3,5-Lutidine coordinated zinc(II) aryl carboxylate complexes: Precursors for zinc(II) oxide

Article abstract of DOI:10.1016/j.ica.2011.01.083

The reaction of Zn(κ²O,O′-OAc)₂· 2H₂O with two equiv of 3,5-lutidine in methanol at room temperature for 12 h afforded [Zn(OAc)₂(3,5-lutidine)₂]· H ₂O (1) in 91% yield. The acetate exchange

Full text of DOI:10.1016/j.ica.2011.01.083

Inorganica Chimica Acta 372 (2011) 191–199
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
3,5-Lutidine coordinated zinc(II) aryl carboxylate complexes: Precursors
for zinc(II) oxide
Umesh Kumar a, Jency Thomas b, Rajamani Nagarajan a, Natesan Thirupathi a,
⇑
a Department of Chemistry, University of Delhi, Delhi 110007, India
b Department of Chemistry, Indian Institute of Technology Delhi, Delhi 110016, India
a r t i c l e i n f o
a b s t r a c t
The reaction of Zn(j2O,O0–OAc)2ꢀ2H2O with two equiv of 3,5-lutidine in methanol at room temperature
for 12 h afforded [Zn(OAc)2(3,5-lutidine)2]ꢀ H2O (1) in 91% yield. The acetate exchange reaction of 1 with
Article history:
Available online 3 February 2011
two equiv of aryl carboxylic acids in methanol at room temperature for 12 h afforded [Zn(l2-j
1O:j1O0–
This article is dedicated to Prof. S.S.
Krishnamurthy on the occasion of his 70th
birthday.
O2CAr)2(3,5-lutidine)]2 [Ar = C6H5 (2) and C6H4Me-3 (3)], [Zn(OC(O)C6H4Me-2)2(3,5-lutidine)2] (4) and
[Zn(j2O,O0ꢁO2CC6H4Me-4)2(3,5-lutidine)2] (5) in P90% yield. Complexes 1–5 were characterized by
microanalytical, IR, solution (1H and 13C) and solid-state cross-polarization magic angle spinning 13C
NMR and X-ray diffraction data. The zinc atom in 1 is surrounded by nitrogen atom of two 3,5-lutidine
and oxygen atom of two monodentate acetate moiety and thus attains a tetrahedral geometry. One of
the acetate moieties is hydrogen bonded with a water molecule in the crystal lattice. Complexes 2 and
3 possess a dinuclear paddlewheel framework with a square pyramidal geometry around the zinc atom
whereas 4 and 5 are mononuclear species with the zinc atom in tetrahedral and an octahedral geometry,
respectively. Thermogravimetric analyses of 2–5 suggested ZnO as the decomposed product followed by
the confirmation from the powder X-ray diffraction patterns. Enormous gas evolution resulting in porous
ZnO during thermal decomposition was evidenced from scanning electron microscopic images.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Zinc(II) aryl carboxylates
3,5-Lutidine
Acetate exchange reaction
Thermal decomposition studies
ZnO
1. Introduction
relevance as structural and functional model for biologically
important metalloenzymes [18–23], as Lewis acid catalysts for
ZnO is one of the useful materials in photonics, electronics,
optoelectronics, information storage, photography, catalysis, bio-
logical and chemical sensing [1,2]. Several synthetic routes are
known for ZnO powder such as sol–gel method [3,4], pyrolysis of
chelate complexes [5], spray pyrolysis [6], and thermal decomposi-
tion of precursors [7]. Organometallic precursors such as diethyl
zinc [8–10], dicyclohexyl zinc [11], and dimethylzinc [12] were
also used as precursors for nano-sized ZnO. The dialkylzinc precur-
sors are pyrophoric and hence extra precautions need to be taken
in handling these precursors. Hence, there exists a need to synthe-
size air stable and safe to handle zinc containing precursors that
can easily result in the formation of ZnO. Few zinc ketoiminato
complexes [13,14] as well as few Lewis base coordinated zinc(II)
carboxylate complexes [15–17] were also reported to be useful
precursors for ZnO .
the copolymerization of cyclohexene oxide and CO2 to afford poly-
carbonates [24–26], and as secondary building units (SBUs) of the
carboxylate based metal organic frameworks (MOFs) [27–34]. The
nuclearity and carboxylate coordination modes in Lewis base coor-
dinated zinc(II) aryl carboxylate complexes were shown to depend
upon the method of preparation, nature of carboxylate moiety, Le-
wis base, the ratio of reactants and other reaction conditions
[17,35–39].
Recently, we have isolated a series Lewis base coordinated zin-
c(II) acetate and zinc(II) pivalate complexes with di and trinuclear
core as well as a one dimensional coordination polymer from the
condensation reaction involving Zn(j2O,O0–OAc)2ꢀ2H2O (or)
Zn(O2CtBu)2 and Lewis bases in methanol at ambient condition
[40,41]. From this study, it was concluded that subtle basic/steric
properties of Lewis bases and noncovalent interactions in the crys-
tal lattice influence the nuclearity and carboxylate coordination
modes of the products. Further, such complexes upon thermolysis
lead to the formation of volatile species instead of ZnO as revealed
by TGA/DTA studies. In continuation of our work in zinc(II) carbox-
ylate chemistry, we report herein the synthesis, structural aspects
of [Zn(OAc)2(3,5-lutidine)2]ꢀH2O (1) and 3,5-lutidine coordinated
zinc(II) aryl carboxylate complexes 2–5 shown in Chart 1. These
Lewis base coordinated zinc(II) carboxylate complexes consti-
tute an important class of coordination compounds due to their
⇑
Corresponding author. Tel.: +91 (0) 11 2766 6646x189; fax: +91 (0) 11 2766
6605.
