Synthesis, characterization, and electrochemical studies of ternary complexes of lanthanum(III) and cerium(III) with some naphthylideneamino acids and imidazoles

Article abstract of DOI:10.1080/15533170500359711

A new series of ternary lanthanium(III) and cerium(III) complexes containing Schiff bases derived from some amino acids, viz: glycine; alanine; phenylalanine; valine and leucine with 2-hydroxy-1-naphthaldehyde as primary ligands, and 1-methylimidazole & 1,2-dimethylimidazole as secondary ligands were synthesized. The complexes were characterized on the bases of microanalyses, electrical conductance, IR & ¹H NMR spectra, thermal analysis and cyclic voltammetric data. All complexes were found to be non-electrolytes with the general formula of [ML(NO₃) Im·nH₂O] (where M = La(III) or Ce(III), L = naphthylideneamino acids, Im = 1-methylimidazole or 1,2-dimethylimidazole and n = 1 or 2). The redox properties of some of the ternary complexes of La(III) and Ce(III) were examined using cyclic voltammetry in 0.1mol dm^-3 TBAP/ DMSO solutions. The reduction potentials of the investigated complexes showed a dependence upon the nature of the amino acid of the ligand. The stability of the complexes is discussed on the basis of the thermal and electrochemical data. Copyright

Full text of DOI:10.1080/15533170500359711

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Synthesis, Characterization, and Electrochemical
Studies of Ternary Complexes of Lanthanum(III) and
Cerium(III) with Some Naphthylideneamino Acids and
Imidazoles
Mostafa K. M. Rabia a , Gamila Y. Aly b , Mohamed M. El-Dessouki a & Maha A. F. Al-Mohanna c
a Department of Chemistry, Faculty of Science, South Valley University, Sohag, Egypt
b Department of Chemistry, Faculty of Science, Alexandria University, Alexandria, Egypt
c Girls College of Education (Scientific Departments), Riyadh, K. S. A.
Version of record first published: 31 Jan 2012.
To cite this article: Mostafa K. M. Rabia, Gamila Y. Aly, Mohamed M. El-Dessouki & Maha A. F. Al-Mohanna (2005):
Synthesis, Characterization, and Electrochemical Studies of Ternary Complexes of Lanthanum(III) and Cerium(III) with Some
Naphthylideneamino Acids and Imidazoles, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry,
35:10, 801-809
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Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 35:801–809, 2005
Copyright # 2005 Taylor & Francis, Inc.
ISSN: 1553-3174 print/1532-2440 online
DOI: 10.1080/15533170500359711
Synthesis, Characterization, and Electrochemical Studies of
Ternary Complexes of Lanthanum(III) and Cerium(III) with
Some Naphthylideneamino Acids and Imidazoles
Mostafa K. M. Rabia
Department of Chemistry, Faculty of Science, South Valley University, Sohag, Egypt
Gamila Y. Aly
Department of Chemistry, Faculty of Science, Alexandria University, Alexandria, Egypt
Mohamed M. El-Dessouki
Department of Chemistry, Faculty of Science, South Valley University, Sohag, Egypt
Maha A. F. Al-Mohanna
Girls College of Education (Scientific Departments), Riyadh, K. S. A.
1982; Mahmoud et al., 1987a, 1987b; Wang and Chang,
A new series of ternary lanthanium(III) and cerium(III) com- 1991, 1994a, 1994b; Abdel-Mawgoud, 1995, 1996; Abdel-
plexes containing Schiff bases derived from some amino acids,
viz: glycine; alanine; phenylalanine; valine and leucine with
Mawgoud et al., 1991; Kureshy et al., 1993; Kureshy and
Khan, 1993; Sharma et al., 1996; Tarafder and Khan, 1997;
2-hydroxy-1-naphthaldehyde as primary ligands, and 1-methyli-
midazole & 1,2-dimethylimidazole as secondary ligands were
synthesized. The complexes were characterized on the bases of
Guayngbin et al., 1998) have received much attention due to
their biological importance (Matthews and Joy, 1991;
microanalyses, electrical conductance, IR & 1H NMR spectra, Angoso et al., 1992). In addition, the complexes of amino
thermal analysis and cyclic voltammetric data. All complexes
were found to be non-electrolytes with the general formula of
.
