A study on fluoride detection and assembly of hydroxyaromatic aldoximes caused by tetrabutylammonium fluoride

Article abstract of DOI:10.1039/c4ce02311k

Tetrabutylammonium fluoride (TBAF) forms cocrystal H₂NAP·TBAF with 2-hydroxynaphthaldoxime (H₂NAP) or cocrystal 2(H₃OHPA)·TBAF with 2,3-dihydroxyphenylaldoxime (H₃OHPA), whereas a similar reaction with 2,4-dihydroxyphenylaldoxime (H₃PHPA) forms tetrabutylammonium (TBA) salt TBA(H_2.5PHPA)₂. Formation of these cocrystals or salts is accompanied by a color change which enables the detection of fluoride ions. Cocrystal H₂NAP·TBAF has a layered structure formed by hydrogen bonds between the fluoride ions and parent oxime molecules; the tetrabutylammonium cations are held in between layers of anionic assemblies. On the other hand, cocrystal 2(H₃OHPA)·TBAF has a grid-like architecture constructed from hydrogen bonds between the parent oxime molecules and fluoride ions. TBA cations are encapsulated within the grids. It is shown that salt TBA(H_2.5PHPA)₂ forms anionic assemblies to encapsulate tetrabutylammonium cations which are devoid of fluoride ions. By interactions of the tetrabutylammonium fluoride ions with H₃PHPA molecules, an anionic assembly is formed by the sharing of protons, which possesses a grid-like structure. The formation of such an assembly causes color change which enables one to detect fluoride ions by visual means. This journal is

Full text of DOI:10.1039/c4ce02311k

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Table of content entry
Study on fluoride detection and assembling of hydroxyaromatic aldoximes caused
by tetrabutylammonium fluoride
\
Encapsulation of tetrabutylammonium cations
Different assemblies formed by interactions of tetrabutylammonium fluoride with hydroxyꢀ
aromatic oximes show characteristic optical properties
A. Tarai and J. B. Baruah
Study on fluoride detection and assembling of hydroxyaromatic aldoximes caused by
tetrabutylammonium fluoride
Arup Tarai, Jubaraj B. Baruah*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati ꢀ781 039,
Assam, India. Fax: +91ꢀ361ꢀ2690762; Ph. +91ꢀ361ꢀ2582311;
email: juba@iitg.ernet.in http://www.iitg.ernet.in/juba
Abstract:
Tetrabutylammonium fluoride (TBAF) forms cocrystal H NAP.TBAF with 2ꢀ
2
hydroxynaphthaldoxime (H NAP) or cocrystal 2(H OHPA).TBAF with 2,3ꢀ
2
3
dihydroxyphenylaldoxime (H OHPA). Whereas similar reaction of 2,4ꢀ
3
dihydroxyphenylaldoxime (H PHPA) forms tetrabutylammonium (TBA) salt
3
TBA(H PHPA) . Formation of these cocrystals or salt accompanies color change which
2
.5
2
enables detection of fluoride ions. Cocrystal H NAP.TBAF has layered structure formed
2
by hydrogen bonds of fluoride ions with parent oxime molecules; tetrabutylammonium
1

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cations are held in between layers formed by anionic assemblies. On the other hand,
cocrystal 2(H OHPA).TBAF has a gridꢀlike architecture constructed by hydrogen bonds
3
between parent oxime molecules and fluoride ions. TBA cations are encapsulated within
the grids. It is shown that salt TBA(H PHPA) forms anionic assemblies to encapsulate
2
.5
2
tetrabutylammonium cation which is devoid of fluoride ion. By interactions of
tetrabutylammonium fluoride ions with H PHPA molecules, an anionic assembly is
3
formed by sharing of protons, which possesses gridꢀlike structure. Formation of such
assembly causes color change which enables one to detect fluoride ion by visual means.
Keywords:
Hydroxyaromatic aldoxime; Selfꢀassembly; Fluoride ions; Deprotonation.
Introduction:
Oximes constitute an important class of organic compounds which are used to protect
1
2
carbonyl groups and also used as ligands. From crystal engineering point of view,
oximes have attracted attention; they form various cocrystals whose structures are guided
3
by substituent atoms and other functional groups. Different catemers are formed by selfꢀ
3a
assemblies of heterocyclic aromatic oximes.
