N-H…O, C-H… O hydrogen-bonded supramolecular frameworks in 4-fluoroanilinium and dicyclohexylaminium picrate salts

Article abstract of DOI:10.1007/s11224-019-01471-1

The asymmetric unit of compound (I), 4-fluoroanilinium picrate, C₆H₇NF⁺.C₆H₂N₃O₇ ^? contain one 4-fluoroanilinium cation and one picrate anion whereas in compound (II),

Full text of DOI:10.1007/s11224-019-01471-1

Structural Chemistry
https://doi.org/10.1007/s11224-019-01471-1
ORIGINAL RESEARCH
N-H…O, C-H… O hydrogen-bonded supramolecular frameworks
in 4-fluoroanilinium and dicyclohexylaminium picrate salts
Saminathan Kolandaivelu1 & Jagan Rajamoni2 & Sivakumar Kandasamy2
Received: 28 October 2019 /Accepted: 3 December 2019
#
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The asymmetric unit of compound (I), 4-fluoroanilinium picrate, C6H7NF+.C6H2N3O7− contain one 4-fluoroanilinium cation and
one picrate anion whereas in compound (II), dicyclohexylaminium picrate, C12H22N+.C6H2N3O7− the asymmetric unit contains
two sets of dicyclohexylaminium cation and picrate anion due to conformational difference between the molecules. In (I), all
three nitro groups of the picrate anion are positionally disordered over two sites refined to major and minor components. The
molecular ions of (I), interlinked through N–H O and C–H O hydrogen bonds forming two-dimensional supramolecular
sheet along (-1 0 1) plane. Whereas in (II), the symmetry-independent molecules labeled as A and B molecule form independent
one-dimensional supramolecular tape extending along (1 1 0) and (1 0 0) direction. The supramolecular tapes are interlinked
through C–H O interaction to form three-dimensional network in the crystalline solid in (II).
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Keywords Supramolecular Hydrogen bond Picrate Framework FT-IR Motif
Introduction
engineering as hydrogen bonded motifs between building
blocks that can be used to propagate networks or supramo-
lecular structures [6, 7]. Formation of salts and co-crystals
favors the understanding of supramolecular synthon which
enables us to enhance the desired properties. Picric acid
forms crystalline co-crystals and salts with various organic
molecules by virtue of its acidic nature and forms salts
through specific electrostatic and hydrogen bonding inter-
actions. Picric acid (2,4,6 trinitrophenol) is an organic acid
which is used in dyeing industry and explosive. Picric acid
is used in human therapy as treating burns, antiseptic, and
astringent agent [8]. The presence of electron-withdrawing
groups makes it as a π-acceptor for a neutral carrier donor
molecule. A variety of picrate salts have been previously
reported by us and others such as piperidinium picrate, 3-
methylanilinium picrate, l-prolinium picrate, and 2-amino
4,6 dimethoxypyrimidinium picrate [9–12]. It is observed
that picrate salts form interesting hydrogen-bonded supra-
molecular motifs and one-, two-, and three-dimensional
networks with respect to the nature of the substitution pres-
ent in cations. Reported literature shows that bulk crystals
of picrate salts are best candidates which exhibit good non-
linear optical properties [13, 14]. In the present work, we
have studied the crystal structure and hydrogen-bonded
supramolecular networks in 4-fluoroanilinium picrate and
dicyclohexylamminium picrate salts as follows.
