Gallium(III) complexes based on N,N′-bis(salicylidene)propane-1,3- diamine and its derivatives

Article abstract of DOI:10.1016/j.poly.2013.02.057

The reactions of N,N′-bis(salicylidene)propane-1,3-diamine (salpropH₂) and its substituted derivatives with Ga(acac)₃ afforded the complexes [Ga(acac)(salprop)]·0.5H₂O (1), [Ga(acac)(5Clsalprop)] (2), [Ga(acac)(5Brsalprop)] (3), [Ga(acac)(5NO ₂salprop)] (4) and [Ga(acac)(5Mesalprop)] (5), in high yields. The crystal structures of all complexes have been determined by single-crystal X-ray crystallography. All complexes are mononuclear with the Ga(III) atoms being in octahedral environments surrounded by one tetradentate chelate 5Rsalprop ^2- ligand and one bidentate chelate acac^- ligand. The free ligands exhibit photoluminescence which was found to be increased upon complex formation. The substituted derivatives of the salpropH₂ ligand bearing either electron-donating methyl groups or electron-withdrawing groups, such as Cl, Br and NO₂ at the fifth position of both salicylidene rings were found to modify the emission maximum of the free ligands and the complexes.

Full text of DOI:10.1016/j.poly.2013.02.057

Polyhedron 64 (2013) 77–83
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Gallium(III) complexes based on N,N0-bis(salicylidene)propane-1,3-diamine
and its derivatives
Sotiria Tella a, Vlasoula Bekiari b, Vadim G. Kessler c, Giannis S. Papaefstathiou a,
⇑
a Laboratory of Inorganic Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, Zografou 157 71, Greece
b Department of Aquaculture and Fisheries, Technological Educational Institute of Messolonghi, 30200 Messolonghi, Greece
c Department of Chemistry, Swedish University of Agricultural Sciences, P.O. Box 7015, 750 07 Uppsala, Sweden
a r t i c l e i n f o
a b s t r a c t
The reactions of N,N0-bis(salicylidene)propane-1,3-diamine (salpropH2) and its substituted derivatives
with Ga(acac)3 afforded the complexes [Ga(acac)(salprop)]ꢀ0.5H2O (1), [Ga(acac)(5Clsalprop)] (2),
[Ga(acac)(5Brsalprop)] (3), [Ga(acac)(5NO2salprop)] (4) and [Ga(acac)(5Mesalprop)] (5), in high yields.
The crystal structures of all complexes have been determined by single-crystal X-ray crystallography.
All complexes are mononuclear with the Ga(III) atoms being in octahedral environments surrounded
by one tetradentate chelate 5Rsalprop2ꢁ ligand and one bidentate chelate acacꢁ ligand. The free ligands
exhibit photoluminescence which was found to be increased upon complex formation. The substituted
derivatives of the salpropH2 ligand bearing either electron-donating methyl groups or electron-
withdrawing groups, such as Cl, Br and NO2 at the fifth position of both salicylidene rings were found
to modify the emission maximum of the free ligands and the complexes.
Article history:
Available online 5 March 2013
Dedicated to Professor George Christou on
the occasion of his 60th birthday.
Keywords:
Crystal structure
Gallium(III) complexes
Photoluminescence
Schiff base complexes
Six-coordinated Ga(III) complexes
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
these complexes may be tuned by attaching Electron Withdraw-
ing chemical Groups (EWGs) or Electron Donating chemical
Group 13 metal complexes have emerged as leading materials
for optoelectronic devices such as light emitting diodes (LEDs)
since they often exhibit high fluorescence in the solid state and
good thermal stability [1–17]. Alq3 (qH = 8-hydroxyquinoline) is
probably the best representative of this class of compounds exhib-
iting both photoluminescence (PL) and electroluminescence (EL)
[3–6]. It has been shown that replacement of Al(III) with Ga(III)
has resulted in materials with improved properties such as higher
electroluminescence yields [7–9]. An alternative route to tune/
modify the electronic properties of these materials is to introduce
substituents on the periphery of the complexes [10–12]. It has
been found that methylation of the 8-hydroxyquinoline ligand
modifies/improves the physical properties (e.g. increases the glass
transition temperature) and increases the operating voltages of
the EL devices [13].
Groups (EDGs) on the saph2ꢁ ligands.
Following the previous published work, we herein report a
series of mononuclear Ga(III) complexes based on N,N0-bis
(salicylidene)propane-1,3-diamine (salpropH2) and its substituted
derivatives. In an attempt to tune/modify the emission maxima,
EWGs such as Cl, Br and NO2, as well as EDGs such as methyl
groups were introduced on the periphery of the Schiff base ligand.
2. Experimental
2.1. General and physical measurements
All manipulations were performed under aerobic conditions.
