Literature DB >> 31391970

Crystal structure, Hirshfeld surface analysis and HOMO-LUMO analysis of (E)-N'-(3-hy-droxy-4-meth-oxy-benzyl-idene)nicotinohydrazide monohydrate.

Palaniyappan Sivajeyanthi1, Bellarmin Edison1, Kasthuri Balasubramani1, Ganesan Premkumar2, Toka Swu2.   

Abstract

The mol-ecule of the title class="Chemical">Schiff base compound, C14<class="Chemical">span class="Species">H13N3O3·H2O, displays a trans configuration with respect to the C=N bond. The dihedral angle between the benzene and pyridine rings is 29.63 (7)°. The crystal structure features inter-molecular N-H⋯O, C-H⋯O, O-H⋯O and O-H⋯N hydrogen-bonding inter-actions, leading to the formation of a supramolecular framework. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H⋯H (37.0%), O⋯H/H⋯O (23.7%)), C⋯H/H⋯C (17.6%) and N⋯H/H⋯N (11.9%) inter-actions. The title compound has also been characterized by frontier mol-ecular orbital analysis.

Entities:  

Keywords:  Hirshfeld surface analysis; Schiff base; crystal structure; inter­molecular inter­actions

Year:  2019        PMID: 31391970      PMCID: PMC6658940          DOI: 10.1107/S2056989019006492

Source DB:  PubMed          Journal:  Acta Crystallogr E Crystallogr Commun


Chemical context

class="Chemical">Schiff bases are nitro­gen-containing compounds that were first obtained by the condensation reaction of <class="Chemical">span class="Chemical">aromatic amines and aldehydes (Schiff, 1864 ▸). A wide range of these compounds, with the general formula RHC=NR 1 (R and R 1 can be alkyl, aryl, cyclo­alkyl or heterocyclic groups) have been synthesized. Schiff bases are of great importance in the field of coordination chemistry because they are able to form stable complexes with metal ions (Souza et al., 1985 ▸). The chemical and biological significance of Schiff bases can be attributed to the presence of a lone electron pair in the sp 2-hybridized orbital of the nitro­gen atom of the azomethine group (Singh et al., 1975 ▸). These compounds are used in the fields of organic synthesis, chemical catalysis, medicine and pharmacy, as well as other new technologies (Tanaka et al., 2010 ▸). Schiff bases are also used as probes for investigating the structure of DNA (Tiwari et al., 2011 ▸) and have gained special attention in pharmacophore research and in the development of several bioactive lead mol­ecules (Muralisankar et al., 2016 ▸). Schiff bases showing photochromic and thermochromic properties have been used in information storage, electronic display systems, optical switching devices and ophthalmic glasses (Amimoto et al., 2005 ▸). As a further contribution to this field of research, we report herein the crystal structure of the title compound, (E)-N′-(3-hy­droxy-4-meth­oxy­benzyl­idene)nicotinohydrazide monohydrate.

Structural commentary

The asymmetric unit of the title compound (Fig. 1 ▸) consists of one independent class="Chemical">Schiff base mol­ecule diclass="Chemical">splaying a trans configuration with reclass="Chemical">spect to the C=N bond and a <class="Chemical">span class="Chemical">water mol­ecule. All the bond lengths are within the normal ranges (Allen et al., 1987 ▸). The C7=N3 bond length of 1.274 (2) Å is consistent with a double-bond character. The C6—N2 and N2—N3 bond lengths of 1.343 (2) and 1.3866 (16) Å, respectively, are comparable to those observed in related compounds (Sivajeyanthi et al., 2017 ▸; Balasubramani et al., 2018 ▸). The O1/C6/N2/N3/C7 core is almost planar (r.m.s. deviation = 0.022 Å) and forms dihedral angles of 20.75 (7) and 8.93 (5)°, respectively, with the pyridine and benzene rings.
Figure 1

The asymmetric unit of the title compound with displacement ellipsoids drawn at the 50% probability level..

