Fluorescent aluminum chelate complexes as modified precursors for nano-structured alumina

Article abstract of DOI:10.1080/00958972.2017.1279280

A series of new mononuclear heteroleptic derivatives of aluminum(III), {[(CH₃COCHCOCH₃)AlL] (1 and 4)}, {[(C₆H₅COCHCOC₆H₅)AlL] (2, 5, and 7)}, and {[(C₉H₆NO)AlL] (3 and 6)}, have been synthesized by reacting Al(OPrⁱ)₃ with tridentate Schiff base H₂L^x (H₂L¹?=?C₁₃H₁₀BrNO₂; H₂L²?=?C₁₄H₁₃NO₃; H₂L³?=?C₁₇H₁₃NO₂) and β-diketone/8-hydroxyquinoline (β-diketone?=?acetylacetone/dibenzoylmethane) in 1 : 1 : 1 stoichiometry using anhydrous benzene and ethanol. All the complexes were characterized by elemental analysis, FTIR, and NMR (¹H and ¹³C) spectral studies. Molecular structures obtained from single-crystal XRD of aqua 1 (1a) and DMSO coordinated 2 (2a) authenticate their existence. Further, nanostructured α-alumina was synthesized from 1 by well-established sol–gel method and was characterized by powder XRD, TEM, and EDX analyses.

Full text of DOI:10.1080/00958972.2017.1279280

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Fluorescent aluminium chelate complexes as
modified precursors for nano-structured alumina
Vuppalapati Giri Prasanth, Ravindranath S. Rathore, Madhvesh Pathak &
Kulathu Iyer Sathiyanarayanan
To cite this article: Vuppalapati Giri Prasanth, Ravindranath S. Rathore, Madhvesh Pathak
&
Kulathu Iyer Sathiyanarayanan (2017): Fluorescent aluminium chelate complexes as
modified precursors for nano-structured alumina, Journal of Coordination Chemistry, DOI:
0.1080/00958972.2017.1279280
1
To link to this article: http://dx.doi.org/10.1080/00958972.2017.1279280
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Date: 17 January 2017, At: 22:06

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://dx.doi.org/10.1080/00958972.2017.1279280
Fluorescent aluminium chelate complexes as modified precursors for nano-
structured alumina
VUPPALAPATI GIRI PRASANTH†, RAVINDRANATH S. RATHORE‡, MADHVESH PATHAK*† and
#
KULATHU IYER SATHIYANARAYANAN †
†
‡
School of Advanced Sciences, VIT University, Vellore 632014, Tamilnadu, India
Centre for Biological Sciences, School of Earth, Biological and Environmental Sciences,
Central University of South Bihar, Patna 800014, India
A series of new mononuclear heteroleptic derivatives of aluminium(III),
{
{
[(CH COCHCOCH )AlL] (1 and 4)}, {[(C H COCHCOC H )AlL] (2, 5 and 7)} and
3
3
6
5
6
5
i
[(C H NO)AlL] (3 and 6)}, have been synthesized by reacting Al(OPr ) with tridentate
9
6
3
x
1
2
3
Schiff base H L (H L = C H BrNO ; H L = C H NO ; H L = C H NO ) and
2
2
13 10
2
2
14 13
3
2
17 13
2
β-diketone/8-hydroxyquinoline (β-diketone = acetylacetone/dibenzoylmethane) in 1:1:1
stoichiometry using anhydrous benzene and ethanol. All the complexes were characterized by
1
13
elemental analysis, FTIR and NMR ( H and C) spectral studies. Molecular structures
obtained from single crystal XRD of aqua 1 (1a) and DMSO coordinated 2 (2a) authenticate
their existence. Further, nano-structured α-alumina was synthesized from 1 by well-
established sol-gel method and was characterized by powder XRD, TEM and EDX analyses.
Keywords: Aluminium; Metallo-organic complex; Schiff bases; β-Diketones; Alumina
1
. Introduction
Alumina is one of the best ceramic materials used predominantly in insulators, composites,
grinding materials, lining material of furnaces, laboratory instruments, catalysis, orthopedics,
*
Corresponding author. Email: madhveshpathak@vit.ac.in (M. Pathak)
#
Co-corresponding author. Email: sathiya_kuna@hotmail.com (K.I. Sathiyanarayanan)
1

