Mixed-ligand complexes of Ni(II), Cu(II), and Zn(II) with 5-chlorosalicylaldehyde and β-diketones

Article abstract of DOI:10.1081/SIM-120037518

Mixed-ligand complexes of the types M(5-Clsal)L and Ni(5-ClSal)L(H ₂O)₂ (where M = copper(II) or zinc(II), 5-ClsalH = 5-chlorosalicylaldehyde and HL = 2,4-pentanedione, 1-phenyl-1,3-butanedione, or 1,3-diphenyl-1,3-propanedione) have

Full text of DOI:10.1081/SIM-120037518

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Mixed‐Ligand Complexes of Ni(II), Cu(II), and Zn(II)
with 5‐Chlorosalicylaldehyde and β‐Diketones
R. N. Prasad a , Mithlesh Agrawal a & Remesh George a
a Department of Chemistry, University of Rajasthan, Jaipur, 302004, India
Version of record first published: 16 Nov 2010.
To cite this article: R. N. Prasad , Mithlesh Agrawal & Remesh George (2004): Mixed‐Ligand Complexes of Ni(II), Cu(II),
and Zn(II) with 5‐Chlorosalicylaldehyde and β‐Diketones, Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry, 34:5, 943-952
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 5, pp. 943–952, 2004
Mixed-Ligand Complexes of Ni(II), Cu(II),
and Zn(II) with 5-Chlorosalicylaldehyde
and b-Diketones
*
R. N. Prasad, Mithlesh Agrawal, and Remesh George
Department of Chemistry, University of Rajasthan, Jaipur, India
ABSTRACT
Mixed-ligand complexes of the types M(5-Clsal)L and Ni(5-Clsal)L(H2O)2
(where M ¼ copper(II) or zinc(II), 5-ClsalH ¼ 5-chlorosalicylaldehyde
and HL ¼ 2,4-pentanedione, 1-phenyl-1,3-butanedione, or 1,3-diphenyl-
1,3-propanedione) have been synthesized by 1 :1 : 1 molar reactions of
metal chlorides with 5-chlorosalicylaldehyde and b-diketones. The resulting
complexes have been characterized by elemental analyses, TLC, conduct-
1
ances, thermal analysis, magnetic moments, IR, electronic, and H NMR
spectra.
Key Words: Mixed-ligand complexes; Thin layer chromatography;
Magnetic moments; IR spectra; Electronic spectra.
*
Correspondence: R. N. Prasad, Department of Chemistry, University of Rajasthan,
Jaipur 302004, India; E-mail: prasadraghunandan@yahoo.com.
943
DOI: 10.1081/SIM-120037518
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Prasad, Agrawal, and George
INTRODUCTION
Mixed-ligand complexes play important roles in biological processes, as
exemplified by many instances in which enzymes are known to be activated by
metal ions.[1,2] Such complexes have been implicated in the storage and trans-
port of active substances through membranes.[3] Interest in mixed chelation
also arises from the study of mechanisms of organic reactions, where the
metal ion or the bound ligand is activated for selective reactions. Hydrolysis
of a-amino acid esters, stereoselective decarboxylation, Schiff base for-
mation, and amino acid oxidase models provide typical examples.[4] Many
mixed-ligand complexes are finding applications in the microelectronic
industry, chemical vapor deposition of metals and as drugs.[5,6] Hence, the
investigations on mixed-ligand complexes have been carried out in our labora-
tories. These investigations will help in understanding the role of metal ions in
the active sites of metalloenzymes, studying the toxic effects of metal ions,
detoxification mechanisms, and drug designing.[7]
Mixed-ligand complexes of Ni(II), Cu(II), and Zn(II) of the type MLL0
with aldehydes and ketones have been reported.[8–10] However, the mixed-
ligand complexes of these metals with substituted salicylaldehydes have
not been reported, so far except for complexes of alkaline earth metals
reported earlier from our laboratories.[11–13] In the present paper, mixed-
ligand complexes of the types M(5-Clsal)L (M ¼ Cu(II) and Zn(II)) and
Ni(5-Clsal)L(H2O)2 (where 5-ClsalH ¼ 5-chlorosalicylaldehyde and HL ¼
2,4-pentanedione (acacH), 1-phenyl-1,3-butanedione (bzacH), or 1,3-diphenyl-
1,3-propanedione (dbzmH), Fig. 1) are described.
Figure 1. Structures of the ligands.

