layer of fumaric acid alternates with two layers of glycine (Fig. 2). In each layer of glycine, the hydrogen bonds generate a graph set motif R44(19) (Etter, 1990; Bernstein et al., 1994) (Fig.3, Table 1). Further H bonds involving the water and the fumaric acid result in the formation of a three dimensional network (Fig. 2, Table 1). Unlike the other amino acid fumaric acid complexes (Alagar et al., 2003a,b ) there are hydrogen bonds found between the fumaric acid molecules.

Related literature top

For general background, see: Alagar et al. (2003a,b); Kvick et al. (1980). For hydrogen-bonding motifs, see: Etter (1990); Bernstein et al. (1994).

Experimental top

Colourless single crystals of the complex were grown, as transparent needles by slow evaporation method from a saturated aqueous solution containing glycine and fumaric acid in 1: 1 stoichiometric ratio.

Refinement top

H atoms attached to C and N atoms were found in difference Fourier but introduced in calculated position and treated as riding on their parent atoms with C-H= 0.97Å (CH2) or 0.93Å (aromatic) and N-H= 0.89\%A with Uiso = 1.2Ueq(C) for CH and Uiso = 1.5Ueq(N). H atoms of water molecule were located in difference Fourier maps and included in the subsequent refinement using restraints (O-H= 0.85 (1)Å and H···H= 1.39 (2)Å) with Uiso(H) = 1.5Ueq(O).

