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 August 1; 66(Pt 8): o1933–o1934.
Published online 2010 July 7. doi:  10.1107/S1600536810025912
PMCID: PMC3007456

2-Amino-4-methylpyridinium 2-hy­droxy-3,5-dinitro­benzoate

Abstract

In the anion of the title mol­ecular salt, C6H9N2 +·C7H3N2O7 , the two nitro groups are twisted from the attached benzene ring with dihedral angles of 27.36 (10) and 4.86 (11)°. The anion is stabilized by an intra­molecular O—H(...)O hydrogen bond, which generates an S(6) ring motif. In the crystal, the cations and anions are linked by N—H(...)O and C—H(...)O inter­actions and are further consolidated by C—H(...)π inter­actions, to generate a three-dimensional network. A short O(...)N contact of 2.876 (2) Å also occurs.

Related literature

For substituted pyridines, see: Pozharski et al. (1997 [triangle]); Katritzky et al. (1996 [triangle]). For details of hydrogen bonding, see: Scheiner (1997 [triangle]); Jeffrey & Saenger (1991 [triangle]); Jeffrey (1997 [triangle]). For 2-amino-substituted pyridines, see: Navarro Ranninger et al. (1985 [triangle]); Luque et al. (1997 [triangle]); Qin et al. (1999 [triangle]); Ren et al. (2002 [triangle]); Rivas et al. (2003 [triangle]); Jin et al. (2001 [triangle]); Albrecht et al. (2003 [triangle]). For Lewis bases with 3,5-dinitrosalicylic acid, see: Hindawey et al. (1980 [triangle]); Issa et al. (1981 [triangle]). For hydrogen-bond motifs, see: Bernstein et al. (1995 [triangle]). For related structures, see: Quah et al. (2008a [triangle],b [triangle], 2010 [triangle]). For reference bond lengths, see: Allen et al. (1987 [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-o1933-scheme1.jpg

Experimental

Crystal data

  • C6H9N2 +·C7H3N2O7
  • M r = 336.27
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-66-o1933-efi1.jpg
  • a = 6.0111 (15) Å
  • b = 9.652 (3) Å
  • c = 24.436 (6) Å
  • β = 100.546 (7)°
  • V = 1393.8 (7) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.13 mm−1
  • T = 100 K
  • 0.48 × 0.08 × 0.06 mm

Data collection

  • Bruker SMART APEXII DUO CCD diffractometer
  • Absorption correction: multi-scan (SADABS; Bruker, 2009 [triangle]) T min = 0.939, T max = 0.992
  • 12178 measured reflections
  • 3229 independent reflections
  • 2283 reflections with I > 2σ(I)
  • R int = 0.057

Refinement

  • R[F 2 > 2σ(F 2)] = 0.047
  • wR(F 2) = 0.153
  • S = 1.03
  • 3229 reflections
  • 222 parameters
  • H-atom parameters constrained
  • Δρmax = 0.31 e Å−3
  • Δρmin = −0.44 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/S1600536810025912/hb5538sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810025912/hb5538Isup2.hkl

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

Acknowledgments

The authors thank Universiti Sains Malaysia (USM) for the Research University Golden Goose Grant (1001/PFIZIK/811012). CKQ thanks USM for the award of a USM fellowship. MH thanks USM for the award of a postdoctoral fellowship.

supplementary crystallographic information

Comment

Pyridine and its derivatives play an important role in heterocyclic chemistry (Pozharski et al., 1997; Katritzky et al., 1996). They are often involved in hydrogen-bond interactions (Jeffrey & Saenger, 1991; Jeffrey, 1997; Scheiner, 1997). There are numerous examples of 2-amino-substituted pyridine compounds in which the 2-aminopyridines act as neutral ligands (Navarro Ranninger et al., 1985; Qin et al., 1999; Ren et al., 2002; Rivas et al., 2003) or as protonated cations (Luque et al., 1997; Jin et al., 2001; Albrecht et al., 2003). The nitrosubstituted aromatic acid 3,5-dinitro salicylic acid (DNSA) has proven potential for formation of proton-transfer compounds, particularly because of its acid strength (pKa = 2.18), its interactive ortho-related phenolic substituent group together with the nitro substituents which have potential for both π···π interactions as well as hydrogen-bonding interactions. A large number of both neutral and proton-transfer compounds of Lewis bases with DNSA, together with their IR spectra have been reported (Hindawey et al., 1980; Issa et al., 1981) in the literature. Since our aim is to study some interesting hydrogen bonding interactions, the crystal structure of the title compound is presented here.