E-mail addresses: tnat@chemistry.du.ac.in, thirupathi_n@yahoo.com (N. Thir-
upathi).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.083

192
U. Kumar et al. / Inorganica Chimica Acta 372 (2011) 191–199
Ar Ar
Me
Me
Me
Me
Me
O
O
O
O
Me
N
N
Zn
O
Zn
O
N
H
Zn
Me
O
O
O
O
Me
N
O
O
H
Ar Ar
Ar = C6H5 (2); C6H4Me-3 (3)
Me
O
Me
1
Me
Me
Me
Me
Ar
Ar
N
N
O
O
O
O
O
O
O
O
Ar
Ar
Zn
Zn
Me
OC(O)Ar
OC(O)Ar
N
N
Me
5, Ar = C6H4Me-4
Me
Me
4, Ar = C6H4Me-2
Chart 1.
complexes upon thermolysis afforded porous ZnO as confirmed by
powder X-ray diffraction data and scanning electron microscopic
images.
ca. 20 mL and left at room temperature for several hours to afford
1 as colorless crystals. Crystals were separated and washed with
cold n-hexane to afford 1 in 91% yield (3.45 g, 8.30 mmol). FT-IR
(KBr, cmꢁ1): 3434 (br) for
CO), 1399 (vs) for
v
(H2O), 1618 (sh), 1603 (vs) for
vasym(O-
v
sym(OCO). 1H NMR (CDCl3, 300 MHz, d ppm):
2. Experimental
2.09 (s, 6H, OC(O)CH3), 2.33 (s, 12H, NC5H3(CH3)2-3,5), 7.45 (s,
2H, 4H NC5H3(CH3)2-3,5), 8.35 (s, 4H, 2H & 6H NC5H3(CH3)2-3,5).
13C NMR (CDCl3, 75.5 MHz, d ppm): 18.0, 22.3 (CH3), 133.9,
139.8, 146.7 (NC5H3(CH3)2-3,5), 179.2 (OC(O)). MS (TOF, ES+) m/z
(intensity %): 398 [M–H2O + H]+ (1 0 0). Anal. Calc. for
2.1. Materials and methods
Zn(j2O,O0–OAc)2ꢀ2H2O, 3,5-lutidine, benzoic acid, o-toluic acid,
m-toluic acid and p-toluic acid were purchased from commercial
sources and used as received. Elemental analyses were performed
on an Elementar Analysensysteme GmbH VarioEL V3.00. The IR
spectral data were obtained on a Shimadzu IR435 spectrometer
C
18H24N2O4ZnꢀH2O (415.81): C, 52.00; H, 6.30; N, 6.74. Found: C,
52.50; H, 6.47; N, 6.71%.
2.3. [Zn(l2-j
1O:j1O0–O2CC6H5)2(3,5-lutidine)]2 (2)
using KBr pellet in the frequency range 400–4000 cmꢁ1 1H and
.
13C NMR spectra were recorded on an Avance Bruker-300 NMR
spectrometer operating at field strengths of 300 and 75ꢀ5 MHz,
respectively and chemical shifts are reported relative to tetrameth-
ylsilane (TMS) or residual solvent signal. The solid-state cross-
polarization magic angle spinning (CP-MAS) 13C NMR spectra were
recorded on a DSX-300 MHz spectrometer and the chemical shifts
were referenced with respect to TMS. TOF-MS spectra were re-
corded on a Micromass LCT KC 455 instrument using electrospray
positive ion mode. The thermal analyses (TGA/DTA) were carried
out on a combined TGA/DTA Shimadzu (model TA-60WS) instru-
ment at a heating rate of 10 °C/min. Powder X-ray diffraction
(PXRD) patterns were recorded on Philips Xpert and Bruker D8 Ad-
vance instruments. The scanning electron microscopic (SEM)
images were obtained using Hitachi 7500 as well as FEI Quanta
200F microscopes. The reported yield of 1 is based on Zn(j2O,O0–
OAc)2ꢀ2H2O and those of 2–5 are based on 1.
Complex 1 (2.00 g, 4.81 mmol) was dissolved in methanol
(60 mL). To the aforementioned solution, benzoic acid (1.26 g,
10.31 mmol) was added pinch wise and the resulting homoge-
neous solution was stirred at room temperature for 12 h. The vol-
atiles were removed under vacuum to afford colorless solid. The
solid was purified by crystallization from methanol/chloroform
mixture at room temperature over a period of one week to afford
2 as colorless crystals in quantitative yield (1.99 g, 2.40 mmol).
FT-IR (KBr, cmꢁ1): 1641 (s), 1576 (m) for
vasym(OCO), 1459 (m),
1408 (s) for
v
sym(OCO). 1H NMR (CDCl3, 300 MHz, d ppm): 2.29
(s, 12H, NC5H3(CH3)2-3,5), 7.30 (t, 8H, 3H & 5H C6H5, JHH = 8.87 Hz),
7.34 (s, 2H, 4H NC5H3(CH3)2-3,5), 7.43 (t, 4H, 4H C6H5,
JHH = 7.31 Hz), 8.11 (d, 8H, 2H & 6H C6H5, JHH = 7.49 Hz), 8.51 (s,
4H, 2H & 6H NC5H3(CH3)2-3,5). 13C NMR (CDCl3, 75ꢀ5 MHz, d
ppm): 18.2 (CH3), 127.5, 130.3, 131.4, 133.6, 134.6, 140.8, 146.5
(ArC), 174.0 (OC(O)). MS (TOF, ES+) m/z (intensity %): 831 [M+H]+
(8). Anal. Calc. for C42H38N2O8Zn2 (829.55): C, 60.81; H, 4.62; N,
3.38. Found: C, 60.77; H, 4.98; N, 3.38%.
2.2. [Zn(OAc)2(3,5-lutidine)2]ꢀH2O (1)
Zn(j2O,O0–OAc)2ꢀ2H2O (2.00 g, 9.11 mmol) was dissolved in
methanol (70 mL). To the aforementioned solution, 3,5-lutidine
(2.00 g, 18.68 mmol) in methanol (10 mL) was added drop wise
and the resulting solution was stirred at room temperature for
12 h. The reaction mixture was concentrated under vacuum to
2.4. [Zn(l2–j
1O:j1O0–O2CC6H4Me-3)2(3,5-lutidine)]2 (3)
Complex 1 (2.00 g, 4.81 mmol) was dissolved in methanol
(60 mL). To the aforementioned solution, m-toluic acid (1.40 g,

U. Kumar et al. / Inorganica Chimica Acta 372 (2011) 191–199
193
10.31 mmol) was added pinch wise and the resulting homoge-
2.6. [Zn(j2O,O0–O2CC6H4Me-4)2(3,5-lutidine)2] (5)
neous solution was stirred at room temperature for 12 h. The
volatiles were removed under vacuum to afford colorless solid.
The solid was purified by crystallization from chloroform/aceto-
nitrile mixture at room temperature over a period of one week
to afford 3 as colorless crystals in 90% yield (1.92 g, 2.16 mmol).