Gallium metal, acetylacetone, salicylaldehyde, substituted salicyl-
aldehydes, 1,3-diaminopropane and all solvents were obtained
from commercial sources and used as received. Ga(acac)3 was
prepared following literature procedures [18]. Microanalyses (C,
H, N) were performed with an EA 1108 Carlo Erba analyzer. IR
spectra were recorded on a Shimadzu FT/IR IRAffinity-1 spectrom-
eter with samples prepared as KBr pellets. TGA diagrams were re-
corded on a Mettler-Toledo TGA/DSC1 instrument under a N2 flow
of 50 ml/min. Emission and excitation spectra were recorded on a
Shimadzu RF-5301PC spectrofluorophotometer on powdered
samples dispersed and squeezed on a quartz plate.
An alternative route to create such materials with improved
properties is to partly replace the 8-hydroxyquinolate with Schiff
bases bearing phenolate groups [14]. We and others have recently
shown that Ga(III) complexes with the Schiff base ligand N-
salicylidene-o-aminophenol (saphH2) exhibit bright luminescence
[15–17]. We also demonstrated that the electronic properties of
⇑
Corresponding author. Tel.: +30 210 727 4840.
E-mail address: gspapaef@chem.uoa.gr (G.S. Papaefstathiou).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.02.057

78
S. Tella et al. / Polyhedron 64 (2013) 77–83
N
N
N
N
N
N
OH
HO
OH
HO
OH
HO
Cl
Cl
Br
Br
salpropH2
5ClsalpropH2
5BrsalpropH2
N
N
N
N
OH
HO
OH
HO
O2N
NO2
H3C
CH3
5NO2salpropH2
5MesalpropH2
Fig. 1. The structures of the double Schiff base ligands discussed in the text.
Table 1
Crystallographic data for complexes 1–5.
Compound reference
1
C
2
3
4
5
Chemical formula
Formula weight
Crystal system
Unit cell dimensions
a (Å)
22H24GaN2O4.50
C22H21Cl2GaN2O4
518.03
orthorhombic
C22H21Br2GaN2O4
606.95
orthorhombic
C22H21GaN4O8
539.15
orthorhombic
C24H27GaN2O4
477.20
orthorhombic
458.15
orthorhombic
8.1261(1)
14.035(2)
18.291(3)
90
8.4012(1)
14.028(2)
18.851(3)
90
8.7846(9)
13.850(1)
18.922(1)
90
8.361(1)
14.010(3)
18.979(4)
90
18.628(3)
8.288(1)
14.663(2)
90
b (Å)
c (Å)
a
(°)
b (°)
90
90
2086.0(6)
P212121
4
1.353
12912
4959
0.0377
0.0398
0.0707
0.0715
0.0793
1.002
90
90
2221.7(6)
P212121
4
1.511
15431
5020
0.0378
0.0369
0.0752
0.0559
0.0828
0.917
90
90
2302.1(4)
P212121
4
4.697
19969
5651
0.0354
0.0392
0.0945
0.0546
0.1019
1.041
90
90
2223.2(8)
P212121
4
1.296
26186
5723
0.0237
0.0263
0.0701
0.0291
0.0716
1.013
90
90
c
(o)
V (Å3)
2263.8(7)
Pna21
4
1.248
19265
5030
0.0222
0.0283
0.0752
0.0325
0.0775
1.012
Space group
Z
l
(mmꢁ1
)
Reflections measured
Independent reflections
Rint
R1 values (I > 2r(I))
wR(F2) values (I > 2
R1 values (all data)
r(I))
wR(F2) values (all data)
Goodness-of-fit on F2
2.2. Compound preparation
with n-hexane (2 ꢂ 5 mL) and dried in air. Yield 0.12 g, 58%. Anal.
Calc. for C22H24GaN2O4.5: C, 57.67; H, 5.28; N, 6.11. Found: C,
57.71; H, 5.23; N, 6.17%. IR (KBr pellets, cmꢁ1): 1620w, 1587w,
1536w, 1519w, 1466w, 1445w, 1383w, 1338w, 1315w, 1275w,
1210w, 1195w, 1146w, 1125w, 1079w, 1065w, 1015w, 923w,
898w, 797w, 762w, 738w, 604w.
Method B: Salicylaldehyde (0.094 mL, 0.900 mmol), 1,3-diami-
nopropane (0.037 mL, 0.450 mmol) and Ga(acac)3 (0.165 g,
0.450 mmol) were refluxed in 20 mL toluene for 50 min. The resul-
tant clear yellow solution was cooled to room temperature and
layered with n-hexane (40 mL). Yellow crystals of 1 were formed
within a week. The crystals were isolated by vacuum filtration,
washed with n-hexane (2 ꢂ 5 mL) and dried in air. Yield 0.14 g,
67%. Anal. Calc. for C22H24GaN2O4.5: C, 57.67; H, 5.28; N, 6.11.
