Synthesis and spectral studies of transition metal complexes with 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,7,11,14-tetraene, a fourteen-membered tetradentate macrocyclic ligand

Article abstract of DOI:10.1081/SIM-100106858

Complexes of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Pd(II) and Cu(II) with a fourteen-membered macrocyclic ligand have been prepared and characterized by magnetic moment, infrared, electronic and EPR spectral studies. All of complexes were found to have six-coordinate geometry and are of the high-spin type except the Pd(II) complex which is four-coordinate, square-planar and diamagnetic.

Full text of DOI:10.1081/SIM-100106858

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SYNTHESIS AND SPECTRAL STUDIES OF
TRANSITION METAL COMPLEXES WITH
5,7,12,14-TETRAMETHYL-1,4,8,11-
TETRAAZACYCLOTETRADECA-4,7,11,14-TETRAENE, A
FOURTEEN-MEMBERED TETRADENTATE MACROCYCLIC
LIGAND
Sulekh Chandra a , Karuna Gupta a & Sangeeta Sharma a
a Department of Chemistry , Zakir Husain College, University of Delhi , J. L. Nehru Marg,
New Delhi, 110002, India
Published online: 15 Feb 2007.
To cite this article: Sulekh Chandra , Karuna Gupta & Sangeeta Sharma (2001) SYNTHESIS AND SPECTRAL STUDIES OF
TRANSITION METAL COMPLEXES WITH 5,7,12,14-TETRAMETHYL-1,4,8,11-TETRAAZACYCLOTETRADECA-4,7,11,14-TETRAENE,
A FOURTEEN-MEMBERED TETRADENTATE MACROCYCLIC LIGAND, Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry, 31:7, 1205-1215, DOI: 10.1081/SIM-100106858
To link to this article: http://dx.doi.org/10.1081/SIM-100106858
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(7), 1205–1215 (2001)
SYNTHESIS AND SPECTRAL STUDIES OF
TRANSITION METAL COMPLEXES WITH
5,7,12,14-TETRAMETHYL-1,4,8,11-
TETRAAZACYCLOTETRADECA-4,7,11,14-
TETRAENE, A FOURTEEN-MEMBERED
TETRADENTATE MACROCYCLIC
LIGAND
Sulekh Chandra,* Karuna Gupta, and Sangeeta Sharma
Department of Chemistry, Zakir Husain College,
University of Delhi, J. L. Nehru Marg,
New Delhi-110002, India
ABSTRACT
Complexes of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Pd(II)
and Cu(II) with a fourteen-membered macrocyclic ligand
have been prepared and characterized by magnetic moment,
infrared, electronic and EPR spectral studies. All of com-
plexes were found to have six-coordinate geometry and are of
the high-spin type except the Pd(II) complex which is four-
coordinate, square-planar and diamagnetic.
*Corresponding author. E-mail: amit1984@mantraonline.com
1205
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

1206
CHANDRA, GUPTA, AND SHARMA
INTRODUCTION
Transition metal complexes of synthetic macrocyclic ligands are of
significance because porphyrins and cobalamines play vital roles in biological
systems. Such chelating molecules are important since they are capable of
furnishing an environment of controlled geometry and ligand field strength.
Curtis and coworkers1 were first to report the synthesis of some macrocyclic
ligands, especially of hexamethyltetraazacyclotetradecatetraene. Since then,
several other macrocyclic ligands such as cyclam2, cyclen3, aminobenzalde-
hyde trimers and tetramers4, reaction products of various polyamines5,6
and 2,6-diacetylpyridine779 have been reported. Some a-diketones are also
capable of forming macrocyclic ligands.
Here we report the synthesis and characterization of Cr(III), Mn(II),
Fe(III), Co(II), Ni(II), Pd(II) and Cu(II) complexes of the macrocyclic
ligand 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,7,11,14-tet-
raene, abbreviated as Tmtacdte (Fig. 1). Although the Co(II) and Ni(II)
complexes of this ligand have been reported earlier by Singh et al.10 but the
anions used were different than what we have used in this paper. So
the results obtained are also different, As Singh et al.10 have reported the
complexes to have low-spin and square-planar geometry while in the present
case we found the complexes to have high-spin and six-coordinate geometry.
EXPERIMENTAL
Preparation of Complexes
A tempelate reaction was carried out for the formation of the com-
plexes. A hot ethanolic solution (20 mL) of the metal salt (0.025 mol) was
mixed with a hot ethanolic solution (20 mL) of ethylenediamine (3 g,
Figure 1. Structure of the macrocyclic ligand tmtacdte.

