Synthesis, characterization, photoluminescence, and computational studies of monoorgano-gallium and -indium complexes containing dianionic tridentate ONE (E = O or S) Schiff bases

Article abstract of DOI:10.1021/om201030d

The reactions of triorgano-gallium and -indium etherate with dianionic tridentate Schiff bases (2-hydroxy-N-salicylideneaniline (1a), 2-hydroxy-N-(2-hydroxy-3-methoxybenzylidene)aniline (1b), and 2-mercapto-N-salicylideneaniline (1c)) in benzene yielded complexes of the type [RM{O(2-C₆H₃R′-3)-CH=N(2-C₆H ₄)E}] (where R = Me, Et; M = Ga, In; R′ = H, OMe; E = O, S) in nearly quantitative yields. These complexes have been characterized by elemental analysis, IR, UV-vis, and NMR (¹H and ¹³C{¹H}) spectroscopy. The molecular structures of [MeGa(-O(2-C₆H ₄)-CH=N(2-C₆H₄)-O-)] (2a) and [MeGa(-O(2-C ₆H₃OMe-3)-CH=N(2-C₆H₄)-O-)] (2b) were established by X-ray crystallography. Photoluminescence data of these complexes showed that the quantum yield was mainly affected by the substituent/groups attached to the phenyl moiety of the ligands rather than the metal atom. Density functional theory calculations have been used to assess all the possible structures and to evaluate the complexation energies corresponding to [MeM{O(2-C₆H₄)-CH=N(2-C₆H₄)E}] (M = Ga, In; E = O, S) complexes.

Full text of DOI:10.1021/om201030d

Article
pubs.acs.org/Organometallics
Synthesis, Characterization, Photoluminescence, and Computational
Studies of Monoorgano-Gallium and -Indium Complexes Containing
Dianionic Tridentate ONE (E = O or S) Schiff Bases
Nisha Kushwah,† Manoj K. Pal,† Amey Wadawale,† V. Sudarsan,† Debashree Manna,‡
Tapan K. Ghanty,‡ and Vimal K. Jain*,†
‡
†Chemistry Division, Theoretical Chemistry Section, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
S
* Supporting Information
ABSTRACT: The reactions of triorgano-gallium and -indium
etherate with dianionic tridentate Schiff bases (2-hydroxy-N-
salicylideneaniline (1a), 2-hydroxy-N-(2-hydroxy-3-
methoxybenzylidene)aniline (1b), and 2-mercapto-N-salicyli-
deneaniline (1c)) in benzene yielded complexes of the type
[RM{O(2-C6H3R′-3)-CHN(2-C6H4)E}] (where R = Me,
Et; M = Ga, In; R′ = H, OMe; E = O, S) in nearly quantitative
yields. These complexes have been characterized by elemental analysis, IR, UV−vis, and NMR (1H and 13C{1H}) spectroscopy.
The molecular structures of [MeGa(−O(2-C6H4)-CHN(2-C6H4)-O−)] (2a) and [MeGa(−O(2-C6H3OMe-3)-CHN(2-
C6H4)-O−)] (2b) were established by X-ray crystallography. Photoluminescence data of these complexes showed that the
quantum yield was mainly affected by the substituent/groups attached to the phenyl moiety of the ligands rather than the metal
atom. Density functional theory calculations have been used to assess all the possible structures and to evaluate the complexation
energies corresponding to [MeM{O(2-C6H4)-CHN(2-C6H4)E}] (M = Ga, In; E = O, S) complexes.
luminescence. Metal chelates derived from tridentate dianionic
Schiff bases have been shown to be highly luminescent.18 The
photophysical properties of monoorgano-gallium complexes are
little explored. With this perspective and in pursuance of our interest
on organo-gallium and -indium complexes, we have syn-
thesized monoorgano-gallium and -indium complexes with dian-
ionic tridentate Schiff bases. To understand the structural aspects
and to assess the luminescence properties, complexes with ligands
containing ring substitution by an electron-withdrawing group
(OMe) and one of the phenolates by a thiolate group have also
been investigated. Results of this work are presented herein.
INTRODUCTION
■
The chemistry of organo-gallium/-indium complexes derived
from an internally functionalized anionic oxo-ligand has been
an active area of extensive current research due to several obvious
reasons.1 These complexes exhibit rich structural diversity1−3 and
show interesting photophysical4−6 and antitumor7 properties.
They find applications in catalysis8,9 and as single-source molecular
precursors for deposition of metal oxide thin films.10
Schiff bases are an important family of internally function-
alized ionic ligands. These ligands have played a pivotal role in
the development of coordination chemistry. Both anionic (e.g.,
N-phenylsalicylidineimine11) and dianionic ligands (such as
Salen12) have been employed for the synthesis of complexes of
group 13 metals. Organo-gallium and -indium complexes conta-
ining these ligands have been isolated in the form of monomers,
dimers, and trimers.2,4,6,9,12
Luminescence from complexes of group 13 metals, in particular
AlQ3,13 has been exploited for organic light emitting diodes
(OLEDs).14 The essential requirements for a complex that can be
used for OLED applications include high fluorescence in the solid
state, high electron mobility, thermal stability (glass transition
temperature above 200 °C and decomposition temperature above
400 °C), and low vapor pressure to aid preparation of good-
quality thin films at relatively low temperatures. A number of studies
are reported regarding the light-emitting aluminum and gallium
complexes. Gallium complexes have been projected as promising
candidates15 to replace aluminum derivatives, as they exhibit better
efficiency than AlQ3.16 Gallium complexes, both classical17,18 and
organometallic derivatives,4−6 have been reported to exhibit bright
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Complexes. Treat-
ment of trialkyl-gallium/-indium etherate with dianionic
tridentate ligands, 2-hydroxy-N-salicylideneaniline, 2-hydroxy-
N-(2-hydroxy-3-methoxybenzylidene)aniline, and 2-mercapto-
N-salicylideneaniline, in benzene at room temperature afforded
complexes of composition [RM{O(2-C6H3OR′-3)-CHN(2-
C6H4)E}] (R = Me, Et; M = Ga, In; R′ = H, Me; E = O, S) as
pale yellow crystalline solids (Scheme 1). These complexes are
1
stable in air, as there was no change in the H NMR spectrum
of 2a after keeping it in open air for 4 days.
