Engineering second-order nonlinear optical activity by means of a noncentrosymmetric distortion of the [Te-N]2 supramolecular synthon

Article abstract of DOI:10.1021/cg101060s

Moderate steric repulsion within the supramolecular ribbon chains assembled by 1,2,5-telluradiazole derivatives causes a distortion of the [Te-N] ₂ supramolecular synthon which removes the inversion center from the four-membered virtual ring. T

Full text of DOI:10.1021/cg101060s

DOI: 10.1021/cg101060s
Engineering Second-Order Nonlinear Optical Activity by Means of a
Noncentrosymmetric Distortion of the [Te-N]2 Supramolecular Synthon
2010, Vol. 10
4959–4964
Anthony F. Cozzolino, Qin Yang, and Ignacio Vargas-Baca*
Department of Chemistry and Chemical Biology, McMaster University, 1280 Main Street West,
Hamilton, Ontario L8S 4M1, Canada
Received August 12, 2010; Revised Manuscript Received September 20, 2010
ABSTRACT: Moderate steric repulsion within the supramolecular ribbon chains assembled by 1,2,5-telluradiazole derivatives
causes a distortion of the [Te-N]2 supramolecular synthon which removes the inversion center from the four-membered virtual
ring. This geometrical feature can propagate through the lattice, creating a noncentrosymmetric crystal with second-order
nonlinear optical (NLO) properties. This principle was demonstrated in the cases of 3,4-dicyano-1,2,5-telluradiazole and
5,6-dichlorobenzo-2,1,3-telluradiazole. The second harmonic generation efficiency of these materials, however, is modest
because the molecular dipole moments have a nearly antiparallel arrangement in the ribbons. The structure of 5-benzoylbenzo-
2,1,3-telluradiazole demonstrates that it is indeed possible to extend this strategy to generate acentric crystals of benzo-2,1,3-
telluradiazoles featuring pendant groups (including NLO chromophores) and in this way design more efficient NLO materials.
Chart 1
Introduction
In the crystal structures, 1,2,5-telluradiazole (1a, Chart 1)
and its annulated derivatives exhibit intermolecular associa-
tion, forming ribbon chains and, in sterically encumbered
cases, dimers (Scheme 1).1-4 The supramolecular structural
element that builds these arrangements;the supramolecular
synthon5;is a virtual four-membered ring that features two
antiparallel Te N secondary bonding interactions (SBIs).
3 3 3
The binding energy of the [Te-N]2 supramolecular synthon is
large enough to induce a geometric distortion of the aromatic
system in phenanthro(9,10-c)-1,2,5-telluradiazole (2) in order
to accommodate the formation of the ribbon.3 In a case with
smaller but still significant steric repulsion, 4,5,6,7-tetrafluoro-
benzo-2,1,3-telluradiazole (3a) assembles ribbon chains
which appear significantly distorted as compared to the
ribbons in the structure of benzo-2,1,3-telluradiazole
(3b).2 Two types of distortion of the [Te-N]2 supra-
molecular synthon lead to distinct crystalline polymorphs of
3a. One phase (β) features centrosymmetric [Te-N]2 supra-
Scheme 1. Supramolecular Assemblies of 1,2,5-Telluradiazoles
Formed by the [Te-N]2 Supramolecular Synthon:
(a) Ribbon Chain; (b) Dimer
˚
molecular synthons with longer (2.8 A) Te N SBIs; this
3 3 3
array is metastable and switches to the thermodynamically
preferred structure by a thermochromic phase transition.6 In
the R phase, all the [Te-N]2 supramolecular synthons are
equal but distorted and the ribbons are puckered. The overall
distortion in this case is best described as the combination
of two motions: one is an in-plane motion that produces
two different SBI lengths (Scheme 2a), and the other is a
rotation of the rings with respect to each other (Scheme 2b).
Each of these distortions on its own implies the removal
of the inversion center of the [Te-N]2 supramolecular
synthon. Even though the overall lattice of R-3a is racemic
and thus centrosymmetric, if this feature were to propagate
throughout the lattice by virtue of other intermolecular inter-
actions and packing, the result would be a noncentrosym-
metric crystal. Here we report that it is indeed possible to take
advantage of such steric effects to promote crystallization in a
noncentrosymmetric lattice with the consequent second-order
nonlinear optical activity.
