Preparation and Characterization
of Some Targeted Complexes of Chromium
Deepak
Kumar1*, K.
Akhtar2, R. Ranjan2 and M. Alam1
1University Department of Chemistry,
Ranchi University, Ranchi-834008
2PG Department of Chemistry, Ranchi
College, Ranchi-834008
*Corresponding
Author E-mail: dsinha56.56@gmail.com
ABSTRACT:
The present paper
investigates the preparation and characterisation of targeted complexes of
chromium using di-tertiary butyl
chromate (TBC) - a Cr(VI) based oxidant, one easily oxidisable and good
chelating agent along with another good ligand - with following aims:
a.Whether Cr in reduced
state enters into complexation with the oxidised fragment(s) or with the
unreacted substrate(s)?
b.And if yes whether the
process is selective as far as the nature of ligands are concerned? What we
want to see that if this process can provide a mean to gauze the co-ordinating
‘power’ of the various potential chelating groups present in the system, at
least, qualitatively?
KEY WORDS: TBC, TBA, FTIR, TLC, TGA, DTA.
INTRODUCTION:
A number of Cr (VI) based oxidants are being used to carry out
oxidation of a wide variety of organic substrates.1-10
Important among these are di-tertiary butyl chromate, di-isopropyl chromate,
chromium peroxide etherate, pyridine chromium peroxide and 2,2-bipyridyl
chromium peroxide. But owing to several merits,11-13 the use of di-tert-butyl chromate (TBC) as an
oxidant is well documented. Not only it is exploited to carry out oxidation but
also for complex formation.14-22 The unreacted substrate and
various products formed during the oxidation - all can be potential candidates
for finding place in the co-ordination sphere of the metal, particularly in
reduced state. Hitherto only one substrate is being used to start with, but in
this work two substrates have been taken thereby giving more ‘option’ to the
metal.
EXPERIMENTAL:
Case 1
1.56 g of 2,2’-bipyridyl was taken in 10 ml of TBA and 1 ml of
salicylaldehyde was added to it. This was refluxed for 5-10 minutes.1.5 g of
CrO3 was dissolved in 5 ml of TBA. These two solutions (first one
still hot) were mixed slowly, stirred and then refluxed using water condenser.
A brown solid product precipitated, which was separated out and
washed with water and then finally with TBA. Purity was tested with TLC using
silica gel. The product was named BP-SA 107 and kept in air tight bottle.
Quantitative analysis of the sample for C, H, N, was carried out using CHN
analyser. Cr content was determined by titration and finally by AAS. Oxygen
content was ascertained by difference. IR Spectra was obtained and thermal
analysis (TG and DTA) was carried out.
RESULT AND DISCUSSION:
Colour of the sample BP-SA 107:
Brown
Percentage composition of the sample: C(32.820),
H(4.377), N(4.578), O(37.737) and Cr(20.488)
Empirical formula: C17H27N2O14Cr2
IR absorption peak at 776.38cm-1 is a characteristic of
di-substituted aromatic nucleus and the peak at 1446.61 cm-1 is due
to C=C skeletal in plane vibration for aromatic nucleus. The peak at 3078.39 cm-1
is the familiar C-H stretching vibration of aromatic compounds. IR band at
1604.77 cm-1 points the presence of COO- group. Peaks at
659.66 cm-1 is due to Cr-O stretching and at 513.07 cm-1
is for Cr-N stretching. Peak at 3383.14 cm-1 is for O-H stretching
in co-ordinated water (Fig 1). The shifting of peaks for COO- from
normal~1650 cm-1 to lower value ~1600 cm-1 indicates that
it is involved in complexation with metal.
Fig 1: IR Spectra of BP-SA 107
Fig 2: TGA Graph of BP-SA 107
On the basis of these facts,
Proposed molecular formula: C17H27N2O14Cr2
Probable structure: C7H5O3.C10H8N2.7H2O.Cr2O4
or
C6H4 (OH)COO-.C10H8N2.7H2O.Cr2O4
Heating upto 200oC
results in the loss of 90g( loss of five water molecules), then in the range 200-500 oC a loss of
321.16g occurs indicating the expulsion of both the major ligands- salicylate
and bipyridyl units accounting for a loss of 293g and two water molecules, an additional loss of
36g making the overall loss 329g. After that the loss is continuing very
slowly(fig 2). Both the above mentioned losses appear to support the proposed
structure.
Case 2
1.56 g of 2,2’-bipyridyl was taken in 10 ml of TBA and 1 ml of
salicylaldehyde was added to it. This was refluxed for 5-10 minutes. 1.0 g of
CrO3 was dissolved in 5 ml of TBA. These two solutions (first one
still hot) were mixed slowly, stirred and then refluxed using water condenser.
A brown solid product was separated out which was washed with water and then
finally with TBA. Purity was tested with TLC using silica gel. The product was
named BP-SA 108 and kept in air tight bottle. Quantitative analysis of the
sample for C,H,N, was carried out using
CHN analyser. Cr content was determined by titration and finally by
AAS. Oxygen content was ascertained by
difference. IR Spectra was obtained and thermal analysis (TG and DTA) was
carried out.
