Synthesis and characterization of some group 12 metal complexes with tellurium containing 10-membered tetraazamacrocyclic ligands

Article abstract of DOI:10.1155/2011/768192

A new series of 10-membered tellurium containing tetraazamacrocyclic complexes, [ML1Cl2], [ML2Cl2] and [ML3Cl2], where [M=Zn(II), Cd(II), Hg(II); L1, L2 and L3=10-membered tellurium containing tetraazamacrocyclic ligands] have been prepared via the templa

Full text of DOI:10.1155/2011/768192

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(3), 1158-1163
http://www.e-journals.net
Synthesis and Characterization of Some Group
12 Metal Complexes with Tellurium Containing
10-Membered Tetraazamacrocyclic Ligands
NITU and K. K. VERMA*
Department of Chemistry
Maharshi Dayanand University, Rohtak -124001, India
vermakk123@rediffmail.com
Received 12 October 2010; Accepted 17 December 2010
Abstract: A new series of 10-membered tellurium containing tetraazamacrocyclic
complexes, [ML1Cl2], [ML2Cl2] and [ML3Cl2], where [M=Zn(II), Cd(II),
Hg(II); L1, L2 and L3=10-membered tellurium containing tetraazamacrocyclic
ligands] have been prepared via the template condensation of ethylenediamine
and diaryltellurium dichlorides, R2TeCl2, (R=p-hydroxyphenyl, 3-methyl-4-
hydroxyphenyl, p-methoxyphenyl) in the presence of metal chlorides. These
complexes have been characterized by elemental analyses, conductivity
measurements, infrared, electronic absorption and proton magnetic resonance
spectral studies. IR and PMR spectra confirm the formation of 10-membered
tetraazamacrocycle skeleton and their tetradentate nature. An octahedral
geometry has been assigned to all the metal complexes on the basis of various
physicochemical studies.
Keywords: Tellurium, Tetraazamacrocycles, Diaryltellurium dichlorides, Ethylenediamine, Template
condensation.
Introduction
The coordination chemistry of organotellurium ligands containing hard donor atoms such as
nitrogen and oxygen along with soft tellurium is interesting as such ligand framework can
provide ‘insight’ into competitive coordination behaviour between the hard and soft donors
towards a metal center1,2. Such molecular systems may be important in transition metal
catalyzed asymmetric synthesis3,4 and as single source precursors in MOCVD processes5-7
Also, macrocycle complexes are significant as they have been found to act as possible
models for biochemically important proteins and enzymes8-12
.
.
Some recent publications13-17 exhibit the development of tellurium containing macrocycles.
Srivastava et al.18 reported the route of synthesis of metal complexes with tellurium containing