Experimental Section
Materials and Methods. All starting materials were reagent grade
and were used as received unless it is otherwise stated. Diamino-
maleonitrile, 1,2-diamino-4,5-dichlorobenzene, 3,4-diaminobenzo-
phenone, and pyridine were purchased from Aldrich. Triethylamine
was purchased from Anachemia; toluene and methylene chloride
*Corresponding author. Telephone: 905 525 9140, ext 23497. Fax: 905 522
2509. E-mail: vargas@chemistry.mcmaster.ca.
r
2010 American Chemical Society
Published on Web 10/12/2010
pubs.acs.org/crystal

4960 Crystal Growth & Design, Vol. 10, No. 11, 2010
Cozzolino et al.
Scheme 2. Non-centrosymmetric Distortions of the [Te-N]2
Supramolecular Synthon: (a) In-Plane; (b) Out-of-Plane
where Iω is the averaged intensity of the pump measured at the
reference photodiode and deff = 1/2χ(2). The calibration constant, K,
was determined with a standard of KDP.
Synthesis of TeN2C2(CN)2 (1b). TeCl4 (0.10 g, 0.37 mmol) was
dissolved in 3 mL of pyridine. This was added dropwise with stirring
to a solution of diaminomaleonitrile (0.04 g, 0.37 mmol) in 3 mL of
the same solvent. The mixture was stirred for an additional 5 min,
and an excess of Et3N (3.5 mmol, 0.5 mL) was added. Stirring was
continued for 10 min, and the solution was filtered. A yellow solid
was precipitated from the filtrate at -20 ꢀC and filtered off. The
final product was sublimed under dynamic vacuum (60 mTorr)
at 100 ꢀC to give a yellow powder. Yield after sublimation: 0.06 g
(0.33 mmol, 89%), mp 130 ꢀC (dec.). 13C{1H} NMR (50 MHz,
d6-DMSO): δ 141.2 (4ꢀ); 119.3 (CN). 125Te NMR (158 MHz,
TeMe2): δ 2408. Raman (cm-1): 2224s, 1397vs, 1262w, 683vs, 538
m, 462w, 311s. IR (cm-1): 2226 m, 1513vs, 1390 m, 1264vs, 1106vs,
705vs, 693vs, 576vs. EI HRMS m/z (ion, %, calc): 233.9181 (Mþ, 20,
231.9185), 181.9137 (Mþ - 2CN, 20, 181.9124), 129.9027 (Teþ, 100,
129.9062). Single crystals for X-ray diffraction were grown from
pyridine at -20 ꢀC.
The benzo-2,1,3-telluradiazoles, 3c and 3d, were prepared using a
slightly different method in which TeCl4 (0.16 g, 0.59 mmol) was
dissolved in 3 mL of pyridine and added dropwise with stirring to a
solution of 4,5-dichloro-o-phenylenediamine and 4-benzoyl-o-phe-
nylenediamine, respectively (0.57 mmol), in 3 mL of the same sol-
vent. The mixture was stirred for 5 min, and an excess of Et3N
(7 mmol, 1.0 mL) was added. Stirring was continued for 10 min, and
toluene was added to the mixture to precipitate the product. The
solid was washed three times with 5 mL of toluene. The crude pro-
duct was recrystallized from pyridine and washed with 5 mL of
were purchased from Caledon. TeCl4 was prepared by reaction of
Cl2 with elemental Te purchased from Cerac. Pyridine and triethy-
lamine where dehydrated over CaH2 before use, and the toluene and
methylene chloride were passed through an Innovative Technolo-
gies solvent purification system. The manipulation of air sensitive
materials was performed under an atmosphere of anhydrous argon
or nitrogen with standard Schlenk and glovebox techniques.
