Synthesis, spectral and thermal characterization of nano-sized, oxo-centered, trinuclear carboxylate-bridged chromium(III) complexes of hydroxycarboxylic acids

Article abstract of DOI:10.1016/j.molstruc.2008.12.029

Complexes of the type [Cr₃O(OOCR^*)₃(OOCR)₃]⁺ [R^* = C₆H₄OH, (R′); C₆H₅CH(OH), (R″) or (C₆H₅)₂C(OH), (R′″) and R =

Full text of DOI:10.1016/j.molstruc.2008.12.029

Journal of Molecular Structure 920 (2009) 472–477
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectral and thermal characterization of nano-sized, oxo-centered,
trinuclear carboxylate-bridged chromium(III) complexes of hydroxycarboxylic acids
*
B.P. Baranwal , Talat Fatma, Anand Varma
Department of Chemistry, DDU Gorakhpur University, Gorakhpur, Uttar Pradesh 273 009, India
a r t i c l e i n f o
a b s t r a c t
Complexes of the type [Cr3O(OOCR*)3(OOCR)3]+ [R* = C6H4OH, (R0); C6H5CH(OH), (R00) or (C6H5)2C(OH),
(R000) and R = C15H31 or C17H35] were synthesized by substitutions of acetate ions from their respective
acetato complexes, in toluene under reflux. The characterization of the complexes were carried out by
spectral (infrared, electronic, FAB mass and powder XRD) studies, elemental analyses, molar conductance
and magnetic susceptibility measurements. Their thermal decompositions have been studied by using
dynamic, nonisothermal thermogravimetry (TG) and differential scanning calorimetry (DSC). Infrared
spectra suggested bidentate and bridging nature of both the carboxylate and hydroxycarboxylate anions
Article history:
Received 29 September 2008
Received in revised form 8 December 2008
Accepted 8 December 2008
Available online 24 December 2008
Keywords:
Chromium(III)
Oxo-centered
Carboxylate
Hydroxycarboxylate
Nano-sized
along with masym(Cr3O) vibrations in the complexes. FAB mass spectrometry showed trinuclear nature of
the complexes. Molar conductance value of the complexes showed the complexes were 1:1 electrolyte.
Magnetic moment values and electronic spectra of these complexes were in support of an octahedral
environment around the chromium(III) ion. X-ray diffraction data indicated the nano-sized powder.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
of chromium(III) with higher fatty acids and hydroxycarboxylic
acids are not reported so far. In view of these objectives, we report
Trinuclear, oxo-centered, carboxylate-bridged complexes of the
general composition [M3O(OOCR)6(L)3]+ (M = 3-d metal atom,
RCOOH = carboxylic acid, L = terminal ligand like water, methanol,
pyridine, etc.) represents one of the most intensely studied class of
polynuclear compounds [1]. These species have been of continual
interest for several reasons: they serve as a suitable models to
study electronic and magnetic metal–metal interactions in clusters
[2–7], they display properties of homogeneous catalysts in various
oxidation reactions [8]. They behave as precursors for clusters of
higher nuclearity whose unusual structural design and physical
properties open new opportunities for experimental modeling of
biocatalysis and their structural variations allow a close examina-
tion of parameters affecting the metal–ligand aggregates [9,10]. In
recent years, these multinuclear carboxylate assemblies of chro-
mium(III) have been increasingly used as functional biomimetic
models to study insulin related functions of the unique low-molec-
ular-weight chromium-binding-oligopeptide (LMWCr) [11–13]
which have been proposed as possible nutritional supplements
and therapeutics for adult-onset diabetes [14].
here synthesis of some
oxylato) chromium(III)acetate complexes following substitutions
of acetate ions of the 3-oxo-tri(acetato)tri(carboxylato)chro-
mium(III)acetate. Coordination behaviour of the ligands has been
discussed to arrive at their structure on the basis of spectral, ther-
mal and magnetic studies.
l3-oxo-tri(carboxylato)tri(hydroxycarb-
l
2. Experimental
2.1. Materials and physico-chemical measurements
All the reactions were carried out under anhydrous conditions.