TRANSITION METAL COMPLEXES
1207
0.05 mol) and with an ethanolic solution (20 mL) of acetylacetone (5 mL,
0.05 mol) in the presence of a few drops of conc. HCl. The solution was
refluxed for about four to five hours in each case. The complexes pre-
cipitated out on cooling the reaction mixture overnight. They were filtered,
washed with ethanol and dried over P4O10. Yields, 58775%.
PhysicalMeasurements
Microanalyses (C, H and N) of these complexes were carried out on a
Carlo-Erba 1106 elemental analyzer. IR spectra were recorded on a Perkin
Elmer 137 instrument as Nujol mulls [for (1) and (7)] or KBr pellets [for (2),
(3), (4), (5) and (6)]. Electronic spectra were recorded in DMF solution on a
Shimadzu UV mini-1240 spectrophotometer. The molar conductance was
measured on a Elico conductivity bridge (type C M 82 T).
Magnetic susceptibility measurements (Gouy balance) were made at
room temperature using CuSO4.5H2O as callibrant. EPR spectra of the
complexes were recorded as powdered samples at room temperature on an
E-4 EPR spectrometer using DPPH as the g-marker. The molecular weights
of complexes were determined cryoscopically in benzene.
RESULTS AND DISCUSSION
The analytical and molar conductance (Table I) values of all the
complexes in DMF solution suggest that general formulas of the complexes
are [MLCl2] (where M ¼ Mn(II), Co(II), Ni(II), Cu(II) and L ¼ Tmtacdte),
[M0LCl2]Cl (where M0 ¼ Cr(III) and Fe(III)) and ½PdLŠCl2 for the Pd com-
plex. The IR spectra of the ligand and complexes show moderate-intensity
absorptions in the range 160071700 cmÀ1 attributable to the imine
11
nðC›NÞ but no bands are observed for free > C›O or primary diamine
indicating that complete condensation has occurred. A shift in the absorp-
tion of the nðC›NÞ frequency for the complexes suggests coordination
through > C›N.
The formation of the complexes may be represented by the following
equations
MCl2 þ 2H2NCH2CH2NH2 þ 2CH2COCH2COCH3
Ethanol
ÀÀÀÀÀ! ½MðTmtacdeÞCl2Š þ 2H2O
a few drops
of conc: HCl
M ¼ Mn; Co; Ni and Cu