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945
EXPERIMENTAL
Materials
5-Chlorosalicylaldehyde (Aldrich), benzoylacetone (Fluka), and dibenzoyl-
methane (Sisco) were purified by recrystallization from hot ethanol. Acetyl-
.
acetone (K. Light) and ethanol were purified by distillation. NiCl2 6H2O
.
(Fluka), CuCl2 2H2O (Fluka), and ZnCl2 (Fluka) were of AR grade.
Synthesis of Mixed-Ligand Complexes of
Ni(II), Cu(II), and Zn(II)
To an ethanolic solution of Ni(II) or Cu(II) chloride (about 3.4 mmol in
10 mL) a mixture of the two-carbonyl compounds (3.4 mmol each) in ethanol
(10 mL) was added with stirring. A clear solution was obtained. The pH of the
reaction mixture was raised to ꢀ5.5 by adding 5% aqueous sodium hydroxide
solution dropwise with stirring. The pH was measured with the help of pH
paper and stirring was continued for 3–4 hr. The solid complexes, which sep-
arated were filtered off, washed with ethanol, and dried under reduced
pressure.
The zinc(II) mixed-ligand complexes were prepared similarly, except a
5% aqueous ammonia solution was used instead of a 5% aqueous sodium
hydroxide solution.
Analytical Methods
Nickel and zinc were determined volumetrically by EDTA titration using
eriochrome black T as indicator. Copper was determined volumetrically by
sodium thiosulfate solution using starch as indicator.[14] Carbon and hydrogen
analyses were carried out on a Heraeus Carlo Erba 1108 instrument. Specific
conductances were measured at room temperature in DMSO by a Systronics
direct reading 304 conductivity meter, using a glass cell having a cell constant
of 1.0 cm21. TG and differential thermal analyses (DTA) studies were carried
out on a Rigaku Thermoflex PTC-10A instrument under nitrogen atmosphere.
Infrared spectra of KBr pellets of the complexes were recorded in the region
400–4000 cm21 on a Nicolet Magna-550 FT IR spectrophotometer. Elec-
tronic spectra were recorded in DMSO on a Hitachi U-2000 spectropho-
tometer in the range 200–1100 nm. 1H NMR spectra were recorded in
DMSO-d6 on a Jeol FX 90 Q FT NMR spectrometer at 90 MHz using TMS
as reference. Magnetic measurements were carried out at room temperature
on a Gouy balance using Hg[Co(CNS)4] as calibrant.

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Prasad, Agrawal, and George
RESULTS AND DISCUSSION
The reactions of the hydrated metal ions with 5-chlorosalicylaldehyde and
b-diketones (acetylacetone, benzoylacetone, or dibezoylmethane) in 1 : 1 : 1
molar ratios result in the formation of mixed-ligand complexes [(I) or (II) in
Fig. 2].
The Ni(II) complexes are green, the Cu(II) complexes are grey, and the
Zn(II) complexes are yellow solids. They are insoluble in chloroform, carbon
tetrachloride, benzene, nitrobenzene, and methanol but soluble in DMSO. The
properties and analyses of the complexes are recorded in Table 1. The conduc-
tances of the complexes are very low (5–30 V21 cm2 mol21) indicating their
non-electrolytic nature.[15]
Thin Layer Chromatography
TLC of all the mixed-ligand complexes was performed on silica gel G
using benzene–petroleum ether (b.p. 40–60 8C) (1 : 1, v/v) as the mobile
Figure 2. Synthesis of mixed-ligand complexes.

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947
m

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Prasad, Agrawal, and George
phase and the retention times were compared with those of the corresponding
bis-complexes, e.g., M(5-Clsal)2 and ML2. All the mixed-ligand complexes
show single spots with Rf values being intermediate between the two corre-
sponding symmetrical bis-complexes. This indicates that these are indeed
mixed-ligand complexes rather than mixtures of the two corresponding bis-
complexes.
Thermal Analysis
Thermogravimetric (TGA) and DTA of the mixed-ligand complexes were
carried out to confirm the presence of coordinated water molecules. The weight
loss observed by TGA in the 120–150 8C range for the Ni(II) complexes
corresponds to two coordinated water molecules, e.g., in Ni(5-Clsal)(acac)
(H2O)2, the weight loss found is 10.1%, calcd. 10.3%. This is confirmed by
a sharp endothermic peak observed in the 130–175 8C range in the DTA of
the nickel(II) complexes. TGA and DTA studies of the Cu(II) and Zn(II)
complexes confirm the absence of coordinated water molecules in these
complexes.
Infrared Spectra
In the IR spectra of the mixed-ligand complexes, strong absorption bands
in the region 1580–1650 cm21 maybe attributed to coordinated C55O groups
and those in the region 1475–1580 cm21 to C55C stretching modes. In free
acetylacetone and benzoylacetone, the n(C55O) band[16] has been reported
at 1724 cm21 and in 5-chlorosalicylaldehyde, the n(C55O) band appears at
1680 cm21. Thus, the shift of n(C55O) bands to the lower wave number
side in the mixed-ligand complexes supports the coordination of the C55O
group to the metal ion. Shifting of these bands to lower wave number on
complexation with the metal ion has been reported.[17,18] In the spectra of
the mixed-ligand complexes, weak to medium intensity absorption bands in
the region 405–525 cm21, which are not present in the free ligands, maybe
attributed to n(M–O) vibrations.[19] However, the IR data could be as well
explained by [M(5-Clsal)2 þ ML2] mixture as by M(5-Clsal)L.
Magnetic Moments
For the Cu(II) complexes, the meff values (at ꢀ302 K) are in the range
1.76–2.18 B.M., which are slightly higher than those expected for a d9 system