The CN absorption in the IR spectra of the complexes con-
taining a O∧N∧O donor set is shifted to lower wave numbers (15−
30 cm−1) than the absorption for the corresponding free ligands.
Received: October 25, 2011
Published: May 3, 2012
© 2012 American Chemical Society
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1
Interestingly the H NMR spectra of gallium complexes (2a
and 2b) in CD2Cl2 showed two set of resonances of nearly
equal integration at room temperature, whereas under similar
conditions only one set of resonances are observed in DMSO-
Scheme 1. Synthesis of Monoorgano-Gallium and -Indium
Complexes
1
d6 as described above. In contrast the H NMR spectra of the
indium (2f) complex exhibited only one set of resonances in both
CD2Cl2 and DMSO-d6. This suggests that gallium complexes exist
in a mixture of monomeric−dimeric forms in dichloromethane
solution (Scheme 2), whereas indium complexes retained their
dimeric structure in solution.
Scheme 2
Crystal Structures of 2a and 2b. The molecular structures
of 2a and 2b were established by single-crystal X-ray diffraction
analysis. ORTEP drawings are shown in Figures 1 and 2, and the
The shift was rather small for complexes derived from the O∧N∧S
donor set. The shifting was more pronounced in the case of indium
complexes with reference to the analogous gallium derivatives,
indicating stronger coordination of nitrogen to the indium atom.
The IR spectra of the complexes displayed an absorption in the
region 560−605 cm−1, which was absent in the spectra of free
ligands. This absorption has been assigned to metal−carbon
stretching based on the M−C stretching reported in the literature
for organogallium/indium complexes.19−21
1
The H and 13C{1H} NMR spectra, recorded in DMSO-d6,
showed characteristic peaks due to alkyl metal and ligand
protons/carbons. The methyl metal singlets appeared in the
region δ −0.65 to −0.27 ppm. The 1H NMR spectra exhibited a
singlet in the region 8.51−8.89 ppm, characteristic of
coordination of the imino nitrogen atom of the −CHN−
group to the metal center. The alkylmetal carbon resonances in
the 13C NMR spectra appeared in the expected region. The
benzothiazoline carbon resonance of 1c at δ 63.5 ppm appeared
in the region 166.4−172.0 ppm in its complexes, which is
characteristic for the CN group. Similarly 1a and 1b and
their complexes showed a CN signal in their 13C NMR
spectra in the region 159.4−171.4 ppm. The C-1 resonances for
the salicyladehyde and o-valine fragments are shielded (0.3−3.4
ppm), while the C-1 signal for the o-aminophenol fragment is
deshielded (5.4−8.8 ppm). In contrast a reverse trend was
noticed for the complexes containing a O∧N∧S ligand; that is,
C-1 for the salicyladehyde fragment is deshielded (7.2−11.1
ppm), and the o-aminothiophenol fragment is shielded (5.1−
7.2 ppm). In the former complexes, the o-aminophenol frag-
ment acts as a bridge, as confirmed by X-ray structural analyses
of 2a and 2b. It can be inferred that in the O∧N∧S complexes
the o-aminothiophenol fragment may be at a terminal position.
This may be due to the preference of a hard metal center for
the hard ligand (oxygen) in a bridging position. The o-
aminothiophenol fragment of O∧N∧S is known to act as both a
bridging ligand as in [{O(MeC6H3)CHN(C6H4)S)}2{Ti-
(OPri)2}2]22 and a terminal ligand as in [{O(C6H4)CHN(C6H4)-
S)}2{Ti(OPri)2}2].22
Figure 1. Crystal structure of [MeGa(−O-(2-C6H4)-CHN(2-
C6H4)-O−)]·CH2Cl2 (2a) grown in dichloromethane solvent.
selected interatomic parameters are given in Tables 1 and 2.
Both complexes crystallize with two molecules of dichloromethane.
