Organic mandelates as promising materials with non-linear optical application

Article abstract of DOI:10.1007/s11224-010-9635-5

The application of organic salts of mandelic acid (MA) as new materials for optical and non-linear-optical (NLO) application is discussed, using four novel organic salts, i. e. pyridinium-4-aldoxime mandelate (1), 1-aminoisoquinolinium mandelate mandelic

Full text of DOI:10.1007/s11224-010-9635-5

Struct Chem (2010) 21:989–993
DOI 10.1007/s11224-010-9635-5
ORIGINAL RESEARCH
Organic mandelates as promising materials with non-linear
optical application
•
B. B. Ivanova M. Spiteller
Received: 2 May 2010 / Accepted: 4 June 2010 / Published online: 30 June 2010
Ó Springer Science+Business Media, LLC 2010
Abstract The application of organic salts of mandelic acid
(MA) as new materials for optical and non-linear-optical
(NLO) application is discussed, using four novel organic
salts, i.e. pyridinium-4-aldoxime mandelate (1), 1-amino-
isoquinolinium mandelate mandelic acid (2), 2-amino-8-
hydroxyquinolinium mandelate (3) and phenylalaninamide
mandelate monohydrate (4). The crystal structures, optical
and NLO properties are studied by the application of single
crystal X-ray diffraction, UV–VIS–NIR spectroscopy,
conventional and linear polarized infrared (IR-LD) spec-
troscopy, thermal methods as well as quantum chemical
(ab initio and DFT) calculations.
doubling effect of optical wavelength electromagnetic
radiation, is attractive area of modern materials research and
crystal engineering [1–10]. It is known that various organic
and inorganic compounds possess the ability to double the
frequency of laser light passing through them, this ability is
known as SHG and provides the ability to produce laser light
of higher energy than that provided by the initial laser light
source. Known organic compounds, possessing such prop-
erties are for example urea, cadmium–thiourea complexes,
L-arginium dihydrogen phosphate monohydrate, some
siloxane and silicone polymeric liquid crystals, stilbene-
containing liquid crystals, some silver-containing emul-
sions, dipotassium tartrate hemihydrate, potassium sodium
tartrate tetrahydrate, compounds having large secondary
molecular susceptibilities (beta-values) such as 4-(N-pyrr-
olidino)-3-(N-ethanamido)-nitrobenzene and 4-(dimethyl-
amino)-3-(N-ethanamido)-nitrobenzene, and blends of large
beta-value compounds with polypeptides [11]. The organic
salts of mandelic acid (MA) are especially attractive tem-
plates for incorporation into crystalline materials with NLO
properties, because of the presence of an additional OH-
group to the carboxylic one, promotes hydrogen bonding
with the base. Hydrogen bonding also tends to increase the
thermal stability and mechanical strength of the crystalline
material, and to suppress the formation of crystalline
hydrates. The corresponding organic base is preferably an
amine, imine [1–4, 11–15] or heterocycle with basic nitro-
gen atoms. For these reasons the current research is focused
on design, synthesis and isolation of the organic mandelates
(Scheme 1). Their spectroscopic properties and structures
are elucidated by conventional and IR-LD spectroscopy,
UV–VIS-NIR, thermal methods and single crystal X-ray
diffraction. The optical and NLO optical properties are
predicted by application of quantum chemical calculations
at ab initio and DFT levels of approximation.
Keywords Organic mandelate crystals ꢀ
Optical and NLO properties
Introduction
The design of non-linear optical devices incorporating sec-
ond harmonic generator materials, which produce frequency
Author name B. B. Ivanova is same as B. Koleva during the period
2006–2009.
Electronic supplementary material The online version of this
article (doi:10.1007/s11224-010-9635-5) contains supplementary
material, which is available to authorized users.
B. B. Ivanova (&) ꢀ M. Spiteller (&)
¨
Institut fu¨r Umweltforschung, Universitat Dortmund,
Otto-Hahn-Strasse 6, 44221 Dortmund, Germany
e-mail: BIvanova@chem.uni-sofia.bg
B.Koleva@infu.tu-dortmund.de
M. Spiteller
e-mail: spiteller@infu.tu-dortmund.de
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Struct Chem (2010) 21:989–993
Scheme 1 Pyridinium-4-
aldoxime mandelate (1),
1-aminoisoquinolinium
mandelate mandelic acid (2),
2-amino-8-hydroxyquinolinium
mandelate (3) and
O
O
O
HO
HO
HO
OH
O
O
N
N
H
H
x
x
x
HO
N
NH2
phenylalaninamide mandelate
monohydrate (4)
(1)
(2)
O
O
HO
HO
H3N
O
O
O
N
H
NH2
NH2
x
x
H2O
OH
x
Results and discussion
hydroxyquinolinium mandelate (3) crystallizes in
monoclinic P21/c space group (Fig. S1c). The cations and
MA anions form 3D networks via NHꢀꢀꢀO (2.740, 3.016,
a
Pyridinium-4-aldoxime mandelate (1) crystallizes in the
non-centrosymmetric tetragonal P43 space group (Fig. S1a)
indicating NLO properties in the bulk. The unit cell con-
tains 16 species, forming a 3D network (Fig. 1a) by means
of moderate to strong N?HꢀꢀꢀO, OHꢀꢀꢀOCO hydrogen bonds
˚
˚
2.900 A) and OHꢀꢀꢀOCO (2.471, 2. 962 A) interactions
(Fig. S1c). The sub-structural fragment of the MA anion is
an isolated moiety. As with 1-aminoisoquinoline and its
monocation, the weak basic character of the NH2-group
limits the formation of the dication (Scheme S1) with
excess MA. The NH2-group takes part in the conjugation
with the quinoline fragment, thus leading to a singly
charged redistribution value of -0.842 in the neutral spe-
cies and -0.756 in corresponding cation (Scheme S1).
