PMCCPMCCPMCC

Search tips
Search criteria 

Advanced

 
Logo of actaeInternational Union of Crystallographysearchopen accessarticle submissionjournal home pagethis article
 
Acta Crystallogr Sect E Struct Rep Online. 2010 May 1; 66(Pt 5): o1202–o1203.
Published online 2010 April 28. doi:  10.1107/S1600536810014959
PMCID: PMC2979176

(E)-N′-(2,4,6-Trihydroxy­benzyl­idene)isonicotinohydrazide sesquihydrate

Abstract

In the title compound, C13H11N3O4·1.5H2O, the pyridine ring forms a dihedral angle of 1.50 (6)° with the benzene ring. An intra­molecular O—H(...)N hydrogen bond forms a six-membered ring with an S(6) ring motif. In the crystal structure, one water mol­ecule is disordered over two positions around an inversion centre with site-occupancy factors of 0.5. Inter­molecular O—H(...)N, O—H(...)O, N—H(...)O and C—H(...)O hydrogen bonds consolidate the structure into a three dimensional network. A π–π stacking inter­action with a centroid–centroid distance of 3.5949 (7) Å is also present.

Related literature

For biological applications of isoniazid derivatives, see: Janin (2007 [triangle]); Maccari et al. (2005 [triangle]); Slayden & Barry (2000 [triangle]). For the biological activity of Schiff bases, see: Kahwa et al. (1986 [triangle]). For related structures, see: Naveenkumar et al. (2009 [triangle]); Naveenkumar, Sadikun, Ibrahim, Quah & Fun (2010 [triangle]); Naveenkumar, Sadikun, Ibrahim, Yeap & Fun (2010 [triangle]); Shi (2005 [triangle]). For hydrogen-bond motifs, see: Bernstein et al. (1995 [triangle]). For bond-length data, see: Allen et al. (1987 [triangle]). For the synthesis, see: Lourenco et al. (2008 [triangle]). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-66-o1202-scheme1.jpg

Experimental

Crystal data

  • C13H11N3O4·1.5H2O
  • M r = 300.27
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-66-o1202-efi1.jpg
  • a = 8.4639 (1) Å
  • b = 13.2279 (2) Å
  • c = 13.4363 (2) Å
  • β = 120.037 (1)°
  • V = 1302.30 (3) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.12 mm−1
  • T = 100 K
  • 0.48 × 0.46 × 0.19 mm

Data collection

  • Bruker SMART APEXII CCD area-detector diffractometer
  • Absorption correction: multi-scan (SADABS; Bruker, 2009 [triangle]) T min = 0.944, T max = 0.977
  • 14912 measured reflections
  • 3795 independent reflections
  • 3090 reflections with I > 2σ(I)
  • R int = 0.025

Refinement

  • R[F 2 > 2σ(F 2)] = 0.045
  • wR(F 2) = 0.139
  • S = 1.05
  • 3795 reflections
  • 244 parameters
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 0.38 e Å−3
  • Δρmin = −0.38 e Å−3

Data collection: APEX2 (Bruker, 2009 [triangle]); cell refinement: SAINT (Bruker, 2009 [triangle]); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 [triangle]).

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810014959/is2532sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810014959/is2532Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

This research was supported by Universiti Sains Malaysia (USM) under the University Research Grant (1001/PFARMASI/815005). HKF and WSL thank USM for the Research University Golden Goose Grant (1001/PFIZIK/811012). HSNK and WSL are grateful for the award of USM fellowships for financial assistance.

supplementary crystallographic information

Comment

In the search of new compounds, isoniazid derivatives have been found to possess potential tuberculostatic activity (Janin, 2007; Maccari et al., 2005; Slayden & Barry, 2000). Schiff bases have attracted much attention because of their biological activity (Kahwa et al., 1986). As a part of a current work of synthesis of (E)-N'-(substituted-benzylidene)isonicotinohydrazide derivatives, in this paper we present the crystal structure of the title compound.

The asymmetric unit of the title compound (Fig. 1), contains one (E)-N'-(2,4,6-trihydroxybenzylidene) isonicotinohydrazide and one and a half water molecules. The partially-occupied water molecule (O2W, H1W2, H2W2) is disordered across a crystallographic inversion center. The pyridine ring (C9–C11/N3/C12/C13) is essentially planar with a maximum deviation of 0.006 (1) Å at atom C9 and forms a dihedral angle of 1.51 (6)° with the benzene ring (C1–C6). An intramolecular O1—H1O1···N1 hydrogen bond forms a six-membered ring with an S(6) ring motif (Bernstein et al., 1995). The bond lengths are within normal values (Allen et al., 1987) and are comparable to those observed for closely related structures (Naveenkumar et al., 2009; Naveenkumar, Sadikun, Ibrahim, Quah & Fun, 2010; Naveenkumar, Sadikun, Ibrahim, Yeap & Fun, 2010; Shi, 2005).