Computing details top

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf–Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996), ORTEP-32 for Windows (Farrugia, 1998) and PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), with the atom-labeling scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms are represented as small spheres of arbitrary radii. H bonds are shown as dashed lines.
[Figure 2] Fig. 2. The crystal packing of the molecules down the b axis.
[Figure 3] Fig. 3. Cyclic chain between the glycine molecules generating a graph set motif R44(19).
Glycinium hydrogen fumarate glycine solvate monohydrate top
Crystal data top
C2H6NO2+·C4H3O4·C2H5NO2·H2OF(000) = 600
Mr = 284.23Dx = 1.498 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 25 reflections
a = 13.0580 (12) Åθ = 2–25°
b = 6.8251 (7) ŵ = 0.14 mm1
c = 15.3263 (14) ÅT = 293 K
β = 112.65 (2)°Needle, colourless
V = 1260.6 (3) Å30.18 × 0.16 × 0.11 mm
Z = 4
Data collection top
Nonius MACH3
diffractometer
1922 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.020
Graphite monochromatorθmax = 25.0°, θmin = 2.6°
ω–2θ scansh = 015
Absorption correction: ψ scan
(North et al., 1968)
k = 18
Tmin = 0.923, Tmax = 0.953l = 1816
2742 measured reflections2 standard reflections every 60 min
2219 independent reflections intensity decay: none
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.033Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.095H atoms treated by a mixture of independent and constrained refinement
S = 1.04 w = 1/[σ2(Fo2) + (0.0522P)2 + 0.4133P]
where P = (Fo2 + 2Fc2)/3
2219 reflections(Δ/σ)max < 0.001
182 parametersΔρmax = 0.18 e Å3
3 restraintsΔρmin = 0.21 e Å3
Crystal data top
C2H6NO2+·C4H3O4·C2H5NO2·H2OV = 1260.6 (3) Å3
Mr = 284.23Z = 4
Monoclinic, P21/nMo Kα radiation
a = 13.0580 (12) ŵ = 0.14 mm1
b = 6.8251 (7) ÅT = 293 K
c = 15.3263 (14) Å0.18 × 0.16 × 0.11 mm
β = 112.65 (2)°
Data collection top
Nonius MACH3
diffractometer
1922 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.020
Tmin = 0.923, Tmax = 0.9532 standard reflections every 60 min
2742 measured reflections intensity decay: none
2219 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0333 restraints
wR(F2) = 0.095H atoms treated by a mixture of independent and constrained refinement
S = 1.04Δρmax = 0.18 e Å3
2219 reflectionsΔρmin = 0.21 e Å3
182 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 > 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
xyzUiso*/Ueq
O10.35547 (8)0.60201 (18)0.80983 (7)0.0389 (3)
O30.00347 (8)0.78212 (19)1.08657 (7)0.0422 (3)
H30.06310.78941.11900.063*
O20.30562 (8)0.70595 (18)0.69432 (7)0.0425 (3)
O50.25539 (10)0.00488 (18)0.92332 (8)0.0484 (3)
O60.39983 (11)0.16938 (19)1.01858 (9)0.0537 (3)
H60.37680.25270.97700.081*
O70.14606 (12)0.02415 (18)0.57652 (9)0.0534 (3)
N10.08905 (10)0.19739 (19)0.76699 (8)0.0333 (3)
H1A0.02020.15040.74570.050*
H1B0.08910.32050.78620.050*
H1C0.13250.12460.81520.050*
O80.08973 (12)0.14584 (19)0.68336 (9)0.0559 (4)
O40.05847 (8)0.72700 (18)0.97294 (7)0.0401 (3)
N20.29350 (10)0.30064 (19)1.04930 (9)0.0338 (3)
H2A0.22240.26821.03230.051*
H2B0.31300.38331.09790.051*
H2C0.30330.35781.00090.051*
C80.13098 (13)0.1921 (2)0.69080 (11)0.0362 (4)
H8A0.20820.23190.71570.043*
H8B0.08950.28460.64190.043*
C20.13519 (11)0.7110 (2)0.93693 (10)0.0302 (3)
H20.18840.70590.96340.036*
C10.01744 (11)0.7426 (2)1.00091 (9)0.0280 (3)
C30.16785 (12)0.6899 (2)0.84527 (10)0.0346 (3)
H3A0.11410.69230.81940.041*
