Synthesis, characterization and spectra of lanthanide(III) hydrazone complexes: The X-ray molecular structures of the erbium(III) complex and the ligand

Article abstract of DOI:10.1016/S0277-5387(00)00580-5

A series of nine new lanthanide(III) complexes of the type [Ln(PBH)₂(NO₃)₂] NO₃·xH₂O (PBH = 2-pyridinecarboxaldehyde benzoylhydrazone) have been prepared and studied by IR, UV-Vis and mass spectra. In addition the crystal structures of PBH·H₂O and [Er(PBH)₂(NO₃₎₂] NO₃·1.5H₂O have been solved. Erbium atom is ten-coordinate and the coordination polyhedron is best described as a distorted bicapped square antiprism.

Full text of DOI:10.1016/S0277-5387(00)00580-5

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Polyhedron 19 (2000) 2629–2637
Synthesis, characterization and spectra of lanthanide(III)
hydrazone complexes
The X-ray molecular structures of the erbium(III) complex and the
ligand
Damianos G. Paschalidis a,*, Ioannis A. Tossidis a, Maria Gdaniec b
a Department of Chemistry, Aristotle Uni6ersity, 54006 Thessaloniki, Greece
b Faculty of Chemistry, A. Mickiewicz Uni6ersity, 60-780 Poznan, Poland
Received 4 April 2000; accepted 28 August 2000
Abstract
A series of nine new lanthanide(III) complexes of the type [Ln(PBH)2(NO3)2]NO3·xH2O (PBH=2-pyridinecarboxaldehyde
benzoylhydrazone) have been prepared and studied by IR, UV–Vis and mass spectra. In addition the crystal structures of
PBH·H2O and [Er(PBH)2(NO3)2]NO3·1.5H2O have been solved. Erbium atom is ten-coordinate and the coordination polyhedron
is best described as a distorted bicapped square antiprism. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Lanthanide; Erbium complex; Hydrazone
1. Introduction
2. Experimental
The chemistry of the trivalent lanthanide ions has
expanded rapidly in the last 40 years. The interest in the
lanthanide complexes is chiefly ruled by their promising
utilization due to their low toxicity and their powerful
paramagnetic and luminescent properties [1–3]. Even
though the lanthanide complexes are associated with
important biological uses as diagnostic tools [4–7]. It is
known that a considerable amount of work has been
done on complexes with hydrazones because of their
ability to chelate with metal ions [8–19], but little work
has been reported on crystal structures of such deriva-
tives of lanthanide elements [20–22]. In the course of
our studies of the chemistry of lanthanide chelate com-
pounds we have prepared and characterized a consider-
able number of chelates containing hydrazones as
ligands, thus we report here a series of nine new lan-
thanide(III) complexes of the type [Ln(PBH)2(NO3)2]-
NO3·xH2O, the crystal structure of the erbium complex
and the structure of the free ligand.
2.1. Starting materials and procedures
Lanthanide nitrates (99.9%) Ln(NO3)3·xH2O (x=5
for Eu, Tb, Dy, Ho, Er, Yb and x=6 for Y, Nd, Gd)
were purchased from Aldrich Chemicals and were used
without further purification. Lanthanide salts were
stored in a dessicator to prevent hydration. The PBH
ligand was prepared as previously described [23]. All
solvents were reagent grade and anhydrous. Micro-
analyses (C, H, N) were taken with a Perkin–Elmer
analyzer model 2400. Melting points were determined
with a Bu¨chi silicon oil bath apparatus and are uncor-
rected. Molar conductivities were measured on a WTW
model LF 530 conductivity bridge employing a cali-
brated immersion type cell, which had a cell constant of
0.996. This represents a mean value calibrated at 25°C
with potassium chloride solutions. Temperatures were
controlled with an accuracy of 90.1°C using a Haake
thermoelectric circulating system of water. Experimen-
tal and theoretical details for the conductivity measure-
ments were reported elsewhere [24]. Room temperature
magnetic susceptibility measurements in solid state were
* Corresponding author. Tel.: +30-31-90-8171; fax: +30-31-90-
8171.