Organic solvents (Qualigens) were dried and distilled before use by
standard methods [18]. Carboxylic acids were used after distilla-
tion under reduced pressure (mp of palmitic acid: 63 °C and stearic
acid: 70 °C). Hydroxycarboxylic (salicylic, mandelic and benzilic)
acids (BDH) were used after purification. Chromium was estimated
gravimetrically as lead chromate [19]. Acetic acid in the collected
azeotrope was estimated with standard sodium hydroxide using
phenolphthalein indicator.
Electronic spectra were recorded on a Cary 2390 spectropho-
tometer in Nujol, infrared spectra were recorded on a Perkin-Elmer
model 125 FTIR spectrophotometer in KBr discs in the range 4000–
400 cmꢀ1. FAB mass data were obtained on a JEOL SX 102/ DA-
6000 mass spectrometer using m-nitrobenzyl alcohol (NBA) as a
matrix from CDRI Lucknow. Powder X-ray diffraction data were
Perusal of the literature reveals that a number of transition met-
als form complexes with hydroxycarboxylic ligands [15–17], but
studies on chromium(III) complexes with such ligands are very
limited. It has also been found that the mixed-ligand complexes
* Corresponding author. Tel.: +91 551 2203459.
E-mail address: drbpbaranwal@yahoo.com (B.P. Baranwal).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.12.029

B.P. Baranwal et al. / Journal of Molecular Structure 920 (2009) 472–477
473
collected on a MiniFlex2 goniometer from MANIT Bhopal, India.
Molar conductances were measured on century CC-601 digital con-
ductivity meter at 10ꢀ2–10ꢀ3 molar solutions in nitrobenzene. Ele-
mental analyses (C, H) were done on a Haraleus 1108 analyzer. TG-
DSC curves were obtained by using a NETZSCH STA 409 PG/PC
This was purified by reprecipitation from benzene–methanol mix-
ture (1:4 ratio). Other mixed-ligand complexes were synthesized
following the same procedure and the analytical results are sum-
marized in Table 1.
instrument under
a
nitrogen atmosphere (flow rate of
3. Results and discussion
100 ml minꢀ1) with a heating rate 10 °C minꢀ1. Magnetic suscepti-
bility data were obtained from polycrystalline samples on a Gouy
balance using Hg[Co(SCN)4] as a calibrant.
A number of trinuclear, oxo-centered, mixed carboxylato com-
plexes of chromium(III) of the general formula [Cr3O(OOC-
CH3)3(OOCR)3](OOCCH3) were synthesized by the substitutions of
2.2. Synthesis of [Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH
acetate ions from [Cr3(OOCCH3)7(OH)2]
(l3-oxo-(aqua)hepta-
kis(acetato)chromium(III)) with long chain carboxylic acids in 1:3
molar ratios using toluene as a solvent, and the product obtained
were reprecipitated with benzene–methanol mixture (1:4 ratio).
A solution of salicylic acid (0.82 g; 5.91 mmol) in toluene was
added to
a
toluene solution of [Cr3O(OOCCH3)3(OOC-
C15H31)3](OOCCH3)ꢁ3CH3OH (2.50 g; 1.97 mmol) [5]. The reaction
mixture was refluxed for 13 h with slow and continuous fraction-
ation of acetic acid–toluene azeotrope (bp 106 °C). The progress
of the reaction was followed by estimating the CH3COOH content
in the collected azeotrope. Excess solvent was removed under re-
duced pressure (1.5 mm/60 °C) to yield a yellowish-green solid.
½Cr3ðOOCCH3Þ ðOHÞ ꢂ þ 3RCOOH Toluene
ƒ!
7
2
Reflux
½Cr3OðOOCCH3Þ3ðOOCRÞ3ꢂðOOCCH3Þ þH2O " þ3CH3COOH "
ð1Þ
A
where R = C15H31 or C17H35
.
Table 1
Analytical and conductance results for the chromium(III) complexes.