RESULT AND DISCUSSION:
Colour of the sample BP-SA 108:
Brown
Percentage composition of the sample: C(33.890), H(4.502), N(5.650), O(38.734) and
Cr(17.524)
Empirical formula: C17H27N2O14Cr2
IR absorption peak at 779.26cm-1 is a characteristic of
di-substituted aromatic nucleus and the peak at 1450.47 cm-1 is due
to C=C skeletal in plane vibration for aromatic nucleus. The peak at 3074.53 cm-1
is the familiar C-H stretching vibration of aromatic compounds. IR band at
1604.77 cm-1 points the presence of COO- group. Peaks at
at 659.66 cm-1 is due to Cr-O stretching and one at around 500cm-1
is for Cr-N stretching. Peak at 3387.00 cm-1 is for O-H stretching
in co-ordinated water (Fig 3). The shifting of peaks for COO- from
normal~1650 cm-1 to lower value ~1600 cm-1 indicates that
it is involved in complexation with metal.
On the basis of these facts,
Proposed molecular formula: C17H27N2O14Cr2
Probable structure: C7H5O3.C10H8N2.7H2O.Cr2O3
or C6H4(OH)COO-.C10H8N2.7H2O.Cr2O3
Fig 3: IR Spectra of BP-SA 108
Fig 4: TGA Graph of BP-SA 108
Heating upto 200oC
is found to result in the loss of 94g
(loss of five water molecules), then in the range 200-500 oC
a loss of 328.3g takes place indicating the expulsion of two water molecule,
salicylate and bipyridyl units accounting for a loss of 329g (Fig 4). After
that the loss is continuing. Both the above mentioned losses appear to support
the proposed structure.
Case 3
1.56 g of 2,2’-bipyridyl was taken in 10 ml of TBA and 1 ml of
salicylaldehyde was added to it. This was refluxed for 5-10 minutes. 0.5 g of
CrO3 was dissolved in 5 ml of TBA. These two solutions (first one
still hot) were mixed slowly, stirred and then refluxed using water condenser.
A brown solid product was separated out which was washed with water and then
finally with TBA. Purity was tested with TLC using silica gel. The product was
named BP-SA 109 and kept in air tight bottle. Quantitative analysis of the
sample for C,H,N, was carried out using
CHN analyser. Cr content was determined by titration and finally by AAS.
Oxygen content was ascertained by difference. IR Spectra was obtained and
thermal analysis (TG and DTA) was carried out.
RESULT AND DISCUSSION:
Colour of the sample BP-SA 109:
Brown
Percentage composition of the sample: C(36.690), H(4.223), N(6.339), O(33.664) and Cr(19.084)
Empirical formula : C17H23N2O11Cr2
IR absorption peak at 779.24cm-1 is a characteristic of
di-substituted aromatic nucleus and the peak at 1454.33 cm-1 is due
to C=C skeletal in plane vibration for aromatic nucleus. The peak at 3074.53 cm-1
is the familiar C-H stretching vibration of aromatic compounds. IR band at
1604.77 cm-1 points the presence of COO- group. Peaks at
659.66 cm-1 is due to Cr-O stretching and at 470.63 cm-1
is for Cr-N stretching. Peak at 3402.43.00 cm-1 is for O-H
stretching in co-ordinated water (Fig 5). The shifting of peaks for COO- from
normal~1650 cm-1 to lower value ~1600 cm-1 indicates that
it is involved in complexation with metal.
On the basis of these facts,
Proposed molecular formula: C17H23N2O11Cr2
Probable structure: C7H5O3.C10H8N2.5H2O.Cr2O4 or
C6H4(OH)COO-.C10H8N2.5H2O.Cr2O4
On thermal analysis, it is found that heating upto 200oC
is accompanied with the loss of 57g (loss of three water molecules), then in
the range 200-500 oC a loss of 342g occurs indicating the expulsion
of both the major ligands - salicylate and bipyridyl units accounting for a
loss of 293g and two water molecules, an additional loss of 36g making the
overall loss 329g (Fig 6). After that the loss is continuing. Both the above
mentioned losses appear to support the proposed structure.
CONCLUSIONS:
In the cases cited above, salicylaldehyde is oxidised to salicylic
acid and Cr in reduced state enters into complexation with salicylate ion and
2, 2’-bipyridyl along with water that might have been formed during the
process. Both salicylate as well as
bipyridyl making their appearance in the co-ordination sphere in all cited
complexes indicates their strong co-ordinating capacity. Cr complexes with such
ligands are well known.23-27 It is not out of place to mention that
Cr is not that much differentiating as
far as the affinity for a particular chelating agent is concerned. In other
words, it is not ‘choosy’ to the extent of making any ligand ‘untouchable’ so
far entry to metal’s co-ordination sphere is concerned!
Fig 5: IR Spectra of BP-SA 109
Fig 6: TGA Graph of BP-SA 109
ACKNOWLEDGEMENT:
The authors duly acknowledge the kind co-operation of Central
Instrumentation Facility, BIT, Mesra, Ranchi.
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M. , Asian J. Research Chem192,5(2), Feb
2012
Received on
07.12.2013 Modified on 15.12.2013
Accepted on
12.01.2014 © AJRC All right
reserved
Asian J. Research
Chem. 7(2): February
2014; Page 115-119