Synthesis, X-ray diffraction analysis, and chemical-optical characterizations of boron complexes from bidentate ligands

Article abstract of DOI:10.1016/j.poly.2012.06.043

Herein is reported the synthesis and X-ray diffraction analysis for three boron complexes (2a-2c) prepared from the reaction of bidentate ligands (1a-1c) and diphenylborinic acid. Chemical characterization for the borinates is completed with IR, UV-Vis an

Full text of DOI:10.1016/j.poly.2012.06.043

Polyhedron 43 (2012) 194–200
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, X-ray diffraction analysis, and chemical–optical characterizations of
boron complexes from bidentate ligands
a
b
Mario Rodríguez a, José Luis Maldonado a, , Gabriel Ramos-Ortíz , Oscar Domínguez ,
⇑
Ma. Eugenia Ochoa b, Rosa Santillan b, , Norberto Farfán c, Marco-Antonio Meneses-Nava a,
⇑
Oracio Barbosa-García a
a Centro de Investigaciones en Óptica, Apdo. Postal 1-948, 37000 León, Gto., Mexico
b Depto. de Química, Centro de Investigación y de Estudios Avanzados del IPN, Apdo. Postal 14-740, 07000 México, D.F., Mexico
c Facultad de Química, Depto. de Química Orgánica, Universidad Nacional Autónoma de México, 04510 México, D.F., Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein is reported the synthesis and X-ray diffraction analysis for three boron complexes (2a–2c) pre-
pared from the reaction of bidentate ligands (1a–1c) and diphenylborinic acid. Chemical characterization
for the borinates is completed with IR, UV–Vis and NMR techniques, particularly 11B NMR spectra con-
firmed the formation of boron complexes. X-ray diffraction analysis showed that for compounds 2a
Received 17 February 2012
Accepted 19 June 2012
Available online 26 June 2012
and 2c a non-planar conformation for the main
compound 2b the planar conformation is preserved. Additionally, cubic nonlinear optical (NLO) proper-
ties were evaluated, through the optical susceptibility v(3) (-3
), using the THG Maker-Fringes
technique. Results showed that v(3) response decreases from ligands to boron complexes; this behavior
could be attributed to a structural conformation or deformation of the electronic -system after boron
p-backbone is acquired after boron complexation; for
Keywords:
Borinates
X-ray analysis
Cubic NLO properties
THG Maker-Fringes technique
x, x, x, x
p
complexation. The demonstrated electronic and structural features of these borinates could be useful
for new strategies in the design of novel NLO dyes.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
arises from the interaction of an intense electromagnetic field with
matter that produces new field components, which could differ in
Comprehension of the structural and electronic properties of
organic boron compounds containing the N ? B coordinative bond
have let their use in different fields of applications such as in
supramolecular chemistry [1], as a labeled of biological molecules
frequency, amplitude, phase, path, polarization, etc. These NLO
properties are of enormous technological importance for optical
devices with applications in data storage, communication, switch-
ing, image processing, and computing. Organic and organometallic
materials are attractive for these applications because in many
cases they exhibit exceptional NLO features, and in addition, satis-
factory mechanical and structural properties (processing, stability,
etc.). In particular, considerable efforts to develop materials with
third-order nonlinear properties have focused on conjugated
organic–organometallic molecules and polymers, containing donor
[2], and as sensors [3]. For those compounds having a p-conjugated
system, they have also been used as optoelectronic materials with
applications in light-emitting diodes (OLEDs) [4], photorefractive
(PR) polymers [5], and as dopants of liquid crystals [6]. In particu-
lar, the N ? B bond results interesting when the ‘‘p’’ orbital of the
boron atom is involved with the non-bonding electron pair of the
nitrogen producing a dative bond or a donor–acceptor complex
[7]. For instance, the electronic characteristics promoted for this
(D) and acceptor (A) groups bridged by a
different arrangements [13–15]; one of the most efficient and
widely study structure is precisely the D– –A one [14,15]. Cubic
p-electronic system in
bond on
p-systems have been employed to tune the luminescent
p
properties of organic materials [8]. Very recently, for some inter-
esting four-coordinate boron complexes, their luminescent proper-
ties were also reported [9].
With respect to the search for novel organic and organometallic
compounds with linear and nonlinear optical responses, there is an
extensive investigation [10–12]. Nonlinear optical (NLO) behavior
NLO response is governed at the macroscopic level by the third
order susceptibility v(3) and offers a more varied and richer behav-
ior than second-order NLO processes due to higher dimensionality
of the frequency space [12,16]. Some molecular characteristics
have been identified to increase v(3) as the conjugation length,
heteroaromatic conjugation, degree of strength of the D/A substit-
uents, and the molecular asymmetry [15–18].