Supra­molecular features

In the crystal of the title compound (Fig. 2 ▸), the class="Chemical">water mol­ecule inter­acts with three neighbouring <class="Chemical">span class="Chemical">nicotinohydrazide mol­ecules with the O4 water oxygen atom acting as a hydrogen acceptor through N2—H2N⋯O4 and C2—H2⋯O4 hydrogen bonds (Table 1 ▸), and both water H atoms acting as bifurcated donors to form rings of (5) graph-set motif. The nicotinohydrazide mol­ecules are further linked by O—H⋯N and C—H⋯O hydrogen bonds to form a three-dimensional network.
Figure 2

Crystal packing of the title compound, viewed down the a axis. Hydrogen bonds are shown as dashed lines.

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A D—HH⋯A DA D—H⋯A
O4—H4WA⋯O2i 0.852.283.0483 (17)150
O4—H4WA⋯O3i 0.852.493.2011 (16)141
O4—H4WB⋯O1ii 0.852.082.8429 (19)150
O4—H4WB⋯N3ii 0.852.503.1875 (18)139
N2—H2N⋯O40.862.062.8889 (18)162
O2—H10⋯N1iii 0.821.962.7411 (17)159
C2—H2⋯O40.932.253.129 (2)156
C4—H4⋯O3iv 0.932.453.347 (2)163

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) .

Hirshfeld surface analysis

The three-dimensional d norm surface is a useful tool for analy<span class="Gene">sing and visualizing the inter­molecular inter­actions, as it shows negative or positive values depending on whether an inter­molecular contact is shorter or longer, reclass="Chemical">spectively, than the sum of the van der Waals radii (Spackman & Jayatilaka, 2009 ▸; McKinnon et al., 2007 ▸). The d norm surface of the title compound is shown in Fig. 3 ▸. The red points, which represent closer contacts and negative d norm values, correclass="Chemical">spond to the N—H⋯O, O—H⋯O, O—H⋯N and C—H⋯O inter­actions. Two-dimensional fingerprint plots from the Hirshfeld surface analysis (Fig. 4 ▸) provide information about the inter­molecular contacts and their percentage distributions on the Hirshfeld surface. The percentage of H⋯H contacts as closest contacts on the Hirshfeld surfaces is a universally applicable measure of the crystal lattice energy and can be used as a reference for the importance of other types of contacts. In the title compound, the percentage contributions of the various inter­molecular contacts to the total Hirshfeld surface are as follows: H⋯H (37.0%), C⋯H/H⋯C (17.6%), N⋯H/H⋯N (11.9%), C⋯N/N⋯C (3.7%), O⋯H/H⋯O (23.7%), C⋯C (4.5%), N⋯N (0.3%) and O⋯C/C⋯O (1.2%).
Figure 3

Hirshfeld surfaces of the title compound mapped over d norm.

Figure 4

Two-dimensional fingerprint plots for the title compound and relative contributions of the atom pairs to the Hirshfeld surface.

Frontier mol­ecular orbitals

The HOMO (highest occupied mol­ecular orbital) acts as an electron class="Species">donor and LUMO (lowest occupied mol­ecular orbital) acts as an electron acceptor. If the HOMO–LUMO energy gap is small, then the mol­ecule is highly polarizable and has high chemical reactivity. The energy levels for the title compound were computed by DFT-B3LYP/6-311G++(d,p) method (Sivajeyanthi et al., 2017 ▸). The energy levels, energy gaps, chemical <class="Chemical">span class="Disease">hardness, chemical potential, electronegativity and electrophilicity index are given in Table 2 ▸. As shown in Fig. 5 ▸, the frontier mol­ecular orbital LUMO is located over the whole of the mol­ecule. The energy gap of the mol­ecule clearly shows the charge-transfer inter­action involving donor and acceptor groups. If the HOMO–LUMO energy gap is small, then the mol­ecule is defined as soft, i.e. it is highly polarizable and has high chemical reactivity, whereas if the energy gap is large the mol­ecule can be defined as hard. Therefore from Table 2 ▸ we conclude that the title mol­ecule belongs to the really hard materials.
Table 2

Calculated frontier mol­ecular orbital energies (eV)

FMOEnergy
E HOMO −5.7171
E LUMO −1.8174
E HOMO−1 −6.5750
E LUMO+1 −1.2770
(E HOMO − E LUMO) gap3.8997
(E HOMO−1 − E LUMO+1) gap5.2980
Chemical hardness1.9498
Chemical potential3.7672
Electronegativity−3.7672
Electrophilicity index3.6393
Figure 5

Mol­ecular orbital energy levels of the title compound.