paints, sensors, cosmetics, and glasses. This is due to its mechanical strength, thermal
conductivity, band gap, heat resistance, corrosion resistance, wither resistance, melting point,
chemical inertness and bio-compatibility [1-6]. The enhanced thermal, optical, mechanical
and chemical properties of nano-structured alumina are appropriate for the above applications
[
7-11].
Aluminium alkoxides are usually employed as molecular precursors for nano alumina
through sol-gel processing. As a result of their higher Lewis acidity and tendency to form
complexes with coordination numbers higher than their valency, alkoxides of aluminium are
extremely susceptible to hydrolysis and produce precipitates with ill-defined oxo/hydroxo
framework instead of colloidal gels upon reaction with water [12]. This results in Al O with
2
3
higher particle size. Aluminium alkoxides with retarded moisture sensitivity could be
synthesized by substituting one or more easily hydrolysable alkoxy groups on aluminium
with hydrolytically stable chelating agents [13-15]. The bi- or multidentate ligands induce
stability against moisture to the modified aluminium alkoxide through chelation and by
occupying the additional coordination sites on the aluminium center. The controlled
hydrolysis of these aluminium alkoxides modified with chelating agents by employing the
well-renowned sol-gel technique results in nano-structured alumina. Several ligands such as
β-diketones, β-ketoesters, carboxylic acids, amino alcohols, diols, oximes and Schiff bases
have already been used as modifiers [16-19]. There are very few reports on modified
aluminium alkoxides being used as precursors for nano alumina. Very recently, Sanwaria
et al. reported the synthesis of nano alumina from 8-hydroxyquinoline and salicylaldehyde
modified aluminium isopropoxide [15, 20]. In our previous attempts, we modified the
hydrolytic stability of zirconium isopropoxide using β-diketones, tridentate Schiff bases and
tetradentate salen ligands [19, 17].
Encouraged by the aforementioned achievements, we investigate new modifications
of aluminium triisopropoxide by introducing tridentate Schiff bases and bidentate β-
diketones/8-hydroxyquinoline to obtain metallo-organic derivatives of aluminium(III).
Consequently, 1 (described herewith) has emerged as an effective precursor to the synthesis
of nano-structured alumina.
2. Experimental
2
.1. General
All the derivatives were synthesized under stringent anhydrous conditions. Reagents and
solvents used were dried according to conventional methods [20]. Aluminium(III)
2

isopropoxide, 8-hydroxyquinoline, acetylacetone and dibenzoylmethane were procured from
Sigma Aldrich. Melting points of new complexes were ensured from Elchem digital melting
-1
point apparatus. Infrared spectra (4,000–400 cm ) were obtained from a SHIMADZU IR
affinity 1 spectrometer. UV-Vis spectra were recorded on a JASCO V-670 UV-Vis
1
13
spectrophotometer. NMR ( H and C) spectra were collected from a Bruker AVANCE III
00 spectrometer in DMSO d solution at 400 and 100.65 MHz frequency with TMS as an
4
6
internal standard. Powder XRD data were obtained from an X-ray BRUKER D8 Advance
X-ray diffractometer. TEM analysis was carried out using a JEOL JEM 2100 high resolution
transmission electron microscope. Fluorescence spectra of the complexes were measured in
DMSO using a Hitachi F-7000 FL spectrophotometer. Elemental analyses of complexes were
performed on an Elementar Vario EL III instrument.
1
2
3
2
.2. Synthesis of Schiff base ligands H L , H L and H L
2
2
2
1
2
3
Tridentate Schiff base ligands H L , H L and H L were prepared by treating 2-aminophenol
2
2
2
with 5-bromosalicylaldehyde, 3-methoxysalicylaldehyde and 2-hydroxy-1-naphthaldehyde in
equimolar ratios employing methanol as solvent [21-26].
2
2
.3. Synthesis of complexes
.3.1. Synthesis of [(CH COCHCOCH )Al(L )(EtOH)] (1). Ethanolic Schiff base H L
1
1
3
3
2
(2.92 g, 10 mmol), acetylacetone (1.00 g, 10 mmol) and aluminium(III) isopropoxide (2.04 g,
10 mmol) were reacted in 1:1:1 stoichiometry using benzene as solvent. The contents were
refluxed on a fractionating column for 2 h and the isopropanol liberated during the course of
the reaction was fractionated out along with ethanol and benzene. Excess solvent was
removed under vacuum and the resultant reddish brown product was washed repeatedly with
1
n-hexane. (Yield, 4.53 g, 98.0%). mp = 234-236 °C. H NMR (400 MHz, DMSO d , 25 °C):
6
δ (ppm) 1.05-1.09 (t, 3 H, J = 8.0 Hz, CH3 of ethanol), 1.70 (s, 3 H, CH3 of acetylacetone), 2.02 (s,
3
H, CH3 of acetylacetone), 3.44-3.49 (m, 2 H, CH2 of ethanol), 4.37-4.40 (t, 1 H, J = 4 Hz,
OH of ethanol), 5.51 (s, 1 H, CH of acetylacetone), 6.52-6.58 (m, 3 H, Ar-H), 6.99-7.03 (m, 1 H,
Ar-H), 7.29-7.31 (d, 1 H, J = 8.0 Hz, Ar-H), 7.54-7.55 (d, 1 H, J = 8.0 Hz, Ar-H), 7.62-7.63
1
3
(
d, 1 H, J = 4.0 Hz, Ar-H), 8.86 (s, 1 H, N=CH). C NMR (100.65 MHz, DMSO d , 25 °C):
6
δ (ppm) 18.53, 26.44, 56.02, 100.78, 104.70, 114.23, 114.65, 117.30, 121.70, 123.48, 129.66,
133.19, 135.13, 136.12, 154.36, 160.01, 163.97, 189.57, 190.94. FTIR (solid KBr) ν =
3

