Synthesis, characterization, photoluminescence and computational studies of mono- and diorgano-gallium complexes containing azo linked salicylaldimine Schiff bases

Article abstract of DOI:10.1016/j.jorganchem.2014.10.024

The reactions of triorgano-gallium etherate with azo linked salicylaldimine Schiff bases in benzene gave complexes of the type [R₂GaOC₆H₃(NNPh) (CHNAr)], [R₂GaOC₆H₃(NNPh) (CHNCH₂

Full text of DOI:10.1016/j.jorganchem.2014.10.024

Journal of Organometallic Chemistry 776 (2015) 98e106
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization, photoluminescence and computational
studies of mono- and diorgano-gallium complexes containing azo
linked salicylaldimine Schiff bases
Manoj K. Pal a, Nisha Kushwah a, Amey P. Wadawale a, Debashree Manna b, V. Sudarsan a,
,
*
Tapan K. Ghanty b, Vimal K. Jain a
a Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
b Theoretical Chemistry Section, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of triorgano-gallium etherate with azo linked salicylaldimine Schiff bases in benzene gave
complexes of the type [R2GaOC6H3(N]NPh) (CH]NAr)], [R2GaOC6H3(N]NPh) (CH]NCH2e)]2,
[{R2GaOC6H3(N]NPh) (CH]NCH2CH2}3N] and [C6H5eN]NeC6H3(40-OGaRO)-30-CH]NeC6H4] (R ¼ Me
or Et; Ar ¼ Ph or tol-4). These complexes have been characterized by elemental analysis, IR, UVeVis, NMR
(1H and 13C{1H}) spectroscopy. The molecular structures of [Me2GaOC6H3(N]NPh)CH]NPh]$½C6H6
(5a$½C6H6) and [Me2GaOC6H3(N]NPh) (CH]Ntol-4)] (5c) were established by X-ray crystallography.
Density functional calculations have also been performed to obtain structure and energetic information
for the bare ligands and the metal-ligand complexes. Photoluminescence studies of these complexes
showed that the quantum yield is always higher than that of the corresponding ligands and the emission
peaks of complexes are blue shifted with respect to ligand.
Received 23 June 2014
Received in revised form
10 October 2014
Accepted 16 October 2014
Available online 6 November 2014
Keywords:
Organogallium
Phenylazo salicyldehyde
Schiff base
© 2014 Elsevier B.V. All rights reserved.
Photoluminescence
X-ray structure
Introduction
organometallic [2e4,9,17], have been designed with reference to
their photo-physical properties. Diorganogallium complexes with
There has been an enduring interest for quite some time in
organogallium complexes derived from internally functionalized
anionic oxo-ligands [1]. These complexes exhibit a wide structural
diversity [1e3] and polymorphism [4]; find applications in catalysis
[4,5], materials science [6,7] and biomedical imaging [8] and show
interesting photo-physical properties [2e4,9].
anionic bidentate ligands capable of forming six-membered chelate
rings preferentially exist as four-coordinate monomeric species.
The hydrolytic stability of these complexes varies with the nature of
ligand, N-alkyl salicylaldimidate complexes being hydrolytically
most stable [18]. The latter complexes are photo emissive in solu-
tion [2,4].
Remarkable photo-physical properties of group 13 metal com-
plexes, in particular tris(8-hydroxyquinolate)aluminum(III) (AlQ3)
[10], have been extensively exploited in organic light emitting di-
odes (OLEDs) display devices [11]. The low photo-luminescent
quantum yield and electron mobility of AlQ3 necessitated explo-
ration of a wide range of luminescent group 13 metal complexes
[11,12]. The higher power efficiency of GaQ3 in light emitting de-
vices than that of AlQ3 [13] suggests that the gallium complexes
may be better luminescent material for display applications.
Accordingly gallium complexes, both classical [14e16] and
There are numerous photochromic anionic ligands, in particular
compounds with azo chromophore (eN]Ne) are of considerable
interest. Besides their classical applications in synthetic azo dyes and
pigments [19], pharmaceuticals [20], their use in photo-responsive
biomaterials is emerging [21]. Photochromism of azobenzene
chromophores on light irradiation is well documented [22,23]. The
5-phenylazo salicylidene imines represent an interesting family of
photochromic molecules [24,25] and have been utilized to prepare
metal complexes [26] and several of them exhibit photo-
luminescence in solution. With this perspective we have synthe-
sized a series of mono- and diorgano-gallium complexes derived
from 5-phenylazo salicylidene imine ligands (1e4) and character-
ized them by spectroscopic methods, and studied their photo-
physical properties. Results of this work are reported herein.
* Corresponding author. Tel.: þ91 22 2559 5095; fax: þ91 22 2550 5151.
E-mail address: jainvk@barc.gov.in (V.K. Jain).
http://dx.doi.org/10.1016/j.jorganchem.2014.10.024
0022-328X/© 2014 Elsevier B.V. All rights reserved.

M.K. Pal et al. / Journal of Organometallic Chemistry 776 (2015) 98e106
99
Results and discussion
temperature afforded dialkyl or monoalkyl gallium complexes
(Scheme 1) as yellow to orange-red solids or paste.