Crystal engineering of organic solids, especially with re-
spect to understanding the nature of various intermolecular
interactions, have profoundly influenced the concept of
supramolecular chemistry [1, 2]. The nature of intermolec-
ular interactions influences crystal engineering including
hydrogen bond, weak interaction, halogen bond, π…π in-
teraction, and short contacts between molecular or ionic
compounds [3]. The specificity, directionality, and predict-
ability of intermolecular interaction/hydrogen bond can be
utilized to assemble supramolecular structures with con-
trolled dimensionality which tend to exhibit interesting
electrical, magnetic, and optical properties of our interest
[4, 5]. Among all non-covalent interactions, hydrogen
bond plays an important role in chemistry, biology, and
materials science. Identifying hydrogen-bonded motifs
and supramolecular synthons are very important to crystal
* Jagan Rajamoni
phyjagan@gmail.com
1
Department of Physics, University V.O.C.College of Engineering,
Anna University, Tuticorin 628008, India
2
Department of Physics, Anna University, Chennai 600 025, India

Struct Chem
Experimental
vibrations on the higher side suggests the formation of picrate
salt. From the spectral studies, it is reported that the NH2
(amine) group gives rise to six characteristic vibrations—
asymmetric and symmetric stretching, scissoring, rocking,
wagging, and twisting modes. The asymmetric and symmetric
stretching modes generally absorbs in the region 3550–
3250 cm−1, the former mode being at a higher magnitude than
the latter. The scissoring and twisting modes appear at
1619 cm−1 and 1054 cm−1, respectively, is due to the salt
formation between 4-fluoroaniline and picric acid; phenolic
hydrogen of picric acid is transferred to the aniline forming
Synthesis and crystallization
Compound (I) was prepared by taking an equimolar mixture
of 4-fluoroaniline (1.11 g, 0.01 mol) and picric acid (2.29 g,
0.01 mol) in ethanol solution. The mixture was continuously
stirred for 2 h to attain a homogenous solution. The saturated
yellow-colored solution was filtered to a clean beaker and kept
for crystallization without any atmospheric disturbance. Good
diffraction quality yellow-colored crystals were obtained after
2 weeks.
+
NH3 ion, and hence, the bond is formed between the anion
Similarly, compound (II) was prepared by taking an equi-
molar mixture of dicyclohexylamine (1.81 g, 0.01 mol) and
picric acid (2.29 g, 0.01 mol) in ethanol solution. The mixture
was continuously stirred for an hour until it attains the state of
homogenous solution. The resultant saturated solution was
filtered in a clean beaker and kept aside for crystallization by
the method of slow evaporation. Good diffraction quality
yellow-colored crystals were obtained after 10 days. The
chemical diagram of compounds (I) and (II) is shown in
Scheme 1.
and cation. As a result of this, the vibrations of NH3+ ion are
shifted to lower wave numbers. As shown in Fig. 1, the me-
dium intensity band centered at 3149 cm−1 in the spectrum of
(I) could be due to NH3+ asymmetric stretching vibration. The
symmetric NH3+ vibration appears at 2860 cm−1 in the spec-
trum of (I). The corresponding asymmetric vibrations appear
at around 1483 cm−1 and 1506 cm−1.The vibrational spectrum
of 4-fluoroaniline has been investigated and the C – F
stretching vibration appears at 1227 cm−1 with medium
intensity.
FT-IR studies
dicyclohexylamminium picrate
The presence of functional groups in the molecular crystal is
found from FT-ITanalysis. FT-IR spectrum of (I) and (II) was
recorded in the region 4000–400 cm−1 at room temperature
using Perkin Elmer Spectrum1 FT-IR Spectrometer by KBr
pellet method.
The asymmetric and symmetric stretching vibrations of the
NO2 group have strong absorptions in regions 1570–
1485 cm−1 and 1370–1320 cm−1, respectively. As expected,
the strong band observed at 1341 cm−1 in the FT-IR spectrum
(Fig. 2) could be attributed to NO2 symmetric vibrations. The
asymmetric stretching vibrations of the NO2 group appear at
1530 cm−1. In phenols, a broad absorption band appears in the
region 2500–3500 cm−1 which is primarily due to the OH
stretching vibration. The broad medium intensity band cen-
tered at 3417 cm−1 in the spectrum of (II) could be attributed
to phenolic OH stretching vibration. In the spectrum of (II)
4-fluoroanilinium picrate
The NO2 asymmetric stretching vibrations appear in the re-
gion 1557–1570 cm−1. The two bands that appear in the re-
gion 1330–1370 cm−1 in the spectra of the above salts could
be attributed to NO2 symmetric stretching vibrations. The shift
in the frequencies of NO2 asymmetric and symmetric
+
(shown in Fig. 2), the NH2 vibration is present. The weak
intensity bands that appear at 3183 cm−1 and 3142 cm−1 could
Scheme 1 Schematic diagram of
compounds (I) and (II)

Struct Chem
Fig. 1 FT-IR spectrum of
compound (I)
+
be attributed to NH2 asymmetric stretching vibrations. The
Single crystal X-ray data collection and refinement
corresponding symmetric vibration appears at 2808 cm−1. The
bands that appear in the region 1610–1557 cm−1 are due to
Intensity data collection for both the compounds (I) and
(II) were performed using Enraf-Nonius CAD-4 diffrac-
tometer with CuKα radiation employed by ω-2θ scan
mode at room temperature. Single crystals of (I) and
(II) having size 0.35 × 0.25 × 0.20 mm was used for sin-
gle crystal X-ray diffraction experiments, after careful
selection using a polarizing microscope. Accurate unit
cell parameters and orientation matrix for both crystals
+
NH2 deformation vibration and this overlaps with the NO2
vibrations. The out-of-plane deformation of NH2+ appears at
795 cm−1 and 935 cm−1. The methylene (CH2) stretching vi-
brations appear at around 2939 cm−1. The deformations of
methylene groups give rise to absorption at 1483 cm−1. The
presence of NH2+ vibrations confirms the transfer of protons
from the picric acid to the counter cation.