3053.32, 2966.52, 1614.42, 1583.56, 1540.62, 1072.42, 729.09, 638.44, 540.07. Anal. Calcd
for C H AlBrNO : C, 51.96; H, 4.58; N, 3.03%. Found: C, 51.79; H, 4.63; N, 3.10%.
2
0
21
5
Because of similarity in the synthetic process, identical route has been adopted to
make the products (2-7).
1
1
2
.3.2. Synthesis of [(C H COCHCO C H )Al(L )(EtOH)] (2). Ethanolic Schiff base H L
6
5
6
5
2
(
(
(
(
2.92 g, 10 mmol), dibenzoylmethane (2.24 g, 10 mmol) and aluminium(III) isopropoxide
1
2.04 g, 10 mmol). Stoichiometry: 1:1:1. (Yield, 5.74 g, 97.9%). mp = 219-221 °C. H NMR
400 MHz, DMSO d , 25 °C): δ (ppm) 1.05-1.09 (t, 3 H, J = 8.0 Hz, CH3 of ethanol), 3.47-3.49
6
m, 2 H, CH2 of ethanol), 4.37-4.40 (t, 1 H, J = 4 Hz, OH of ethanol), 6.52-6.59 (m, 3 H, Ar-H),
6
.99-7.03 (t, 1 H, J = 8 Hz, Ar-H), 7.10 (s, 1 H, Ar-H), 7.26-7.28 (d, 1 H, J = 8.0 Hz, Ar-H),
.35-7.39 (t, 2 H, J = 8.0 Hz, Ar-H), 7.46-7.50 (t, 1 H, J = 8.0 Hz, Ar-H), 7.57-7.61 (t, 2 H,
7
J = 8.0 Hz, Ar-H), 7.64-7.66 (d, 2 H, J = 8.0 Hz, Ar-H), 7.69-7.70 (d, 1 H, J = 4.0 Hz, Ar-H),
.79-7.81 (d, 2 H, J = 8.0 Hz, Ar-H), 8.26-8.28 (d, 2 H, J = 8.0 Hz, Ar-H), 9.02 (s, 1 H,
7
1
3
N=CH). C NMR (100.65 MHz, DMSO d , 25 °C): δ (ppm) 18.55, 56.02, 93.58, 104.84,
6
1
14.41, 114.70, 117.29, 121.78, 123.49, 127.43, 127.84, 128.43, 128.59, 129.74, 132.16,
1
32.24, 133.34, 135.20, 136.19, 137.35, 137.46, 154.50, 160.02, 164.03, 182.96, 183.77.
FTIR (solid KBr) ν = 3059.10, 2960.73, 1581.63, 1525.69, 1024.20, 754.17, 655.8, 615.29,
5
6
6
18.85. FTIR (solid KBr) ν = 3043.67, 2960.73, 1608.63, 1583.32, 1526.48, 1089.83, 768.71,
34.85, 538.85. Anal. Calcd for C H AlBrNO : C, 61.45; H, 4.30; N, 2.39%. Found: C,
3
0
25
5
1.17; H, 4.28; N, 2.31%.
1
1
2
1
1
.3.3. Synthesis of [(C H NO)Al(L )(EtOH)] (3). Ethanolic Schiff base H L (2.92 g,
9
6
2
0 mmol), 8-hydroxyquinoline (1.45 g, 10 mmol) and aluminium(III) isopropoxide (2.04 g,
1
0 mmol). Stoichiometry: 1:1:1. (Yield, 4.95 g, 98.2%). mp = 242-244 °C. H NMR
(
400 MHz, DMSO d , 25 °C): δ (ppm) 1.08-1.12 (t, 3 H, J = 8.0 Hz, CH3 of ethanol), 3.47-3.50
6
(m, 2 H, CH2 of ethanol), 4.41-4.43 (t, 1 H, J = 4 Hz, OH of ethanol), 6.41-6.45 (t, 2 H, J = 8 Hz,
Ar-H), 6.59-6.63 (t, 1 H, J = 8 Hz, Ar-H), 6.88-6.90 (d, 1 H, J = 8 Hz, Ar-H), 6.99-7.03 (t, 1
H, J = 8 Hz, Ar-H), 7.10-7.12 (d, 1 H, J = 8 Hz, Ar-H), 7.26-7.28 (d, 1 H, J = 8.0 Hz, Ar-H),
7.38-7.41 (m, 1 H, Ar-H), 7.50-7.54 (t, 1 H, J = 8.0 Hz, Ar-H), 7.73-7.74 (d, 1 H, J = 4.0 Hz,
Ar-H), 7.76 (s, 1 H, Ar-H), 7.95-7.96 (d, 1 H, J = 8.0 Hz, Ar-H), 8.35-8.37 (d, 1 H, J = 8.0
1
3
Hz, Ar-H), 9.21 (s, 1 H, N=CH). C NMR (100.65 MHz, DMSO d , 25 °C): δ (ppm) 18.54,
6
5
6.03, 105.02, 110.85, 111.18, 114.65, 114.83, 117.50, 121.55, 121.79, 123.54, 129.11,
4