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Mixed-Ligand Complexes
949
(1.73 B.M.) and maybe due to the incomplete quenching of orbital contri-
bution to the magnetic moment[20] or due to spin–orbit coupling.[21] The
meff values in the range 2.00–2.25 B.M. have been reported for mixed-ligand
complexes of Cu(II) with 3-chloro-, 3-nitro-, or aryl-substituted 2,4-pentane-
diones and 2,20-bipyridine or 1,10-phenanthroline.[22] For the Ni(II) com-
plexes, the meff values were observed in the range 2.72–2.87 B.M.
suggesting a distorted octahedral geometry.[23] The Zn(II) complexes are
diamagnetic.
Electronic Spectra
The electronic spectra of the Cu(II) complexes exhibit a broad band at 655–
665 nm (1 ¼ 78–107 L mol21 cm21) suggesting a square-planar geometry.[24]
This broad band does not show any sign of splitting, suggesting that all the
d–d transitions are lying within this broad band.[25] In the case of the nickel(II)
complexes, the absorption band at 694–715 nm (1 ¼ 12–17L mol21 cm21
)
maybe assigned to the A2g(F) ! T1g(F) transition.[26] The A2g(F) ! T1g
(P) transition band merges with the strong charge transfer band at 437–443 nm
(1 ¼ 318–615 L mol21 cm21). These observed transitions suggest a pseudo-
octahedral environment around the nickel atom in the mixed-ligand
complexes.[26] Similar results have been reported for octahedral nickel(II)
mixed-ligand complexes with b-diketones and nitrogen donor ligands.[27]
In all the mixed-ligand complexes of Ni(II), Cu(II), and Zn(II), strong absorp-
tion bands at 311–325 nm (1 ¼ 320–547 L mol21 cm21) and 367–372 nm
(1 ¼ 273–533 L mol21 cm21) maybe due to intra-ligand transitions (n ! pꢀ
3
3
3
3
and p ! pꢀ) and the band at 399–443 nm (1 ¼ 318–615 L mol21 cm21
)
maybe a charge transfer band.
Nuclear Magnetic Resonance Spectra
In free 5-chlorosalicylaldehyde the CH proton gives a singlet at d
10.36 ppm, which is shifted upfield in the mixed-ligand complexes of Zn(II)
and then appears at d 10.01–10.07 ppm confirming the coordination of the
C55O group of the aldehyde to the zinc atom. The OH proton peak of free
5-chlorosalicylaldehyde (d 10.88 ppm) disappears in the spectra of the
mixed-ligand complexes supporting the binding of the zinc atom to the
phenolic oxygen of the OH group through the replacement of the hydrogen
atom. In free acetylacetone, benzoylacetone, and dibenzoylmethane, the
singlets due to the CH protons have been reported at d 5.54, 6.18, and
6.82 ppm, respectively.[28] In the Zn(II) mixed-ligand complexes, these

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Prasad, Agrawal, and George
singlets are observed at d 5.44, 5.98, and 6.71 ppm, respectively. In free acet-
ylacetone and benzoylacetone, the CH3 proton singlets have been reported at d
1.99 and 2.19 ppm, respectively,[28] and in the Zn(II) mixed-ligand complexes,
these singlets appear at d 1.77 and 2.01 ppm, respectively. Thus, the upfield
shift of the CH and CH3 protons of the b-diketone ligands in the mixed-ligand
complexes confirms the coordination of these ligands to the zinc atom. Similar
upfield shifts of CH and CH3 protons have been reported for b-diketonates of
Group II, III, and IV metals.[28–30]
Thus, the spectral and magnetic studies support the proposed structures of
the mixed-ligand complexes in Fig. 2.
ACKNOWLEDGMENTS
The authors are thankful to the Head, Department of Chemistry, Univer-
sity of Rajasthan, Jaipur, for providing laboratory facilities, the Head, Depart-
ment of Chemistry, Banasthali Vidyapith, Banasthali, Rajasthan, for magnetic
data, the Head, Department of Chemistry, University of Delhi, Delhi, for ther-
mal analyses and the Director, C.D.R.I., Lucknow for C and H analyses.
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Received January 8, 2003
Accepted February 17, 2004
Referee I: D. T. Haworth
Referee II: E. Sinn

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