Intramolecularly coordinated azobenzene selenium derivatives: Effect of strength of the Se...N intramolecular interaction on luminescence

Article abstract of DOI:10.1039/c0dt01319f

A series of selenium derivatives (6-12) of 2-phenylazophenyl have been synthesized using o-lithiation route. The effect of the strength of the intramolecular Se...N interaction on the absorption spectra as well as emission spectra has been studied. The st

Full text of DOI:10.1039/c0dt01319f

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2011, 40, 4489
www.rsc.org/dalton
PAPER
Intramolecularly coordinated azobenzene selenium derivatives: Effect of
strength of the Se ◊ ◊ ◊ N intramolecular interaction on luminescence†
Kriti Srivastava,a Tapash Chakraborty,a Harkesh B. Singh*a and Ray J. Butcherb
Received 1st October 2010, Accepted 21st February 2011
DOI: 10.1039/c0dt01319f
A series of selenium derivatives (6–12) of 2-phenylazophenyl have been synthesized using o-lithiation
route. The effect of the strength of the intramolecular Se ◊ ◊ ◊ N interaction on the absorption spectra as
well as emission spectra has been studied. The studies suggest that the secondary bonding Se ◊ ◊ ◊ N
interaction give rise to fluorescence, however, the strength of Se ◊ ◊ ◊ N interaction cannot be directly
correlated with the intensity of the fluorescence. TD-DFT calculations show that the main transition
involved in the absorption spectra of the compound is the ligand based p–p* type.
Introduction
Azobenzene and its derivatives are of current interest due to
their promising applications as sensors in biochemical activity,1
molecular switches,2 nanodevices3 and as p-conjugate spacers.4
Azobenzene is a widely used chromophore5 and many of its
derivatives are used in the dye industries as colour enhancers.
It undergoes thermal or photochemical interconversion between
its cis- and trans-forms due to the flexibility of the azo-group,6
and hence does not show appreciable luminescence. However,
the interaction of nitrogen atoms of the azo-group, with in-built
acceptor atoms capable of forming five-membered chelate ring,
imparts rigidity to the structure and thereby hinders their tendency
to undergo photoisomerization. There are a few reports on the
study of the fluorescent properties of such azobenzene derivatives
where the enhancement in emission has been achieved by the
intramolecular coordination of the azobenzene nitrogen atom with
palladium (1–3) (Chart 1).7 The interaction of the nitrogen atom
lone pair of the azo group with Lewis acids not only eliminates
the possibility of its further interaction with the other nitrogen
atom but also imparts the required rigidity to the system giving
a nearly planar configuration. Kawashima and coworkers8 have
utilized this concept and reported the most intensely fluorescent
Chart
fluorescence.
1 ortho-Coordinated azobenzene derivatives exhibiting
boron substituted azobenzene system (4) (Chart 1).
It has been shown by our group9 and others10 that organose-
lenium/tellurium compounds having suitably positioned het-
eroatoms (N, O or S) act as good acceptors. Although McWhin-
nie and coworkers have synthesized a series of azobenzene
derivatives of tellurium,11 there are no reports for the synthe-
sis of the selenium derivatives of azobenzene. The selenium
derivatives of methyl substituted azobenzene such as 1,2-di-p-
tolyldiazeneselenenyl chloride, bis(1,2-di-p-tolyldiazene)selenide,
bis(1,2-di-p-tolyldiazene)diselenide, (1,2-di-p-tolyldiazene)phenyl
selenide and palladium complex of (1,2-di-p-tolyldiazene)phenyl
selenide have been reported by Jones and Ram´ırez de Arellano.12
In this paper we report the synthesis, structure and the effect of the
strength of the Se ◊ ◊ ◊ N interaction on the fluorescence property of
the selenium derivatives of 2-phenylazophenyl.
aDepartment of Chemistry, Indian Institute of Technology Bombay, Powai,
Mumbai 400076, (India). E-mail: chhbsia@chem.iitb.ac.in; Fax: (+ 91)22-
2572-3480; Tel: 022-2576 7190
bDepartment of Chemistry, Howard University, Washington, D.C, 20059,
USA
† Electronic supplementary information (ESI) available: Important spec-
troscopic data for all the compounds, optimized geometry along with
coordinates, computational details. CCDC reference numbers 777091–
777095. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c0dt01319f
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 4489–4496 | 4489
©

View Article Online
Table 1 Comparison of experimental 77Se NMR with computed data for
6–12
Results and discussion
Synthesis of the compounds
Entry
77Se(expt) (ppm)
77Se(cal)a (ppm)
Lithiation of 2-iodoazobenzene (5) at -114 ◦C in ether
followed by the treatment of resulting (2-phenylazophenyl-
C,N¢)lithium with SeCl2 yielded the desired product bis(2-
phenylazophenyl-C,N¢)selenide (6) in 19% yield along with
(2-phenylazophenyl-C,N¢)selenenyl(II) chloride (7) and (2-
phenylazophenyl-C,N¢)selenenyl(II) iodide (8) in 14% and 8%
yield respectively (Scheme 1). The formation of 7 is probably
due to the partial substitution of the chloro group in SeCl2.
The exchange reaction between 7 and in situ generated LiI
may result in the formation of the iodide derivative 8. Com-
pounds 6–8 were separated by column chromatography and were
crystallized from chloroform–hexane (6), ethylacetate/hexane
(7) and acetone/hexane (8). All the three isolated compounds
were found to be stable in the solid state as well as in so-
lution. (2-Phenylazophenyl-C,N¢)selenenyl(II) chloride (7) was
also prepared by reaction of SeCl4 with bis(2-phenylazophenyl-
C,N¢)mercuric(II) in tetrahydrofuran.12b
6
384
391
1063
1150
995
840
202
450
7
1142
1074
1093
873
215
475
8
9
10
11
12
a Values are referenced with respect to Me2Se at B3LYP/6-311+G(d,p).