Synthesis and characterization of complexes
The IR spectra of these complexes displayed absorptions in the
regions 557e591 and 515e536 cmꢀ1, which were absent in the
corresponding free ligands. These absorptions have been assigned
to GaeC and GaeO, respectively based on IR spectral data for
similar compounds [2,4,27] and [Me2Ga(OH)]4 [28]. The absorption
due to azomethine linkage (eCH]Ne) are slightly shifted to lower
wave numbers with respect to the free ligand on coordination of
Reactions of [5-(phenylazo)-N-(aniline)salicylidene] (1a), [5-
(phenylazo)-N-(p-toluidine)salicylidene] (1b), bis(5-phenylazo sal-
icyldehyde)ethylenediimine (2), tris{(5-phenylazo salicyldehyde)
amino ethyl}amine (3) and [5-(phenylazo)-N-(2-hydroxyphenyl)
salicylidene] (4), with trialkyl gallium etherate in benzene at room
Scheme 1. Synthesis of organogallium complexes.

100
M.K. Pal et al. / Journal of Organometallic Chemistry 776 (2015) 98e106
nitrogen atom to gallium. The stretchings due to azo functional
group (N]N) are also shifted to lower wave numbers (13e23 cmꢀ1
(5c) were established by single crystal X-ray diffraction analyses.
Perspective drawings are depicted in Figs. 1 and 2, while their
selected interatomic parameters are given in Table 1. Both the
complexes are discrete monomers with four coordinated gallium.
The metal atom in each complex is coordinated to two methyl
carbon atoms, phenolate oxygen and azomethine nitrogen forming
)
on coordination with ligand (in gallium complexes
1468e1483 cmꢀ1 and for free ligands 1487e1499 cmꢀ1).
The 1H and 13C NMR spectra, recorded in dmso-d6, displayed
characteristic peaks with expected multiplicities for metal alkyl and
ligand fragment. The dimethylgallium complexes showed a charac-
a
distorted
tetrahedral
structure.
The
six-membered
teristic high-field singlet due to methyl group at
d
~ ꢀ0.30 and ꢀ5.3
O1eC3eC2eC2eN1eGa1 chelate rings are almost but not
completely planar with gallium atom and slightly above the mean
plane (0.011 Å for 5a and 0.162 Å for 5c). The inter-planar angle
between the O1eC3eC2eC2eN1eGa1 mean plane and the
C14eC15eC16eC17eCe18eC19 mean plane is 88.9ꢁ for 5a and
76.7ꢁ 5c (Figs. 1b and 2b). The phenylazo salicylidene fragment is
slightly twisted along the N]N with a torsion angle 179.6 (4) and
179.6 (7)ꢁ in 5a and 5c respectively. The fragment
O1eC3eC2eC2eN1 is coplanar with the adjoining phenyl ring of
phenylazo salicylidene group. The GaeC [4,29], GaeO [4,6,30,31]
and GaeN [2,4,30,31] distances are in conformity with the values
reported in the literature such as [Me2GaOC6H4CH]NCH2e]2,
to ꢀ6.2 ppm in the 1H and 13C NMR spectra, respectively. The methyl
resonance for mono methylgallium complex (8a) is further shielded.
The 13C NMR resonances due to eCH]Ne in diorgano gallium
complexes is deshielded by 5.7e7.2 ppm from the respective reso-
nance for the free ligand, while for mono-organo gallium complexes
(8a, 8b) the signal is shielded by 2.6 ppm from 4. The proton reso-
nances of eCH]Ne group, however, showed a different pattern. The
signal is shielded for complexes derived from 1a and 1b, while there
is deshielding for complexes formed from 2 and 3, whereas the
resonance is little influenced for the complexes formed by 4. The 13
C
NMR resonances assignable to C-2, C-3 and C-40 are deshielded with
respect to the corresponding resonances for the free ligand.
Organogallium complexes derived from salicylidene based li-
gands are known to exist as discrete monomeric molecules [2,4,18].
The spectroscopic data for structurally characterized complexes (5a
and 5c, see later) are similar to the data for other complexes indi-
cating that various complexes have formulation as shown in
Scheme 1, which is further substantiated by analytical data.
[MeGa{eO(2-C6H4)eCH]N(2-C6H4)eOe}]
and
[Me2Ga(-
O2CeC5H4N-2)]2, etc. In case of 5c intra-molecular short contacts
N2/H16eC16 (2.687 Å) between the azobenzene nitrogen and the
phenyl salicylidene lead to the formation of weakly bonded dimers
(Fig. 2c) whereas 5a is devoid of any such interactions.
The electron releasing methyl group in the para position of aryl
ring in the azomethine group is evident from Table 1. The azome-
thine linkage (C1eN1) is marginally shortened in tolyl substituted
derivate (5c) than that of the phenyl substituted complex (5a).
Consequently the Ga1eN1 bond is slightly elongated while the
Ga1eO1 bond is shortened in the case of 5c as compared to the
corresponding values in 5a. The C20eGa1eN1 angle is marginally
Crystal structures of 5a and 5c
The molecular structures of [Me2GaOC6H3(N]NPh)CH]
NPh]$½C6H6 (5a$½C6H6) and [Me2GaOC6H3(N]NPh)CH]Ntol-4]
Fig. 1. (a) ORTEP drawing of [Me2GaOC6H3(N]NPh) (CH]NPh)]$½C6H6 (5a$½C6H6) with 25% thermal ellipsoid probability. Hydrogen atoms are omitted for clarity (b) Twist along
the N]N in [Me2GaOC6H3(N]NPh) (CH]NPh)]$½C6H6 (5a$½C6H6) with torsion angle 179.6 (4)ꢁ.