Complex 1 (2.00 g, 4.81 mmol) was dissolved in methanol
(60 mL). To the aforementioned solution, p-toluic acid (1.40 g,
10.31 mmol) was added pinch wise and the resulting homoge-
neous solution was stirred at room temperature for 12 h. The vol-
atiles were removed under vacuum to afford colorless solid. The
solid was purified by crystallization from chloroform/acetonitrile
mixture at room temperature over a period of one week to afford
5 as colorless crystals in 90% yield (2.62 g, 4.76 mmol). FT-IR
FT-IR (KBr, cmꢁ1): 1605 (s), 1583 (s) for
1400 (vs) for
v
asym(OCO), 1426 (s),
v
sym(OCO). 1H NMR (CDCl3, 300 MHz, d ppm):
2.29 (s, 12H, C6H4(CH3)-3), 2.32 (s, 12H, NC5H3(CH3)2-3,5), 7.22
(m, 4H, 5H C6H4(CH3)-3), 7.25 (d, 4H, 4H C6H4(CH3)-3,
JHH = 7.50 Hz), 7.46 (s, 2H, 4H NC5H3(CH3)2-3,5), 7.92 (d, 4H, 6H
C6H4(CH3)-3, JHH = 10.80 Hz), 7.94 (s, 4H, 2H C6H4(CH3)-3), 8.50
(s, 4H, 2H & 6H NC5H3(CH3)2-3,5). 13C NMR (CDCl3, 75ꢀ5 MHz,
(KBr, cmꢁ1): 1544 (s) for sym(OCO). 1H
vasym(OCO), 1405 (vs) for v
NMR (CDCl3, 300 MHz, d ppm): 2.30 (s, 12H, NC5H3(CH3)2-3,5),
2.37 (s, 6H, C6H4(CH3)-4), 7.15 (d, 4H, 3H & 5H C6H4(CH3)-4,
JHH = 7.86 Hz), 7.43 (s, 2H, 4H NC5H3(CH3)2-3,5), 8.04 (d, 4H, 2H &
d
ppm): 18.3, 21.2 (CH3), 127.5, 131.1, 132.2, 133.7, 134.6,
137.2, 140.8, 146.7 (ArC), 174.32 (OC(O)). Note: Only 8 carbon
resonances were observed for ArC rather than the expected 9
resonances presumably due to overlapping peaks. MS (TOF,
ES+) m/z (intensity %): 886 [M+H]+ (83). Anal. Calc. for
C46H46N2O8Zn2 (885.70): C, 62.38; H, 5.23; N, 3.16. Found: C,
62.21; H, 5.21; N, 3.02%.
6H C6H4(CH3)-4, JHH = 7.93 Hz), 8.45 (s, 4H, 2H
&
6H
NC5H3(CH3)2-3,5). 13C NMR (CDCl3, 75ꢀ5 MHz, d ppm): 18.2, 21.4
(CH3), 128.2, 130.2, 131.7, 134.2, 140.2, 141.0, 146.8 (ArC), 173.7
(OC(O)). MS (TOF, ES+) m/z (intensity %): 550 [M+H]+ (13). Anal.
Calc. for C30H32N2O4Zn (549.98): C, 65.52; H, 5.86; N, 5.09. Found:
C, 65.11; H, 5.83; N, 4.98%.
2.7. Crystal structure determinations
2.5. [Zn(OC(O)C6H4Me-2)2(3,5-lutidine)2] (4)
X-ray diffraction studies of suitably sized crystals mounted on a
capillary were carried out on a BRUKER AXS SMART-APEX diffrac-
Complex 1 (2.00 g, 4.81 mmol) was dissolved in methanol
(60 mL). To the aforementioned solution, o-toluic acid (1.40 g,
10.31 mmol) was added pinch wise and the resulting homoge-
neous solution was stirred at room temperature for 12 h. The vol-
atiles were removed under vacuum to afford colorless solid. The
solid was purified by crystallization from chloroform/acetonitrile
mixture at room temperature over a period of one week to afford
4 as colorless crystals in 90% yield (2.38 g, 4.33 mmol). FT-IR
tometer with a CCD area detector [(Mo K
monochromator] [42]. Frames were collected at 100 K for complex
1 and at 298 K for complexes 2–5 by , ø and 2h rotation at 10 s
a) 0.71073 Å, graphite
x
per frame with SMART [42]. The measured intensities were reduced
to F2 and corrected for absorption with SADABS [43]. Structure solu-
tion, refinement, and data output were carried out with the SHELXTL
program [44]. Non-hydrogen atoms were refined anisotropically.
C–H hydrogen atoms were placed in geometrically calculated posi-
tions by using a riding model. Images were created with the Dia-
mond program [45]. Hydrogen bonding interactions in the crystal
lattice were calculated with SHELXTL [44]. The X-ray crystallographic
parameters, details of data collection and structure refinement are
presented in Table 1.
(KBr, cmꢁ1): 1637 (vs), 1562 (m) for
vasym(OCO), 1437 (m) and
1402 (s) for
v
sym(OCO). 1H NMR (CDCl3, 300 MHz, d ppm): 2.29
(s, 12H, NC5H3(CH3)2-3,5), 2.57 (s, 6H, C6H4(CH3)-2), 7.14 (br, 4H,
3H & 5H C6H4(CH3)-2), 7.26 (t, 2H, 4H C6H4(CH3)-2, JHH = 6.99 Hz),
7.46 (s, 2H, 4H NC5H3(CH3)2-3,5), 7.95 (d, 2H, 6H C6H4(CH3)-2,
JHH = 7.33 Hz), 8.48 (s, 4H, 2H & 6H NC5H3(CH3)2-3,5). 13C NMR
(CDCl3, 75ꢀ5 MHz, d ppm): 18.4, 21.8 (CH3), 127.2, 129.9, 130.6,
134.5, 135.2, 138.6, 140.6, 146.9 (ArC), 175.9 (OC(O)). Note: Only
8 carbon resonances were observed for ArC rather than the ex-
pected 9 resonances presumably due to overlapping peaks. MS
(TOF, ES+) m/z (intensity %): 551 [M+H]+ (5). Anal. Calc. for
3. Results and discussion
3.1. Synthesis
C30H32N2O4Zn (549.98): C, 65.52; H, 5.86; N, 5.09. Found: C,
Zn(j2O,O0–OAc)2ꢀ2H2O was treated with 3,5-lutidine in 1:2 mol
65.26; H, 5.81; N, 4.87%.
ratio in methanol at room temperature for 12 h that afforded
Table 1
Crystallographic and experimental data for 1–5.