7 with an excess of hydrazine hydrate at room temperature gave
the desired bis(2-phenylazophenyl-C,N¢)diselenide (12) as a yellow
precipitate (Scheme 2).
Compounds 6–12 were characterized by FT-IR, H, 13C, 77Se
1
NMR spectroscopy, ES-MS and elemental analysis. ES-MS
spectra of compounds 7, 8, 9, 11 and 12 did not show the molecular
ion peak, however, the highest peak at m/z 261 corresponding to
[C12H9N2Se]+ was observed. For compound 6 and 10 molecular
ion peaks were observed at 443 [M + 1H]+ and 459 [M + 1H]+
respectively. The 77Se NMR chemical shift of the synthesized
derivatives is given in Table 1. The 77Se NMR signal for 6 appeared
at 384 ppm. The signal for the chloro derivative 7 appeared at 1142
ppm, whereas for the bromo derivative 9 and iodo derivative 8, the
signals appeared at 1093 and 1074 ppm respectively. The upfield
shift in 77Se NMR chemical shift for compound 9 or 8 as compared
to 7 can be related to their differences in electronegativity as well as
to the strength of Se ◊ ◊ ◊ N interaction (vide infra). The 77Se NMR
signal for 10 appeared at 873 ppm. The upfield shifting of 77Se
NMR signal for the reduced derivative 11 compared to 6 could
be due to weak Se ◊ ◊ ◊ N interaction in the former. The 77Se NMR
spectrum for 12 showed the presence of a signal at 475 ppm.
Scheme 1 Synthesis of 6, 7, 8 and 9.
The treatment of (2-phenylazophenyl-C,N¢)lithium with SeBr4
gave a dark brown solid and a red liquid (Scheme 1). The
solid when dissolved in acetone/hexane mixture resulted in the
isolation of red crystals of (2-phenylazophenyl-C,N¢)selenenyl(II)
bromide (9). Decomposition of the deep red liquid during column
chromatography made its purification difficult. The oxidation of
bis(2-phenylazophenyl-C,N¢)selenide (6) by m-CPBA at -78 ◦C
gave bis(2-phenylazophenyl-C,N¢)selenoxide (10), whereas, its
reduction with LiAlH4 under refluxing condition gave partly
reduced bis(2-phenylhydrazophenyl-C,N¢)selenide (11) (Scheme
2). The reduced derivative 11 was found to be unstable at room
temperature if kept for a few hours. Inspite of its unstable nature,
we were successful in characterization of 11 by all spectroscopic
techniques. Suitable crystals of 11 for structure determination
could not be obtained. Treatment of the ethanolic solution of
Description of the structures
Molecular geometry of 6 is shown in Fig. 1. Selected bond lengths
and bond angles are given in Table 2. The geometry around
selenium atom in 6 is T-shaped. The azobenzene rings are twisted
with respect to each other at an angle of 66.58◦. The intramolecular
˚
N2B ◊ ◊ ◊ Se distance is 2.621(5) A with the N2B ◊ ◊ ◊ Se–C1A angle of
about 168.06(17)◦ and indicates a good overlap between the donor
(N2B) and the acceptor (Se–C1A). The distance is fairly shorter
than the sum of the van der Waals radii of selenium (1.90 A) and
nitrogen (1.55 A).13 The C1A–Se–C1B angle is about 99.2(2) . Due
to the presence of the intramolecular Se ◊ ◊ ◊ N interaction, the trans
Se–C1A bond length (1.953(5) A) is slightly longer than Se–C1B
˚
◦
˚
˚
˚
˚
(1.918(5) A), yet these are in close agreement to the value of 1.93 A
for Se–C bond as suggested by Pauling.14 Although, the distance
˚
between Se and N1A (3.070(4) A) is also less than sum of the van
der Waals radii of selenium and nitrogen, DFT calculations did
not show any interaction between them (vide infra).
An ORTEP view of 7 is shown in the Fig. 2, and selected
bond lengths and bond angles are listed in Table 2. Compound
7 crystallizes with two molecules in the asymmetric unit. The
geometry around selenium is T-shaped and is close to the previ-
ously reported 1,2-di-p-tolyldiazeneselenenyl chloride and other
derivatives.9e,12a,15 The intramolecular N2A ◊ ◊ ◊ Se1 (1.965(5) A)
˚
Scheme 2 Synthesis of 10, 11 and 12.
4490 | Dalton Trans., 2011, 40, 4489–4496
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
◦
˚
Table 2 Important bond length (A) and bond angle ( ) for 6–10
Entry
6
7 X = Cl1
8 X = I
9 X = Br
10 X = O
Se–C
Se ◊ ◊ ◊ N
Se–X
C–Se–C/X
N ◊ ◊ ◊ Se–C/X
1.918(5)/1.953(5)
2.621(5)
—
99.2(2)
168.06(17)
1.874(6)
1.965(5)
2.493(16)
93.3(2)
1.874(5)
2.053(5)
2.829(7)
96.95(18)
176.39(13)
1.854(2)
2.025(2)
2.665(4)
96.06(7)
174.73(6)
1.953(16)/1.953(15)
2.735(9)
1.664(12)
97.25(7)
169.26(6)
174.13(15)
Fig. 3 Molecular structure of8 with 50% probability of thermal ellipsoids.
Fig. 1 Molecular structure of6 with 50% probability of thermal ellipsoids.
Fig. 4 Molecular structure of9 with 50% probability of thermal ellipsoids.
Fig. 2 Molecular structure of7 with 50% probability of thermal ellipsoids.