In the crystal packing (Fig. 2), intermolecular O1W—H1W1···O4, O1W—H2W1···O2, O2W—H1W2···O4, O2W—H2W2···O4, N2—H1N2···O1W, O2—H1O2···N3, O3—H1O3···O1, O3—H1O3···O2W, C4—H4A···O2W, C7—H7A···O1W and C10—H10A···O1W hydrogen bonds (Table 1) consolidate the structure into a three dimensional network. The crystal structure is further stabilized by π–π stacking interactions involving the pyridine (Cg1) and benzene (Cg2) rings with a centroid–centroid distance of 3.5949 (7) Å (symmetry code = -1+x, y, z).

Experimental

The isoniazid derivative was prepared following the procedure by Lourenco et al. (2008). (E)-N'-(2,4,6-trihydroxybenzylidene)isonicotinohydrazide hydrate was prepared by reaction between the 2,4,6-trihydroxy benzaldehyde (1.0 eq) with isoniazid (1.0 eq) in ethanol/water. After stirring for 1 to 3 h at room temperature, the resulting mixture was concentrated under reduced pressure. The residue after being purified by washing with cold ethanol and ethyl ether, afforded the pure derivative. Colourless single crystals suitable for X-ray analysis were obtained by recrystallization with methanol.

Refinement

All the H atoms were located from a difference Fourier map. H1W1, H2W1, H1W2 and H2W2 were allowed to ride on their parent atoms to which they were attached, with Uiso(H) = 1.5Ueq(parent atom). The remaining H were refined freely. [O—H = 0.74 (3)–0.974 (10) Å, N—H = 0.88 (2) Å and C—H = 0.895 (19)–1.025 (18) Å]. The partially-occupied disordered water molecule was fixed at 50% occupancy in the final refinement.

Figures

Fig. 1.
The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme. Dashed line indicates the intramolecular hydrogen bond. Atom O2WA was generated by symmetry code -x+1, -y+1, -z.
Fig. 2.
The crystal packing of the title compound, viewed along the c axis. Intermolecular interactions are shown as dashed lines. H atoms not involved in the intermolecular interactions (dashed lines) have been omitted for clarity.

Crystal data

C13H11N3O4·1.5H2OF(000) = 628
Mr = 300.27Dx = 1.531 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 6535 reflections
a = 8.4639 (1) Åθ = 2.3–30.0°
b = 13.2279 (2) ŵ = 0.12 mm1
c = 13.4363 (2) ÅT = 100 K
β = 120.037 (1)°Block, brown
V = 1302.30 (3) Å30.48 × 0.46 × 0.19 mm
Z = 4

Data collection

Bruker SMART APEXII CCD area-detector diffractometer3795 independent reflections
Radiation source: fine-focus sealed tube3090 reflections with I > 2σ(I)
graphiteRint = 0.025
[var phi] and ω scansθmax = 30.0°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Bruker, 2009)h = −11→9
Tmin = 0.944, Tmax = 0.977k = −16→18
14912 measured reflectionsl = −18→18

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.045Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.139H atoms treated by a mixture of independent and constrained refinement
S = 1.05w = 1/[σ2(Fo2) + (0.086P)2 + 0.1988P] where P = (Fo2 + 2Fc2)/3
3795 reflections(Δ/σ)max = 0.001
244 parametersΔρmax = 0.38 e Å3
0 restraintsΔρmin = −0.38 e Å3