E-mail address: dpasch@chem.auth.gr (D.G. Paschalidis).
0277-5387/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0277-5387(00)00580-5

2630
D.G. Paschalidis et al. / Polyhedron 19 (2000) 2629–2637
done with a Johnson Matthey magnetic susceptibility
balance MSB-MKI type. IR spectra were recorded in
the 4000-250 cm−1 region on a Perkin–Elmer 1650
FT-IR spectrophotometer using KBr pellets. Calibra-
tion of frequency reading was made with polystyrene
film. Electronic spectra in the region 200–1100 nm were
measured on a Shimadzu-160A dual beam spectropho-
tometer using 1 cm, teflon stoppered, quartz absorption
cells. The absorption spectra of solid compounds were
measured on mulls that were prepared by grinding the
dry solid and then regrinding it into a paste with
paraffin oil (Nujol). This paste was spread on a disk of
filter paper; the proper thickness of the sample was
determined by trial and error. A disk of filter paper,
dampened with paraffin oil, was placed in the reference
position. All spectroscopic measurements were made at
room temperature (ꢀ20°C). Mass spectra were mea-
sured on a RMU-6L Hitachi Perkin–Elmer mass spec-
trometer with ionization source of T-2p type operating
at 70 eV.
mmol). The solution was allowed to stand at 20–22°C.
After a few days crystals were isolated from the solu-
tion. Crystals suitable for the X-ray structure determi-
nation were obtained only in the case of Er-complex.
The crystals were of poor quality, fragile and usually
twinned. After inspection of a big number of crystals by
microscopy a transparent crystal was isolated and used
for data collection. Table 1 reports analytical data of
the compounds.
2.4. Crystal structure determinations
The X-ray data for PBH were collected on a Kuma
KM-4 diffractometer using graphite monochromatized
Cu Ka radiation. The structure was solved by direct
methods using the SHELXS-97 program [25]. Full-matrix
least squares refinement was carried on F2 with
SHELXS-97 program [26]. All non hydrogen atoms have
been refined anisotropically. The hydrogen atoms have
been placed in calculated positions and refined using a
riding model.
The data for the Er-complex were collected on a
KumaCCD diffractometer using graphite monochrom-
atized Mo Ka radiation with detector-to-crystal dis-
tance of 6 cm. More than a hemisphere of reciprocal
space was covered by combination of four sets of
exposures; each set had a different €-angle (0, 90, 180,
270) and each exposure of 30s covered 0.75° in ꢀ.
Coverage of the unique set is over 98% complete. The
2.2. Ligand
The ligand 2-pyridinecarboxaldehyde benzoylhydra-
zone (PBH), was prepared according to a procedure
reported elsewhere [23] and recrystallized a minimum of
three times from a hot methanol–water mixture. The
ligand was crystallized from an acetonitrile solution by
slow evaporation at 20–22°C. After a few days pris-
matic crystals were isolated from the solution. Analyti-
cal data for PBH are summarized in Table 1.
collected data were reduced using the program KM4RED
[27]. The structure was solved by direct methods with
the program SHELXS-97 [25] and refined by full-matrix
least-squares on F2 with SHELXL-97 program [26]. Non-
coordinated nitrate anion has been found disordered
over two positions with occupancy factor equal to 1/2.
A relatively high electron density maximum at hydro-
gen bond distance from its symmetry equivalent at
position 1−x, y, 1.5−z and at hydrogen bond dis-
2.3. Preparation of Y, Nd, Eu, Gd, Tb, Dy, Ho, Er,
and Yb complexes of PBH. General procedure
A methanol solution (5 ml) of PBH (973 mg, 4
mmol) was added slowly to a methanol solution (5 ml)
of the appropriate lanthanide nitrate hydrated (2
Table 1
Colours, partial elemental analyses, molar conductivities and magnetic susceptibilities of the PBH ligand and for lanthanide(III) chelates
a
Compound
Colour
Melting point
(°C)
Found (calc.%)
C
\M v (B.M.)