Fig. 5 shows the molecular structure of the selenoxide 10
stabilized by intramolecular coordination. Selected bond lengths
and bond angles are listed in Table 2. The geometry around
selenium atom is distorted tetrahedral with N2B ◊ ◊ ◊ Se O bond
angle being 169.26(6)◦. The secondary bonding Se ◊ ◊ ◊ N2B dis-
˚
and N2B ◊ ◊ ◊ Se2 (2.002(5) A) distances in both the asymmet-
ric units of 7 are shorter than the related derivatives 1,2-
di-p-tolyldiazeneselenenyl chloride (2.025(3) A) and [2-(4,4-
dimethyl-2-oxazolinyl)phenyl]selenenyl chloride (2.052(2) A).
Nonetheless, it is comparable to [2-(2-phenyl-5,6-dihydro-4H-
1,3-oxazinyl)]selenenyl chloride (1.964(3) A). Another notable
feature of the structure is the presence of weak intermolecular in-
12a
˚
15b
˚
˚
tance 2.735(9) A, is longer than that observed in preceding
9e
˚
structures. The longer Se ◊ ◊ ◊ N distance or weaker interaction in
10 could be probably due to the higher energy difference between
˚
˚
teraction between hydrogen and chlorine H3BA ◊ ◊ ◊ Cl1 2.784(2) A
the overlapping orbitals. The Se O distance 1.664(12) A is
(C3B–H3BA ◊ ◊ ◊ Cl1; 131.01(36)◦).
considerably shorter than the sum of covalent radii for oxygen and
˚
˚
The strength of intramolecular Se ◊ ◊ ◊ N interaction depends
on several factors and one of them is a proper overlap of
donor and acceptor orbitals which in turn depends on the angle
formed between these orbitals. It can be seen from Table 2 that
the strength of intramolecular Se ◊ ◊ ◊ N interaction is higher in
selenenyl chloride 7, selenenyl bromide 9 (Fig. 4) and selenenyl
iodide 8 (Fig. 3). This is also supported by the concomitant
increase in N ◊ ◊ ◊ Se–X bond angles which are closer to linearity
than those in other derivatives.
selenium (O, 0.68 A; Se, 1.22 A) indicating a double bond character
and the value is in close agreement with that of reported struc-
˚
tures such as bis(p-methoxyphenyl)selenoxide (1.665(2) A), 4-[(-)-
menthyloxycarbonyl]phenyl 2,4,6-tri-isopropylphenyl selenoxide
˚
(1.662(7) A), 2,3-dihydro-2-isopropyl-7-(N-isopropylcarbamoyl)-
˚
1,2-benzisoselenazole-1,1,3-oxide (1.664(3) A), 1,1¢-dinaphthyl
˚
selenoxide (1.653(3) A), bis(2,4,6-trimethylphenyl)selenoxide
˚
(1.674(4) A), bis(N,N-dimethylbenzylaminephenyl)selenoxide
16
˚
(1.701(3) A) and many more. Interestingly, the structure shows
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 4489–4496 | 4491
©

View Article Online
A considerable shift was observed in the lmax for all the
selenium derivatives (6–10 and 12) as compared to azobenzene
and 5, suggesting a change in their electronic environment. This
change may arise due to the presence of different substituents on
selenium as well as difference in the secondary bonding Se ◊ ◊ ◊ N
intramolecular interaction energy (vide infra). In the case of 8, a
relatively weak absorption at lmax 297 nm due to p–p* transition
is also observed. The transitions with their respective absorption
coefficients are given in Table 3.
From Table 3 it can be seen that the halo derivatives 7, 8
and 9 possessing stronger secondary bonding Se ◊ ◊ ◊ N interaction
(63–75 kcal mol-1) show bathochromic shift in comparison to
other derivatives (6, 10 and 12), which have relatively weaker
intramolecular Se ◊ ◊ ◊ N interaction (5–18 kcal mol-1). This implies
that strong intramolecular Se ◊ ◊ ◊ N interactions may play some
role in reducing the energy gap between the orbitals involved in
transition and thereby leading to bathochromic shift in absortion
spectra.
Fig. 5 Molecular structure of 10 with 50% probability of thermal
ellipsoids.
The fluorescence studies for all compounds (azobenzene, 5–
10 and 12) were carried out at 273 K in chloroform at 2 ¥ 10-7
M concentration. When irradiated at their respective absorption
wavelengths (320–355 nm), nearly all the selenium derivatives of
2-phenylazophenyl 6–10 and 12 showed emission in the region
of 350–400 nm (Fig. 7). See Figure S4 and S5 in Supplementary
Information.† Similar to the absorption spectra, a bathochromic
shift was observed in the fluorescence spectra (Fig. 7). However,
as expected, no remarkable enhancement of intensity in the
fluorescence spectra was observed for the compounds except 6.
The quantum yield for the synthesized compounds (6–10 and
12) (Table 3) was found to be lower than that reported for
the intramolecularly B–N coordinated azobenzene derivative.8
However, some of the azobenzene selenium derivatives were found
to exhibit higher value of quantum yield in comparison to the
palladium derivative‡ (0.012).7b
the presence of a relatively strong C–H ◊ ◊ ◊ O secondary interaction
in one dimension (along a axis) with H ◊ ◊ ◊ O◦ distance being
all previously reported structure of selenoxides,16 except bis(N,N-
dimethylbenzylaminephenyl)selenoxide16e which have either poly-
meric or dimeric structure due to secondary Se ◊ ◊ ◊ O interaction,
in the case of 10 such interaction was absent and 10 exists as a
monomer.
˚
2.324(4) A and C–H ◊ ◊ ◊ O angle being 164.18(11) . In contrast to
Absorption and emission spectroscopy
The UV-visible spectra for azobenzene, (2-phenylazophenyl-
C,N¢)iodide (5) and compounds 6–10 and 12 (Fig. 6) were recorded
at 10-5 M concentration at room temperature in chloroform.