Possibility to prepare oximes through
4
green methodologies have enhanced future course of chemistry with oximes.
Hierarchical effect of weak interactions help to generate specific assemblies of oximes.
5
Despite of having a good amount literature data on structural motifs of oximes, there are
6
limited concerted affords to unearth their utilities. On the other hand, quaternary
2

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OH
N
OH
N
O
N
OH
NR
4
H
H
R4 NF
H
N
H
H
O
O
OH
ONR
OH
4
H
N
NR
4
OH
A
B
C
D
Cocrystal
Salts
OH
N
OH
OH
N
N
OH
OH
OH
OH
OH
H PHPA(3)
H NAP (1)
H OHPA(2)
2
3
3
Figure 1: Structures of oximes 1ꢀ3. AꢀD are some possible cocrystals and salts of
quaternary ammonium fluoride with 2ꢀhydroxyphenylaldoxime.
7
ammonium fluorides form adducts with oximes causing visual color change. It is also a
well known fact that fluoride ions deprotonate hydroxy groups to cause colour change of
8
chromophoric substances. Thus, combination of these two facts would help to design
sensor for fluoride. Varieties in packing patterns of selfꢀassemblies of hydroxyꢀaromatic
oximes would depend on the components. As an illustration 2ꢀhydroxybenzaldoxime on
interaction with a quaternary ammonium fluoride would lead to different compositions of
ꢀ
ꢀ
coꢀcrystals or salt such as AꢀD shown in figure 1. Due to ability of HF or F ions to
2
9
stabilize different hydrogen bonded assemblies many possibilities in packing pattern can
be anticipated. Thus, understanding of assemblies of cocrystals or deprotonated
supramolecular assemblies of hydroxyaromatic oximes with/by fluoride ions may emerge
as a lead to prepare assemblies with potential applications. With such anticipations
structures and optical properties associated with different supramolecular assemblies
generated by oximes 1ꢀ3 on interaction with tetrabutylammonium fluoride are studied.
Results and discussion
Fluoride assisted assemblies of oximes 1-3:
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Tetrabutylammonium fluoride (TBAF) and 2ꢀhydroxynaphthaldoxime (H NAP, 1), forms
2
cocrystal H NAP.TBAF (4), on the other hand 2,3ꢀdihydroxyphenylaldoxime (H OHPA,
2
3
2
) forms cocrystal 2(H OHPA).TBAF (5) with TBAF. 2,4ꢀdihydroxyphenylaldoxime
3
(
H PHPA, 3) reacts with tetrabutylammonium fluoride to cause deprotonation of a
3
phenolic hydroxy group to form assembly of a tetrabutylammonium (TBA) salt
TBA(H PHPA) (6). Constituents of the cocrystals (4 and 5) and salt (6) are shown in
2
.5
2
figure 2.
H
NOH
OH
OH
H
NOH
OH
Bu NF
4
Bu NF
4
2
H NAP. TBAF(4)
2
2(H OHPA). TBAF (5)
3
H
OH
HO
N
N
OH
OH
H
O
H
O
NBu
4
TBA 2.5
PHPA)
(
H
(6)
2
Figure 2: Cocrystals and salt from aldoximes
Structures of 4, 5 and 6 are determined by single crystal Xꢀray diffraction and they are
also characterized by spectroscopic techniques. Cocrystal 4 is formed by 1 and TBAF in
1
:1 molar ratio. Crystal packing of 4 has oxime molecules forming chainꢀlike structures.
Such chainꢀlike structures extending along cꢀcrystallographic axis are formed by bridging
hydrogen bonds between oxime molecules and fluoride ions. Each fluoride ion is
connected to two oxime molecules from two opposite directions. One side of fluoride ion
is connected through OꢀH···F interaction involving OH group of oxime functionality.