General Instrumentation. IR spectra were recorded on a Nicolet
6700 FT-IR spectrometer with a resolution of 4 cm-1. Raman
spectra were acquired with a Renishaw Invia spectrometer exciting
at 785 nm, 30 mW, averaging 10 scans (10 s each). The 1H and 13
C
NMR spectra were acquired on a Bruker AV200 (200.13 MHz)
1
spectrometer or a Bruker Avance 500 (500.13 MHz). H and 13C
chemical shifts are reported in ppm with respect to tetramethylsilane
and were measured using the resonances of the solvent (DMSO: 1H
δ 2.50 ppm, 13C δ 39.52 ppm) as internal standards, and the posi-
tions of the 125Te resonances were referenced to an external standard
solution of Ph2Te2 in CH2Cl2 (δ 420.36; 125Te NMR) previously
referenced to Me2Te (δ 0.00; 125Te NMR) as described elsewhere.2
The diffuse-reflectance spectra were measured with an illuminated
(tungsten halogen light source) integrating sphere (Ocean Optics
ISP-REF) attached to a photodiode array spectrophotometer
(OceanOpticsSD2000) and are reportedrelativetoa PTFE standard
(OceanOptics WS-1). Eachmeasurementwas anaverage of100scans
that were integrated over 3 ms using a boxcar smoothing of 10 points
and was corrected for stray light and dark current. High resolution
electron-ionization mass spectrometry was performed on a Micro-
mass GCT (GC-EI/CI time of flight) mass spectrometer. Melting
points were measured on a Thomas-Hoover melting point apparatus
and are reported uncorrected.
Second Harmonic Generation. A custom-built harmonic-light
spectrometer7 was employed for these measurements. An Nd:
YAG laser (Continuum Surelite II) was used as the light source.
This system delivered IR pulses with a repetition frequency of 10 Hz,
a width of 5-7 ns, and up to 655 mJ of energy at a wavelength of
1064 nm. A combination of an iris, a half-wave achromatic retarder,
and a polarizer was used to modulate the intensity of the laser (Iω),
which was monitored with a photodiode with a 177 ps rise time
(Newport Model 818-BB-30) and a beam splitter. The intensity of
light scattered in the visible was measured with an end-on photo-
multiplier tube (Oriel 773346) with operating range 185-850 nm,
gain above 5 ꢀ 105, responsivity 3.4 ꢀ 104 A/W, and rise time 15 ns.
This detector received light through an assembly of an 850-nm
cutoff short-pass filter (CVI); a crown-glass planoconvex lens of
diameter 25.4 mm and focal length 50 mm; and an interferential
filter (CVI) centered at 532 nm, with a nominal 10-nm fwhm spectral
band. The PMT was normally operated under a 1000 V bias pro-
vided by a regulated power supply (Oriel 70705); the PMT output
was delivered to a 350-MHz voltage amplifier (Oriel 70723). The
responses of the two detectors were independently calibrated with
a power meter (Melles Griot 13PEM001). The response of each
detector was kept within its calibration range by means of neutral
density filters (CVI) and measuredwith a boxcar integrator (Stanford
Research 250), whose output was acquired with a digital oscilloscope
card (National Instruments NI 5112 PCI) installed in a PC and
controlled with a custom LabView Virtual Instrument.