1
2
3
4
5
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
18H24N2O5Zn
C42H38N2O8Zn2
829.52
triclinic
C46H46N2O8Zn2
885.63
triclinic
C30H32N2O4Zn
549.97
monoclinic
P21/n
8.227(2)
36.602(7)
9.607(2)
90.00
105.191(3)
90.00
C30H32N2O4Zn
549.97
orthorhombic
Ibca
413.78
triclinic
P1
ꢀ
ꢀ
ꢀ
P1
P1
9.727(2)
10.361(3)
10.471(2)
92.678(3)
109.155(3)
103.752(4)
959.3(4)
2
10.282(2)
10.700(2)
10.801(3)
63.411(3)
66.928(3)
79.322(4)
977.6(4)
1
10.734(9)
10.897(9)
11.359(10)
63.774(14)
81.812(14)
63.460(13)
1063.8(16)
1
15.676(5)
16.656(6)
21.058(7)
90.00
90.00
90.00
5498(3)
8
1.329
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
2792.1(9)
4
1.308
Z
Density (calcd) (g cmꢁ3
)
1.433
1.409
1.382
T (K)
100(2)
298(2)
298(2)
298(2)
298(2)
k (Mo K
(Mo K
R1, wR2 [I > 2
a
a
) (Å)
0.71073
1.310
0.0497, 0.0547
0.1443, 0.1549
0.71073
1.281
0.0490, 0.0633
0.1150, 0.1280
0.71073
1.182
0.0524, 0.0793
0.1062, 0.1220
0.71073
0.916
0.0575, 0.0712
0.1383, 0.1498
0.71073
0.930
0.0486, 0.0538
0.1183, 0.1219
l
) (cmꢁ1
)
r
(I)]a
R1, wR2 (all data)a
h
i
1=2
2
2
a
R1
¼
R
jjFoj ꢁ jFcjj=
RjFoj; wR2
¼
R
wðjFoj ꢁ jFcjÞ =
R
wjFoj
.

194
U. Kumar et al. / Inorganica Chimica Acta 372 (2011) 191–199
[Zn(OAc)2(3,5-lutidine)2]ꢀH2O (1) as colorless solid in 91% yield.
Complex 1 was treated with two equiv of aryl carboxylic acids
shown in Chart 2 in methanol at room temperature for 12 h that
afforded complexes 2–5 in P90% yield. Our objectives were two
fold; to probe the role of subtle steric/basic properties of the aryl
carboxylic acids on the nuclearity/carboxylate coordination modes
of the products and to use such products as precursors for ZnO.
Me
Me
Me
O
OH
O
OH
.
O
OH
O
OH
pKa [46]:
4.20
3.91
4.25
4.37
Chart 2.
Fig. 3. ORTEP representation of 3 at the 30% probability level. Hydrogen atoms are
omitted for clarity.
Fig. 1. ORTEP representation of 1 at the 30% probability level. Hydrogen atoms are
omitted for clarity.
Fig. 4. ORTEP representation of 4 at the 30% probability level. Hydrogen atoms are
omitted for clarity.
3.2. Molecular and crystal structures
The molecular structures of 1–5 were determined by X-ray dif-
fraction data. The molecular structures of 1–5 with atom labeling
scheme are shown in Figs. 1–5, respectively. Selected bond param-
eters for 1–5 are listed in Table 2. Complex 1 crystallized as a
monohydrate and in this complex the zinc atom surrounded by
two oxygen atoms of the monodentate acetate and nitrogen atoms
of two 3,5-lutidine and thus attains a tetrahedral geometry.
Zn(OAc)2(pyridine)2 was shown to crystallize in triclinic and
tetragonal space groups [47]. The Zn–O [1.981(2) and 1.965(2) Å]
and C@O [1.232(5) and 1.235(5) Å] distances are longer but the
Zn–N [2.015(3) and 2.041(3) Å] distances are shorter in complex
1 than those observed in Zn(OAc)2(pyridine)2 [triclinic: Zn–O,
1.945(3) and 1.941(2) Å; C@O, 1.218(4) and 1.218(4) Å; Zn–N,
2.047(2) and 2.076(2) Å]. The bond distance variation may be
Fig. 2. ORTEP representation of 2 at the 30% probability level. Hydrogen atoms are
omitted for clarity.

U. Kumar et al. / Inorganica Chimica Acta 372 (2011) 191–199
195
Fig. 5. ORTEP representation of 5 at the 30% probability level. Hydrogen atoms are omitted for clarity.
Table 2
2.970(1) Å in 2 is slightly longer than that observed in the structur-
ally related [Zn(l2
j1O:j1O0–O2CC6H5)2(pyridine)]2 (I) [2.958(1) Å]
[35] indicating the influence of higher basicity of 3,5-lutidine than
Selected bond lengths (Å) and bond angles (°) for 1–5.
-
1
Zn1–O1
Zn1–N2
C15–C16
C17–C18
1.981(2)
2.041(3)
1.510(5)
1.516(5)
Zn1–O3
C15–O1
C17–O3
1.965(2)
1.299(4)
1.286(5)
Zn1–N1
C15–O2
C17–O4
2.015(3)
1.232(5)
1.235(5)
that of pyridine. The non-bonded ZnꢀꢀꢀZn distance in I, 2 and 3
[2.965(2) Å] is slightly shorter than that observed in [Zn(l2
-
j1O:j1O0–O2CC6H5)2(quinoxaline)]2 (II) [2.990(1) Å] [38].
O1–Zn1–O3 99.09(10)
O1–Zn1–N1 110.52(11)
O1–Zn1–N2 105.24(11) O3–Zn1–N1 106.40(11) O3–Zn1–N2 105.24(11)
N1–Zn1–N2 126.60(12) O1–C15–O2 122.7(3) O3–C17–O4 124.5(3)
Complex 4 is a mononuclear species with the zinc atom sur-
rounded by oxygen atom of two monodentate o-toluate moieties
and nitrogen atom of two 3,5-lutidine and the zinc atom thus at-
tains a tetrahedral geometry. The zinc atom in 5 resides on a crys-
tallographic C2 axis and is surrounded by two oxygen atom of a
chelating p-toluate and nitrogen atom of 3,5-lutidine and their C2
symmetry related p-toluate and 3,5-lutidine and thus zinc atom at-
tains an octahedral geometry.