Database survey

A search of the Cambridge Structural Database (Version 5.40, update November 2018; Groom et al., 2016 ▸) for uncoordinated N′-(benzyl­idene)class="Chemical">nicotinohydrazide derivatives O-substituted at the 3,4 positions of the <class="Chemical">span class="Chemical">benzene ring yielded three hits, namely N′-(1,3-benzodioxol-5-yl­methyl­ene)nicotinohydrazide monohydrate (refcode BUDNIY; Bao et al., 2009 ▸), N′-(3,4-di­meth­oxy­benzyl­idene)nicotinohydrazide monohydrate (XODZOH; Novina et al., 2014 ▸) and the isomer N′-(4-hy­droxy-3-meth­oxy­benzyl­idene)nicotinohydrazide monohydrate (SEZREV; Shi et al., 2007 ▸). The conformation of the last mol­ecule differs from the title compound mainly in the relative orientation of the pyridine ring with respect to the carbonyl group, as indicated by the value of 158.03 (15)° for the O1—C6—C1—C2 torsion angle in the title compound and of 10.2 (3)° for the corresponding angle in SEZREV. Moreover, in SEZREV the water mol­ecule acts as acceptor of three H atoms from the same nicotinohydrazide mol­ecule and as donor in two O—H⋯O hydrogen bonds.

Synthesis and crystallization

The title compound was synthesized by the reaction of a 1:1 molar ratio mixture of a hot ethano­lic solution (20 ml) of class="Chemical">nicotinohydrazide (0.137 mg) and a hot ethano­lic solution of 3-hy­droxy-4-meth­oxy benzaldehyde (0.152 mg). After refluxing for 8 h, the solution was then cooled and kept at room temperature to precipitate. Colourless block-shaped crystals suitable for X-ray analysis were obtained by slow evaporation of a 10 ml <class="Chemical">span class="Chemical">dimethyl sulfoxide/water (1:1 v/v) solution.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. <span class="Disease">H atoms were positioned geom­etrically (O—H = 0.82 Å, N–H = 0.86 Å, C—H = 0.93–0.96 Å) and refined as riding with U iso(H) = 1.2U eq(C,N) or 1.5U eq(O, C-meth­yl)
Table 3

Experimental details

Crystal data
Chemical formulaC14H13N3O3·H2O
M r 289.29
Crystal system, space groupMonoclinic, P21/c
Temperature (K)295
a, b, c (Å)7.1153 (4), 11.0075 (6), 18.2771 (10)
β (°)105.766 (5)
V3)1377.64 (14)
Z 4
Radiation typeMo Kα
μ (mm−1)0.10
Crystal size (mm)0.30 × 0.25 × 0.18
 
Data collection
DiffractometerAgilent Xcalibur Eos
Absorption correctionMulti-scan (CrysAlis PRO; Agilent, 2012)
T min, T max 0.969, 0.981
No. of measured, independent and observed [I > 2σ(I)] reflections8396, 2549, 2027
R int 0.027
(sin θ/λ)max−1)0.606
 
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S 0.036, 0.101, 1.04
No. of reflections2549
No. of parameters192
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å−3)0.16, −0.13

Computer programs: CrysAlis PRO (Agilent, 2012 ▸), SHELXS97 (Sheldrick, 2008 ▸), SHELXL2017 (Sheldrick, 2015 ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸) and Mercury (Macrae et al., 2006 ▸).