There are two independent molecules of 2a in the crystal unit cell,
which differ very slightly in bond lengths, angles, and torsion angles;
only one of them is shown in the figure. The coordination geometry
defined by “μ2-O∧N∧O∧C” donor atoms around the gallium atom
can be described as square pyramidal on the basis of τ indices
(0.016 for 2a and 0.01 for 2b). Five-coordinate geometries in metal
complexes can be quantified using the τ index, as described by
Addision.23
Both the complexes are dimeric with no unusual short inter-
molecular contacts. The Schiff base ligand is coordinated through
one nitrogen atom and two phenolate oxygen atoms; one of them
(o-aminophenol fragment) is μ2-bridging. All these atoms lie in the
equatorial positions. The two bridging phenolate oxygens form a
planar four-membered Ga2O2 ring. The five- and six-membered
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Table 1. Selected Geometric Parameters (Å/deg) for
[MeGa(−O(2-C6H4)-CHN(2-C6H4)-O−)] (2a)
molecule a
molecule b
Ga1−O1
Ga1−O2
Ga1−N1
Ga1−C14
Ga1−O2′
Ga1′−O2
O1−C1
O2−C8
N1−C7
N1−C13
O1−Ga1−N1
O1−Ga1−O2
O1−Ga1−O2′
O1−Ga1−C14
N1−Ga1−O2
N1−Ga1−O2′
N1−Ga1−C14
O2−Ga1−O2′
O2−Ga1−C14
O2′−Ga1−C14
Ga1−O2−Ga1′
1.891(5)
2.018(4)
2.059(6)
1.930(9)
1.984(5)
1.984(5)
1.329(8)
1.360(8)
1.286(8)
1.408(8)
89.1(2)
Ga2−O3
Ga2−O4
Ga2−N2
Ga2−C28
Ga2−O4′
Ga2′−O4
O3−C15
O4−C23
N2−C21
N2−C22
O3−Ga2−N2
O3−Ga2−O4
O3−Ga2−O4′
O3−Ga2−C28
N2−Ga2−O4
N2−Ga2−O4′
N2−Ga2−C28
O4−Ga2−O4′
O4−Ga2−C28
O4′−Ga2−C28
Ga2−O4−Ga2′
1.887(5)
2.013(5)
2.050(5)
1.937(8)
1.995(4)
1.995(4)
1.312(8)
1.357(7)
1.284(9)
1.418(9)
89.2(12)
136.4(2)
90.6(2)
137.7(3)
90.1(2)
113.0(3)
77.7(2)
112.9(3)
78.0(2)
134.3(2)
111.7(3)
72.6(2)
136.6(2)
110.9(3)
72.6(2)
109.2(3)
110.5(3)
107.4(2)
110.5(3)
109.0(3)
107.4(2)
Table 2. Selected Geometric Parameters (Å/deg) for
[MeGa(−O(2-C6H3OMe-3)-CHN(2-C6H4)-O−)] (2b)
Ga1−O1
1.870(3)
Ga1′−O2
1.932(3)
Ga1−O2
2.126(3)
O1−C1
1.287(4)
Ga1−O2′
1.932(3)
O2−C8
1.341(4)
Ga1−N1
1.992(3)
N1−C7
1.282(5)
Ga1−C14
1.924(4)
N1−C13
1.402(5)
O1−Ga1−N1
O1−Ga1−O2
O1−Ga1−O2′
O1−Ga1−C14
N1−Ga1−O2
N1−Ga1−O2′
92.64(13)
157.84(12)
93.55(12)
103.73(16)
75.94(11)
114.35(12)
N1−Ga1−C14
O2−Ga1−O2′
O2−Ga1−C14
O2′−Ga1-C14
Ga1−O2−Ga1′
125.58(17)
74.70(11)
98.33(15)
115.89(17)
105.30(11)
Figure 2. (a) Crystal structure of [MeGa(−O(2-C6H3OMe-3)-CH
N(2-C6H4)-O−)] (2b) grown in dichloromethane solvent. (b)
Packing diagram.
chelate rings formed by O∧N∧O ligands are puckered. The two
six-membered rings lie (on either side) one above and other below
the Ga2O2 ring at an angle of 57.24° and 56.39° in 2a and 65.66°
in 2b. The Ga−C,3,9,24,25 Ga−N,3,9 and Ga−O3,5,9,25 distances are
well in agreement with those reported in the literature for organo-
gallium compounds. The bridging Ga−O distance is slightly
longer than nonbridging Ga−O distances.
Photophysical Properties. Figure 3 shows the emission
spectra of 1a, 1b, and 1c obtained after excitation at wave-
lengths corresponding to their respective excitation peak maxi-
mum. The emission spectra of 1a and 1b are identical and consist
of two significantly overlapping peaks with peak maxima around
518 and 553 nm. Unlike this, a broad peak around 453 nm
was observed for 1c. On the basis of earlier studies on similar
ligands,15,26 the observed emission peak has been attributed to
significantly overlapping π*→π and π*→n electronic transitions.
Incorporation of a methoxy group in one of the phenyl rings (1b)
did not have any effect on the emission and excitation maxima.
However, replacement of phenolic OH (1a) by a SH group (1c)
resulted in a blue shift of the emission maximum (453 nm). The
electron density created within the ligand moiety could be lower
when an OH group is replaced by a SH group. Lower electron
densities stabilize the ligand moiety as well as decrease the extent
of electron−electron repulsion, and hence higher energy is re-
quired to excite the electron from lower levels to higher energy
levels. This leads to a blue shift in the emission and excitation peak
maxima. Among the three ligands, the maximum quantum yield of
emission has been observed for 1a (7%). This is because the
radiative recombination of electrons and holes are severely affected
by the nonradiative processes like C−H and O−H vibrations as
well as the presence of heavier elements (like S). The ligand 1a
has relatively fewer C−H linkages as compared to 1b and also
does not have heavier elements like S as in 1c and hence shows
the highest quantum yield of luminescence.