We have previously reported the NLO properties of some series
of ligands and boron complexes containing the coordinative N ? B
bond on electronic push–pull systems [19–21]. These compounds
⇑
Corresponding authors. Tel.: +52 477 441 4200; fax: +52 477 441 4209.
E-mail addresses: jlmr@cio.mx (J.L. Maldonado), rsantill@cinvestav.mx (R.
Santillan).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.06.043

M. Rodríguez et al. / Polyhedron 43 (2012) 194–200
195
show v(3) values between 1.1 and 11 ꢀ 10ꢁ12 esu at infrared laser
wavelengths. Some optical applications of these ligands and boron
compounds have been demonstrated by our group and others, they
include switch properties [22], photorefractive polymers [5,23,24],
and photovoltaic devices (OPVs cells) [25,26]. In this work, the syn-
thesis of the ligands 1b–1c was carried out for a better understand-
ing of the effect on the chemical–optical features due to the
planarity and electronic properties modifications, promoted for
nic acid obtained by hydrolysis of the ethanolamine ester complex
[28]. Formation of the boron compounds was confirmed through
IR, 1H, 13C and 11B NMR techniques. Evidence for the creation of
borinates was obtained from the signal of the tetra-coordinated
boron atom at 5.4 ppm for 2a [9], 11.6 ppm for 2b and 6.0 ppm
for 2c in the 11B NMR spectra [19].
the coordinated N ? B bond on the aza-p-backbone. We report
2.2.1. 2b: N,N-Diethyl-4-((2,2-diphenyl-6-nitrobenzo[d][1,3,2]
oxazaborol-3(2H)-ylidene)methyl) benzenamine
the chemical characterization for the boron complexes 2b–2c;
their structures, including those for ligands 1b–1c and the very
recently reported borinate 2a [9], were confirmed by X-ray diffrac-
tion analysis. NLO properties for these ligands and their borinates,
The title compound was prepared from the reaction of ligand 1b
0.85 g (2.7 mmol) and diphenylborinic acid 0.51 g (2.8 mmol) in
ethyl ether as a solvent at reflux temperature for 2 h to give
0.95 g (2.1 mmol, 74% yield). MP 198–200 °C. IR mmax (ATR):
2986, 1607, 1598, 1513, 1403, 1327, 1274, 1197, 1152, 1069,
particularly the cubic susceptibility
v
(3), were also investigated.
875, 742, 704 cmꢁ1 1H NMR (CDCl3, 300 MHz) d: 1.14 (6H, t,
.
2. Experimental
J = 6.9 Hz, CH3), 3.50 (4H, q, J = 6.9 Hz, N-CH2), 6.36 (2H, d,
J = 9 Hz, H-1), 7.24–7.18 (6H, m, H-m,m0,p,p0), 7.46 (1H, d,
J = 8.7 Hz, H-9), 7.54 (4H, d, J = 6.6 Hz, H-o,o0), 7.62 (1H, d,
J = 9 Hz, H-1), 7.64 (1H, s, H-12), 7.70 (1H, d, J = 8.7 Hz, H-10),
8.58 (1H, s, H-7) ppm. 13C NMR (CDCl3, 75 MHz) d: 12.4 (CH3),
44.9 (N-CH2), 109.3 (C-12), 110.8 (C-2), 112.1 (C-10), 113.4 (C-9),
115.3 (C-6), 126.7 (C-p,p0), 127.3 (C-m,m0), 133.2 (C-o,o0), 138.4
(C-1), 140.0 (C-8), 148.6 (C-11), 152.9 (C-3), 155.9 (C-7), 158.5
(C-13) ppm. 11B NMR (CDCl3, 96 MHz) d: 11.5 ppm. HRMS Calc.
m/z for C29H29BN3O3 [M++H]+: 478.2300. Found: 478.2290, error
1.0343 ppm.
2.1. Materials and methods
All starting materials were purchased from Aldrich Chemical Co.
Solvents were used without further purification. 1H and 13C NMR
data of borinate 2a were compared with the information found
in the cited Ref. [9]. Melting points were obtained with an electro-
thermal 9200 apparatus and are uncorrected. Infrared spectra were
measured on a FT-IR spectrometer Spectrum RX1 Perkin–Elmer
using attenuated total reflection (ATR). 1H, 13C and 11B NMR spec-
tra were recorded on Jeol ECA +500 and Bruker Advance DPX 300
spectrometers. Chemical shifts (ppm) are relative to (CH3)4Si for
1H and 13C and BF3ꢂEt2O for 11B.