toluene. The telluradiazole was separated from the Et3N HCl by
3
density using CH2Cl2. The product obtained in this way could be
further purified by an additional recrystallization and/or sublima-
tion under vacuum as necessary. TeN2C6H2Cl2 (3c): Red/purple
crystalline solid. Yield after recrystallization: 0.13 g (0.43 mmol,
76%). mp >200 ꢀC. 1H NMR (200 MHz, d6-DMSO): δ 7.86 (s, 2H,
aryl). Raman (cm-1): 1487w, 1476w, 1415 m, 1349w, 1273s, 725w,
691s, 642w, 505w, 483w, 380w, 344m, 327w, 285w, 274m, 237s,
210w, 192m, 179s, 154m, 128m, 115vs. IR (cm-1): 1487s, 1478m,
1417s, 1343m, 1270s, 1085vs, 979m, 852s, 84s, 825s, 727vs, 645w,
482m, 452vs. EI HRMS m/z (ion, %, calc): 301.8645 (Mþ, 20,
301.8657). Single crystals for X-ray diffraction were grown by
slowly cooling down to room temperature a saturated solution
prepared in pyridine at 100 ꢀC. TeN2C13H8O (3d): Orange crystal-
line solid. Yield after recrystallization: 0.23 g (0.48 mol, 86%). mp
>200 ꢀC. 1H NMR (200 MHz, d6-DMSO): δ 7.86, 7.82, 7.74, 7.72,
7.67, 7.63, 7.60, 7.56 (8H, m). 13C{1H} NMR (50 MHz, d6-DMSO):
δ 132.5 (1C, 3ꢀ), 131.1 (1C, 3ꢀ), 129.3 (2C, 3ꢀ), 128.4 (2C, 3ꢀ), 128.1
(1C, 3ꢀ), 125.6 (1C, 3ꢀ). Raman (cm-1): 1641s, 1597m, 1488w, 1427s,
1347w, 1326m, 1298s, 1139w, 1115w, 1025w, 996w, 788vw, 754vw,
689vs, 562w, 399m, 338w, 305w, 274w, 214vs, 165m. IR (cm-1):
3056w, 1642vs, 1595m, 1577w, 1516w, 1493w, 1446m, 1433w, 1329s,
1310m, 1301m, 1238s, 1175w, 1141w, 1117w, 960w, 940w, 890s,
883m, 822m, 805m, 791m, 718vs, 705m, 682m, 630w, 594w, 565w,
509w, 439m. EI HRMS m/z (ion, %, calc): 337.9678 (Mþ, 50,
337.9699). Single crystals for X-ray diffraction were grown by
sublimation under static vacuum at 120 ꢀC.
X-ray Crystallography. All samples were handled under Para-
tone-N oil (Hampton Research) at room temperature. Crystals of
1b (0.42 ꢀ 0.40 ꢀ 0.07 mm3), 3c (0.60 ꢀ 0.10 ꢀ 0.08 mm3), and 3d
(0.40 ꢀ 0.20 ꢀ 0.01 mm3) were mounted on MiTeGen Micromounts
(Ithaca, NY) using Paratone-N oil. Data for 1b and 3d were
collected on a SMART APEX II diffractometer utilizing Mo KR
˚
radiation (λ = 0.71073 A, graphite monochromator) and equipped
with an Oxford cryostream 700 low temperature accessory. Data for
3c were collected on a P4 Bruker diffractometer upgraded with a
Bruker SMART 1K CCD detector and a rotating anode utilizing
˚
Mo KR radiation (λ = 0.71073 A, graphite monochromator) and
equipped with an Oxford Cryostream 700 low temperature acces-
sory. Redundant data sets were collected, in 0.36ꢀ steps in φ or ω,
with a crystal-to-detector distance of 4.947 cm for 1b, 4.999 cm for
3c, and 4.958 cm for 3d. Preliminary orientation matrices were
obtained from the first frames using the Bruker APEX2 software
suite8 for 1b and 3c and CELL_NOW9 for 3d. The final cell
The coefficient deff of each sample was evaluated by an adapta-
tion of the Kurtz-Perry method7 using 7-mm-diameter pellets
hand-pressed in a stainless steel die from freshly ground and sieved
crystals. The averaged intensity of the signal (I2ω) was fitted to
I2ω ¼ Kdeff 2Iω
ð1Þ
2

Article
Crystal Growth & Design, Vol. 10, No. 11, 2010 4961
Table 1. Crystallographic and Refinement Parameters for 1b, 3c, and 3d
Table 2. Selected Bond Distances and Angles for 1b, 3c, and 3d
compound
1b
3c
3d
1b
3ca
3d
empirical formula
crystal system
space group
