Studies on the pyrazine complexes of some diaryltellurium dihalides

Article abstract of DOI:10.13005/ojc/290409

Nine new Pyrazine Complexes of diaryltelluriumdihalides, R ₂TeX₂.Pyz (R =p-methoxyphenyl, p-hydroxyphenyl and 3-methyl- 4-hydroxy phenyl; X=Cl, Br, I; Pyz = pyrazine) have been prepared by reactions of diaryltelluriumdihalides with pyrazine in 1:1 molar ratio. These complexes have been characterized by elemental analysis, conductance and cryoscopic measurements, infrared and proton magnetic resonance spectral studies. Conductance studies in nitrobenzene, acetone and acetonitrile predict their non-electrolyte type behaviour in these solvents, which is well supported by cryoscopic data in nitrobenzene. IR and 1H NMR studies suggest the unidentate nature of pyrazine in these complexes, involving only one nitrogen atom in coordination. Thus, tellurium in R₂TeX₂.Pyz complexes attains a coordination number of five probably in a square pyramidal.

Full text of DOI:10.13005/ojc/290409

ISSN: 0970-020 X
CODEN: OJCHEG
2013, Vol. 29, No. (4):
Pg. 1339-1349
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Studies on the Pyrazine Complexes of
Some Diaryltellurium Dihalides
JITENDER KUMAR NARWAL*, SHASHI CHHABRA,
RAJESH KUMAR MALIK, SAPANA GARG and K.K. VERMA
*JVMGRR College, Department of Chemistry, CharkhiDadri, Haryana, India.
Department of Chemistry, Maharshi Dayanand University, Rohtak, India.
*Corresponding author Email: jitender.narwal@yahoo.com
http://dx.doi.org/10.13005/ojc/290409
(Received: Septembe 01, 2013; Accepted: October 15, 2013)
ABSTRACT
Nine new Pyrazine Complexes of diaryltelluriumdihalides, R2TeX2.Pyz (R =p-methoxyphenyl,
p-hydroxyphenyl and 3-methyl- 4-hydroxy phenyl; X=Cl, Br, I; Pyz = pyrazine) have been prepared
by reactions of diaryltelluriumdihalides with pyrazine in 1:1 molar ratio.These complexes have been
characterized by elemental analysis, conductance and cryoscopic measurements, infrared and
proton magnetic resonance spectral studies. Conductance studies in nitrobenzene, acetone and
acetonitrile predict their non-electrolyte type behaviour in these solvents, which is well supported by
cryoscopic data in nitrobenzene. IR and 1H NMR studies suggest the unidentate nature of pyrazine
in these complexes, involving only one nitrogen atom in coordination.Thus, tellurium in R2TeX2.Pyz
complexes attains a coordination number of five probably in a square pyramidal.
Key words: Diaryltellurium dihalides, Pyrazine complexes.
INTRODUCTION
ShekharSrivastava and coworkers3 have
prepared R2TeX2.L type compounds where R =
benzyl and L = 2,2'-bipridyl; 1,10-phenanthroline
and neocuproine. In these adducts, donor ligands
are coordinated to tellurium atom. In the view of
this and in continuation of our earlier work4,5 on
reactions of various diorganyltelluriumdihalides
R2TeX2with some N-donor bases we hereby, report
the synthesis and characterization of pyrazine
complexes of bis(p-hydroxyphenyl),bis(3-methyl-4-
hydroxyphenyl),bis(p-methoxy phenyl) tellurium(IV)
dihalides.
Aryltelluriumtryhalidesareknowntobehave
as Lewis acids and form molecular complexes with
several nitrogen, oxygen and sulphur donor bases.
It has been reported1 that Lewis acidity of tellurium
atom falls significantly on going from RTeX3 to R2TeX2.
Kulkarni and coworkers screened the adducts of a,a’
–bis(3-nitro/amino benzoyl) tellurium dichloride with
N donor bases for biological activity and were found
to be effective Ach E inhibiting agents2.