[ML(NO3)Im nH2O] (where M 5 La(III) or Ce(III), L 5
acid Schiff bases are considered to be potential antibacterial
and anticancer reagents (Chohan et al., 1998; Kong et al.,
1999). However, interactions between such metal complexes
and secondary neutral ligands in ternary systems has received
some of the ternary complexes of La(III) and Ce(III) were minor attention (Rao et al., 1986, 1987; Arulsamy and Zacharias,
naphthylideneamino acids, Im 5 1-methylimidazole or 1,2-
dimethylimidazole and n 5 1 or 2). The redox properties of
examined using cyclic voltammetry in 0.1 mol dm23 TBAP/
DMSO solutions. The reduction potentials of the investigated com-
plexes showed a dependence upon the nature of the amino acid of
the ligand. The stability of the complexes is discussed on the basis
of the thermal and electrochemical data.
1991; Kureshy and Khan, 1994; Abdel-Mawgoud, 1998).
Following our recent work on N-naphthylideneamino acid
complexes (Aly et al., 2004), we report here the synthesis
and the spectroscopic and electochemical studies of ternary
complexes of La(III) and Ce(III) containing Schiff bases
derived from glycine, alanine, phenylalanine, valine and
leucine and 2-hydroxy-1-naphthaldehyde as primary ligands,
and monodentate nitrogen donors, namely, 1-methylimidazole
and 1,2-dimethylimidazole as secondary ligands. A compari-
son between the stability of the La(III) and Ce(III) complexes
was determined on the basis of the thermal and electrochemical
data. The ligands used here have the following structures as
shown in Figure 1.
Keywords ternary complexes, La(III) complexes, Ce(III) com-
plexes, naphthylideneamino acid, Schiff bases, cyclic
voltammetry
INTRODUCTION
The metal complexes of Schiff bases derived from o-hydro-
xyaromatic aldehydes and amino acids (MacDonald et al.,
EXPERIMENTAL
Received 23 November 2004; accepted 18 July 2005.
Address correspondence to Mostafa K. M. Rabia, Department of
Chemistry, Faculty of Science, South Valley University, Sohag,
Egypt. E-mail: mostafarabia@hotmail.com.
Materials
2-Hydroxy-1-naphthaldehyde, amino acids viz: glycine (gly);
alanine(ala);phenylalanine(phenala);valine(val)andleucine(leu),
801

802
M. K. M. RABIA ET AL.
SMDE 303A comprising a hanging mercury drop electrode
(HMDE) as working electrode, a platinum wire auxiliary elec-
trode, and an Ag/AgNO3 reference electrode was used. The
concentration of the supporting electrolyte, tetrabutylammo-
nium perchlorate (TBAP), was maintained at 0.1 mol dm23
.
RESULTS AND DISCUSSION
The microanalytical data for the prepared La(III) and
Ce(III)–naphthylideneamino acid–imidazole ternary com-
plexes (Table 1) suggest the general molecular formula
.
[M(III)(naphthylideneamino acid) (NO3)-Im nH2O] (where
M ¼ La(III) or Ce(III), Im ¼ 1-methylimidazole or 1,2-
dimethylimidazole and n ¼ 1 or 2). This formula suggests
that the divalent anions of the naphthylideneamino acids are
coordinated to the central metal ion as tridentate ligands,
whereas the neutral molecules of the 1-methylimidazole or
1,2-dimethylimidazole are coordinated to the central metal
ion as monodentate ligands.
FIG. 1. Structure of the ligands.
1-methylimidazole(1-mIm), 1,2-dimethylimidazole(1,2-mIm),
.
.
La(NO3)3 6H2O and Ce(NO3)3 6H2O as well as solvents
used were obtained from Fluka or BDH and used as supplied.