Figure 4 shows the emission spectra of gallium complexes (2a,
2b, and 3a). The emission spectra of the complexes are broader
and red-shifted compared to that of free ligands. Red shift in the
emission maxima has been attributed to an increase in the electron
density in the ligand moiety brought about by the combined effect
of removal of protons from OH/SH groups as well as its
coordination to metal atom. The broadening may be due to lack of
flexibility with the ligand moiety caused by the formation of coord-
ination polyhedra with the Ga atom. Even though ligands 1a
and 1b have comparable emission maxima and intensities, their
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Figure 3. Emission spectra from ligands (a) 1a, (b) 1b, and (c) 1c in
dichloromethane. The excitation wavelengths are 468 nm for 1a and
1b ligands and 388 nm for the 1c ligand.
Figure 4. Emission spectra from complexes (a) 2a (b) 2b, and (c) 3b
in dichloromethane. The excitation wavelength is 490 nm.
Computational Studies. It has not been possible for us to
determine the X-ray structures of all the complexes. Therefore,
we have adopted density functional theory to determine the
structures of all the complexes in a systematic way. For this
purpose we have optimized structures of the free ligands and
all the complexes resulting from these ligands with Ga(III)
and In(III) ions. For the free ligand two conformations are
possible, viz., anti and syn, and the corresponding optimized
structures are given in the Supporting Information. The anti
conformation is more stable irrespective of the donor atoms
involved; that is, except for nitrogen the other two donor
centers are oxygen or one is oxygen and another is sulfur. We
have used two different initial structures for each of the
complexes considered in this work, and the corresponding
optimized structures are given in Figure 6. In the case of form A,
bridging bonds are associated with five-membered rings, whereas
for form B bridging bonds are associated with six-membered rings.
The minimum energy structure involving form A (bearing only O
and N atoms) consists of a bridged structure with four-membered,
five-membered, and six-membered rings lying one after another
(Figure 6a). It is true for both Ga and In complexes. On the other
hand, the minimum energy structure for form B (bearing O, S, and
N atoms) corresponds to a structure where four-membered, six-
membered, and five-membered rings are placed one after another
complexes (2a and 2b) exhibited different emission maxima. This
can be attributed to the presence of OCH3 groups, leading to
increased electron density in the ligand moiety after deprotonation
of OH groups. For 3a, the effects are much more significant due
to the greater electron-donating nature of sulfur compared to
oxygen after deprotonation, consequently resulting in higher elec-
tron density in the ligand moiety and associated increase in the
extent of electron−electron repulsion. This facilitates excitation of
electrons from the ground state to the excited state. This is respon-
sible for the red shift of the emission maximum for the complex as
compared to the free ligand. Similar results were also observed for
indium complexes (Table 3).
Emission spectra were also recorded by replacing the
methyl group attached to the metal atom with an ethyl group.
The emission spectra from representative indium complexes
(2f and 2h) are shown in Figure 5. The emission maximum,
line shape, and quantum yields are unaffected by replacement
of the methyl group by an ethyl group (Table 3). This is
because the emission and excitation peaks are characteristic of
the transitions taking place between the energy levels of the
ligand moiety and the groups attached with the metal atom.
The measured quantum yields for the complexes are lower
than that reported for other gallium complexes.
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Table 3. UV−Vis Absorption, Excitation, and Emission Data of Ligands and Their Monoorgano-Gallium and -Indium
Complexes in Dichloromethane
compound
UV−vis absorption, λ in nm excitation λ in nm emission λ in nm quantum yield (η) in %
HO(2-C6H4)-CHN(2-C6H4)-OH (1a)
270, 353
468
518, 553
517, 554
465
7
2
1
2
3
2
5
3
1
1
1
1
1
1
1
HO(2-C6H3OMe-3)-CHN(2-C6H4)-OH (1b)
HO(2-C6H4)-CHN(2-C6H4)-SH (1c)
278, 345
468
259,286, 310, 333, 350
243, 305, 346, 414
251, 317, 360, 427
251, 281, 308, 426
245, 303, 349, 416
251, 315, 333, 361, 429
251, 285, 308, 428
292, 315, 370, 430
317, 370, 431
390
[MeGa(−O(2-C6H4)-CHN(2-C6H4)-O−)] (2a)
[MeGa(−O(2-C6H3OMe-3)-CHN(2-C6H4)-O−)] (2b)
[MeGa(−O(2-C6H4)-CHN(2-C6H4)-S−)] (3a)
[EtGa(−O-(C6H4)-CHN-(C6H4)-O−)] (2c)
[EtGa(−-O-(C6H3OMe-3)-CHN-(C6H4)-O−)] (2d)
[EtGa(−O(2-C6H4)-CHN(2-C6H4)-S−)] (3b)
[MeIn(−O-(C6H4)-CHN-(C6H4)-O−)] (2e)
[MeIn(-O-(C6H3OMe-3)-CHN-(C6H4)-O−)] (2f)
[MeIn(−O(2-C6H4)-CHN(2-C6H4)-S−)] (3c)
[EtIn(−O-(C6H4)-CHN-(C6H4)-O−)] (2g)
[EtIn(−O-(C6H3OMe-3)-CHN-(C6H4)-O−)] (2h)
[EtIn(−O-(C6H4)-CHN-(C6H4)-S−)] (3d)
488
580
275, 490
350, 490
488
580
680
576
490
560
350, 490
275, 355, 473
275, 355, 490
350
680
555
580
254, 282, 338, 428
250, 295, 358, 415
316, 362, 432
560
501
552
350, 500
388, 480
554, 580
630
254, 280, 364, 418
Figure 5. Emission spectra from complexes (a) 2f and (b) 2h in
dichloromethane. Excitation wavelength is 355 nm.