The asymmetric unit of the title compound contains one 2-amino-4-methyl-pyridinium cation and one 3,5-dinitrosalicylate anion. A proton transfer from the carboxyl group of 3,5-dinitrosalicylic acid to atom N1 of 2-amino-4-methylpyridinium resulted in the formation of ions. The bond lengths (Allen et al., 1987) and angles in the title compound (Fig. 1) are within normal ranges and comparable with the related structures (Quah et al., 2010, 2008a, b). In the 3,5-dinitrosalicylate anion, the two nitro groups are twisted slightly from the attached ring. The dihedral angles between benzene ring (C8—C12) and the two nitro groups (O2/O3/N3/C8 and O4/O5/N4/C10) are 27.36 (10) and 4.86 (11)°, respectively. The 2-amino-4-methylpyridinium cation is essentially planar, with the maximum deviation of 0.012 (2) Å for atoms N2 and C4; and make a dihedral angle of 7.16 (8)° with the benzene ring of 3,5-dinitrosalicylate anion. The molecular structure is stabilized by an intramolecular O1–H1O1···O7 hydrogen bond which generates an S(6) ring motif (Bernstein et al., 1995). There is a short O3···N3 contact (symmetry code: 2 - x, -y, 2 - z) with distance = 2.876 (2) Å which is shorter than the sum of van der Waals radii of the oxygen and nitrogen atoms.

In the crystal packing, the cations and anions are linked to form a three-dimensional network (Fig. 2) by intermolecular N1–H1N1···O6, N2–H1N2···O7, N2–H2N2···O1, N2–H2N2···O2, C2–H2A···O2, C4–H4A···O6, C5–H5A···O5 and C9–H9A···O3 interactions and are further consolidated by C–H···π (Table 1) interactions.

Experimental

A hot methanol solution (20 ml) of 2-amino-4-methylpyridine (27 mg, Aldrich) and 3,5-dinitrosalicylic acid (57 mg, Merck) were mixed and warmed over a heating hotplate magnetic stirrer hotplate for a few minutes. The resulting solution was allowed to cool slowly to room temperature and yellow needles of (I) appeared after a few days.

Refinement

O– and N-bound H atoms were located in a difference Fourier map and refined freely [O1—H1O1 = 0.9856 Å, N—H = 0.9478 - 0.9833 Å]. The remaining H atoms were positioned geometrically and refined using a riding model with C—H = 0.93–0.98 Å and Uiso(H) = 1.2 or 1.5 Ueq(C). A rotating-group model was applied for the methyl groups. The highest residual electron density peak is located at 0.79 Å from H6B and the deepest hole is located at 0.70 Å from N4.

Figures

Fig. 1.
The molecular structure of (I) showing 50% probability displacement ellipsoids for non-H atoms. The intramolecular hydrogen bond is shown in dashed line.
Fig. 2.
The crystal structure of (I) viewed along the a axis. H atoms not involved in intermolecular interactions (dashed lines) have been omitted for clarity.

Crystal data

C6H9N2+·C7H3N2O7F(000) = 696
Mr = 336.27Dx = 1.602 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 2122 reflections
a = 6.0111 (15) Åθ = 2.7–26.4°
b = 9.652 (3) ŵ = 0.13 mm1
c = 24.436 (6) ÅT = 100 K
β = 100.546 (7)°Needle, yellow
V = 1393.8 (7) Å30.48 × 0.08 × 0.06 mm
Z = 4

Data collection

Bruker SMART APEXII DUO CCD diffractometer3229 independent reflections
Radiation source: fine-focus sealed tube2283 reflections with I > 2σ(I)
graphiteRint = 0.057
[var phi] and ω scansθmax = 27.6°, θmin = 1.7°
Absorption correction: multi-scan (SADABS; Bruker, 2009)h = −7→7
Tmin = 0.939, Tmax = 0.992k = −12→12
12178 measured reflectionsl = −31→26

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)] = 0.047Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.153H-atom parameters constrained
S = 1.02w = 1/[σ2(Fo2) + (0.0909P)2] where P = (Fo2 + 2Fc2)/3
3229 reflections(Δ/σ)max = 0.001
222 parametersΔρmax = 0.31 e Å3
0 restraintsΔρmin = −0.44 e Å3