Found: C, 57.70; H, 5.25; N, 6.15%. IR (KBr pellets, cmꢁ1): 1620w,
1587w, 1536w, 1519w, 1466w, 1445w, 1383w, 1338w, 1315w,
1275w, 1210w, 1195w, 1146w, 1125w, 1079w, 1065w, 1015w,
923w, 898w, 797w, 762w, 738w, 604w.
2.2.1. Synthesis of N,N0-bis(salicylidene)propane-1,3-diamine
(salpropH2) and its substituted derivatives
SalpropH2 was prepared by the condensation in absolute ethanol
of 1,3-diaminopropane with salicylaldehyde in accordance with lit-
erature methods [19]. The substituted derivatives of the Schiff base
were prepared by replacing salicylaldehyde with 2-hydroxy-5-
chloro-benzaldehyde, 2-hydroxy-5-bromo-benzaldehyde, 2-hydro-
xy-5-nitro-benzaldehyde and 2-hydroxy-5-methyl-benzaldehyde.
The chemical structures of the Schiff bases are shown in Fig. 1.
2.2.2. [Ga(acac)(salprop)]ꢀ0.5H2O (1)
Method A: SalpropH2 (0.127 g, 0.450 mmol) and Ga(acac)3
(0.165 g, 0.450 mmol) were refluxed in 20 mL toluene for 50 min.
The resultant yellow solution was filtered and layered with n-hex-
ane (40 mL). X-ray quality, yellow crystals of 1 were formed within
a week. The crystals were isolated by vacuum filtration, washed

S. Tella et al. / Polyhedron 64 (2013) 77–83
79
Cl2
Br2
N2
N2
N2
O1
O2
O1
O4
O4
O4
Ga1
N1
Ga1
N1
Ga1
O2
O1
N1
O2
O3
O3
O3
Cl1
Br1
Fig. 2. ORTEP diagrams of the molecular structures of 1 (left), 2 (middle) and 3 (right). Color code: Ga, green; O, red; N, blue; Cl and Br, yellow; C, gray; H, white. (Color online.)
O8
N4
O7
N2
N2
O1
O1
O4
O4
Ga1
Ga1
O3
O2
N1
N1
O2
O3
O6
N3
O5
Fig. 3. ORTEP diagrams of the molecular structures of 4 (left) and 5 (right). Color code: same as in Fig. 2. (Color online.)
2.2.3. [Ga(acac)(5Clsalprop)] (2)
4.01; N, 5.43%. IR (KBr pellets, cmꢁ1): 1622w, 1592w, 1525w,
Method A: Ga(acac)3 (0.102 g, 0.280 mmol) and 5ClsalpropH2
(0.098 g, 0.280 mmol) were dissolved in methanol (12 mL). The
solution was stirred for 30 min and left undisturbed to evaporate
at room temperature. Light yellow crystals of 2 were formed over
a period of two days. The crystals were isolated by vacuum filtra-
tion, washed with Et2O (2 ꢂ 5 mL) and dried in air. Yield 0.08 g,
56%. Anal. Calc. for C22H21Cl2GaN2O4: C, 51.01; H, 4.09; N, 5.41.
Found: C, 51.05; H, 4.02; N, 5.38%. IR (KBr pellets, cmꢁ1): 1622w,
1592w, 1525w, 1459w, 1382w, 1307w, 1175w, 822w, 800w,
708w, 414w.
1459w, 1382w, 1307w, 1175w, 822w, 800w, 708w, 414w.
2.2.4. [Ga(acac)(5Brsalprop)] (3)
Method A: Ga(acac)3 (0.102 g, 0.280 mmol) and 5BrsalpropH2
(0.123 g, 0.280 mmol) were dissolved in methanol (10 mL). The
solution was stirred for 45 min and left undisturbed to evaporate
at room temperature. Orange crystals of 3 were formed over a per-
iod of a week. The crystals were isolated by vacuum filtration,
washed with Et2O (2 ꢂ 5 mL) and dried in air. Yield 0.12 g, 70%.
Anal. Calc. for C22H21Br2GaN2O4: C, 43.54; H, 3.49; N, 4.62. Found:
C, 43.48; H, 3.40; N, 4.70%. IR (KBr pellets, cmꢁ1): 1635m, 1620m,
1591m, 1525m, 1456m, 1379, 1306m, 1227w, 1172w, 1132w,
1073w, 1062w, 1020w, 846w, 822w, 799w, 774w, 685w, 641w,
557w.