Crystal structure: contains datablock(s) global, I, 1. DOI: 10.1107/S2056989019006492/rz5252sup1.cif Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989019006492/rz5252Isup2.hkl Click here for additional data file. Supporting information file. DOI: 10.1107/S2056989019006492/rz5252Isup3.cml CCDC reference: 1587259 Additional supporting information: crystallographic information; 3D view; checkCIF report
C14H13N3O3·H2OF(000) = 608
Mr = 289.29Dx = 1.395 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 7.1153 (4) ÅCell parameters from 3729 reflections
b = 11.0075 (6) Åθ = 3.9–29.2°
c = 18.2771 (10) ŵ = 0.10 mm1
β = 105.766 (5)°T = 295 K
V = 1377.64 (14) Å3Block, colourless
Z = 40.30 × 0.25 × 0.18 mm
Agilent Xcalibur Eos diffractometer2549 independent reflections
Radiation source: fine-focus sealed tube2027 reflections with I > 2σ(I)
Detector resolution: 15.9821 pixels mm-1Rint = 0.027
ω scansθmax = 25.5°, θmin = 3.9°
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2012)h = −8→8
Tmin = 0.969, Tmax = 0.981k = −13→12
8396 measured reflectionsl = −22→22
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.036H-atom parameters constrained
wR(F2) = 0.101w = 1/[σ2(Fo2) + (0.0462P)2 + 0.2987P] where P = (Fo2 + 2Fc2)/3
S = 1.04(Δ/σ)max < 0.001
2549 reflectionsΔρmax = 0.16 e Å3
192 parametersΔρmin = −0.13 e Å3
0 restraintsExtinction correction: SHELXL2017 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.030 (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.
xyzUiso*/Ueq
O3−0.03769 (14)0.40424 (10)0.06695 (6)0.0455 (3)
O20.20750 (15)0.23383 (10)0.06507 (7)0.0537 (3)
H100.2870880.1781880.0735270.081*
O11.15498 (17)0.21431 (11)0.30304 (8)0.0604 (4)
N30.85559 (17)0.37007 (12)0.26300 (7)0.0418 (3)
N21.03456 (17)0.40123 (12)0.31206 (7)0.0410 (3)
H2N1.0531280.4722350.3323970.049*
N11.61018 (19)0.51282 (12)0.42610 (8)0.0452 (4)
C80.5291 (2)0.43898 (15)0.20366 (8)0.0371 (4)
C90.4682 (2)0.33704 (14)0.15750 (8)0.0384 (4)
H90.5559240.2744290.1574430.046*
C100.2791 (2)0.32888 (14)0.11216 (8)0.0372 (4)
C110.1465 (2)0.42290 (14)0.11294 (8)0.0355 (4)
C120.2059 (2)0.52410 (15)0.15746 (9)0.0409 (4)
H120.1184190.5867910.1576760.049*
C130.3972 (2)0.53171 (15)0.20196 (9)0.0423 (4)
H130.4377300.6007720.2313190.051*
C14−0.1795 (2)0.49637 (17)0.06553 (10)0.0492 (4)
H14A−0.1929060.5081960.1159020.074*
H14B−0.3027910.4720170.0322560.074*
H14C−0.1381930.5709370.0474680.074*
C70.7260 (2)0.45278 (15)0.25379 (8)0.0411 (4)
H70.7584410.5253520.2802650.049*
C61.1785 (2)0.31829 (14)0.32729 (9)0.0390 (4)
C21.4323 (2)0.47808 (14)0.38578 (8)0.0387 (4)
H21.3435940.5378880.3627460.046*
C11.3728 (2)0.35815 (13)0.37638 (8)0.0354 (4)
C51.5059 (2)0.27035 (15)0.41019 (10)0.0502 (4)
H51.4720880.1886030.4044000.060*
C41.6891 (2)0.30435 (17)0.45260 (11)0.0599 (5)
H41.7806140.2463980.4762870.072*
C31.7334 (2)0.42511 (17)0.45907 (10)0.0533 (5)
H31.8570460.4476330.4882540.064*
O41.07802 (17)0.65762 (11)0.34578 (7)0.0594 (4)
H4WA1.0340300.6969740.3775880.089*
H4WB1.0435300.6926740.3027880.089*
U11U22U33U12U13U23
O30.0286 (5)0.0448 (7)0.0558 (7)0.0044 (5)−0.0009 (5)−0.0023 (5)