C70.12086 (12)0.0101 (2)0.64808 (10)0.0324 (3)
C40.28582 (11)0.6623 (2)0.77979 (9)0.0287 (3)
C60.33294 (12)0.0206 (2)0.99677 (10)0.0338 (3)
C50.36250 (13)0.1231 (2)1.07712 (11)0.0388 (4)
H5A0.44010.15911.09710.047*
H5B0.35230.06181.13030.047*
O1W0.07651 (14)0.58567 (19)0.80916 (10)0.0601 (4)
H1W0.071 (2)0.631 (4)0.8594 (11)0.090*
H2W0.088 (2)0.682 (3)0.7788 (15)0.090*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0269 (5)0.0548 (7)0.0319 (5)0.0017 (5)0.0080 (4)0.0105 (5)
O30.0298 (5)0.0669 (8)0.0243 (5)0.0018 (5)0.0042 (4)0.0097 (5)
O20.0319 (6)0.0647 (8)0.0241 (5)0.0057 (5)0.0034 (4)0.0094 (5)
O50.0503 (7)0.0474 (7)0.0359 (6)0.0032 (5)0.0039 (5)0.0119 (5)
O60.0615 (8)0.0406 (7)0.0504 (7)0.0074 (6)0.0119 (6)0.0091 (6)
O70.0852 (9)0.0354 (6)0.0595 (8)0.0111 (6)0.0498 (7)0.0103 (6)
N10.0337 (6)0.0342 (7)0.0303 (6)0.0007 (5)0.0105 (5)0.0021 (5)
O80.0896 (10)0.0358 (7)0.0515 (7)0.0176 (6)0.0374 (7)0.0025 (6)
O40.0281 (5)0.0617 (8)0.0274 (5)0.0029 (5)0.0073 (4)0.0041 (5)
N20.0350 (6)0.0359 (7)0.0314 (6)0.0050 (5)0.0137 (5)0.0077 (5)
C80.0411 (8)0.0313 (8)0.0408 (9)0.0030 (6)0.0208 (7)0.0021 (6)
C20.0274 (7)0.0322 (8)0.0286 (7)0.0027 (6)0.0081 (6)0.0002 (6)
C10.0304 (7)0.0261 (7)0.0236 (7)0.0020 (6)0.0062 (6)0.0007 (5)
C30.0261 (7)0.0472 (9)0.0278 (7)0.0007 (6)0.0074 (6)0.0036 (6)
C70.0327 (7)0.0300 (8)0.0332 (8)0.0023 (6)0.0115 (6)0.0001 (6)
C40.0267 (7)0.0317 (7)0.0245 (7)0.0028 (6)0.0062 (6)0.0031 (6)
C60.0356 (8)0.0343 (8)0.0340 (8)0.0081 (6)0.0161 (7)0.0030 (6)
C50.0367 (8)0.0410 (9)0.0333 (8)0.0007 (7)0.0074 (6)0.0067 (7)
O1W0.1029 (11)0.0375 (7)0.0570 (8)0.0019 (7)0.0496 (8)0.0013 (6)
Geometric parameters (Å, º) top
O1—C41.2375 (17)N2—H2B0.8900
O3—C11.2826 (17)N2—H2C0.8900
O3—H30.8200C8—C71.511 (2)
O2—C41.2691 (17)C8—H8A0.9700
O5—C61.2021 (19)C8—H8B0.9700
O6—C61.296 (2)C2—C31.309 (2)
O6—H60.8200C2—C11.4869 (19)
O7—C71.2643 (19)C2—H20.9300
N1—C81.4686 (19)C3—C41.4917 (19)
N1—H1A0.8900C3—H3A0.9300
N1—H1B0.8900C6—C51.504 (2)
N1—H1C0.8900C5—H5A0.9700
O8—C71.2185 (19)C5—H5B0.9700
O4—C11.2267 (18)O1W—H1W0.858 (10)
N2—C51.472 (2)O1W—H2W0.852 (10)
N2—H2A0.8900
C1—O3—H3109.5O4—C1—O3124.08 (13)
C6—O6—H6109.5O4—C1—C2121.76 (12)
C8—N1—H1A109.5O3—C1—C2114.14 (12)
C8—N1—H1B109.5C2—C3—C4124.12 (14)
H1A—N1—H1B109.5C2—C3—H3A117.9
C8—N1—H1C109.5C4—C3—H3A117.9
H1A—N1—H1C109.5O8—C7—O7124.76 (15)
H1B—N1—H1C109.5O8—C7—C8119.37 (13)
C5—N2—H2A109.5O7—C7—C8115.87 (13)
C5—N2—H2B109.5O1—C4—O2125.13 (13)
H2A—N2—H2B109.5O1—C4—C3120.55 (12)
C5—N2—H2C109.5O2—C4—C3114.32 (13)
H2A—N2—H2C109.5O5—C6—O6126.57 (15)
H2B—N2—H2C109.5O5—C6—C5122.03 (15)
N1—C8—C7111.70 (12)O6—C6—C5111.39 (13)
N1—C8—H8A109.3N2—C5—C6111.37 (12)
C7—C8—H8A109.3N2—C5—H5A109.4
N1—C8—H8B109.3C6—C5—H5A109.4
C7—C8—H8B109.3N2—C5—H5B109.4
H8A—C8—H8B107.9C6—C5—H5B109.4
C3—C2—C1123.39 (14)H5A—C5—H5B108.0
C3—C2—H2118.3H1W—O1W—H2W107.4 (19)
C1—C2—H2118.3
O5—C6—C5—N26.3 (2)O7—C7—C8—N1174.08 (13)
O6—C6—C5—N2174.52 (13)O8—C7—C8—N15.8 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3···O2i0.821.662.4743 (15)174
O6—H6···O7ii0.821.702.4871 (17)160
N1—H1A···O1iii0.892.012.8891 (17)168
N1—H1B···O1W0.891.862.7475 (19)172
N1—H1C···O50.892.012.8907 (18)168
N2—H2A···O4iv0.891.982.8386 (16)162
N2—H2B···O1v0.891.982.8638 (17)170
N2—H2C···O7vi0.891.932.8000 (17)164
O1W—H1W···O40.86 (1)1.93 (1)2.7825 (17)178 (2)
O1W—H2W···O8vii0.85 (1)1.88 (1)2.7133 (18)165 (2)
Symmetry codes: (i) x+1/2, y+3/2, z+1/2; (ii) x+1/2, y+1/2, z+3/2; (iii) x1/2, y1/2, z+3/2; (iv) x, y1, z; (v) x, y, z+2; (vi) x+1/2, y1/2, z+3/2; (vii) x, y+1, z.