M.K. Pal et al. / Journal of Organometallic Chemistry 776 (2015) 98e106
101
Fig. 2. (a) ORTEP drawing of [Me2GaOC6H3(N]NPh) (CH]Ntol-4)] (5c) with 25% thermal ellipsoid probability. Hydrogen atoms are omitted for clarity; (b) Twist along the N]N in
[Me2GaOC6H3(N]NPh) (CH]Ntol-4)] (5c) with torsion angle 179.6 (7)ꢁ; (c) Dimers of [Me2GaOC6H3(N]NPh) (CH]Ntol-4)] (5c) formed due to NeCH short interactions.
compressed in 5c than 5a, while converse is noted in
C20eGa1eC21 angle.
The nep* transitions for these groups, being symmetry forbidden,
could not be detected. The organo-gallium complexes, in general,
exhibited three absorption maxima which are red shifted from the
values for the corresponding free ligand. The low energy shoulder
Photo-physical properties
~430 nm is arising due to the nep* transitions. Appearance of this
Electronic absorption and emission spectra of the ligands and
their organogallium complexes were recorded in dichloromethane
and the resulting data are summarized in Table 2. The electronic
spectra of free ligands displayed two broad peaks at ~275 nm and in
the region 334e361 nm, the latter being more intense. The weak
absorption in the complexes is indicative of less symmetric envi-
ronment of the ligand moiety in the complexes. The red shift of the
pep* transitions in the complexes can be attributed to the increase
in electron density in the ligand moiety brought about by the
combined effect of the removal of proton present in the OH group of
the salicylidene ligand accompanied by coordination with the
gallium atom [3].
When a dichloromethane solution of 5c was exposed to UV-
radiation, there was a gradual change in the absorption spectrum
with increase in the time duration of irradiation (Fig. 3). The initial
absorption at 367 and 431(sh) nm are blue-(~344 nm) and red-
absorption at ~275 nm is attributed to
omatic ring [26f]. Alternatively this can also arise from the cis form
of the ligand [32]. Since the * transitions of imine linkage and
pep* transitions in the ar-
p
ep
the azo group appear in a close proximity, the two may overlap in
each other. Thus the broad absorption in the region 334e361 nm
may be assigned to
pep* transitions in CH]N and N]N groups.

102
M.K. Pal et al. / Journal of Organometallic Chemistry 776 (2015) 98e106
Table 1
excitation peaks (Stokes shift) for the ligands are in the range of
135e151 nm. Such a large value of Stokes shift indicates that the
excited state of the ligands undergo significant changes with ab-
sorption of UV light. It is worth noting that many of the salicylidene
aniline based ligands undergo intra-molecular proton transfer re-
action in the excited state and is characterized by large Stokes Shift
[33e35]. Higher values of the Stokes shift observed in the present
study indeed confirm the occurrence of excited state intra-
molecular proton transfer (ESIPT) in these ligands. The electron
donating substituents on the phenyl ring attached to the azome-
thine group in the ligands increase the electron density in the
ligand and hence favors the excited state proton transfer reaction
thereby stabilizing the keto group. This leads to marginal changes
in the emission peak maxima. Once the ligand undergoes
complexation with the metal, the excited state proton transfer
phenomenon does not occur and this is reflected in the low values
of Stokes shift observed from the complexes. A similar trend is also
observed in our earlier studies [3] involving gallium complexes.
Unlike the spectra of free ligands, the emission spectra from the
complexes showed asymmetric peak centered ~400 nm and are
blue shifted with respect to the free ligand. The blue-shift in the
emission spectra is due to the absence of ESIPT in the gallium
complexes [3]. Quantum yield values are always higher for the
complexes compared to the ligands (Table 2). This could be due to
reduced extent of non-radiative processes in the absence of ESIPT.
The ligands 2 and 3 and their complexes (6a, 6b, 7a and 7b) are
non-emissive in solution at room temperature. The emission from
such ligands and their complexes appear to be significantly
quenched by non-radiative processes occurring in the excited
Selected bond lengths (Å) and angles (ꢁ) for [Me2GaOC6H3(N]NPh)CH]
NPh]$½$C6H6 (5a$½$C6H6) and [Me2GaOC6H3(N]NPh)CH]Ntol-4] (5c).
(5a$½C6H6)
(5c)
Ga1eC20
Ga1eC21
Ga1eO1
Ga1eN1
C1eN1
N2eN3
C6eN2
C8eN3
1.950 (5)
1.949 (5)
1.908 (3)
2.029 (4)
1.286 (6)
1.248 (5)
1.414 (6)
1.427 (6)
1.927 (9)
1.965 (10)
1.865 (7)
2.037 (7)
1.273 (10)
1.247 (9)
1.420 (11)
1.408 (12)
C20eGa1eC21
C20eGa1eN1
C21eGa1eN1
C20eGa1eO1
C21eGa1eO1
O1eGa1eN1
C1eN1eGa1
C14eN1eGa1
C3eO1eGa1
C6eN2eN3
125.7 (2)
108.1 (2)
107.17 (19)
109.8 (2)
108.4 (2)
92.50 (14)
123.6 (3)
117.0 (3)
129.5 (3)
114.5 (4)
114.9 (4)
119.4 (4)
127.5 (5)
105.0 (4)
108.4 (4)
110.8 (4)
107.2 (4)
92.1 (3)
124.3 (7)
116.1 (6)
129.3 (6)
115.2 (8)
114.4 (8)
119.5 (8)
N2eN3eC8
C1eN1eC14
(~436 nm) shifted and initial color change was also noted (yellow to
yellow orange). Such blue and red shift in the absorption peak
maxima have been reported on conversion of the trans isomer to cis
form of azobenzene based systems [32]. On refluxing this solution
(40 ꢁC), color was faded slightly with the change in absorption
maxima indicating the conversion of cis form to more stable trans
form (Fig. 3) [32]. Similar changes in the absorption spectra of the
free ligand were also observed (Supplementary information),
However, these changes were rather small relative to the
complexes.