2.2.2. 2c: N,N-Diethyl-2,2-diphenyl-3-(3,5-dinitrophenyl)-2H-
benzo[e][1,3,2]oxazaborinin-7-amine
2.2. Synthesis
The title of compound was prepared from the reaction of ligand
1c 0.96 g (2.7 mmol) and diphenylboronic acid 0.51 g (2.8 mmol)
in ether ethylic as a solvent at reflux temperature for 3 h to give
1.04 g (2.1 mmol, 71% yield). IR (ATR): 3102, 1597, 1528, 1489,
The ligands 1a–1c (see Scheme 1) were obtained from classical
imine formation reaction, through condensation of the correspond-
ing aldehyde and amine in methanol as a solvent at reflux temper-
ature using a Dean–Stark trap for removing the water obtained
during the reaction [27]. Compounds 1a and 1b have a strong elec-
tron donor (Et2N) group and acceptor (NO2) group connected to the
1458, 1431, 1342, 1264, 1217, 1121, 979, 726, 705 cmꢁ1 1H NMR
.
(CDCl3, 300 MHz) d: 3.85 (3H, OCH3), 7.29–7.17 (6H, m, H-
m,m0,p,p0), 7.41 (4H, d, J = 6.6 Hz, H-o,o0), 7.81 (1H, d, J = 6.9 Hz, H-
5), 8.22 (2H, s, H-9), 8.35 (1H, s, H-11), 8.81 (1H, s, H-7) ppm. 13C
NMR (CDCl3, 75 MHz) d: 56.0 (C-OCH3), 102.0 (C-2), 111.2 (C-4),
117.1 (C-11), 124.7 (C-9), 127.1 (C-p,p0), 127.5 (C-m,m0), 131.4 (C-
6), 133.4 (C-o,o0), 134.5 (C-5), 147.2 (C-10), 148.0 (C-8), 161.5 (C-
7), 166.8 (C-3), 170.9 (C-1) ppm. 11B NMR (CDCl3, 96 MHz) d:
6.0 ppm. HRMS Calc. m/z for C26H21BN3O6 [M++H]+: 482.1526.
Found: 482.1517, error 1.6749 ppm.
conjugated electronic
p-backbone for the generation of a ‘‘push–
pull’’ architecture on these molecules. Furthermore, the combina-
tion of salicylaldehyde–aniline or benzaldehyde–aminophenol in
1a–1b promotes the formation of six or five boron heterocycle
members after boron complexation, respectively. Compounds
2a–2c were prepared from the equimolar reactions of their
corresponding ligands 1a–1c with freshly liberated diphenylbori-
Scheme 1. Reaction of ligands 1a–1c with phenylboronic acid to obtain boron derivates 2a–2c.

196
M. Rodríguez et al. / Polyhedron 43 (2012) 194–200
2.3. Single crystal X-ray structure determinations
unit cell. In general, X-ray analysis of compounds 1b and 1c
showed a main -backbone containing two aromatic ring linked
p
Suitable crystals for X-ray diffraction analysis of ligands and
boron complexes were grown from saturated methanol, chloro-
form or dichloromethane solutions at room temperature. Crystal
growing up was got for slow evaporation of the solvent (3–4 days).
All diffraction data were measured using an Enraf Nonius
Kappa-CCD diffractometer with graphite monochromated
by azomethine (HC@N) moiety near to a planar conformation, this
feature is also showed for the reported compound 1a. Compounds
1a–1c have in their structure the HO–C–C–C–N@ or @N–C–C–OH
fragment, which were employed for the boron complexation in
2a–2c, for these compounds
a tetrahedral boron atom was
confirmed by their X-ray diffraction analysis. The main structural
feature after boron complexation in 2a and 2c (2c has two
molecules in the asymmetric unit) is the twisted conformation of
kMo
= 0.71073 Å. Frames were collected at T = 293 K via x/u
K
a
rotation. Direct methods SIR2004 [29] and SHELXS-86 [30] were used
for structure solution and the SHELXL-97 [31] software package for
refinement and data output. C–H hydrogen atoms were placed in
geometrically calculated position using a riding model.
the aza-p-backbone as is shown by the torsion angles for the
C(7)–N-ph (ph = C(8)–C(9)) fragment, which exhibits values of
43.4(6)° and 46.7(4)° (ꢁ51.1(4)°), respectively. In comparison,
their corresponding ligands 1a and 1c present values of 10.6(4)°
[35] and 39.0(3)°, respectively. This bent structure for compounds
2a and 2c could be attributed to the steric effect provoked by the
two phenyl groups bonded directly to the boron atom (see Section
3 on the next paragraph about boron angles). Furthermore, the
bond distances for Cph–C@N–Cph fragment indicate the electronic
changes after boron complexation: the largest variation is over
the bond connecting the aromatic ring and the iminic carbon atom
2.4. THG Maker-Fringe measurements and linear absorption
The nonlinear optical measurements were performed in solid
state (solid films) using the guest (molecule)–host (polymer) ap-
proach. Mixtures of polystyrene (PS) and compounds 1a–1c and
2a–2c 70:30 wt.% ratio, respectively, were dissolved in chloroform.