1
1
6
5
29.95, 130.22, 133.19, 135.41, 136.56, 138.15, 138.24, 141.98, 156.44, 159.50, 159.58,
64.15. FTIR (solid KBr) ν = 3059.63, 2962.84, 1609.47, 1591.41, 1523.08, 1072.42, 752.53,
80.39, 540.70. Anal. Calcd for C H AlBrN O : C, 56.82; H, 3.97; N, 5.52%. Found: C,
2
4
20
2
4
7.10; H, 3.87; N, 5.66%.
2
2
2
.3.4. Synthesis of [(CH COCHCOCH )Al(L )(EtOH)] (4). Ethanolic Schiff base H L
3
3
2
(2.43 g, 10 mmol), acetylacetone (1.00 g, 10 mmol) and aluminium(III) isopropoxide (2.04 g,
1
1
0 mmol). Stoichiometry: 1:1:1. (Yield, 3.94 g, 95.3%). mp = 252-254 °C. H NMR
(
400 MHz, DMSO d , 25 °C): δ (ppm) 1.05-1.09 (t, 3 H, J = 8.0 Hz, CH3 of ethanol), 1.70 (s,
6
3
H, CH3 of acetylacetone), 2.02 (s, 3 H, CH3 of acetylacetone), 3.42-3.48 (m, 2 H, CH2 of ethanol), 3.69 (s,
3
H, OCH ), 4.36-4.38 (t, 1 H, J = 4 Hz, OH of ethanol), 5.51 (s, 1 H, CH of acetylacetone), 6.49-6.56
3
(
m, 3 H, Ar-H), 6.89-6.91 (d, 1 H, Ar-H), 6.96-7.00 (t, 1 H, J = 8.0 Hz, Ar-H), 7.06-7.08 (d,
H, J = 8.0 Hz, Ar-H), 7.57-7.59 (d, 1 H, J = 8.0 Hz, Ar-H), 8.85 (s, 1 H, N=CH). C NMR
1
3
1
(
100.65 MHz, DMSO d , 25 °C): δ (ppm) 18.54, 26.47, 56.01, 56.03, 100.76, 113.84, 113.97,
6
1
14.37, 116.95, 117.04 119.85, 126.10, 129.04, 133.47, 150.87, 155.69, 156.32, 159.88.
FTIR (solid KBr) ν = 3047.30, 2967.23, 1609.52, 1591.27, 1523.94, 1123.84, 711.73, 675.09,
575.85. Anal. Calcd for C H AlNO : C, 61.01; H, 5.85; N, 3.39%. Found: C, 60.08; H,
21 24 6
5.74; N, 3.47%.
2
2
2
.3.5. Synthesis of [(C H COCHCO C H )Al(L )(EtOH)] (5). Ethanolic Schiff base H L
6
5
6
5
2
(
(
(
(
(
(
2
2.43 g, 10 mmol), dibenzoylmethane (2.24 g, 10 mmol) and aluminium(III) isopropoxide
1
2.04 g, 10 mmol). Stoichiometry: 1:1:1. (Yield, 5.25 g, 97.7%). mp = 225-227 °C. H NMR
400 MHz, DMSO d , 25 °C): δ (ppm) 1.05-1.08 (t, 3 H, J = 8.0 Hz, CH3 of ethanol), 3.45-3.46
6
d, 2 H, J = 8.0 Hz, CH2 of ethanol), 3.60 (s, 3 H, OCH ), 4.38 (s, 1 H, OH of ethanol), 6.51-6.57
3
m, 3 H, Ar-H), 6.86-6.88 (d, 1 H, J = 8 Hz, Ar-H), 6.95-6.99 (t, 1 H, J = 8 Hz, Ar-H), 7.10
s, 1 H, Ar-H), 7.13-7.15 (d, 1 H, J = 8.0 Hz, Ar-H), 7.47-7.69 (m, 7 H, Ar-H), 7.78-7.80 (d,
1
3
H, J = 8.0 Hz, Ar-H), 8.27-8.29 (d, 2 H, J = 8.0 Hz, Ar-H), 9.01 (s, 1 H, N=CH). C NMR
(
100.65 MHz, DMSO d , 25 °C): δ (ppm) 18.54, 55.91, 56.01, 79.16, 93.53, 113.98, 114.14,
6
1
14.41, 116.80, 117.01, 119.93, 126.09, 127.42, 127.83, 128.30, 128.41, 128.57, 129.10,
32.10, 133.63, 137.48, 150.87, 155.82, 156.28, 159.91, 182.95, 183.61. FTIR (solid KBr)
1
ν = 3043.83, 2942.65, 1611.28, 1588.92, 15425.47, 1074.18, 766.15, 642.83, 542.29. Anal.
Calcd for C H AlNO : C, 69.27; H, 5.25; N, 2.61%. Found: C, 69.48; H, 5.63; N, 2.53%.
3
1
28
6
5