Fig. 2 FT-IR spectrum of
compound (II)

Struct Chem
atoms were refined isotropically. In compound (I), all
three nitro (NO2) groups of the picrate anions are posi-
tionally disordered over two sites with refined occupan-
cies of 0.804(10) and 0.196(10), respectively. The N-O
bond distances of major and minor components of all the
three NO2 groups are fixed to a distance of 1.24(1) Å
using suitable restraint (DFIX). Atomic displacement pa-
rameters of adjacent atoms were made similar using suit-
able similarity restraints (SIMU) with an effective stan-
dard uncertainty (s.u.) of 0.02 Å for the major and minor
components, respectively. Similarly, in compound (II),
one of the nitro groups (ortho position) of the picrate
anion-A is positionally disordered over two sites with
refined occupancies of 0.784(6) and 0.216(6), respective-
ly. Similar to (I), the N-O bond distance of the disor-
dered NO2 group is restrained to a distance of 1.24(1) Å
followed by the atomic displacement parameters of adja-
cent atoms made similar using suitable similarity re-
straints (SIMU) with an effective s.u. of 0.02 Å. All
the hydrogen atoms for (I) and (II) were identified from
the different electron density map and refined according-
ly. Hydrogen atoms associated with the carbon atoms
were optimized and allowed to ride on the parent atoms
with a C-H distance of 0.97 Å for CH2 and 0.93 Å for
aromatic CH and 0.98 Å for methine CH with Uiso(H) =
1.2Ueq(C). Whereas, the hydrogen atoms bound to N
atoms of both compounds were refined freely with their
N-H distances restrained to a value of 0.90(1) Å. The
molecular graphic images of the molecules were drawn
using the ORTEP [18] and Mercury 3.9 [19] program.
Both structures (I) and (II) (Figs. 3 and 4) were depos-
ited in Cambridge Structural Database, and their refer-
ence IDs are CCDC 1938032 and CCDC 1938033.
Fig. 3 Displacement ellipsoid plot of compound (I) drawn at 40%
probability level. Only the major component of the disordered picrate
anion is shown for clarity
were obtained by a least-square fit of 25 reflections. The
intensity data for (I) and (II) were collected in the θ—
range from 4.35° to 67.86° and 2.312° to 67.726°, re-
spectively. During data collection, two standard reflec-
tions were monitored for every 100 measurements (re-
flections), and it showed no significant intensity varia-
tions. The intensities were corrected for Lorentz and po-
larization factor corrections using the XCAD4 computer
program [15] followed by the absorption correction car-
ried out using ψ scan data [16].
