Crystal and molecular structure of 4-aminobenzohydrazide

Article abstract of DOI:10.1007/s10870-009-9667-0

The molecule of 4-aminobenzohydrazide is essentially planar and geometric parameters conform to literature precedents. Supramolecular N- H???O and N-H???N interactions combine to link molecules of 4-aminobenzohydrazide into a three-dimensional network. Weaker N-H???N and N-H???π interactions consolidate the structure. The compound crystallizes in the monoclinic space group P2 ₁/n with a = 5.411(2) A, b = 14.000(6) A, c = 9.894(4) A, β = 103.917(7)°, and Z = 4.

Full text of DOI:10.1007/s10870-009-9667-0

J Chem Crystallogr (2010) 40:397–401
DOI 10.1007/s10870-009-9667-0
ORIGINAL PAPER
Crystal and Molecular Structure of 4-Aminobenzohydrazide
•
Ali Haider Zareen Akhter
•
•
Humaira Masood Siddiqi Edward R. T. Tiekink
Received: 12 October 2009 / Accepted: 3 December 2009 / Published online: 13 December 2009
ꢀ Springer Science+Business Media, LLC 2009
Abstract The molecule of 4-aminobenzohydrazide is
essentially planar and geometric parameters conform to lit-
erature precedents. Supramolecular N–HꢀꢀꢀO and N–HꢀꢀꢀN
interactions combine to link molecules of 4-aminobenzohyd-
razide into a three-dimensional network. Weaker N–HꢀꢀꢀN
and N–Hꢀꢀꢀp interactions consolidate the structure. The
compound crystallizes in the monoclinic space group P21/n
polymers more thermally resistant [8–10]. However,
rigidity of the backbone renders them insoluble in most
organic solvents and imparts high softening temperatures.
These shortcomings make them generally difficult or too
expensive to process, thus restricting their applications.
Therefore, solubilization of high temperature polymers has
been targeted by several means, such as by the incorpo-
ration of flexible linkages [8–10], bulky substituents
[11–14], non-coplanar or alicyclic units [15, 16], or pendent
flexible groups [17]. Hence, different classes of polymer
such as polyimides, polyamides, poly(amide-hydrazide)s,
poly(imide-hydrazide)s have been extensively studied.
In this connection, the introduction of hydrazide or amide
plus hydrazide linkages into the backbone of the polymer
chain is a viable alternative to improve the processability of
high temperature resistive polymers. Further, the presence
of hydrazide groups in the main chain can be exploited by
converting them into the more chemically resistant and
thermally stable oxadiazole structure by heating the polymer
in the bulk or fiber form at elevated temperatures [18]. The
title compound, 4-aminobenzohydrazide, was prepared as a
part of an on-going research program aimed at the design
and synthesis of structurally modified hydrazide for incor-
poration in high temperature polymers. Herein, the synthesis
and crystal and molecular structures of 4-aminobenzohyd-
razide are reported.
˚
˚
˚
with a = 5.411(2) A, b = 14.000(6) A, c = 9.894(4) A,
b = 103.917(7)8, and Z = 4.
Keywords Hydrazide ꢀ Hydrogen bonding ꢀ
N–Hꢀꢀꢀp interaction
Introduction
High temperature resistive polymers have been the subject
of considerable investigation in recent years owing to their
ability to exhibit high thermo-oxidative stability, resistance
to environmental degradation, and superior dielectric,
thermal, adhesive, dimensional stability, and mechanical
properties [1–7]. These properties are strongly influenced
by their chemical structure, i.e. by both the chemical
composition and molecular configuration. In particular,
polymers containing aromatic rings in the main chain have
received special attention as their presence makes these
A. Haider ꢀ Z. Akhter (&) ꢀ H. M. Siddiqi
Department of Chemistry, Quaid-i-Azam University,
Islamabad 45320, Pakistan
Experimental
Materials and Physical Measurements
e-mail: zareenakhter@yahoo.com
E. R. T. Tiekink (&)
All reagents were of AR grade and were used without further
purification. The precursor molecule, 1,4-bis(4-nitro-
benzoyloxymethyl)benzene, was prepared using literature
Department of Chemistry, University of Malaya,
Kuala Lumpur 50603, Malaysia
e-mail: edward.tiekink@gmail.com
123