Reactantsa (g; mmol)
Productb (Colour) (% yield)
Found (Calculated)
Conductance
ꢀ1 cm2 molꢀ1
)
(
X
CH3COOH in azeotrope (g) Cr
C
H
[Cr3O(OOCCH3)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH [Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH
0.31
(0.36)
10.40
59.10
8.19
(2.50; 1.97) + R0COOH (0.82; 5.91)
(Yellowish green) (76) (1)
(10.36) (59.07) (8.24) 41
[Cr3O(OOCCH3)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH [Cr3O(OOCR0)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH
0.34
(0.31)
9.85 60.52 8.61
(9.82) (60.48) (8.57) 37
10.15 59.87 8.41
(10.09) (59.80) (8.40) 32
9.55 61.04 8.65
(9.56) (61.12) (8.72) 45
8.76 64.31 8.10
(8.80) (64.28) (8.00) 39
8.45 65.24 8.27
(8.40) (65.25) (8.30) 33
(2.32; 1.71) + R0COOH (0.71; 5.14)
(Green) (78) (2)
[Cr3O(OOCCH3)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH [Cr3O(OOCR00)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH
0.40
(0.43)
(3.00; 2.36) + R00COOH (1.08; 7.09)
(Dark green) (84) (3)
[Cr3O(OOCCH3)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH [Cr3O(OOCR00)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH
0.38
(0.43)
(3.20; 2.36) + R00COOH (1.08; 7.10)
(Dark green) (84) (4)
[Cr3O(OOCCH3)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH [Cr3O(OOCR000)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH 0.35
(2.63; 2.07) + R000COOH (1.42; 6.22)
(Green) (79) (5)
(0.37)
[Cr3O(OOCCH3)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH [Cr3O(OOCR000)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH 0.31
(2.50; 1.85) + R000COOH (1.27; 5.26)
(Dark green) (83) (6)
(0.33)
a
Reflux about 13–16 h, C6H4OH; (R0), C6H5CH(OH); (R00) and (C6H5)2C(OH); (R000).
Reprecipitated product in benzene–methanol mixture (1:4).
b
Fig. 1. Room-temperature electronic spectrum of [Cr3O(OOCR00)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH.

474
B.P. Baranwal et al. / Journal of Molecular Structure 920 (2009) 472–477
Table 2
Electronic spectral transitions (cmꢀ1) and magnetic moment values for the complexes.
4
Complexesa
Observed transitions from A2 g (F) to
B (cmꢀ1
)
b
leff (B.M.)
4T2 g (F) (
m
1, 10 Dq)
4T1 g (F) (m2
)
4T1 g (P) (m3
)
[Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH
[Cr3O(OOCR0)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH
[Cr3O(OOCR00)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH
[Cr3O(OOCR00)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH
[Cr3O(OOCR000)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH
[Cr3O(OOCR000)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH
17110
16880
16695
17271
16630
16770
22882
23215
23105
22728
23015
22780
36715
36743
36471
36797
36329
36262
551
621
633
514
630
582
0.60
0.66
0.68
0.55
0.67
0.62
3.40
3.36
3.39
3.33
3.38
3.34
a
R0 = C6H4OH; R00 = C6H5CH(OH); and R000 = (C6H5)2C(OH).
Table 3
Thermoanalytical results for the chromium(III) complexes.
Complex
Step
Decomp.
TG weight loss (%)
Found
DSC
Inference
Temp. (°C)
Cacld.