Also see Figure S1, S2 and S3 in Supplementary Information.†
The spectra show mainly two types of transitions for all the
compounds. The band lying in the range of 300–350 nm is
associated with symmetry allowed ligand based p–p* transition.
The relatively lower intensity bands lying in the region of 400–
470 nm originates due to n-p* transition.
Fig. 7 Emission spectra of compound 6–10 and 12 at 2 ¥ 10-7 M.
Fig. 6 Graphical representation of UV-vis spectra for 5–10 and 12 in
CHCl3 at 10-5 M concentration.
‡ Palladium derivative 2 in the reference 7b was synthesized and its
quantum yield was measured.
4492 | Dalton Trans., 2011, 40, 4489–4496
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Table 3 Spectroscopic data for azobenzene, 5–10 and 12 recorded in CHCl3
lmax (Abs) (nm)
p–p*
e (M-1 cm-1)
Entry
n–p*
p–p*
n–p*
lmax (Ems) (nm)
UF
Azobenzene
322
323
322
349
351, 297
355
330
440
442
404
432
472
439
450
445
42000
23000
58000
58000
40000, 40000
38000
79000
1120
580
—
—
—
—
5
6
15000
11700
8400
12200
2600
1900
358
387
372
395
358
380
0.040#
0.0091#
0.0058#
0.079#
0.042#
0.0072#
7
8
9
10
12
339
41000
#
lmax (Abs) = Wavelength of absorption, lmax (Ems) = Wavelength of emission, = quantum yield for all the compounds have been calculated by using
“anthracene” as a standard at 0-6 M in CHCl3. For “anthracene” the quantum yield in CHCl3 is 0.11.17
Table 4 Comparison of the experimentally obtained structural param-
Table 5 Pictorial representation of molecular orbital involved in UV-vis
transition for 6
˚
eters (A and deg) with that computed at B3LYP/6-31+G(d) and NBO
interaction energy at 6-311+G(d,p) level
Entry
HOMO-2
LUMO + 1
◦
a
Entry rSe ◊ ◊ ◊ N (A) qN ◊ ◊ ◊ Se–O/C/Se ( )a qSe
qN
ESe ◊ ◊ ◊ N (kcal mol-1)
˚
6
6
2.623
(2.621)
2.110
(1.965)
2.217
(2.053)
2.139
(2.025)
2.818
(2.735)
2.898
—
170.69
(168.06)
173.79
0.531 -0.232 10.77
0.690 -0.279 75.44
0.498 -0.234 62.76
0.607 -0.262 73.80
1.437 -0.220 4.91
0.393 -0.454 3.99
0.314 -0.225 18.17
7
(174.15)
176.39
8
(176.39)
175.24
9
(174.73)
168.15
(169.26)
167.01
10
11
12
Table S1†). A pictorial representation of the orbitals involved in
transition for 6 is shown in Table 5.
The peak at lmax 297 in 8 arises due to the transition between lig-
and based HOMO-4 and substituent (Se–I) based LUMO orbital
(see Supplementary Information Table S1).† These assignments
are made by comparing the observed and the computed transitions
on the basis of respective absorptivity and oscillator strength
values. The details of transitions along with the molecular orbitals
involved are given in Table 6. For n-p* transitions see Table S2 in
Supplementary Information.†
2.520
—
174.07
a Experimental values are given in parenthesis qSe charge on selenium, qN
charge on nitrogen
Computational studies
Quantification of Se ◊ ◊ ◊ N interaction in the synthesized com-
pounds. Density functional theory (DFT) calculations were
performed on all the synthesized compounds (6–12) using Gaus-
sian03 package.18 These electronic structure calculations have
been used as a tool in explaining the existing secondary bonding
intramolecular interactions. Beside other parameters, the Se ◊ ◊ ◊ N
distances obtained from these calculations were found to be in
good agreement with that observed for the crystal geometry for
compound 6–10. The second order perturbation energies were
obtained from NBO analyses19 for Se ◊ ◊ ◊ N interaction in all the
compounds. These values were found to be of the order of 3.99 kcal
mol-1 for 11 to the maximum upto 75.44 kcal mol-1 for 7. The
values are summarized in the Table 4.
Experimental section
All the reactions were carried out under strict exclusion of
oxygen and moisture. Starting material (2-phenylazophenyl-
C,N¢)mercury(II) chloride,20 2-iodoazobenzene21 was prepared
from reported literature procedure. n-BuLi, Selenium powder,
LiAlH4 were purchased from Sigma-Aldrich and SeBr4 from Alfa
Aesar. Solvents used were dried according to standard method
and were freshly distilled under N2 atmosphere prior to use.
