Complexes of copper(II) with 2,3-dimethyl-4-formyl(benzhydrazide)-1-phenyl-3-pyrazolin-5-one

Article abstract of DOI:10.1081/SIM-120024311

Copper(II) complexes of the Schiff base 2,3-dimethyl-4-formyl-(benzhydrazide)-1-phenyl-3-pyrazolin-5-one (L) of the general formula [Cu(L)₂]X₂ (X = ClO₄ or NO ₃), [Cu(L)CI2] and [Cu(L)₂Br₂] have been synthesized and characterized by elemental analyses, electrical conductance in non-aqueous solvents, infrared, electronic and EPR spectra, as well as magnetic susceptibility measurements. In these complexes, the ligand acts as a neutral bidentate unit coordinating through the azomethine nitrogen atom and the carbonyl oxygen of the pyrazolone ring. In the perchlorate and nitrate complexes both anions remain ionic, while in the corresponding halide complexes both anions are coordinated to the metal ion. The perchlorate, nitrate and chloride complexes are of square-planar geometry while the bromide complex is of distorted octahedral geometry.

Full text of DOI:10.1081/SIM-120024311

SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 33, No. 8, pp. 1307–1318, 2003
Complexes of Copper(II) with 2,3-Dimethyl-4-
formyl(benzhydrazide)-1-phenyl-3-
pyrazolin-5-one
*
K. C. Raju and P. K. Radhakrishnan
School of Chemical Sciences, Mahatma Gandhi University,
Kottayam, Kerala, India
ABSTRACT
Copper(II) complexes of the Schiff base 2,3-dimethyl-4-formyl-(benzhy-
drazide)-1-phenyl-3-pyrazolin-5-one (L) of the general formula
[Cu(L)2]X2 (X = ClO4 or NO3), [Cu(L)Cl2] and [Cu(L)2Br2] have been
synthesized and characterized by elemental analyses, electrical conduc-
tance in non-aqueous solvents, infrared, electronic and EPR spectra, as
well as magnetic susceptibility measurements. In these complexes, the
ligand acts as a neutral bidentate unit coordinating through the azomethine
nitrogen atom and the carbonyl oxygen of the pyrazolone ring. In the
perchlorate and nitrate complexes both anions remain ionic, while in the
corresponding halide complexes both anions are coordinated to the metal
ion. The perchlorate, nitrate and chloride complexes are of square-planar
geometry while the bromide complex is of distorted octahedral geometry.
*
Correspondence: P. K. Radhakrishnan, School of Chemical Sciences, Mahatma
Gandhi University, Kottayam 686 560, Kerala, India; E-mail: mgu@vsnl.com.
1307
DOI: 10.1081/SIM-120024311
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

1308
Raju and Radhakrishnan
INTRODUCTION
The interesting and varied ligand behavior of hydrazines and
hydrazones towards transition metal ions is well known.[1] The pharmaco-
logical application of antipyrine-based ligands and their metal complexes
have been extensively studied.[2–4] As an extension of our studies on metal
complexes with antipyrine derivatives,[5–10] we report here the synthesis
and structural investigation on copper(II) complexes of a new pyrazolone-
hydrazide Schiff base ligand 2,3-dimethyl-4-formyl(benzhydride)-1-phenyl-
3-pyrozolin-5-one (L). (Figure 1).
RESULTS AND DISCUSSION
The formation of the complexes can be represented by the general
equation shown below:
CuCl2 þ L ! CuðLÞCl2 and CuX2 þ 2L
! CuðLÞ2X2 ðX ¼ ClO4; NO3 or BrÞ
All the complexes are light-yellow in color except the bromide complex
which is brown. They are non-hygroscopic solids soluble in DMF, ethanol,
methanol and nitrobenzene, but insoluble in benzene, chloroform, ethyl
acetate and toluene. The analytical data (Table 1) indicate that the complexes
have the general formulae Cu(L)2X2 (X = ClO4, NO3 or Br) and Cu(L)Cl2.
The molar conductance values of the complexes (Table 2) in DMF,
methanol and nitrobenzene (10–3 M solutions) are in the range expected for
1:2 electrolytes for perchlorate and nitrate complexes, while the cor-
responding chloride and bromide complexes behave as non-electrolytes.[11]
Figure 1. 2,3-Dimethyl-4-formyl(benzhydrazide)-1-phenyl-3-pyrazolin-5-one (L).