Temp. (°C)
Peak
1
1st
2nd
3rd
184–334
334–452
452–528
>528
10.95
53.29
26.13
10.30
50.92
27.33
312
425
507
Exoa
Liberation of 3CH3OH and CH3COOꢀ moieties
Liberation of all fatty acid groups
Liberation of salicylic acid
Endob
Exoa
Cr2O3 as residue
2
3
4
1st
2nd
3rd
192–340
340–462
462–530
>530
10.63
55.04
23.47
9.76
53.52
25.88
318
452
518
Exoa
Exoa
Exoa
Liberation of 3CH3OH and CH3COOꢀ moieties
Liberation of all fatty acid groups
Liberation of salicylic acid
Cr2O3 as residue
1st
2nd
3rd
172–328
328–435
435–530
>530
12.37
47.23
29.91
10.02
49.53
29.31
315
419
522
Exoa
Liberation of 3CH3OH and CH3COOꢀ moieties
Liberation of all fatty acid groups
Liberation of mandelic acid
Endob
Exoa
Cr2O3 as residue
1st
2nd
3rd
185–340
340–425
425–535
>535
12.01
51.22
28.15
9.51
52.14
27.80
325
418
515
Endob
Endob
Exoa
Liberation of 3CH3OH and CH3COOꢀ moieties
Liberation of all fatty acid groups
Liberation of mandelic acid
Cr2O3 as residue
5
1st
2nd
3rd
172–318
318–436
436–520
>520
175–320
320–445
445–530
>530
7.13
48.50
35.44
8.74
43.16
38.40
290
405
512
Exoa
Liberation of 3CH3OH and CH3COOꢀ moieties
Liberation of all fatty acid groups
Liberation of benzilic acid
Endob
Exoa
Cr2O3 as residue
6
1st
2nd
3rd
10.23
48.39
32.65
8.34
45.74
36.66
302
418
510
Exoa
Exoa
Exoa
Liberation of 3CH3OH and CH3COOꢀ moieties
Liberation of all fatty acid groups
Liberation of benzilic acid
Cr2O3 as residue
Note. (+) a, exo (exothermic); (ꢀ) b, endo (endothermic); Calcd. calculated ; Temp, temperature ; Decomp., decomposition.
Fig. 2. Thermogram of [Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH.

B.P. Baranwal et al. / Journal of Molecular Structure 920 (2009) 472–477
475
A þ CH3OH ¼ ½Cr3OðOOCCH3Þ3ðOOCRÞ3ꢂðOOCCH3Þ ꢁ 3CH3OH
3.1. Infrared spectra
The acetate ions of these products were further substituted with
hydroxycarboxylic (salicylic, mandelic or benzilic) acids in reflux-
ing toluene and products were finally reprecipitated from their
benzene solution by adding an excess of methanol:
In FTIR spectra of the synthesized complexes, the characteristic
(C@O) and d (OAH) of free carboxylic acids at 1710 and 935 cmꢀ1
m
,
respectively, were found absent. The OAH stretching vibration of
free hydroxyl group of hydroxycarboxylic acid was noticed at
ꢄ3400 cmꢀ1 in the IR spectra of the complexes, which indicated
that the hydroxyl group of hydroxycarboxylic acid was not bound
to chromium and it was remained in free state. Two strong bands
were found in the range 1640–1585 and 1436–1400 cmꢀ1 which
could be assigned due to (masymOCO) (antisymmetric) and (msymO-
CO) (symmetric) vibrations of the carboxylate ions, respectively
[21]. The differences between the symmetric and antisymmetric
½Cr3OðOOCCH3Þ ðOOCRÞ ꢂðOOCCH3Þ ꢁ 3CH3OH þ 3RꢃCOOH
3
3
Toluene
ƒ!
½Cr3OðOOCRꢃÞ ðOOCRÞ ꢂðOOCCH3Þ þ 3CH3COOH "
3
3
Reflux
þ 3CH3OH "
ð2Þ
ð3Þ
where R* = C6H4OH (R0), C6H5CH(OH) (R00) or (C6H5)2C(OH) (R000).
½Cr3OðOOCRꢃÞ ðOOCRÞ ꢂðOOCCH3Þ þ CH3OH
! ½Cr3OðOOCRꢃÞ ðOOCRÞ ꢂðOOCCH3Þ ꢁ 3CH3OH
3
3
ðExcessÞ
stretches,
D
[
m
asym(OCO) ꢀ
msym(OCO)] were in the range 150–
160 cmꢀ1, which were less than that for monodentate NaOOCCH3
(184 cmꢀ1) [22]. This indicated the carboxylate groups of both car-
boxylic acids and hydroxycarboxylic acids were coordinated to
chromium in a bidentate and bridging mode involving coordina-
tion of both the oxygen atoms of the ligands [22]. A medium band
observed at ꢄ680 cmꢀ1 was attributed to d (CO2) of bridging car-
boxylate anion [22]. The broad band observed at ꢄ3150 cmꢀ1
was assigned to the OAH stretching of coordinated methanol
[6,7]. An absorption near 540 cmꢀ1 could be assigned to asymmet-
ric stretching of the Cr3O core [23]. The bands below 500 cmꢀ1 may
be ascribed to CrAO vibrations [22].