2
3
2
3
Zn1–N1
Zn1–O1
Zn1–O2
O2–Zn1–O3 87.35(9)
O2–Zn1–O4 88.8(1)
O3–Zn1–O4 159.04(9) 159.2(1)
O2–Zn1–O1 158.79(9) 159.1(1)
O3–Zn1–O1 88.63(9)
2.040(2)
2.024(2)
2.060(2)
2.042(3)
2.029(3)
2.040(3)
89.1(1)
87.6(1)
Zn1–O3
Zn1–O4
Zn1ꢀꢀꢀZn1
2.044(2)
2.028(2)
2.970(1)
2.029(3)
2.062(3)
2.965(2)
88.9(1)
100.1(1)
105.1(1)
95.6(1)
100.8(1)
O4–Zn1–O1 87.52(9)
O2–Zn1–N1 95.41(9)
O3–Zn1–N1 99.19(9)
O4–Zn1–N1 101.68(9)
O1–Zn1–N1 105.79(9)
86.9(1)
Complexes 3–5 possess an intermolecular C–HꢀꢀꢀO interaction in
the crystal lattice and such interaction is illustrated in Figs. 6–8,
respectively. The O3 atom of the syn–syn bidentate bridging m-tol-
uate moiety in 3 forms a C–HꢀꢀꢀO hydrogen bonding with one of the
hydrogen atoms (H23A) bonded to methyl carbon of the m-toluate
moiety of the inversion related adjacent molecule. The O2 atom of
the monodentate o-toluate in 4 is involved in a bifurcated intermo-
lecular C–HꢀꢀꢀO hydrogen bonding with H20 of the o-toluate moiety
of the translation related adjacent molecule and the other with
H6C of 3,5-lutidine of the inversion related adjacent molecule.
The O1 atom of the chelating p-toluate moiety in 5 is involved in
C–HꢀꢀꢀO hydrogen bonding with the hydrogen atom H7C of one of
the methyl groups of 3,5-lutidine present in the inversion related
adjacent molecule. The C–HꢀꢀꢀO hydrogen bonding in complexes 3
and 5 grows along c-axis and a-axis, respectively to afford a one-
dimensional chain (see Figs. 6 and 8).
We have shown that less basic and sterically more hindered o-
toluate in mononuclear complex 4 is coordinated to the zinc atom
in monodentate coordination mode whereas more basic and steri-
cally less hindered benzoate and m-toluate in dinuclear complexes
2 and 3 are coordinated to the zinc atom in syn–syn bidentate
bridging coordination mode. The sterically less hindered and even
more basic p-toluate in the mononuclear complex 5 is coordinated
to the zinc atom in a chelating coordination mode. The shift of the
carboxylate coordination mode from monodentate in 4 to syn–syn
bidentate bridging in 2 and 3 and to the chelating in 5 implied lar-
gely the influence of basicity of the lone pair on the carbonyl oxy-
gen of the carboxylate moiety and sterics. Such ‘carboxylate shift’
process has important implications for metalloenzymes in under-
standing their catalytic activities [51–54].
4
Zn1–O1
Zn1–N2
C15–C16
C23–C24
O3–Zn1–N1 130.8(2)
O1–C15–C16 116.1(3)
O3–C23–C24 119.8(5)
1.986(3)
2.024(2)
1.509(5)
1.521(6)
Zn1–O3
C15–O1
C23–O3
O1–Zn1–N1 106.0(1)
O3–Zn1–N2 108.6(2)
O2–C15–C16 122.2(3)
O4–C23–C24 117.4(6)
1.972(4)
1.272(4)
1.222(6)
Zn1–N1
C15–O2
C23–O4
O1–Zn1–N2 96.9(1)
O1–C15–O2 121.7(3)
O3–C23–O4 122.8(5)
2.082(3)
1.218(4)
1.250(7)
5
Zn1–O1
O1–C8
2.114(3)
1.255(4)
Zn1–O2
O2–C8
O1–Zn1–O2 105.6(1)
2.258(2)
1.247(4)
Zn1–N1
C8–C9
O1–Zn1–N1 98.51(9)
N1–Zn1–N1 95.0(1)
O2–C8–C9 120.1(3)
2.103(2)
1.498(4)
O1–Zn1–O1 160.7(2)
O2–Zn1–N1 153.81(9) O2–Zn1–O2 90.2(1)
O1–C8–O2 121.0(3) O1–C8–C9 118.9(3)
ascribed to higher basicity of 3,5-lutidine (pKa: 6.15) in the former
compared with pyridine (pKa: 5.23) [46] in Zn(OAc)2(pyridine)2
and the involvement of C@O oxygen in 1 in intermolecular O–
HꢀꢀꢀO/C–HꢀꢀꢀO hydrogen bonding in the crystal lattice.
Complexes 2 and 3 consist of a paddlewheel framework where-
in the pair of zinc atoms is bridged by four syn–syn bidentate
bridging carboxylate moieties. 3,5-lutidine is coordinated to each
zinc atom along the non-bonded ZnꢀꢀꢀZn axis and thus the zinc
atom attains a square pyramidal geometry. It was shown that the
non-bonded MꢀꢀꢀM distance and O–C–O angle in the carboxylate
bridged paddlewheel dinuclear complexes depend upon the induc-
tive effect and steric bulk of the substituent on the carbonyl carbon
[48]. The molecular structures of several Lewis base coordinated
zinc(II) aryl carboxylate complexes with a paddlewheel framework
are known [17,35–39,49,50]. The non-bonded ZnꢀꢀꢀZn distance,

196
U. Kumar et al. / Inorganica Chimica Acta 372 (2011) 191–199
Fig. 6. Packing diagram of 3 illustrating a C–HꢀꢀꢀO hydrogen bonding in the crystal lattice. Hydrogen bond parameters, C23–H23A: 0.96 Å; H23AꢀꢀꢀO3: 2.68 Å, C23ꢀꢀꢀO3: 3.60 Å,
C23–H23AꢀꢀꢀO3: 158°.
Fig. 7. Packing diagram of 4 illustrating a C–HꢀꢀꢀO hydrogen bonding in the crystal lattice. Hydrogen bond parameters, C20–H20: 0.93 Å; H20ꢀꢀꢀO2: 2.64 Å, C20ꢀꢀꢀO2: 3.52 Å,
C20–H20ꢀꢀꢀO2: 157° and C6–H6C: 0.96 Å; H6CꢀꢀꢀO2: 2.46 Å, C6ꢀ ꢀ ꢀO2: 3.42 Å, C6–H6Cꢀ ꢀ ꢀO2: 173°.
3.3. Spectroscopic studies
(R = Me; M = Na [60] and R = C6H5, C6H4Me-2, C6H4Me-3 and
C6H4Me-4; M = K [61]) are also included in Table 3 to unambigu-
ously assign the carboxylate coordination modes in complexes 1–
5.
IR spectroscopy is one of the useful techniques to assign the car-
boxylate coordination modes and the following trend is generally
accepted as a guideline to differentiate various carboxylate coordi-
nation modes [55–58].