Emission spectra of the ligands and their complexes were
recorded in dichloromethane and the resulting data are summa-
rized in Table 2. Emission spectra of ligands 1a, 1b and 4 are char-
acterized by a broad peak centered at ~460 nm with a shoulder in
the higher energy region (~400 nm) (Fig. 4). Corresponding exci-
tation spectra (monitored at the emission maxima) also showed an
asymmetric line shape with a shoulder towards higher energy
states (p* or s*) of the molecules. These non-radiative processes
normally depend on the nature of the existing inter- and intra-
molecular interactions in such molecules in a particular medium.
Alternatively the non-rigidity of 2 and 3 and their complexes may
be contributing to their non-emissive nature. An increase in rigidity
often results in decrease in non-radiative decay leading to
enhanced fluorescence.
Theoretical studies
The optimized structures of bare salicylaldimine Schiff base (1b)
and its diorganogallium complex (5c) in trans and cis forms are
depicted in Figs. 5 and 6, respectively. As has been shown experi-
mentally above the trans form of free ligands as well as the com-
plexes are more stable as compared to the corresponding cis form.
This is also substantiated theoretically. The calculated metal ligand
bond lengths (Table 3) are longer for the cis form than that for the
values. The two peaks can be attributed to the
taking place with the trans and cis forms of the ligand molecules
respectively. The weak peak at the lower energy of the excitation
peak originates from the forbidden n /
pep* transition
p* transition. The differ-
ence in the wavelength maximum corresponding to emission and
Table 2
UVevis absorption, excitation and emission data of ligands and their organo gallium complexes in dichloromethane.
Compounds
UVeVis absorption,
l
in nm
Excitation
l
in nm
Emission
l
in nm
Stoke shift
Quantum
yield (h) in %
[PheN]NeC6H3(40eOH)e30-CH]NePh] (1a)
[PheN]NeC6H3(40eOH)e30-CH]N-tol-4)] (1b)
[{PheN]NeC6H3(40eOH)e30-CH]NeCH2}2] (2)
[{PheN]NeC6H3(40eOH)e30-CH]NeCH2CH2}3N] (3)
[PheN]NeC6H3(40eOH)e30-CH]NeC6H4(OH-200)] (4)
[Me2GaOC6H3(N]NPh) (CH]NPh)] (5a)
[Et2GaOC6H3(N]NPh) (CH]NPh)] (5b)
[Me2GaOC6H3(N]NPh) (CH]Ntol-4)](5c)
[Et2GaOC6H3(N]NPh) (CH]Ntol-4)](5d)
[Me2GaOC6H3(N]NPh) (CH]NCH2e)]2 (6a)
[Et2GaOC6H3(N]NPh) (CH]NCH2e)]2 (6b)
[{Me2GaOC6H3(N]NPh) (CH]NCH2CH2}3N] (7a)
[{Et2GaOC6H3(N]NPh) (CH]NCH2CH2}3N] (7b)
[C6H5eN]NeC6H3(40-OGaMeO)-30-CH]NeC6H4] (8a)
[C6H5eN]NeC6H3(40-OGaEtO)-30-CH]NeC6H4] (8b)
274, 334
271, 336
285,361
275, 346
314
318
465
460
e
151
142
3
3
e
269, 337
321
365
356
364
357
456
415
407
415
403
e
135
50
51
51
46
2
5
5
7
3
316, 364, 429(sh)
317, 370, 435(sh)
324, 366, 430(sh)
322, 370, 431(sh)
285, 361
274, 361
287, 363
282, 365
314 (sh), 369, 438
316(sh), 370, 436
e
e
e
357
351
406
408
49
57
8
9

M.K. Pal et al. / Journal of Organometallic Chemistry 776 (2015) 98e106
103
Fig. 3. UV absorption spectra of complex (5c) in dichloromethane on exposure UV radiation for different time periods followed by heating.
Fig. 4. Emission spectra for ligand (1b) and complex (5c) and the corresponding excitation spectra.
Fig. 5. Optimized structure of bare [5-(phenylazo)-N-(p-toluidine)salicylidene] (1b) a) trans and b) cis isomers.
Fig. 6. Optimized structure of a) Ga-trans isomer and b) Ga-cis isomer of 5c.

104
M.K. Pal et al. / Journal of Organometallic Chemistry 776 (2015) 98e106
Table 3
according to literature procedures [26,37,38] and were character-
ized by NMR spectroscopy (Supplementary material).
Calculated M-L bond distances (Å) for Ga complexes using def-TZVP/BP86 method.