Phenylalaninamide mandelate monohydrate (4), crystal-
lizes in the non-centrosymmetric space system C2, sup-
posing NLO properties in the bulk (Fig. S1d). The self-
assembly motif of the mandelate is infinite chains, formed
˚
(2.706, 2.605 A). The MA anions form dimers via
˚
OHꢀꢀꢀOCO bonds (2.759, 2.792 A). 1-Aminoisoquinolini-
um mandelate mandelic acid (2) crystallizes in a triclinic
ꢀ
P1 space group (Fig. S1b). The structure consists of cat-
ionic 1-aminoisoquinoline, mandelate anion and neutral
MA (Fig. 1b). The weak basic character of the 1-amino
substituent limits the protonation of the NH2 group in the
presence of the second molecule MA. As with (1), the MA
˚
species forms dimers through OHꢀꢀꢀOCOH (2.878 A)
˚
bonds. Each of the latter sub-structures is joined into infi-
˚
by means of the OHꢀꢀꢀOCO hydrogen bonds (2.805 A). The
nite chains through OHꢀꢀꢀOCO (2.566 A) bonds (Fig. 1b).
cations are joined by the anions and the solvent molecules
The cations interact with the MA species by N?HꢀꢀꢀO
through the moderately strong intermolecular NHꢀꢀꢀO
˚
hydrogen bonds (2.912, 3.011, 2.777 A). 2-Amino-8-
˚
hydrogen bonds (3.026, 2.776, 2.815, 2.840, 3.042 A)
Fig. 1 PLUTON diagrams of
the unit cell content, hydrogen
bonding pattern in the structures
(1)–(4), labelling with (a)–(d),
respectively, as well as
photographs of the crystals
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Struct Chem (2010) 21:989–993
991
Fig. 2 Solid-state IR spectra of noncentrosymmetric crystals (1)–(4)
(Fig. 1d). The experimental crystallographic refinement
data are summarized in Table S1.
The solid-state IR spectra of compounds (1)–(4) are
depicted in Fig. 2. The characteristic multicomponent
maximum within 3100–3000 cm-1 in all IR-spectra is
assigned to the mOH stretching vibration of the hydrogen
Fig. 3 Transmission UV–VIS–NIR spectra of aqueous solution of a
mandelic acid at pH 4 and 9, pyridine-aldoxime, 1-aminoisoquinoline
and 2-amino-8-hydroxyquinoline; b compounds (1)–(4) at a concen-
tration 2.10–5 mol/l and 1 cm path length
bonded OH-group. The IR-bands about at 1550 and
and msCOO- vibrations of
1400 cm-1 belong to the m
as
COO-
the MA anion, respectively. IR-spectrum of (2), shows a
band of mC=O vibration at 1724 cm-1 (Fig. 3(2)) of the
protonated COOH group of the neutral MA. The IR-bands
at 3454 and 3378 cm-1 can be assigned to the corre-
sponding mOH vibrations. In contrast to local C2v* symmetry
of the carboxylate anion (COO-), characterizing the
redistribution of the negative charge, the neutral COOH
group reveals a typical C=O bond and the local Cs sym-
metry. The values of the C–O bonds in the MA anion in (2)
substituted phenyl-fragments [12]. These data compare with
the theoretical value of 240 nm and f = 0.013. The MA
anion exhibits a hypsochromic shift of the B-band and dis-
appearance of the n ? p* transition as a result of distortion
of the C=O double bond in the COOH-group of the neutral
acid. MA is transparent within the range of 204–1100 nm.