Special details

Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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)

xyzUiso*/UeqOcc. (<1)
O1W0.52172 (13)0.55973 (6)0.31668 (9)0.0306 (2)
H1W10.47840.52430.26490.046*
H2W10.51740.51820.36040.046*
O2W0.4201 (3)0.47492 (16)−0.05523 (19)0.0394 (5)0.50
H1W20.49910.5075−0.06090.059*0.50
H2W20.45650.46230.01320.059*0.50
O21.48904 (12)0.38723 (8)0.43699 (8)0.0293 (2)
O31.05057 (15)0.11707 (7)0.32046 (9)0.0306 (2)
O40.34364 (13)0.43232 (6)0.12386 (8)0.0280 (2)
C10.99950 (15)0.38970 (8)0.31225 (10)0.0201 (2)
C21.17860 (16)0.42239 (9)0.35826 (11)0.0232 (3)
C31.31689 (15)0.35102 (9)0.39166 (10)0.0209 (2)
C41.27822 (16)0.24762 (9)0.37910 (10)0.0216 (2)
C51.09857 (16)0.21590 (8)0.33268 (9)0.0193 (2)
C60.95461 (15)0.28593 (8)0.29762 (9)0.0169 (2)
C70.76941 (16)0.25025 (8)0.25037 (9)0.0188 (2)
C80.32356 (16)0.34043 (8)0.13119 (10)0.0192 (2)
C90.13728 (15)0.29709 (8)0.08915 (9)0.0168 (2)
C100.09871 (15)0.19404 (8)0.07857 (10)0.0185 (2)
C11−0.08123 (16)0.16375 (9)0.03428 (10)0.0204 (2)
C12−0.18124 (17)0.32760 (10)0.01401 (11)0.0247 (3)
C13−0.00643 (17)0.36473 (9)0.05683 (11)0.0229 (2)
N10.63769 (13)0.31447 (7)0.21721 (8)0.0204 (2)
N20.46426 (13)0.27539 (8)0.17637 (8)0.0190 (2)
N3−0.22009 (14)0.22835 (8)0.00221 (8)0.0223 (2)
O10.86777 (13)0.46088 (7)0.28226 (10)0.0343 (3)
H2A1.208 (2)0.4987 (14)0.3659 (15)0.040 (4)*
H4A1.371 (3)0.1941 (13)0.4038 (14)0.034 (4)*
H7A0.751 (2)0.1759 (14)0.2465 (14)0.038 (5)*
H10A0.191 (2)0.1392 (12)0.1008 (14)0.030 (4)*
H11A−0.111 (2)0.0914 (12)0.0240 (14)0.031 (4)*
H12A−0.275 (3)0.3696 (13)−0.0081 (15)0.038 (4)*
H13A0.015 (3)0.4324 (14)0.0657 (15)0.040 (5)*
H1N20.456 (3)0.2097 (15)0.1781 (16)0.042 (5)*
H1O10.763 (3)0.4296 (17)0.2534 (18)0.067 (7)*
H1O21.567 (4)0.3379 (19)0.460 (2)0.082 (8)*
H1O31.115 (4)0.083 (2)0.318 (2)0.091 (9)*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
O1W0.0255 (5)0.0203 (4)0.0424 (6)−0.0037 (3)0.0141 (4)−0.0053 (4)
O2W0.0331 (11)0.0438 (12)0.0422 (12)−0.0075 (9)0.0195 (10)−0.0002 (9)
O20.0091 (4)0.0362 (5)0.0367 (5)−0.0001 (3)0.0070 (4)−0.0033 (4)
O30.0389 (6)0.0164 (4)0.0446 (6)0.0028 (4)0.0270 (5)−0.0006 (4)
O40.0243 (5)0.0181 (4)0.0412 (5)−0.0043 (3)0.0159 (4)0.0009 (3)
C10.0129 (5)0.0171 (5)0.0280 (6)0.0008 (4)0.0084 (5)−0.0002 (4)
C20.0152 (5)0.0197 (5)0.0339 (6)−0.0024 (4)0.0116 (5)−0.0053 (4)
C30.0104 (5)0.0295 (6)0.0202 (5)−0.0005 (4)0.0056 (4)−0.0026 (4)
C40.0172 (6)0.0261 (6)0.0211 (5)0.0076 (4)0.0092 (5)0.0031 (4)
C50.0219 (6)0.0181 (5)0.0193 (5)0.0026 (4)0.0114 (5)0.0009 (4)
C60.0137 (5)0.0174 (5)0.0169 (5)−0.0011 (4)0.0057 (4)−0.0002 (4)
C70.0178 (5)0.0200 (5)0.0170 (5)−0.0042 (4)0.0076 (4)−0.0005 (4)
C80.0161 (5)0.0204 (5)0.0195 (5)−0.0037 (4)0.0078 (4)−0.0004 (4)
C90.0139 (5)0.0194 (5)0.0163 (5)−0.0016 (4)0.0068 (4)0.0007 (4)
C100.0132 (5)0.0200 (5)0.0201 (5)−0.0012 (4)0.0067 (4)0.0003 (4)
C110.0146 (5)0.0242 (6)0.0206 (5)−0.0041 (4)0.0073 (4)−0.0024 (4)
C120.0169 (6)0.0289 (6)0.0277 (6)0.0051 (5)0.0109 (5)0.0052 (5)
C130.0209 (6)0.0202 (5)0.0278 (6)0.0017 (4)0.0124 (5)0.0035 (4)
N10.0117 (4)0.0254 (5)0.0200 (5)−0.0053 (4)0.0048 (4)0.0015 (4)
N20.0114 (4)0.0199 (5)0.0215 (5)−0.0052 (3)0.0052 (4)0.0005 (3)
N30.0135 (4)0.0324 (5)0.0195 (5)−0.0008 (4)0.0073 (4)0.0004 (4)
O10.0166 (5)0.0175 (4)0.0695 (7)0.0026 (3)0.0221 (5)0.0055 (4)