Crystal structures of compounds (I) and (II) was
solved by direct methods procedure using the SHELXS-
2018 [17] program and refined by Full-matrix least
squares procedure on F2 using SHELXL-2018 [17] pro-
gram (Table 1). All the non-hydrogen atoms were sub-
jected to anisotropic refinement whereas the hydrogen
Fig. 4 Displacement ellipsoid
plot of compound (II) drawn at
40% probability level. Only the
major component of the
disordered picrate anion is shown
for clarity

Struct Chem
Result and discussion
Structural features
4-fluoroanilinium picrate
the picrate anion show the characteristic values, with C1-
O1 bond length [1.236(2) Å (A), 1.246(2) Å (B)] showing
a deviation between single and double bond characters
and C1-C2 distances [1.449(3) Å (A), 1.446(3) Å (B)]
and C1-C6 distances [1.445(3) Å (A), 1.442(3) Å (B)]
are longer and deviating from the average standard aro-
matic C-C value [1.375(3) Å (A), 1.376(3) Å (B)], as
observed in other picrate salts. This lengthening of C1-
C2 and C1-C6 bonds is ascribed to the dissociation hy-
drogen from the phenolic OH group to the nitrogen atom
of the dicyclohexylamine molecule leading to the conver-
sion of neutral picric acid to an anionic picrate salt. The
N-O bond distance of the nitro group in the anion A varies
from 1.195(3) Å to 1.228(2) Å and for anion B it ranges
from 1.216(2) Å to 1.234(2) Å whereas the C-N distance
varies from 1.443(2) Å to 1.464(3) Å for the anion A and
the same varies from 1.437(2) Å to 1.460(2) Å for the
anion B. This disordered ortho nitro group deviates sig-
nificantly from the benzene ring moiety of the picrate ion
by 33.56(2)° [O2-N2-O3] and 33.06(2)° [O2’-N1-O3’] for
the major and minor components while the other ortho
nitro group (6th position) is almost coplanar with benzene
ring moiety of the picrate ion A [O6-N3-O7, 2.99(2)°].
The para nitro group [O4-N2-O5] of the picrate ion A
has an intermediate deviation of 13.98(3)° from the ben-
zene ring moiety. Similarly, one of the ortho nitro groups
of the picrate ion B deviates significantly with a dihedral
angle of 43.45(3)° [O2-N1-O3] and 9.62(3)° [O6-N3-O7]
from the benzene ring moiety, and the para nitro group
(4th position) has the tilting angle 11.85(2)°. The tilting
behavior of the para nitro groups (O4-N2-O5) and the 6th
positioned ortho nitro groups (O6-N3-O7) is different
from the other structures, where the para nitro groups
lie in the benzene plane and the ortho nitro groups deviate
well from this plane (about 30–60°). This is attributed to
the intermolecular interactions between the molecular ions
through well-defined hydrogen bonds and short contacts.
The bond lengths of the protonated nitrogen atom N4 of
the cation are found to be 1.501(2) Å [N4-C7] and
1.509(2) Å [N4-C13] for molecule A and that of molecule
B are 1.501(2) Å and 1.504(2) Å which is longer than the
unprotonated C-N bond distances in dicyclohexylamine
[23]. The mean plane calculation for the benzene planes
of the picrate ions shows that the atom C2A of anion A
deviates maximum [− 0.023(2)], and C1B of anion B has
the maximum deviation of 0.032(2). The dihedral angle
between the anions [4.2(1)°] shows that they are essen-
tially parallel to each other.
The asymmetric unit comprises one 4-fluoroanilinium cation
and a picrate anion. In the picrate anion, all the three nitro
groups are disordered over two positions with refined site
occupancies of 0.804(10) and 0.196(10), respectively.
Interestingly, from the refinement, it is observed that all the
nitro groups take same major and minor occupancies. The
bond lengths and angles of the picrate anion show the charac-
teristic values, with C1-C2, 1.440(2) Å, C1-C6, 1.439(2) Å,
which are longer and deviate from the regular aromatic values,
also the C1-O1 value is 1.258(2) Å, which is intermediate
between the single and double bonds. These effects are due
to the dissociation of a hydroxyl proton at O1, leading to a
conversion of neutral to an anionic state of the molecule.