Special details

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

xyzUiso*/Ueq
N10.2405 (3)0.80105 (17)0.83755 (7)0.0179 (4)
H1N10.13250.73480.84550.034 (7)*
N20.5190 (3)0.75204 (18)0.91264 (7)0.0220 (4)
H1N20.41460.68100.92190.052 (9)*
H2N20.66550.76640.93400.063 (10)*
C10.4517 (3)0.8236 (2)0.86605 (8)0.0170 (4)
C20.5856 (3)0.9234 (2)0.84489 (9)0.0187 (4)
H2A0.73210.94080.86360.022*
C30.5022 (3)0.9946 (2)0.79722 (9)0.0187 (4)
C40.2784 (3)0.9680 (2)0.76912 (9)0.0199 (4)
H4A0.21791.01630.73690.024*
C50.1541 (3)0.8708 (2)0.79013 (9)0.0192 (4)
H5A0.00760.85180.77180.023*
C60.6432 (4)1.1006 (2)0.77401 (9)0.0231 (5)
H6A0.77901.11810.80060.035*
H6B0.55871.18500.76660.035*
H6C0.68201.06620.74010.035*
O11.1381 (2)0.34244 (14)0.99102 (6)0.0198 (3)
H1O11.23040.41810.97980.119 (16)*
O20.9779 (2)0.16274 (14)1.05842 (6)0.0218 (4)
O30.7607 (2)0.00824 (15)1.01170 (7)0.0242 (4)
O40.1674 (2)0.17877 (16)0.86962 (7)0.0264 (4)
O50.2470 (3)0.33999 (17)0.81463 (7)0.0321 (4)
O60.9513 (2)0.60237 (15)0.85954 (6)0.0219 (3)
O71.2134 (2)0.53070 (14)0.93122 (6)0.0206 (3)
N30.8463 (3)0.12385 (17)1.01644 (7)0.0176 (4)
N40.2953 (3)0.26704 (18)0.85650 (7)0.0212 (4)
C70.9355 (3)0.32562 (19)0.96014 (9)0.0159 (4)
C80.7863 (3)0.2196 (2)0.97011 (8)0.0169 (4)
C90.5784 (3)0.1992 (2)0.93658 (9)0.0172 (4)
H9A0.48370.12790.94380.021*
C100.5143 (3)0.2876 (2)0.89190 (8)0.0176 (4)
C110.6536 (3)0.3935 (2)0.88017 (9)0.0179 (4)
H11A0.60660.45150.84990.022*
C120.8626 (3)0.4127 (2)0.91368 (8)0.0164 (4)
C131.0164 (3)0.5246 (2)0.89969 (9)0.0175 (4)

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
N10.0180 (8)0.0159 (8)0.0193 (9)−0.0010 (6)0.0019 (7)−0.0004 (7)
N20.0196 (8)0.0221 (9)0.0226 (10)−0.0029 (7)−0.0002 (7)0.0060 (7)
C10.0167 (9)0.0148 (9)0.0197 (11)0.0023 (7)0.0034 (8)−0.0016 (8)
C20.0175 (9)0.0153 (9)0.0229 (11)0.0004 (7)0.0029 (8)0.0005 (8)
C30.0221 (10)0.0133 (9)0.0218 (11)0.0011 (8)0.0066 (8)−0.0027 (8)
C40.0242 (10)0.0159 (10)0.0195 (11)0.0034 (8)0.0039 (8)0.0006 (8)
C50.0181 (9)0.0189 (10)0.0195 (11)0.0037 (8)0.0008 (8)−0.0012 (8)
C60.0278 (11)0.0168 (10)0.0256 (12)0.0000 (8)0.0069 (9)0.0029 (9)
O10.0170 (7)0.0188 (7)0.0215 (8)−0.0024 (6)−0.0014 (6)0.0008 (6)
O20.0205 (7)0.0234 (8)0.0200 (8)−0.0013 (6)−0.0001 (6)−0.0001 (6)
O30.0203 (7)0.0164 (7)0.0353 (9)−0.0040 (6)0.0033 (6)0.0049 (7)
O40.0200 (7)0.0276 (8)0.0309 (9)−0.0066 (6)0.0028 (6)−0.0028 (7)
O50.0303 (9)0.0338 (9)0.0272 (9)−0.0016 (7)−0.0084 (7)0.0069 (7)
O60.0245 (8)0.0183 (7)0.0216 (8)−0.0039 (6)0.0006 (6)0.0028 (6)
O70.0182 (7)0.0181 (7)0.0244 (8)−0.0021 (5)0.0009 (6)0.0025 (6)
N30.0152 (8)0.0162 (8)0.0218 (9)−0.0002 (6)0.0042 (7)0.0022 (7)
N40.0187 (8)0.0203 (9)0.0238 (10)0.0003 (7)0.0016 (7)−0.0026 (8)
C70.0144 (9)0.0144 (9)0.0186 (10)0.0010 (7)0.0021 (8)−0.0025 (8)
C80.0186 (9)0.0139 (9)0.0177 (10)0.0021 (7)0.0020 (8)−0.0006 (8)
C90.0169 (9)0.0142 (9)0.0207 (11)−0.0004 (7)0.0037 (8)−0.0017 (8)
C100.0161 (9)0.0162 (9)0.0191 (11)0.0008 (7)−0.0007 (8)−0.0028 (8)
C110.0198 (9)0.0159 (9)0.0181 (10)0.0043 (8)0.0035 (8)0.0000 (8)
C120.0164 (9)0.0132 (9)0.0199 (11)0.0005 (7)0.0038 (8)−0.0018 (8)
C130.0189 (9)0.0144 (9)0.0193 (11)−0.0002 (7)0.0040 (8)−0.0001 (8)