Figure 6. Optimized structure of (a) M-form A and (b) M-form B
complexes, where M = Ga/In and E = O/S.
(Figure 6b). Some of the optimized geometrical parameters are given
in Supporting Information. It is clear that the In−L bond distances
are always larger as compared to the Ga−L distance because of the
larger size of In. For form B M−N bond distances are larger for both
In and Ga. Bond lengths from X-ray crystal structure of Ga-form A
(E = O) are given in Tables 1 and 2. The bridging M−O bond distances
are 2.018 and 1.984 Å, while M−N, M−O, and M−C bond distances
are 2.059, 1.891, and 1.930 Å, respectively. For obtaining the com-
plexation energy value of a particular complex, we have considered the
total energy of the complex, ligands, and the metal ion, which are
involved in the formation of that complex. The calculated complexation
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containing 0.24 g (2.12 mmol) of Me3Ga) was added a solution
of (2-hydroxyphenyl)salicylideneimine (450 mg, 2.11 mmol)
with stirring, which continued for 3 h. The solvent was
evaporated under reduced pressure to give a yellow, crystalline
solid (600 mg, 96% yield), which was recrystallized from
dichloromethane−hexane as a colorless crystalline solid, mp
260 °C. The compound could not be sublimed at 200 °C at 34
mm/Hg. Anal. Calcd for C14H12GaNO2·0.5(CH2Cl2): C, 51.45;
H, 3.87; N, 4.13. Found: C, 51.77; H, 3.78; N, 4.18. IR (ν
Table 4. Calculated Complexation Energies (eV) for In and
Ga Complexes Using the def2-TZVP/BP86 Method
complex name
complexation energy
Ga-form A (E = O) (2a)
Ga-form A (E = S)
−129.03
−127.83
−128.68
−127.94
−118.06
−117.36
−117.90
−117.41
Ga-form B (E = O)
Ga-form B (E = S) (3a)
In-form A (E = O) (2e)
In-form A (E = S)
1
in cm−1): 1614 (CN); 580 (Ga−C). H NMR in DMSO-d6:
3
−0.62 (s, MeGa); 5.74 (CH2Cl2); 6.56 (t, JHH = 7.3 Hz, 1H);
6.70 (dd, 8.5 Hz, 3H); 7.04 (t, 3JHH = 7.8 Hz, 1H); 7.27 (t, 3JHH
=
In-form B (E = O)
7.3 Hz, 1H); 7.40 (d, 3JHH = 7.3 Hz, 1H); 7.55 (d, 3JHH = 7.7 Hz,
1H); 8.87 (s, −CHN−, 1H) [1H NMR in CD2Cl2: −0.36 (s,
3H); 7.04 (m, 3H); 7.22 (m, 2H); 7.39 (m, 5H); 7.54 (m, 2H);
In-form B (E = S) (3c)
3
MeGa); −0.03 (s, MeGa); 6.69 (t, JHH = 7.2 Hz, 1H); 6.86 (m,
energy values and charge values on the metal and donor centers
are also given in the Supporting Information.
3
7.63 (d, JHH = 8.1 Hz, 1H); 8.48 (s, −CHN−, 1H); 8.77 (s,
−CHN−, 1H)]. 13C{1H} NMR in DMSO-d6: −7.1 (s, MeGa);
115.4, 115.6, 116.5, 117.6, 120.3, 122.3, 130.0, 132.6, 134.4, 134.8,
157.7, 159.5, 166.9 (s, −CHN−).
CONCLUSION
■
Air- and moisture-stable, photoemissive monoorgano-gallium and
-indium complexes derived from dianionic tridentate Schiff bases
have been isolated conveniently. They are dimeric molecules with
phenolate bridges in the solid state. The gallium complexes exist as
a mixture of monomeric and dimeric forms in dichloromethane
solution. These complexes are emissive in solution at room tem-
perature, and the emission peaks are red-shifted with respect to the
peaks for corresponding free ligands. The complexes derived from
O∧N∧O ligands comprise a bridged structure with four-, five-, and
six-membered rings lying one after another, while complexes con-
taining O∧N∧S ligands adopt a structure with four-, six-, and five-
membered rings one after another.
[MeGa(−O(2-C6H3OMe-3)-CHN(2-C6H4)-O−)] (2b). 2b was
prepared similarly to 2a in (720 mg) 91% yield and recrystallized
from dichloromethane. Mp: 275 °C. Anal. Calcd for
C15H14GaNO3·CH2Cl2: C, 46.76; H, 3.92; N, 3.41. Found: C, 47.26;
1
H, 3.94; N, 3.54. IR (ν in cm−1): 1613 (CN); 582 (Ga−C). H
NMR in DMSO-d6: −0.65 (s, MeGa); 3.73 (s, OMe); 5.72 (CH2Cl2)
3
3
6.52−6.58 (m, 1H); 6.64 (t JHH = 8.0 Hz, 2H); 6.92 (d, JHH = 7.6
3
Hz, 1H); 6.98−7.05 (m, 3H); 7.53 (d, JHH = 7.8 Hz, 1H); 8.84
(s, −CHN−, 1H) [1H NMR in CD2Cl2: −0.36 (s, MeGa); −0.00
3
(s, MeGa); 3.91 (s, OMe); 3.99 (s, OMe); 6.62 (d, JHH = 7.5 Hz,
1H); 6.80 (m, 3H); 7.05 (m, 5H); 7.33 (m, 2H); 7.54 (m, 2H); 7.92
3
(d, JHH = 8.1 Hz, 1H); 8.46 (s, −CHN−, 1H); 8.77 (s, −CH
N−, 1H)]. 13C{1H} NMR in DMSO-d6: −7.2 (s, MeGa); 55.9 (s,
OMe); 115.3, 115.6, 117.6, 119.7, 125.7, 130.0, 132.6, 152.0, 157.4,
157.7, 159.4 (s, −CHN−).