1208
CHANDRA, GUPTA, AND SHARMA

TRANSITION METAL COMPLEXES
1209
M0Cl3 þ 2H2NCH2CH2NH2 þ 2CH2COCH2COCH3
Ethanol
ÀÀÀÀÀ! ½M0ðTmtacdeÞCl2ŠCl þ 2H2O
a few drops
M0o¼f coCncr: HaCnld Fe
Chromium(III) Complex
The room temperature magnetic moment (3.78 B.M.) of the Cr(III)
complex lies within the range expected for high-spin octahedral Cr(III)
complexes. The electronic spectrum of the complex recorded in DMF dis-
plays four bands at 18,400 (n1) (e ¼ 32 moleÀ1 cmÀ1), 22,500 (n2)
(e ¼ 43 moleÀ1 cmÀ1), 24,900 (n3) (e ¼ 54 moleÀ1 cmÀ1) and 28,900 (n4) cmÀ1
(e ¼ 67 L moleÀ1 cmÀ1). Six-coordinate complexes with Oh symmetry show
three spin-allowed bands12 of which the highest energy band assignable to the
4A2g ! T1gðPÞ transition occurs around 30,000 cmÀ1. The spectrum of the
4
complex under study shows four bands below 30,000 cmÀ1, which cannot be
interpreted in terms of idealized symmetry elements in the complexes. Such
six-coordinated chromium(III) complexes can have either C4v or D4h sym-
metry. In the present complex, the four transitions observed may be assigned
a
b
4
4
4
4
4
4
4
4
to B1g ! Egðn1Þ, B1g ! B2gðn2Þ; B1g ! A1gðn3Þ and B1g ! Egðn4Þ
transitions arising from the lifting of the degeneracy of the orbital triplet (in
octahedral symmetry) in order of increasing energy and assuming D4h sym-
metry around the metal ion. In Oh symmetry, n1 and n2 are derived from the
4T2g level, whilst n3 and n4 from 4T1g(F). The C4v symmetry has been ruled out
because of the greater splitting of the first band and lower intensity of
spectral bands. On the basis of symmetry arguments Lever et al.13 have
devised a normalised spherical harmonic Hamiltonion (NSH) theory
applicable to molecule of D4h. The newly developed NSH theory relates the
classical ligand field parameters to NSH absolute ligand field parameters.
For our complex the NSH parameters are Dqxy ¼ 2; 250; Dt ¼ 469;
Dqz ¼ 1430; Ds ¼ 764; DS ¼ À5348; DT ¼ À6357; DQ ¼ À26746; DT=DQ
¼ 0:237: DQ is a measure of the average ligand field experienced by the
metal ion unlike the classical Dq, which is the measure of the in-plane
ligand field. The DT=DQ ratio provides the amount of distortion of the
molecule. The value of DT=DQ is 0.237 and thus indicates that the com-
plexes are moderately distorted. The EPR spectrum of the complex has
been recorded as a polycrystalline sample at room temperature. The g-
value is found to be 1.938. The g-value was calculated using the expres-
sion, g ¼ 2:0023 ð1 À 4lÞ= ð10DqÞ where l is the spin orbit coupling

1210
CHANDRA, GUPTA, AND SHARMA
constant for the metal ion in the complex. It was noted that the reduction
of the spin orbit coupling constant from the free ion value of 90 cmÀ1 for
chromium(III) may be employed as a measure of metal ligand covalency.
It is possible to derive a covalency parameter l, analogous to the nephe-
lauxetic parameter which is the ratio of the spin orbit coupling constant
for the complex and the free Cr(III) ion. This also indicates appreciable
covalent character in the complex.
Manganese(II) Complex
This complex shows a magnetic moment corresponding to five
unpaired electrons i.e., 5.94 B.M., which indicates that Mn(II) is high-spin in
this case. The electronic spectrum of the complex displays weak absorption
bands at 17,900 (e ¼ 43 moleÀ1 cmÀ1), 24,600 (e ¼ 48 moleÀ1 cmÀ1), 29,400
(e ¼ 63 moleÀ1 cmÀ1) and 31,700 cmÀ1 (e ¼ 106 L moleÀ1 cmÀ1) character-
istic of octahedral geometry20. These bands may be assigned to A1g
!
6
4
4
4
4
4
6
4
4
6
4
6
4
T1gð GÞ; A1g ! Eg; A1gð GÞ; A1g ! Egð DÞ; and A1g ! T1g ð PÞ
transitions, respectively. High values of extinction coefficient may be due to
lower symmetry or mixing of charge transfer. The value for the ligand field
parameters have been calculated (Dq ¼ 1790 cmÀ1, B ¼ 686 cmÀ1, b ¼ 0.86
and C ¼ 3548:6 cmÀ1). The value of Dq could be evaluated with the help of
the curve transition energies vs. Dq by Orgel14 using the energy due to the
transition A1g ! T1g (4G). Parameters B and C were calculated by using
the methods reported earlier15,16. The calculated value of b indicates that the
complex under study has covalent character. The EPR spectrum of the
complex has been recorded as polycrystalline sample and in DMF solution.
The polycrystalline sample gives one broad isotropic signal centered at
approximately the free electron g-value (g0 ¼ 2:0023). The broadening of
the spectrum probably is due to spin relaxation17. In DMF solution the
complex gives an EPR spectrum containing six lines arising due to hyperfine
interaction17719 between the unpaired electrons with the 55Mn nucleus
(I ¼ 5=2). The nuclear magnetic quantum number, MI, corresponding to the
lines are À5=2; À3=2; À1=2; þ3=2; þ5=2 from low to high field.
6
4
Iron(III) Complex
The iron(III) complex was found to have the composition FeLCl3.
This complex shows a magnetic moment corresponding to five unpaired
electrons (i.e., 6.0 B.M.), indicating the presence of high-spin Fe(III) ion.