The solid films were deposited on fused silica substrates (1 mm-
thick) by using the spin coating technique. The prepared films
had typical thickness between 77 and 170 nm with good optical
quality. Absorption spectra of the spin-coated films were obtained
with a spectrophotometer (Perkin–Elmer Lambda 900). Sample
thickness was measured by a Dektak 6M profiler.
Cph–C from compound 2a (1.394(7) Å) and 2c (1.406(4) Å,
1.393(4) Å) to ligands 1a (1.425(3) Å) and 1c (1.439(2) Å). How-
ever, the X-ray diffraction analysis for compound 2b showed that
the formation of five-membered heterocycle after boron complex-
ation conserves the planar conformation in the aza-p-backbone,
being the C(7)–N–C(8)–C(9) torsion angle of 1b (5.1(4)°) and 2b
(1.4(3)°), (see Table 2). Moreover, the change in the distance for
the bond Cph–C is shorter than that for compounds 2a and 2c.
Previous to get the X-ray data of compound 2a, a theoretical
THG Maker-Fringes setup is reported elsewhere [32,33]. Briefly,
it consisted of a Nd-YAG laser-pumped optical parametric oscilla-
tor (OPO) that delivered pulses of 8 ns at a repetition rate of
10 Hz. A fundamental wavelength of 1200 nm (idler beam) was
used. The output of the OPO system was focused into the films
with a 30-cm focal-length lens to form a spot with a radius of
approximation of this structure was developed using the GAUSSIAN
-
98 program package [36] within the framework of the density
functional theory (DFT) at the B3PW91/6-31G⁄ level. Its metric
parameters were taken from the X-ray data of 2c. The theoretical
estimation of the torsion angle for C@N-ph fragment is of 40°,
which is close to the experimental value of 43.4(6)°.
approximately 150 lm. Typical energies in our measurements
were set at 1 mJ per pulse at sample position (corresponding to
peak intensities of ꢃ0.18 GW/cm2). The third-harmonic beam, as
a bulk effect, emerging from the films was separated from the
pump beam by using a color filter and detected with a PMT and
a Lock-in amplifier. The THG measurements were performed for
incident angles in the range from ꢁ40° to 40° with steps of 0.27°.
All the experiment was computer-controlled.
Analyses of angles around the boron atom for compounds 2a–2c
confirm the tetrahedral geometry surrounding this atom; data are
shown in Table 3. A detailed analysis confirms that in compounds
2a and 2c, the complexation of the boron atom produces a six-
membered heterocycle with angles from 105.5(3)° to 118.8(3)°
around this one. In contrast, for compound 2b the formation of a
heterocycle with five members is produced after the complexation
reaction and shows angles from 98.90(15)° to 118.95(18)° around
the boron atom. A comparison of the angle O–B–N for boron com-
pounds showed that in compound 2b (98.90(15)°) it is consider-
ably smaller than that of the same fragment in derivative 2a
(105.7(3)°) and 2c (106.5(2)°, 104.4(2)°). This angle change in bor-
on compounds, could give an explanation of the bent structure
showed for 2a and 2c. Larger angles for O–B–N, 105.7(3)° in 2a
and 106.5(2)°, 104.4(2)° in 2c, close to the two phenyl rings bonded
In the Maker-Fringes technique, the third-harmonic peak inten-
x
sity I3 from the substrate-film structure is compared to that one
produced from the substrate alone. Then, the nonlinear suscepti-
bility v(3) in a film of thickness Lf is determined from:
!
1=2
ꢀ
ꢁ
x
x
If3
Is3
ð3Þ 2
p
a
=2
a
vð3Þ
¼
vs
Lc;s
ð1Þ
1 ꢁ expð Lf =2Þ
where vðs3Þ and Lc,s are the nonlinear susceptibility and coherence
length, respectively, for the substrate at the fundamental wave-
length, and
a is the film absorption coefficient at the harmonic
wavelength [34]. In our calculation we considered vðs3Þ ¼ 3:1ꢀ
to the boron atom at the main p-backbone, develop a steric effect
that promotes a bent structure in such compounds. On the con-
trary, with a smaller angle, (98.90(15)° in 2b, a flat conformation
in the p-backbone is observed. Furthermore, the molecular elonga-
10ꢁ14 esu and Lc,s = 9.0
lm for the fused silica substrate [32,33].
Our samples satisfied the condition Lf << Lc,s in which the Eq. (1) is
valid.
tion between the aromatic ring and the boron heterocycle on 2b re-
duces the steric effect, in contrast to compounds 2a and 2c where a
bent conformation is promoted by this fact.