EXPERIMENTAL SECTION
■
Materials and Physical Measurements. All experiments involving
organo-gallium/ -indium compounds were carried out in anhydrous
conditions under a nitrogen atmosphere using Schlenk techniques. Solvents
were dried using standard methods. The R3Ga·OEt2 (R = Me, Et) were
prepared using a gallium−magnesium alloy and alkyl iodide in diethyl ether,
while R3In·OEt2 (R = Me or Et) were obtained by a reaction between
anhydrous InCl3 and RMgI in diethyl ether.9 Ether contents in each
[EtGa(−O(2-C6H4)-CHN(2-C6H4)-O−)] (2c). 2c was prepared
similarly to 2a in (360 mg) 97% yield. Mp: 220 °C. Anal. Calcd for
C15H14GaNO2·0.5H2O: C, 56.48; H, 4.74; N, 4.39. Found: C, 57.14;
1
H, 4.55; N, 4.54. IR (ν in cm−1): 1615 (CN); 575 (Ga−C). H
NMR in DMSO-d6: 0.12 (q, 3JHH = 7.6 Hz, −CH2Ga); 0.75 (t, 3JHH
=
7.8 Hz, CH3CH2Ga); 6.57−6.74 (m, 5H); 7.04 (t, 3JHH = 7.1 Hz, 1H);
7.27 (t, 3JHH = 8.0 Hz, 1H); 7.37 (d, 3JHH = 6.3 Hz, 1H); 7.55 (d, 3JHH
=
1
preparation were evaluated by H NMR integration. The ligands were
7.5 Hz, 1H); 8.89 (s, −CHN−, 1H). 13C{1H} NMR in DMSO-d6: 4.4
(s, −CH2Ga); 10.2 (s, CH3CH2Ga); 115.5, 116.5, 117.6, 120.5, 122.2,
122.3, 130.0, 132.9, 134.4, 134.8, 157.8, 167.4 (s, −CHN−).
prepared by condensation reaction between a salicyaldehyde and an
equivalent amount of o-aminophenol or o-aminothiophenol in refluxing
benzene as described in the literature.22,27,28
[EtGa(−O(2-C6H3OMe-3)-CHN(2-C6H4)-O−)] (2d). 2d was pre-
pared similarly to 2a in (350 mg) 92% yield. Mp: 175 °C (dec). Anal.
Calcd for C16H16GaNO3·0.5H2O: C, 55.05; H, 4.90; N, 4.01. Found:
C, 54.84; H, 4.73; N, 3.81. IR (ν in cm−1): 1613 (CN); 578 (Ga−C).
Infrared spectra were recorded as KBr plates on a Jasco FT-IR 6100
spectrometer. The NMR spectra were recorded on a Bruker Avance-II
300 MHz spectrometer in 5 mm tubes as CDCl3 or DMSO-d6 solutions.
Chemical shifts were referenced to internal chloroform or dimethyl
sulfoxide peak. Electronic spectra were recorded in dichloromethane on a
UV−vis Jasco V-630 spectrophotometer. All luminescence measurements
were carried out at room temperature by using an Edinburgh Instruments
FLSP 920 system, having a 450W Xe lamp as the excitation source for
steady-state measurements. Red-sensitive PMT was used as the detector.
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.
Quantum-Chemical Calculations. Geometries of all the bare
dianionic ligands and the resulting complexes involving Ga3+ and In3+ ions
have been optimized fully using the Turbomole 6.0 program.29 For this
purpose we have used density functional theory with Becke’s exchange
functional30 in conjunction with Perdew’s correlation functional31 (BP86).
Standard def2-TZVP basis sets have been used for all the atoms at the all-
electron level except for In. For the In atom, 28 core electrons have been
considered using an effective core potential, and the remaining electrons
have been treated explicitly.
3
1H NMR in DMSO-d6: 0.10 (q, JHH = 8.0 Hz, −CH2Ga); 0.74
3
(t, JHH = 8.0 Hz, CH3CH2Ga); 3.75 (s, OMe); 6.57−6.67 (m, 3H);
3
7.01−6.92 (m, 3H); 7.54 (d, JHH = 7.8 Hz, 1H); 8.89 (s, −CH
N−).13C{1H} NMR in DMSO-d6: 4.3 (s, −CH2Ga); 10.2 (s,
CH3CH2Ga); 56.1 (s, OMe); 115.2, 115.5, 117.5, 120.1, 125.6,
129.9, 132.9, 152.0, 157.8, 159.9 (s, −CHN−).
[MeIn(−O(2-C6H4)-CHN(2-C6H4)-O−)] (2e). 2e was prepared
similarly to 2a in (590 mg) 91% yield. Mp: 270 °C (dec). Anal.
Calcd for C15H12InNO2·0.5C6H6: C, 53.68; H, 3.97; N, 3.68. Found:
C, 53.64; H, 4.04; N, 4.07. IR (ν in cm−1): 1603 (CN); 524 (In−C).