Other side has an OꢀH···F interaction with phenolic hydroxy group and a CꢀH···F
interaction of a hydrogen atom at orthoꢀposition to the hydroxy group to form a chelateꢀ
4

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like motif. Such interactions inhibit the orthoꢀhydroxy group to form conventional
intramolecular hydrogen bond. Carbonꢀfluorine bonds have role in oximes to form
3
different cocrystals, in the present case we observed that priority to form OꢀH···F
interactions along with a weak CꢀH···F interaction to form cyclic motif, is more
favorable than formation of an intramolecular cyclic hydrogen bonded motif. A
schematic drawing showing these interactions in 4 are shown in figure 3a. Although
oximes can selfꢀassemble to form various catemers, strong participation of fluoride ions
6
a
in hydrogen bond do not allow formation of any of the conventional catemers. In crystal
lattice of cocrystal 4, tetrabutylammonium ions are held between two such chains, which
are stabilized by CꢀH···O and CꢀH···F interactions. Some of the important hydrogen
bond parameters are listed in table 1. Fluoride ion of cocrystal 4 (figure 3b) also interacts
with two tetrabutylammonium cations through CꢀH···F interactions. Thus, fluoride ions
act as a bridging ions for two different types of hydroxy groups at two ends of oxime
molecules.
H
H
H
N
F
H
H
O
H O
F
O
H
F
H
N
N
O
O H
O H
H
H
F
(a)
(b)
5

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Figure 3: (a) Representation of chain formed through fluoride ions interacting with OꢀH
and CꢀH bond at one end and through OH of oxime at other end. (b) Packing of cocrystal
4
to show chainꢀlike arrangement of oxime molecules in structure holding
terabutylamminium cations in between layers.
Table 1: Hydrogen bond parameters of 4, 5 and 6
Compound No.
DꢀH···A
d
DꢀH(Å)
d
H···A (Å)
d
D···A(Å)
∠ D−H···A
°)
(
4
0.82
1.74
2.58
2.45
2.555(3)
3.468
173
158
142
O(1)ꢀH(1A)···F(1) [ꢀx, 1/2+y, 1/2ꢀz]
C(8) –H(8)···F(1) [1ꢀx, 1/2 +y,1/2 ꢀz]
C(20) –H(20A) ···F(1) [x, 1/2 ꢀy,1/2 +z]
0
0
.93
.97
3.276(4)
5
6
0.82
1.79
1.74
1.77
2.579(3)
2.556(2)
2.576(3)
161
171
165
O(3)ꢀH(3A) ···F(1) [x, ꢀ1+y, ꢀ1+z]
O(1)ꢀH(1) ···F(1) [x, y, ꢀ1+z]
O(6)ꢀH(6) ···F(1) [1+x, y, z]
0
0
.82
.82
0
.82
1.90
2.679(1)
158
O(3)ꢀH(3A) ···O(1) [1/2+x, 1/2+ y, z]
Coꢀcrystal 5 is formed between oxime 2 and TBAF in 2 : 1 molar ratio. Composition
1
of this cocrystal is also established from integration of proton signals in HꢀNMR spectra.
1
The HꢀNMR spectra of cocrystal 5, shows clearly discernable signals from
tetrabutylammonium cations in aliphatic region; integration of this set of signals
correspond to one molecule TBAF with respect to two molecules of oxime 2. Assembling
process in this case is also guided by strong OꢀH···F interactions, which results 4 + 4
cyclic units between four molecules of oximes with four fluoride ions (figure 4a).
Fluoride ions act as central point to grow such cyclic structures to make gridꢀlike
arrangements. Each cyclic unit holds tetrabutylammonium cations within them. Two
hydroxy groups and two oxime from four independent 2,3ꢀdihydroxyphenylaldoxime
molecules are involved in OꢀH···F interactions to contribute to coordination environment
of fluoride ions in cocrystal 5 (figure 4b). Thus, fluoride ions adopt tetraherdral hydrogen
bonds environment around them. Fluoride ions while acting as connect to form two
dimensional gridꢀlike structures, they assist in encapsulation of tetrabutylammonium
cations within the grids through weak CꢀH···F interactions. Thus, this structure provides
an example of a fluoride assisted assembly to encapsulate TBA cations. Each 2,3ꢀ
dihydroxyphenylaldoxime molecule possesses intramolecular hydrogen bond between
6

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N O
H O
O H
H
F
F
H
O
N
H
H
O
O
Cation
O
H
O
H
N
O
F
H
O
N H
O
H
H
F
O
(a)
(b)
Figure 4: (a) Representation of fluoride assisted cyclic motif observed in the packing of
cocrystal 5. (b) Packing pattern of fluoride assisted assembly of 5 showing encapsulation
of tetrabutylammonium cations.
nitrogen atom of oxime and hydroxyꢀgroup present at orthoꢀposition. Thus, presence and
absence of intramolecular hydrogen bond between hydroxy group and oxime nitrogen is a
prime difference in structures of cocrystals 4 and 5. It may be noted that hydroxy group
7
a
of oxime interacts with fluoride ions but we have dealt with hydroxyꢀaromatic oximes,
of which phenolic hydroxy groups play important roles to guide their packing patterns.