Copper(II) Complexes
1309

1310
Raju and Radhakrishnan
Table 2. Molar conductance dataa of the copper(II) complexes of L (in ohm–1
cm2 mol–1).
Molar conductance
Complex
DMF
Methanol
Nitrobenzene
[Cu(L)2](ClO4)2
[Cu(L)2](NO3)2
[Cu(L)Cl2]
164.70
148.23
43.92
203.13
192.15
38.43
55.99
50.51
8.78
[Cu(L)2Br2]
45.01
49.41
10.98
a10–3 M solutions used.
Thus, the complexes may be formulated as [Cu(L)2X2] (X = ClO4 or NO3),
[Cu(L)Cl2] and [Cu(L)2Br2].
Infrared Spectra
The important infrared spectral data of the ligand and its complexes are
presented in Table 3. The infrared spectral bands at 1674 and 1630 cm–1
are characteristic of n(C=O) of the pyrazolone ring and the benzoyl moiety
respectively.[8] In all reported complexes, the band at 1674 cm–1 is shifted
to the region 1642–1654 cm–1 indicating that the carbonyl oxygen is
involved in coordination.[8] The band corresponding to n(C=O) of the
Table 3. Important IR spectral bands (cm–1) of L and its copper complexes.
[Cu(L)2]-
(ClO4)2
[Cu(L)2]-
(NO3)2
L
[Cu(L)Cl2]
[Cu(L)2Br2]
Assignment
1674 s
1630 s
1654 s
1630 s
1551 s
1008 w
1986 s
623 m
–
1652 s
1629 s
1558 s
1008 w
–
1642 s
1629 s
1560 s
1010 w
–
1653 s
1632 s
1560 s
1007 w
–
n(C=O) ring
n(C=O)
n(C=N)
1571 s
998 w
n(N–N)
–
–
–
–
–
–
–
–
n3-ionic ClO4
n4-ionic ClO4
n3-ionic NO3
n2-ionic NO3
n(Cu–Cl)
n(Cu–Br)
n(Cu–N)
–
–
–
1378 s
821 m
–
–
–
–
–
–
–
310 m
–
–
–
–
292 m
460 w
555 w
458 w
552 w
459 w
550 w
458 w
550 w
n(Cu–O)
s = strong, m = medium, w = weak.