3
3
All the above reactions were carried out in toluene because of
the advantage that it forms an azeotrope with acetic acid (bp
106 °C) liberated during the course of reactions which could be
fractionated out to push the reaction in the forward direction.
The reactions were facile and their progress could be followed
by estimating the acetic acid content in the collected azeotrope.
All the complexes isolated during the present investigations are
non-volatile coloured solids. The complexes were soluble in
non-polar organic solvents including benzene, toluene, chloro-
form, dichloromethane, etc. The values of molar conductances
in
nitrobenzene
were
found
in
the
range
33–
3.2. Electronic spectra and magnetic moments
45 ohmꢀ1 cm2 molꢀ1 which clearly indicated that all the com-
plexes were 1:1 electrolyte [20]. The complexes did not have
sharp melting point and all of them were decomposed at around
425–535 °C temperature.
The electronic spectrum of
a
representative complex
[Cr3O(OOCR00)3(OOCC17H35)3](OOCCH3)ꢁ3CH3OH is given in (Fig. 1
and Table 2). The spectra of the complexes exhibited two spin–al-
lowed bands at 16,630–17,271 and 22,728–23,215 cmꢀ1 which
4
4
could be assigned to A2g(F) ? 4T2g (F) ( 1) and A2g(F) ? 4T1g (F)
m
(m
2), respectively. These bands suggested an octahedral environ-
ment around chromium(III) in the complexes and the lowest en-
ergy band ( 1) is equal to the crystal field splitting i.e. 10 Dq
[24]. The position of the third band 4A2g (F) ? 4T1g (P) (
3), the Ra-
cah parameter (B) and the nephelauxetic ratio (b) have been calcu-
lated using Eqs. (4)–(6) given by Underhill and Billing [25]
Table 4
FAB mass data of [Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3).3CH3OH.
m
Peak position
Expected fragmentation species
Calcd. mol. wt.
m
1472
1413
1347
1095
842
[Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ2CH3OH
[Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)
[Cr3O(OOCR0)3(OOCC15H31)3]+
[Cr3O(OOCR0)3(OOCC15H31)2]2+
[Cr3O(OOCR0)3(OOCC15H31)]3+
[Cr3O(OOCR0)3]4+
1473
1409
1350
1094
839
340 Dq þ 18ðm2
B ¼ m3 m2 ꢀ 30 Dq=15
b ¼ Bcomplex=Bfree ion
þ
m3ÞDq þ m2
ꢁ
m3 ¼ 0
ð4Þ
ð5Þ
ð6Þ
þ
578
583
Fig. 3. FAB mass spectrum of [Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH.

476
B.P. Baranwal et al. / Journal of Molecular Structure 920 (2009) 472–477
Table 5
Powder XRD data of [Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH.
1. ½Cr3OðOOCR0Þ ðOOCC15H31Þ ꢂðOOCCH Þ ꢁ 3CH OH Temp:range
ƒƒƒƒƒƒ!
3
3
3
3
184—334 ꢅC
Cr3OðOOCR0Þ ðOOCC15H31Þ þ CH3COOH þ 3CH3OH
Peak No.
2 Theta (°)
Flex width
d-Value
Intensity
I/Io
2. Cr3OðOOCR0Þ3ðOOCC15H31Þ3
½Cr OðOOCR0Þ ꢂ4þ þ gaseous
Temp:range
1
2
3
4
19.400
21.400
24.000
59.000
1.176
0.941
0.941
1.176
4.5717
4.1487
3.7048
1.5643
169
798
323
21
22
100
41
ƒƒƒƒƒƒ!
3
3
3
3
334—452 ꢅC
product
Temp:range
ƒƒƒƒƒƒ!