2
2
2
1
1
.3.6. Synthesis of [(C H NO)Al(L )(EtOH)] (6). Ethanolic Schiff base H L (2.43 g,
9
6
2
0 mmol), 8-hydroxyquinoline (1.45 g, 10 mmol) and aluminium(III) isopropoxide (2.04 g,
1
0 mmol). Stoichiometry: 1:1:1. (Yield, 4.42 g, 96.5%). mp = 246-248 °C. H NMR
(
400 MHz, DMSO d , 25 °C): δ (ppm) 1.05-1.08 (t, 3 H, J = 8.0 Hz, CH3 of ethanol), 3.42-3.48
6
(
m, 5 H, CH & OCH3 singlet merged with multiplet), 4.37-4.39 (t, 1 H, J = 4 Hz, OH of ethanol), 6.36-
2
6.38 (d, 1 H, J = 8 Hz, Ar-H), 6.52-6.57 (q, 2 H, J = 4 Hz, Ar-H), 6.80-6.82 (d, 1 H, J = 8 Hz,
Ar-H), 6.85-6.87 (d, 1 H, J = 8 Hz, Ar-H), 6.92-6.95 (t, 1 H, J = 8 Hz, Ar-H), 7.07-7.09 (d, 1
H, J = 8 Hz, Ar-H), 7.11-7.13 (d, 1 H, J = 8.0 Hz, Ar-H), 7.35-7.38 (q, 1 H, J = 4 Hz, Ar-H),
7
.48-7.52 (t, 1 H, J = 8.0 Hz, Ar-H), 7.73-7.75 (d, 1 H, J = 8.0 Hz, Ar-H), 7.90-7.91 (d, 1 H,
1
3
J = 4.0 Hz, Ar-H), 8.32-8.34 (d, 1 H, J = 8.0 Hz, Ar-H), 9.17 (s, 1 H, N=CH). C NMR
100.65 MHz, DMSO d , 25 °C): δ (ppm) 18.54, 55.24, 56.01, 79.16, 110.61, 111.09, 114.13,
(
6
114.53, 115.86, 117.22, 119.48, 121.76, 125.80, 129.15, 129.32, 130.23, 133.46, 138.14,
138.24, 141.93, 150.81, 156.21, 157.68, 159.39, 159.72. FTIR (solid KBr) ν = 3064.38,
2953.83, 1604.42, 1581.71, 1532.49, 1088.48, 739.86, 653.75, 547.83. Anal. Calcd for
C H AlN O : C, 65.50; H, 5.06; N, 6.11%. Found: C, 64.92; H, 5.03; N, 6.38%.
25
23
2
5
3
3
2
.3.7. Synthesis of [(C H COCHCO C H )Al(L )(EtOH)] (7). Ethanolic Schiff base H L
6
5
6
5
2
(
(
(
(
2.63 g, 10 mmol), dibenzoylmethane (2.24 g, 10 mmol) and aluminium(III) isopropoxide
1
2.04 g, 10 mmol). Stoichiometry: 1:1:1. (Yield, 5.48 g, 98.3%). mp = 233-235 °C. H NMR
400 MHz, DMSO d , 25 °C): δ (ppm) 1.05-1.08 (t, 3 H, J = 8.0 Hz, CH3 of ethanol), 3.42-3.48
6
m, 2 H, CH2 of ethanol), 4.36-4.39 (t, 1 H, J = 4 Hz, OH of ethanol), 6.54-6.56 (d, J = 8 Hz, 1 H,
Ar-H), 6.57-6.61 (t, 1 H, J = 8 Hz, Ar-H), 6.83-6.85 (d, J = 8 Hz, 1 H, Ar-H), 6.96-7.00 (t,
H, J = 8 Hz, Ar-H), 7.12 (s, 1 H, Ar-H), 7.26-7.37 (m, 3 H, Ar-H), 7.44-7.77 (m, 9 H,
Ar-H), 7.97-7.99 (d, 1 H, J = 8.0 Hz, Ar-H), 8.30 (s, 2 H, Ar-H), 8.58-8.60 (d, 1 H, J =
1
1
3
8
1
1
.0 Hz, Ar-H), 9.76 (s, 1 H, N=CH). C NMR (100.65 MHz, DMSO d , 25 °C): δ (ppm)
6
8.54, 56.00, 93.58, 109.65, 114.38, 114.77, 116.76, 119.85, 122.06, 124.88, 126.06, 127.45,
28.31, 128.60, 128.73, 132.15, 134.06, 134.70, 135.44, 137.54, 150.18, 159.59, 166.48.
FTIR (solid KBr) ν = 3062.74, 2948.18, 1603.15, 1587.06, 1086.24, 751.22, 662.58, 556.94.
Anal. Calcd for C H AlNO : C, 73.24; H, 5.06; N, 2.51%. Found: C, 73.18; H, 5.13; N,
3
4
28
5
2.32%.
6