O20.0385 (6)0.0378 (6)0.0712 (8)0.0062 (5)−0.0085 (5)−0.0115 (6)
O10.0513 (7)0.0382 (7)0.0744 (9)−0.0022 (5)−0.0127 (6)−0.0079 (6)
N30.0309 (6)0.0455 (8)0.0416 (7)−0.0061 (6)−0.0029 (5)0.0026 (6)
N20.0311 (6)0.0390 (7)0.0448 (7)−0.0032 (6)−0.0037 (5)−0.0026 (6)
N10.0361 (7)0.0419 (8)0.0509 (8)−0.0062 (6)0.0006 (6)0.0030 (6)
C80.0317 (7)0.0424 (9)0.0351 (8)−0.0033 (7)0.0054 (6)0.0051 (7)
C90.0306 (7)0.0373 (8)0.0437 (8)0.0036 (6)0.0039 (6)0.0062 (7)
C100.0343 (8)0.0327 (8)0.0408 (8)−0.0019 (6)0.0038 (6)0.0024 (7)
C110.0281 (7)0.0388 (9)0.0369 (8)−0.0003 (6)0.0039 (6)0.0052 (7)
C120.0369 (8)0.0403 (9)0.0435 (8)0.0051 (7)0.0073 (6)−0.0004 (7)
C130.0399 (8)0.0422 (9)0.0412 (8)−0.0020 (7)0.0049 (7)−0.0052 (7)
C140.0325 (8)0.0598 (11)0.0520 (10)0.0118 (8)0.0056 (7)0.0013 (8)
C70.0348 (8)0.0446 (9)0.0397 (8)−0.0055 (7)0.0030 (6)0.0012 (7)
C60.0370 (8)0.0345 (9)0.0398 (8)−0.0047 (7)0.0007 (6)0.0025 (7)
C20.0320 (8)0.0364 (8)0.0432 (8)−0.0003 (6)0.0023 (6)0.0041 (7)
C10.0321 (7)0.0359 (8)0.0345 (7)−0.0008 (6)0.0026 (6)0.0024 (6)
C50.0457 (9)0.0361 (9)0.0580 (10)−0.0003 (7)−0.0041 (8)0.0050 (8)
C40.0432 (10)0.0477 (11)0.0728 (13)0.0060 (8)−0.0114 (9)0.0120 (9)
C30.0328 (8)0.0540 (11)0.0611 (11)−0.0043 (8)−0.0075 (7)0.0063 (9)
O40.0627 (8)0.0475 (7)0.0583 (7)0.0186 (6)−0.0002 (6)−0.0017 (6)
O3—C111.3664 (17)C12—C131.386 (2)
O3—C141.4257 (19)C12—H120.9300
O2—C101.3627 (18)C13—H130.9300
O2—H100.8198C14—H14A0.9600
O1—C61.2223 (19)C14—H14B0.9600
N3—C71.274 (2)C14—H14C0.9600
N3—N21.3866 (16)C7—H70.9300
N2—C61.343 (2)C6—C11.4950 (19)
N2—H2N0.8602C2—C11.383 (2)
N1—C31.333 (2)C2—H20.9300
N1—C21.3355 (19)C1—C51.376 (2)
C8—C131.381 (2)C5—C41.376 (2)
C8—C91.400 (2)C5—H50.9300
C8—C71.459 (2)C4—C31.364 (3)
C9—C101.378 (2)C4—H40.9300
C9—H90.9300C3—H30.9300
C10—C111.404 (2)O4—H4WA0.8500
C11—C121.377 (2)O4—H4WB0.8495
C11—O3—C14117.37 (12)H14A—C14—H14B109.5
C10—O2—H10109.5O3—C14—H14C109.5
C7—N3—N2114.41 (13)H14A—C14—H14C109.5
C6—N2—N3118.71 (13)H14B—C14—H14C109.5
C6—N2—H2N120.6N3—C7—C8123.07 (15)
N3—N2—H2N120.7N3—C7—H7118.5
C3—N1—C2116.76 (14)C8—C7—H7118.5
C13—C8—C9118.80 (13)O1—C6—N2122.66 (13)
C13—C8—C7117.90 (14)O1—C6—C1120.37 (14)
C9—C8—C7123.31 (14)N2—C6—C1116.97 (13)
C10—C9—C8120.43 (14)N1—C2—C1123.65 (14)
C10—C9—H9119.8N1—C2—H2118.2
C8—C9—H9119.8C1—C2—H2118.2
O2—C10—C9124.50 (13)C5—C1—C2117.67 (13)
O2—C10—C11115.81 (12)C5—C1—C6118.33 (14)
C9—C10—C11119.69 (14)C2—C1—C6123.84 (13)
O3—C11—C12125.07 (13)C4—C5—C1119.55 (15)
O3—C11—C10114.71 (13)C4—C5—H5120.2
C12—C11—C10120.22 (13)C1—C5—H5120.2
C11—C12—C13119.40 (14)C3—C4—C5118.38 (15)
C11—C12—H12120.3C3—C4—H4120.8
C13—C12—H12120.3C5—C4—H4120.8
C8—C13—C12121.44 (15)N1—C3—C4123.96 (15)
C8—C13—H13119.3N1—C3—H3118.0
C12—C13—H13119.3C4—C3—H3118.0
O3—C14—H14A109.5H4WA—O4—H4WB109.5
O3—C14—H14B109.5
D—H···AD—HH···AD···AD—H···A
O4—H4WA···O2i0.852.283.0483 (17)150
O4—H4WA···O3i0.852.493.2011 (16)141
O4—H4WB···O1ii0.852.082.8429 (19)150
O4—H4WB···N3ii0.852.503.1875 (18)139
N2—H2N···O40.862.062.8889 (18)162
O2—H10···N1iii0.821.962.7411 (17)159
C2—H2···O40.932.253.129 (2)156
C4—H4···O3iv0.932.453.347 (2)163
  7 in total