C4N4Te C6H2Cl2N2Te C13H8N2OTe
orthorhombic orthorhombic monoclinic
Intramolecular
˚
Te-N1 (A)*
2.022(6)
2.035(6)
1.300(9)
1.306(9)
1.443(8)
82.5(2)
2.01(1), 2.04(2)
2.02(1), 2.05(2)
1.33(2), 1.29(2)
1.36(2), 1.28(2)
1.45(2), 1.46(2)
84.2(6), 84.4(6)
112(1), 108(1)
109(1), 108(1)
2.02(1)
2.03(2)
1.29(2)
1.29(2)
1.50(2)
82.8(5)
112(1)
111(1)
P212121
5.983(2)
7.781(3)
12.932(5)
90
Pca21
C2
˚
Te-N2 (A)*
N1dC (A)*
˚
a (A)
7.588(2)
7.744(2)
28.008(6)
90
10.647(7)
7.761(5)
14.31(1)
90
˚
˚
b (A)
˚
N2dC (A)*
˚
c (A)
˚
C-C (A)*
R (deg)
β (deg)
γ (deg)
N-Te-N (deg)*
Te-N1dC (deg)*
Te-N2dC (deg)*
90
90
90
90
96.78(2)
90
111.1(5)
109.9(4)
3
˚
V (A )
602.0(4)
4, 2.556
173(2)
1645.9(6)
8, 2.426
173(2)
1174(1)
4, 1.900
173(2)
Z, F(calc) (g cm-3
T (K)
)
3
Intermolecular
˚
Te N1 (A)*
3 3 3
2.767(6)
2.659(6)
67.1(2)
69.6(2)
109.7(2)
113.5(2)
2.51(1), 2.54(1)
2.89(1), 2.87(1)
72.4(5), 73.2(5)
64.2(5), 65.8(5)
104.9(6), 103.3(6)
118.2(7), 117.5(6)
2.68(2)
2.80(2)
71.6(6)
68.8(5)
107.7(7)
111.8(7)
μ (mm-1
θ range
limiting indices
)
4.840
4.192
1.45-28.85
-8 e h e 9
2.516
2.87-23.28
-10 e h e 11
˚
Te N2 (A)*
3 3 3
3.06-32.03
-8 e h e 8
-11 e k e 8
N2-Te N1 (deg)*
3 3 3
N1-Te N2 (deg)*
3 3 3
-10 e k e 10 0 e k e 8
Te-N1-Te (deg)*
Te-N2-Te (deg)*
-19 e l e 18 -37 e l e 37 0 e l e 15
refl collec/unique
R(int)
no. of parameters
twin fraction
twinning
9691/2087
0.0748
83
12915/3931
0.0870
200
1164/1164
0.0000
155
a The measurements are duplicated because the asymmetric unit
consists of two molecules; the two sets are equal within 3σ.
0.244
racemic
0.360
racemic
0.440
180ꢀ; [001]
While a number of inorganic crystals, such as β-BaB2O4, are
now routinely used in tunable coherent light sources, the
rational design of nonlinear optical (NLO) supramolecular
materials remains an important topic of research. The most
straightforward approach in this area relies on using strong,
well-defined supramolecular interactions to influence the
organization of molecules in the lattice. In this context,
hydrogen bonding has been used to engineer acentric crystal
lattices.32,33 For example, benzoic acids that form acentric
ribbon chains tend to crystallize in acentric space groups, as
is observed in 11 of 21 cited examples.34 Of these, the ortho-
substituted rings show the highest preference for acentric
spacial arrangement as a result of interchain interactions.
The use of noncentrosymmetric supramolecular ribbons to
promote a noncentric lattice has been extended to include
other types of supramolecular interactions. There are several
examples of coordination polymers with acentric bridging
ligands that promote acentric lattice formation.35-37 It is,
therefore, reasonable to expect that noncentrosymmetric
distortions to the [Te-N]2 synthon could be used to build
noncentrosymmetric ribbon chains and noncentrosymmetric
crystals. This approach requires the identification of molec-
ular building blocks for which the steric repulsion would
be sufficient to cause the distortion but not so large as to
prevent association. With this in mind, we chose to investi-
gate the structures of 3,4-dicyano-1,2,5-telluradiazole (1b)
and 5,6-dichlorobenzo-2,1,3-telluradiazole (3c), which can be
conveniently prepared with small modifications of the pub-
lished general method2 from readily available diamines.
