Synthetic and spectroscopic studies of some nitrato-lanthanide(III) hydrazone complexes of higher coordination Number

Article abstract of DOI:10.1081/SIM-200026268

The reactions of the lanthanide(III) ions Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, and Yb, with pyridine-2-carboxaldehyde-4-chlorobenzoylhydrazone (PpClBH) leads to the formation of complexes corresponding to the formulae [Ln(PpClBH)₂(NO

Full text of DOI:10.1081/SIM-200026268

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Synthetic and Spectroscopic
Studies of Some
Nitrato–Lanthanide(III)
Hydrazone Complexes of
Higher Coordination Number
Damianos G. Paschalidis a
a Department of Chemistry , Aristotle
University , Thessaloniki, 54124, Greece
Published online: 16 Nov 2010.
To cite this article: Damianos G. Paschalidis (2004) Synthetic and Spectroscopic
Studies of Some Nitrato–Lanthanide(III) Hydrazone Complexes of Higher
Coordination Number, Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry, 34:8, 1401-1415, DOI: 10.1081/SIM-200026268
To link to this article: http://dx.doi.org/10.1081/SIM-200026268
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 8, pp. 1401–1415, 2004
Synthetic and Spectroscopic Studies of Some
Nitrato–Lanthanide(III) Hydrazone
Complexes of Higher Coordination Number
*
Damianos G. Paschalidis
Department of Chemistry, Aristotle University, Thessaloniki, Greece
ABSTRACT
The reactions of the lanthanide(III) ions Y, La, Ce, Pr, Nd, Eu, Gd, Tb,
Dy, Ho, Er, and Yb, with pyridine-2-carboxaldehyde-4-chlorobenzoyl-
hydrazone (PpClBH) leads to the formation of complexes corresponding
to the formulae [Ln(PpClBH)2(NO3)3], (Ln ¼ La, Ce, and Pr) and
[Ln(PpClBH)2(NO3)2]NO3 (Ln ¼ Y, Nd, Eu, Gd, Tb, Dy, Ho, Er, and
Yb). Twelve new compounds have been prepared. The complexes were
characterized by means of elemental analyses, conductivity measure-
ments, magnetic moments, and spectroscopic studies (IR, UV-VIS, and
1H NMR). The coordination number of 12 have been proposed for the
La, Ce, and Pr complexes, while for the Y, Nd, Eu, Gd, Tb, Dy, Ho,
Er, and Yb compounds the coordination number is reduced to 10. This
change in coordination number is consistent with the lanthanide contrac-
tion. Complexes having coordination numbers greater than ten appear
*
Correspondence: Damianos G. Paschalidis, Department of Chemistry, Aristotle
University, Thessaloniki 54124, Greece; E-mail: dpasch@chem.auth.gr.
1401
DOI: 10.1081/SIM-200026268
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Paschalidis
to be limited to the lighter lanthanides. PpClBH has been characterized by
1
elemental analysis, IR, UV, and H NMR.
Key Words: Lanthanide; Nitrate; Complexes; Hydrazones; Antimicrobial.
INTRODUCTION
Interest in the study of hydrazones has been growing because of their anti-
microbial, antituberculosis, and antitumor activity.[1–8] In continuation of our
studies on lanthanide complexes of hydrazone-containing ligands.[9,10] we are
reporting herein the synthesis of nitrato lanthanide(III) chelates with pyridine-
2-carboxaldehyde-4-chlorobenzoylhydrazone (PpClBH; Fig. 1). The proper-
ties of the complexes were investigated using elemental analyses, magnetic
1
and molar conductance measurements, and IR, UV, H NMR spectral data.
In this paper, the results obtained for the lanthanide(III)–hydrazone com-
plexes of higher coordination number are compared with those previously
obtained for analogous complexes.[9,10] We have now prepared 12 new com-
pounds of the types: [Ln(PpClBH)2(NO3)3] (Ln ¼ La, Ce, Pr) and
[Ln(PpClBH)2(NO3)2]NO3 (Ln ¼ Y, Nd, Eu, Gd, Tb, Dy, Ho, Er, Yb) with
coordination numbers of 12 and 10, respectively.
RESULTS AND DISCUSSION
The formation of the complexes between the lanthanide nitrate salt and
hydrazone is summarized in Eqs. (1) and (2):
LnðNO3Þ3 ꢀ 6H2O þ 2PpClBH ꢁ! ½LnðPpClBHÞ2ðNO3Þ3ꢂ þ 6H2O
ðLn ¼ La; Ce; PrÞ
ð1Þ
LnðNO3Þ3 ꢀ 5H2O þ 2PpClBH ꢁ! ½LnðPpClBHÞ2ðNO3Þ2ꢂNO3 þ 5H2O
ðLn ¼ Y; Nd; Eu; Gd; Tb; Dy; Ho; Er; YbÞ ð2Þ
Figure 1. The ligand PpClBH.