Similar effect is observed on other reported salts like 2,2′-
bipyridinium picrate [20] and 4-dimethylaminopyridinium
picrate [21]. The N-O bond distances associated with the nitro
group of picrate anion varies from 1.225(4) Å to 1.240(4) Å
whereas the C-N distances vary from 1.455(2) Å to 1.460(2)
Å which are very much similar to other picrate salts reported
in the literature [22]. In the picrate anion, the nitro group at
para position is planar with phenyl moiety whereas nitro
groups at 2,6 ortho positions deviate significantly from the
phenyl plane due to steric effect. The dihedral angle between
the ortho NO2 groups and the benzene plane is observed to be
38.62(4)° and 21.09(1) ° for major and minor conformations
and 60.55(4)° and 37.40(4)° for major and minor conformers
of 2nd and 6th position respectively. The para nitro group
(O4-N2-O5) makes a lesser tilt with the benzene plane com-
pared with the ortho positioned nitro groups with a measured
dihedral angle of 11.32(2)° and 18.02(2)° for major 2nd and
minor conformations, respectively. The 4-fluoroanilinium
molecular ions show the characteristic geometrical parameters
except for the C-N bond length involving the protonated ni-
trogen atom, C7-N4 is 1.467(2) Å which is longer than the
neutral value. The picrate and 4-fluoroanilinium ions lie par-
allel to (2 0-1) and (0 1-1) crystallographic planes,
respectively.
dicyclohexylaminium picrate
In dicyclohexylamminum picrate salt (II), the asymmetric
unit comprises two sets of anions and cations represented
as A and B set of molecules. One of the ortho nitro
groups (2nd position) of the picrate ion A has positional
disorder, and hence, it was resolved into two components.
The occupancies for major and minor components are
0.784(6) and 0.216(6), respectively. The bond lengths of
Supramolecular features
Both picrate salts (I) and (II) exhibit interesting self-
assembled supramolecular features in the crystal structure

Struct Chem
and is discussed in this section. As picrate anions contain good
hydrogen bond acceptor oxygen atom from NO2 and O-
group, the molecular self-assembly is mainly due to N–H O
and C–H O hydrogen bonds. The details of the hydrogen
bond geometry are given in Tables 2 and 3 for (I) and (II),
respectively.
(1-x, 1-y, 2-z) forming N4–H4A O1 and N4–H4C O1ii hy-
drogen bonds. Inversion related anions and cations form
2
R4 (8) supramolecular motif [24] through N4–H4A O1 and
N4–H4C O1ii. The nitrogen atom at (x, y, z) form bifurcated
hydrogen bonds, N4–H4A O1, N4–H4A O7 and N4–
H4C O1ii, N4–H4C O2 through H4A and H4C with accep-
2
tor oxygen atoms O1, O7 and O1, O2 to construct a R1 (6)
motif. In general, inversion related 4-fluoroanilinium cations
4-fluoroanilinium picrate
2
and picrate anions are linked together by fused R4 (8) and
2
R1 (6) motifs which constructs the basic molecule. Adjacent
In the hydrogen-bond formation of compound (I), the proton-
dissociated oxygen atom O1 at (x,y,z) acts as a bifurcated
acceptor for hydrogen atoms at H4A at (x,y,z) and H4C at
molecular motifs are interlinked through N4–H4B O6 hy-
drogen bond, which generated to a one-dimensional infinite
Table 1 Crystal structure
refinement details of compounds
Parameters
Compound (I)
Compound (II)
(I) and (II)
Empirical formula
C12 H9 F N4 O7
340.23
C18 H26 N4 O7
410.43
Formula weight
Temperature (K)
296(2)
296(2)
Wavelength (Å)
1.54184
1.54184
Crystal system, space group
Triclinic, P -1
Triclinic, P -1
Unit cell dimensions
a(Å)
8.2800(14)
8.7430(6)
b(Å)
8.4330(14)
11.4872(10)
21.349(3)
c(Å)
10.3200(19)
97.070(12)
α(°)
98.744(9)
β(°)
95.880(14)
98.822(8)
γ(°)
99.760(14)
101.499(7)
Volume (Å3)
699.1(2)
2039.0(3)
Z, Calculated density (Mg/m3)
2, 1.616
4, 1.337
Absorption coefficient (mm−1
)
1.259
0.874
F(000)
348
872
Crystal size (mm)
0.350 × 0.300 × 0.250
4.352 to 67.865
0 < =h < =9,
− 10 < =k < =9,
− 12 < =l < =12
2718/2531
0.350 × 0.300 × 0.250
2.132 to 67.926
0 < =h < =10,
− 13 < =k < =13,
− 25 < =l < =25
7720/7191
Theta range for data collection (°)
Limiting indices
Reflections collected/unique
(R(int) = 0.0350)
100.00%
(R(int) = 0.0143)
96.90%
Completeness to theta = 67.684
Absorption correction
Psi-scan
Psi-scan
Max. and min. transmission
Refinement method
0.924 and 0.867
Full-matrix least-squares on F2
2531/63/285
1.078
0.900 and 0.850
Full-matrix least-squares on F2
7191/26/555
1.026
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices (I > 2sigma(I))
R1 = 0.0480
wR2 = 0.1321
R1 = 0.0524
wR2 = 0.1370
0.022(2)
R1 = 0.0404
wR2 = 0.1089
R1 = 0.0653
wR2 = 0.1232
0.0057(3)
R indices (all data)
Extinction coefficient
Largest diff. peak and hole (e.Å−3
)
0.365 and − 0.205
0.19 and − 0.17

Struct Chem
Table 2 Hydrogen bond geometries of compound (I)
of bifurcated hydrogen bonds with H4A2 at (x, y, z) and
oxygen atoms O1A and O7A of same asymmetric unit.