452—528 ꢅC
4þ
3. ½Cr3OðOOCR0Þ ꢂ
Cr O þ gaseous product
2
3
3
3
The end product in all the cases was Cr2O3 which was confirmed
by estimation of chromium gravimetrically.
The values of B and b were found 514–633 cmꢀ1 and 0.62 0.07,
respectively (Table 2). The reduction of Racah parameter from the
free Cr3+ value (933 cmꢀ1) [24] suggested considerable covalent
character of metal–ligand bonds in these complexes.
3.4. FAB mass, powder XRD and structural elucidation
The magnetic moment of oxo-centered trinuclear chromium car-
boxylate complexes have been explained in detail by earlier workers
[26,27]. The magnetic moment of these complexes were found in the
range 3.37 0.03 B.M. at room temperature (T = 298 K) and the val-
ues are given in Table 2. These values are lower than the calculated
FAB mass spectrum of
a
representative complex
[Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH has been recorded
(Fig. 3) and positions of the peaks are given in Table 4. The peaks
revealed a distinctive set of ions with masses corresponding to
the cation and fragments of parent ions derived by loss of the li-
gands [29].
l
s.o. value for Cr3+ (d3 system, 3.87 B.M.) which could be interpreted
due to the presence of superexchange interactions [26] between Cr3+
Single crystals of the complexes could not be prepared to get
the XRD and hence the powder diffraction data were obtained for
structural characterization. The powder X-ray diffraction spectrum
for [Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH was recorded
(Fig. 4) and the peaks have been indexed by the crystal system (Ta-
ble 5). The lattice parameters (d, 2h, height and area) indicated the
pattern of the sample matched well with those of other trinuclear
chromium(III) oxo-carboxylate assemblies reported earlier
[11,26,27]. With the help of the data obtained from the powder
XRD, the particle size of the complexes has been calculated using
the standard equation given by Scherrer [30].
ions. InthesecomplexesCrAOACrbridgeshowsweakantiferromag-
netic interactions and the oxygen atom provides
p-pathways for
antiferromagnetic behaviour. In other words, Cr3+ ions of trinuclear
oxo-centered chromium(III) (S = +3/2) assemblies are antiferromag-
netically coupled resulting in an S = +1/2 ground state [23]. This is
similar to the trinuclear carboxylates of chromium(III) containing
a central l3AO core [28].
3.3. Thermal studies
The details of TG and DSC data for the complexes are given in
D ¼ Kk=ðb cos hÞ
ð7Þ
Table
3
and
a
thermogram of complex [Cr3O(OOCR0)3
where, D is the average size of the crystal gain; K is constant
(=0.94); k is X-ray wavelength (=1.5406 Å); h is Bragg diffraction an-
gle; b is integral peak width of the diffraction peak.
(OOCC15H31)3](OOCCH3)ꢁ3CH3OH is given in Fig. 2. The complexes
were decomposed in three steps and the pattern of decomposition
is given below:
Fig. 4. Powder XRD spectrum of [Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH.

B.P. Baranwal et al. / Journal of Molecular Structure 920 (2009) 472–477
477
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Fig. 5. Proposed structure for [Cr3O(OOCR*)3(OOCR)3(L)3]+ (where: R* = C6H4OH;
(R0), C6H5CH(OH); (R00) or (C6H5)2C(OH); (R000); R = C15H31 or C17H35 and L = CH3OH).
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The size for the representative complex was obtained 15.0 nm
and on this basis it could be concluded that the complex
[Cr3O(OOCR0)3(OOCC15H31)3](OOCCH3)ꢁ3CH3OH is
a nano-sized
oxo-bridged complex of chromium(III) with an octahedral struc-
ture. On the basis of spectral, thermal and magnetic studies, a plau-
sible structure for the complexes is established (Fig. 5) in which
chromium(III) is situated in an octahedral environment and one
carboxylate and one hydroxycarboxylate ligands are bridged be-
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Authors are thankful to the UGC, New Delhi [DSA and No. F.31-
126/ 2005 (SR)] for financial supports. They also thank CDRI, Luc-
know for doing microanalysis and FAB mass of the samples and
MANIT Bhopal for recording powder XRD data.