All complexes are air-stable and soluble in Lewis bases such
as DMF and DMSO, but are sparingly soluble in most other
organic solvents and water. The molar electrical conductivities
of the ternary complexes, measured in DMF, were found to be
in the range of 10.1–35.9 V21 cm2 mol21, typical of non-
electrolytes. In general, the mechanism of the formation of
these La(III)- and Ce(III)-naphthylideneamino acid-imidazole
ternary complexes can be represented by the following equation:
Synthesis of the Complexes
The ternary complexes for all the subject amino acids and
imidazoles were prepared in situ by the same general procedure
as follows: 2-Hydroxy-1-naphthaldehyde (0.86 g, 5 mmol) dis-
solved in hot ethanol (20 mL) was added, gradually with
stirring, to a mixture of amino acid (5 mmol) and anhydrous
sodium acetate (0.41 g, 5 mmol) dissolved in a 1 : 1 water–
ethanol mixture (20 mL); the reaction mixture was stirred for
30 min on a water bath at 708C. Then a mixture of metal salt
(5 mmol) and anhydrous sodium acetate (0.41 g, 5 mmol) dis-
solved in a 1 : 1 water–ethanol mixture (20 mL) was added,
drop-wise with stirring, to the above mixture and the reaction
mixture is lefted to 2 h. To this reaction mixture was added a
M(NO3Þ3 ꢀ 6H2O þ H2L þ Im
ꢁ! ½ML(NO3ÞIm ꢀ nH2Oꢂ þ 2HNO3 þ ð6 ꢁ nÞH2O ð1Þ
where H2L ¼ naphthylideneamino acid, Im ¼ 1-methylimida-
zole or 1,2-dimethylimidazole and n ¼ 1 or 2.
5 mmol of imidazoles dissolved in ethanol (20 mL), and the Infrared Spectra
resulting mixture is refluxed at 70–808C on a water bath for
2 h and then is left to cool (258C) with stirring for 24 h. The
resulting precipitate was filtred and washed with ethanol
(96%) and then with ether and is dried in vacuo over P2O5.
The important infrared bands of the ternary complexes and
their tentative assignments are presented in Table 2. The IR
spectra of all La(III) and Ce(III) complexes show a broad
band at 3428–3321 cm21, supporting the presence of water
molecules as indicated by the chemical analysis data listed in
Table 1. The absorption band in the 1620–1544 cm21 region
Physical Measurements
The electrolytic conductance measurements were made at of all ternary complexes could be attributed to the nC¼Nimid.
298 K in DMF using a Jenway 4020 Conductivity Meter. The of the neutral ligand (1-mIm and 1,2-mIm). The strong band
IR spectra were recorded on FT-IR 1650 Perkin Elmer Spectro- at 1649–1626 cm21 is due to the imino group of the Schiff
photometer using KBr pellets. Elemental analyses of the com- base. The absorption bands at 1563–1540, 1423–1396 and
plexes were carried out at the Microanalytical Laboratory, 1361–1301 cm21 can be assigned, respectively, to the stretch-
Cairo University, Egypt, and the Central Laboratory of the ing vibrations of the coordinated CO22 asymmetric, CO22 sym-
Faculty of Pharmacy, King Saud University, Riyadh. metric and C-O phenolic groups of the primary ligand
Thermal studies were carried out using a Perkin-Elmer (naphthylideneamino acid) (Westland and Arafder, 1981;
1
Thermal Analyser (heating rate ¼ 208C/min). The H NMR Addison and Gathehouse, 1960). The bands in the regions
spectra in deturated dimethyl sulfoxide (DMSO-d6), with tetra- 1268–1182 and 1087–1005 cm21 arise from the NO32 anion,
methylsilane as internal standard, were obtained using a Varian coordinated as monodentate ligand to the metal ion. The far–
EM-390 90 MHz NMR Spectrophotometer. The electrochemi- IR spectra of all complexes show bands in the region 468–
cal data were obtained with an EG & G 363A electrochemistry 405 cm21, which are assigned to nM-O or nM-N vibrations
system. A three-electrode electrolysis cell system model (Bellamy, 1966; Aminabhavi et al., 1984).

TABLE 1
Elemental analysis of La(III) and Ce(III) ternary complexes
Formula
weight
(% yield)
% Analysis found/(calcd.)
L
Colour decomp.
temp. ( 8C)
(V21cm2
Compound, Empirical formula
C
H
N
mol21
)
La(III) complexes
.
[La(naph gly)(NO3)(H2O)1-mIm] H2O
.