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J Chem Crystallogr (2010) 40:397–401
procedures [19, 20]. Elemental Analyses for C, H and N were
performed on a Carlo Erba Corporation Model 1104 element
analysis instrument.
Scheme for atom labelling. 13C NMR (DMSO-d6) in d
(ppm) and J (Hz): 166.9 (C = O), 152.0 (H2N–C), 120.4
(–C–C = O), 128.9 (a,a’), 113.1 (b,b’).
Synthesis
X-Ray Crystallography
A two neck 250 mL round bottom flask was charged with
freshly synthesized 1,4-bis(4-nitrobenzoyloxymethyl)ben-
zene (1.0 g, 2.29 mmol), hydrazine monohydrate (10 mL)
and ethanol (80 mL). The resultant mixture was refluxed
for 1 h. After the addition of 5% palladium on carbon (Pd/
C, 0.2 g), the mixture was further refluxed for 15 h and
filtered hot to remove Pd/C. The crude solid was recrys-
tallized from ethanol to afford 4-aminobenzohydrazide
(yield 73%, mp = 239 ꢁC), which was then analyzed by
single crystal techniques. Elemental analysis. Found: C =
55.09, H = 5.97, N = 27.80. C7H9ON3 requires: C =
Intensity data for a colorless block were collected at 98 K on
a Rigaku AFC12/Saturn724 CCD fitted with Mo Ka radia-
tion. The data set was reduced using standard methods [21].
The structure was solved by direct methods with SHELXS-
97 [22] and refined by a full-matrix least-squares procedure
on F2 using SHELXL-97 [22] with anisotropic displacement
parameters for non-hydrogen atoms and a weighting scheme
of the form w = 1/[r2(F2o) ? (0.138P)2 ? 0.254P] where
P = (F2o ? 2F2c)/3. All hydrogen atoms were located in a
difference Fourier map, including N–H hydrogen atoms, but
were included in the final refinement in their calculated
positions. For the N–H atoms, the positions were refined with
55.60, H = 5.96, N = 27.81 %. IR (KBr pellet) in cm-1
:
3450 t(NH st), 3340, 3250 t(NH2 st), 1600 t(C = O st). 1H
NMR (DMSO-d6) in d (ppm) and J (Hz): 9.29 (1H, s,
C–NH–NH2), 7.56 (8.4) (2H, d, a,a’), 6.54 (9.0) (2H, d,
b,b’), 5.59 (2H, s, –NH2), 4.31 (2H, s, NH–NH2); see
the restraints N–H = 0.880 0.001 A or 0.910 0.001 A.
Crystal data and refinement details are given in Table 1.
Figure 1, showing the atom labeling scheme, was drawn with
50% displacement ellipsoids using ORTEP-3 [23] and the
˚
˚
Table 1 Crystal data and
Empirical formula
C7H9N3O
refinement details
for 4-aminobenzohydrazide
Formula weight
151.17
Crystal habit, color
Crystal system
Space group
Block, colorless
Monoclinic
P21/n
˚
a (A)
5.411(2)
˚
b (A)
14.000(6)
9.894(4)
˚
c (A)
b (8)
103.917(7)
3
˚
Volume (A )
727.5(5)
Z
4
Density (calculated, g cm-3
)
1.380
Absorption coefficient (mm-1
)
0.098
F(000)
320
Crystal size (mm)
0.11 9 0.18 9 0.46
2.6–26.5
h Range for data collection (8)
Reflections collected
Independent reflections
Rint
2977
1491
0.019
Reflections with I C 2r(I)
Number of parameters
Goodness-of-fit on F2
a, b for weighting scheme
Final R indices [I C 2r(I)]
R indices (all data)
1435
115
1.04
0.043, 0.345
R1 = 0.038, wR2 = 0.094
R1 = 0.039, wR2 = 0.095
0.26, -0.22
-3
)
˚
Largest difference peak and hole (A
CCDC deposition no.
749935
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399
remaining figures were drawn with DIAMOND [24]. Data
manipulation and interpretation were accomplished using
WinGX [25] and PLATON [26].
the C3–C4–C7–O1, N3–N2–C7–C4, and N3–N2–C7–O1
torsion angles of -13.17(17), 175.32(9), and -4.05(17)ꢁ,
respectively. Indeed, the maximum deviation from the least-
squares plane through all non-hydrogen atoms is -0.212(1)
˚
A for atom O1. The angles about the carbonyl-C7 atom range
Results and Discussion
from a narrow 116.80(10)ꢁ for N2–C7–C4 to a wide
122.45(10)ꢁ for O1–C7–C4, consistent with significant car-
˚
bonyl character in the C7=O1 bond (1.2408(14) A). The
The title 4-aminobenzohydrazide was prepared in accord
with the following Scheme 1: and characterized spectro-
scopically (see Experimental). Full structural characteriza-
tion was afforded by single crystal X-ray crystallography.
˚
N2–C7 bond distance is 1.3368(15) A and N2–N3 is
˚
1.4222(14) A. These values are, respectively, equal within
experimental error to those found in the crystal structure of
˚
benzhydrazide, i.e. 1.240(3), 1.338(5), and 1.415(4) A [27].
In fact, a search in the CSD [28] shows that for 24 entries with
the H2N–N(H)C(=O)C6 fragment in single component
structures, the average C=O, N–C and N–N distances are
1.235, 1.332 and 1.416, respectively.
Of particular interest is the crystal packing. Geometric
parameters describing the most prominent intermolecular
interactions are collected in Table 2. From Fig. 1 it is clear