2
.4. X-ray crystallography
Single crystals of 1a (C H AlBrNO ·C H N) and 2a (C H D AlBrNO S·2(C D OS)) were
1
8
17
5
2
3
30 19
6
5
2
6
grown from 1 (C H AlBrNO ·C H OH) and 2 (C H AlBrNO ·C H OH) in acetonitrile -
1
8
15
4
2
5
28 19
4
2
5
THF mixture and DMSO d , respectively. XRD data were collected on a single-crystal
6
Bruker SMART APEX2 diffractometer [27]. The structure was solved by applying the direct
phase-determination technique using SHELXS-86 and refined by full-matrix least squares on
2
F using SHLEXL-13 [28, 29]. Polar hydrogens were refined isotropically while remaining
hydrogens have been fixed stereochemically and refined with the riding options. The
2
distances of hydrogens are aromatic/sp C-H = 0.93 Å, methyl C-H = 0.96 Å, O-H = 0.75(3) -
0.88(4) Å and Uiso = 1.2/1.5 (for methyl hydrogens). Ueq(parent) and hydrogens attached to
water molecules were isotropically refined. In the final cycle of refinement, reflections (011)
and (100) in 1a and reflections (001), (100) and (010) in 2a were omitted as they were
severely affected by beam-stop. Essential crystal data are listed in table 1. Crystallographic
data have been deposited at the Cambridge Crystallographic Data Center with entry numbers
CCDC 1027480 (1a) and CCDC 1027481 (2a). Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44
(0)1223 336033 or E-mail: deposit@ccdc.cam.ac.uk).
2
.5. Synthesis of nano Al O from 1 by sol-gel
2
3
Four grams of 1 was weighed and dissolved in hot anhydrous ethyl alcohol and 5 ml conc.
HCl was added while stirring the solution. Further, a drop of distilled H O - C H OH mixture
2
2
5
in 1:5 ratio was added to the resultant fluorescent green solution. No instant formation of gel
was observed. Excess distilled water along with ethanol was added in small lots sporadically
for 8 h with continuous stirring. In order to complete the hydrolysis of complex, stirring of
the reaction mixture was continued for 48 h. The fluorescent green gel obtained was heated in
a preheated oven (above 100 °C) for 10 h and the resultant xerogel was ground to give a
creamy white powder. The powder produced was repeatedly washed with water and acetone
to remove organic and inorganic impurities. The resultant powder was sintered in a muffle
furnace at 1100 °C for 4 h to obtain white nano alumina.
3
3
. Results and discussion
.1. Synthesis and characterization
i
The one pot protonolysis reaction of Al(OPr ) with relevant Schiff bases and
3
β-diketonates/8-hydroxyquinoline in 1:1:1 molar ratio using anhydrous mixture of ethanol
7

and benzene yielded the desired derivatives (1-7) (scheme 1). The liberated alcohol (along
with benzene) during the course of reaction was continuously ejected out of the fractionating
column to push the reaction in the forward direction [30]. The reddish-brown crude products
obtained were washed repeatedly with dry chloroform to remove unreacted starting materials.
Complexes were readily soluble in DMSO and poorly soluble in common organic solvents
like dichloromethane, chloroform and toluene. All the derivatives were sparingly soluble in
hot acetonitrile whereas 1 was fairly soluble in hot ethanol. Complexes 1-7 have been
1
13
characterized by elemental analysis, UV-Vis, FTIR and NMR ( H and C) spectral studies.
Scheme 1. Synthetic scheme for heteroleptic derivatives (1-7) of aluminium(III).
Our efforts to produce crystals of 1 in moisture-free environment were unsuccessful.
Later, 1 was boiled in acetonitrile and the resulting solution was filtered. The filtrate obtained
was subjected for slow evaporation in ambient condition to afford brown crystals of 1
coordinated with water molecule i.e. 1a. Interestingly, crystals of 2 appeared in the DMSO d6
solution prepared in an NMR tube collected for recording its NMR spectra. DMSO d6
8

coordinated with aluminium of 2 and resulted in 2a. Molecular structures of 1a and 2a were
determined by single crystal XRD analysis.
3.1.1. FTIR spectra. Interpretation of the typical bands in the FTIR spectra of all these new
derivatives was carried out by comparing them with the spectra of free ligands i.e.
acetylacetone, dibenzoylmethane, 8-hydroxyquinoline and tridentate Schiff base ligands
1
2
3
(
H L , H L and H L ). Disappearance of the peaks corresponding to free OH of ligands and
2 2 2
-1
appearance of sharp peaks at 650 cm confirmed deprotonation of ligands as well as Al-O
-1
bond formation. A sharp peak at 540 cm could be attributed to Al-N bond. A downfield shift
-1
in the C=N stretching frequency from 1650 to 1610 cm confirms coordination of CN- with
aluminium. Bidentate coordination and quasiaromatic nature of β-diketonates were evidenced
-1
by shift of C
O stretching frequency from 1740 to 1580 cm and by appearance of the C
-1
C peak at 1540 cm . The characteristic stretching frequencies of Ar–H and C–H bonds
-1
were observed as medium intensity bands around 3050 and 2950 cm , respectively.
3.1.2. NMR. Absence of peaks corresponding to hydroxyl protons of 8-hydroxyquinoline,
1
enolic β-diketonates and Schiff base ligands in the H NMR spectra of these derivatives
indicated deprotonation of these ligands upon complexation. Presence of a triplet at 1.05 -
1.12 ppm, a multiplet at 3.42 - 3.50 ppm and a triplet at 4.36 - 4.43 ppm due to methyl,
methylene and hydroxyl protons indicated the presence of ethanol as an adduct in all the
derivatives. Further, peaks at 18.53 - 18.55 ppm and 56.00 - 56.03 ppm (corresponding to
1
3
CH and CH of ethanol) in the C NMR of these complexes confirmed the presence of ethyl
3
2
alcohol.
3.1.3. Structure of aluminium(III) complexes. The molecular structures of 1a and 2a are
displayed in figure 1. Important bond distances and angles are given in supplementary
table S1. The crystal structures of these six-coordinate aluminium complexes reveal
octahedral geometry. The Al is coordinated by a tridentate N-(5-bromosalicylidene)-o-
aminophenolate, a bidentate, aetylacetonate and a water molecule in 1a, while a tridentate,
N-(5-bromosalicylidene)-o-aminophenolate, a bidentate 1,3-diphenylpropane-1,3-dionate and
a DMSO in 2a. In the chelated complexes, the O…O and O…N bite distances vary in the
following ranges: in 1a, 2.610(3)-2.725(3); 2.577(3)-2.821(3) Å, in 2a, 2.599(3)-2.712(3);
2.570(3)-2.841(3) Å, while the bite angles O-Al-O and O-Al-N vary in following ranges, 1a,
9