Physical techniques
1H, and 13C NMR spectra were recorded on Varian VXR 400S
spectrometer, chemical shifts were referred by taking tetram-
ethylsilane (Me4Si) as internal standard. 77Se NMR spectra were
recorded on Varian VXR 300S spectrometer with dimethylselenide
(Me2Se) as external standard. FT-IR spectra were recorded as
KBr pellets on a Nicolet Impact 400 FTIR spectrometer. The
Electro-spray mass spectra (ES-MS) were performed in a Q-Tof
micro (YA-105) mass spectrometer. Melting points was recorded
on Veego VMP-I instrument. Elemental analyses were performed
Effect of the strength of Se ◊ ◊ ◊ N interaction on electronic
properties. Time-dependent DFT calculations performed at the
B3LYP/6-31+G(d) level of theory also support that the absorption
bands in the region of lmax 300–360 nm arise mainly due to p–p*
transition (Table 5). The orbitals involved in the UV-vis transitions
for all the compounds are mainly ligand based and transitions take
place from occupied orbitals (HOMO-2, HOMO-3 and HOMO-
4) to LUMO or LUMO + 1 (see Supplementary Information
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 4489–4496 | 4493
©

View Article Online
Table 6 Comparison of the experimental and computed absorption wavelength along with their respective oscillatory strength and percentage
contribution of molecular orbital at B3LYP/6-31+G(d)
Excitation Wavelength
Entry
MO
LUMO
lmax (exp)
322
lmax (cal)
Oscillatory Strength (f )
6
7
HOMO-2 (37%)
HOMO-3 (64%)
HOMO-2 (47%)
HOMO-3 (68%)
HOMO-4 (73%)
HOMO-4 (57%)
HOMO-2 (54%)
HOMO-2 (53%)
HOMO-4 (46%)
LUMO + 1
LUMO
336 &
333
331 &
342
349
352 &
365
0.2767
0.4822
0.1810
0.1824
0.4044
0.2669
0.1968
0.0804
0.6344
349
8
9
LUMO
LUMO
351
355
10
12
LUMO
LUMO
330
339
364
343
on a Carlo-Erba model 1106 elemental analyzer. The UV-vis
spectral analysis was recorded on a Jasco-570 spectrophotometer.
Fluorescence studies were carried out using a Perkin-Elmer LS55
luminescence spectrometer.
151.8, 144.6, 140.7, 135.2, 132.7, 132.6, 130.5, 130.4, 128.8, 123.1.
77Se NMR (300 MHz, CDCl3): d = 1074. ES-MS: m/z 261 [M–I]+.
FT-IR: (nN N) 1617, (nC–H) 766 cm-1. Anal. Calc. for C12H9N2ISe:
C, 37.24; H, 2.34; N, 7.24. Found: C, 37.64; H, 1.65; N, 6.90.
(2-phenylazophenyl-C,N¢)selenenyl bromide (9). To the solu-
tion of 2-iodoazobenzene (1.20 g, 3.9 mmol) in dry ether (40 mL)
was added a solution of n-BuLi (2.7 mL, 4.3 mmol) dropwise
at -114 ◦C. The reaction mixture was stirred for 0.5 h at this
temperature. To this was then added SeBr4 (1.55 g, 3.9 mmol)
and the reaction mixture was allowed to attain room temperature.
Dark brown solid started precipitating after 1 h. The stirring was
continued for further 2 h and reaction mixture was filtered off and
volume was reduced. The brown solid obtained from filtration
was dissolved in ethylacetate/acetone and kept for crystallization
to af◦ford dark black-red crystals of 9. Yield: 0.30 g, 24%. M.p 154–
156 C. 1H NMR (400 MHz, CDCl3): d = 8.97 (dd, 3J = 7.6 Hz,
4J = 1.5 Hz, 1H), 8.54 (dd, 3J = 7.3 Hz, 4J = 1.5 Hz, 1H), 8.08 (td,
Synthesis
bis(2-phenylazophenyl-C,N¢)selenide (6). To a solution of 2-
iodoazobenzene (3.00 g, 9.74 mmol) in dry ether (40-50 mL)
was added a solution of n-BuLi (6.70 mL, 10.70 mmol) dropwise
at -114 ◦C. The reaction mixture was stirred for 0.5 h at this
temperature. To the reaction mixture was then added a solution
22
of SeCl2 (Se; 0.39 g, 4.94 mmol, SO2Cl2; 0.40 mL, 4.96 mmol)
in tetrahydrofuran (10 mL) (prepared in a separate Schlenk
flask) dropwise. The temperature was maintained at -114 ◦C
during the transfer. After addition, the reaction was allowed
to attain the room temperature slowly. After stirring for 7 h
at this temperature (monitored via TLC), the reaction mixture
was filtered through celite pad and the solvent volume reduced.
The crude reaction mixture was loaded on silica gel column for
purification. The elution of column with petroleum ether gave
unreacted azobenzene and 6, further treatment with petroleum
ether/ethyl acetate (99 : 1; 98 : 2) gave 7 and 8 as yellow and black
solid respectively.
4
3J = 6.7 Hz, J = 1.5 Hz, 2H), 7.84–7.74 (m, 2H), 7.67–7.58 (m,
3H). 13C NMR (400 MHz, CDCl3): d = 151.8, 145.2, 144.8, 132.9,
132.7, 131.5, 130.5, 130.0, 129.0, 122.8. 77Se NMR (300 MHz,
CDCl3): d = 1093. ES-MS: m/z 260 [M–Br]+. FT-IR: (nN N) 1617,
(nC–H) 768 cm-1. Anal. Calc. for C12H9N2BrSe: C, 42.38; H, 2.67;
N, 8.24. Found: C, 42.38.; H, 2.29; N, 7.74.
◦
1
6 Yield: 0.40 g, 19%. M.p 102–104 C. H NMR (400 MHz,
CDCl3): d = 8.00–7.82 (m, 6 H), 7.53–7.41 (m, 8 H), 7.37 (td, 3J =
bis(2-phenylazophenyl-C,N¢)selenoxide (10). The solution of
m-chloroperbenzoic acid (0.03 g, 0.17 mmol) in dry
dichloromethane (15 mL) was cooled to -78 ◦C. To it was added
6 (0.08 g, 0.18 mmol) and the mixture was allowed to stir at this
temperature for 20 to 25 min. Then it was poured into a solution
containing saturated NaHCO3 and dichloromethane, the organic
layer was separated, washed thrice with water, dried over MgSO4
and filtered. The filtrate was concentrated to give an orange solid of
the desired compound. Light orange crystals of 10 were obtained
from acetonitrile–hexane. Yield: 0.07 g, 87%. M.p 192–194 ◦C.