Experimental details

Crystal data
Chemical formulaC2H6NO2+·C4H3O4·C2H5NO2·H2O
Mr284.23
Crystal system, space groupMonoclinic, P21/n
Temperature (K)293
a, b, c (Å)13.0580 (12), 6.8251 (7), 15.3263 (14)
β (°) 112.65 (2)
V3)1260.6 (3)
Z4
Radiation typeMo Kα
µ (mm1)0.14
Crystal size (mm)0.18 × 0.16 × 0.11
Data collection
DiffractometerNonius MACH3
diffractometer
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.923, 0.953
No. of measured, independent and
observed [I > 2σ(I)] reflections
2742, 2219, 1922
Rint0.020
(sin θ/λ)max1)0.594
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.033, 0.095, 1.04
No. of reflections2219
No. of parameters182
No. of restraints3
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.18, 0.21

Computer programs: CAD-4 EXPRESS (Enraf–Nonius, 1994), XCAD4 (Harms & Wocadlo, 1996), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEPIII (Burnett & Johnson, 1996), ORTEP-32 for Windows (Farrugia, 1998) and PLATON (Spek, 2003).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3···O2i0.821.662.4743 (15)173.7
O6—H6···O7ii0.821.702.4871 (17)159.9
N1—H1A···O1iii0.892.012.8891 (17)168.1
N1—H1B···O1W0.891.862.7475 (19)172.1
N1—H1C···O50.892.012.8907 (18)168.4
N2—H2A···O4iv0.891.982.8386 (16)162.3
N2—H2B···O1v0.891.982.8638 (17)170.2
N2—H2C···O7vi0.891.932.8000 (17)164.1
O1W—H1W···O40.858 (10)1.925 (10)2.7825 (17)178 (2)
O1W—H2W···O8vii0.852 (10)1.883 (11)2.7133 (18)165 (2)
Symmetry codes: (i) x+1/2, y+3/2, z+1/2; (ii) x+1/2, y+1/2, z+3/2; (iii) x1/2, y1/2, z+3/2; (iv) x, y1, z; (v) x, y, z+2; (vi) x+1/2, y1/2, z+3/2; (vii) x, y+1, z.
 

Acknowledgements

SN thanks the DST for the FIST programme.

References

First citationAlagar, M., Krishnakumar, R. V., Rajagopal, K., Subha Nandhini, M. & Natarajan, S. (2003b). Acta Cryst. E59, o952–o954.  Web of Science CSD CrossRef IUCr Journals Google Scholar
First citationAlagar, M., Krishnakumar, R. V., Subha Nandhini, M. & Natarajan, S. (2003a). Acta Cryst. E59, o857–o859.  Web of Science CSD CrossRef IUCr Journals Google Scholar
First citationBernstein, J., Etter, M. C. & Leiserowitz, L. (1994). Structure Correlation, Vol. 2, edited by H.-B. Bürgi & J. D. Dunitz, pp. 431–507. New York: VCH.  Google Scholar
First citationBurnett, M. N. & Johnson, C. K. (1996). ORTEPIII. Report ORNL-6895. Oak Ridge National Laboratory, Tennessee, USA.  Google Scholar
First citationEnraf–Nonius (1994). CAD-4 EXPRESS. Enraf–Nonius, Delft, The Netherlands.  Google Scholar
First citationEtter, M. C. (1990). Acc. Chem. Res. 23, 120–126.  CrossRef CAS Web of Science Google Scholar
First citationFarrugia, L. J. (1997). J. Appl. Cryst. 30, 565.  CrossRef IUCr Journals Google Scholar
First citationHarms, K. & Wocadlo, S. (1996). XCAD4. University of Marburg, Germany.  Google Scholar
First citationKvick, Å., Canning, W. M., Koetzle, T. F. & Williams, G. J. B. (1980). Acta Cryst. B36, 115–120.  CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
First citationNorth, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351–359.  CrossRef IUCr Journals Web of Science Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationSpek, A. L. (2003). J. Appl. Cryst. 36, 7–13.  Web of Science CrossRef CAS IUCr Journals Google Scholar

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