1H NMR in DMSO-d6: −0.28 (s, MeIn); 6.43 (t, 3JHH = 7.3 Hz, 1H);
3
3
6.51 (t, JHH = 7.2 Hz, 1H); 6.60 (t, JHH = 7.3 Hz, 2H); 6.96
(t, 3JHH = 7.5 Hz, 1H); 7.18 (t, 3JHH = 7.7 Hz, 1H); 7.38 (d, 3JHH = 7.3
3
Hz, 1H); 7.47 (d, JHH = 7.8 Hz, 1H); 8.78 (s, −CHN−, 1H).
13C{1H} NMR in DMSO-d6: −4.3 (s, MeIn); 113.5, 113.8, 115.7,
119.1, 120.4, 122.9, 128.6, 128.8 (benzene), 133.7, 134.2, 136.1, 159.2,
161.2, 171.4 (s, −CHN−).
[MeIn(−O(2-C6H3OMe-3)-CHN(2-C6H4)-O−)] (2f). 2f was pre-
pared similarly to 2a in (500 mg) 97% yield). Mp: 280 °C (dec). Anal.
Calcd for C15H14InNO3: C, 48.55; H, 3.80; N, 3.77. Found: C, 47.61;
Synthesis of Monoorgano-Gallium and -Indium Com-
plexes. [MeGa(−O(2-C6H4)-CHN(2-C6H4)-O−)] (2a). To a
benzene solution (25 mL) of trimethylgallium etherate (0.56 g,
H, 4.25; N, 3.47. IR (ν in cm−1): 1603 (CN); 526 (In−C). H
1
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dx.doi.org/10.1021/om201030d | Organometallics 2012, 31, 3836−3843

Organometallics
Article
NMR in DMSO-d6: −0.27 (s, MeIn); 3.69 (s, OMe); 6.45 (m, 2H);
123.4, 126.7, 132.7, 134.6, 136.3, 141.2, 146.4, 164.9, 172.0 (s, −
CHN−).
3
3
6.58 (d, JHH = 7.5 Hz, 1H); 6.81 (d, JHH = 7.5 Hz, 1H); 6.93−7.02
3
(m, 2H); 7.45 (d, JHH = 7.8 Hz, 1H); 8.75 (s, −CHN−, 1H) [1H
X-ray Crystallography. Intensity data for [MeGa(−O(2-C6H4)-
CHN(2-C6H4)-O−)] (2a) and [MeGa(−O(2-C6H3OMe-3)-CH
N(2-C6H4)-O−)] (2b) crystallized from dichloromethane (both
triclinic) were collected at room temperature on a Rigaku AFC 7S
diffractometer using graphite-monochromated Mo Kα radiation. The
structures were solved using direct methods32 and refined by full matrix
least-squares method on F2 33 using data corrected for absorption effects
using empirical procedures.34 All non-hydrogen atoms were refined aniso-
tropically, and hydrogen atoms were placed in their geometrically
idealized positions with coordinates and thermal parameters riding on
host atoms. The molecular structures are drawn using ORTEP.35 Crystallo-
graphic and structural determination data are given in the Supporting
Information.
NMR in CD2Cl2: −0.02 (s, MeIn); 4.00 (s, OMe); 6.56 (t, 3JHH = 7.5
3
3
Hz, 1H); 6.62 (d, JHH = 8.4 Hz, 1H); 6.96 (t, JHH = 7.8 Hz, 1H);
3
7.06 (m,3H); 7.34 (d, JHH = 7.8 Hz, 1H); 8.71 (s, −CHN−, 1H].
13C{1H} NMR in DMSO-d6: −4.2 (s, MeIn); 55.6 (s, OMe); 112.8,
113.7, 114.5, 115.7, 118.9, 119.6, 127.7, 128.6, 134.8, 152.4, 159.5,
160.8 (s, −CHN−).
[EtIn(−O(2-C6H4)-CHN(2-C6H4)-O−)] (2g). 2g was prepared
similarly to 2a in (510 mg) 96% yield. Mp: 215 °C (dec). Anal.
Calcd for C15H14NO2In·2H2O: C, 46.06; H, 4.63; N, 3.58. Found: C,
46.24; H, 3.30; N, 1.90. IR (ν in cm−1): 1610 (CN); 525 (In−C).
1H NMR in DMSO-d6: 0.56 (q, JHH = 8.1 Hz, −CH2In); 1.24
3
(t, 3JHH = 8.0 Hz, CH3CH2In); 6.42−6.53 (m, 3H); 6.59 (d, 3JHH = 8.4
Hz, 1H); 6.96 (t, 3JHH = 7.7 Hz, 1H); 7.18 (t, 3JHH = 7.7 Hz, 1H); 7.37
(d, 3JHH = 7.8 Hz, 1H); 7.45 (d, 3JHH = 8.1 Hz, 1H); 8.75 (s, −CH
N−). 13C{1H} NMR in DMSO-d6: 8.2 (s, −CH2In); 12.4 (s,
CH3CH2In); 113.7, 113.9, 115.8, 119.1, 120.4, 123.0, 133.8, 134.3,
136.1, 159.3, 160.4, 161.0, 171.4 (s, −CHN−).