Geometric parameters (Å, °)

O1W—H1W10.7630C6—C71.4445 (15)
O1W—H2W10.8193C7—N11.2908 (15)
O2W—O2Wi1.569 (4)C7—H7A0.994 (18)
O2W—H1W20.8308C8—N21.3428 (15)
O2W—H2W20.8278C8—C91.4973 (15)
O2—C31.3546 (14)C9—C101.3923 (15)
O2—H1O20.87 (3)C9—C131.3928 (16)
O3—C51.3544 (14)C10—C111.3881 (15)
O3—H1O30.72 (3)C10—H10A0.998 (17)
O4—C81.2380 (13)C11—N31.3380 (15)
C1—O11.3573 (14)C11—H11A0.981 (16)
C1—C21.3888 (16)C12—N31.3434 (16)
C1—C61.4115 (15)C12—C131.3817 (17)
C2—C31.3918 (16)C12—H12A0.892 (19)
C2—H2A1.033 (18)C13—H13A0.908 (18)
C3—C41.3968 (17)N1—N21.3845 (13)
C4—C51.3884 (17)N2—H1N20.87 (2)
C4—H4A0.984 (18)O1—H1O10.87 (3)
C5—C61.4107 (15)
H1W1—O1W—H2W193.9C6—C7—H7A117.1 (10)
O2Wi—O2W—H1W261.0O4—C8—N2122.62 (11)
O2Wi—O2W—H2W250.9O4—C8—C9120.43 (10)
H1W2—O2W—H2W2109.7N2—C8—C9116.95 (9)
C3—O2—H1O2110.3 (18)C10—C9—C13118.27 (11)
C5—O3—H1O3115 (2)C10—C9—C8124.21 (10)
O1—C1—C2117.87 (10)C13—C9—C8117.51 (10)
O1—C1—C6120.62 (10)C11—C10—C9118.50 (11)
C2—C1—C6121.50 (10)C11—C10—H10A116.6 (9)
C1—C2—C3119.12 (10)C9—C10—H10A124.9 (9)
C1—C2—H2A120.4 (10)N3—C11—C10123.51 (11)
C3—C2—H2A120.4 (10)N3—C11—H11A117.2 (10)
O2—C3—C2116.54 (11)C10—C11—H11A119.3 (10)
O2—C3—C4122.33 (11)N3—C12—C13122.98 (11)
C2—C3—C4121.13 (11)N3—C12—H12A116.4 (11)
C5—C4—C3119.20 (10)C13—C12—H12A120.7 (11)
C5—C4—H4A116.4 (10)C12—C13—C9119.18 (11)
C3—C4—H4A124.4 (10)C12—C13—H13A120.3 (12)
O3—C5—C4122.73 (11)C9—C13—H13A120.5 (12)
O3—C5—C6115.90 (10)C7—N1—N2116.89 (10)
C4—C5—C6121.35 (10)C8—N2—N1117.66 (10)
C5—C6—C1117.70 (10)C8—N2—H1N2126.0 (13)
C5—C6—C7119.87 (10)N1—N2—H1N2116.2 (13)
C1—C6—C7122.43 (10)C11—N3—C12117.55 (10)
N1—C7—C6119.76 (10)C1—O1—H1O1107.7 (15)
N1—C7—H7A123.1 (10)
O1—C1—C2—C3178.88 (11)C1—C6—C7—N11.73 (16)
C6—C1—C2—C3−0.63 (19)O4—C8—C9—C10170.29 (11)
C1—C2—C3—O2−179.37 (10)N2—C8—C9—C10−9.79 (16)
C1—C2—C3—C40.32 (19)O4—C8—C9—C13−8.54 (16)
O2—C3—C4—C5179.54 (10)N2—C8—C9—C13171.38 (10)
C2—C3—C4—C5−0.15 (18)C13—C9—C10—C111.26 (16)
C3—C4—C5—O3−178.26 (10)C8—C9—C10—C11−177.57 (10)
C3—C4—C5—C60.26 (17)C9—C10—C11—N3−0.76 (17)
O3—C5—C6—C1178.08 (10)N3—C12—C13—C90.27 (19)
C4—C5—C6—C1−0.54 (16)C10—C9—C13—C12−1.03 (17)
O3—C5—C6—C7−0.98 (15)C8—C9—C13—C12177.87 (10)
C4—C5—C6—C7−179.60 (10)C6—C7—N1—N2−177.87 (9)
O1—C1—C6—C5−178.77 (10)O4—C8—N2—N10.86 (17)
C2—C1—C6—C50.73 (17)C9—C8—N2—N1−179.06 (9)
O1—C1—C6—C70.27 (17)C7—N1—N2—C8−173.68 (10)
C2—C1—C6—C7179.76 (11)C10—C11—N3—C12−0.01 (17)
C5—C6—C7—N1−179.26 (10)C13—C12—N3—C110.26 (18)