H
N
PBH·H2O
white
white
light pink
cream
white
yellow
light yellow
yellow
pale yellow
yellow
103
225
237
238
231
247
225
221
207
212
64.02 (64.18)
41.09 (41.01)
39.60 (39.54)
38.22 (38.29)
38.53 (38.46)
38.28 (38.39)
37.92 (37.80)
37.61 (37.69)
37.62 (37.58)
37.07 (36.93)
5.38 (5.38)
3.46 (3.44)
2.95 (2.93)
3.05 (3.09)
2.97 (2.98)
2.95 (2.97)
3.02 (3.05)
3.05 (3.04)
3.00 (3.03)
3.12 (3.10)
17.34 (17.27)
16.61 (16.55)
15.92 (15.96)
15.40 (15.45)
15.57 (15.53)
15.46 (15.49)
15.20 (15.26)
15.17 (15.21)
15.19 (15.17)
14.95 (14.90)
[Y(NO3)2(PBH)2]NO3·2H2O
[Nd(NO3)2(PBH)2]NO3·0.5H2O
[Eu(NO3)2(PBH)2]NO3·1.5H2O
[Gd(NO3)2(PBH)2]NO3·H2O
[Tb(NO3)2(PBH)2]NO3·H2O
[Dy(NO3)2(PBH)2]NO3·1.5H2O
[Ho(NO3)2(PBH)2]NO3·1.5H2O
[Er(NO3)2(PBH)2]NO3·1.5H2O
[Yb(NO3)2(PBH)2]NO3·2H2O
101 dia.
110 3.58
88
3.60
102 7.34
94
87
9.53
10.41
108 10.21
89
90
9.42
4.63
a Units: mol−1 cm2 V−1 in CH3OH.

D.G. Paschalidis et al. / Polyhedron 19 (2000) 2629–2637
2631
Table 2
tance to N(9A) and O(2D) has been attributed to a water
molecule. Because this water molecule was situated only
Crystal data and structure refinement parameters
,
1 A from O(1C) of the disordered nitrate ion its occu-
Empirical formula
Formula weight
Crystal size (mm)
Crystal colour
Temperature (K)
Crystal system
C
243.26
13H13N3O2
C26H25ErN9O12.5
830.81
0.25×0.25×0.15
pale yellow
293(2)
pancy has to be fractional and equal to that of the nitrate
anion D. The disordered nitrate anions and disordered
water molecule have been refined with isotropic displace-
ment parameters. All other non-hydrogen atoms have
been refined anisotropically. The hydrogen atoms have
been placed in calculated positions and refined using a
riding model. Restraints have been imposed on bond
distances, angles and planarity of disordered nitrate
groups. Crystallographic and structure determination
data, for both structures, are listed in Table 2.
0.45×0.45×0.30
pale yellow
293(2)
orthorhombic
Pbca
monoclinic
C2/c
Space group
Unit cell dimensions
,
a (A)
7.1431(9)
11.990(1)
29.475(2)
90
90
90
2524.4(4)
8
1.280
26.902(1)
18.390(1)
15.259(1)
90
123.06(1)
90
6326.9(6)
8
1.744
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
3. Results and discussion
Dcalc (Mg m−3
)
)
Dobs (Mg m−3
1.73
3.1. General characteristics
,
Wavelength (A)
Monochromator
1.54178
graphite
0.71073
graphite
2.731
The PBH is a white crystalline solid. The analytical
results agree with the molecular formula C13H13N3O2
(PBH·H2O). The [Ln(PBH)2(NO3)2]NO3·xH2O com-
plexes synthesized and investigated in this work were
crystalline solids. The analytical results agree with the
molecular formula LnC26H22N9O11·nH2O where n=0.5
for LnꢀNd complex, n=1 for Gd and Tb complexes,
n=1.5 for Eu, Dy, Ho and Er complexes and n=2 for
Y and Yb complexes. The complexes can be easily
dissolved in alcohol, methanol, acetonitrile, dimethylfor-
mamide and dimethylsulfoxide but they are not soluble
in nonpolar organic solvents. The room temperature
magnetic moments of the complexes, corrected for dia-
magnetism, show very little deviation from van Vleck
values [28], indicating minor participation of 4f-electrons
in the bond formation. The molar conductivity measure-
ments show that the complexes are 1:1 electrolytes.