7.6 Hz, 4J = 1.2 Hz, 2H), 7.27 (td, 3J = 7.9 Hz, 4J = 1.5 Hz, 2H). 13
C
NMR (400 MHz, CDCl3): d = 152.5, 152.1, 134.3, 133.0, 131.3,
131.3, 129.2, 128.0, 123.3, 121.1. 77Se NMR (300 MHz, CDCl3):
d = 384. ES-MS: m/z 443 [M + 1H]+, 260 [M–1H–C12H9N2]+. FT-
IR: (nN N) 1583, (nC–H) 772 cm-1. Anal. Calc. for C24H18N4Se: C,
65.31; H, 4.11; N, 12.69. Found: C, 65.20; H, 3.78; N, 12.06.
◦
1
7 Yield: 0.40 g, 14%. M.p 135–137 C. H NMR (400 MHz,
CDCl3): d = 8.98 (d, 3J = 8.2 Hz, 1H), 8.57 (d, 3J = 7.9 Hz, 1H),
8.07 (d, 3J = 7.0 Hz, 2H), 7.82–7.73 (m, 2H), 7.62 (d, 3J = 6.4 Hz,
3H). 13C NMR (400 MHz, CDCl3): d = 151.9, 147.2, 145.0, 132.9,
132.6, 130.5, 129.8, 129.7, 128.9, 122.6. 77Se NMR (300 MHz,
3
4
1H NMR (400 MHz, CDCl3): d = 8.02 (dd, J = 7.6 Hz, J =
3
4
2.1 Hz, 2H), 7.93 (dd, J = 7.0 Hz, J = 2.1 Hz, 2H), 7.85 (dd,
CDCl3): d = 1142. ES-MS: m/z 231 [M–Cl–N2]+. FT-IR: (nN
)
3J = 7.3 Hz, J = 1.2 Hz, 4H), 7.64–7.57 (m, 4H), 7.44–7.40 (m,
4
N
1617, (nC–H) 766 cm-1. Anal. Calc. for C12H9N2ClSe: C, 48.75; H,
3.07; N, 9.48. Found: C, 48.22; H, 2.60; N, 8.31.
2H), 7.31 (t, 3J = 7.9 Hz, 4H). 13C NMR (400 MHz, CDCl3): d =
151.8, 149.8, 141.7, 132.7, 132.2, 131.9, 129.3, 128.2, 123.5, 122.3.
77Se NMR (300 MHz, CDCl3): d = 873. ES-MS: m/z 459 [M +
1H]+. FT-IR: (nN N) 1617, (nSe–O) 815, (nC–H) 773 cm-1. Anal. Calc.
for C24H18N4OSe: C, 63.02; H, 3.97; N, 12.25. Found: C, 63.42; H,
3.72; N, 11.53.
8 Yield: 0.20 g, 8%. M.p 90–92 ◦C. 1H NMR (400 MHz, CDCl3):
d = 8.75 (dd, 3J = 6.1 Hz, 4J = 3.6 Hz, 1H), 8.44 (dd, 3J = 6.1 Hz, 4J =
3.6 Hz, 1H), 8.06 (d, 3J = 7.4 Hz, 2H), 7.75 (dd, 3J = 6.1 Hz, 4J =
3.6 Hz, 2H), 7.69–7.57 (m, 3H). 13C NMR (400 MHz, CDCl3): d =
4494 | Dalton Trans., 2011, 40, 4489–4496
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Table 7 Crystal data and structural refinement parameter for 6, 7, 8, 9, and 10
Compound reference
6
7
8
9
10
Chemical formula
Formula Mass
Crystal system
C24H18N4Se
441.38
Monoclinic
6.6012(2)
14.1846(5)
21.3931(6)
90.00
91.785(3)
90.00
2002.18(11)
200(2)
P121/n1
4
Mo-Ka
1.893
20121
6503
0.0583
0.0817
C12H9ClN2Se
295.62
Orthorhombic
21.7803(5)
7.4278(2)
28.0087(8)
90.00
90.00
90.00
4531.2(2)
200(2)
Pbca
16
Mo-Ka
3.521
127615
7919
0.1338
0.0639
0.1548
C12H9IN2Se
387.07
Monoclinic
4.7893(2)
18.4538(10)
13.7159(9)
90.00
91.237(6)
90.00
1211.94(11)
200(2)
P121/n1
4
Mo-Ka
5.618
10827
3995
0.0498
0.0509
C12H9BrN2Se
340.08
Monoclinic
5.0040(3)
15.4165(8)
15.0856(5)
90.00
90.843(3)
90.00
1163.64(10)
200(2)
P121/n1
4
Mo-Ka
6.632
9770
3831
0.0433
0.0327
C24H18N4OSe
457.38
Triclinic
˚
a/A
7.6202(3)
10.8698(7)
14.2205(11)
109.327(7)
91.414(5)
109.014(5)
1039.21(11)
200(2)
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
Unit cell volume/A
T/K
Space group
¯
P1
No. of formula units per unit cell, Z
2
Radiation type
Mo-Ka
1.830
15375
6806
0.0335
0.0315
0.0592
0.0568
0.0648
0.936
Absorption coefficient, m/mm-1
No. of reflections measured
No. of independent reflections
Rint
Final R1 values (I > 2s(I))
Final wR(F2) values (I > 2s(I))
Final R1 values (all data)
Final wR(F2) values (all data)
Goodness of fit on F2
0.1888
0.1317
0.2109
1.112
0.1101
0.1091
0.1210
0.868
0.0526
0.0820
0.0571
0.840
0.1585
0.2254
1.094
bis(2-phenylhydrazophenyl-C,N¢)selenide (11). To the solution
of 6 (0.46 g, 1.04 mmol) in tetrahydrofuran (15 mL) at 0 ◦C was
added LiAlH4 (0.04 g, 1.04 mmol) portion wise. The mixture was
allowed to come to the room temperature slowly. The colour of
reaction mixture changed from deep red to light orange and finally
to light yellow. Reaction was stopped after 3.5 h (monitored via
TLC), usual work up procedure was followed. The crude product
so obtained was treated with hexane to get 11 as off-white solid.