TRANSITION METAL COMPLEXES
1211
The electronic spectrum of this complex shows two electronic spectral bands
at 19,200 (e ¼ 76 moleÀ1 cmÀ1) and 23,000 (e ¼ 89 L moleÀ1 cmÀ1) which are
characteristic of octahedral geometry.
Cobalt(II) Complex
The magnetic moment (4.9 B.M.) of the cobalt(II) complex lies within
the range expected for high-spin octahedral Co(II) complexes20. The elec-
tronic spectrum exhibits
a
broad band at ca. 8,850 cmÀ1
(e ¼ 65 moleÀ1 cmÀ1) and two shoulders at 14,300 (e ¼ 73 moleÀ1 cmÀ1) and
20,600 cmÀ1 (e ¼ 93 L moleÀ1 cmÀ1) on the rising charge transfer band,
4
4
4
4
4
4
tentatively assigned to T1g ! T2gðn1Þ; T1g ! A2gðn2Þ and T1g ! T1g
ðPÞðn3Þ, transitions, respectively. The low value of n2=n1 ð1:75Þ may be due
to distortion of the octahedral structure20,21. This is consistent with the very
broad nature of the n1 band, which may be assigned to the envelope of the
4
4
4
4
4
transitions from Egð T1gÞ to the components B2g and Eg of T2g, char-
acteristic of tetragonally-distorted octahedral environment. A complex of
this ligand reported by Singh et al.10 with cobalt nitrate is low-spin in nature
while we observed a high-spin nature of the complex reported by us. The
reason for this difference is yet not certain, but it might be due to the bulky
nature of ligand. The EPR spectrum of the complex under study was
recorded at liquid nitrogen temperature because the rapid spin lattice
relaxation of Co(II) broadened the lines at higher temperatures
(g11 ¼ 3:109 and g? ¼ 2:6122). The large deviation of the g-values from
the spin-only value (g ¼ 2:0023) is due to the large angular momentum
contribution.
Nickel(II) Complex
This complex shows a magnetic moment corresponding to two
unpaired electrons. The electronic spectrum of the nickel complex shows
two well defined bands at 10,570 (e ¼ 34 L moleÀ1 cmÀ1) and 16,400
(e ¼ 68 L moleÀ1 cmÀ1
)
cmÀ1 assignable to A2g ! T2gðFÞðn1Þ, and
3
3
3A2g ! T1g ðFÞðn2Þ, transitions, respectively. Here splitting of the n1 band
is not observed which is generally observed in D4h symmetry. So Dt, DqE
and DqA cannot be calculated. The third d-d transition band (n3) which
may be obscured by the more intense charge transfer band, is calculated to
be at 25,780 cmÀ1. The value of n2=n3 is 1.52 and the ligand field para-
meters Dq, B and b have been found20 to be 1057 cmÀ1, 630 cmÀ1 and
0.605, respectively. All of these values, together with the magnetic moment
3