Infrared spectra were recorded as KBr plates on a Jasco FT-IR
6100 spectrometer. The NMR (1H and 13C{1H}) spectra were
recorded on a Bruker Avance-II 300 spectrometer in 5 mm tubes as
CDCl3/dmso-d6 solutions. Chemical shifts were referenced to in-
ternal chloroform/dimethyl sulfoxide peak. Electronic spectra were
recorded in dichloromethane on a UVevis Jasco V-630 spectro-
photometer. All luminescence measurements were carried out at
room temperature on an Edinburgh Instruments FLSP 920 system,
having a 450 W Xe lamp. Quantum yields were measured using an
integrating sphere coated with BaSO4. All emission spectra were
corrected for the detector response and excitation spectra for the
lamp profile. Emission measurements were carried out with a
resolution of 5 nm.
Complex
GaeO
GaeN
GaeC
Ga-trans isomer
Ga-cis isomer
1.960
1.959
2.080
2.087
1.960
1.988
trans isomer. The calculated complexation energies (Table 4) also
suggest that the trans isomer is more stable as compared to the cis
isomer. Total energies for the free ligand and the complex also
suggest that for both the cases, trans isomers are more stable.
However, experimentally it has been found that on UV irradiation
some amount of trans isomer is converted to the corresponding cis
form and again on application of heat cis isomer reverts back to
trans isomer for both bare ligands and complexes. This is due to a
very small energy differences between the cis and trans isomers.
We have also calculated the atomic charges on the metal and donor
centers for the organo-gallium complexes with azo linked salicy-
laldimine Schiff bases. However there is not much difference in the
atomic charge values (Table 5) on the metal and donor centers for
both the isomers.
X-ray crystallography
Intensity data for [Me2GaOC6H3(N]NPh)CH]NPh]$½C6H6
(5a$½C6H6) and [Me2GaOC6H3(N]NPh) (CH]Ntol-4)] (5c) were
collected at room temperature on a Rigaku AFC 7S diffractometer
using graphite monochromated Mo-Ka radiation (0.71069 Å). The
structures were solved using direct methods [39] and refined by full
matrix least square method [40] on F2 using data corrected for
absorption effects using empirical procedures [41]. All non-
hydrogen atoms were refined anisotropically and hydrogen atoms
were placed in their geometrically idealized positions with coor-
dinate and thermal parameters riding on host atoms. The molecular
structures are drawn using ORTEP [42]. Crystallographic and
structural determination data are listed in Table 6.
Conclusion
Mono- and di-organo gallium complexes derived from azo
linked salicyladimine Schiff base have been synthesized. Mono-
nuclear complexes are emissive in solution at room temperature.
The emission peaks are blue-shifted with respect to the peak for the
corresponding free ligand, but the Stokes shifts for the free ligands
are always larger than that for the complexes. The quantum yields
of the complexes are always higher than that for the corresponding
ligands.
Theoretical calculations
Theoretical calculations were carried out (for 1b and 5c) using
density functional theory with Turbomole program package [43].
All the atoms have been treated at the all electron level and def-
Experimental
Materials and physical measurements
Table 6
All experiments involving organo-gallium compounds were
carried out in anhydrous conditions under a nitrogen atmosphere
using Schlenk techniques. Solvents were dried using standard
methods. Triorganogallium etherates (R3Ga.OEt2; R ¼ Me, Et) were
prepared using galliumemagnesium alloy (Mg5Ga2) and alkyl io-
dide in diethyl ether. Ether contents in each preparation were
evaluated by 1H NMR integration [36]. The ligands, [5-(phenylazo)-
N-(aniline)salicylidene] (1a), [5-(phenylazo)-N-(p-toluidine)sali-
cylidene] (1b), bis(5-phenylazo salicyldehyde)ethylenediimine (2),
tris{(5-phenylazo salicyldehyde)amino ethyl}amine (3) and [5-
(phenylazo)-N-(2-hydroxyphenyl)salicylidene] (4), were prepared
Crystallographic and structural refinement data for [Me2GaOC6H3(N]NPh) (CH]
NPh)]$½$C6H6 (5a$½$C6H6) and [Me2GaOC6H3(N]NPh) (CH]Ntol-4)] (5c).
Formula
C21H20GaN3O. ½$C6H6 C22H22GaN3O (5c)
(5a$½ C6H6)
M
439.17
414.15
Size (mm)
Crystal system
Space group
a/Å
b/Å
c/Å
0.20 ꢂ 0.15 ꢂ 0.05
0.25 ꢂ 0.20 ꢂ 0.10
Triclinic
Triclinic
ꢀ
P ı
ꢀ
P ı
7.176 (2)
13.198 (2)
13.218 (3)
118.850 (12)
90.03 (3)
99.63 (2)
1076.2 (4)
2
7.144 (5)
12.300 (8)
13.124 (8)
65.03 (5)
84.27 (5)
77.35 (5)
1020.1 (11)
2
ꢁ
a
b
g
/
/
ꢁ
ꢁ
/
V/Å3
Table 4
Calculated complexation energies (eV) for Ga complexes using def-TZVP/BP86
method.
