Hydrogen-bonded sheets in 2-(2-aminophenyl)-1H-benzimidazol-3-ium dihydrogen phosphate

Article abstract of DOI:10.1107/S010827010801456X

The title salt, C13H12N3 ⁺·H2PO4 ^-, contains a nonplanar 2-(2-amino-phenyl)-1H-benzimidazol-3-ium cation and two different dihydrogen phosphate anions, both situated on twofold rotation axes in the space group C2. The anions are linked by O - H...O hydrogen bonds into chains of R 2 ²(8) rings. The anion chains are linked by the cations, via hydrogen-bonding complementarities and electrostatic inter-actions, giving rise to a sheet structure with alternating rows of organic cations and inorganic anions. Comparison of this structure with that of the pure amine reveals that the two compounds generate characteristically different sheet structures. The anion-anion chain serves as a template for the assembly of the cations, suggesting a possible application in the design of solid-state materials.

Full text of DOI:10.1107/S010827010801456X

organic compounds
Acta Crystallographica Section C
Crystal Structure
1H-benzimidazol-3-ium dihydrogen phosphate, (I). Benz-
imidazolylaniline (BIMD) is a derivative of pharmaceutically
Communications
´
useful benzimidazole compounds (Velık et al., 2004, and
references therein).
ISSN 0108-2701
The asymmetric unit of (I) (Fig. 1) comprises one BIMD
cation and one-half of two different dihydrogen phosphate
(DPH) anions (P1/O1/O2 and P2/O3/O4) lying across twofold
rotation axes along (0, y, 12) and (0, y, 0), respectively. BIMD is
nonplanar, with the planes of the benzimidazole heterocycle
(N1/C2/N3/C3a/C4–C7/C7a) and aniline (N14/C8–C13)
making an angle of 38.6 (1)ꢂ; the N1—C2—C8—C13 torsion
angle is 36.7 (4)ꢂ. In DPH, the two P—O distances for the OH
groups, as expected, are significantly longer [P1—O2 =
Hydrogen-bonded sheets in
2-(2-aminophenyl)-1H-benzimid-
azol-3-ium dihydrogen phosphate
S. Shylaja,a K. N. Mahendra,a K. B. R. Varma,b
T. Narasimhamurthyb and R. S. Rathorec*
˚
˚
1.561 (2) A and P2—O4 = 1.563 (2) A] than the other two
aDepartment of Chemistry, Bangalore University, Bangalore 560 056, India,
bMaterials Research Centre, Indian Institute of Science, Bangalore 560 012, India,
and cSchool of Biotechnology, Devi Ahilya University, Indore 452 001, India
Correspondence e-mail: ravindranath_rathore@yahoo.com
˚
˚
[P1—O1 = 1.5015 (17) A and P2—O3 = 1.4996 (17) A].
ꢁ
In (I), the H2PO4 anions are linked by two O—Hꢀ ꢀ ꢀO
hydrogen bonds (Table 1) to form an R22(8) ring (Bernstein et
al., 1995). The hydrogen bond involving atom O2 as donor is
the more nearly linear of these and has a shorter Hꢀ ꢀ ꢀO
distance. The R22(8) ring motif, extending on either side, gives
rise to a chain (Fig. 2). This hydrogen-bonded anionic
framework serves as template for the assembly of the cations,
resulting in a sheet structure parallel to the bc plane with
alternate rows of cations and anions. Due to amine–imine
tautomerism, there are two equivalent salt links, N3—
H3ꢀ ꢀ ꢀO1 and N1—H1ꢀ ꢀ ꢀO3i [symmetry code: (i) x, 1 + y, z].
The sheet, apart from the salt bridges, is stabilized by N14—
H14Aꢀ ꢀ ꢀO1 hydrogen bonds. Intersheet contact is maintained
by C11—H11ꢀ ꢀ ꢀO4ii [symmetry code: (ii) 21 + x, 21 + y, 1 + z] and
van der Waals interactions. Atom H14B does not participate in
any nonbonded interaction scheme. However, this is not an
unusual observation in the case of amino groups. The char-
acteristic sheet structure in the present example is mainly the
result of the complementary nature of the molecules, i.e. one
with an excess of donors and the other deficient in them, in an
Received 8 March 2008
Accepted 14 May 2008
Online 7 June 2008
+
The title salt, C13H12N3 ꢀH2PO4ꢁ, contains a nonplanar 2-(2-
aminophenyl)-1H-benzimidazol-3-ium cation and two
different dihydrogen phosphate anions, both situated on
twofold rotation axes in the space group C2. The anions are
linked by O—Hꢀ ꢀ ꢀO hydrogen bonds into chains of R22(8)
rings. The anion chains are linked by the cations, via hydrogen-
bonding complementarities and electrostatic interactions,
giving rise to a sheet structure with alternating rows of
organic cations and inorganic anions. Comparison of this
structure with that of the pure amine reveals that the two
compounds generate characteristically different sheet struc-
tures. The anion–anion chain serves as a template for the
assembly of the cations, suggesting a possible application in
the design of solid-state materials.
Comment
Anions serve as useful building blocks for the formation of
self-assembled supramolecular architectures in both organic
and inorganic systems (Gale, 2000, 2001). They can assemble
in well defined fashions and, by relying on the combined
strength of electrostatic and hydrogen-bonding interactions, it
is possible to generate reproducible topologies. Partially
protonated oxoanions derived from sulfuric and phosphoric
acids are two such interesting systems (Braga et al., 2004). We
are particularly interested in observing how dihydrogen
phosphate would assemble and its role in molecular associa-
tion. In this context, we report here the preparation and
structural characterization of the title salt, 2-(2-aminophenyl)-
Figure 1
A view of (I), showing the atom-numbering scheme. Displacement
ellipsoids are drawn at the 30% probability level and H atoms are shown
as small spheres of arbitrary radii. Dashed lines represent hydrogen
bonds. [Symmetry codes: (i) ꢁx, y, 1 ꢁ z; (ii) ꢁx, y, ꢁz.]
Acta Cryst. (2008). C64, o361–o363
doi:10.1107/S010827010801456X
# 2008 International Union of Crystallography o361