546 (48)
560 (59)
636 (65)
570 (25)
584 (40)
560 (45)
574 (58)
37.9 (37.4)
38.9 (38.6)
4 5.7 (45.3)
42.0 (42.1)
42.8 (43.1)
38.3 (38.6)
40.1 (39.7)
3.5 (3.5)
3.6 (3.7)
3.9 (3.9)
4.1 (4.0)
4.5 (4.3)
3.8 (3.7)
4.3 (4.5)
10.5 (10.3)
10.1 (10.0)
9.1 (8.8)
Pale Yellow (.300)
Yellow (220)
19.1
35.9
31.4
22.3
30.2
20.7
10.1
C17H19LaN4O8
.
[La(naph ala)(NO3)(H2O)1-mIm] H2O
.
C18H21LaN4O8
.
.
[La(naph phala)(NO3)(H2O)1-mIm] H2O
C24H25LaN4O8
Yellow (.300)
Pale Green (.300)
Yellow (.300)
Yellow (.300)
Yellow (.300)
[La(naph.val)(NO3)(H2O)1-mIm]
C20H23LaN4O7
.
[La(naph leu)(NO3)(H2O)1-mIm]
9.7 (9.8)
9.5 (9.6)
C21H25LaN4O7
.
.
[La(naph gly)(NO3)(H2O)1,2-mIm] H2O
C18H21LaN4O8
9.8 (10.0)
9.5 (9.7)
.
[La(naphala)(NO3)(H2O)1,2-mIm] H2O
C19H23LaN4O8
Ce(III) complexes
.
.
[Ce(naph gly)(NO3)(H2O)1-mIm] H2O
C17H19CeN4O8
547 (52)
561 (47)
637 (63)
571 (28)
585 (50)
560 (49)
575 (45)
37.8 (37.3)
38.9 (38.5)
45.1 (45.2)
41.6 (42.0)
42.7 (43.1)
38.6 (38.5)
39.3 (39.6)
3.3 (3.5)
3.7 (3.7)
4.1 (3.9)
4.2 (4.0)
4.2 (4.3)
3.7 (3.7)
4.0 (4.0)
10.3 (10.2)
10.2 (10.0)
8.7 (8.8)
Pale Yellow (.300)
Green (.300)
16.4
24.6
25.8
12.6
27.5
19.2
20.5
.
[Ce(naph.ala)(NO3)(H2O)1-mIm] H2O
C18H21CeN4O8
.
.
Ce(naph phala)(NO3)-(H2O)1-mIm] H2O
C24H25CeN4O8
Pale Green (.300)
Green (.300)
Ce(naph.val)(NO3)(H2O)1-mIm]
C20H23CeN4O7
.
[Ce(naph leu)(NO3)(H2O)1-mIm]
9.6 (9.8)
9.4 (9.6)
Green (225)
C21H25CeN4O7
.
.
[Ce(naph gly)(NO3)(H2O)1,2-mIm] H2O
C18H21CeN4O8
9.8 (10.0)
9.5 (9.7)
Pale Green (.300)
Pale Green (240)
.
[Ce(naph.ala)(NO3)(H2O)1,2-mIm] H2O
C19H23CeN4O8

TABLE 2
IR frequenciesa,b of La(III) and Ce(III) ternary complexes
nazo
(C55N)
nimid
(C55N)
n(C55C) þ
nsym
(COO2)
nph
(C22O)
n
n
(M22L)
Compound
n(H2O) þ n(OH)
nasy (COO2)
(NO23 )
La(III) complexes
.
.
[La(naph gly)(NO3)(H2O)1-mIm] H2O
.
3416 br
3403 br
3387 br
1649 vs
1633 vs
1629 vs
1632 vs
1637 vs
1637 vs
1645 vs
1575 vs
1544 vs
1546 vs
1556 vs
1563 vs
1600 vs
1580 vs
1545, 1518 vs
1546 vs
1545 vs
1400 s
1310 vs
1359 vs
1360 s
1261, 1005
410 m
433 m
427 m
405 m
467 m
—
.
[La(naph ala)(NO3)(H2O)1-mIm] H2O
1404 vs
1407 vs
1410 s
1191 s
.
.
[La(naph phala)(NO3)(H2O) 1-mIm] H2O
1017 m
1182
1018 s
.
[La(naph val)(NO3)(H2O)1-mIm]
3428 br
3321 br
1556 vs
1563 vs
1312 s
.
[La(naph leu)(NO3)(H2O)1-mIm]
1423 vs
1422 s
1407 vs
1352 vs
1301 vs
1311 s
.