Copper(II) Complexes
1311
benzoyl moiety remains practically unaltered in all of these complexes at
about 1630 cm–1, indicating the non-coordination of benzoyl carbonyl in
these complexes.[12] The strong band observed at 1571 cm–1 in the ligand,
attributed to the C=N stretching vibration, is shifted to 1551–1560 cm–1,
indicating coordination of the azomethine nitrogen in the complexes.[8] The
n(N–N) band at 998 cm–1 in the ligand spectrum is shifted to higher
frequency (1007–1010 cm–1) in the complexes, which further supports the
bonding through the azomethine nitrogen.[13]
In the perchlorate complex, the band observed at 1086 cm–1 is assigned
to the n3 vibration of uncoordinated perchlorate ion of Td symmetry.[14]
This is supported by the presence of a medium intensity band at 623 cm–1
due to n4 vibration of perchlorate ion of Td symmetry.[14]
In the nitrate complex, a strong band at 1378 cm–1 and a medium
intensity band at 821 cm–1 are attributed n3 and n2 vibration of uncoor-
dinated nitrate ion of D3h symmetry.[15]
In the far-infrared spectrum of the chloride and bromide complexes the
Cu–Cl and Cu–Br, stretching vibrations occur at 310 and 292 cm–1,
respectively, that are not present in the ligand spectrum.
The above observations, along with the conductance data, confirm that
perchlorate and nitrate ions remain ionic in these complexes while chloride
and bromide ions are coordinated to the metal ion. Further, n(Cu–N) and
n(Cu–O) stretching vibrations are observed at about 460 and 550 cm–1,
respectively, in all these complexes.
Electronic Spectra
The electronic spectral data of the ligand and complexes in the solid
state (using Nujol) with their tentative assignments are given in Table 4. In
the complexes both n!p* and p!p* bands were found to be red-shifted
to the regions 22,123–22,471 and 39,682–40,816 cm–1, respectively, com-
pared to the ligand. The band observed in the region 13,477–13,820 cm–1 is
attributed to 2B1g!2A1g transitions consistent with a square-planar
geometry[16] around the copper(II) ion in all the complexes except in the
bromide complex. In the bromide complex, the broad band at 19,608 cm–1
indicates tetragonal configuration around copper(II) ions.[17,18] The electronic
spectra of all the complexes exhibit an intense absorption band in the region
33,222–33,444 cm–1 which might be due to a charge transfer process.
Magnetic Moment Data
The molar magnetic moments of copper(II) complexes vary in the
range 1.61 to 2.01 B.M. This clearly indicates that the complexes, except

1312
Raju and Radhakrishnan
Table 4. Electronic spectral data (in Nujol) and magnetic moments of the copper(II)
complexes of L.
Complex
L
Abs.max. (cm–1)
Tentative assignment
meff (B.M.)
23,866
41.153
22,123
40,485
33,444
13,477
22,371
40,485
33,333
13,386
22,471
40,816
33,333
13,820
22,172
39,682
33,222
19,608
n!P*
P!P*
[Cu(L)2](ClO4)2
[Cu(L)2](NO3)2
[Cu(L)Cl2]
n!P*
2.01
P!P*
Charge transfer
2
2B1g! A1g
n!P*
1.95
1.61
1.68
P!P*
Charge transfer
2
2B1g! A1g
n!P*
P!P*
Charge transfer
2
2B1g! A1g
[Cu(L)2Br2]
n! P*
P! P*
Charge transfer
d–d transition
the chloride complex, are monomeric and any metal–metal interaction is
absent in these complexes.[17] The magnetic moment of the chloride
complex is slightly lower than that expected which may be due to metal-
metal interaction.[19]
EPR Spectra
The X-band EPR spectra of the copper(II) complexes were recorded in
1:1 methanol–toluene mixture at liquid nitrogen temperature using DPPH
free radical as the ‘g’ marker (Figure 2). All the complexes have a well-
resolved g and a broadened g region. In all the spectra, no superhyperfine
k
?
splitting from the ligand part is observed.
The various spin Hamiltonian parameters computed are presented in
Table 5. The trend g > g > 2.0023 indicates that the unpaired electron is
?
most likely in the dxk2 ꢀy2 orbital.[20] The covalency parameter a2 is cal-
culated using the Kivelson and Neiman equation.[21]
3
a2Cu ¼ ꢀðAk=0:036Þ þ ðgk ꢀ 2:002Þ þ ðg? ꢀ 2:002Þ þ 0:04
7