Method B: 5-chlorosalicylaldehyde (0.088 g, 0.560 mmol), 1,3-
diaminopropane (0.023 mL, 0.280 mmol) and Ga(acac)3 (0.102 g,
0.280 mmol) were refluxed in methanol (12 mL) for 50 min. The
resultant clear yellow solution was left undisturbed to evaporate
at room temperature. Yellow crystals of 2 were formed within four
days. The crystals were isolated by vacuum filtration, washed with
Et2O (2 ꢂ 5 mL) and dried in air. Yield 0.06 g, 41%. Anal. Calc. for
Method B: 5-bromosalicylaldehyde (0.110 g, 0.560 mmol), 1,3-
diaminopropane (0.023 mL, 0.280 mmol) and Ga(acac)3 (0.102 g,
0.280 mmol) were refluxed in methanol (15 mL) for 50 min. The
resultant clear orange solution was left undisturbed to evaporate
C22H21Cl2GaN2O4: C, 51.01; H, 4.09; N, 5.41. Found: C, 51.07; H,

80
S. Tella et al. / Polyhedron 64 (2013) 77–83
Table 2
Selected bond distances (Å) and angles (°) in 1–5.
Compound reference
1
2
3
4
5
Ga(1)–O(1)
Ga(1)–O(2)
Ga(1)–O(3)
Ga(1)–O(4)
Ga(1)–N(1)
Ga(1)–N(2)
1.994(2)
2.000(2)
1.911(2)
1.923(2)
2.059(3)
2.077(3)
1.995(2)
1.990(2)
1.910(2)
1.908(2)
2.062(3)
2.050(3)
1.992(3)
1.991(3)
1.901(3)
1.906(3)
2.070(4)
2.053(3)
1.974(1)
1.958(1)
1.930(1)
1.924(1)
2.066(1)
2.064(1)
1.994(2)
2.009(1)
1.911(2)
1.920(1)
2.058(2)
2.059(2)
O(1)–Ga(1)–O(2)
O(1)–Ga(1)–O(3)
O(1)–Ga(1)–O(4)
O(2)–Ga(1)–O(3)
O(2)–Ga(1)–O(4)
O(3)–Ga(1)–O(4)
O(1)–Ga(1)–N(1)
O(2)–Ga(1)–N(1)
O(3)–Ga(1)–N(1)
O(4)–Ga(1)–N(1)
O(1)–Ga(1)–N(2)
O(2)–Ga(1)–N(2)
O(3)–Ga(1)–N(2)
O(4)–Ga(1)–N(2)
N(1)–Ga(1)–N(2)
87.97(8)
89.82(9)
89.35(9)
91.62(1)
176.54(1)
90.55(1)
172.75(1)
84.83(1)
91.16(1)
97.82(1)
92.80(9)
89.70(1)
177.11(1)
88.25(1)
86.40(1)
88.16(1)
91.88(1)
89.09(9)
90.56(1)
177.07(1)
90.53(1)
173.17(1)
85.18(1)
89.71(1)
97.54(1)
91.96(1)
90.43(1)
176.06(1)
88.66(1)
86.58(1)
87.74(1)
89.76(1)
176.06(1)
92.32(1)
88.32(1)
90.59(1)
86.19(1)
173.65(1)
89.51(1)
97.74(1)
91.17(1)
91.60(1)
176.00(1)
88.76(1)
86.68(1)
89.90(6)
93.64(7)
87.38(6)
90.17(7)
177.13(6)
89.08(6)
175.38(7)
86.60(7)
89.39(6)
96.16(7)
91.93(7)
92.08(7)
174.00(6)
88.93(6)
85.19(7)
86.75(7)
91.95(8)
91.54(7)
92.87(9)
177.76(8)
88.63(9)
169.13(8)
82.41(7)
89.40(8)
99.27(7)
91.68(8)
91.70(9)
174.32(8)
86.90(9)
87.86(8)
GaN4O8: C, 49.01; H, 3.93; N, 10.39. Found: C, 49.06; H, 3.88; N,
10.30%. IR (KBr pellets, cmꢁ1): 1649m, 1631s, 1603m, 1558s,
1532m, 1507w, 1486m, 1440w, 1379w, 1319s, 1284w, 1246w,
1217w, 1192w, 1130w, 1102m, 1016w, 955w, 946w, 836w, 798w,
755w, 699w, 691w, 650w, 576w, 515w.
2.2.6. [Ga(acac)(5Mesalprop)] (5)
Method A: Ga(acac)3 (0.102 g, 0.280 mmol) and 5MesalpropH2
(0.087 g, 0.280 mmol) were dissolved in
a mixture of n-
hexane(12 mL) and dichloromethane (6 mL). The yellow solution
was stirred for 15 min and left undisturbed to evaporate at room
temperature. Yellow-orange crystals of 5 were formed over a per-
iod of a week. The crystals were isolated by vacuum filtration,
washed with Et2O (2 ꢂ 5 mL) and dried in air. Yield 0.07 g, 52%.