D
mcalcd ¼ 1818:1dr þ 16:47ðhOCO ꢁ 120Þ þ 66:8
ð1Þ
In Eq. (1) dr is the difference between two C–O bond lengths (in
D
D
m
m
¼ masymðOCOÞ ꢁ msymðOCOÞ
Å) and hoco is the OCO angle (in °). Eq. (1) was applied by us [40]
and others [58] to better interpret values of several Lewis base
D
m
chelating <
Dm bridging < Dm ionic < Dm monodentate
coordinated zinc(II) carboxylate complexes bearing distinct car-
boxylate coordination modes. According to Eq. (1), the variation
of 0.01 Å in dr or 1° in hoco gives rise to a change of 16–18 cmꢁ1
The values obtained from IR data, and from X-ray diffraction
D
m
data using Tasumi’s equation (Eq. (1)) [59] for complexes 1–5 are
listed in Table 3. The values for the corresponding RC(O)OM
D
m
in the value of Dm. Sometimes, a significant deviation was observed

U. Kumar et al. / Inorganica Chimica Acta 372 (2011) 191–199
197
Fig. 8. Packing diagram of 5 illustrating a C–Hꢀ ꢀ ꢀO hydrogen bonding in the crystal lattice. Hydrogen bond parameters, C7–H7C: 0.96 Å; H7Cꢀ ꢀ ꢀO1: 2.68 Å, C7ꢀ ꢀ ꢀO1: 3.62 Å,
C7–H7Cꢀ ꢀ ꢀO1: 167°.
The solution 1H and 13C NMR spectral pattern of 1–5 appeared
deceptively simple and less informative for the structural elucida-
Table 3
IR spectral data (cmꢁ1) of 1–5.
D
mcalcd
mexp
D
m
for
Coordination mode
tion. This artifact could be due to sample dissociation or due to a
rapid ‘carboxylate shift’ process that occurs on a time scale faster
than NMR time scale [40,63]. The solid-state CP-MAS 13C NMR
was proven as a useful technique to distinguish various acetate
coordination modes of zinc(II) acetate complexes [40,64,65].
Sometimes, even crystallographically different carbonyl carbons
of the carboxylate moieties were distinguished with the aid of so-
(
D
)
RC(O)OM
1
2
3
4
5
234 (204)
233 (219)
173 (182)
167 (168)
157 (179)
193 (183)
193 (200)
164 (160)
98 (139)
164
monodentate (hydrogen bonded)
monodentate
136
170
146
145
syn–syn bidentate bridging
syn–syn bidentate bridging
syn–syn bidentate bridging
syn–syn bidentate bridging
monodentate
lid-state CP-MAS 13C NMR data [65]. Hence, solid-state CP-MAS 13
C
monodentate
chelating
NMR data was recorded for 1–5 and the respective dC values are
listed in Table 4.
The solid-state CP-MAS 13C NMR spectrum of 1 revealed two
peaks at dC = 176.6 and 181.1 ppm assignable to OC(O) carbon nu-
clei. The dC = 176.6 ppm value is assigned to the carbonyl carbon of
the monodentate acetate [40,64] and the dC = 181.1 ppm value is
assigned to the carbonyl carbon of the monodentate acetate
Table 4
Solid state CP-MAS 13C NMR data (ppm) for 1–5.
CH3
ArC
OC(O)
1
2
3
4
5
17.1, 18.3,
20.4, 25.0
16.4
134.9, 141.6, 145.3
176.6,
181.1
170.0,
171.6
169.6,
171.6
172.6,
175.6
174.1
125.1, 127.6, 129.7, 131.0, 132.8, 135.5,
138.4, 142.1, 144.8
125.9, 128.2, 129.9, 131.5, 133.4, 136.3,
138.4, 144.5
15.6, 16.2,
20.0
17.2, 21.7,
24.2
16.6, 17.6,
20.8
125.7, 127.3, 132.5, 135.0, 141.0, 145.5
126.0, 127.0, 128.6, 133.0, 143.0, 143.9
between the
Dmcalcd and Dmexp values due to the involvement of
carbonyl oxygen in H-bonding [62] and also due to the cage defor-
mation [40,58].
There is a fairly good agreement between Dmcalcd and Dmexp val-
ues for one of the monodentate acetate coordination modes in 1,
both syn–syn bidentate bridging coordination modes in 2, one of
the syn–syn bidentate bridging coordination modes in 3, and both
monodentate carboxylate coordination modes in 4. However, there
is a significant deviation between Dcalcd and Dexp values for one of
the monodentate acetate coordination modes in 1, one of the syn–
syn bidentate bridging coordination modes in 3 and the chelating
coordination mode in 5. The aforementioned deviation may be as-
cribed to the presence of an intermolecular O–HꢀꢀꢀO/C–HꢀꢀꢀO hydro-
gen bonding interactions in the crystal lattice.
Fig. 9. Thermogravimetric traces of 2–5 in air.

198
U. Kumar et al. / Inorganica Chimica Acta 372 (2011) 191–199
Fig. 10. Differential thermal analyses of 2–5 in air.
Fig. 13. SEM image of highly porous ZnO obtained after calcination of 4 at 450 °C
for 6 h in air.
moiety which is hydrogen bonded to a water molecule. Interest-
ingly, four types of 13C NMR signals (dC = 17.1, 18.3, 20.4, and
25.0 ppm) were observed for CH3 carbon of 1 indicating a chemical
shift anisotropy of CH3 carbon of two distinct 3,5-lutidine and ace-
tate moieties and this observation is consistent with the structure
found in the crystal lattice. Complexes 2–4 revealed two types of
13C NMR signals whereas complex 5 revealed only one for the car-
bonyl carbon as the formerly mentioned complexes possess two
crystallographically distinct carbonyl carbon whereas the latter
possess only one.
Complexes 1–5 revealed a cluster of peaks centered at m/
z = 398, 831, 886, 551, and 550 amu, respectively characteristic of
[MꢁH2O+H]+ (1) and [M+H]+ (2–5) moities due to different iso-
topes of zinc.
