Synthesis and characterization of mixed ligand complexes of copper(II), nickel(II), cobalt(II

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Polyherlion Vol. 4. No. 3. pp. 415-479, 1985 
Printed in Great Britain 
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SYNTHESIS AND CHARACTERIZATION OF MIXED LIGAND 
COMPLEXES OF COPPER( NICKEL@), COBALT(U) AND 
ZINC(H) WITH GLYCINE AND URACIL OR ZTHIOURACIL 
MADHU GUPTA and M. N. SRIVASTAVA* 
Chemical Laboratories, University of Allahabad, Allahabad, India 
(Received 15 November 1983 ; accepted after revision 22 May 1984) 
Abstract-Mixed ligand complexes of Cu(II), Ni(II), Co(I1) and Zn(I1) formed with glycine and 
uracil or 2-thiouracil have been synthesized and characterized by elemental analysis, 
conductance, spectral (IR and electronic spectra) and magnetochemical measurements. 
Results show that glycine is bidentate in all cases ; uracil behaves as a bidentate ligand in Cu(I1) 
complex, coordinating through its one carbonyl oxygen and nitrogen, whereas in other cases it 
is only monodentate, coordinating only through nitrogen. With thiouracil, coordination 
occurs from carbonyl oxygen and one nitrogen in Cu(I1) and Ni(I1) complexes, but in the Co(I1) 
complex coordination occurs from thionyl sulphur and nitrogen. In the Zn(I1) complex it 
shows tridentate behaviour, coordinating through oxygen, sulphur and one nitrogen. Mixed 
Cu(II), Co(I1) and Zn(I1) complexes of uracil and of Ni(II) and Zn(I1) with thiouracil are 
octahedral, whereas the mixed Ni(I1) complex with uracil shows distorted tetrahedral 
geometry, and the mixed Co(H)-thiouracil complex is square planar. The mixed Cu(II)- 
thiouracil complex has a binuclear structure, with square planar arrangement around each 
copper atom. 
Mixed ligand complexes are well known to play an 
important role in biological systems’ and are being 
muchinvestigatedinsoJutionRecentlySrivastavaet 
at? studied potentiometr%z3Sl_v the formation of 
some mixed ligand transition metal complexes in 
solution, formed with aspartic/glutamic acid and 
utrac3 or thymine. The present paper describes the 
preparation and characterization of some mixed 
ligand Cu(II), Ni(II), Co(I1) and Zn(I1) complexes 
formed wick &tine and uracil or 2-thiouracil and 
their structural studies by spectral (IR and electronic 
spectra) and magnetochemical measurements. 
EXPERIMENTAL 
Materials 
Glycine (B.D.H.), uracil (Fluka), 2-thiouracil 
(B.D.H.), cupric chloride (B.D.H., AR) nickel 
*Author to whom all correspondence should be 
a&resseb. 
chloride (B.D.H., AR) cobalt chloride (Chemapol) 
zinc chloride (Merck) and sodium hydroxide 
(Merck). 
ss&dQns ofuras?Jand2-~~T~ wsJeJXr~rzX3 
by dissolving them in one equivalent of alkali. 
Preparaticm 
The metal ion and the two ligand solutions 
(g(ycine ancl uraci({Z-fhiauraci:I) were mixed in a 
molar ratio of 1: 1: 1, in the order of uracil/2- 
thiouracil followed by glycine and the pH of the 
mixture solutions was adjusted to 6-7 by further 
adding alkali, where necessary. On first adding uracil 
or 24hiouraci1, precipitates appeared [Cu(II) : 
green ; Ni(I1) : light green ; Co(I1) : pink-violet ; 
Zn(I1): colourless] which dissolved on adding 
glycine to yield clear solutions. The products were 
obtained by concentration and adding alcohol. They 
were washed first with 50% alcohol-water mixture, 
then with absolute alcohol a number of times and 
finally with ether and dried in an air oven at 50°C. 
The &Xo&r&?zA% we_rE &so &zQi?zr 3a a?? ti_r oY&z? 
475 
476 M. GUPTA and M. N. SRIVASTAVA 
successively at 100 and 150°C for about 2 h each time 
to note any loss of water on heating. It is observed 
that on heating at 100°C the mixed complexes of 
Cu(I1) and Ni(I1) with uracil and of Co(I1) with 
2-thiouracil lose one water molecule, whilst Co(I1) 
with uracil and of Cu(I1) with 2-thiouracil lose two 
molecules; on the Zn(I1) complex with 2-thiouracil 
there was practically no effect. The mixed Zn(I1) 
complex with uracil loses one water molecule at 
100°C and one more on further heating at 150°C. In 
the mixed Ni(I1) thiouracil complex, the loss of water 
begins from 100°C and is completed by 15O”C, the 
total loss corresponding to one water molecule. 