Lanthanide Hydrazone Complexes
1403
The analytical data of the complexes (Table 1) indicate a 1 : 2 metal to ligand
stoichiometry corresponding to the molecular formula C26H20Cl2LnN9O11.
The complexes are air-stable, crystalline solids, slightly soluble (,1%
w/v) in methanol, ethanol, and acetonitrile, very soluble in DMF and
DMSO, but insoluble in chloroform, dichloromethane, and diethyl ether.
The molar conductances of 0.001 M acetonitrile and methanol solutions of
2
the La, Ce, and Pr complexes lie below 10 S cm mol21, indicating their
non-electrolytic nature, but the corresponding values for the Y, Nd, Eu,
Gd, Tb, Dy, Ho, Er, and Yb compounds are consistent with 1 : 1 electrolytic
behavior.
.
.
Magnetic Moments
Room temperature magnetic moments for the complexes are given in
Table 1. The lanthanide ions containing unpaired 4f electrons are all paramag-
netic. Since these electrons are well shielded by the 5s25p6 octet, both in their
spin and orbital motions, the magnetic moments of the present lanthanide(III)
complexes show very little deviation from Van Vleck values[11] indicating
minor participation of 4f electrons in the bond formation.
Electronic Spectra
The electronic spectra of all complexes recorded in Nujol (Table 2) and in
methanol solutions (Table 3) are almost identical. This observation may
suggest that the complexes seem to maintain the same stereochemistry in
the solid and solution phases. The ligand PpClBH shows an intense absorption
band (band I) at 44,248 cm21 (methanol solution) and 40,650 cm21 (Nujol),
which shifts to higher wave length with increasing solvent polarity, and is
assigned to a p ! p ꢃ transition of the rings.[12] A red shift of this absorption
band in the complexes relative to the free ligand is observed when the nitrogen
of the pyridine ring is coordinated to metal.[12] Another absorption band (band
II) at 40,485 cm21 (methanol solution) and 33,333 cm21 (Nujol) appears in
the spectrum of the free ligand and is attributed to intraligand transitions of
the p ! p ꢃ type located mainly on the C55N group.[12] This band in the
spectra of the complexes is shifted toward higher frequencies,
ꢀ38,000 cm21. This is a fact that suggests the coordination of the hydrazone
via the azomethine nitrogen atom. The free ligand shows an intense absorption
band (band III) at 33,112 cm21 (methanol solution) and 27,397 cm21 (Nujol),
which is assigned to an n ! p ꢃ transition located on the carbonyl group. In
our complexes, this band is shifted by ꢀ2000 cm21. This shift supports the