87.41(11)-94.67(10); 83.13(9)-91.01(9)°, in 2a, 87.69(11)-93.82(11); 82.89(11)-92.24(11)°.
The coordination bond distances were Al-O (β-diketone), 1.853(2)-1.907(2) Å, Al-O (Schiff
base), 1.824(3)-1.871(2) Å, and Al-N, 2.007(2)-2.014(3) Å. The bond distances were in
agreement with similar complexes reported by Qiu et al. and Malcolm et al. [31, 32]. The
acetonitrile in 1a and DMSO in 2a merely act as fillers. The prominent interaction in 1a i.e.
1
2
2
(
HOH) O-H…O (L ) resulted in hydrogen bonded R (8) dimer as shown in figure 1. Water
further participated in O-H···N≡C (acetonitirile) as another hydrogen bonding interaction
figure 1a). Further packing was by either weak C-H…O or van der Waal interactions.
Relevant observed data of 1a and 2a are listed in table 2.
(
3
.2. Absorption and photoluminescence studies
In view of the poor solubility of these derivatives in common organic solvents, UV-Visible
figure 2) and fluorescence spectra (figure 3) of 1, 3, 4 and 6 were recorded in DMSO.
(
Dibenzoylmethane derivatives (2, 5 and 7) are fluorescent inactive whereas acetylacetonate
derivatives and 8-hydroxyquinolate derivatives exhibit green fluorescence. UV-Visible
absorption spectra of 1, 3, 4 and 6 exhibited absorption maxima at 446, 440, 448 and 444 nm.
Emission peaks of 1, 3, 4 and 6 were observed at 537, 520, 543 and 527 nm upon excitation
at 446, 440, 448 and 444 nm. The band gap energies of 1, 3, 4 and 6 were calculated as 2.31,
2.39, 2.29 and 2.35 eV from their corresponding fluorescence spectra which indicate green
light emitting nature of these molecules. The relative fluorescence quantum yields (Ф ) (with
F
reference to Alq ) of 1, 3, 4 and 6 are higher than Alq (table 3) [33].
3
3
3
.3. Synthesis and characterization of nano-structured alumina by sol–gel technique
To achieve nano alumina in uniform morphology, primarily
1
[
(CH COCHCOCH )Al(L )(EtOH)] was subjected to controlled hydrolysis by addition of
3
3
one drop of distilled water-ethanol mixture (1:5) and afterwards complete hydrolysis was
ensured while adding excess water-ethanol mixture in acidic medium. The solution was
stirred for 48 h to furnish fluorescent gel and further gel was heated at 100 °C for 10 h to
yield creamy white xerogel. The powdered xerogel was washed repeatedly with water and
acetone. Finally, the sample was sintered at 1100 °C for 4 h. Characterization of the freshly
obtained nano Al O white powder was performed by using appropriate techniques such as
2
3
powder XRD, FTIR, TEM and EDX. The synthesis of nano-structured alumina is
schematically shown below:
1
0

-1
Presence of a broad intense peak at 520 cm belonging to Al-O stretch confirmed the
-1
formation of Al O . A medium intense peak at 1400 cm could be an overtone. The phases of
2
3
the alumina synthesized were determined by comparing the powder XRD diffraction patterns
figure 4) of these materials with the reported ones (standard JCPDS values). The Al O3
(
2
synthesized by sintering at 1100 °C showed 2θ peaks at 25.26° (012), 34.87° (104), 37.47°
110), 43.03° (113), 52.28° (024), 57.21° (116), 60.98° (018), 66.28° (214), 67.89° (300) and
6.60° (1010) corresponding to α-Al O (JCPDS No. 046-1212).
(
7
2
3
The average particle size of alumina was calculated from the powder XRD by
applying Debye–Scherrer equation and was found to be 24.7 nm, in agreement with the
average particle size obtained from TEM analysis (figure 5). The morphology of the nano-
structured alumina synthesized from the new aluminium derivative was studied by TEM
analysis. Uniformity in the shape of the finely dispersed alumina nanoparticles was evident
from the lower and higher magnification images of TEM analysis. The particles were
10-70 nm with an average particle size of 40 nm. The alpha phase of the alumina
nanoparticles was further confirmed by the three selected area electron diffraction patterns.
The EDX mapping witnessed the high purity of this nano-sized alumina.
4
. Conclusion
In the present investigation, a series of new aluminium(III) derivatives was synthesized and
characterized. Fine and discrete nanoparticles of α-alumina were prepared from 1 by sol-gel
technique. Al O nanoparticles synthesized were 10-70 nm with average particle size of
2
3
4
0 nm.
1
1