The IR spectra were recorded on a Perkin-Elmer 
spectrophotometer model 177 covering the range 
4000--65Ocm- in KBr discs. The absorption spectra 
were recorded in aqueous solutions in the range 33s 
900 nm on a Beckman spectrophotometer model 26. 
The reflectance spectra of insoluble complexes were 
recorded in MgO on a spectrophotometer VSU-2P 
in the range 220-1000 nm. 
RESULTS AND DISCUSSION 
Given formulae (Table 1) conform to analytical 
data. Conductance measurements show that the 
mixed complexes of Ni(I1) and Co(H) with uracil are 
1: 1 electrolytes, whereas the corresponding com- 
plexes of Cu(I1) and Zn(I1) are 1: 2 electrolytes. The 
mixed 2-thiouracil complexes are insoluble in water, 
as well as in common organic solvents. 
IR studies 
Some principal IR frequencies of the ligands and 
their mixed metal complexes are given in Table 2. 
Results show that the vNH$ of glycine3*4 (3150 
cm-‘) disappears on coordination, and instead 
vNH frequencies appear in. the 3400-3200 cm-’ 
region in the metal complexes. v,,COO- and 
v,COO- frequencies of course appear in their usual 
region around 1600 and 1400 cm-’ respectively. The 
vC=O bands of uracil(l712 and 1655 cm-‘) are in 
general little affected in the metal complexes, but in 
the Cu(I1) complex the 1712 cm-l band is con- 
siderably lowered in its position to 1670 cm-‘. Its 
vNH + vCH bands (3 130 and 3070 cm- ‘) appear 
around 3060 cm- ’ in the metal complexes. 
In 2-thiouracil complexes its secondary amide I 
band vC=O (1685 cm-l) is considerably lowered 
to 1650-1640 cm- ’ in Cu(I1) and Zn(I1) complexes, 
and to 1670 cm- ’ in the Ni(I1) complex, whereas in 
the Co(I1) complex there is little effect. The vNH + 
vCH bands (3125 and 3075-3030 cm-‘) appear in 
the 3160-3000 cm- ’ region in the metal complexes. 
The thioamide(II1) bandse6 (1150 cm - ‘) is raised to 
1180-1170 cm-’ [in the Co(H) complex it is un- 
‘affected] whereas the thioamide(IV) band’ (840 
cm- ‘) (possibly having a major contribution from 
vc=s)s*g is lowered to 830-825 cm- ’ in Co(I1) 
and Zn(I1) complexes, but in Cu(I1) and Ni(I1) 
complexes its position remains unchanged. 
In addition the metal complexes also show 
Table 1. Analytical data of complexes and some physical properties* 
y0 Loss in AM 
Found (talc.) (%) weight (H,O) (ohm-’ 
cm2 
Complex Colour M C H N S 100°C 150°C mol- ‘) 
NMWWJWW21 * HP Blue 18.5 20.7 3.22 12.4 - 4.4 - 220.0 
(18.3) (20.8) (3.17) (12.1) 
NaCNi(gly)(Ur)(OH)] - H,O Green 19.2 23.7 3.26 13.8 - 5.7 - 142.3 
(19.4) (23.8) (3.31) (13.9) 
NW4dyMW21 - 2&O Pink 11.8 29.8 3.81 17.3 - 6.8 - 83.8 
(12.1) (29.5) (3.89) (17.2) 
Naz[Zn(gly)(Ur)(OH),(H,O)l - H,O Colourless 17.7 19.8 3.06 11.4 - 4.4 5.2 252.0 
(17.8) (19.6) (3.00) (11.4) 
CCu2WMWWl * 2&O Green 32.0 18.0 3.20 10.5 8.0 9.0 0.6 - 
(31.9) (18.0) (3.26) (10.5) (8.0) 
CNi(glyXTurXH~O)21 - Hz0 Yellowish-green 18.6 22.8 4.20 13.5 10.1 2.6 2.1 - 
(18.7) (22.9) (4.14) (13.3) (10.2) 
CCo(glyXTur)l* I-W Grey 21.3 25.7 3.28 15.2 11.6 6.3 - - 
(21.2) (25.9) (2.23) (15.1) (11.5) 
CZn(glyNTurKH2011 Colourless 23.1 25.4 3.12 14.7 11.4 - - - 
(22.9) (25.3) (3.16) (14.7) (11.3) 
* All the complexes did not melt up to 300°C. Ur, uracil; Tur, 2-thiouracil; gly, glycine. 