1404
Paschalidis
m

Lanthanide Hydrazone Complexes
1405
Table 2. Electronic spectral data from Nujol mull spectra of PpClBH and lantha-
nide(III) complexes.
Band I
v (cm21
Band II
v (cm21
Band III
v (cm21
)
Compounds
)
)
PpClBH
40,650
40,650
40,322
40,485
40,983
40,816
40,816
39,062
40,816
40,650
40,650
40,485
40,485
33,333
33,333
33,333
33,333
33,557
33,444
33,444
33,222
33,444
33,444
33,333
33,333
33,444
27,397
27,624
25,773a
27,624
25,062a
27,932
27,932
25,906
25,974
28,011
27,855
27,777
[Y(NO3)2(PpClBH)2]NO3
[La(NO3)3(PpClBH)2]
[Ce(NO3)3(PpClBH)2]
[Pr(NO3)3(PpClBH)2]
[Nd(NO3)2(PpClBH)2]NO3
[Eu(NO3)2(PpClBH)2]NO3
[Gd(NO3)2(PpClBH)2]NO3
[Tb(NO3)2(PpClBH)2]NO3
[Dy(NO3)2(PpClBH)2]NO3
[Ho(NO3)2(PpClBH)2]NO3
[Er(NO3)2(PpClBH)2]NO3
[Yb(NO3)2(PpClBH)2]NO3
aBroad.
coordination of the ligand to the lanthanide through the carbonyl oxygen.
The spectral data for the assignments of the f–f transitions (Table 4)
are made by comparison with Carnall’s data on aqueous solutions of
lanthanide(III) salts.[13]
Infrared Spectra
The most important bands, in the region 4000–250 cm21 and the pro-
posed assignments for the free ligand (PpClBH) and the complexes are
listed in Table 5. The medium-intensity band at 3200 cm21 of the free
ligand, due to n(N–H), is observed at the same region, 3174–3243 cm21, in
the complexes. A strong band at 1667 cm21 in PpClBH (due to n(C55O)), is
shifted by ꢀ50–60 cm21 upon complexation to lower frequencies because
of coordination of the carbonyl oxygen with lanthanide ion. The appearance
of the n(N–H) and n(C55O) bands in the spectra of all complexes is evidence
for the coordination of the hydrazone with the metal as neutral ligand.[14] For
the complexes the n(C55N) band appears at the 1557–1565 cm21 region
which is 30–40 cm21 lower in frequency than the corresponding band of
free PpClBH. This indicates that the azomethine nitrogen is coordinated to
the metal. The low-energy pyridine ring in-plane and out-of-plane vibrations

1406
Paschalidis

Lanthanide Hydrazone Complexes
1407
Table 4. Electronic spectral data (Nujol mull) of the lanthanide(III) chelates in the
visible region.
Frequency
(cm21
Compounds
)
Assignments
1
[Pr(NO3)3(PpClBH)2]
16,863
20,492
11,547
12,579
13,643
14,837
17,241
19,120
10,870
12,315
15,576
18,692
22,222
10,406
19,268
20,661
10,235
3H4 ! D2
3
! P0
4
[Nd(NO3)2(PpClBH)2]NO3
4I9/2 ! F3/2
2
! H9/2
!
4F7/2
4
! F9/2
4
! G5/2
4
! G7/2
6
[Dy(NO3)2(PpClBH)2]NO3
[Ho(NO3)2(PpClBH)2]NO3
6H15/2 ! F7/2
6
! F5/2
5
5H8 ! F5
5
! F4
5
! G6
4
[Er(NO3)2(PpClBH)2]NO3
[Yb(NO3)2(PpClBH)2]NO3
4I15/2 ! I11/2
2
! H11/2
!
4F7/2
2F7/2 ! F5/2
2
are observed in the spectrum of the ligand at 622 and 406 cm21, respectively,
but the corresponding bands for the complexes are shifted to higher frequen-
cies at 632–636 and 417–420 cm21, respectively, which is an indication of
the coordination of the heterocyclic nitrogen.[15–18] The appearance of a
strong band at ꢀ1384 cm21 only in the spectra of the Y, Nd, Eu, Gd, Tb,
Dy, Ho, Er, and Yb complexes indicates the presence of ionic nitrates (D3h
symmetry, free NO23 ion). All the spectra also demonstrate the presence of
coordinated nitrates. Two strong bands observed at 1477–1491 and 1281–
1328 cm21 assigned to the n4 and n1 vibrational modes of the nitrate
group, respectively (C2V symmetry, coordinated nitrate group). The
magnitude of the splitting (n4–n1) is ꢀ180 cm21 in all complexes and is
typical of bidentate bonding of nitrates.[19] This value is confirmed in related
hydrazone–lanthanide complexes by their spectral and structural data.[9,10]
1H NMR Spectra
The 1H NMR spectra of the hydrazone and the Y and La complexes were
recorded in DMSO-d6 solution. The spectral data with their assignments are