Z
dcalc/g cmꢀ3
1.355
1.348
m
q
(mmꢀ1)/F(000)
for data collection/ꢁ
1.297/454
2.892e27.506
ꢀ5 ꢃ h ꢃ 9
ꢀ17 ꢃ k ꢃ 16
ꢀ17 ꢃ l ꢃ 17
4947
1.364/428
2.92e27.505
ꢀ9 ꢃ h ꢃ 5
ꢀ15 ꢃ k ꢃ 15
ꢀ17 ꢃ l ꢃ 16
4619
Complex
Complexation energies (eV)
Limiting indices
Ga-trans isomer
Ga-cis isomer
ꢀ49.12
ꢀ48.45
No. of unique reflns
No. of obsd reflns with I > 2
Data/restraints/parameters
s
(I)
2612
4947/2/264
0.0638/0.1315
1249
4619/0/247
0.0778/0.1557
Table 5
Calculated atomic charges (Natural population analysis) on metal and donor
centers of Ga complexes using def-TZVP/BP86 method.
Final R1,
(R_factor_gt/wR_factor_gt)
R1, R2 (all data)
uR2 indices
u
0.1616/0.1520
0.3418/0.2430
Complex
qGa
qO
qN
qC
(R_factor_all/wR_Factor_ref)
Ga-trans isomer
Ga-cis isomer
1.590
1.591
ꢀ0.694
ꢀ0.694
ꢀ0.535
ꢀ0.528
ꢀ1.192
ꢀ1.194
Goodness of fit on F2
0.989
0.625 and ꢀ0.714
0.904
0.409 and ꢀ0.686
Largest diff. peak and hole (e Åꢀ3
)

M.K. Pal et al. / Journal of Organometallic Chemistry 776 (2015) 98e106
105
TZVP basis sets. The calculations have been performed with the
generalized gradient approximation level of theory using Becke's
exchange functional [44] in conjunction with Perdew's correlation
functional (BP86) [45]. The metal-ligand bond lengths and
complexation energy values have been calculated for the com-
plexes. Charge distributions on the metal and donor centers have
also been calculated using the natural population analysis scheme
for the organo-gallium complexes with azo linked salicylaldimine
Schiff bases.
[Me2GaOC6H3(N]NPh) (CH]NCH2e)]2 (6a)
Prepared similar to 5a in 78% yield, mp 100 ꢁC (decomp.). Anal.
Calcd. for C32H34Ga2N6O2: C, 57.12; H, 5.08; N, 12.46%. Found: C,
57.09; H, 5.21; N, 12.42%. IR (y
in cmꢀ1): 1627 (C]N); 1474 (N]N);
588 (GaeC); 544, 533 (GaeO). 1H NMR (dmso-d6)
d: e0.29 (s,
Me2Ga); 3.92 (s, eCH2e, 4H); 6.86 (d, 3JHH ¼ 8.4 Hz, 1H); 7.48e7.54
(m, 6H); 7.78 (d, 3JHH ¼ 7.5 Hz, 4H); 7.94 (d, 3JHH ¼ 8.1 Hz, 2H); 8.01
(s, 2H), 8.71 (s, eCH]Ne, 2H). 13C{1H} NMR (dmso-d6)
d: e6.2 (s,
Me2Ga); 57.0 (eCH2), 117.8 (C-1), 122.1, 122.9, 1283, 129.4, 130.5,
133.3, 142.6, 152.0, 169.1(C-2), 172.7 (s, eCH]Ne).
Synthesis of complexes
[Et2GaOC6H3(N]NPh) (CH]NCH2e)]2 (6b)
[Me2GaOC6H3(N]NPh) (CH]NPh)] (5a)
Prepared similar to 6a in 66% yield, mp 155 ꢁC Calcd. for
To a benzene solution (25 mL) of trimethylgallium etherate
(274 mg, containing 100 mg (0.87 mmol) Me3Ga), was added a
solution of 1a (262 mg, 0.87 mmol) with stirring which continued
for 10 h. The solvent was evaporated under a reduced pressure to
give an orange-red crystalline solid, which was recrystallized from
hexane as an orange-red crystalline solid (254 mg, 73% yield), mp
133 ꢁC, Anal. Calcd. for C21H20GaNO3: C, 63.03; H, 5.04; N, 10.50%.
C36H42Ga2N6O2: C, 59.21; H, 5.80; N, 11.52%. Found: C, 59.32; H,
5.73; N, 11.16%. IR (
y
in cmꢀ1): 1621 (C]N); 1473 (N]N); 560
3
(GaeC); 532 (GaeO). 1H NMR (dmso-d6)
d
: 0.41 (q, JHH ¼ 7.9 Hz
3
eCH2Ga); 1.00 (t, JHH ¼ 7.8 Hz CH3CH2Ga); 3.92 (s, eCH2e, 4H);
6.89 (d, 3JHH ¼ 9.0 Hz, 2H); 7.46e7.57 (m, 6H); 7.79 (d, 3JHH ¼ 7.2 Hz,
4H); 7.96 (d, 3JHH ¼ 9.3 Hz, 2H); 8.01 (s, 2H); 8.80 (s, eCH]Ne, 2H).
13C{1H} NMR (dmso-d6): 3.8 (s, eCH2Ga); 10.0 (s, CH3CH2Ga); 56.4
(NCH2), 118.3 (C-1), 122.5, 123.2, 128.8, 129.2, 129.8, 130.9, 133.8,
142.8, 152.5, 170.3 (C-2), 173.6 (s, eCH]Ne).