Crystal Structures of 1b and 3c. Crystallographic data and
final refinement parameters for all new compounds are
collected in Table 1, and selected bond distances and angles
are presented in Table 2. The crystal structures of 1b and 3c
display the expected ribbon chains and do crystallize in non-
centrosymmetric space groups (Figures 1-4). There are one
and two molecules in the asymmetric units of 1b and 3c,
respectively. Considering the magnitudes of the standard
deviations in bond lengths and angles, both molecules have a
pseudo-C2v symmetry. Both systems are essentially planar,
within the magnitudes of the standard deviations. Also, there
are no significant differences between the molecular dimen-
sions of 1b and 1a or between those of 3c and 3b. In both
instances, the ribbon chains are assembled along the [0, 1, 0]
axis by the [Te-N]2 supramolecular synthon but with
R1a/wR2a (I > 2σ(I)) 0.0451/0.0835 0.0634/0.1561 0.0546/0.1100
R1a/wR2a for all data 0.0696/0.0909 0.1085/0.1732 0.0722/0.1157
goodness-of-fit on F2 0.987
1.058
1.021
larg diff peak/hole
)
2.302/-1.097 2.738/-2.178 1.508/-1.212
-3
˚
(e A
3
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|; wR2 = { [w(Fo2 - Fc2)2]/ w(Fo2)2}1/2
.
parameters were obtained by refinement on the positions of selected
reflections with I > 10σ(I) after integration of all the frames using
the Bruker APEX2 software suite8 for each of 1b, 3c, and 3d. The
data was empirically corrected for absorption and other effects
using the Bruker APEX2 software suite;8 3d data was corrected
using TWINABS.10 The structures were solved by Patterson heavy
atom methods and refined by full-matrix least-squares on all F2
data using SHELXL11 as part of the WinGX package.12 The non-H
atoms were refined anisotropically, while H atoms were constrained
to idealized positions using appropriate riding models. Molecular
graphics were produced using ORTEP-313 or Mercury 2.2.14
Computational Methods. The structures considered in this study
were fully optimized using the ADF DFT package (SCM, versions
2008.01 to 2009.01).15-17 The Adiabatic Local Density Approxima-
tion (ALDA) was used for the exchange-correlation kernel,18,19
and the differentiated static LDA expression was used with the
Vosko-Wilk-Nusair parametrization.20 The calculations of model
geometries were gradient-corrected with the exchange and correla-
tion functionals of the gradient correction proposed by Perdew
and Wang,21,22 which usually reproduces satisfactorily the geome-
tries of heavy main-group systems.23 Geometry optimizations were
conducted using a triple-ζ all-electron basis set with one polariza-
tion function and applying the zeroth order regular approxima-
tion (ZORA) with specially adapted basis sets.24-28 Geometry
constraints were used when point group symmetry was applicable.
Visualization of the computational results was performed using the
ADF-GUI.29
Results and Discussion
Design Rationale. Interest in materials with crystal struc-
tures that lack an inversion center derives, in great part, from
their potential applications in optical technologies.30,31 It
can be shown that because their even-order dielectric sus-
ceptibilities (χ(n)) are different from zero, their macroscopic
polarization (P, eq 2) enables interactions with electric fields
(E);including those of optical origin;that result in phe-
nomena such as the electro-optic Pockels effect and Second
Harmonic Generation (SHG).
P ¼ χð1ÞE þ χð2ÞEE þ χð3ÞEEE þ :::
ð2Þ

4962 Crystal Growth & Design, Vol. 10, No. 11, 2010
Cozzolino et al.
Figure 1. ORTEP and numbering scheme for the asymmetric unit
in the crystal structure of 1b. Displacement ellipsoids are shown at
the 50% probability level.
Figure 4. Two views of the crystal structure of 3c: (a) along (0, 1, 0);
(b) along (1, 0, 0). Models presented as ball and stick; different layers
are represented with different shades of gray for clarity.
Figure 2. Ball and stick representation of two views of the crystal
structure of 1b: (a) along (0, 1, 0) and (b) along (1, 0, 0).
Figure 5. Kurtz-Perry SHG measurements for 1b, 3c, and 3d.
Figure 3. ORTEP and numbering scheme for the asymmetric unit
in the crystal structure of 3c. Displacement ellipsoids are shown at
the 50% probability level.
Figure 6. Diffuse reflectance spectra in the visible of 1b ( ),
3c (;), and 3d (- - -).