.
[La(naph gly)(NO3)(H2O)1,2-mIm] H2O
3500–3061 br
3415–3925 br
1540 vs
1542 vs
1244, 1080
1267, 1070
.
[La(naph.ala)(NO3)(H2O)1,2-mIm] H2O
—
Ce(III) complexes
.
.
[Ce(naph gly)(NO3)(H2O)1-mIm] H2O
3412 br
3384 br
3382 br
1649 vs
1632 vs
1629 vs
1626 vs
1631 vs
1648 vs
1636 vs
1579 vs
1545 vs
1545 vs
1544 vs
1558 vs
1580 vs
1620 vs
1545, 1517 vs
1544 vs
1545 vs
1400 vs
1406 s
1309 s
1361 vs
1360 s
1261, 1005
413 m
468 m
423 m
408 m
466 m
—
.
[Ce(naph.ala)(NO3)(H2O)1-mIm] H2O
1192 m
1257 m
1187 s
.
.
[Ce(naph phala)(NO3)(H2O)1,2-mIm] H2O
Ce(naph.val)(NO3)(H2O)1-mIm]
1406 vs
1396 vs
1415 s
3399 br
3418 br
1544 vs
1558 vs
1356 vs
1354 vs
1313 s
.
[Ce(naph leu)(NO3)(H2O)1-mIm]
1188, 1016 m
1268, 1070 s
1248, 1087 s
.
[Ce(naph gly)(NO3)(H2O)1,2-mIm] H2O
.
[Ce(naph.ala)(NO3)(H2O)1,2-mIm] H2O
.
3530–2930 br
3440–2930 br
1540 vs
1540 vs
1408 s
1424 vs
1303 vs
—
an (M22L) is M22N or M22O.
bbr: broad; m: medium; s: strong; vs: very strong.

CHARACTERIZATION AND ELECTROCHEMICAL STUDIES OF TERNARY La(III) AND Ge(III) COMPLEXES
805
1HNMR Spectra
base molecules. The thermogravimetric residues of the com-
plexes are composed of the metal oxides or carbonates. An
important observation from these thermal data is that the
La(III) complexes are slightly less thermally stable than their
Ce(III) analogs (c.f. Table 4).
1
.
HNMR spectra of the La(naph gly)(NO3)1-mIm 2H2O,
.
.
.
.
La(naph ala)(NO3)1-mIm 2H2O and La(naph phala)(NO3)
.
1-mIm 2H2O complexes were recorded in DMSO-d6. The
chemical shift, d, values of these complexes and their assign-
ments are given in Table 3. The resonance at 4.2–4.3 ppm
arises from the asymmetric proton (CH), while the doublet at
ELECTROCHEMICAL RESULTS
.
.
3.5 ppm in the La(naph phala)(NO3)1-mIm 2H2O complex
is assigned to the CH2 group. The signals at 8.0–8.9 ppm for
the three complexes are due to the coordinated azomethine
group (Kureshy and Khan, 1993), and the signals in the 6.6–
8.0 ppm range are assigend to the phenyl protons of the
naphthaldehyde and phenylalanine moieties. A signal due to
the protons of 1–methylimidazole for the three complexes
appears in the range 1.2–2 ppm. The disappearance of the
signal appeared in the 10.5–13.2 ppm range for the free
primary ligand (Aly et al., 2004), confirms the deprotonation
of the carboxylic and phenolic protons of the ligand and the
participation of their oxygen atoms in the formation of the
complex.
Cyclic voltammetric behaviour of some of the ternary com-
plexes were recorded in DMSO solutions containing 0.1 mol
dm23 TBAP as background electrolyte, using a hanging
mercury drop electrode (HMDE) at 258C. The cyclic voltammo-
.
.
.
grams of La(naph gly)(NO3) 1-mIm 2H2O, Ce(naph gly)
.
.
.
(NO3)1-mIm 2H2O and Ce(naph gly)(NO3)1,2-mIm 2H2O
complexes are characterized by three cathodic irreversible
waves, lacking their anodic partners in the potential range of
–1.4–(22.4) V (c.f. Figure 2). On the other hand, the cyclic
.
.
voltammograms of the La(naph phala)-(NO3)1-mIm 2H2O,
.
La(naph leu) (NO3)1-mIm H2O and Ce(naph phala)-
.