An expected N–H O hydrogen bond is absent between
H A atoms H4A1 O7A whose D A distance is ob-
served as 3.317(2) Å, which is longer than the standard
value. The O- oxygen atom acts as bifurcated acceptor
atom for two types of hydrogen bonds N4A–H4A O1A
and C18A–H18A O1A. Adjacent A set of anion-cationic
D–H...A
d(D–H)
d(H A)
d(D···A)
<(DHA)
C12–H12···O4i
C12–H12···O7
N4–H4A···O1
N4–H4C···O1ii
N4–H4B···O6iii
0.93
2.64
3.299(9)
3.314(3)
2.8272(19)
2.798(2)
3.037(6)
128.6
0.93
2.56
138.3
0.878(10)
0.890(10)
0.881(10)
1.963(11)
1.932(12)
2.172(13)
167.5(19)
164(2)
167(2)
2
substructure is further linked through a R2 (8) motif made
Symmetry codes: (i) -x,-y,-z + 1; (ii) -x + 1,-y + 1,-z + 2; (iii) -x + 1,-y,-
z + 2
of two C–H O interaction C17A–H17A O4A and
C13A–H13A O5A which further develops to a one-
dimensional supramolecular tape extending infinitely
along the (1 1 0) direction as shown in Fig. 8a.
Similarly, in the case of B-molecules, inversion-related
anions and cations are interlinked through N–H O hydro-
gen bonds N4B–H4B2 O1B, N4B–H4B2 O7B and
supramolecular tape along the crystallographic (0 1 0) direc-
tion as shown in Fig. 5. It is observed that the (0 1 0) tape is
2
2
4
made of R4 (8), R1 (6), and R4 (12) motifs with the centroid
2
2
2
4
N4B–H4B1 O7B to form R4 (8) and R1 (6) motif (Fig.
7b). C–H O interactions have a significant role in the
construction of hydrogen-bonded motif. The inversion-
related dicyclohexylamminium cation and picrate anions
are linked through C–H O interactions such as C18B–
H18C O1B and C18B–H18C O2B, which in turn forms
of R4 (8) and R4 (12) rings occupy the center of inversion at
(1/2, ½, 1) and (1/2, 0, 1,) respectively. Adjacent supramolec-
ular tapes are further connected through a weak C–H O in-
teraction (C12–H12 O4), which generates to a two-
dimensional supramolecular sheet extending parallel to (−1
0 1) plane (Fig. 6).
2
an additional R1 (6) motif. Proton dissociated oxygen at-
om O2B acts as bifurcated acceptor atom for N–H O and
C–H O hydrogen bonds which develop to a R2 (6) motif.
dicyclohexylaminium picrate
1
Moreover, as depicted in Fig. 8b, adjacent B set of anions
and cations are further interlinked through a weak C–H
O interaction (C15–H15C O6B) and a C–H π contact
(C16B–H16D π1, where π1 = C1B/C2B/C3B/C4B/C5B/
C6B with D A distance of 3.816(4) Å and D–H A angle
of 129.01°) form a one-dimensional tape extending infi-
nitely along the crystallographic (1 0 0) direction. In the
crystal structure, the (1 1 0) and (1 0 0) one-dimensional
supramolecular tapes are interlinked through two C–H O
hydrogen bonds C10A–H10B O4B and C11A–H11A
O3B to construct a three-dimensional supramolecular
framework in the crystal structure.