organic compounds
chains of R22(8) type, forming a honeycomb structure (Braga et
al., 2004). Some interesting packings have been observed. The
oxoanion–oxoanion one-dimensional motif in NELVUV gives
rise to a sheath-like structure of cations around it (Light et al.,
2001). In LELXIJ, the linear DPH chains form a hydrated
layer structure, resulting in alternating cationic and anionic
layers (Braga et al., 1999) The oligomeric assembly of DPH
observed in (I) serves as an interesting example of a template-
assembled supramolecular architecture.
Experimental
Initially, compound (II) was synthesized by standard phosphoric acid
cyclization, i.e. the Phillips method (Phillips, 1928a,b), by heating
equimolar quantities of technical grade 1,2-phenylenediamine and
2-aminobenzoic acid (anthranilic acid) in polyphosphoric acid for 4 h
at about 473 K [yield 60%, m.p. 484 (1) K]. Compound (I) was
prepared from (II) by dissolving it in ethanol and adding dropwise an
equimolar quantity of 85% syrupy orthophosphoric acid. The
resulting grey precipitate was filtered off, washed with water and
dried at 323–333 K in an oven [yield 86%, m.p. 545 (1) K]. Compound
(I) was crystallized from a mixture of methanol and water (70:30 v/v)
by slow evaporation; colourless crystals appeared within a week.
The second-harmonic generation (SHG) efficiency of (I) was
measured relative to potassium dihydrogen phosphate (KDP) by a
standard powder technique (Kurtz & Perry, 1968) using an Nd:YAG
laser (ꢁ = 1064 nm, 8 ns pulse and 3.4 mJ per pulse). The compound
exhibits a weak activity of 0.15 times that of KDP.
Figure 2
The hydrogen-bonded sheet structure of (I) in the bc plane, formed by
alternating rows of organic cations and inorganic anions. Only relevant H
atoms are shown. [Symmetry code: (i) x, 1 + y, z.]
attempt to make up this numerical imbalance. Using the idea
of hydrogen-bond complementarity, which involves both
geometric factors and a suitable balance of the number of
hydrogen-bond donors and acceptors, several self-assembled
supramolecular architectures have been designed (Aakerby &
Schultheiss, 2007, and references therein).
As the CSD search was quite time-consuming, it was carried out in
stages. Firstly, a sub-database of 132 structures containing dimeric
DPH units was created. The final search for infinitely extended chains
was then carried out using this sub-database, yielding 27 hits.
The structure of the corresponding neutral imidazole,
namely 2-(1H-benzimidazol-2-yl)aniline, (II), has been
reported previously in the space group Pbca (Das et al., 2003;
Shylaja et al., 2008). It is interesting to compare the packing of
salt (I) with the neutral imidazole, (II), primarily because (II)
is deficient in acceptors while (I) has an excess of them. The
packing in (II) is characterized by BIMD molecules forming a
sheet structure in the ab plane. BIMD molecules are arranged