Geometric parameters (Å, °)

N1—C11.349 (2)O1—H1O10.9856
N1—C51.359 (3)O2—N31.234 (2)
N1—H1N10.9560O3—N31.226 (2)
N2—C11.330 (3)O4—N41.229 (2)
N2—H1N20.9833O5—N41.232 (2)
N2—H2N20.9478O6—C131.241 (2)
C1—C21.413 (3)O7—C131.291 (2)
C2—C31.366 (3)N3—C81.455 (3)
C2—H2A0.9300N4—C101.450 (2)
C3—C41.417 (3)C7—C81.411 (3)
C3—C61.504 (3)C7—C121.416 (3)
C4—C51.358 (3)C8—C91.377 (3)
C4—H4A0.9300C9—C101.383 (3)
C5—H5A0.9300C9—H9A0.9300
C6—H6A0.9600C10—C111.385 (3)
C6—H6B0.9600C11—C121.381 (3)
C6—H6C0.9600C11—H11A0.9300
O1—C71.320 (2)C12—C131.501 (3)
C1—N1—C5122.49 (18)O3—N3—O2123.37 (17)
C1—N1—H1N1127.8O3—N3—C8117.70 (16)
C5—N1—H1N1109.6O2—N3—C8118.93 (16)
C1—N2—H1N2116.8O4—N4—O5123.33 (18)
C1—N2—H2N2120.1O4—N4—C10118.81 (17)
H1N2—N2—H2N2122.9O5—N4—C10117.86 (17)
N2—C1—N1117.93 (18)O1—C7—C8122.67 (18)
N2—C1—C2124.26 (18)O1—C7—C12120.20 (18)
N1—C1—C2117.80 (18)C8—C7—C12117.10 (17)
C3—C2—C1120.67 (19)C9—C8—C7122.50 (19)
C3—C2—H2A119.7C9—C8—N3116.15 (17)
C1—C2—H2A119.7C7—C8—N3121.34 (17)
C2—C3—C4119.33 (19)C8—C9—C10118.22 (19)
C2—C3—C6121.29 (19)C8—C9—H9A120.9
C4—C3—C6119.38 (18)C10—C9—H9A120.9
C5—C4—C3118.77 (19)C9—C10—C11121.79 (18)
C5—C4—H4A120.6C9—C10—N4118.56 (18)
C3—C4—H4A120.6C11—C10—N4119.65 (18)
C4—C5—N1120.93 (18)C12—C11—C10119.70 (19)
C4—C5—H5A119.5C12—C11—H11A120.2
N1—C5—H5A119.5C10—C11—H11A120.2
C3—C6—H6A109.5C11—C12—C7120.68 (18)
C3—C6—H6B109.5C11—C12—C13119.52 (18)
H6A—C6—H6B109.5C7—C12—C13119.77 (17)
C3—C6—H6C109.5O6—C13—O7124.53 (18)
H6A—C6—H6C109.5O6—C13—C12119.82 (18)
H6B—C6—H6C109.5O7—C13—C12115.65 (17)
C7—O1—H1O1116.1
C5—N1—C1—N2178.61 (18)N3—C8—C9—C10−179.85 (17)
C5—N1—C1—C2−0.4 (3)C8—C9—C10—C110.6 (3)
N2—C1—C2—C3−178.7 (2)C8—C9—C10—N4−179.81 (17)
N1—C1—C2—C30.2 (3)O4—N4—C10—C95.3 (3)
C1—C2—C3—C40.3 (3)O5—N4—C10—C9−174.93 (18)
C1—C2—C3—C6−179.65 (19)O4—N4—C10—C11−175.09 (18)
C2—C3—C4—C5−0.8 (3)O5—N4—C10—C114.7 (3)
C6—C3—C4—C5179.17 (19)C9—C10—C11—C120.0 (3)
C3—C4—C5—N10.7 (3)N4—C10—C11—C12−179.65 (18)
C1—N1—C5—C4−0.1 (3)C10—C11—C12—C7−0.4 (3)
O1—C7—C8—C9−177.55 (19)C10—C11—C12—C13177.93 (18)
C12—C7—C8—C90.3 (3)O1—C7—C12—C11178.16 (18)
O1—C7—C8—N31.6 (3)C8—C7—C12—C110.3 (3)
C12—C7—C8—N3179.39 (17)O1—C7—C12—C13−0.2 (3)
O3—N3—C8—C926.5 (3)C8—C7—C12—C13−178.04 (17)
O2—N3—C8—C9−152.80 (18)C11—C12—C13—O62.8 (3)
O3—N3—C8—C7−152.64 (18)C7—C12—C13—O6−178.83 (19)
O2—N3—C8—C728.0 (3)C11—C12—C13—O7−176.29 (18)
C7—C8—C9—C10−0.7 (3)C7—C12—C13—O72.1 (3)

