Luminescent N-arylphthalimidino derivatives 2- and 4-(1-oxo-1H-2,3- dihydroisoindol-2-yl)benzoic acid: Examples of a new class of reaction induced crystallization for an organic compound

Article abstract of DOI:10.1039/b908853a

Luminescent phthalimidino derivatives 2- and 4-(1-oxo-1H-2,3- dihydroisoindol-2-yl)benzoic acid were prepared and characterized, and their crystallization revealed a new approach for the crystallization of an organic compound which is induced by a reactio

Full text of DOI:10.1039/b908853a

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Luminescent N-arylphthalimidino derivatives 2- and
4-(1-oxo-1H-2,3-dihydroisoindol-2-yl)benzoic acid: examples of a new
class of reaction induced crystallization for an organic compoundw
Yun Chen,* Hui Li and Shuanglian Cai
Received (in Cambridge, UK) 5th May 2009, Accepted 30th June 2009
First published as an Advance Article on the web 21st July 2009
DOI: 10.1039/b908853a
Luminescent phthalimidino derivatives 2- and 4-(1-oxo-1H-2,3-
dihydroisoindol-2-yl)benzoic acid were prepared and characterized,
and their crystallization revealed a new approach for the
crystallization of an organic compound which is induced by a
reaction but not the synthetic reaction itself.
Wan et al.,5 since the characteristic signals commensurate with
the practicable metastable binary base product6 which support
the dihydroxyl intermediate arising from the double addition
of the two amines to the two formyl groups of OPA were
observed in ESI-MS in the course of the condensation reaction
and feathering out following the finish of the reaction.
The colorless single crystalsz of 1 and 2 were fortunately
obtained from their solution of EtOH–H2O, accompanying an
oxidation of coexisting cuprous halide with a gradual color
change to dark green. Moreover, the crystals can also be
obtained from the reaction mixture of OPA and aminobenzoic
acid with the presence of CuX (X = Cl, Br) and O2
(Scheme 1). However, when the same reaction was deliberately
carried out under nitrogen atmosphere avoiding the oxidation
of Cu(I), and, withal, some other transition metal halide MX2
(X = Cl, Br; M = Mn, Co, Ni, Cu and Zn) was applied
instead of cuprous, no single crystal could be found. These
results directly or indirectly support the inductive effect of the
oxidation process of cuprous ion in the crystallization of the
two compounds. Here the oxidized Cu2+ cation presumably
provided a nucleus for the title compounds to crystallize onto,
and this was followed by a growth step. Although more
detailed related studies on the inducing mechanism are needed,
this is really a new crystallizing approach differing from the
abovementioned SRC.
The growing technique of reaction-induced crystallization and
phase-separation has attracted considerable interest due to its
great virtue of being practical especially for crystallizing
difficult solid-state materials, catalysts, polymorphic drugs
and new supramolecular architecture.1 In this approach, it
is generally considered that a desired insoluble crystal is
produced by either synthetic reaction or decomposition
reaction of precursor species under some kind of controlling
conditions (often hydrothermal or diffusional),2 that is to say,
the crystal is the product of the inducing reaction itself
(referred to here as ‘‘self reaction-induced crystallization’’, or
SRC for short). Thus, it is mostly applicable to those
precursors which display reasonably simple reactivity, and
its application hitherto has been mostly limited to the field
of inorganic compounds and coordination compounds with
very few examples of an organic cocrystal.1–3 However, these
results do not mean that reaction-induced crystallization is
unsuitable for simple organic molecule species which is firmly
required in so many cases. One of the alternative simple
strategies may be using the slow-paced relatively independent
inorganic reaction instead of the intricate synthetic organic
reaction itself as crystallizing inducer to shift the solubility
little-by-little so as to allow easy access to crystallization.
Herein, we report the first examples of this completely new