3.4. Thermal decomposition studies
The TGA of complex 1 indicated loss of a water molecule (exper-
imental weight loss 4.25%; Theoretical weight loss: 4.33%) in 37–
175 °C temperature range. No residue was left at the end of ther-
molysis event and this is likely due to the volatile nature of com-
plex 1. The TGA and DTA traces of 2–5 carried out in air are
shown in Figs. 9 and 10, respectively. The TGA data of 2–5 indi-
cated loss of 3,5-lutidine and CO2 molecule in sequence as verified
by weight loss calculations. The total weight loss corresponded to
ZnO in each case as the decomposed product. Depending upon the
nature of carboxylate moieties and nuclearity/carboxylate coordi-
nation modes present in 2–5, different number of intermediates
were observed in the TGA/DTA traces. The DTA traces revealed
the weight losses to be exothermic. Complexes 2–5 were sepa-
rately calcined at 350 °C for 3 h in air that yielded thermodynam-
ically stable hexagonal form of ZnO as deduced from the PXRD
pattern. The observed PXRD pattern matched well with the
authentic ZnO (ICSD-067454) in each case. As a representative
example, PXRD pattern and SEM image for ZnO obtained from
the decomposition of 4 are presented in Figs. 11 and 12, respec-
tively. The porous nature of ZnO shown in the SEM image may
be ascribed to the huge amount of CO2 evolved during thermolysis
event as hypothesized in the thermogravimetric traces. However,
ZnO obtained from the aforementioned experimental condition
was dirty white in color possibly arising due to incomplete
Fig. 11. PXRD pattern of ZnO obtained by calcination of 4 at 350 °C for 3 h in air.
Fig. 12. SEM image of highly porous ZnO obtained after calcination of 4 at 350 °C
for 3 h in air.

U. Kumar et al. / Inorganica Chimica Acta 372 (2011) 191–199
199
[9] I. Alessandri, M. Zucca, M. Ferroni, E. Bontempi, L.E. Depero, Cryst. Growth Des.
9 (2009) 1258.
[10] D.C. Kim, J.H. Lee, H.K. Cho, J.H. Kim, J.Y. Lee, Cryst. Growth Des. 10 (2010) 321.
[11] M.L. Kahn, M. Monge, V. Collière, F. Senocq, A. Maisonnat, B. Chaudret, Adv.
Funct. Mater. 15 (2005) 458.
combustion. On heating the complex 4 at 450 °C for 6 h in air re-
sulted in off-white ZnO indicating the complete removal of carbon.
The morphology of ZnO was different under this condition as ob-
served from the SEM image shown in Fig. 13.
[12] K. Black, A.C. Jones, I. Alexandrou, P.N. Heys, P.R. Chalker, Nanotechnology 21
(2010) 045701.
[13] D. Bekermann, D. Rogalla, H.-W. Becker, M. Winter, R.A. Fischer, A. Devi, Eur. J.
Inorg. Chem. (2010) 1366.
4. Concluding remarks
[14] J.S. Matthews, O.O. Onakoya, T.S. Ouattara, R.J. Butcher, Dalton Trans. (2006)
3806.
[15] M. Hamid, A.A. Tahir, M. Mazhar, F. Ahmad, K.C. Molloy, G. Kociok-Kohn, Inorg.
Chim. Acta 361 (2008) 188.
[16] A. Cingolani, S. Galli, N. Masciocchi, L. Pandolfo, C. Pettinari, A. Sironi, Dalton
Trans. (2006) 2479.
The mononuclear complex 1 and four 3,5-lutidine coordinated
zinc(II) aryl carboxylate complexes (2–5) were synthesized in high
yield and structurally characterized. Complex 1 possesses two dis-
tinct acetate and 3,5-lutidine moieties as one of the acetates forms
an intermolecular O–HꢀꢀꢀO hydrogen bonding with a lattice water
molecule as revealed by X-ray diffraction data and further sup-
ported by solid-state CP-MAS 13C NMR data. Complexes 2 and 3
possess a paddlewheel framework, whereas complexes 4 and 5
possess a mononuclear framework with the zinc atom in tetrahe-
dral and an octahedral geometry, respectively. It was observed that
subtle basic/steric properties of the carboxylate moieties influence
their coordination modes which in turn influence the nuclearity of
the products. As basicity of the carbonyl oxygen of the carboxylate
moiety increases in complexes 2–5, its tendency to coordinate with
the Zn center also increases. Hence, the carboxylate coordination
mode shifts from the monodentate in 4 to syn–syn bidentate bridg-
ˇ
[17] V. Zelenák, M. Sabo, W. Massa, P. Llewellyn, Inorg. Chim. Acta 357 (2004) 2049.
[18] W. Maret, Y. Li, Chem. Rev. 109 (2009) 4682.
[19] J. Weston, Chem. Rev. 105 (2005) 2151.
[20] G. Parkin, Chem. Rev. 104 (2004) 699.
[21] W.N. Lipscomb, N. Sträter, Chem. Rev. 96 (1996) 2375.
[22] D.E. Wilcox, Chem. Rev. 96 (1996) 2435.
[23] B.L. Vallee, D.S. Auld, Acc. Chem. Res. 26 (1993) 543.
[24] D.J. Darensbourg, Chem. Rev. 107 (2007) 2388.
[25] G.W. Coates, D.R. Moore, Angew. Chem., Int. Ed. 43 (2004) 6618.
[26] D.J. Darensbourg, J.R. Wildeson, J.C. Yarbrough, Inorg. Chem. 41 (2002) 973.
[27] D.J. Tranchemontagne, J.L. Mendoza-Cortés, M. O’Keeffe, O.M. Yaghi, Chem.
Soc. Rev. 38 (2009) 1257.
[28] B.S. Luisi, Z. Ma, B. Moulton, J. Chem. Crystallogr. 37 (2007) 743.
[29] S.I. Vagin, A.K. Ott, B. Rieger, Chem. Ing. Tech. 79 (2007) 767.
[30] N.L. Toh, M. Nagarathinam, J.J. Vittal, Angew. Chem., Int. Ed. 44 (2005) 2237.
[31] O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature
423 (2003) 705.
ing in 2 and 3 and to the chelating in 5. The solid-state CP-MAS 13
C
[32] M. Eddaoudi, D.B. Moler, H. Li, B. Chen, T.M. Reineke, M. O’Keeffe, O.M. Yaghi,
Acc. Chem. Res. 34 (2001) 319.
[33] M. Eddaoudi, H. Li, T. Reineke, M. Fehr, D. Kelley, T.L. Groy, O.M. Yaghi, Top.
Catal. 9 (1999) 105.
[34] P. Hubberstey, K. Lin, N.R. Champness, M. Schröder, in: L. MacGillivray (Ed.),
Metal–Organic Frameworks: Design and Application, John Wiley and Sons,
Inc., Hoboken, NJ, USA, 2010, pp. 131–164 (Chapter 4).
[35] A. Karmakar, R.J. Sarma, J.B. Baruah, Inorg. Chem. Commun. 9 (2006) 1169.