Absorption coefficient 0.730
(mm−1
)
Diffractometer used
F(000)
q Range (°)
Index ranges
Kuma KM-4
1024
KumaCCD
3296
4.16–28.28
−355h535
−245k524
−175l50
18947
7722 [Rint=0.0283]
3.00–67.61
05h58
05k514
05l535
2273
Reflections collected
Independent reflections 2273
Completeness to q (%) 99.2
Absorption correction none
98.4
„ scan
full-matrix
Refinement method
full-matrix
least-squares on F2 least-squares on F2
Data/restraints/
2273/0/216
7722/14/433
parameters
Goodness-of-fit on F2 1.055
0.928
Final R indices
[I\2|(I)]
R indices (all data)
R1=0.0397,
R1=0.0366,
wR2=0.0885
R1=0.0665,
wR2=0.0943
wR2=0.1128
R1=0.0515,
wR2=0.1226
3.2. Description of the structure of the ligand
Largest diff. peak and 0.217 and −0.142 1.990 and −0.810
−3
,
hole (e A
)
The crystals of PBH are made up of orthorhombic unit
cells, each containing eight monomeric C13H11N3O
molecules and eight water molecules. A displacement
ellipsoid plot of the PBH molecule with the atomic
numbering is shown in Fig. 1, selected bonds lengths and
angles are given in Table 3. The bonds and angles
observed in this structure are normal and the molecule
Table 3
,
Selected bond lengths (A) and angles (°) for PBH·H2O
O(8)ꢁC(7)
N(9)ꢁN(10)
C(7)ꢁN(9)
N(10)ꢁC(11)
C(11)ꢁC(12)
C(7)ꢁC(1)
N(13)ꢁC(12)
N(13)ꢁC(14)
1.224(2)
1.373(2)
1.352(2)
1.268(2)
1.465(2)
1.493(2)
1.335(2)
1.336(2)
C(12)ꢁN(13)ꢁC(14)
C(7)ꢁN(9)ꢁN(10)
N(9)ꢁN(10)ꢁC(11)
O(8)ꢁC(7)ꢁN(9)
O(8)ꢁC(7)ꢁC(1)
N(9)ꢁC(7)ꢁC(1)
N(10)ꢁC(11)ꢁC(12)
117.65(13)
118.86(12)
116.04(12)
122.49(13)
121.56(12)
115.92(13)
121.01(13)
Fig. 1. Crystal structure of C13H11N3O·H2O showing the atom num-
bering scheme. The thermal ellipsoids are drawn at 30% probability.

2632
D.G. Paschalidis et al. / Polyhedron 19 (2000) 2629–2637
Table 4
3.3. Description of the structure of
[Er(C13H11N3O)2(NO3)2]NO3·1.5H2O
,
Hydrogen bonds (A) and angles (°) for PBH·H2O
DꢁH···A
d(DꢁH) d(H···A) d(D···A) B(DHA)
The X-ray study revealed that the crystals of
[Er(PBH)2(NO3)2]NO3·1.5H2O are made up of mono-
clinic unit cells, each containing eight monomeric com-
plex cations [Er(PBH)2(NO3)2]+, 16 ionic nitrates with
occupancy of 1/2 and 16 water molecules eight of which
have occupancy of 1/2. A diagram of the molecular
structure and the atom numbering system used is
shown in Fig. 2. The two ligand molecules coordinated
with the same metal atom are labeled A and B. Selected
bond lengths and angles are given in Table 5. The ErIII
atom is ten-coordinate by linking to two tridentate
PBH ligands and two bidentate nitrate ligands. Non-co-
ordinated nitrate anion has been found to be disordered
over two positions with occupancy factor equal to 1/2.