1159
K. K. VERMA et al.
macrocycles. In continuation of our earlier work19,20 on such macrocyclic complexes, we
herein report the synthesis and characterization of divalent zinc, cadmium and mercury
complexes with three novel tellurium tetraazamacrocycles, (Te2N4 system).
Experimental
The chemicals, tellurium tetrachloride (Aldrich), ethylenediamine, ZnCl2, CdCl2.2.5 H2O,
HgCl2, phenol, o-cresol and anisole (Loba Chemie) were of reagent grade. All the solvents
were purified and dried before use by conventional methods.
Preparation of diaryltellurium dichlorides
Bis(p-hydroxyphenyl)-, bis(3-methyl-4-hydroxyphenyl) and bis(p-methoxyphenyl) tellurium
dichlorides were prepared by direct reactions of TeCl4 with phenol21, o-cresol22 and anisole23
respectively as reported in the literature. All the preparations were carried out in dry
conditions under an atmosphere of nitrogen.
Preparation of complexes
The 10-membered tellurium tetraazamacrocyclic metal complexes have been synthesized by
the template condensation reaction of metal chlorides with diaryltellurium dichlorides and
ethylenediamine in 1: 2: 2 molar ratios.
A general method for the preparation of these 1, 6-diaryltellura –2, 5, 7, 10-tetraazacy-
clodecane metal complexes is given below: A saturated solution of 4.0 mmol of
diaryltellurium dichloride in methanol was added slowly and with constant stirring to a
methanolic (~ 5 mL) solution of 4.0 mmol of ethylenediamine taken in a R.B. flask. A
distinct change in colour with slight turbidity was observed. The contents were refluxed for
2-3 h followed by addition of a saturated methanolic solution of 2.0 mmol of metal
dichloride. An immediate change in colour was observed. The solution was then refluxed for
3-4 h and concentrated to about one third of the original volume and cooled. This resulted in
the separation of a coloured solid. This was filtered, washed with benzene/petroleum ether
and dried in a vacuum desiccator over P4O10.
Physical measurements
Elemental analysis for C, H, N for the zinc and cadmium complexes were obtained from
SAIF, Panjab University, Chandigarh on a CARLO ERBA Model 1106. Tellurium and
chlorine contents were determined volumetrically24. Metals were estimated on atomic
absorption spectrophotometer (ECIL Model No. 4129). The conductance measurements in
DMSO were performed on a systronic type 305 conductivity bridge at 25 2 °C using a dip
type cell with smooth platinum electrodes. The electronic spectra were recorded in
dimethylsulphoxide at 25 2 °C on a thermo spectronic UV-1 spectrophotometer. The IR
spectra (4000-400 cm-1) were recorded as KBr pellets on a Perkin Elmer Model 2000 FTIR
1
Spectrometer at SAIF, Panjab University, Chandigarh. H NMR spectra were recorded in
DMSO – d6 on BRUKER XWIN – NMR AVANCE 300 operating at 300.13 MHz, using
tetramethylsilane as an internal reference. The NMR spectra were obtained from
Kurukshetra University, Kurukshetra.
Results and Discussion
Diaryltellurium dichlorides when condensed with ethylenediamine in presence of metal
dichlorides in 2: 2: 1 molar ratios, yield the desired complexes as shown below

Synthesis and Characterization of Some Group 12 Metal Complexes
CH2 – CH2
1160
2 R2TeCl2 + 2H2N
NH2 + MCl2
CH2
CH2
H
H
R
R
N
N
R
Cl
M
Cl
Te
Te
H
H
N
R
N
CH2
CH2
Where
L1
; R = p-hydroxyphyenyl
; R = 3-methyl-4-hydroxyphyenyl
; R = p-methoxyphenyl
= ZnII, CdII and HgII
L2
L3
M
These complexes are coloured, crystalline, air stable solids and are soluble only in polar
donor organic solvents. The analytical data and some physical properties of these complexes
are given in Table 1.
Conductance studies
The molar conductance values for these complexes (except ZnL2Cl2 and HgL2Cl2) in DMSO
at ca. 10-3 M are lower than the ranges reported25 for 1:1 type electrolytes, reflecting their
partial dissociation in this solvent. The molar conductance for ZnL2Cl2 is close to those of
1:1 electrolytes and for HgL2Cl2 is higher than those of 1:1 type electrolytes. These two
complexes probably ionize into [ML2Cl.DMSO]+ and Cl− ions due to the solvation process,
since DMSO is known to be a good donor25. So, on the basis of conductance studies, these
complexes in general may be represented as [MLCl2].
Magnetic and electronic spectral studies
As expected, these d10 metal ion complexes are diamagnetic in nature. No d-d
transitions are observed for these complexes consistent with the d10 configuration. The
electronic absorption spectra of these complexes display a broad and intense band in the
region 32000-22000 cm-1 due to CT transitions26,27. The n-π* and π-π* bands of the
ligand may also be mixed with this charge transfer band27. This band sweeps the near
UV portion of electromagnetic radiation and extends in the visible region, with
successively diminishing absorbance up to 500 nm. This is responsible for the colour of
the complexes.
Infra-red spectra
The important IR bands and their assignments are tabulated in Table 2. The spectra are quite
complex and an attempt has thus been made to draw the conclusions by comparing the
spectra of metal complexes with those of corresponding constituent diarytellurium
dichlorides and ethylenediamine.