ASSOCIATED CONTENT
■
S
* Supporting Information
CCDC-Nos. 848250 and 848251 contain the supplementary
crystallographic data for [MeGa(−O(2-C6H4)-CHN(2-
C6H4)-O−)] (2a) and [MeGa(−O(2-C6H3OMe-3)-CH
N(2-C6H4)-O−)] (2b), respectively, for this paper. This
material is available free of charge via the Internet at http://
pubs.acs.org. These data can also be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK [fax: + 44-1223/336-033; e-mail:
deposit@ccdc.cam.ac.uk]. Optimized structures of the ligands
and the selected geometricla parameters of the complexes.
[EtIn(−O(2-C6H3OMe-3)-CHN(2-C6H4)-O−)] (2h). 2h was pre-
pared similarly to 2a in (450 mg) 95% yield. Mp: 250. Anal. Calcd for
C16H16InNO3: C, 49.90; H, 4.19; N, 3.64. Found: C, 49.70; H, 4.60;
N, 3.84. IR (ν in cm−1): 1605 (CN); 524 (In−C). H NMR in
1
CDCl3: 0.90−0.99 (m, −CH2In); 1.08 (t, 3JHH = 7.7 Hz, CH3CH2In);
3
3
3.98 (s, OMe); 6.51 (t, JHH = 7.5 Hz, 1H); 6.67 (d, JHH = 8.4 Hz,
1H); 6.81 (t, 3JHH = 7.8 Hz, 1H); 6.94−7.02 (m, 3H); 7.30 (d, 3JHH
=
7.8 Hz, 1H); 8.60 (s, −CHN−). 13C{1H} NMR in CDCl3: 5.6
(s, −CH2In); 11.5 (s, CH3CH2In); 56.2 (s, OMe); 114.5, 114.6, 115.0,
118.1, 120.0, 121.8, 126.1, 130.2, 132.6, 149.8, 156.9, 161.7
(s, −CHN−).
[MeGa(−O(2-C6H4)-CHN(2-C6H4)-S−)] (3a). 3a was prepared
similarly to 2a in (1.13 g) 97% yield. Mp: 255 °C. Anal. Calcd for
C14H12GaNOS.H2O: C, 50.98; H, 4.28; N, 4.25. Found: C, 50.87; H,
4.05; N, 5.23. IR (ν in cm−1): 1620 (CN); 598 (Ga−C). 1H NMR
in DMSO-d6: −0.55 (s, MeGa); 6.75 (t, 3JHH = 7.7 Hz, 1H); 7.05 (m);
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: jainvk@barc.gov.in. Fax: +91-22-2550-5151. Tel:
+91-22-2559-5095.
3
3
7.33 (br); 7.46 (d, JHH = 7.2 Hz); 7.59 (d, JHH = 7.2 Hz); 8.73
(s, −CHN-, 1H). 13C{1H} NMR in DMSO-d6: −4.2 (s, MeGa);
117.0, 117.2, 120.4, 122.3, 124.1, 128.5, 131.0, 135.1, 135.5, 140.0,
142.5, 161.0, 166.0 (s, −CHN−).
Notes
The authors declare no competing financial interest.
[EtGa(−O(2-C6H4)-CHN(2-C6H4)-S−)] (3b). 3b was prepared
similarly to 2a in (250 mg) 94% yield. Mp: 207 °C (dec). Anal.
Calcd for C15H14GaNOS·0.5H2O: C, 53.77; H, 4.51; N, 4.18. Found:
C, 53.69; H, 4.41; N, 3.76. IR (ν in cm−1): 1620 (CN); 598 (Ga−
ACKNOWLEDGMENTS
■
We thank Drs. T. Mukherjee and D. Das for encouragement of
this work.
1
3
C). H NMR in DMSO-d6: 0.17 (q, JHH = 7.6 Hz, −CH2Ga); 0.70
3
3
(t, JHH = 7.7 Hz, CH3CH2Ga); 6.73 (t, JHH = 6.0 Hz, 2H); 6.80
3
3
REFERENCES
(d, JHH = 8.1 Hz, 1H); 7.03 (m, 3H); 7.45 (d, JHH = 7.0 Hz, 1H);
7.60 (d, 3JHH = 6.0 Hz, 1H); 8.79 (s, −CHN−, 1H). 13C{1H} NMR
in DMSO-d6: 7.2 (s, −CH2Ga); 10.4 (s, CH3CH2Ga); 116.8, 117.0,
122.1, 122.3, 123.9, 128.4, 130.9, 135.0, 135.4, 143.2, 161.2, 161.5,
166.4 (s, −CHN−).
■
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3
C). H NMR in DMSO-d6: −0.30 (s, MeIn); 6.55 (t, JHH = 7.3 Hz,
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3
3
7.34 (m, 3H); 7.41 (d, JHH = 7.8 Hz, 1H); 8.26 (d, JHH = 2.7 Hz);
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(s, MeIn); 114.2, 119.3, 120.6, 123.1, 123.4, 126.7, 132.5, 134.7,
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H, 3.84; N, 3.49. IR (ν in cm−1): 1616 (CN); 539 (In−C). H
1
3
3
NMR in DMSO-d6: 0.52(q, JHH = 8.0 Hz, −CH2In); 1.11 (t, JHH
=
3
3
7.6 Hz, CH3CH2In); 6.54 (t, JHH = 6.7 Hz, 1H); 6.63 (d, JHH = 8.4
Hz); 7.21−7.43 (m,); 8.58 (s, −CHN−). 13C{1H} NMR in DMSO-
d6: 10.0 (s, −CH2In); 12.4 (S, CH3CH2In); 114.1, 119.2, 120.6, 123.0,
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