1.  Towards quantitative analysis of intermolecular interactions with Hirshfeld surfaces.

Authors:  Joshua J McKinnon; Dylan Jayatilaka; Mark A Spackman
Journal:  Chem Commun (Camb)       Date:  2007-10-07       Impact factor: 6.222

2.  A short history of SHELX.

Authors:  George M Sheldrick
Journal:  Acta Crystallogr A       Date:  2007-12-21       Impact factor: 2.290

3.  Synthesis and DNA binding studies of Ni(II), Co(II), Cu(II) and Zn(II) metal complexes of N1,N5-bis[pyridine-2-methylene]-thiocarbohydrazone Schiff-base ligand.

Authors:  A D Tiwari; A K Mishra; S B Mishra; B B Mamba; B Maji; S Bhattacharya
Journal:  Spectrochim Acta A Mol Biomol Spectrosc       Date:  2011-04-20       Impact factor: 4.098

4.  (E)-N'-(1,3-Benzodioxol-5-ylmethyl-ene)nicotinohydrazide monohydrate.

Authors:  Feng-Yu Bao; Hai-Yan Zhang; Ying-Xia Zhou; Su Hui
Journal:  Acta Crystallogr Sect E Struct Rep Online       Date:  2009-09-05

5.  Crystal structure refinement with SHELXL.

Authors:  George M Sheldrick
Journal:  Acta Crystallogr C Struct Chem       Date:  2015-01-01       Impact factor: 1.172

6.  (E)-N'-(3,4-Di-meth-oxy-benzyl-idene)nicotinohydrazide monohydrate.

Authors:  J Josephine Novina; G Vasuki; M Suresh; M Syed Ali Padusha
Journal:  Acta Crystallogr Sect E Struct Rep Online       Date:  2014-06-18

7.  The Cambridge Structural Database.

Authors:  Colin R Groom; Ian J Bruno; Matthew P Lightfoot; Suzanna C Ward
Journal:  Acta Crystallogr B Struct Sci Cryst Eng Mater       Date:  2016-04-01
  7 in total

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