Table 1. Analytical data, physical properties, yields and molar conductance for metal complexes
Empirical Formula
(Formula Weight)
C28H32Cl2N4
M.P. °C Yield
(dec.)
Analysis found (calculated), %
Cl Te
8.44 28.93
(38.21) (3.66) (6.37) (8.06) (29.00) (7.43)
40.80 4.14 5.62 7.62 27.65 6.91
(41.05) (4.31) (5.98) (7.57) (27.26) (6.98)
40.91 4.21 5.76 7.49 27.35 6.85
(41.05) (4.31) (5.98) (7.57) (27.26) (6.98)
36.03 3.08 5.82 7.50 27.65 11.55
(36.27) (3.48) (6.94) (7.65) (27.53) (12.13)
38.62 3.89 5.16 7.39 25.50 10.92
(39.09) (4.10) (5.70) (7.21) (25.96) (11.43)
38.91 3.97 5.58 7.02 25.84 11.31
(39.09) (4.10) (5.70) (7.21) (25.96) (11.43)
6.80 25.14 19.69
(6.98) (25.55) (19.76)
6.50 23.72 18.26
(6.62) (23.82) (18.72)
6.53 23.75 18.55
(6.62) (23.82) (18.72)
ΛM at ca.10-3 M ohm-1
cm2 mol-1 in MSO
26.7
Complex
[ZnL1Cl2]
[ZnL2Cl2]
[ZnL3Cl2]
[CdL1Cl2]
[CdL2Cl2]
[CdL3Cl2]
[HgL1Cl2]
[HgL2Cl2]
[HgL3Cl2]
Colour
%
C
38.01
H
3.16
N
6.13
M
7.36
Bright
orange
100-101 82
O4Te2Zn (880.1)
C32H40Cl2N4
O4Te2Zn (936.2)
C32H40Cl2N4
O4Te2Zn (936.2)
C28H32Cl2N4
O4Te2Cd (927.1)
C32H40Cl2N4
O4Te2Cd (983.2)
C32H40Cl2N4
O4Te2Cd (983.2)
C28H32Cl2N4
O4Te2Hg (1015.3)
C32H40Cl2N4
O4Te2Hg (1071.4)
C32H40Cl2N4
O4Te2Hg (1071.4)
Brown 158-160 82
63.4
20.2
37.5
33.6
22.5
60.7
108.4
46.5
Pale
118-120 63
white
Dark
178-180 48
red
Orange
180-185 77
pink
Light
117-121 65
brown
130-133
Red
52 (33.12) (3.18) (5.52)
Dark
brown
120-125 67 (35.87) (3.76) (5.23)
Brown 108-110 51 (35.87) (3.76) (5.23)
Table 2. Important IR data (cm-1) for metal complexes
νN−H
Complex
N-H def.
N-H out of the plane bending
νC−N
[ZnL1Cl2]
[ZnL2Cl2]
[ZnL3Cl2]
[CdL1Cl2]
[CdL2Cl2]
[CdL3Cl2]
[HgL1Cl2]
[HgL2Cl2]
[HgL3Cl2]
3145 m
3160 m
3240 m
3155 m
3190 m
3260 m
*
1625 sh
1640 m
1651 m
1631 m
1635 m
1652 m
1635 m
1640 sh
1654 m
825 s
813 s
822 s
828 s
813 s
822 s
825 vs
813 m
821 s
1174 s
1174 m
1176 s
1172 s
1174 m
1176 vs
1172 s
1175 m
1176 s
3165 m
3250 m
*mixed with υO-H, s = strong, m = medium, vs. = very strong, sh = shoulder