Copper(II) Complexes
1313
Figure 2. EPR spectra of the complexes. A = [Cu(L)2](ClO4)2, B = [Cu(L)2](NO3)2,
C = [Cu(L)Cl2], D = [Cu(L)2Br2].
In the present case, a2 is in the range 0.74 to 0.76 indicating the fairly
covalent nature in the metal-ligand bonding.[17] Furthermore, the shape of
the EPR spectra indicates that the geometry around the copper(II) ion is
square planar in the perchlorate, nitrate and chloride complexes with an
elongated octahedron in the bromide complex as is evident from the less
intense low-field side and high-intense high-field side.[17]
Based on the results of the present study, the structure shown in
Figure 3 may be assigned to these complexes.
Table 5. EPR bonding parameters of the copper(II) complexes of L at liquid
nitrogen temperature.
Complex
g
k
g
?
A
A
gav
a2
k
?
[Cu(L)2](ClO4)2
[Cu(L)2](NO3)2
[Cu(L)Cl2]
2.30
2.30
2.31
2.31
2.05
2.06
2.07
2.07
140.00
140.00
140.00
135.00
86.66
86.66
83.33
80.00
2.13
2.14
2.15
2.15
0.75
0.75
0.76
0.75
[Cu(L)2Br2]

1314
Raju and Radhakrishnan
EXPERIMENTAL
The metal salts, Cu(ClO4)2ꢁ6H2O, Cu(NO3)2ꢁ6H2O, CuCl2ꢁ2H2O, and
CuBr2ꢁ4H2O, were prepared from Analar BDH copper carbonate and the
respective 50% acids and crystallized out by evaporating the solution on a
steam bath. For example, CuCl2ꢁ2H2O was prepared as follows. Copper
carbonate was dissolved in hot 50% hydrochloric acid. A slight excess of
metal carbonate was used. The undissolved carbonate was removed by
filtration. The filtrate was concentrated by evaporation when green crystals
of CuCl2ꢁ2H2O separated.
Preparation of the Ligand
The ligand 2,3-dimethyl-4-formyl(benzhydrazide)-1-phenyl-3-pyrazo-
lin-5-one (L) was prepared and characterized as reported earlier.[8]
Preparation of the Complexes
Perchlorate Complex
A quantity of 0.371 g (1 mmol) of Cu(ClO4)2ꢁ 6H2O in ethyl acetate
(10 mL) was added to a boiling suspension of 0.736 g (2.2 mmol) of the
ligand in ethyl acetate (100 mL). The resulting solution was refluxed for
about 4 h on a boiling steam bath. The complex precipitated on cooling,
was filtered and washed several times with hot benzene to remove the
excess ligand. It was dried under vacuum over phosphorus(V) oxide.
Nitrate and Chloride Complex
A quantity of 0.256 g (1 mmol) of Cu(NO3)2ꢁ6H2O or 0.170 g (1 mmol)
of CuCl2ꢁ2H2O in acetone (10 mL) was added to a boiling suspension of
0.736 g (2.2 mol) of the ligand for Cu(NO3)2ꢁ6H2O or 0.401 g (1.2 mmol) of
the ligand for CuCl2ꢁ2H2O in acetone (100 mL). The mixture was refluxed
for about 4 h on a steam bath. The precipitated complex was cooled, filtered
and washed several times with hot benzene to remove the excess ligand. It
was dried under vacuum over phosphorus(V) oxide.
Bromide Complex
A quantity of 0.295 g (1 mmol) of CuBr2ꢁ4H2O in acetonitrile (10 mL)
was added to a boiling solution of 0.736 g (2.2 mmol) of the ligand in
acetonitrile (100 mL). The solution was refluxed for about 3 h on a steam

Copper(II) Complexes
1315
Figure 3. [Cu(L)2]X2 (X = ClO4 or NO3), [Cu(L)2Br2] and [Cu(L)Cl2].