In the crystal structure of compound (II), the anions and
cations of A and B symmetry independent molecules form
independent hydrogen-bonded motif which in turn devel-
op in to a supramolecular framework through C–H O
interaction. In A-molecule, the inversion-related anions
and cations are linked through strong N–H O hydrogen
bonds N4–H4A2 O1A, N4–H4A2 O7A and N4–
2
H4A1 O6A to form two types of ring motifs R1 (6)
4
2
and R4 (12) (Fig. 7a). Here R1 (6) is formed as a result
Table 3 Hydrogen bond geometries of compound (I)
D–H A
d(D–H) d(H A)
d(D A)
<(DHA)
Cambridge structural database analysis
N4A–H4A1···O6Ai
N4A–H4A2···O1A
N4A–H4A2···O7A
C13A–H13A···O5Aii 0.98
C14A–H14B···O5Biii 0.97
0.902(9) 2.429(15) 3.164(2)
0.896(9) 1.913(12) 2.759(2)
0.896(9) 2.499(16) 3.146(2)
138.8(16)
156.9(17)
129.5(15)
161.8
A search of Cambridge Structural Database (CSD version
5.40) [25] has been done in order to understand the for-
mation of hydrogen-bonded motifs as observed above in
closely relevant structures of compounds (I) and (II). As
observed in (I), in the crystal structure of 2-
hydroxyanilinium picrate (ref. code TEZMAO) [26], the
inversion-related anions and cations are interlinked
through N–H O hydrogen bonds forming similar motifs
2.59
2.47
2.54
3.539(2)
3.263(3)
3.297(3)
138.3
C18A–H18A···O1A
N4B–H4B1···O7Biii
N4B–H4B2···O1B
N4B–H4B2···O7B
C18B–H18C···O1B
C18B–H18C···O2B
0.97
135
0.904(9) 2.095(10) 2.9986(19) 177.7(17)
0.897(9) 1.862(11) 2.7038(18) 155.5(16)
2
2
2
0.897(9) 2.410(15) 3.047(2)
128.2(14)
132.8
such as R1 (6), R4 (8), R1 (6) fused together which ex-
4
0.97
0.97
2.51
2.64
3.249(2)
3.577(2)
tends to one-dimensional tape through R4 (12) motif. Unit
161.4
cell parameters of both the structures are similar to each
other except for slight difference in angles. Also, in the
crystal structure of anilinium picrate (ref. code
Symmetry codes: (i) -x + 1,-y,-z; (ii) x + 1,y + 1,z; (iii) -x + 1,-y,-z + 1

Struct Chem
Fig. 5 Part of the crystal structure
of (I) showing the formation of
N–H O hydrogen-bonded one-
dimensional tape built through
2
2
4
R1 (6), R4 (8), R4 (12) motif ex-
tending along (0 1 0) direction.
Hydrogen atoms not involved in
hydrogen bonds are omitted for
clarity
ZZZLBS02) [27] and 2-iodoanilinium picrate (ref. code
ZEDPON01) [28] the inversion-related anions and cations
are interlinked through N–H O hydrogen bonds forming
effect. Attempt was made for CSD search relevant to
compound (II) with cyclohexyl amine and NH2 substitu-
+
tion. But during the search, to our observation, in the
crystal structure of cyclohexylaminium picrate salt (Ref.
code GAWCOX) [30] and Gabapentinium picrate (Ref.