Anal. Calc. for C24H27GaN2O4: C, 60.41; H, 5.70; N, 5.87. Found: C,
60.48; H, 5.60; N, 5.90%. IR (KBr pellets, cmꢁ1): 2922m, 2866m,
1654m, 1638s, 1624s, 1617s, 1610s, 1595s, 1576m, 1570m,
1565w, 1560m, 1554m, 1543s, 1540s, 1534s, 1525s, 1522s,
1518s, 1507w, 1472s, 1387s, 1323m, 1308s, 1256w, 1212w,
1166m, 1072w, 954w, 926w, 806w, 777w.
Fig. 4. Representation of the real (36.418.53.6)-hex network (left) and the
(36.414.58)- bct-8-Pccn net (right), adopted by 1 and 5, respectively.
at room temperature. Orange crystals of 3 were formed within a
week. The crystals were isolated by vacuum filtration, washed with
Et2O (2 ꢂ 5 mL) and dried in air. Yield 0.10 g, 59%. Anal. Calc. for
C
22H21Br2GaN2O4: C, 43.54; H, 3.49; N, 4.62. Found: C, 43.50; H,
3.42; N, 4.68%. IR (KBr pellets, cmꢁ1): 1635m, 1620m, 1591m,
1525m, 1456m, 1379, 1306m, 1227w, 1172w, 1132w, 1073w,
1062w, 1020w, 846w, 822w, 799w, 774w, 685w, 641w, 557w.
Method B: 5-methylsalicylaldehyde (0.076 g, 0.560 mmol), 1,3-
diaminopropane (0.023 mL, 0.280 mmol) and Ga(acac)3 (0.102 g,
0.280 mmol) were refluxed a mixture of n-hexane (12 mL) and
dichloromethane (6 mL) for 30 min. The resultant clear yellow
2.2.5. [Ga(acac)(5NO2salprop)] (4)
Method A: Ga(acac)3 (0.102 g, 0.280 mmol) and 5NO2salpropH2
(0.104 g, 0.280 mmol) were refluxed in a mixture of ethanol
(15 mL) and dichloromethane (15 mL) for 30 min. The resultant
yellow solution was filtered and layered with n-hexane (60 mL).
X-ray quality, yellow-orange crystals of 4 were formed within a
week. The crystals were isolated by vacuum filtration, washed with
n-hexane (2 ꢂ 5 mL) and dried in air. Yield 0.11 g, 73%. Anal. Calc.
for C22H21GaN4O8: C, 49.01; H, 3.93; N, 10.39. Found: C, 49.04; H,
3.90; N, 10.32%. IR (KBr pellets, cmꢁ1): 1649m, 1631s, 1603m,
1558s, 1532m, 1507w, 1486m, 1440w, 1379w, 1319s, 1284w,
1246w, 1217w, 1192w, 1130w, 1102m, 1016w, 955w, 946w,
836w, 798w, 755w, 699w, 691w, 650w, 576w, 515w.
Method B: 5-nitrosalicylaldehyde (0.093 g, 0.560 mmol), 1,3-
diaminopropane (0.023 mL, 0.280 mmol) and Ga(acac)3 (0.102 g,
0.280 mmol) were refluxed in a mixture of ethanol (15 mL) and
dichloromethane (15 mL) for 30 min. The resultant yellow solution
was filtered and layered with n-hexane (60 mL). X-ray quality,
yellow-orange crystals of 4 were formed within a week. The crystals
were isolated by vacuum filtration, washed with n-hexane
(2 ꢂ 5 mL) and dried in air. Yield 0.09 g, 60%. Anal. Calc. for C22H21
Fig. 5. Photoluminescence spectra of the free ligands in the solid-state.

S. Tella et al. / Polyhedron 64 (2013) 77–83
81
solution was left undisturbed to evaporate at room temperature.
Yellow-orange crystals of 5 were formed within a week. The
crystals were isolated by vacuum filtration, washed with
Et2O (2 ꢂ 5 mL) and dried in air. Yield 0.05 g, 38%. Anal. Calc. for
C
24H27GaN2O4: C, 60.41; H, 5.70; N, 5.87. Found: C, 60.45; H,
5.62; N, 5.92%. IR (KBr pellets, cmꢁ1): 2922m, 2866m, 1654m,
1638s, 1624s, 1617s, 1610s, 1595s, 1576m, 1570m, 1565w,
1560m, 1554m, 1543s, 1540s, 1534s, 1525s, 1522s, 1518s,
1507w, 1472s, 1387s, 1323m, 1308s, 1256w, 1212w, 1166m,
1072w, 954w, 926w, 806w, 777w.