1316
Raju and Radhakrishnan
bath. The complex precipitated on cooling was filtered and washed several
times with hot benzene to remove the excess ligand. It was dried under
vacuum over phosphorus(V) oxide.
Analyses and Physical Methods
All the complexes were analysed for metal and halide contents by the
standard methods[22] and the perchlorate content by the Kurz method.[23] The
molar conductances of the complexes in DMF, methanol and nitrobenzene
(10–3 M) solutions were measured at room temperature using a Toshniwal
conductivity bridge with a dip-type conductance cell (cell constant = 1.094).
The infrared spectra of the ligand and complexes were recorded in the range
4000–400 cm–1 on a Shimadzu IR-470 spectrophotometer. Electronic spectra
of the ligand and complexes were measured in the solid state (paste with
Nujol) on a Shimadzu UV 160A spectrophotometer in the range 1,100–200
nm. The EPR spectra of the complexes were recorded in methanol-toluene
(1:1) at liquid nitrogen temperature using a Varian E-112 EPR spectropho-
tometer. DPPH free radical was the ‘g’ marker. C, H, and N analyses were
carried out using a Heraeus CHNO rapid analyzer. Magnetic susceptibility
measurements were done at room temperature by the Guoy method using
mercury(II)tetrathiocyanatocobaltate(II) as the calibrant.
ACKNOWLEDGMENTS
We thank the Heads of the Regional Sophisticated Instrumentation
Centers at the Indian Institute of Technology, Chennai, and the Indian
Institute of Technology, Mumbai, for some instrumental analyses. We also
thank the Mahatma Gandhi University, Kottayam, for providing laboratory
facilities and the University Grants Commission for awarding a Teacher
Fellowship to one of us (KCR) under the faculty improvement program.
Also, we wish to express our heartfelt thanks to Dr. Siby Joseph and Dr.
N.T. Madhu for some fruitful discussions.
REFERENCES
1. Pelizzi, E.; Pelizzi, G.; Predieri, G.; Resolva, S. Investigation into aroyl
hydrazones as chelating agents. J. Chem. Soc. Dalton Trans. 1982, 1349.
2. Singh, L.; Mohan, G.; Parashar, R.K.; Tripathi, S.P.; Sharma, R.C.
Studies on antiinflammatory activity of some lanthanone complexes of
bioactive organic molecules. Curr. Sci. 1986, 55, 846–848.

Copper(II) Complexes
1317
3. Alice, C.J.; Prabhakaran, C.P. Synthesis and characterization and bio-
logical studies of Pd(II) complexes of some ON and NS donors. Ind. J.
Chem. 1990, 29A, 491–493.
4. Alaudeen, M.; Abraham, A.; Radhakrishnan, P.K. Synthesis and
antibacterial activity of rare-earth-perchlorate complexes of 4-21-
hydroxynaphthylazo)antipyrine. Proc. Ind. Acad. Sci. (Chem. Sci.)
1995, 107, 123–126.
5. Joseph, S.; Radhakrishnan, P.K. Yttrium and lanthanide perchlorate
complexes of N,N1-bis(4-antipyrylmethylidene)ethylenediamine. Synth.
React. Inorg. Met.-Org. Chem. 1998, 28 (3), 423–435.
6. Madhu, N.T.; Radhakrishnan, P.K. Copper(II) complexes of 1,2-di(imi-
no-41-antipyrinyl)ethane and 4-N-(41-antipyrylmethylidene)amino-
antipyrine. Synth. React. Inorg. Met.-Org. Chem. 2001, 31 (2), 315–330.
7. Madhu, N.T.; Radhakrishnan, P.K. Cobalt(II) complexes of 1,2-Di-
(imino-41-antipyrinyl)ethane and 4-N-(41-antipyrylmethylidene) ami-
noantipyrine. Transition Met. Chem. 2000, 25, 287–292.
8. Ajithkumar, G.; Radhakrishnan, P.K. Yttrium and lanthanide nitrate com-
plexes of 2,3-dimethyl-4-formyl(benzhydrazide)-1-phenyl-3-pyrazolin-
5-one. Synth. React. Inorg. Met.-Org. Chem. 2002, 32 (4), 831–842.
9. Raju, K.C.; Radhakrishnan, P.K. Complexes of copper(II) with N,N1-bis
(4-antipyrylmethylidene)ethylenediamine. Synth. React. Inorg. Met.-
Org. Chem. 2002, 32 (6), 1117–1128.
10. Raju, K.C.; Radhakrishnan, P.K. Complexes of cobalt(II) with N,N1-bis
(4-antipyrylmethylidene)ethylenediamine. Synth. React. Inorg. Met.-
Org. Chem. 2002, 32 (10), 1719–1728.
11. Geary, W.J. The use of conductivity measurements in organic solvents
for the characterization of coordination compounds. Coord. Chem. Rev.
1971, 7, 81–115.
12. Kumar, P.A. Synthesis and spectral studies of some seven-coordinated
rare earth metal complexes. Synth. React. Inorg. Met.-Org. Chem.
1997, 27 (4), 577–588.
13. Singh, B.; Narang, K.K. Rachana srivastava. Studies on complexes of
cobalt(II), nickel(II), copper(II) and cadmium(II) with acetophenone
oxalolyldihydrazones. Synth. React. Inorg. Met.-Org. Chem. 2001, 31
(8), 1387–1401.
14. Scholer, R.P.; Merbach, A.E. Raman and infrared study of hexamethyl-
phosphoramide complexes of lanthanide perchlorates. Inorg. Chim.
Acta 1975, 15, 15–20.
15. Gatehouse, B.M.; Livingstone, S.E.; Nyholm, R.S. Infrared spectra of
some nitrato and other oxyanion coordination complexes. J. Inorg.
Nucl. Chem. 1958, 8, 75–78.
16. Nawar, N.; Khattab, M.A.; Hosny, N.M. Some metal(II) complexes of