.
.
(NO3)1-mIm 2H2O complexes exhibit two irreversible
waves only in the range of potential –1.4–(22.2)V.
The absence of the third wave can be attributed to its mergence
with the cathodic limit of the solvent. The Schiff bases and imi-
Thermal Analysis
The thermal behaviour of the ternary complexes of La(III) dazoles ligands are electroinactive in this range of potentials.
and Ce(III) follows very similar patterns. Data for thermogravi- Accordingly, the observed waves are assigend to the
metric curves (TG) obtained in a nitrogen atmosphere with a reduction of the complex species. Examination of Figure 2
heating rate 208C min21, are shown in Table 4. These data reveals that no anodic waves are observed on the positive-
reveal an initial mass loss at 65–1008C in some complexes cor- going scan, corresponding to their cathodic waves. Such irre-
responding to the loss of hydration water molecules; the mass versibilty is observed at the entire scan rates of investigation
loss of the coordinated water molecules occurs at 150–2508C. (100–500 mVs21), and is attributed to a slow one electron-
These observed weight losses are in good agreement with the transfer process or to a fast one electron-transfer process
loss of water calculation (c.f. Table 4). The complexes coupled with a follow-up chemical reaction occurring along
undergo further decomposition that continues up to 6008C each of the three CV waves. The obtained cathodic waves
and probably consists of the loss of the imidazoles and Schiff were analysed upon the experimental parameters such as
TABLE 3
1HNMR spectra of La(III) ternary complexes
Compound
d ppm
Assignment
.
.
[La(naph gly)(NO3)(H2O)1-mIm] H2O
8.7
(s, 1H, CH55N)
6.6–7.9
4.3
1.2–1.9
(m, 6H, aromatic)
(4H) H2O þ CH2
1-mIm protons
.
.
[La(naph ala)(NO3)(H2O)1-mIm] H2O
8.9
(s, 1H, CH55N)
(m, 6H, aromatic)
6.7–8
4.3
1.2–2.0
(m, 1H, CHasy
)
Protons of (CH3amino acid þ 1-mIm)
(s, 1H, CH55N)
.
.
[La(naph phala)(NO3)(H2O) 1-mIm] H2O
8.0
6.5–7.5
4.2
3.5
(m, 11H, aromatic)
(m, 1H, CHasy
)
(d, 2H, CH2 J ¼ 6.75)
0.9–1.8
1-mIm protons

806
M. K. M. RABIA ET AL.
TABLE 4
Thermal data for La(III) and Ce(III) ternary complexes
% Wt. loss
found/calc.
Compound
Temp(8C)
Expected gp. loss
Residue
La2O3
La(III) complexes
.
[La(naph gly)(NO3)(H2O)1-mIm] H2O
.
170
220
6.4/6.6
12.0/12.1
17.6/18
70.8/70
3.5/3.3
12.4/14.8
—
2H2O
NO23
1-mIm
250
390
Org. ligand
H2O
H2O þ NO23
Org. ligand
H2O
.
[La(naph ala)(NO3)(H2O)1-mIm] H2O
.
80
200
La2O3 þ La2(CO3)3
390
70
.
[La(naph phala)(NO3)(H2O)1-mIm] H2O
.
2.9/2.8
3.0/2.9
—
La2(CO3)3
175
200
H2O
NO23
380
150
63.5/64
3.2/3.0
10.7/10.9
16.6/16.3
—
1-mIm þorg. ligand
NO23
1-mIm
.
[La(naph leu)(NO3)(H2O)1-mIm]
H2O
La2(CO3)3
La2(CO3)3
La2(CO3)3
220
300
400
Org. ligand
H2O
.
[La(naph gly)(NO3)(H2O)1,2-mIm] H2O
.
65–100
150–220
250–400
400–600
65–100
170–220
300–600
3.4/3.2
15.0/14.7
20.0/20.8
59.6/59.2
3.2/3.1
14.0/14.3
60.0/60
H2O þ NO23
1,2-mIm
Org. ligand
H2O
.
[La(naph ala)(NO3)(H2O)1,2-mIm] H2O
.
H2O þ NO23
1,2-mIm þ Org. ligand
Ce(III) complexes
.
[Ce(naph gly)(NO3)(H2O)1-mIm] H2O
.