2.3. Single-crystal X-ray crystallography
The data collection for the single crystals of the compounds stud-
ied carried out at room temperature using Mo K
a radiation
(k = 0.71073 Å) on a SMART CCD 1 k diffractometer (for 1) and on
a Bruker SMART Apex-II diffractometer (for 2–5). Complete crystal
data and parameters for data collection and processing are reported
in Table 1.
Fig. 6. Photoluminescence spectra of complexes 1–5 in the solid-state.
The structures were solved by direct methods using SHELXS-86
[20] and refined by full-matrix least-squares techniques on F2 with
SHELXL-97 [21]. The coordinates of the metal atoms were obtained
from the initial solutions and for all other non-hydrogen atoms
found in subsequent difference Fourier syntheses. All non-hydrogen
atoms were refined by full-matrix techniques first in isotropic and
then in anisotropic approximation. Hydrogen atoms coordinates
were calculated geometrically and included into the final refine-
ment in isotropic approximation except those for the atom C(15)
in the structure of complex 4, where the disorder in the propylene
backbone made the calculation impossible for two different orienta-
tions simultaneously and the average H-atoms were found in the
difference Fourier synthesis.
3.2. Description of structures
Complexes 1–4 crystallize in the orthorhombic space group
P212121, while complex 5 crystallizes in the orthorhombic space
group Pna21. The molecular structures of 1–3 and 4–5 are shown
in Figs. 2 and 3, respectively, while selected bond distances and an-
gles for all complexes are listed in Table 2. The molecular structures
of all complexes are very similar and therefore a general description
for all complexes will follow. The GaIII ion is in a distorted octahedral
geometry being surrounded by one tetradentate chelate 5Rsal-
prop2ꢁ ligand and a bidentate chelate acacꢁ ligand. The 5Rsalprop2ꢁ
ligand is coordinated through the imine nitrogen atoms and the
deprotonated hydroxyl oxygen atoms of the phenolate groups cre-
ating three six-membered chelate rings around the GaIII atom. A
bidentate chelate acacꢁ ligand completes the octahedron and in-
creases the number of the six-membered chelate rings around the
metal atom to four. The Ga–Oacac [Ga(1)–O(1) and Ga(1)–O(2)] dis-
tances are very similar in all five complexes ranging from 1.958(1)
to 2.009(1) Å. The same is true for the Ga–Ophenolate [Ga(1)–O(3)
and Ga(1)–O(4)] and the Ga–Nimine [Ga(1)–N(1) and Ga(1)–N(2)]
distances, with the former ranging between 1.901(3) and
1.930(1) Å and the latter between 2.050(3) and 2.077(3) Å. A pro-
found structural difference at the molecular level between the five
complexes is the out of plane distance between the GaIII atom and
the mean plane of the three carbon atoms and the two oxygen atoms
of the acac– ligand. The relative distances are 0.212 Å (1), 0.013 Å
(2), 0.242 Å (3), 0.158 Å (4) and 0.581 Å (5).
3. Results and discussion
3.1. Brief synthetic comments
Complexes 1–5, can be regarded as ligand substitution products,
obtained by the reaction between Ga(acac)3 (acacH = 2,4,-pentane-
dione) and the appropriate tetradentate double Schiff base ligand
5RsalpropH2 (R = H salpropH2, R = Cl 5ClsalpropH2, R = Br 5Brsal-
propH2, R = NO2 5NO2salpropH2 and R = Me 5MesalpropH2). This
procedure involves the synthesis and isolation of the double Schiff
base ligands prior to the reaction with the gallium salt. Alterna-
tively, all complexes can be synthesized directly from the 1:2:1
reaction between 1,3-diaminopropane, the appropriate 5Rsalicylal-
dehyde and Ga(acac)3. Eq. (1) summarizes the preparation of the
complexes
R
R
O
O
O
O
solvent
-2H2O
H2N
NH2
+
Ga
O
+
2
CH3
HC
O
O
Ga
O
CH
OH
O
C
O
N
CH2
CH2
CH2
+
2
C
O
O
O
N
CH3
CH
R
R
O
Ga
O
O
O
O
solvent
+
N
N
O
C
H
C
H
R
OH
OH
[Ga(acac)(5Rsalprop)]

82
S. Tella et al. / Polyhedron 64 (2013) 77–83
Besides the structural similarities at the molecular level, the
affect the electronic properties of the both the free ligands and the
respective complexes and modulates the emission maxima of the
materials in the solid-state.