The linking of the PBH ligand to the metal atom is
accomplished through the pyridine nitrogen, the azome-
thine nitrogen and the carbonyl oxygen. Thus two
five-membered chelate rings are formed.
As expected, the situation with respect to the coordi-
nation polyhedra for ten-coordination is complex.
Three polyhedra are generally considered [31]: the bi-
capped square antiprism, the bicapped dodecahedron,
and a polyhedron of C26 symmetry derived from the
triangular faced dodecahedron. Calculation of the lig-
and–ligand repulsion energies, reported elsewhere [32],
shows that the bicapped square antiprism is the favored
arrangement. In our case the coordination polyhedron
around the Er atom is a distorted bicapped square
antiprism and is shown in Fig. 3. O(2B), O(8B), O(2A),
N(13B) define the one square face of the polyhedron
a
O(1W)ꢁH(1W)···O(8)
0.85(3)
0.85(3)
0.87(3)
0.88(2)
0.96(2)
0.96(2)
2.24(3)
2.50(3)
2.02(3)
1.99(2)
2.49(2)
2.45(2)
3.010(2) 152(2)
3.097(2) 129(2)
2.873(2) 166(3)
2.852(2) 165(1)
3.266(2) 138(1)
3.310(2) 149(1)
O(1W)ꢁH(1W)···N(10) a
O(1W)ꢁH(2W)···N(13) b
N(9)ꢁH(9A)···O(1W)
C(11)ꢁH(11A)···O(1W)
C(6)ꢁH(6A)···O(1W)
a Symmetry transformations used to generate equivalent atoms:
−x+1/2, y−1/2, z.
b Symmetry transformations used to generate equivalent atoms:
x+1/2, −y+1/2, −z+1.
is in the keto tautomeric form. The C(7)ꢁO(8) [1.224(2)]
and N(9)ꢁN(10) [1.373(2) A] bond lengths indicate
,
bond orders of two and one, respectively, confirming
that the crystal contains the keto tautomer [29]. The
structural conformation of the molecule is the E isomer
(at the N(10)ꢀC(11) double bond), the most common
conformation for analogous derivatives [30]. The dihe-
dral angles between the mean planes of the phenyl and
pyridine rings is 28.23(9)°; these two rings make angles
of 22.64(10) and 5.65(9)° with the central hydrazone
mean plane [O(8)ꢁC(7)ꢁN(9)ꢁN(10)ꢁC(11)]. The hydra-
zone molecules are approximately aligned perpendicu-
lar to the a-axis. The crystal structure is stabilized by
extensive hydrogen bonding involving the water and the
hydrazone molecules. The water molecule present is
involved in a variety of NꢁH···O, OꢁH···O, CꢁH···O
and HꢁO···N hydrogen bonds. Selected hydrogen-bond
parameters are given in Table 4.
Fig. 2. Crystal structure of [Er(C13H11N3O)2(NO3)2]NO3·1.5H2O showing the atom numbering scheme. The thermal ellipsoids are drawn at 30%
probability; hydrogen atoms are omitted for clarity.

D.G. Paschalidis et al. / Polyhedron 19 (2000) 2629–2637
2633
Table 5
Selected
All the water molecules are involved in hydrogen
bond formation with PBH ligands. The crystal struc-
ture is stabilized by a complicated hydrogen-bond net-
work in which imine hydrogen forms a hydrogen bond
with a water oxygen atom. One oxygen of each non-co-
ordinated nitrate ion is hydrogen bonded to a water
molecule. Additional hydrogen bonding occurs between
water–water molecules. A diagram showing this net-
work is given in Fig. 4. Selected hydrogen bond lengths
and angles are given in Table 6.