1318
Raju and Radhakrishnan
O-aminoacetophenonebenzoylhydrazone. Their preparation, character-
ization and antimicrobial activity. Synth. React. Inorg. Met.-Org. Chem.
1990, 29 (8), 1365–1384.
17. Shetty, S.N.; Murthy, A.S.R.; Timbe, G.L. Synthesis and spectral
characterization of copper(II) complexes of dithiosemicarbazone. Ind.
J. Chem. 1993, 32A, 3180322.
18. Dey, K.; Nandi, K.K. Transition and non-transition metal complexes
with 1-formylferrocene-4-methoxybenzoyl hydrazone and 1-acetylfer-
rocene-4-methoxybenzoylhydrazone. Synth. React. Inorg. Met.-Org.
Chem. 1999, 29 (3), 419.
19. Dey, K.; Bandyopadhyay, D. Synthesis and characterization of
complexes of nickel(II), cobalt(II) and cobalt(III) with morpholine N-
thiohydrazones formed from salicylaldehyde and 2-hydroxyacetophe-
none. Ind. J. Chem. 1992, 31A, 34–38.
20. Singh, B.; Yadav, B.P.; Aggarwal, R.C. Synthesis and characterization
of 1-phenyl-5-benzol-4-thiobiuret complexes with oxovanadium(IV),
cobalt(II) and (III), nickel(II), copper(II), cadmium(II) and mercury(II).
Ind. J. Chem. 1984, 23A, 441–444.
21. Kivelson, D.; Neiman, R. ESR studies on the bonding in copper
complexes. J. Chem. Phys. 1961, 35 (1), 149–155.
22. Bassett, J.; Denny, R.C.; Jeffrey, G.H.; Mendhen, J. Titrametric
analysis. In Vogel’s Text Book of Quantitative Inorganic Analysis, 5th
Ed.; ELBS: London, 1961; 341–379.
23. Kurz, E.; Kober, G.; Berl, M. Determination of perchlorates by fusion
with nitrite. Anal. Chem. 1958, 30 (12), 1983–1986.
Received August 16, 2002
Accepted April 17, 2003
Referee I: M. Bayachou
Referee II: J. Protasiewicz

Copyright of Synthesis & Reactivity in Inorganic & Metal-Organic Chemistry is the property of Marcel Dekker
Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright
holder's express written permission. However, users may print, download, or email articles for individual use.