The pyridine-4-aldoxime and the substituted quinolines
exhibit a series of absorption maxima at 240–290 nm with em
within range of 800–1200 l mol-1 cm-1. 1-Aminoisoquin-
oline is characterized by the highest wavelength band at
335 nm and em 1198 l mol-1 cm-1. These bands belong to
the transitions 8A00 ? 9A00 in the quinoline fragments
(Scheme S3). The observed vibronic structure is also typical
for the electronic spectra of substituted naphthalenes [12,
13] and could be analogous to quinolines. The effect of the
protonation of the counterions leads to a bathochromic shift
of the highest wavelength UV-bands within 15–60 nm
(Fig. 3b). The compounds (1) and (4) are transparent within
the larger transmission window within 280–1100 nm, while
for the compounds (2) and (3) the corresponding ranges are
346–1100 nm and 353–1100 nm, respectively. The data are
in accord with the theoretical values 350 and 360 nm
(Scheme S3) and the f values of 0.017 and 0.023, respec-
tively. The protonation of the quinoline derivatives leads to a
decrease in the energy difference and to a bathochromic shift
of the corresponding maxima. The energy values of MOs
˚
are 1.263, 1.244 A, while the corresponding values in the
˚
neutral acid are 1.206 and 1.300 A, respectively. The
characteristics out-of-plane IR bands of the monosubsti-
tuted benzene ring in MA species are observed at about
760, 730 and 690 cm-1 (Fig. 2(1)–(4)). The cationic
fragments in (2) and (3) are characterized by Cs molecular
symmetry of the neutral and protonated forms (Scheme
S1). The corresponding IR spectra reveal out-of-plane
maxima within the range 960–600 cm-1 typical for these
systems (Scheme S2; Fig. S2) overlapping with those of
MA moieties.
The transmission UV–VIS–NIR spectra of compounds
(1)–(4) and the starting compounds within the range 190–
1100 nm are depicted in Fig. 3. Neutral MA is characterized
by a weak UV-band at 260 nm (em = 621 l mol-1 cm-1),
belonging to B-band of the substituted benzene ring, over-
lapped with the n ? p* transition of the C=O group. The
observed vibronic structure of the B band is typical for
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Struct Chem (2010) 21:989–993
8A00 and 9A00 in the cation of 2-amino-8-hydroxyquinoline
are -3.079 and 0.3682 eV (MO6-2X XC, Table 1).
Calculations at MO5, MO5-2X, MO6 and MO6-2X XC
functional levels were performed and complete the eluci-
dation of the electronic spectra of the systems (1)–(3)
[16–18]. The data are summarized in Table 1. As with the
calculation of the optical properties of small L-tryptophan-
containing peptides or NLO materials based on barbiturate
salts [19, 20] the DFT approximation at B3LYP level of
theory, yielded serious shortcomings. The so-called M06-
class functional [16–18] was used to enforce some funda-
mental exact constraints yielding a good correlation
between the theoretical and the experimental values. The
data show that M06 has good accuracy for medium-range
correlation energy as has M06-2X, which has excellent
predicts accurate valence and Rydberg electronic excita-
tion energies. For the systems (1)–(3), the differences
between the theoretical and the experimental electronic
spectra are in the range within 3–7 nm, thus indicating the
good correlation for the substituted heterocyclics.
Conclusions
The search for new organic materials with NLO properties
on the basis of the salts of mandelic acid provided encour-
aging results, yielding four novel derivatives; pyridinium-4-
aldoxime mandelate (1), 1-aminoisoquinolinium mandelate
mandelic acid (2), 2-amino-8-hydroxyquinolinium man-
delate (3) and phenylalaninamide mandelate monohydrate
(4). The structures and optical properties of compounds
(1)–(4) are elucidated by single crystal X-ray diffraction,
UV–VIS-NIR, IR-LD spectroscopy and thermal methods.
The theoretical quantum chemical calculations were carried
out to predict the optical properties of these systems.
Compounds (1) and (4) crystallize in the non-centrosym-
metric space groups P43 and C2, thus indicating the NLO
properties in the bulk. Mandelic acid species form dimers in
˚
(1) by the OHꢀꢀꢀOCO bonds (2.759, 2.792 A) and infinite
˚
chains in (4) by OHꢀꢀꢀOCO bonds (2.805 A), respectively.
ꢀ
Compounds (2) and (3) crystallize in the triclinic P1 and
monoclinic P21/c space groups, respectively. The self-
assembly sub-structures of the mandelic acid species are
˚
dimers (OHꢀꢀꢀOCOH, 2.878 A) in (2) and isolated anion in
(3), respectively. Instead that compounds (1) and (4) crys-
tallized in non-centrosymmetric space groups, the proper-
ties of these crystals are such as to include some of the most
important characteristic desired for practical application in
useful for crystal engineering and NLO technology. The
compounds are characterized by high solubility in aqueous
media, allowing reasonable rate of crystal growth and good
properties, particularly in the cases of (1) and (4). The
compounds possess high thermal stability at temperatures
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Struct Chem (2010) 21:989–993
993
X2S diffractometer. B.I. and M.S. thank the DAAD for a grant within
the priority program ‘‘Stability Pact South-Eastern Europe’’. M.S.
wishes to thank the DFG for Grant SP 255/21-1.
higher than 500 °C, neither are they hygroscopic. All the
crystals are colourless and posses a large transmission
window with a range 260–1100 nm as well as low intensive
IR bands within the range 5000–400 cm-1. Compound (1)
forms hydrate-free crystals, thus avoiding the evaporation of
water and degradation under prolonged exposure to laser
radiation.
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Acknowledgements B. I. wishes to thank Alexander von Humboldt
Foundation for the Fellowship and for the donation of a Bruker Smart
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