1408
Paschalidis

Lanthanide Hydrazone Complexes
1409
given in Table 6. The spectra of the complexes showed a downfield shift of the
NH signal from 12.15 (PpClBH) to ꢀ12.50 ppm (complexes) suggesting the
coordination of the hydrazone in the keto form.[20–22] The ring proton
signals undergo broadening and a downfield shift showing involvement of
the pyridine nitrogen in the coordination.[20–22] The N55CH signal undergoes
a downfield shift in the Y and La complexes, compared with the free PpClBH
ligand, suggesting coordination of the azomethine nitrogen to the Ln(III) ions.
CONCLUSIONS
The elemental analyses show that the stoichiometric ratio metal to ligand
is 1 : 2 in all complexes and involving three nitrate ions for each metal atom.
The molar conductivity measurements show that the complexes of the lighter
lanthanides (La, Ce, and Pr) are non-electrolytes, but the complexes of the
heavier lanthanides, including yttrium, are 1 : 1 electrolytes. Infrared spectral
data give evidence for the coordination of the keto form of the hydrazone to
the lanthanide ion via the azomethine nitrogen, pyridine nitrogen, and
carbonyl oxygen. The infrared spectra also demonstrate the presence of
only bidentate coordinated nitrate ions in the complexes of the lighter lantha-
nides (La, Ce, Pr) and the presence of bidentate and ionic nitrates in the com-
plexes with the heavier lanthanides (Nd, Eu, Gd, Tb, Dy, Ho, Er, Yb) and
Y. Consequently, the formulae of the complexes are [Ln(PpClBH)2(NO3)3]
(Ln ¼ La, Ce, Pr) and [Ln(PpClBH)2(NO3)2]NO3 (Ln ¼ Y, Nd, Eu, Gd, Tb,
Dy, Ho, Er, Yb) with coordination numbers of 12 and 10, respectively.
Based on these data and the x-ray crystallographic data of analogous
compounds, trinitratobis[N-(2-pyridinylmeythylene)-N0-benzoyl-hydrazino]
cerium(III) acetone dihydrate (coordination polyhedron: icosahedron)[9] and
Table 6. 1H NMR spectral data d (ppm) of PpClBH, Y(III), and La(III) complexes.
Protons
PpClBH
[Y(NO3)2(PpClBH)2]NO3
[La(NO3)3(PpClBH)2]
N55C–H
C1-H
C2-H
C3-H
C4-H
C5-H
C6-H
N–H
3.60 s
7.45 d
7.89 d
8.63 d
7.64 m
7.95 m
8.06 d
12.15 s
3.63 s
7.57 d
7.97 d
8.66 d
7.64 m
7.98 d
8.31 d
12.50 s
3.75 s
7.58 d
7.98 d
8.72 d
7.66 m
7.97 d
8.14 d
12.52 s
Note: s, singlet; d, doublet; m, multiplet.

1410
Paschalidis
dinitratobis[N-(2-pyridinylmethylene)-N0-benzoyl-hydrazino]erbium(III) nitrate
sesquihydrate (coordination polyhedron: bicapped square antiprism),[10]
the proposed structures for the complexes are shown in Figs. 2 and 3.
The coordination polyhedra in the solid state may be an icosahedron
(Fig. 4) for the complexes of the formula [Ln(PpClBH)2(NO3)3] and a
bicapped square antiprism (Fig. 5) for the compounds of the type
[Ln(PpClBH)2(NO3)2]NO3.
EXPERIMENTAL
Materials and Methods
All chemicals were purchased from Aldrich Chemicals and were
used without further purification. All solvents were dried and distilled
prior to use. The PpClBH was prepared by adding (4.7 mL) of pyridine-
2-carboxaldehyde (5.35 g, 50 mmol) to a methanolic solution (100 mL) of
4-chlorobenzoic hydrazide (8.53 g, 50 mmol) and heating the reaction
solution under reflux for 4 hr. After cooling the reaction mixture to room temp-
erature, a crude white product was formed which was filtered, washed with
methanol, and recrystallized from methanol. Yield: 7.80 g (60%); mp:
178 8C; Found: C, 60.17; H, 3.89; N, 16.34; Calc. for C13H10ClN3O
(259.69): C, 60.12; H, 3.88; N, 16.18.: PpClBH was also characterized by
1
IR and H NMR spectra.
Figure 2. Proposed structure for the complexes [Ln(PpClBH)2(NO3)3] (Ln ¼ La, Ce,
and Pr).