Symmetry codes: (i) −x+1, −y+1, −z.

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
O1W—H1W1···O40.762.052.8134 (13)176
O1W—H2W1···O2ii0.822.092.8886 (14)165
O2W—H1W2···O4i0.832.062.864 (3)162
O2W—H2W2···O40.832.172.844 (3)139
N2—H1N2···O1Wiii0.87 (2)1.99 (2)2.8548 (13)170 (3)
O1—H1O1···N10.87 (3)1.78 (2)2.5696 (15)149 (2)
O2—H1O2···N3iv0.87 (3)1.82 (3)2.6470 (14)158 (3)
O3—H1O3···O1v0.72 (3)2.16 (3)2.7579 (15)142 (3)
O3—H1O3···O2Wvi0.72 (3)2.40 (3)2.970 (2)138 (3)
C4—H4A···O2Wvi0.984 (18)2.290 (17)3.135 (2)143.3 (14)
C7—H7A···O1Wiii0.993 (19)2.539 (19)3.3185 (16)135.2 (14)
C10—H10A···O1Wiii0.996 (18)2.355 (18)3.3063 (17)159.4 (13)

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

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: IS2532).

References

  • Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1–19.
  • Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl.34, 1555–1573.
  • Bruker (2009). APEX2, SAINT and SADABS Bruker AXS Inc., Madison, Wisconsin, USA.
  • Cosier, J. & Glazer, A. M. (1986). J. Appl. Cryst.19, 105–107.
  • Janin, Y. L. (2007). Bioorg. Med. Chem.15, 2479–2513. [PubMed]
  • Kahwa, I. A., Selbin, J., Hsieh, T. C.-Y. & Laine, R. A. (1986). Inorg. Chim. Acta, 118, 179–185.
  • Lourenco, M. C. S., Ferreira, M. L., de Souza, M. V. N., Peralta, M. A., Vasconcelos, T. R. A. & Henriques, M. G. M. O. (2008). Eur. J. Med. Chem.43, 1344–1347. [PubMed]
  • Maccari, R., Ottana, R. & Vigorita, M. G. (2005). Bioorg. Med. Chem. Lett.15, 2509–2513. [PubMed]
  • Naveenkumar, H. S., Sadikun, A., Ibrahim, P., Loh, W.-S. & Fun, H.-K. (2009). Acta Cryst. E65, o2540–o2541. [PMC free article] [PubMed]
  • Naveenkumar, H. S., Sadikun, A., Ibrahim, P., Quah, C. K. & Fun, H.-K. (2010). Acta Cryst. E66, o291. [PMC free article] [PubMed]
  • Naveenkumar, H. S., Sadikun, A., Ibrahim, P., Yeap, C. S. & Fun, H.-K. (2010). Acta Cryst. E66, o579. [PMC free article] [PubMed]
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
  • Shi, J. (2005). Acta Cryst. E61, o3933–o3934.
  • Slayden, R. A. & Barry, C. E. (2000). Microbes Infect.2, 659–669. [PubMed]
  • Spek, A. L. (2009). Acta Cryst. D65, 148–155. [PMC free article] [PubMed]

Articles from Acta Crystallographica Section E: Structure Reports Online are provided here courtesy of International Union of Crystallography