peripheral substitution at the salicylidene rings has largely affected
the supramolecular structures of the complexes. All complexes ex-
hibit two C–Hꢀ ꢀ ꢀO intermolecular interactions between one of the
imine carbon atoms and one of the phenolate oxygen atoms and
several C–Hꢀ ꢀ ꢀpphenolate interactions (Tables S1–S5). Complex 1
interacts with eight neighboring molecules creating a three-
dimensional (36.418.53.6)-hex network (Fig. 4) through two
4. Conclusions
A family of mononuclear Ga(III) complexes based on N,N0-bis(sal-
icylidene)propane-1,3-diamine (salpropH2) and its substituted
derivatives with EDGs or EWGs at the fifth position of the salicylid-
ene rings has been synthesized and structurally characterized. All
complexes comprise an octahedral GaIII atom being surrounded by
a tetradentate, tris-chelate 5Rsalprop2– (R = H, Cl, Br, Me or NO2)
ligand and a bidentate chelate acac– ligand. Both free ligands and
complexes display photoluminescence in the solid-state in the vis-
ible region. The peripheral substitution of the salpropH2 ligand with
EDGs or EWGs modulates the emission maxima of the free ligands
and the complexes with the latter displaying hypsochromic shifts
with respect to the emission of the free ligands.
C–Hꢀ ꢀ ꢀOphenolate (one unique) and six C–Hꢀ ꢀ ꢀ
pphenolate (three unique)
interactions. Complexes 2 and 4 are connected to six neighboring
molecules through two C–Hꢀ ꢀ ꢀOphenolate (one unique) and four
C–Hꢀ ꢀ ꢀpphenolate (two unique) interactions, each creating a regular
two-dimensional 36 network, complex 3 interacts with four of its
neighbors through two C–Hꢀ ꢀ ꢀOphenolate (one unique) and two
C–Hꢀ ꢀ ꢀpphenolate (one unique) interactions to create a regular two-
dimensional 44 net (square-grid), while complex 5 connects to eight
neighbors through two C–Hꢀ ꢀ ꢀOphenolate (one unique) and six
C–Hꢀ ꢀ ꢀpphenolate (three unique) interactions to create a three-
dimensional (36.414.58)-bct-8-Pccn net (Fig. 4).
Acknowledgements
3.3. Thermal stability
The Special Account for Research Grants (SARG) of the National
and Kapodistrian University of Athens and the Bodossaki Founda-
tion are gratefully acknowledge for partial support of this work.
Thermogravimetric analysis (Fig. S1) reveals that complex 1
looses the solvate water molecule and degrades above 150 °C,
complex 5 is also stable up to ꢃ150 °C, while complexes 2–4 are
stable up to ꢃ225 °C.
Appendix A. Supplementary data
3.4. Solid-state emission
CCDC 920125-920129 contain the supplementary crystallo-
graphic data for 1–5. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or e-mail: de-
posit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.poly.2013.02.057.
Gallium complexes with Schiff bases bearing aromatic groups
are known to exhibit interesting luminescence properties [15–17].
The solid-state emission spectra of the five free Schiff base ligands
and complexes 1–5 are shown in Figs. 5 and 6, respectively. The
emission spectra were obtained after excitation at the peak maxi-
mum of the relevant excitation spectrum, except for the spectrum
of 5MesalpropH2, which was excited at 280 nm. The excitation
spectra of the ligands and complexes are shown in Figs. S2 and S3,
respectively. SalpropH2 exhibits an emission band with a maximum
at 495 nm. By attaching the EDG methyl groups at the fifth position
of the salicylidene rings of the ligand a hypsochromic shift of
ꢃ15 nm of the emission maximum is observed. The exact opposite
is observed when the EWG –Cl or –Br are attached on the same po-
sition of the ligand; ligands 5ClsalpropH2 and 5BrsalpropH2 dis-
played emission maxima at 510 nm and 504 nm, respectively,
which are 15 nm and 9 nm bathochromically shifted with respect
to the salpropH2 emission. The presence of –NO2 groups, which
are EWG inductively and EWG by resonance, on the fifth position
of the salicylidene rings results in even larger bathochromic shift
of the emission maximum by 102 nm with respect to the salpropH2
emission.
References
[1] A.R. Barron, A.N. Maclnnes, in: R.B. King (Ed.), Encyclopedia of Inorganic
Chemistry, vol. 3, Wiley, New York, 1994, pp. 1249–1269.
[2] F.A. Ponce, D.B. Bour, Nature 386 (1997) 351.
[3] C.W. Tang, S.A. Van Slyke, Appl. Phys. Lett. 51 (1987) 913.
[4] C.H. Chen, J.M. Shi, Coord. Chem. Rev. 171 (1998) 161.
[5] S. Wang, Coord. Chem. Rev. 215 (2001) 79.
[6] M. Cölle, J. Gmeiner, W. Milius, H. Hillebrecht, W. Brütting, Adv. Funct. Mater.