Yield: 0.12 g, 26%. M.p. ~50 ◦C. 1H NMR (400 MHz, CDCl3): d =
7.50 (dd, 3J = 7.6 Hz, 4J = 1.5 Hz, 1H), 7.19 (t, 3J = 7.0 Hz, 1H),
7.10 (t, 3J = 7.6 Hz, 2H), 7.01 (dd, 3J = 8.1 Hz, 4J = 1.2 Hz, 1H),
6.81–6.73 (m, 2H), 6.63 (d, 3J = 7.6 Hz, 2H), 6.43 (s, 2H), 5.60 (s,
129.5, 129.1, 127.3, 126.9, 123.1. 77Se NMR (300 MHz, CDCl3):
d = 475. ES-MS: m/z 261 [M–C12H9N2Se]+. FT-IR: (nN N) 1617,
(nC–H) 774 cm-1. Anal. Calc. For C24H18N4Se2: C, 55.40; H, 3.49;
N, 10.77. Found: C, 54.72; H, 3.69; N, 9.77.
Crystal structure determination
X-ray diffraction data (Table 7) were obtained on Oxford
Diffraction Gemini diffractometer using Mo-Ka radiation (l =
˚
0.71073 A). The structure solution was achieved by using direct
methods as implemented in SHELXS-97.23 The structure was
refined by full least-squares methods using SHELXL-97.24
1
2H). H NMR (400 MHz, CDCl3, D2O exchange): d = 7.50 (dd,
4
3
3J = 7.6 Hz, J = 1.5 Hz, 1H), 7.19 (t, J = 7.0 Hz, 1H), 7.10 (t,
3J = 7.6 Hz, 2H), 7.01 (dd, 3J = 8.1 Hz, 4J = 1.2 Hz, 1H), 6.81–6.73
(m, 2H), 6.63 (d, 3J = 7.6 Hz, 2H). 13C NMR (400 MHz, CDCl3):
d = 148.8, 148.4, 136.0, 130.4, 129.5, 120.4, 120.3, 112.7, 112.5.
77Se NMR (300 MHz, CDCl3): d = 215. ES-MS: m/z 261 [M–2H–
C12H11N2]+. FT-IR: (nN–H) 3328, (nC–H) 747 cm-1. Anal. Calc. for
C24H22N4Se: C, 64.72; H, 4.98; N, 12.58. Found: C, 65.18; H, 4.94;
N, 11.78.
Conclusions
In conclusion, we have successfully synthesized and characterized
a series of ortho-selenenylated azobenzene derivatives including
the first partly reduced derivative bis(2-phenylhydrazophenyl-
C,N¢)selenide (11). It was observed that the secondary bonding
Se ◊ ◊ ◊ N interaction gives rise to fluorescence, however, their
strength cannot be directly correlated with the intensity of the
fluorescence.
bis(2-phenylazophenyl-C,N¢)diselenide (12). To the suspension
of 6 (0.10 g, 0.34 mmol) in absolute ethanol (20 mL), was added
dropwise an ethanolic solution (3 mL) of hydrazine hydrate
(0.13 mL, 2.47 mmol) at room temperature. As the addition
proceeded, the color of the reaction mixture changed from yellow
to red. After the addition was complete, the reaction mixture was
allowed to stir for 3 h at room temperature and a suspension
formed. The reaction mixture was then cooled to 0 ◦C and filtered.
The precipitate so◦obtained was dried under vacuum. Yield: 0.04 g,
44%. M.p. 90–92 C. 1H NMR (400 MHz, CDCl3): d = 8.06–8.03
Acknowledgements
This work was supported by Department of Science and Technol-
ogy (DST), New Delhi–110016 (India). K. S and T.C thank CSIR
for SRF. We gratefully acknowledged computational facilities of
IIT Bombay Computer Center.
Notes and references
1 I. Willner, S. Rubin and A. Riklin, J. Am. Chem. Soc., 1991, 113, 3321.
2 (a) Z. Sekkat and M. Dumont, Appl. Phys. B: Photophys. Laser Chem.,
1992, 54, 486; (b) Z. F. Liu, K. Hashimoto and A. Fujishima, Nature,
1990, 347, 658.
3
4
(m, 6H), 7.90 (dd, J = 7.9 Hz, J = 1.2 Hz, 2H), 7.57–7.51 (m,
6H), 7.39 (td, 3J = 7.2 Hz, 4J = 1.2 Hz, 2H), 7.29–7.25 (m, 2H). 13
NMR (400 MHz, CDCl3): d = 151.4, 151.3, 131.8, 131.6, 131.3,
C
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 4489–4496 | 4495
©

View Article Online
3 (a) P.-O. Astrand, P. S. Ramanujam, S. Hvilsted, K. L. Bak and S. P.
A. Sauer, J. Am. Chem. Soc., 2000, 122, 3482; (b) I. A. Banerjee, L. Yu
and H. Matsui, J. Am. Chem. Soc., 2003, 125, 9542.
4 (a) M. Kurosawa, T. Nankawa, T. Matsuda, K. Kubo, M. Kurihara
and H. Nishihara, Inorg. Chem., 1999, 38, 5113; (b) S.-S. Sun and A. J.
Lees, J. Am. Chem. Soc., 2000, 122, 8956; (c) P. J. Mosher, G. P. A. Yap
and R. J. Crutchley, Inorg. Chem., 2001, 40, 1189.
(c) N. Al-Salim, A. A. West, W. R. McWhinnie and T. A. Hamor, J.