Found: C, 62.99; H, 4.88; N, 10.27%. IR (y
in cmꢀ1): 1620 (C]N);
1474 (N]N); 590 (GaeC); 530 (GaeO). 1H NMR (dmso-d6)
d: ꢀ0.29
3
(s, Me2Ga); 6.92 (d, JHH ¼ 9.3 Hz, 1H); 7.44 -7.57 (m, 8H); 7.81(d,
3JHH ¼ 7.8 Hz, 2H); 8.01(d, d, (2.4 Hz) 3JHH ¼ 9.0 Hz, 1H); 8.27 (s, 1H);
[{Me2GaOC6H3(N]NPh) (CH]NCH2CH2}3N] (7a)
8.91 (s, eCH]Ne, 1H). 13C{1H} NMR (dmso-d6)
d
: ꢀ5.8 (s, Me2Ga);
Prepared similar to 5a in 84% yield, mp 89 ꢁC. Anal. Calcd. for
118.4 (C-1), 121.8, 122.1, 123.1, 128.1, 128.3, 129.4, 130.0, 130.5, 135.4,
142.8 (C-5), 146.3 (C-100), 152.0 (C-10), 169.2 (eCH]Ne), 169.5 (C-2).
All the di-and mono-organo gallium complexes were prepared
in a similar manner in 80e90% yield and were recyrstallized from
toluene-hexane or dichloromethane-hexane mixture in 60e85 %
yield.
C
51H57Ga3N10O3: C, 57.39; H, 5.38; N, 13.12%. Found: C, 57.41; H,
5.24; N, 12.95%.IR
in cmꢀ1): 1628 (C]N); 1474 (N]N);
587(GaeC); 532 (GaeO). 1H NMR (dmso-d6)
: e0.32 (s, Me2Ga);
(y
d
3
3
2.92 (t, JHH ¼ 7.0 Hz, eCH2e, 6H); 3.72 (t, JHH ¼ 6.8 Hz, eCH2e,
3
6H); 6.83(d, JHH ¼ 9.0 Hz, 3H); 7.47e7.55 (m, 9H); 7.77 (d,
3JHH ¼ 6.8 Hz, 6H); 7.91(d, 3JHH ¼ 9.0 Hz, 3H); 8.00 (s, 3H); 8.64 (s,
eCH]Ne, 3H). 13C{1H} NMR (dmso-d6)
d: ꢀ5.9 (s, Me2Ga); 53.7
[Et2GaOC6H3(N]NPh) (CH]NPh)] (5b)
(eCH2e), 54.7(eCH2e), 118.3 (C-1), 122.5, 123.2, 129.8, 130.9, 133.5,
143.0152.5, 169.4(C-2), 171.8 (s, eCH]Ne).
Prepared similar to 5a and dissolved in hexane. The hexane
soluble part was dried under reduced pressure to give a paste in
61% yield. IR (
y
in cmꢀ1): 1614 (C]N); 1471 (N]N); 564 (GaeC);
[{Et2GaOC6H3(N]NPh) (CH]NCH2CH2}3N] (7b)
529 (GaeO). 1H NMR (dmso-d6)
d
: 0.38 (q, 3JHH ¼ 7.8 Hz eCH2Ga);
Prepared in 84% yield, mp 70 ꢁC Calcd. for C57H69Ga3N10O3: C,
3
3
0.93 (t, JHH ¼ 7.9 Hz CH3CH2Ga); 6.93 (d, JHH ¼ 9.0 Hz, 1H);
59.46; H, 6.04; N, 12.16%. Found: C, 59.32; H, 5.73; N, 11.16%. IR (y in
3
3
7.44e7.59 (m, 8H), 7.80 (d, JHH ¼ 7.5 Hz, 2H); 7.98 (d,d JHH ¼ 2.4,
cmꢀ1): 1626 (C]N); 1473 (N]N); 560 (GaeC); 530 (GaeO). 1H
9.0 Hz, 1H); 8.25 (s, 1H), 8.98 (s, eCH]Ne, 1H). 13C{1H} NMR
NMR (dmso-d6)
d
: 0.37 (q, JHH ¼ 7.4 Hz eCH2Ga); 1.00 (t,
3
(dmso-d6)
d
: 4.4 (s, eCH2Ga); 10.0 (s, CH3CH2Ga); 118.9 (C-1), 122.0,
3JHH ¼ 6.9 Hz CH3CH2Ga); 2.95 (s, eCH2e, 6H); 3.71 (s, eCH2e, 6H);
6.86 (d, 3JHH ¼ 8.7 Hz, 3H); 7.50e7.53 (br, m, 9H); 7.76e7.79 (br, m
6H); 7.92 (d, 3JHH ¼ 8.1 Hz, 3H); 8.01 (s, 3H); 8.71 (s, eCH]Ne, 3H).
13C{1H} NMR (dmso-d6): 3.7 (s, eCH2Ga); 10.0 (s, CH3CH2Ga); 53.7
(eCH2e), 54.8 (eCH2e), 118.4 (C-1), 122.5, 123.1, 129.8, 130.8, 133.5,
142.9, 152.5, 170.2(C-2), 172.4 (s, eCH]Ne).
122.5, 123.4, 128.6, 129.0, 129.9, 130.5, 130.9, 135.9, 143.1, 146.9,
152.5, 170.0 (s, eCH]Ne), 170.7 (C-2).