2
2
2
the expected R1 (6), R4 (8), R1 (6) fused motif. In this
4
structure the R4 (12) motif is absent, instead it forms a
+
linear N–H O hydrogen bond between the adjacent
inversion-related anion-cation pair. Interestingly, in both
structures ZZZLBS02 and ZEDPON01, the inversions-
related anionic-cationic pairs are twisted away each other
compared with planar motifs in compound (I). The ex-
pected hydrogen-bonded supramolecular motif is not ob-
served in closely related structure, 4-methylanilinium
picrate (ref. code LIGYAD) [29]. Absence of inversion-
related motifs may be attributed to the large deviation of
both nitro groups from the phenyl plane due to steric
code LORQIT) [31] due to the presence of NH3 group,
the inversion-related anions and cations are interlinked
through N–H O hydrogen bonds showing R12(6),
2
2
R4 (8), R1 (6) motifs fused together which extends to
4
one-dimensional supramolecular tape through R4 (12)
motif. Similar type of supramolecular motifs is observed
in the crystal structures of cyclohexane 1,2 diaminium bis
(picrate) (ref. code HEWFAS) [32] and piperazinium di
picrate (ref. code TONBEF) [33] salts except for the ab-
sence of connecting R44(12) motif. From the above
Fig. 6 Part of the crystal structure of (I) showing the formation of two-dimensional supramolecular sheet extending parallel to (-1 0 1) plane. Hydrogen
atoms not involved in hydrogen bonds are omitted for clarity

Struct Chem
Fig. 7 Part of structure (II) a
shows the formation of inversion
related A set of anions and cations
linked through N–H O and C–
H O hydrogen bonds thus
2
4
constructing R1 (6), R4 (12),
1
R2 (6) motifs and b shows the
formation of inversion related B
set of anions and cations linked
through N–H O and C–H O
hydrogen bonds thus constructing
2
2
1
1
R1 (6), R4 (8), R2 (6), R2 (7)
motifs. Hydrogen atoms not
involved in hydrogen bonds are
omitted for clarity
discussion and comparison with reported structures show
that in picrate salts, the formation of R1 (6) motif is dom-
motifs are expected in most of inversion-related molecules
2
+
+
having NH3 and NH2 functional groups. Absence of
these motifs in organic picrate salts may be attributed
due to the deviation of ortho NO2 groups from mean ben-
zene plane as well as the presence of other functional
inant over other hydrogen bond motifs. This is due to the
presence of deprotonated oxygen atom (O−) and ortho
2
4
NO2 groups. Also, the formation of R4 (8) and R4 (12)
Fig. 8 Part of the crystal structure of (II) showing a the formation of one-
dimensional supramolecular tape constructed by A-set of anions and cat-
ions through N–H O and C–H O hydrogen bonds extending along (1 1
0) direction. b Showing the formation of one-dimensional supramolecular
tape constructed by B-set of anions and cations through N–H O, C–H
O hydrogen bonds and C–H π interaction extending along (1 0 0) direc-
tion. Hydrogen atoms not involved in the hydrogen bonds are omitted for
clarity

Struct Chem
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15. Harms K, Wocadlo S (1995) XCAD4. University of Marburg,
Germany
groups in counter molecule which has the tendency to
form hydrogen bonds with ortho nitro groups.
Conclusion
The presence of functional groups such as NO2, O−, NH2+ and
+
NH3 in 4-fluoranilinium and dicyclhexylaminium picrate
form strong N–H O, C–H O hydrogen bonds leading to
16. North ACT, Phillips DC, Mathews FS (1968). Acta Crystallogr
A24:351–359
the formation of one-, two-, and three-dimensional supramo-
2
lecular frameworks. Picrate salts form interesting R4 (8) and
17. Sheldrick GM (2015). Acta Crystallogr C71:3–8
18. Farrugia LJ (1997). J Appl Crystallogr 30:565
19. Macrae CF, Bruno IJ, Chisholm JA, Edgington PR, McCabe P,
Pidcock E, Rodriguez-Monge L, Taylor R, van de Streekand J,
Wood PA (2008). J Appl Crystallogr 41:466–470
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C (2006). Acta Crystallogr C62:o165–o169
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4
R4 (12) hydrogen-bonded supramolecular motifs in mole-
2
cules having NH2+ and NH3+ groups. Absence of R4 (8) and
4
R4 (12) motifs in certain picrate salts may be due to the devi-
ation of ortho nitro group (NO2) from the mean benzene
plane. Structural and hydrogen bond analysis of picrate salts
shows that the choice of functional group in cation moiety will
help to tune the supramolecular framework/motif of desired
fashion.
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