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EXPERIMENTAL A saturated solution of pyrazine (0.40
Materials and Methods
gm, 5.0 mmol) in benzene (~10 ml) was added to
a saturated solution of 5.0 mmol of R2TeX2 (2.06
All the chemicals used were of Analytical g. 2.51 g. 2.98 g for chloride, bromide and iodide
Reagents grade.Solvents were purified and dried by respectively) in methanol + chloroform (20:80). The
conventional methods.
contents were stirred of 4 h. Orange brown solid
product obtained was filtered, extracted with diethyl
ether and dried over P4O10 in vacuum desiccators.
Preparations
All the preparations have been carried out
in a dry conditions under inert atmosphere of dry Physical studies
nitrogen, as the compounds are sensitive to moisture
and air.
Elemental analysis for Carbon, hydrogen
and nitrogen contents were got estimated from
Sophisticated Analytical Instrumentation Facility,
Punjab University, Chandigarh on a ELEMENTAR
Preparation of Diaryltellurium(IV) Dihalides
Bis(p-hydroxyphenyl)tellurium dichloride, VARIO EL III or CARLO ERBA Model 1108.
bis(3-methyl-4-hydroxyphenyl) tellurium dichloride The conductance studies were carried out in
and bis(p-methoxyphenyl)telIurium dichloride were acetone, nitrobenzene and acetonitrile on a
obtained by reactions of tellurium tetrachloride highly sensitive Systronics Conductivity Bridge
with phenol, o-cresol and anisole respectively. Type 305. A dip type cell with smooth platinum
The diaryltelluriumdichlorides were converted to electrodes was used. The molecular weights of
corresponding dibromides and diiodides by halogen the complexes of diaryltellurium(IV) dihalides have
exchange processes by using KBr or KI in dry been determined cryoscopically using purified
methanol.
nitrobenzene as the solvent. A Beckmann’s freezing
point apparatus is used. Infrared spectra of the
complexes of diaryltelluriumdihalides prepared
Preparation of Pyrazine Complexes
Pyrazine Complexes of Bis(p-hydroxyphenyl) during this course of study have been recorded
tellurium(IV) Dihalides
in the region 4000-400 cm-1 on a SHIMAZDU
A saturated solution of pyrazine (0.40 FTIR-8300 or PERKIN ELMER Model 2000 FTIR
gm, 5.0 mmol) in benzene (~10 ml) was added to Spectrometer using KBr pellet technique. The
a saturated solution of 5.0 mmol of R2TeX2 (1.92 spectra were got recorded from Dr. B.R. Ambedkar
g, 2.37 g, 2.84 g for chloride, bromide and iodide Centre for Biomedical Research, University of
respectively) in about 20 ml of methanol. The Delhi, Kurukshetra University, Kurukshetra and
contents were stirred for about 3 h which resulted in Sophisticated Analytical Instrumentation Facility,
the separation of a dark coloured solid product.This Panjab University, Chandigarh. ‘H NMR spectra
was filtered, extracted with diethyl ether and dried were recorded on a BRUKER AC-300F operating
over P4O10 in vacuum desiccator.
at 299.9486 MHz and BRUKER AVANCE II 400
NMR spectrometer operating at 400.13 MHz.
Pyrazine Complexes of Bis(3-methyl-4- The data were obtained from Sophisticated
hydroxyphenyl) tellurium(IV)Dihalides Analytical instrumentation facility, Punjab University,
Asaturatedsolutionofpyrazine(0.40gm, 5.0 Chandigarh. The solutions were prepared in
mmol) in benzene (~10 ml) was added to a saturated deuterated DMSO-d6.Spectra were recorded at room
solution of 5.0 mmol of R2TeX2 (2.06 g. 2.51 g. 2.98 temperature immediately after preparing the solution
g for chloride, bromide and iodide, respectively) in using tetramethylsilane as an internal reference.
about 20 ml of dry methanol. The contents were
stirred for 4 h. Brown coloured solid product thus
obtained was filtered, washed with diethyl ether and
dried over P4O10 in vacuum desiccator.
RESULTS AND DISCUSSION
Thesediaryltelluriumdihalideswhenreacted
with pyrazine give 1 : 1 type complexes, R2TeX2.L as
Pyrazine Complexes of Bis(p-methoxyphenyl) per scheme-1
tellurium(lV) Dihalides R2TeX2 + Pyz
R2TeX2.Pyz