into a linear chain via intermolecular N—Hꢀ ꢀ ꢀN hydrogen
bonds along the b axis. These chains are linked into sheets by
N—Hꢀ ꢀ ꢀꢀ and C—Hꢀ ꢀ ꢀꢀ interactions (shown in Supplemen-
tary Fig. 3). In view of the inadequate number of acceptors, the
energetically next-favourable ꢀ-acceptors are utilized to fulfil
this imbalance and maximize lattice interactions. The hier-
archical choice of intermolecular interactions is a phenom-
enological rule governing supramolecular assembly.
Crystal data
+
ꢁ
3
˚
V = 1333.2 (3) A
Z = 4
C13H12N3 ꢀH2PO4
Mr = 307.24
Monoclinic, C2
a = 18.3700 (11) A
Mo Kꢃ radiation
ꢄ = 0.23 mmꢁ1
T = 295 (2) K
0.33 ꢃ 0.28 ꢃ 0.22 mm
˚
˚
b = 10.0050 (13) A
˚
c = 7.9145 (14) A
ꢂ = 113.575 (2)ꢂ
Data collection
Bruker SMART CCD area-detector
diffractometer
Absorption correction: multi-scan
(SADABS; Bruker, 2003)
Tmin = 0.91, Tmax = 0.96
6829 measured reflections
2612 independent reflections
2374 reflections with I > 2ꢅ(I)
Rint = 0.025
A search of the Cambridge Structural Database (CSD,
Version 5.28; Allen, 2002) revealed 27 examples of hydrogen-
bonded DPH, forming R22(8) rings and extending into infinite
linear chains (CSD refcodes ACUXIG, BIDPEJ, CLQUON01,
CPAIMZ, DASNUH, DAYHOB, DUNHID, EDUQUP,
EJEGAB, FAXGUH, FEDMIL, FIJHEL, GEXXAI,
GOLTOQ, IDAPEI01, ISUZIF, LELXIJ, MATKAT,
MPHAZP, NELVUV, PAMRAX, PROCPH, REZNEP,
SASBIX, SEGGER, SODCUJ and XAPRUC). FAXGUH
and IDAPE101 are examples of metal-coordinated DPH.
HAHGED is another example containing extended nonlinear
Table 1
Hydrogen-bond and short-contact geometry (A, ).
ꢂ
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
O2—H2Oꢀ ꢀ ꢀO3
O4—H4Oꢀ ꢀ ꢀO1
N1—H1ꢀ ꢀ ꢀO3i
0.81 (3)
0.81 (2)
0.87 (2)
0.875 (17)
0.88 (3)
0.93
1.82 (3)
1.85 (2)
1.875 (19)
1.820 (16)
2.51 (3)
2.52
2.619 (3)
2.641 (3)
2.736 (3)
2.686 (3)
3.128 (4)
3.444 (4)
3.022 (4)
172 (4)
163 (4)
169 (3)
170 (2)
128 (3)
172
N3—H3ꢀ ꢀ ꢀO1
N14—H14Aꢀ ꢀ ꢀO1
C11—H11ꢀ ꢀ ꢀO4ii
N14—H14Aꢀ ꢀ ꢀN3
Symmetry codes: (i) x; y þ 1; z; (ii) x þ ; y þ ; z þ 1.
0.88 (3)
2.44 (3)
125 (3)
1
2
1
2
+
ꢁ
ꢄ
o362 Shylaja et al. C13H12N3 ꢀH2PO4
Acta Cryst. (2008). C64, o361–o363

organic compounds
Refinement
informatics Centre, School of Biotechnology, Devi Ahilya
University, Indore, India.
R[F2 > 2ꢅ(F2)] = 0.035
wR(F2) = 0.090
S = 1.10
2612 reflections
209 parameters
7 restraints
Áꢆmax = 0.32 e A
ꢁ3
˚
ꢁ3
˚
Áꢆmin = ꢁ0.18 e A
Absolute structure: Flack (1983),
with 1224 Friedel pairs
Flack parameter: 0.02 (10)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GD3204). Services for accessing these data are
described at the back of the journal.
H atoms treated by a mixture of
independent and constrained
refinement
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˚
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˚
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Acta Cryst. (2008). C64, o361–o363
Shylaja et al.
C13H12N3 ꢀH2PO4
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