1212
CHANDRA, GUPTA, AND SHARMA
(3.1 B.M), are characteristic of an octahedral geometry for this complex.
Though a complex of this ligand already have been prepared from nickel
acetate, as reported by Singh et al.10, it was found to be diamagnetic, low-
spin, square-planar. While our complex is paramagnetic, high-spin and
octahedral. This difference also might be due to the bulky nature of the
acetate group.
Palladium(II) Complex
This complex is diamagnetic as expected for a low-spin d8 system. The
low-spin square-planar metal complexes are characterized by three spin-
1
1
1
1
allowed d-d bands, corresponding to the A1g ! A2g; A1g ! Bg; and
1
1A1g ! Eg transitions, respectively. The complex under study display two
bands at 21,500 (e ¼ 98 L moleÀ1 cmÀ1) and 27,500 (e ¼ 123 L moleÀ1 cmÀ1
)
cmÀ1, respectively. These bands may be assigned to A1g ! A2gðn1Þ and
1
1
1
1A1g ! B1g (n2) transitions, respectively.
Copper(II) Complex
The magnetic moment of the complex was found to be 1.98 B.M. The
electronic spectrum of the complex displays two bands at 16,000
(e ¼ 54 L moleÀ1 cmÀ1) and 14,085 (e ¼ 63 L moleÀ1 cmÀ1) cmÀ1. The elec-
tronic spectrum of six-coordinate Cu(II) complexes have either D4h or C4v
symmetry, and the Eg and T2g levels of the 2D free ion will split into B1g, A1g,
B2g and Eg levels, respectively. Thus, three spin-allowed transitions are
expected in the visible and near-IR region, but only few complexes are
known, in which such bands are resolved either by ‘‘Gaussian analysis’’ or
by ‘‘Single Crystal Polarization’’ studies21. These bands have been assigned
2
2
to the following transitions, in order of increasing energy, B1g ! A1g
2
2
2
2
2
ðdx2Ày2 dzÞ; B1g ! B2gðdx2Ày2 dxyÞ; and B1g ! Eg ðdx2Ày2 dxz;yzÞ.
The energy level sequence will depend on the amount of tetragonal distor-
tion due to ligand-field and Jahn-teller effects22724. The electronic spectrum
of the complex shows a band at 14,085 cmÀ1 (e ¼ 78 L moleÀ1 cmÀ1) and a
well defined shoulder at 16,000 cmÀ1(e ¼ 89 L moleÀ1 cmÀ1). These may be
2
2
2
assigned to the B1g 2 A1g and B1g ! Eg transitions, respectively. The
EPR spectrum22724 of the present complex exhibits a well resolved aniso-
tropic signals in the parallel and perpendicular 63Cu region. The observed
data show that g11 ¼ 2:36 and g? ¼ 2:08 and the g11 and g? values are closer
to 2 and g11 > g?. This suggests major distortion in the copper(II) complex
from Oh symmetry i.e., D4h symmetry.

TRANSITION METAL COMPLEXES
1213
Figure 2. Suggested structures of the complexes.
Figure 3. Suggested structure of Pd complex.
On the basis of the above studies the following structures may be
suggested for the complexes (Figs. 2 and 3).
ACKNOWLEDGMENT
Thanks are due to the Department of Science and Technology (DST),
New Delhi, and one of us (K G) is thankful to University Grants Com-
mission, Delhi for financial assistance. Also we are thankful to RSIC, IIT
Mumbai for recording EPR spectra.

1214
CHANDRA, GUPTA, AND SHARMA
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Received February 24, 1999
Accepted May 29, 2001
Referee I: K. C. Nathan
Referee II: K. Moedritzer