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Hence such a factor makes much different packing from a packing present in simple
oximes. In both cocrystals 4 and 5 participations of hydroxy group of phenolic part in
construction hydrogen bond bridges with fluoride ions are observed.
Reaction of oxime 3 with tetrabutylammonium fluoride resulted in abstraction of a
proton from a hydroxy group at paraꢀposition of the ring with respect to oxime group to
form a salt 6; which crystallized as a cocrystal of 3. Structure of the salt 6 determined by
single crystal Xꢀray diffraction is comprised of selfꢀassemblies of Vꢀshaped dimeric
assemblies of oxime molecules formed through sharing of proton. Such dimeric motifs
form chainꢀlike structures and chains interact among themselves to make voids which
encapsulate tetrabutylammonium cations as illustrated in figure 5a. In case of 6, hydroxy
group present at paraꢀposition of phenyl ring with respect to oxime group, shows strong
intermolecular hydrogen bond interactions which significantly contribute to the formation
of assemblies. There is also intramolecular hydrogen bond between hydroxy group
present at orthoꢀposition with nitrogen atom of oxime. As a result of these interactions
rectangular gridꢀlike structure having TBA cations within grids are formed which is
shown in figure 5b. There are strong hydrogen bonds between phenolic units through O1ꢀ
H1···O1′ bonds having electrostatic property (Figure 5b). Due to this a short donorꢀ
acceptor bond distance between O1ꢀH1···O1′ (symmetry of ′ = 2ꢀx, y, ½ꢀz) of 2.47 Ǻ is
observed. The hydrogen atom bonded to O1 lies on a twofold axis, whereas the nitrogen
atom (N2) of tetrabutylammonium cation serves as pivot of a twofold axis. Once such
assemblies are connected to each other through hydrogen bonds (O3ꢀH3A···O1) of
oxime group of another molecule, rectangular gridꢀlike structures are formed.
Alternatively structures of such grids can be explained as combination of linear chains in
two different directions to form selfꢀassemblies of anions and neutral molecules. Each
chain when hydrogen bonded to another chain in perpendicular direction they form a grid
like structure. Tetrabutylammonium cations held within the grids of 6 by CꢀH···π
interactions as depicted in figure 5b. There is difference between gridꢀlike structure in
cocrystal 5 and in salt 6; in former case electrostatic interactions of fluoride ions are
involved which is absent in the latter case. Mass spectra of 6 show a mass peak at 547.7
(m/e) which corresponds to anticipated m/e value for an assembly between an anion of 3
and a neutral molecule of 3. Fluoride ions are special due to their small size and ability to
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1
0
act as base. Deprotonation of hydroxy compounds by fluoride ions were reported
1
0a
earlier; but anionic selfꢀassemblies generated by fluoride ions in which fluoride ions
are not a part of such an assembly has not been not reported yet. Selfꢀassembly of
cocrystal of a salt formed by assembly of monoꢀdeprotonated 3 with a neutral molecule
of 3 generated by fluoride ion without being a part of the assembly is exceptional.
H
H
O
H
N
O
O
N H
O
O
H
N
O
H
H
O
O
H
O
H
O
H
N
O
O
H
H
O
N
O
H
O
H
N
Cation
O
O
H
O
O
O
H
N
H
H
N
O
O
H
O
O
H
(a)
(b)
Figure 5: (a) Representative diagram to show assemblies of dimeric motif of monoanion
and neutral oxime 3. (b) Encapsulation of tetrabutylammonium cation in anionic
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assembly of oximes in salt 6 showing the prominent hydrogen bonds (symmetry of ′ = 2ꢀ
x, y, ½ꢀz) and CꢀH···π interactions (Cg1 and Cg2 are the center of gravity of phenoxy
and phenolic rings respectively).
Utility of oximes 1-3 in detection of fluoride ions:
In the present study, we find that interactions of oximes 1ꢀ3 with tetrabutylammonium
fluoride selectively changes color. Independent experiments carried out by adding
tetrabutylammonium fluoride to compounds 1ꢀ3 show new absorption peak at 410 nm for
1
, 371 nm for 2 and 336 nm for 3, respectively (Figures 6dꢀ6e).