180
230
6.3/6.6
11.8/12.0
—
2H2O
CeO2
NO23
—
260
400
69.5/69
6.0/6.3
26.7/27
—
Org. ligand
2H2O
NO23 þ 1-mIm
Org. ligand
H2O
.
[Ce(naph ala)(NO3)(H2O)1-mIm] H2O
.
80–170
250
400
Ce2O3 þ CeO2
.
[Ce(naph phala)(NO3)(H2O)1-mIm] H2O
.
80
180
3.1/3.0
3.0/2.9
9.9/10.3
63.4/63.9
3.3/3.0
11.0/10.9
—
Ce2(CO3)3
H2O
NO23
210
390
Org. ligand
H2O
NO23
1-mIm
.
[Ce(naph leu)(NO3)(H2O)1-mIm]
150
250
Ce2(CO3)3
Ce(CO3)2
Ce(CO3)2
300
400
—
Org. ligand
H2O
.
[Ce(naph gly)(NO3)(H2O)1,2-mIm] H2O
.
65–100
160–250
370–420
420–600
65–100
170–230
300–600
3.3/3.2
14.4/14.7
20.4/20.1
54.5/54.0
3.0/3.1
14.0/14.3
55.9/55.6
H2O þ NO23
1,2-mIm
Org. ligand
H2O
.
[Ce(naph ala)(NO3)(H2O)1,2-mIm] H2O
.
H2O þ NO23
1,2-mIm þ Org. ligand

CHARACTERIZATION AND ELECTROCHEMICAL STUDIES OF TERNARY La(III) AND Ge(III) COMPLEXES
807
for the first, second, and third waves, respectively. These
indicate that the three waves are diffusion-controlled (Bard
and Faulkner, 1980).
Examination of the cyclic voltammetric data show that the
peak potential, Ep, of the three CV waves shift towards
negative potential on increasing the scan rate. The best esti-
mated linear least-squars equation obtained for the first CV
wave is formulated by Eq. (5). The slopes are 32.8 + 0.02,
10.6 + 0.01 and 22.8 + 0.03 mV per decade for the three
CV waves, respectively. These data suggest that, the first CV
wave is due to an irreversible one electron-transfer process,
the second one corresponds to a reversible one electron-
transfer process while the third CV wave is due to a reversible
one electron-tranfer process coupled with an irreversible
follow-up chemical reaction. The follow-up chemical reaction
may be attributed to destruction of the trianionic complex.
Ep ¼ ꢁð1:797 + 0010Þ ꢁ ð32:80 + 0:02Þ ꢃ 10ꢁ3 log v ð5Þ
FIG. 2. Cyclic voltammogram of 1 ꢃ 1023 mol dm23 [La(naph.gly)
(NO3) (H2O)1-mIm] H2O in 0.1 mol dm23 TEAB/DMSO at HMDE,
.
v ¼ 200 mVs21
.
Accordingly, the three processes corresponding to the three
CV waves are described in terms of the following Eqs. (6)–(9).
0
½complexꢂ þ e ꢁ! ½complexꢂꢁ1
1st wave
2nd wave
3rd wave
ð6Þ
ð7Þ
ð8Þ
ð9Þ
electrode potential (E), scan rate (v) and concentration of the
complex and the results are collected in Table 5. For more
justification of these waves, some parameters are inferred
.
from the cyclic voltammetric data of the La(naph gly)(NO3)1-
.
mIm 2H2O complex as a representative example.
½complexꢂꢁ1 þ e !½compexꢂ
2ꢁ
½complexꢂ2ꢁ þ e !½complexꢂ
3ꢁ
3ꢁ
½complexꢂ ꢁ! products
3rd wave
From the results obtained, it is found that the peak current, ip,
of the three CV waves varies with the scan rate and is signifi-
On the basis of the results obtained from the electrochemical
reduction of some of the ternary complexes a number of points
can be drawn from the relative positions of the Ep values:
cantly correlated with the square root of the scan rate, v1/2
The best regression lines obtained are as follows:
.
ip ¼ ð0:78 + 0:01Þv1=2
ip ¼ ð2:05 + 0:03Þv1=2
r ¼ 0:996
r ¼ 0:994
ð2Þ
ð3Þ
1. The Epc shifts to a negative values as the size of the amino
acid side chain increases, i.e., the ease of reduction of the
complexes is in the order:
and
gly . phala . leu
ip ¼ ð4:22 + 0:04Þv1=2
r ¼ 0:997
ð4Þ
TABLE 5
Electrochemical data of some ternary complexes of La(III) and Ce(III) at 258C, v ¼ 200 mV s21
First wave
Second wave
Third wave
Compound
ip/mA
2Ep/V
ip/mA
2Ep/V
ip/mA
2Ep/V
La(III) complexes
.