13 (2003) 108.
[7] P.E. Burrows, L.S. Sapochak, D.M. McCarty, S.R. Forrest, M.E. Thompson, Appl.
Phys. Lett. 64 (1994) 2718.
[8] Y. Wang, W. Zhang, Y. Li, L. Ye, G. Yang, Chem. Mater. 11 (1999) 530.
[9] A. Elschner, H.W. Heuer, F. Jonas, S. Kirchmeyer, R. Wehrmann, K. Wussow,
Adv. Mater. 13 (2001) 1811.
[10] R. Pohl, P. Anzenbacher Jr., Org. Lett. 5 (2003) 2769.
[11] V.A. Montes, G. Li, R. Pohl, J. Shinar, P. Anzenbacher Jr., Adv. Mater. 16 (2004)
2001.
The maxima in the emission spectra of complexes 1–5 are less
broad and hypsochromically shifted compared to that of the
respective free ligands. Since the emission of the complexes is li-
gand-based [22–26] mainly originating from the iminophenolato
chromophore, the role of the GaIII atom is to impose conforma-
tional rigidity, extending the conjugation of the ligand, thus
restricting energy loss via non-radiative decay [25,26]. The unsub-
stituted complex 1 displayed an emission maximum at 442 nm,
which is below the blue light region. All substituted complexes
with either an EDG (5) or an EWG (2–4) display bathochromically
shifted emission with respect to complex 1. Complexes 2, 3 and 5
exhibit emission maxima at 450 nm, 451 nm and 459 nm, respec-
tively, which are all within the blue light region, while complex
4 displays an emission maximum at 589 nm which is at the border
between the yellow and orange light regions. The substitution of
the salicylideno rings of the ligands with either EWG or EDG does
[12] C. Perez-Bolivar, S.Y. Takizawa, G. Nishimura, V.A. Montes, P. Anzenbacher Jr.,
Chem. Eur. J. 17 (2011) 9076.
[13] L.S. Sapochak, A. Padmaperuma, N. Washton, F. Endrino, G.T. Schmett, J.
Marshall, D. Fogarty, P.E. Burrows, S.R. Forrest, J. Am. Chem. Soc. 123 (2001)
6300.
[14] J. Qiao, L.D. Wang, L. Duan, Y. Li, D.Q. Zhang, Y. Qiu, Inorg. Chem. 43 (2004)
5096.
[15] A. Kagkelari, G.S. Papaefstathiou, C.P. Raptopoulou, T.F. Zafiropoulos,
Polyhedron 28 (2009) 3279.
[16] A. Kagkelari, V. Bekiari, E. Stathatos, G.S. Papaefstathiou, C.P. Raptopoulou, T.F.
Zafiropoulos, P. Lianos, J. Lumin. 129 (2009) 578.
[17] N. Kushwah, M.K. Pal, A. Wadawale, V. Sudarsan, D. Manna, T.K. Ghanty, V.K.
Jain, Organometallics 31 (2012) 3836.
[18] C. Birnara, V.G. Kessler, G.S. Papaefstathiou, Polyhedron 28 (2009) 3291.
[19] M.S. Ibrahim, S.E.d.H. Etaiw, Synth. React. Inorg. Met. Org. Chem. 34 (2004)
629.
[20] G.M. Sheldrick, SHELXS-86, University of Göttingen, Germany, Structure Solving
Program, 1986.
[21] G.M. Sheldrick, SHELXL-97, University of Göttingen, Germany, Program for the
Refinement of Crystal Structures from Diffraction Data, 1997.

S. Tella et al. / Polyhedron 64 (2013) 77–83
83
[22] T. Kawasaki, T. Kamata, H. Ushijima, S. Murata, F. Mizukami, Y. Fujii, Y. Usui,
Mol. Cryst. Liq. Cryst. 286 (1996) 257.
[25] Q. Shi, L. Sheng, K. Ma, Y. Sun, X. Cai, R. Liu, S. Wang, Inorg. Chem. Commun. 12
(2009) 255.
[23] X.-X. Zhou, H.-C. Fang, Y.-Y. Ge, Z.-Y. Zhou, Z.-G. Gu, X. Gong, G. Zhao, Q.-G.
Zhan, R.-H. Zeng, Y.-P. Cai, Cryst. Growth Des. 10 (2010) 4014.
[24] M. Maiti, D. Sadhukhan, S. Thakurta, S. Roy, G. Pilet, R.J. Butcher, A. Nonat, L.J.
Charbonniere, S. Mitra, Inorg. Chem. 51 (2012) 12176.
[26] D. Sadhukhan, A. Ray, G. Rosair, L. Charbonnière, S. Mitra, Bull. Chem. Soc. Jpn.
84 (2011) 211.