(a)
(d)
(b)
(e)
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(c)
(f)
ꢀ5
Figure 6: UVꢀvisible spectra of (a) 1, (b) 2, (c) 3 (10 M) in dimethylsuphoxide (DMSO)
ꢀ5
with different tetrabutylammonium salts (100 µl of 10 M solution) showing fluoride salt
only can cause changes in absorptions. UVꢀvisible spectroscopic titration of TBAF (0µlꢀ
ꢀ5
ꢀ5
1
00µl of 10 M solution) with (d) 1; (e) 2 and (f) 3 (10 M solution in DMSO).
However, other tetrabutylammoinum salts such as chloride, bromide, iodide, acetate,
nitrate, bisulphate, biphosphate do not change absorption spectra of compounds 1ꢀ3.
Changes in UVꢀvisible absorption of compounds 1, 2 and 3 are observed in
corresponding titration carried out with each compound by adding solution of
tetrabutylammonium fluoride. Increase in concentration of tetrabutylammonium fluoride
reduces intensity of absorption peak at shorter wavelength while intensity of new
absorption at longer wavelength increases which are shown in figures 6aꢀ6c. Shifts in
absorbance to longer wavelength show change in color. Thus, compounds 1ꢀ3 are suitable
1
1
12
to sense fluoride ions. Deprotonation of phenols and related compounds by fluoride
ions are useful to detect them. On the other hand, there are also examples of hydroxyꢀ
1
3a
13b
naphthalenes and hydroxyꢀanthraquinones which show color change on interactions
with fluoride ions without getting deprotonated. Specific deprotonation by fluoride ions
1
4
of intramolecular hydrogen bonded naphthol derivative was demonstrated earlier. Metal
1
5
complex of receptors containing several hydroxy groups show OꢀH···F interactions and
selective color changes takes place while cocrystals of naphthylaldoxime with fluoride
7
a
16
salt are formed. It was earlier suggested adduct formation of a fluoride salt versus
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deprotonation of acidic compound by fluoride ions are to be carefully distinguished. In
fact, this is true in the present cases and differences in shift of wavelengths in these cases
stems from different types of assemblies. An assembly containing no fluoride ion and the
neutral assembly containing fluoride ions makes a wide difference. Accordingly,
absorption peak of 3 on interaction of fluoride ions appear at 336 nm which is much
lower than absorptions shown by 1 and 2 at 410 nm and 371 nm respectively.
(a)
(b)
.
Figure 7: (a) Color of filter papers preꢀsoaked with oxime 1 followed by soaking in
solutions of different tetrabutylammonium salts. (b) Fluorescence of oxime 1 in DMSO
in presence of different tetrabutylammonium salts on exposure to UVꢀlight at 254 nm
(For each tetrabutylammonium salt, respective anions are shown in figures).
Furthermore the peak observed at 336 nm is identical to absorption maximum shown by a
solution of the salt 6, hence it can be easily suggested that the peak has similarity to
phenoxide ion. The forgoing examples of assemblies 4ꢀ6, suggest that fluoride ions can
act as base to generate new phenolic assemblies with or without being a counterpart of
such an assembly. However, tetrabutylammonium hydroxide shows similar change
(Supporting figure 7S) as that of fluoride ions in the case of 1 and 2 but with a lower
intensity at 410 nm and 371 nm respectively at comparable concentrations. But no change
12

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in UVꢀvisible spectra of compound 3 was caused by tetrabutylammonium hydroxide.
These points suggest that compound 3 is suitable to sense fluoride in a more specific
manner. Color shown by such an assembly in case of 6, formed due to facilitation of
1
7
proton sharing is useful in sensing fluoride ions; which is an exceptional case.