3. Results and discussion
3.1. X-ray diffraction analysis
3.2. Optical measurements
The molecular structures for compounds 1b, 1c, and 2a–2c were
confirmed by X-ray diffraction analysis (see Fig. 1 and Table 1). De-
tails for 1a can be found elsewhere [35]. Compounds 1b–1c, 2a and
2c crystallize in the monoclinic space group P21/c containing four
and eight (2c) molecules per unit cell. Compound 2b crystallizes
Absorption spectra of compounds 1a–1b and 2a–2b were ob-
tained in solid thin polymer films (see Fig. 2; spectra for 1c and
2c were removed for clarity reasons). In general, for compounds
1a–1c a n ? p⁄ electronic transition is the responsible for the main
absorption bands, and it could be modified by the conformational
ꢀ
in triclinic space group P1, with one independent molecule in the

M. Rodríguez et al. / Polyhedron 43 (2012) 194–200
197
Fig. 1. Crystal structures of compounds 1b, 1c, 2a, 2b, and 2c.
Table 1
Selected crystal and refinement data for compounds 1b–1c and 2a–2c.
Crystal dataa
1b
1c
2a
2b
2c
Formula
MW (g/mol)
Crystal system
Space group
a (Å)
C
17H19N3O3
C14H11N3O6
317.26
monoclinic
P21/c
15.6324(6)
6.9274(3)
14.2773(5)
90
114.703(3)
90
1404.63(10)
4
C29H28BN3O3
477.35
monoclinic
P21/c
14.617(3)
18.471(4)
9.824(2)
90
107.87(3)
90
2524.9(9)
4
C29H28BN3O3
477.37
triclinic
C26H20BN3O6
481.26
monoclinic
P21/c
16.3993(7)
20.2180(12)
13.7205(6)
90
90.096(2)
90
4549.2(4)
8
313.35
monoclinic
P21/c
16.9980(6)
7.5664(3)
13.0501(3)
90
106.811(3)
90
1606.69(10)
4
ꢀ
P1
9.7596(3)
11.7284(4)
12.1983(5)
86.609(2)
69.189(2)
72.439(2)
1242.54(8)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalc (g/cm3)
1.295
1.500
1.256
1.276
1.405
Collected reflections
Independent reflections
Observed reflections
9880
3593
3593
0.0763
0.2226
0.287
ꢁ0.177
7159
3191
3191
0.0508
0.1409
0.178
ꢁ0.192
6482
4892
2425
0.0558
0.0796
0.23
ꢁ0.175
7214
5202
2571
0.0591
0.1429
0.206
ꢁ0.168
21223
9820
4961
0.0708
0.2115
0.0204
ꢁ0.236
R1[I > 2
r
(I)]b
c
Rw (all data)
D
D
qmax (e Åꢁ3
qmin (e Åꢁ3
)
)
a
b
c
kMoK = 0.7103 Å.
a
P
P
R ¼ ðF2o ꢁ F2c Þ= F2o.
P
P
2
2 1=2
Rw ¼ ½ wðF2o ꢁ Fc2Þ = wðF2oÞ ꢄ
.
Table 2
Structural parameters of the boron complexation in the C@N-ph fragment.
Table 3
Angle values (°) around boron atom for compound 2a–2c.
Molecule
Cph–C (Å)
C@N (Å)
N–Cph (Å)
Torsion angle (°) C@N-ph
Angle
2a
2b
2ca
1a [35]
2a
1b
1.425(4)
1.394(7)
1.439(3)
1.426(3)
1.439(4)
1.393(4)
1.406 (4)
1.298(4)
1.312(6)
1.278(3)
1.307(2)
1.289(3)
1.308(4)
1.294(4)
1.407(3)
1.433(6)
1.406(3)
1.415(3)
1.408(2)
1.422(4)
1.438(4)
10.6(4)
43.4(6)
5.1(4)
O–B–CPh1
105.5(3)
106.94(17)
105.1(3)
105.7(3)
109.3(3)
109.7(3)
118.8(3)
117.9(3)
106.5(2)
104.4(2)
108.3(3)
108.7(3)
108.3(2)
109.6(3)
O–B–CPh2
110.9(3)
116.8(3)
105.7(3)
111.2(3)
106.2(3)
108.70(18)
118.95(18)
98.90(15)
2b
1.4(3)
1c
39.0(3)
ꢁ51.1(4)
46.7(4)
CPh2–B–CPh2
2ca
O–B–N
a
For this crystal structure there are two sets of values arising from the two
independent molecules.
C
Ph1–B–N
Ph2–B–N
113.34(18)
108.03(16)
C
planarity of the
p-system or by the electronic effect due to the
a
For this crystal structure there are two sets of values arising from the two
N ? B coordinative bond on 2a–2c. In Fig. 2, the absorption band
of compound 2a presented a red shift of 17 nm with respect to
its ligand 1a which is smaller than that observed from 1b to 2b:
56 nm. These results are in agreement with the conformational
parameters observed in solid state, for compounds 1b and 2b, a
independent molecules.
pronounced red shift is related to the contribution of the flat
p-backbone (see Section 3.1) and the
p-electronic polarization
effect due to the N ? B bond. Whereas, for 1a and 2a, the X ray

198
M. Rodríguez et al. / Polyhedron 43 (2012) 194–200
Table 4
Maximum absorption coefficient (a), maximum absorption band (kmax), and cubic
susceptibility (v(3) at 1200 nm) for ligands 1a–1b and boronates 2a–2b into PS
(30:70 wt.%), in solid state.