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Table 3: Molecular Weight Data for Pyrazine Complexes of Diaryltellurium(IV) Dihalidcs
R2TeX2
(R)
Complex
Formula
Weight
Concentration
in mmoles/
Molecular
weight
litre of solvent
found
R2TeCl2
(p-hydroxyphenyl)
R2TeCl2.Pyz
R2TeBr2.Pyz
R2Tel2.Pyz
R2TeCl2.Pyz
R2TcBr2.Pyz
R2Tel2.Pyz
R2TeCl2.Pyz
466.0
553.7
647.7
492.9
581.8
675.8
492.9
1.421
2.137
2.953
3.131
1.377
2.178
2.784
3.182
1.276
2.047
3.009
3.921
1.257
2.193
2.804
3.314
1.078
1.931
2.487
3.208
1.269
2.084
2.978
3.483
1.374
2.038
2.938
412.4
439.9
459.8
470.4
521.7
535.8
546.3
574.6
601.4
620.3
628.8
654.6
453.7
468.9
482.6
501.3
548.7
560.4
579.9
588.3
643.3
657.8
674.3
689.1
451.4
477.6
483.3
R2TeBr2
(p-hydroxyphenyl)
R2TeI2
(p-hydroxyphenyl)
R2TeCl2
(3-methyl-4-hydroxyphenyl)
R2TeBr2
(3-methyl-4-hydroxy phenyl)
R2TeI2
(3-methyl -4-hydroxyphenyl)
R2TeCl2
(p-methoxyphenyl)
All the compounds were analysed for their
tellurium and halogen contents and some for carbon,
hydrogen, nitrogen contents as well(results are given
in table l).These complexes of diaryltellurium(IV)
dihalides are generally coloured, crystalline solid
which are fairly stable in dry air.These are generally
soluble in polar organic solvents and insoluble in non
polar solvents.
X= Cl, Br, I
Pyz = pyrazine
Scheme 1. Formation of Pyrazine complexes
Where
R =p-hydroxyphenyl, 3-methyl-4-
hydroxyphenyl, p-methoxyphenyl
Pyz = pyrazine
The Lmvalues for the pyrazine complexes in
nitrobenzene, acetone and acetonitrile are generally
much lower than those reported for 1 : 1 electrolytes
thus suggesting their non-electrolyte type behaviour
in these solvents. Also the Lmvalues in a particular

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Table 5: IR Data (cm-1) for Pyrazine Complexes of Bis(p-methoxyphenyl)tellurium Dihalides
R2TeCl2.Pyz
R2TeBr2.Pyz
R2TeI2.Pyz
Assignment
3200 s
3178 s
3096 m
2994 m
3129 s
3100 m
3000 m
aromatic C-H strech + n(c H )of Pyz.
3075 m
3010 m
2900 m b
2175 m
2100 mb
2040 m
1900 m
1871 m
2184m
2200 m
2100 mb
2000 m
1975 m
1875 m
1800 m
1725 m
1582 vs
overtones and combination bands
2093 m b
1988 m
1856 m
1743 m
1600 m
1586 s
νc=c
skeletal in plane ring
stretch
1580 vs
1492 s
1456 m
1498 s
1460 m
1410m
1500 s
1487 s
1457 m
n ring of Pyz
1420 m
1300 s
1275 s
1246 vs
1179 vs
1107 m
1399 m
1301 s
1255 s
1175 s
C-O-C
1348 m
1283 s
1258 s
1178s
asym. C-O-C stretch
g ring of Pyz. + aromatic in the plane vib. + sym.
1110m
1110m
stretch.
1053 m
1021 vs
965 s
815 vs
780 s sh
1024 s
1023 vs
1000 w
957 s
880
953 s
835 s
Pyz. unidentate
C-H out of plane H-bending vib + gCH of Pyz.
800
776 m
712 m
610 w
580 w
715 m
690 w
610 w
718 w
640 w
out of the plane ring bending vib.
vs = very strong, s = strong, sh = shoulder, m = medium, w = weak, vw = very weak, b = broad
solvent for pyrazine adducts varies in the order.
R2TeI2.Pyz R2TeBr2.Pyz > R2TeCl2.Pyz
studies as well.
>
IR Spectra
Cryoscopic measurements
The cryoscopic data for the pyrazine
complexes (Table III) show that molecular weights
of these complexes arc quite close to the formula
weights, thus suggesting their molecular monomeric
nature in nitrobenzene, as predicted by conductance
The important IR data (cm-1) for pyrazine
complexes of diaryltelluriumdihalides are presented
in Tables IV and V. The spectra are quite complex
and the frequencies from which concrete conclusion
can be drawn are listed in the Tables. This may be
mentioned that assignments made in the table are