Selective color change caused by fluoride ions allows their easy detection by dipping a
filter paper preꢀsoaked with solution of any of these oximes (1, 2 or 3) in to a solution of
fluoride ions in waterꢀDMSO mixture. A series of experiments by dipping filter paper
independently in different solutions is depicted in figure 7a. It is clear that aqueous
solution containing fluoride ions only develops yellow color on these papers. Thus, these
compounds can have practical utility to test for presence of fluoride ions in water. When
a solution of TBAF is added to a solution of compound 1 in DMSO, it shows
fluorescence emission at 468 nm on excitation at 320 nm, similar peaks are not observed
from solution of 1 containing other tetrabutylammonium salts. On the basis of this
observation, we have developed a technique to visually detect fluoride ions by exposing
solutions containing different anions with 1 by exposing them to UVꢀlight. Solution
containing fluoride ions with 1, exclusively shows a blue fluorescence as illustrated in
figure 7b. Thus, compound 1 could be used as a fluorescence sensor for fluoride ions.
Despite compounds 2 and 3 are useful in detection of fluoride ions by UVꢀvisible
spectroscopy, these two compounds are nonꢀfluorescent hence are not suitable to detect
fluoride ions by fluorescence technique.
Conclusions:
In conclusion, we have shown varieties of selfꢀassemblies generated by fluoride
ions on interactions with hydroxyaromatic oximes. These assemblies carry specific
optical properties and able to provide information to sense fluoride ions visually.
Assembly devoid of fluoride ions as well as assemblies having constituent fluoride ions
may adopt grid like structures to encapsulate cations.
Experimental:
Physical measurements: Infrared spectra of the solid samples were recorded on a Perkinꢀ
−
1
Elmer SpectrumꢀOne FTꢀIR spectrophotometer in the region 4000ꢀ400 cm by making
KBr pellets. UVꢀvisible spectra were recorded on a PerkinꢀElmerꢀLambda 750 UVꢀvis
spectrometer at room temperature. Mass spectra were recorded on a micro mass QꢀTOF
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(waters) mass spectrometer by using an acetonitrileꢀformic acid matrix. Fluorescence
emissions were measured in a PerkinꢀElmer LSꢀ55 spectrofluorimeter by taking definite
amount of solutions of samples and exciting at required wavelengths.
Synthesis and characterization of oximes and fluoride assisted assemblies:
Oximes 1ꢀ3 were prepared from respective hydroxyꢀaromatic aldehyde by reacting them
with hydroxylamine hydrochloride in presence of pyridine. Typical procedure for
synthesis of 2ꢀhydroxynapthaldoxime (1) is as follows: Pyridine (1 mL) was added drop
wise to a solution of hydroxylamine hydrochloride (0.138 g, 2 mmol) dissolved in
ethanol (20 mL). Resulting solution was stirred at room temperature for 15 mins followed
by which 2ꢀhydroxyꢀ1ꢀnaphthaldehyde (0.344 g, 2 mmol) was added and continued
stirring at room temperature for 1 hr. Yellow precipitate of compound 1 was obtained
from the reaction mixture. This was extracted by ethylacetate and water mixture.
1
Removal of ethylacetate in a rotavapor yielded compound 1. Yield: 82 %. HꢀNMR (400
MHz, DMSOꢀd ): 11.53 (s, 1H), 9.04 (s, 1H), 8.48 (d, J = 8.4 Hz, 1H), 7.86 (d, J = 6.4
6
Hz, 1H), 7.84 (d, J = 6.4 Hz , 1H), 7.55 (t, J = 7.2 Hz, 1H), 7.41(t, J = 6.8 Hz, 1H), 7.34
−
1
(
d, 1H). IR (KBr, cm ): 3331 (br, m), 3013 (w), 2924 (w), 2766 (w), 1947 (w), 1758
w), 1632 (s), 1591 (s), 1526 (w), 1464 (w), 1463(m), 1414 (m), 1369 (w), 1310 (m),
(
1
8
1
2
268 (s), 1239 (s), 1182 (s), 1163 (w), 1143 (w), 1079 (w), 1034 (w), 1014 (s) 938 (s),
78 (w), 854 (w), 814 (s), 776 (s), 744 (m), 718 (w), 649 (w), 541(w). Mass (ESI) m/z:
88.0698 (m+1); (Calculated exact mass 187.0633 for C H NO ).