3 3 3
significant distortions. The associated heterocycles are not
coplanar, having a 4.7(1)ꢀ rotation between adjacent hetero-
cycles in the crystal of 1b and 5.5(3)ꢀ in 3c. This deviation is
smaller than the 12.0(4) and 10.8(5)ꢀ observed in R-3a but
larger than the 2.5(4)ꢀ in the case of 1a. The noncentrosym-
metric distortion of the [Te-N]2 supramolecular synthon is
of KH2PO4 (KDP, deff = 0.39 pm/V).41 These values are
small and might be subject to the competing effects of
resonant enhancement and absorption at the wavelength of
the second harmonic (520 nm), as the diffuse reflectance
spectra of these samples suggest (Figure 6). Despite the small
magnitude of deff, these results do confirm that the crystals of
1b and 3c possess a second-order NLO response as a result of
their noncentrosymmetric lattice. The limited solubility of the
compounds precluded accurate measurements of their hy-
perpolarizabilities in solution; thus, their hyperpolarizability
tensors were calculated using TD-DFT. To aid in the inter-
pretation, the calculations were expanded to include 1a, 3b,
and p-nitroaniline (4). For these calculations, single molecule
models were fully optimized, with appropriate symmetry
constraints. The results are presented in Table 3. For con-
venience and because it is the quantity measurable by hyper-
Rayleigh scattering, only the orientational average of each
tensor (Æβæ) is used. The HOMO-LUMO gaps and dipole
also apparent in the asymmetry of Te N SBIs; these differ
3 3 3
˚
by 0.108 A in 1b and an average of 0.36 A in 3c. In the latter
˚
˚
case,thisdifferenceisevenlargerthanthe0.26Aobserved in R-3a.
NLO Properties of 1b and 3c. The SHG efficiency of
crystalline samples of 1b and 3c was examined by evaluating
the deff coefficient using the Kurtz-Perry method with a
fundamental wavelength of 1064 nm (Figure 5). Although
twinning has a detrimental effect on the NLO activity of
single crystals, its impact is less significant in the collective
response of randomly oriented microcrystals.38-40 The val-
ues determined for 1b and 3c were respectively 0.136 ( 0.001
and 0.089 ( 0.002 times the magnitude of the standard

Article
Crystal Growth & Design, Vol. 10, No. 11, 2010 4963
Table 3. DFT and TD-DFT Calculated Values Relevant to the
NLO Activity
compound
static Æβæ (esu ꢀ1030
1b 1a
3d
3c
3b
4
)
2.79 1.60 1.94
3.55 1.68 2.99 15.58 1.88 18.62
6.99 0.04 3.22
8.08 1.93
8.44
SHG1064 Æβæ (esu ꢀ1030
)
μ (D)
2.32 0.13
2.33 2.45
7.91
2.67
HOMO-LUMO gap (eV) 2.84 3.14 2.23
moments are also included in Table 3. Translating the
calculated tensors to the macroscopic susceptibilities would
require intermolecular interactions in addition to the geo-
metric and local field effects to be accounted for,42-44 which
are outside the scope of this work. Nevertheless, the calcu-
lated data is very informative. The calculations do show that
the 1,2,5-telluradiazole and the small modifications here con-
sidered are chromophores with reasonable hyperpolarizabi-
lities, comparable to that of 4 in the best case. The orientation
of the molecules is one of the factors that give the observed
smallSHGefficiencies. The point group of 1b, P212121, isnon-
polar, and thus, there is a mutual cancellation of the molecular
dipole moments causing the macroscopic nonlinear response
to arise only from the octopolar terms of the second-order
susceptibility tensor. On the other hand, the point group of 3c
is polar with an overall dipole parallel to the [0, 0, 1] axis. The
molecular dipoles, however, are aligned in a nearly antipar-
allel fashion. DFT calculations on the asymmetric unit (the
SBI dimer) of 3c gave an overall dipole moment of 1.95 D, but
its projection along the [0, 0, 1] axis is only 0.25 D.
Figure 7. ORTEP and numbering scheme for the asymmetric unit
in the crystal structure of 3d. Displacement ellipsoids are shown at
the 50% probability level.
Extension to a Monosubstituted Benzo-2,1,3-telluradiazole.