class of reaction-induced crystallization in new N-arylphthal-
imidino derivatives 2- and 4-(1-oxo-1H-2,3-dihydroisoindol-
2-yl)benzoic acid (1 and 2), and their preparation, structure
and fluorescence properties are also discussed.
The crystal structure and properties of solid state 1 and 2
are significantly affected by p–p stacking interactions and
numerous hydrogen bonds (such as O–Hꢀ ꢀ ꢀO, C–Hꢀ ꢀ ꢀO,
C–Hꢀ ꢀ ꢀp).7 The melting point of 2 is 43.5 1C higher than that
of 1. The rotation of the molecule 1 round the N–Ar bond is
hampered by the carboxyl and gives rise to its atropoisomerism
(Fig. 1). Although the absolute structure could not be resolved
here,8 the presence of only one enantiomer in the unit cell
indicates the chirality of each crystal with non-centrosymmetric
space group P212121, which is on account of ‘‘spiralling’’
guided by Oꢀ ꢀ ꢀH–C hydrogen bonds as hereinafter-mentioned.
Both the compounds were synthesized by the same one-step
condensation reaction of o-phthalaldehyde (OPA) with o- or
p-aminobenzoic acid without any catalyst4 in the mol ratio of
1 : 1 in ethanol at 90 1C (yield with respect to OPA: 56% for 1,
51% for 2). The mechanism of the reaction may be similar to
but slightly different from that described by Takahashi and
College of Chemistry and Chemical Engineering, Hunan University,
Changsha, Hunan 410082, China. E-mail: cnchenyun@yahoo.com.cn;
Fax: +86-731-8713642; Tel: +86-731-8822275
w Electronic supplementary information (ESI) available: Experimental
details and spectral data. Crystallographic data. CCDC 714750 (1) and
714749 (2). For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b908853a
Scheme
1
Reaction-induced crystallization of title compounds
1 and 2.
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2: lem = 407 nm, lex = 338 nm). The substitution of carboxyl
para to the amide group allows a higher conjugation between
neighboring chromophores in 2, and it increased the fluores-
cence intensity markedly.
In summary, this paper describes the preparation and
structure of two new N-arylphthalimidino derivatives and a
breakthrough in finding a useful approach toward crystal-
lization of difficult to crystallize micromolecular species by
inorganic reaction. Studies on the extension of the application
of this method to similar systems are currently underway.
This work was financially supported by the Open-End Fund of
Main Precise Instrument of Hunan University (0902073). The
authors thank the laboratory of Jian-Hui Jiang for providing
their instruments to carry out the luminescence experiment.
Notes and references
z Crystallographic data for: 1: C15H11NO3, M = 253.25, orthorhombic,
space group P212121 (no. 19),
a
=
5.883(1),
b
=
11.837(3),
cmꢂ3
m = 0.097 mmꢂ1, Z = 4, l = 0.71073 A, T = 273(2) K, 3005
reflections collected, 1227 independent (Rint 0.064), and 867
observed reflections [I 4 2s(I)], 176 refined parameters, R = 0.0709,
c
=
17.492(5) A,
V
=
1218.1(5) A3, Dc
=
1.381
g
,
=
Fig. 1 Partial crystal structures of 1 (above) and 2 (below) showing the
H-bonding and p–p stacking interactions. H atoms are omitted for clarity.
ꢀ
wR2 = 0.1152. 2: C15H11NO3, M = 253.25, triclinic, space group P1
(no. 2), a = 6.4222(3), b = 10.2231(2), c = 10.3311(4) A,
a = 64.642(2), b = 74.415(2), g = 76.328(2)1, V = 584.64(4) A3,
Dc = 1.439 g cmꢂ3, m = 0.101 mmꢂ1, Z = 2, l = 0.71073 A,
Every two neighboring molecules of 1 link to each other by
Oꢀ ꢀ ꢀH–O(COO) forming a zigzag chain, which is stabilized by
the supportive hydrogen bond9 of Oꢀ ꢀ ꢀH–C(aryl) with graph
T
= 273(2) K, 3082 reflections collected, 2058 independent
(Rint = 0.0457), and 1421 observed reflections [I 4 2s(I)], 176 refined
parameters, R = 0.1181, wR2 = 0.1683.
2
set10 R2 (7). Weak Oꢀ ꢀ ꢀH–C(aryl) interchain H-bonds associate
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at almost the same wavelength (1: lem = 409 nm, lex = 345 nm;
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Fig. 2 Absorption (dashed line) and fluorescence (solid line) spectra of
compounds 1 (red) and 2 (blue) in DMF solution at room temperature.
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