1
1
9
2
,3ꢀDihydroxypenylaldoxime (2):
1
Isolated yield: 83%. HꢀNMR (400MHz, DMSOꢀd ): 11.30 (s, 1H), 9.58 (s, 1H), 9.27 (s,
6
1
1
H), 8.31 (s, 1H), 6.91 (d, J = 7.2 Hz, 1H), 6.66 (d, J = 7.6 Hz, 1H), 6.59 (t, J = 8 Hz,
−
1
H). IR (KBr, cm ): 3454 (bm), 1620 (s), 1592 (w), 1478 (s), 1444 (m), 1412 (w), 1347
(m), 1308 (m), 1285 (m), 1251 (m), 1165 (s), 1075 (m), 1030 (s), 967(s), 850 (s), 782(s),
7
1
2
44 (m), 727 (m), 626 (s), 566 (w). Mass (ESI) m/z: 154.1049. (Calculated exact mass
53.0426 for C H NO ).
7
7
3
,4ꢀDiydroxyphenylaloxime (3):
1
Isolated yield: 84%. HꢀNMR (400MHz, DMSOꢀd ): 10.98 (s, 1H), 10.12 (s, 1H), 9.77
6
−
1
(
s, 1H), 8.22 (s, 1H), 7.28 (d, J = 8.8 Hz, 1H), 6.32 (m, 2H). IR (KBr, cm ): 3363 (br,
m), 1643 (m), 1623 (m), 1598 (w), 1524 (s), 1488 (m), 1446 (w), 1365 (w), 1344 (w),
14

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1
304 (s), 1255 (s), 1208 (s), 1170 (m), 1117 (m), 1003 (s), 973 (s), 957 (m), 933 (w), 857
w), 830 (s), 801 (m), 733 (w), 712 (w), 631 (w), 594 (m), 573 (w). Mass (ESI) m/z:
54.1049; (Calculated exact mass 153.0426 for C H NO ).
(
1
7
7
3
Crystals of 4ꢀ6 were obtained by slow evaporation of solution of respective aldoxime (0.1
mmol) and tetrabutylammonium fluoride (0.1 mmol) in methanol.
1
Cocrystal 4 : HꢀNMR (400 MHz, CDCl ): 9.10 (s, 1H, HꢀC=), 8.03 (d, J = 8.4 Hz, 1H,
3
H ), 7.74 (d, J = 6.4 Hz, 1H, H ), 7.67 (d, J = 6.4 Hz, 1H, H ), 7.45 (t, J = 7.2 Hz, 1H,
ar
ar
ar
H ), 7.29 (t, J = 6.8 Hz, 1H, H ), 7.17 (d, 1H, H ), 3.26 (m, 8H, NꢀCH ), 1.61 (m, 8H, ꢀ
ar
ar
ar
2
CH ꢀ), 1.39 (m, 8H, ꢀCH ꢀ), 0.97 (m, 12H, ꢀCH ꢀ). There are deuterium exchangeable
2
2
2
−
1
signals at 2.62 (s, OH) and 1.5 (s, OH). IR (KBr, cm ): 2959 (s), 2872 (s), 2851 (w),
1
1
8
783 (w), 1621 (s), 1594 (m), 1571 (s), 1569 (s), 1431 (s), 1373 (m), 1344 (s), 1306 (m),
274 (w), 1246 (w), 1211(w), 1167 (m), 1108 (w) 1074 (w), 1035 (w), 1002 (w), 937 (s),
80 (m), 828 (s), 783 (w), 760 (m), 668 (w), 582 (w).
1
Cocrystal 5: HꢀNMR (400MHz, DMSOꢀd ): 8.31 (s, 2H, HꢀC=), 6.91 (d, J = 7.2 Hz, 2H,
6
H ), 6.66 (d, J = 7.6 Hz, 2H, H ), 6.56 (t, J = 8.0 Hz, 2H, H ), 3.17 (t, J = 7.6 Hz , 8H,
ar
ar
ar
NꢀCH ꢀ), 1.56 (m, 8H, ꢀCH ꢀ), 1.29 (m, 8H, ꢀCH ꢀ), 0.97 (m, 12H, ꢀCH ). IR (KBr,
2
2
2
3
−
1
cm ): 2961 (w), 2874 (w), 2723 (w), 1624 (m), 1577 (m), 1515 (w), 1473 (m), 1379 (s),
1
8
321 (s), 1269 (s), 1243 (w), 1209 (w), 1166 (w), 1108 (w), 1077 (w), 1011 (s), 941 (w),
82 (w), 846 (s), 780(s), 735(s), 622 (s), 587 (m).