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478 M. GUPTA and M. N. SRIVASTAVA 
Table 3. Magnetic moments and electronic spectral data 
Complex 
Kff 
B.M. (at 306 K) 
Band position 
(103 cm-‘) 
~MW&4WW%I - Hz0 1.90 14.08,29.41 
l?hW-MglyXTurll~ %@ Diamagnetic 15.15,24.39,27.78,33.48 
Na~i(~y~Ur~OH)] - H,O 3.03 13.89,28.57(sh), 33.48 
CWWO’urKI-120)21 * H20 2.92 17.09,28.57 
NCWhMJrM - 2I-W 4.10 13.71(sh), 19.76,26.67 
CW&WWl * I-W 2.49 19.53,28.57 
broad bands in the 3700-3450 cm-’ region, attribu- 
ted to vOH of water or OH- groups.lO 
It may be thus concluded that glycine is bidentate 
in all cases, coor~nating through -NH, and 
COO - groups. In the Cu(I1) complex, uracil acts as a 
bidentate ligand by coordinating through its one 
carbonyl oxygen and nitrogen, whereas in the other 
cases it is only monodentate ~oord~ating through 
only one nitrogen. It may be however noted that 
since the Co(I1) complex is a 1: 1 electrolyte, in it 
deprotonation from only one uracil occurs, the other 
one being simply coordinated to the metal ion. With 
2-thiouracil, in Cu(II) and Ni(I1) complexes 
coordination occurs from the carbonyl oxygen 
(C=O) and nitrogen, in the Co(I1) complex it is from 
thiocarbonyl sulphur (C=S) and nitrogen, whereas 
in Zn(I1) complex thiouracil is possibly tridentate, 
coordinating through carbonyl oxygen, thiocar- 
bony1 sulphur and nitrogen. 
Magnetic moments and electronic spectra 
The magnetic moment of the Cu(IIj-glycine- 
uracil complex is 1.90 B.M. corresponding to one 
unpaired electron. Its electronic spectrum shows a 
charge-transfer band at 29,410 cm-’ and one broad 
asymmetric band with A, at 710 ~(14,085 cm-‘). It 
thus suggests its distorted octahedral structure. But 
the corresponding Cu(II)-thiouracil-glycine com- 
plex is diamagnetic, suggesting its dimetic nature,12 
which is also supported by spectral evidence. Its 
electronic spectrum shows three charge-transfer 
bands at 33,480, 27,780 and 24, 390 cm-‘, out of 
which the band observed at 27,780 cm-l is 
characteristic of dimeric copper complexesi 
The main d-d absorption band is observed at 15,150 
cm -I withashoulder at 12,5OOcm- l.Thecomplexis 
thus dimeric possibly with a square planar 
arrangement around each copper atom. 
The magnetic moments of nickel(H) complexes are 
Ni(II~gly~n~ura~l (peff = 3.03 B.M.) and Ni(II)- 
glycine-Zthiouracil (pll,rf = 2.92 B.M.) suggesting 
that they have octahedral or distorted tetrahedral 
geometry. l4 The electronic spectrum of the 
nickel(II~glycine-thiouracil complex shows two 
bands at 17,095 and 28,570 cm - ’ assigned as it2 and 
v3 transitions’ l respectively. Its v1 transition, 
however could not be observed, as it is likely to 
appear beyond 900 nm. It thus supports its 
octahedral geometry. But the electronic spectrum of 
the nickel{11 j~y~n~ura~l complex shows only 
one d-d absorption band at 13,890 cm‘-‘, and two 
charge-transfer bands at 28,57o(sh) and 33,480 cm-‘. 
It thus suggests a tetrahedral geometry, and the 
13,890 cm-’ band may be assigned as vf transition.11 
The other two vl and v2 transitions would of 
course appear at much lower frequencies beyond 
1000 nm, and hence could not be observed. 
The magnetic moment of the Co(II)-glycine- 
uracil complex is 4.10 B.M. Its electronic spectrum 
shows a charge transfer band at 26,670 cm-l, the v3 
transitionl’ at 19 765 cm-’ and a weak shoulder at 
13,715 cm-l, hus suggesting an octahedral 
geometry. The other two vi and v2 transitions are not 
observed because the v2 transition in Co(U) complexes 
is normally very weak and may or may not 
be observed, whereas the vi transition is likely to 
appear at much lower frequencies beyond 1000 nm. 
The magnetic moment of the Co(II)-glycine- 
thiouracil complex @,rr = 2.49 B.M.) suggests it to 
be a low spin square planar14 complex. The 
electronic spectrum shows a charge-transfer band at 
28,570 cm-‘. The visible d-d band’l is observed at 
19,530 cm-‘, which may be assigned as a transition 
from the lower filled orbitals to the empty d,l_g2 
orbital. 
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