that there is a mismatch between acidic hydrogen atoms,
i.e. there are five N–H atoms available to form hydrogen
bonds, and three hydrogen bond acceptors, i.e. three: 19
oxygen and 29 nitrogen (N1 and N3). This disparity
between donors and acceptors is partly compensated for by
the carbonyl-O1 atom forming two N–HꢀꢀꢀO hydrogen
bonds with symmetry related 4-amino–NH2 hydrogen
atoms. As illustrated in Fig. 2, this results in the formation
of an eight-membered {OꢀꢀꢀH–N–Hꢀꢀꢀ}2 synthon, R24ð8Þ,
involving a total of four molecules. The next most prom-
inent interaction, at least based on distance and angle
considerations, occurs between centrosymmetrically rela-
ted hyrazide-N3 and amide-N2–H atoms resulting in the
formation of a six-membered {H…N–H}2 synthon, R22ð6Þ.
These synthons serve to link the four molecule aggregates
sustained by N–HꢀꢀꢀO hydrogen bonds into a supramolec-
ular chain, with successive pairs of molecules virtually
orthogonal to each other. Expanding these aggregates by
further N–HꢀꢀꢀO and N–HꢀꢀꢀN hydrogen bonds orthogonal
to the chain gives rise to a three-dimensional architecture
as illustrated in projection in Fig. 3.
Scheme 1
The molecular structure of 4-aminobenzohydrazide with
atom labeling is shown in Fig. 1. Excepting hydrazide
hydrogens, the moleculeis essentially planar as evidenced by
From the data included in Table 2, it is evident that the
short and directional N–HꢀꢀꢀO and N–HꢀꢀꢀN hydrogen
bonding interactions dictate the adoption of the observed
Fig. 1 Molecular structure of 4-aminobenzohydrazide. Displacement
ellipsoids are drawn at the 50% probability level
˚
Table 2 Hydrogen bonding parameters (A–HꢀꢀꢀB; A, 8) for 4-aminobenzohydrazide
A
H
B
HꢀꢀꢀB
AꢀꢀꢀB
A–HꢀꢀꢀB
Symmetry operation
N1
N1
N2
N3
N3
H1n
H2n
H3n
H4n
H5n
O1
2.08
2.08
2.12
2.82
2.42
2.9846(19)
2.9326(19)
2.9413(19)
3.4844(18)
3.286(2)
176
156
154
131
159
‘ ? x, ‘ - y, ‘ ? z
1‘ - x, ‘ ? y, ‘ - z
-x, -y, 1 - z
O1
N3
Cg(C1–C6)
N1
1 - x, -y, 1 - z
‘ - x, -‘ ? y, ‘ - z
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J Chem Crystallogr (2010) 40:397–401
Fig. 2 Detail of the
supramolecular association
mediated by N–HꢀꢀꢀO (orange
dashed lines) and N–HꢀꢀꢀN (blue
dashed lines) hydrogen bonding
in the crystal structure of
4-aminobenzohydrazide. The
N–HꢀꢀꢀO and N–HꢀꢀꢀN hydrogen
bonds extend in three
dimensions to form a three-
dimensional network. (Color
figure online)
Fig. 4 Detail of the intermolecular interactions formed by the
terminal –N(H)–NH2 group in 4-aminobenzohydrazide. The weak
N–HꢀꢀꢀN and N–Hꢀꢀꢀp interactions are shown as blue and purple
dashed lines, respectively, and cooperate to reinforce the N–HꢀꢀꢀO
hydrogen bonds. (Color figure online)
[32–34], there are several precedents for N–Hꢀꢀꢀp interac-
tions in the crystallographic literature [35–37]. The last two
interactions, represented in Fig. 4, serve to provide addi-
tional stability to molecules bridged by the N–HꢀꢀꢀO
hydrogen bonds.
In keeping with Etter’s guidelines for hydrogen bond
formation [38], the strongest donors and acceptors in 4-am-
inobenzohydrazide interact to form the framework of the
crystal structure, leaving the hyrazide-N3 hydrogen atoms to
participate in weak or non-conventional interactions.
Fig. 3 Unit cell contents viewed in projection down the b-axis in the
crystal structure of 4-aminobenzohydrazide
network. However, this leaves two acidic hydrogen atoms,
each bound to the hydrazide-N3 atom, yet to be accounted
for. One of these, i.e. H5n, participates in a significantly
weaker N–HꢀꢀꢀN interaction, compared to the aforemen-
tioned N–HꢀꢀꢀN hydrogen bonds, with the 4-amino–N1
atom, Table 2. The remaining H4n atom forms an N–Hꢀꢀꢀp
interaction where the p-system is defined by the C1–C6
aromatic ring. While this type of interaction is not common
let alone fully understood [29–31], certainly not when
compared with now well documented C–Hꢀꢀꢀp contacts
Supplementary Material
CCDC-749935 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or
from the Cambridge Crystallographic Data Centre
(CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax
?44(0)1223-336033; email: deposit@ccdc.ccam.ac.uk].
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J Chem Crystallogr (2010) 40:397–401
401
Acknowledgments The authors are grateful to the Department of
Chemistry, Quaid-i-Azam University, for providing laboratory and
analytical facilities. We are also grateful to the Higher Education
Commission, Pakistan, for their financial support.
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