.
[La(naph gly)(NO3)(H2O)1-mIm] H2O
0.49
0.11
0.16
1.782
1.800
1.880
1.22
0.48
0.54
1.986
1.996
2.054
2.54
2.276
.
.
[La(naph phala)(NO3)(H2O)1-mIm] H2O
.
[La(naph leu)(NO3)(H2O)1-mIm]
Ce(III) complexes
.
.
[Ce(naph gly)(NO3)(H2O)1,2-mIm] H2O
0.34
0.32
0.25
1.848
1.824
1.850
0.86
0.88
0.51
2.050
1.986
2.058
2.24
2.10
2.288
2.280
.
[Ce(naph gly)(NO3)(H2O)1-mIm] H2O
.
.
.
Ce(naph phala)(NO3)(H2O)1-mIm] H2O

808
M. K. M. RABIA ET AL.
Bard, A. J.; Faulkner, I. K. Electrochemical Methods: Fundamentals
and Applications; Wiley: New York, 1980.
2. By comparing the Ep values of La(III) and Ce(III) com-
plexes of the same ligand, it is found that the Ce(III)
complexes are more cathodic than the La(III) complexes.
Thus the Ce(III) complexes are more stable than the
La(III) complexes. This confirmes the thermal data
conclusion mentioned previously.
Bellamy, L. J. The Infrared Spectra of Complex Molecules; John
Wiley: New York, 1966; p. 86.
Chohan, Z. H.; Praveen, M.; Ghaffar, A. Synthesis, characterization
and biological role of anions (nitrate, sulfate, oxalate and
acetate) in Co(II), Cu(II) and Ni(II) metal chelates of some
Schiff base derived from amino acids. Synth. React. Inorg.
Met.-Org. Chem. 1998, 28, 1673–1687.
In conclusion, the results obtained in this work, considered
together, suggest that the 1 : 1 : 1 M-naphthylideneamino acid-
imidazoles ternary complexes can be represented by the
following structural formula:
Guangbin, W.; Zhiwei, M.; Xiaolan, L.; Fangming, M. Synthesis and
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complexes with a new Schiff base containing glycyl-DL-phenyl-
alanine. Synth. React. Inorg. Met.-Org. Chem. 1998, 28, 843–850.
Kong, D.; Zhang, X.; Zhu, Q.; Xie, Y.; Zhou, X. Synthesis, charact-
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their lanthanide complexes, I. Zhongguo Yaowu Huaxue Zazhi
1998, 8, 245–249; Chem. Abst. 1999, 130, 53640.
Kureshy, R. I.; Khan, N. H. Mononuclear chiral ruthenium(II) Schiff
base complexes; synthesis, physicochemical studies and reactivity
with p-acceptor ligands. Polyhedron 1993, 12, 195–201.
Kureshy, R. I.; Khan, N. H. Synthesis, spectroscopic and electrochemical
studies of mixed ligand ruthenium(II) chiral Schiff base complexes
with nitrogen donors. Transition Met. Chem. 1994, 19, 457–460.
Kureshy, R. I.; Khan, N. H.; Abdi, S. H. R.; Bhatt, K. N. Asymmetric
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where: M ¼ La(III) or Ce(III), R ¼ -H (gly), –CH3 (ala),
–CH2ph (phala), –CH(CH3)2 (val) or –CH2CH(CH3)2 (leu),
Im ¼ 1-methylimidazole or 1,2-dimethylimiadzole, A ¼ H2O
at n ¼ 0 and A ¼ 0 at n ¼ 1.
MacDonald, L. G.; Brown, D. H.; Morris, J. H.; Smith, W. E. Copper
Schiff base complexes with polyfunctional amino acids. Inorg.
Chim. Acta 1982, 67, 7–12.
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