Thin films in PS
(30:70 wt.%)
a
kmax
(nm)
v(3)
(ꢀ 104 cmꢁ1
)
(ꢀ 10ꢁ12 esu)
1a
2a
1b
2b
8.2
6.3
4.0
7.5
428
445
444
500
9.5
3.6
5.3
4.1
Notes: 1) For 1c and 2c was not possible to measure
v
(3) due to their poor response.
2) v(3) for fused silica = 3.1 ꢀ 10ꢁ14 esu at 1200 nm.
In general, data show that
v
(3) decreases from ligands 1a–1b to
boron complexes 2a–2b; in the case of 2a a reduction of v(3) by a
factor of 2.6 was observed. With respect to the compounds b, there
was a decrease by just a factor of 1.3 after boron complexation.
Since the conformational arrangement of the
p-skeleton is modi-
Fig. 2. Absorption spectra for compounds 1a–1b and 2a–2b in solid state films
doped into polystyrene (PS) at 30:70 wt.%.
fied with the boron complexation (see X-ray analysis for 2a–2c)
then a plausible explanation for the experimental decrease of the
cubic susceptibility for 2a could be that the boron complexation
promotes a non-planar conformation in the main aza-p-system
diffraction analysis indicates a bent structure, which gives an elec-
tronic transition less efficient and so, smaller red shift than that for
compound 2b.
Additionally, cubic nonlinear susceptibilities for the polymer
films doped with compounds 1a–1b and 2a–2b were evaluated
through the THG Maker-Fringes technique [32,33]. For 1c and 2c,
due to the structural donor–p–acceptor arrangement and strength
of the donor group, the THG signal was very weak and below the
range of sensitivity for our experimental setup, so the estimation
of their v(3) values was not possible. The choice of using this tech-
nique to measure v(3) is because it allowed us to measure pure
electronic NLO effects, which is important for high bandwidth pho-
tonic applications. As an example of these experiments, Fig. 3
shows the so called THG Maker-Fringe pattern for 1a film. As ref-
erence, the figure also includes the THG pattern measured from
the fused silica substrate alone (thickness: 1 mm). These data were
obtained at the fundamental near infrared wavelength of 1200 nm
(THG signal in 400 nm). From these data is estimated that the
third-order nonlinear susceptibility of the 1a film is on the order
of 9.5 ꢀ 10ꢁ12 esu at such fundamental wavelength. Table 4 sum-
marizes the cubic measurements for the other compounds.
Fig. 3. Third-harmonic light pattern as a function of the incident angle for a thin
polymer film (77 nm) (filled circles) doped with 30 wt.% of compound 1a, and for
the 1 mm thick fused silica substrate alone (open circles). The fundamental
wavelength is 1200 nm.
Fig. 4. Wavelength dependence of the v(3) susceptibility for a polymer film doped
with 30 wt.% of compound 1a (graph i) and 2a (graph ii): top and right axes: d and
s, respectively. As reference, the absorption spectrum for the corresponding films is
included (continuous line: bottom and left axes).

M. Rodríguez et al. / Polyhedron 43 (2012) 194–200
199
as is shown in Fig. 1 and data in Table 2 (torsion angles). In the case
of compounds 1b and 2b, even when the X-ray data indicate that
the planarity is preserved after boron complexation and that the
UV spectra show a red shift, not any considerable change is ob-
served for v(3) values. The key to explain this observation could
thank M. Olmos, M.A Leyva and Dr. R. Espinosa-Luna for their tech-
nical assistance.
Appendix A. Supplementary data
be associated with the deformation of the electronic
from ligand to boron complex, ligands have a D– –C@N–
arrangement (effective D– –A push–pull architecture) but the for-
mation of the N ? B bond produces a D– –A system,
–C@N+–
which it also might be viewed as a D– –A– –A structure. In this
p
-system
CCDC 865882, 865883, 865884, 865885 and 865881 contains
the supplementary crystallographic data for 1b, 1c, 2a, 2b and
2c. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
p
p
–A
p
p
p
p
p
way, the D–A combination presented in compounds 2a–2c could
be less efficient for third-harmonic generation than those for the
ligands 1a–1c.
Note that in the calculation of v(3) it is important to consider
the absorption of the films according to the formalism of the
Maker-Fringes technique (see Eq. (1)). The absorption coefficients
References
[1] N. Fujita, S. Shinkai, T.D. James, Chem. Asian J. 3 (2008) 1076.