Synthesis and Characterization of Some Group 12 Metal Complexes
1162
The metal complexes under study did not show bands characteristics of free NH2 group,
instead the entire complexes exhibit a single sharp absorption band at around 3145-3260 cm-1
(sometimes mixed with O-H) attributed to νN-H stretching vibration. The assignment of this
sharp band is based on the fact that macrocyclic ligands which have coordinated secondary
amino group, have bands18,28-30 in the vicinity of 3200 cm-1. This contention finds support28
from appearance of bands of medium to strong intensity at ~1640 cm-1 and ~825 cm-1 assigned
as N-H deformation coupled with N-H out of the plane bending vibrations. Bands at ~1175 cm-1
may be reasonably assigned to C-N stretching vibration18,31,32. The above observation strongly
suggest18,28,31,32 that proposed macrocyclic framework is formed. The formation of tellurium
containing macrocyclic ring is also supported by appearance of new weak intensity bands
around 420-410 cm-1 due to Te-N18,33. Evidence for formation of proposed macrocycles and
coordination through N atoms is further supported by new medium to weak intensity bands
around 480-450 cm-1 assignable to M-N stretching34. The M-Cl, Cd-N and Hg-N vibrations
could not be ascertained due to non-availability of far infrared data.
Proton magnetic resonance spectra
The proton chemical shifts for some representative complexes which are soluble in DMSO-d6
are compiled in Table 3. The phenyl protons in metal complexes resonate at slightly up field
side (6.92-7.65 δ ppm) as compared to parent diaryltellurium dichlorides21,22,35, due to
increase in electron density at the tellurium atom as a result of replacement of 2 Cl by 2 N
(a)
(b)
(a)
atoms. Ethylenediamine,
shows36 two sets of four equivalent protons each
H2N− (CH2 )− NH2
at (a) = 1.19 δ ppm and (b) = 2.74 δ ppm. Metal complexes do not show any signal
attributable to free – NH2, instead a broad singlet at around 1.50-2.05 δ ppm, which may be
assigned to coordinated secondary amino group37 is observed. This confirms the formation
of proposed macrocycle skeleton. The deshielding of –NH– protons further suggests the
donation of electron density to the metal-ions. The methylene protons in these metal
complexes resonate at 2.05-2.50 δ ppm, as a multiplet as reported18,30,32 for other
tetraazamacrocyles derived from ethylenediamine. Also, the independence of aryl proton
chemical shifts on the nature of metal-ion precludes the possibility of Te-M bond. Thus,
PMR studies on these metal complexes support the formation of 10-membered tellurium
tetraazamacrocycles and their tetra dentate ligation behaviour as predicted by IR studies.
Table 3. PMR data (δ ppm) for metal complexes in DMSO-d6
− CH*3
Complex –NH–
–OCH3
---
–CH2–
Phenyl
–OH
6.92d (4H)
7.59d ,7.56s (8H)
6.94d (4H)
[ZnL2Cl2] 2.05s (4H) 2.42s (12H)
2.14m (8H)
9.95b (4H)
[CdL2Cl2] 1.50s (4H) 2.49s (12H)
[HgL2Cl2] 1.60s (4H) 2.50s (12H)
---
---
2.05m (8H)
2.12m (8H)
8.17b (4H)
10.19b (4H)
7.47s, 7.56d (8H)
6.92d (4H)
7.56d , 7.65s (8H)
[ZnL3Cl2] 1.79s (4H)
[CdL3Cl2] 1.75s (4H)
[HgL3Cl2] 1.75s (4H)
---
---
3.79s (12H) 2.50m (8H) 7.16d (8H) 7.41d (8H)
3.78s (12H) 2.50m (8H) 7.16d (8H) 7.74d (8H)
3.81s (12H) 2.50m (8H) 7.16d (8H) 7.52d (8H)
---
----
*May be mixed with solvent peak, s = singlet, d = doublet, m = multiplet, b = broad
Based on analyses, conductance, magnetic, electronic, infrared and proton magnetic
resonance spectral studies, a distorted octahedral geometry involving four N atoms of
tetraazamacrocycle and 2 Cl may be proposed for these d10 metal complexes.

1163
K. K. VERMA et al.
Acknowledgment
The authors are thankful to Maharshi Dayanand University, Rohtak for providing the
necessary facilities.
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