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Table 6: 1H INMR Data (d ppm) for Pyrazine Complexes of
DiaryltelluriumDichlorides in DMSO-d6.
Compound
Chemical Shift
Assignment
R2TeCl2.Pyz
*
(R = p-hydroxyphenyl)
2.21s
6.94d
(6H)
(2H)
-CH3
H
b
R2TeCl2.Pyz
(R = 3-methyl-4-hydroxyphenyl)
Phenyl
Ha &Hc
-OH
Ha (pyrazine)
-OCH3
HB
7.50 - 7.69m
8.05b
(4H)
(2H)
(4H)
(6H)
(4H)
8.61s
3.86s
7.02d
R2TeCl2.Pyz
(R = p-methoxyphenyl)
Phenyl
Ha
Ha(pyrazine)
7.94d
8.60s, 8.22s
(4H)
(4H)
s = singlet, b = broad, m= multiple, cm = complex multiple, d = doublet
* Spectra not well resolved.
based on comparison of spectra of parent R2TeX2and only one N-atom, the low local symmetry experienced
pyrazine.The ring vibrations of these may be mixed by the pyrazine moiety atoms allows a band to appear
with each other.
in the 950-1000 cm-1 region, which may be taken
as an evidence for unidentate nature of pyrazine.
The pyrazine molecule (C4H4N2)has the This band is reported to be absent in the bridged
centrosymmetric and planar structure with D2h polymers where pyrazine functions as bidentate
symmetry in the vapour and solid phases. The ligand. In pyrazine complexes of diaryltellurium(IV)
assignments of the infrared spectra of pyrazine dihalides prepared during this course of study exhibit
in solid6, liquid7-8 and vapour9-10 phases and in a medium to strong intensity band in this region,
solution6,10,11 have been reported to be in accord with thereby confirming the unidentate nature of pyrazine
the D2h symmetry.The important infrared frequencies in these complexes. Thus, tellurium in R2TeX2.Pyz
which are observed10,11 in free pyrazine are 3061, complexes attains a coordination number of five
3011 (nCH), 1483, 1412 (nring), 1150 (nring), 1130 probably in a square pyramidal environment.
(d )9 1061 (d ), 1019 (dring), 785(ucm)and 418(nring).
c H
c H
In metal complexes in which both n-atoms of 1HNMR Spectra
pyrazine are coordinated to two metal atoms, the D2h
The 1H NMR data for pyrazine complexes
symmetry is preserved but is removed in unidentate are given in Table VI. The four equivalent protons
coordination.Several modes of pyrazinein complexes of free pyrazine which resonate at 8.5919d ppm
have upward shift in wave number in comparison appear at slightly downfield side in R2TeCl2.Pyz
with those of free pyrazine.This blue shift in pyrazine complexes due to shifting of electron density from
bands in the complexes indicates the coordination N of pyrazine to Te of R2TeCl2. Also in some cases
through n-atom as in pyridine12,13. This blue shift in separation between the pyrazine protons has
ppyrazine stretching may be due to back bonding been observed which may be due to monodentate
from tellurium to pyrazine ring through formation of nature of pyrazine. Conversely, the aryl protons of
extensive -bonding.
R2TeCl2group resonate at upfield side as compared
to the parent diaryltellurium dichloride, indicating
Lever et al14-17and Kantara18 have reported thereby the shielding of phenyl protons especially
that in complexes where pyrazine is bonded through those orthoto TeCl2 group. This may be due to an

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increase in electron density at the tellurium atom
after accepting the electrons from the pyrazine
molecule. Similar shift has also been reported for
pyridine complexes20,21 of RTeCl3. Thus tellurium in
these pyrazine complexes acquires a coordination
number of five.
been investigated by conductance measurement in
nitrobenzene,acetoneandacetonitrileandcryoscopic
measurement in nitrobenzene. The Structural
aspects of the complexes of diaryltelluriumdihalides
have been investigated conjointly by infrared and
proton magneticre-sonance spectroscopy. These
complexes of diaryl tellurium (IV) dihalides are
generally coloured, crystalline solid which are
fairly stable in air. These are generally soluble in
polar organic solvents and insoluble in non polar
solvents.
CONCLUSION
Bis (p-hydroxyphenyl), bis (3-methyl-4-
hydroxyphenyl) and bis(p-methoxyphenyl) tellurium
(IV) dichlorides are obtained by direct reaction of
tellurium tetrachloride with phenol, o-cresol and
anisole respectively.
ACKNOWLEDGEMENTS
The authors are thankful to Maharshi
Dayanand University, Rohtak for providing the
necessary facilities.
These diaryltelluriumdihalides have been
reacted with pyrazine. The solution behaviour of
complexes of diaryl tellurium (IV) dihalides has
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