[2] K. Gießler, H. Griesser, D. Göhringer, T. Sabirov, C. Richert, Eur. J. Org. Chem.
2010 (2010) 3611.
[3] A.E. Hargrove, R.N. Reyes, I. Riddington, E.V. Anslyn, J.L. Sessler, Org. Lett. 12
(2010) 4804.
(a) at 400 nm for 1a, 1b, 2a and 2b are 6.2, 2.5, 2.9 and
1.5 ꢀ 104 cmꢁ1, respectively, so there is not a significant difference
between them in the v(3) values through three-photon resonance
(about a factor of less than 1.5 times for the largest difference on
the cubic susceptibility values) when using the wavelength of
1200 nm (see Eq. (1)).
[4] Y.L. Rao, S. Wang, Inorg. Chem. 50 (2011) 12263.
[5] J.L. Maldonado, G. Ramos-Ortíz, O. Barbosa-García, M.A. Meneses-Nava, L.
Márquez, M. Olmos-López, H. Reyes, B. Muñoz, N. Farfán, Int. J. Mod. Phys. B 21
(2007) 2625.
[6] S. Schlecht, W. Frank, M. Braund, Eur. J. Org. Chem. 2010 (2010) 3721.
[7] H. Höpfl, J. Organomet. Chem. 581 (1999) 129.
[8] Y. Qin, I. Kiburu, S. Shah, F. Jäkle, Org. Lett. 8 (2006) 5227.
[9] D. Frath, S. Azizi, G. Uldrich, P. Retailleau, R. Ziessel, Org. Lett. 13 (2011) 3414.
[10] S.P. Forrest, M.K. Thompson, Chem. Rev. 107 (2007) 923.
[11] S.R. Marder, J. Mater. Chem. 19 (2009) 7392.
[12] C. Fuentes-Hernández, G. Ramos-Ortíz, S.Y. Tseng, M.P. Gaj, B. Kippelen, J.
Mater. Chem. 19 (2009) 7394.
[13] G. Ramos-Ortíz, J.L. Maldonado, M.C.G. Hernández, M.G. Zolotukhin, S. Fomine,
N. Fröhlich, U. Scherf, F. Galbrech, E. Preis, M. Salmon, J. Cárdenas, M.I. Chávez,
Polymer 51 (2010) 2351.
[14] J.P. Morrall, G.T. Dalton, M.G. Humphrey, M. Samoc, Adv. Organomet. Chem. 51
(2008) 61.
[15] B.J. Coe, J.A. Harris, J.J. Hall, B.S. Brunschwing, S.T. Hung, W. Libaers, K. Clays,
S.J. Coles, P.N. Horton, M.E. Light, M.B. Hursthouse, J. Garín, J. Orduna, Chem.
Mater. 18 (2006) 5907.
[16] H.S. Nalwa, S. Miyata (Eds.), Nonlinear Optics of Organic Molecules and
Polymers, CRC Pres, Boca Raton FL, 1997.
The wavelength dependence of the third-order nonlinear sus-
ceptibility for compounds 1a and 2a was also determined (see
Fig. 4). To clarify this multi-photon resonance, Fig. 4 includes the
linear absorption spectrum of the film (bottom and left axes). Note
that the wavelength scales are arranged in such a way that the top
scale is 3 times the bottom one. Thus, according to the absorption
peaks located at 428 and 445 nm for 1a and 2a, respectively, there
is a slight enhancement of the cubic nonlinearities through three-
photon resonances, which is more notorious for 1a compound than
for 2a.
4. Conclusions
[17] E.E. Moore, D. Yaron, J. Phys. Chem. A 106 (2002) 5339.
[18] S.R. Marder, J.W. Perry, G. Bourhill, C.B. Gorman, B.G. Tiemann, K. Mansour,
Science 261 (1993) 186.
[19] B.M. Muñoz, R. Santillan, M. Rodríguez, J.M. Méndez, M. Romero, N. Farfán, P.G.
Lacroix, K. Nakatani, G. Ramos-Ortíz, J.L. Maldonado, J. Organomet. Chem. 693
(2008) 1321.
[20] M. Rodríguez, R. Castro-Beltrán, G. Ramos-Ortíz, J.L. Maldonado, N. Farfán, O.
Domínguez, J. Rodríguez, R. Santillan, M.A. Meneses-Nava, O. Barbosa-García, J.
Peón, Synth. Met. 159 (2009) 1281.
[21] M. Rodríguez, J.L. Maldonado, G. Ramos-Ortíz, J.F. Lamère, P. Lacroix, N. Farfán,
M.E. Ochoa, R. Santillan, M.A. Meneses-Nava, O. Barbosa-García, K. Nakatani,
New J. Chem. 33 (2009) 1693.