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
N1—H1N1···O6i0.961.752.707 (2)175
N2—H1N2···O7i0.981.932.907 (2)173
N2—H2N2···O1ii0.952.252.974 (2)133
N2—H2N2···O2ii0.952.233.089 (2)151
O1—H1O1···O70.991.602.426 (2)138
C2—H2A···O2ii0.932.543.300 (3)139
C4—H4A···O6iii0.932.533.447 (3)169
C5—H5A···O5iv0.932.373.193 (3)147
C9—H9A···O3v0.932.383.272 (3)161
C6—H6B···Cg1iii0.962.993.623 (2)12

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

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB5538).

References

  • Albrecht, A. S., Landee, C. P. & Turnbull, M. M. (2003). J. Chem. Crystallogr.33, 269–276.
  • 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.
  • Hindawey, A. M., Nasser, A. M. G., Issa, R. M. & Issa, Y. M. (1980). Indian J. Chem. Sect. A, 19, 615–619.
  • Issa, Y. M., Hindawey, A. M., El-Kholy, A. E. & Issa, R. M. (1981). Gazz. Chim. Ital.111, 27–33.
  • Jeffrey, G. A. (1997). An Introduction to Hydrogen Bonding Oxford University Press.
  • Jeffrey, G. A. & Saenger, W. (1991). Hydrogen Bonding in Biological Structures Berlin: Springer.
  • Jin, Z. M., Pan, Y. J., Hu, M. L. & Shen, L. (2001). J. Chem. Crystallogr.31, 191–195.
  • Katritzky, A. R., Rees, C. W. & Scriven, E. F. V. (1996). Comprehensive Heterocyclic Chemistry II Oxford: Pergamon Press.
  • Luque, A., Sertucha, J., Lezama, L., Rojo, T. & Roman, P. (1997). J. Chem. Soc. Dalton Trans. pp. 847–854.
  • Navarro Ranninger, M.-C., Martínez-Carrera, S. & García-Blanco, S. (1985). Acta Cryst. C41, 21–22.
  • Pozharski, A. F., Soldatenkov, A. T. & Katritzky, A. R. (1997). Heterocycles in Life and Society New York: Wiley.
  • Qin, J. G., Su, N. B., Dai, C. Y., Yang, C. L., Liu, D. Y., Day, M. W., Wu, B. C. & Chen, C. T. (1999). Polyhedron, 18, 3461–3464.
  • Quah, C. K., Hemamalini, M. & Fun, H.-K. (2010). Acta Cryst. E66, o1932. [PMC free article] [PubMed]
  • Quah, C. K., Jebas, S. R. & Fun, H.-K. (2008a). Acta Cryst. E64, o1878–o1879. [PMC free article] [PubMed]
  • Quah, C. K., Jebas, S. R. & Fun, H.-K. (2008b). Acta Cryst. E64, o2230. [PMC free article] [PubMed]
  • Ren, P., Su, N. B., Qin, J. G., Day, M. W. & Chen, C. T. (2002). Chin. J. Struct. Chem.21, 38–41.
  • Rivas, J. C. M., Salvagni, E., Rosales, R. T. M. & Parsons, S. (2003). Dalton Trans. pp. 3339–3349.
  • Scheiner, S. (1997). Hydrogen Bonding: a Theoretical Perspective Oxford University Press.
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [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