NMR data was shown to be a useful technique to distinguish even
the crystallographically different OC(O) carbon in complexes 2–5.
The thermal decomposition study of 2–5 demonstrated the use of
these complexes to be potential precursors for ZnO in conjunction
with PXRD pattern and SEM images.
ˇ
ˇ
[36] V. Zelenák, I. Císarová, P. Llewellyn, Inorg. Chem. Commun. 10 (2007) 27.
[37] A. Karmakar, J.B. Baruah, Polyhedron 27 (2008) 3409.
[38] H. Kwak, S.H. Lee, S.H. Kim, Y.M. Lee, B.K. Park, E.Y. Lee, Y.J. Lee, C. Kim, S.-J.
Kim, Y. Kim, Polyhedron 27 (2008) 3484.
Acknowledgments
The authors acknowledge Council of Scientific and Industrial
Research, New Delhi (# 01/(2076)/06 EMR-II) for financial support
and for a fellowship (U.K.). NMR Research center, Indian Institute
of Science, Bangalore 560012 and Department of Chemistry, Indian
Institute of Technology Kanpur, Kanpur 208016 are acknowledged
for the solid-state CP-MAS 13C NMR data for all complexes reported
in this manuscript and crystallographic data for complex 1,
respectively.
[39] K.F. Konidaris, M. Kaplanis, C.P. Raptopoulou, S.P. Perlepes, E. Manessi-Zoupa,
E. Katsoulakou, Polyhedron 28 (2009) 3243.
[40] U. Kumar, J. Thomas, N. Thirupathi, Inorg. Chem. 49 (2010) 62.
[41] U. Kumar, J. Thomas, M. Agarwal, N. Thirupathi, Inorg. Chim. Acta (2011),
doi:10.1016/j.ica.2011.01.040.
[42] SMART, Bruker Molecular Analysis Research Tool, Version 5.0, Bruker Analytical
X-ray Systems, Madison, WI, 2000.
[43] SAINT
-
NT, Version 6.04, Bruker Analytical X-ray Systems, Madison, WI, 2001.
NT, Version 6.12, Reference Manual.
[44] G.M. Sheldrick, SHELXTL
-
[45] B. Klaus, DIAMOND, Version 2.0 c, University of Bonn, Bonn, Germany, 2004.
[46] D.R. Lide (Ed.), CRC Handbook of Chemistry and Physics, 81st ed., CRC Press,
New York, 2000/2001 (Sec. 8).
[47] B. Singh, J.R. Long, F. Fabrizi de Biani, D. Gatteschi, P. Stavropoulos, J. Am.
Chem. Soc. 119 (1997) 7030.
Appendix A. Supplementary material
CCDC 808869, 750049, 750051, 750050, and 750048 contain
the supplementary crystallographic data for compounds 1, 2, 3, 4
and 5, respectively. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.ica.2011.01.083.
[48] Y.B. Koh, G.G. Christoph, Inorg. Chem. 18 (1979) 1122.
[49] H. Nacefoglu, W. Clegg, A.J. Scott, Acta Crystallogr., Sect. E: Struct. Rep. Online
58 (2002) m121.
ˇ
[50] V. Zelenák, M. Sabo, W. Massa, J. Cernak, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 60 (2004) m85.
[51] R.L. Rardin, W.B. Tolman, S.J. Lippard, New J. Chem. 15 (1991) 417.
[52] D.D. LeCloux, A.M. Barrios, T.J. Mizoguchi, S.J. Lippard, J. Am. Chem. Soc. 120
(1998) 9001.
[53] S.F. Sousa, P.A. Fernandes, M.J. Ramos, J. Am. Chem. Soc. 129 (2007) 1378.
[54] M. Torrent, D.G. Musaev, K. Morokuma, J. Phys. Chem. B 105 (2001) 322.
[55] R.C. Mehrotra, R. Bohra, Metal Carboxylates, Academic Press, New York, 1983.
[56] G.B. Deacon, R.J. Philllips, Coord. Chem. Rev. 33 (1980) 227.
[57] K. Nakamoto (Ed.), Infra-red and Raman Spectra of Inorganic and Coordination
Compounds, Wiley, New York, 1997.
References
[1] Ü. Özgur, Y.I. Alivov, C. Liu, A. Teke, M.A. Reshchikov, S. Dog˘an, V. Avrutin, S.-J.
Cho, H. Morkoc, J. Appl. Phys. 98 (2005) 041301.
[2] S.J. Pearton, D.P. Norton, K. Ip, Y.W. Heo, T. Steiner, Prog. Mater. Sci. 50 (2005)
293.
ˇ
[58] V. Zelenák, Z. Vargová, K. Györyová, Spectrochim. Acta Part A 66 (2007) 262.
[59] M. Nara, H. Torii, M. Tasumi, J. Phys. Chem. 100 (1996) 19812.
[60] K. Ito, H.J. Bernstein, Can. J. Chem. 34 (1956) 170.
[3] D.W. Bahnemann, C. Kormann, M.R. Hoffmann, J. Phys. Chem. 91 (1987) 3789.
[4] L. Spanhel, M.A. Anderson, J. Am. Chem. Soc. 113 (1991) 2826.
[5] Y. Inubushi, R. Takami, M. Iwasaki, H. Tada, S. Ito, J. Colloid Interface Sci. 200
(1998) 220.
[6] S.A. Studenikin, N. Golego, M. Cocivera, J. Appl. Phys. 83 (1998) 2104.
[7] N. Audebrand, J.-P. Auffrédic, D. Louër, Chem. Mater. 10 (1998) 2450.
[8] W. Wieldraaijer, J. van Balen Blanken, E.W. Kuipers, J. Cryst. Growth 126 (1993)
305.
[61] J.F. Arenas, S. Montero, J. Morcillo, J.L. Núñez, An. Quim. 69 (1973) 311.
[62] T. Ishioka, Y. Shibata, M. Takahashi, I. Kanesaka, Y. Kitagawa, K.T. Nakamura,
Spectrochim. Acta Part A 54 (1998) 1827.
ˇ
[63] A. Demšar, J. Košmrlj, S. Petricek, J. Am. Chem. Soc. 124 (2002) 3951.
[64] B.-H. Ye, X.-Y. Li, I.D. Williams, X.-M. Chen, Inorg. Chem. 41 (2002) 6426.
[65] P.A. Hunt, B.P. Straughan, A.A.M. Ali, R.K. Harris, B.J. Say, J. Chem. Soc., Dalton
Trans. (1990) 2131.