[22] J.F. Lamère, P.G. Lacroix, N. Farfán, J.M. Rivera, R. Santillan, K. Nakatani, J.
Mater. Chem. 16 (2006) 2913.
[23] J.L. Maldonado, Y. Ponce-de-León, G. Ramos-Ortíz, M. Rodríguez, M.A.
Meneses-Nava, O. Barbosa-García, R. Santillan, N. Farfán, J. Phys. D 42 (2009)
075102.
[24] V.M. Herrera-Ambriz, J.L. Maldonado, M. Rodríguez, R. Castro-Beltrán, G.
Ramos-Ortíz, N.E. Magaña-Vergara, M.A. Meneses-Nava, O. Barbosa-García, R.
Santillan, N. Farfán, F.X. Dang, P.G. Lacroix, I. Ledeoux-Rak, J. Phys. Chem. C 115
(2011) 23955.
[25] F. Qiao, A. Liu, Y. Zhou, Y. Xiao, P.O. Yang, J. Mater. Sci. 44 (2009) 1283.
[26] J.F. Salinas, J.L. Maldonado, G. Ramos-Ortíz, M. Rodríguez, M.A. Meneses-Nava,
O. Barbosa-García, R. Santillan, N. Farfán, Sol. Energy Mater. Sol. Cells 95 (2011)
595.
We have synthesized three borinates 2a–2c and their chemical
structures were established by NMR data; information of com-
pound 2a was compared with data lately reported. Third-order
nonlinear susceptibilities were measured at IR wavelengths for
compounds 1a–1b and 2a–2b. Reduction on the cubic susceptibil-
ity from 1a–1b to 2a–2b (for family c was not possible to measure
v(3) because of the poor THG response) was related to structural
features. Structurally, compound 2a showed a larger twisted con-
formation with respect to its ligand 1a, which was estimated by
computed calculations using the density functional theory (DFT)
at the B3PW91/6-31G⁄ level and confirmed by X-ray diffraction
analysis. In the case of compound 2b, a smaller reduction of v(3)
with respect to that one for 2a, was estimated when going from li-
gands 1b (reduction of 1.3) and 1a (reduction of 2.6), respectively;
it might be just to the deformation of the electronic
D– –A to D– –A– –A after boron complexation in 2b) because the
X-ray data indicate that its planarity is preserved. In the
wavelength dependence of
(3), a slight enhancement through
three-photon resonances was also observed. These -backbones
p system (from
p
p
p
v
p
[27] J.W. Ledbetter, J. Phys. Chem. 72 (1968) 4111.
like systems, as interesting dyes with structural and electronic
features that affect their NLO properties, could have different inter-
esting optical properties, such as Two Photon Absorption (TPA),
particularly, through their re-design with appropriate combination
of the electronic groups.
[28] G. Chremos, H. Weidmann, H. Zimmerman, J. Org. Chem. 26 (1961) 1683.
[29] M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L. De Caro, C.
Giacovazzo, G. Polidori, R. Spagna, J. Appl. Crystallogr. 38 (2005) 381.
[30] G.M. Sheldrick, SHELXS-86 – Program for Crystal Structure Solution, University
of Göttingen, Germany, 1986.
[31] G.M. Sheldrick, SHELXL-97 – Program for the Refinement of Crystal Structure,
University of Göttingen, Germany, 1997.
[32] G. Ramos-Ortíz, J.L. Maldonado, M.A. Meneses-Nava, O. Barbosa-García, M.
Olmos-López, M. Cha, Opt. Mater. 29 (2007) 636.
Acknowledgements
[33] E. Klimova, T. Klimova, J.M. Martínez-Mendoza, L. Ortíz-Frade, J.L. Maldonado,
G. Ramos-Ortíz, M. Flores-Alamo, M. Martínez-García, Inorg. Chim. Acta 362
(2009) 2820.
[34] X.H. Wang, D.P. West, N.B. McKeown, T.A. King, J. Opt. Soc. Am. B 15 (1998)
1895.
M. Rodríguez thanks Postdoctoral CONACyT Grant. This work
was supported by CONACyT projects 55250, 49512, 58783,
83519; CONACyT-SENER 153094 and PAPIIT IN-214010. Authors

200
M. Rodríguez et al. / Polyhedron 43 (2012) 194–200
[35] P.G. Lacroix, F. Averseng, I. Malfant, K. Nakatani, Inorg. Chim. Acta 357 (2004)
3825.
Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul,
B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L.
Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, C.
Gonzalez, M. Challacombe, P.M. W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L.
Andres, C. González, M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 98
(Revision A.9), Gaussian, Inc., Pittsburgh, PA, 1998.
[36] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
V.G. Zakrzewski, J.A. Montgomery, Jr., R.E. Stratmann, J.C. Burant, S. Dapprich,
J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V.
Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J.
Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick, A.D.