Appendix A. Supplementary material
With entry numbers CCDC 1027480 and CCDC 1027481, crystallographic data of 1a and 2a
have been deposited at the Cambridge Crystallographic Data Centre. These data can be
obtained free of charge by requesting to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax: +44 (0)1223 336033 or E-mail: deposit@ccdc.cam.ac.uk).
Acknowledgements
Authors acknowledge VIT University Vellore, India for necessary support to carry out the
present investigations. V.G.P. is personally grateful to the university management for
awarding him stipend as a Research Associate.
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[
[
(
1
3

Figure 1. Ellipsoid diagrams of aluminium six-coordinate (a) 1a and (b) 2a drawn at 25%
probability. Color scheme: C-grey, H-white, Al-purple, Br-brown, N-blue, O-red, S-yellow.
Dashed lines indicate hydrogen bonds.
1
4

Figure 2. UV-Visible spectra of 1, 3, 4 and 6.
1
5

Figure 3. Fluorescence spectra of 1, 3, 4 and 6.
1
6

Figure 4. Powder XRD of Al O heated at 1100 °C.
2
3
1
7

Figure 5. Lower and higher magnification TEM images of Al O nanoparticles (a) and (b),
2
3
SAED pattern of the alumina nanoparticles (c), EDX profile (d) of Al O nanoparticles.
2
3
1
8

Table 1. Crystal data of 1a and 2a.
Crystal data
1a
2a
Empirical formula
Molecular weight
Morphology
Crystallizing solvent
Crystal size (mm)
Cell parameters
a (Å)
C H AlBrNO ·C H N
C H D AlBrNO S·2(C D OS)
18
17
5
2
3
30 19
6
5
2
6
475.27
792.82
Brown, block
Light yellow, block
DMSO(D6)
Acetonitrile and THF
0.30×0.28×0.16
0.19×0.18×0.13
10.9460(7)
19.5042(11)
19.8184(11)
90.0
11.7534(5)
12.4271(6)
12.5355(5)
93.788(2)
92.820(2)
105.153(3)
1759.22(14)
9940
b (Å)
c (Å)
α (°)
β (°)
95.612(2)
90.0
γ (°)
3
V (Å )
Cell measuring reflection
4210.8(4)
9921
θ-range (°)
2.3-25.4
Monoclinic
P21/c
2.3-23.4
Triclinic
P1bar
Crystal system
Space group
Z/Z’
8/2
2
3
Dx(cal.) (g/cm )
1.499
1.497
-1
μ (mm )
2.028
1.420
Absorption correction
F(000)
Multi-scan
1936
Multi-scan
800
Radiation
MoK
MoK
α
α
0
Temperature ( K)
295(2)
295(2)
θ-range (°)
2.07 – 27.2
-14<=h<=14
2.12 – 25.99
-14<=h<=14
-15<=k<=15
-15<=l<=15
φ and ω scans
6924
Index ranges
-
25<=k<=25
25<=l<=25
-
Scan type
φ and ω scans
9366
Independent reflections
Observed [I > 2σ(I)]
5806
4599
2
2
Final R [F > 2(F )]
0.0471
0.0480
2
wR(F ) all
Goodness-of-fit (S)
0.1265
0.1480
0.993
1.022
(
Δ/σ)
0.006
0.001
max
-3
Δρmax and Δρmin (e Å )
0.725, -0.662
1.417, -0.813
6924 / 0 / 430
Data / restraints / parameters 9366 / 0 / 545
2
2
2
2
2
c
w = 1/[σ (F ) + (aP) + bP] where P = (F + 2F )/3, parameters a and b are: 0.0550,
0
o
2
.5562 for 1a and 0.0786, 1.0442 for 2a.
1
9

Table 2. Inter- and intramolecular interactions observed in 1a and 2a.
Donor
D)
H
Acceptor D-H (Å)
(A)
H…A (Å) D…A (Å) Angle (D-
H…A) (°)
(
1
a
O5A
O5A
O5B
O5B
C29
H5A1
H5A2
H5B1
H5B2
H29A
H29B
N2A
O2B
N2B
O2A
0.75(3)
0.80(4)
0.80(3)
0.88(4)
0.96
2.16(3)
1.88(4)
2.27(4)
1.75(4)
2.48
i
2
a
O7
ii
C29
O5
0.96
2.51
Symmetry codes: (i) 1-x, 1-y, -z; (ii) -x, 1-y, -z.
2
0

Table 3. Photophysical properties of 1, 3, 4 and 6.
Compound
λ /nm
abs
λ /nm
flu
Stokes shift (nm) ФF
1
3
4
6
446
440
448
444
537
520
543
527
91
80
95
83
0.499
0.489
0.252
0.381
2
1

2
2