Lanthanide Hydrazone Complexes
1411
Figure 3. Proposed structure for the complexes [Ln(PpClBH)2(NO3)2]NO3 (Ln ¼ Y,
Nd, Eu, Gd, Tb, Dy, Ho, Er, and Yb).
Preparation and Analysis of the Complexes
All operations were carried out in a dry box. The solutions were prepared
in a dry box purged with dried nitrogen gas. All glassware was oven-dried for
one night prior to insertion into the dry box. The [Ln(PpClBH)2(NO3)3] and
Figure 4. Supported coordination polyhedron for the complexes [Ln(PpClBH)2
(NO3)3] (Ln ¼ La, Ce, and Pr. Oc ¼ carbonyl oxygen, On ¼ nitrate oxygen, Np ¼
pyridine nitrogen, Na ¼ azomethine nitrogen).

1412
Paschalidis
Figure 5. Supported coordination polyhedron for the complexes [Ln(PpClBH)2
(NO3)2]NO3 (Ln ¼ Y, Nd, Eu, Gd, Tb, Dy, Ho, Er, and Yb. Oc ¼ carbonyl oxygen,
On ¼ nitrate oxygen, Np ¼ pyridine nitrogen, Na ¼ azomethine nitrogen).
[Ln(PpClBH)2(NO3)2]NO3 complexes were prepared by the following general
procedure: a methanolic solution (10 mL) of PpClBH (1.04 g, 4 mmol) was
added to a methanolic solution (10 mL) of the appropriate lanthanide nitrate
hydrate (2 mmol). The solution was stirred for 10–20 min at room tempera-
ture. Fine microcrystalline products were obtained, which were filtered,
washed with small portions of methanol, and dried in vacuo over anhydrous
calcium chloride. The reactions were carried out in a dry box because of the
better yields that were obtained. E.g. in the case of europium complex the
yield is 78% in a dry box instead of ,10% in air with relative humidity
98%. The analytical data are summarized in Table 1.
Physical Measurements
Microanalyses (C, H, N) were obtained with a Perkin–Elmer analyzer
model 2400. The metal contents of the complexes were determined by titration
with EDTA using xylenol orange as indicator.[23] Melting points were deter-
mined with a Bu¨chi silicon oil bath apparatus and are uncorrected. Molar con-
ductivities were measured on a WTW model LF 530 conductivity bridge
employing a calibrated immersion-type cell, which had a cell constant
of 0.996. This represents a mean value calibrated at 25 8C with potassium

Lanthanide Hydrazone Complexes
1413
chloride solutions. Temperatures were controlled with an accuracy
of + 0.1 8C using a Haake thermoelectric circulating system of water.
Room temperature magnetic susceptibility measurements in the solid state
were done with a MSB-MKI type Johnson Matthey magnetic susceptibility
balance. IR spectra were recorded in the 4000–250 cm21 region on a
Perkin–Elmer 1650 FT-IR spectrophotometer using KBr pellets. Calibration
of frequency readings was made with polystyrene film. Electronic spectra in
the region 200–1100 nm were measured on a Shimadzu-160A dual beam
spectrophotometer using 1 cm, Teflon stoppered, quartz absorption cells.
The absorption spectra of the solid compounds were measured on Nujol
1
mulls. H NMR spectra recorded on a Bruker Aspect 3000 spectrometer
equipped with a spectrospin-Bruker Cryomagnet.
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Accepted March 30, 2004