1
Salt 6 : HꢀNMR (400MHz, DMSOꢀd ): 8.16 (s, 2H , HꢀC=), 7.16 (s, 2H, H ), 6.25. (s,
6
ar
2
H, H ), 6.19 (s, 2H, H ), 3.14 (m, 8H, NꢀCH ꢀ), 1.55 (m, 8H, ꢀCH ꢀ), 1.30 (m, 8H, ꢀ
ar ar 2 2
CH ꢀ), 0.93 (m, 12H, –CH ) and (deuterium exchangeable proton signals at 7.10, 6.85
2
3
−
1
6
.25, 6.19 ppm due to hydroxy protons). IR (KBr, cm ): 2965 (m), 2876 (w), 1614 (s),
515 (m), 1477 (w), 1381 (w), 1328 (w), 1311 (m), 1267 (w), 1208 (s), 1117 (m), 994
1
(m), 969 (m), 887 (w), 757 (w), 733 (w), 651 (w), 576 (m), 506 (m).
Structure determination:
Single crystal Xꢀray diffraction data were collected on an Oxford SuperNova
diffractometer. SMART software was used for data collection, indexing the reflections
and determination of unit cell parameters. Data refinement and cell reductions were
1
8a
carried out by CrysAlisPro . Structures were solved by direct methods and refined by
1
8b
fullꢀmatrix leastꢀsquare calculations using SHELXTL software . All nonꢀhydrogen
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2
atoms were refined in anisotropic approximation against F of all reflections. Hydrogenꢀ
atoms, except those attached to oxygen and some carbon atoms of tetrabutylammonium
ions were placed at their calculated positions and refined with isotropic approximation;
hydrogen atoms attached to oxygen atoms were located in difference Fourier maps and
refined with isotopic displacement coefficients. Crystallographic parameters are
summarized in Table 2.
Table 2: Crystallographic parameters of 4, 5 and 6
Compound No.
Formulae
Cocrystal 4
Cocrystal 5
Salt 6
C H N O
30 49
C H F N O
C H F N O
27
45
2
2
30 50
3
6
3
6
CCDC No.
Mol. wt.
Space group
a /Å
b /Å
c /Å
1003333
448.65
1012763
567.73
Pc
9.5189 (7)
9.4321 (7)
18.7965 (14)
90.00
1012762
547.72
C2/c
16.2317(7)
9.6547 (4)
20.2299 (8)
90.00
P2 /c
1
10.1130 (6)
17.5762 (10)
15.6751 (10)
90.00
α/°
β/°
γ/°
V/ Å
102.831 (6)
90.00
2716.7 (3)
101.203 (4)
90.00
1655.5(2)
99.931 (3)
90.00
3122.8 (2)
3
ꢀ
3
Density/g.cm
1.097
0.073
984
4901
2959
25.25
1.139
0.082
616
2989
1766
25.24
1.165
0.081
1192
2711
1431
24.99
ꢀ
1
Abs. Coeff. /mm
F(000)
Total No. of reflections
Reflections, I > 2σ(I)
Max. θ/°
Ranges (h, k, l)
ꢀ12 ≤ h ≤ 12
ꢀ9 ≤ h ≤ 10
ꢀ19 ≤ h ≤ 18
ꢀ11 ≤ k ≤ 11
ꢀ23 ≤ l ≤ 23
98.50
ꢀ
ꢀ
16 ≤ k ≤ 21
18 ≤ l ≤ 18
ꢀ11 ≤ k ≤ 10
ꢀ22 ≤ l ≤ 22
99.00
Complete to 2θ (%)
99.80
Data/ Restraints/Parameters 4901/ 0/ 319
5031/3/374
1.029
2711/ 8/ 189
1.048
2
Goof (F )
1.051
R indices [I > 2σ (I)]
0.0686
0.1729
0.1120
0.2015
0.0383
0.0919
0.0560
0.1024
0.0736
wR [I > 2σ (I)]
0.1531
2
R indices (all data)
0.1135
wR (all data)
0.1636
2
Supporting information: Crystallographic information files of 4, 5 and 6 are deposited
1
to Cambridge Crystallograpic Center have CCDC Nos. 1003333, 1012763, 1012762. Hꢀ
NMR spectra of the all the compounds and UVꢀvisible titrations of 1, 2 and 3 with
tetrabutylammoinuum hydroxide are supplied as supporting information
.
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(
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19