[Me2GaOC6H3(N]NPh) (CH]Ntol-4)] (5c)
Prepared in 72% yield, mp 78 ꢁC. Anal. Calcd for C22H22GaN3O: C,
63.80; H, 5.35; N,10.16%. Found: C, 63.17; H, 5.02; N,10.25. %. IR (
y in
cmꢀ1): 1617 (C]N); 1473 (N]N), 591(GaeC); 536 (GaeO). 1H NMR
[C6H5eN]NeC6H3(40-OGaMeO)-30-CH]NeC6H4] (8a)
(dmso-d6)
d
: e0.30 (s, Me2Ga); 2.33 (s, eCH3, 3H); 6.90 (d,
Prepared similar to 5a in 85% yield, mp 255 ꢁC (decomp) Anal.
Calcd. for C20H16GaN3O2: C, 60.04; H, 4.03; N, 10.50%. Found: C,
3JHH ¼ 9.0 Hz, 1H); 7.32 (s, 4H); 7.47e7.56 (m, 3H); 7.80 (d,
3JHH ¼ 7.2 Hz, 2H); 7.98(d, d, (1.2 Hz) 3JHH ¼ 9.0 Hz, 1H); 8.23 (s, 1H);
60.03; H, 4.31; N, 10.44, %. IR (
y
in cmꢀ1): 1614 (C]N); 1483 (N]N),
8.86 (s, eCH]Ne, 1H). 13C{1H} NMR (dmso-d6)
d
: e5.3 (s, Me2Ga);
576(GaeC); 515 (GaeO). 1H NMR (dmso-d6)
d: ꢀ0.53 (s, MeGa);
3
3
21.0 (Me), 118.9 (C-1), 122.0, 122.5, 123.4, 128.8, 129.8, 130.8, 130.9,
135.7, 138.2, 143.2, 144.2, 152.5, 168.8 (s, eCH]Ne), 169.8(C-2).
6.60 (t, JHH ¼ 7.02 Hz, 1H); 6.70 (d, JHH ¼ 7.8 Hz, 1H); 6.87(d,
3
3JHH ¼ 9.0 Hz, 1H); 7.08 (t, JHH ¼ 7.5 Hz, 1H); 7.48e7.57 (m, 3H);
7.62 (d, 7.80 3JHH ¼ 7.8 Hz, 1H); 7.80 (d, 3JHH ¼ 7.5 Hz, 2H); 7.90 (d,
[Et2GaOC6H3(N]NPh) (CH]Ntol-4)] (5d)
3JHH ¼ 8.7 Hz, 1H); 8.13 (s, 1H); 9.11 (s, eCH]Ne, 1H). 13C{1H} NMR
Prepared in 63% yield as a paste. IR (
y
in cmꢀ1): 1616 (C]N);
(dmso-d6)
d
: ꢀ6.7 (s, MeGa); 115.7, 115.8, 117.8, 119.7 (C-1), 122.5,
1468 (N]N); 562 (GaeC); 535 (GaeO). 1H NMR (dmso-d6)
d: 0.37
123.5, 127.4, 129.8, 130.5, 130.7, 132.2, 132.3, 143.0, 152.6, 158.0 (s,
(q, 3JHH ¼ 8.0 Hz eCH2Ga); 0.93 (t, 3JHH ¼ 8.0 Hz CH3CH2Ga); 2.36 (s,
eCH]Ne), 159.2 (C-200), 170.6 (C-2).
3
eMe); 6.92 (d, JHH ¼ 9.3 Hz, 1H); 7.35 (s, 4H); 7.49e7.58 (m, 3H);
3
7.80 (d, JHH ¼ 7.2 Hz, 2H); 7.98 (d,3JHH ¼ 2.4, 9.0 Hz, 1H); 8.23 (s,
[C6H5eN]NeC6H3(40-OGaEtO)-30-CH]NeC6H4] (8b)
1H), 8.96 (s, eCH]Ne, 1H). 13C{1H} NMR (dmso-d6)
d: 4.4 (s,
Prepared similar to 5a and washed with hexane to give 86%
eCH2Ga); 10.0 (s, CH3CH2Ga); 21.0 (Me), 118.9 (C-1), 121.7, 122.5,
123.3, 128.9, 129.9, 130.9, 135.7, 138.3, 143.1, 144.5, 152.5, 169.2 (s,
eCH]Ne), 170.6 (C-2).
yield, mp 265 ꢁC (decomp.). Calcd. for C21H18GaN3O2: C, 60.91; H,
4.38; N, 10.14%. Found: C, 60.66; H, 4.25; N, 10.08%. IR (
1615 (C]N); 1473 (N]N), 557 (GaeC); 528 (GaeO). 1H NMR
y
in cmꢀ1):

106
M.K. Pal et al. / Journal of Organometallic Chemistry 776 (2015) 98e106
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(dmso-d6)
d
: 0.20 (q, 3JHH ¼ 8.0 Hz eCH2Ga); 0.81 (t, 3JHH ¼ 8.1 Hz
3
3
T.F. Zafiropoulous, P. Lianos, J. Lumin. 129 (2009) 578.
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CH3CH2Ga); 6.60 (t, JHH ¼ 7.5 Hz, 1H); 6.70 (d, JHH ¼ 8.1 Hz, 1H);
3
3
6.87 (d, JHH ¼ 9.0 Hz, 1H); 7.08 (t, JHH ¼ 7.5 Hz, 1H); 7.49 (d,
3JHH ¼ 6.7 Hz, 1H); 7.54 (t, 3JHH ¼ 7.05 Hz, 2H); 7.63 (d,
3
3JHH ¼ 7.5 Hz, 1H); 7.80 (d, JHH ¼ 7.5 Hz, 2H); 7.90 (d,3JHH ¼ 2.4,
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