As the example of 3c illustrates, formation of ribbon chains
necessarily places the molecular dipoles in a nearly antipar-
allel orientation which will cancel most of the NLO activity.
Therefore, in order to design and build a more efficient NLO
material, the distortion of the [Te-N]2 supramolecular syn-
thon could only be used as a means to induce noncentrosym-
metric packing. It would be indispensable, then, to append
chromophores with larger hyperpolarizabilities and promote
an alignment that preserves molecular dipoles. Simultaneously,
the steric bulk of chromophore groups should distort the
[Te-N]2 supramolecular synthon yet not prevent the forma-
tion of the ribbons. One way in which all of this could be
accomplished is by attaching the chromophore at the 3- or
5-positions of 1 or 2, respectively. To explore this concept,
the commercially available 3,4-diaminobenzophenone was
used to prepare 3d. X-ray crystallography revealed a unit
cell with an asymmetric unit consisting of one molecule
(Figure 7). The internal parameters of the five-membered
heterocycle are the same as in the previously discussed struc-
tures, within the standard deviations. As in the previous
examples, supramolecular ribbon chains are assembled by a
distorted [Te-N]2 supramolecular synthon along a screw
axis perpendicular to the ac plane (Figure 8). The angle of
rotation between neighboring telluradiazole rings is 1.2(4)ꢀ,
Figure 8. Two views of the crystal structure of 3d: (a) along (0, 1, 0);
and (b) along (1, 0, 0). The ball and stick models portray different
layers in distinct shadows of gray for clarity.
absorption at 520 nm. In this case, the point group of the
lattice is polar with an overall dipole parallel to the [0, 1, 0]
axis; the projection of each molecular dipole moment along
this direction is 1.94 D.
Concluding Remarks. It has been previously shown in
several instances that supramolecular interactions such as
hydrogen bonding can promote noncentrosymmetric pack-
ing and thus drive the assembly of NLO crystals.32,33 There
are, however, situations in which the use of other intermo-
lecular forces would be advantageous. For example, in a
hydrogen-bonded NLO material intended for use in electro-
optic modulators, absorption by the vibrational overtones of
N-H and O-H bonds would have a detrimental effect at the
near-infrared wavelengths used in current silica optical fiber
technology.45,46 Supramolecular interactions between heavy
elements, e.g. main-group SBIs, would give materials with
greater near-infrared transparency because their overtones
appear at much longer wavelengths.
Earlier work showed that the interaction between iodo and
nitro functional groups, on its own47 and in combination
with hydrogen bonds,48 can promote parallel alignment of
NLO chromophores in crystal structures. The approach
demonstrated in this report relies on the distortion of a
supramolecular synthon to create a noncentrosymmetric
feature that is able to propagate through the lattice and
can, in principle, be extended to create NLO crystals of
functionalized benzo-2,1,3-telluradiazoles.
˚
and the difference in Te N SBI distances is 0.12 A. The
3 3 3
benzoyl group is rotated by 51(1)ꢀ from the plane of the
benzo-2,1,3-telluradiazole and is interdigitated with the cor-
responding groups pendant from the neighboring ribbons.
This π-stacking interaction appears to facilitate the propa-
gation of noncentrosymmetry throughout the lattice. The
magnitude of deff for 3d was found to be 0.261 ( 0.003 times
that of KDP. The average of the molecular hyperpolariz-
ability calculated by TD-DFT (Table 3) is comparable to the
other values. The diffuse reflectance spectrum of this com-
pound is also shown in Figure 6 and shows significant
Acknowledgment. We acknowledge the continuous sup-
port of NSERC Canada (IVB Discovery Grant, AFC
Scholarship), the Canada Foundation for Innovation, and

4964 Crystal Growth & Design, Vol. 10, No. 11, 2010
Cozzolino et al.
the Ontario Innovation Fund. This work was made possible
bythe facilities ofthe Shared Hierarchical Academic Research
Computing Network (SHARCNET: www.sharcnet.ca) and
Compute/Calcul Canada.
SCM, Theoretical Chemistry, Vrije Universiteit: Amsterdam, The
Netherlands, http://www.scm.com.
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