Chem. Soc., Dalton Trans., 1988, 2363; (d) K. Y. Abid, N. Al-Salim,
M. Greaves, W. R. McWhinnie, A. A. West and T. A. Hamor, J. Chem.
Soc., Dalton Trans., 1989, 1697.
12 (a) P. G. Jones and M. C. Ram´ırez de Arellano, Chem. Ber., 1995, 128,
741; (b) P. G. Jones and M. C. Ram´ırez de Arellano, J. Chem. Soc.,
Dalton Trans., 1996, 2713.
5 (a) H. Zollinger, Colour Chemistry. Synthesis, Properties and Appli-
cations of Organic Dyes and Pigments, VCH, Weinheim, 1987; (b) B.
13 A. Bondi, J. Phys. Chem., 1964, 68, 441.
14 L. Pauling, The Nature of the Chemical Bond, 3rd edn, Cornell
¨
Armag˘an, O. Ozdemir, M. Turan and M. S. C¸ elik, J. Chem. Technol.
University Press, Ithaca, NY, 1960.
Biotechnol., 2003, 78, 725.
15 (a) M. Iwaoka and S. Tomoda, J. Org. Chem., 1995, 60, 5299; (b) G.
Mugesh, A. Panda, H. B. Singh and R. J. Butcher, Chem.–Eur. J., 1999,
5, 1411.
16 (a) J. Beckmann and A. Duthie, Z. Anorg. Allg. Chem., 2005, 631, 1849;
(b) T. Shimizu, K. Kikuchi, Y. Ishikawa, I. Ikemoto, M. Kobayashi and
N. Kamigata, J. Chem. Soc., Perkin Trans. 1, 1989, 597; (c) G. Steinfeld
and B. Kersting, Z. Anorg. Allg. Chem., 2006, 632, 2010; (d) S. Hayashi,
H. Wada, T. Ueno and W. Nakanishi, J. Org. Chem., 2006, 71, 5574;
(e) T. M. Klapo¨tke, B. Krumm and M. Scherr, Inorg. Chem., 2008, 47,
4712.
17 P. Hrdlovic, J. Donovalova, H. Stankovicova and A. Gaplovsky,
Molecules, 2010, 15, 8915.
18 M. J. Frisch, et al. Gaussian 03, revision C.02, Gaussian Inc., Walling-
ford CT, 2004.
6 (a) H. Rau and E. Lu¨ddecke, J. Am. Chem. Soc., 1982, 104, 1616; (b) N.
Biswas and S. Umapathy, Chem. Phys. Lett., 1995, 236, 24; (c) N. Tamai
and H. Miyasaka, Chem. Rev., 2000, 100, 1875.
7 (a) Y. Wakatsuki, H. Yamazaki, P. A. Grutsch, M. Santhanam and C.
Kutal, J. Am. Chem. Soc., 1985, 107, 8153; (b) M. Ghedini, D. Pucci,
G. Calogero and F. Barigelletti, Chem. Phys. Lett., 1997, 267, 341; (c) I.
Aiello, M. Ghedini and M. La Deda, J. Lumin., 2002, 96, 249.
8 J. Yoshino, N. Kano and T. Kawashima, Chem. Commun., 2007, 559.
9 (a) N. Sudha and H. B. Singh, Coord. Chem. Rev., 1994, 135–136,
469; (b) A. Panda, G. Mugesh, H. B. Singh and R. J. Butcher,
Organometallics, 1999, 18, 1986; (c) G. Mugesh and H. B. Singh, Acc.
Chem. Res., 2002, 35, 226; (d) S. S. Zade, H. B. Singh and R. J. Butcher,
Angew. Chem., Int. Ed., 2004, 43, 4513; (e) S. Kumar, K. Kandasamy,
H. B. Singh, G. Wolmersha¨user and R. J. Butcher, Organometallics,
2004, 23, 4199–4208.
10 (a) T. M. Klapo¨tke, B. Krumm and K. Polborn, J. Am. Chem. Soc., 2004,
126, 710; (b) H. Poleschner and K. Seppelt, Chem.–Eur. J., 2004, 10,
6565; (c) C. Wismach, W.-W. du Mont, P. G. Jones, L. Ernst, U. Papke,
G. Mugesh, W. Kaim, M. Wanner and K. D. Becker, Angew. Chem.,
Int. Ed., 2004, 43, 3970; (d) M. Kulcsar, A. Silvestru, C. Silvestru, J.
E. Darke, C. L. B. Macdonald, M. E. Hursthouse and M. E. Light, J.
Organomet. Chem., 2005, 690, 3217.
19 (a) A. E. Reed, L. A. Curtiss and F. Weinhold, Chem. Rev., 1988, 88,
899; (b) E. D. Glendening, A. E. Reed, J. E. Carpenter and F. Weinhold,
NBO Version 3.1.
20 P. V. Roling, J. L. Dill and M. D. Rausch, J. Organomet. Chem., 1974,
69, C33.
21 P. V. Roling, J. Org. Chem., 1975, 40, 2421.
22 A. Maaninen, T. Chivers, M. Parvez, J. Pietikainen and R. S. Laitinen,
Inorg. Chem., 1999, 38, 4093.
23 G. M. Sheldrick, SHELXS-97, Program for the Solution of Crystal
Structures, University of Go¨ttingen, Go¨ttingen (Germany), 1997.
24 G. M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Go¨ttingen (Germany), 1997.
11 (a) R. E. Cobbledick, F. W. E. Einstein, W. R. McWhinnie and F. H.
Musa, J. Chem. Res. (S), 1979, 145; (b) T. A. Hamor, N. Al-Salim, A.
A. West and W. R. McWhinnie, J. Organomet. Chem., 1986, 310, C5;
4496 | Dalton Trans., 2011, 40, 4489–4496
This journal is
The Royal Society of Chemistry 2011
©