,
bond
lengths
(A)
and
angles
(°)
for
[Er(C13H11N3O)2(NO3)2]NO3·1.5H2O
Er(1)ꢁO(8A)
Er(1)ꢁO(3A)
Er(1)ꢁO(2A)
Er(1)ꢁN(13A)
Er(1)ꢁN(10A)
2.366(3) Er(1)ꢁO(8B)
2.420(3) Er(1)ꢁO(2B)
2.447(3) Er(1)ꢁO(3B)
2.603(3) Er(1)ꢁN(10B)
2.574(3) Er(1)ꢁN(13B)
2.361(3)
2.450(3)
2.465(3)
2.535(3)
2.556(3)
O(8B)ꢁEr(1)ꢁO(2B)
O(8A)ꢁEr(1)ꢁO(3B)
76.20(10) O(8A)ꢁEr(1)ꢁO(3A)
72.81(10) O(8A)ꢁEr(1)ꢁO(2B)
85.08(12)
71.90(10)
O(8B)ꢁEr(1)ꢁN(10B) 62.68(10) O(8A)ꢁEr(1)ꢁN(10A) 61.66(11)
O(2A)ꢁEr(1)ꢁN(10B) 68.74(10) O(3A)ꢁEr(1)ꢁN(10A) 69.17(11)
O(2B)ꢁEr(1)ꢁN(10B) 66.63(10) O(3B)ꢁEr(1)ꢁN(10A) 67.53(11)
O(8A)ꢁEr(1)ꢁN(13B) 68.99(10) O(8B)ꢁEr(1)ꢁN(13A) 69.71(10)
O(3A)ꢁEr(1)ꢁN(13B) 73.26(10) O(3A)ꢁEr(1)ꢁN(13A) 72.46(10)
O(2A)ꢁEr(1)ꢁN(13B) 74.70(10) O(2A)ꢁEr(1)ꢁN(13A) 71.58(10)
O(2B)ꢁEr(1)ꢁN(13B) 82.81(11) O(3B)ꢁEr(1)ꢁN(13A) 88.94(11)
N(10B)ꢁEr(1)ꢁN(13B) 61.92(10) N(10A)ꢁEr(1)ꢁN(13A) 61.67(11)
3.4. IR spectroscopic studies
The IR spectra of the complexes in the region 4000–
250 cm−1 are analyzed in comparison with that of the
free ligand. This data gives evidence for the coordina-
tion of the PBH to the metal ion via two nitrogen
atoms and one oxygen. The complexes and the free
PBH show an IR band at 3420–3490 cm−1. This band
is reasonably attributable to the water molecule. The
vibration attributable to the w(NꢁH) mode is observed
at 3186 cm−1 for the free ligand and at 3191–3220
cm−1 for the complexes. This fact suggests that PBH
function as a neutral ligand to the lanthanide(III) ions
[36]. For the complexes, the bands assignable to the
w(CꢀO) and w(CꢀN) vibrations are observed at 1608–
1610 cm−1 and 1567–1572 cm−1, respectively, whereas
the corresponding bands for the free ligand are ob-
O(8B)ꢁEr(1)ꢁO(2A)
85.53(10)
and O(3B), O(8A), O(3A), N(13A) define the other. The
two capping atoms are N(10A) and N(10B). The
polygon formed by N(13A), . . . , O(3B) is very close to
a square. The internal angles range from 85.18(12)–
95.90(13)° averaging to 89.55°; the sides of this face
have lengths in the interval [2.868, 3.552] A with a
mean value of 3.157 A. The figure formed by
O(2A), . . . , O(8B) is less distorted than the other with
,
,
internal angles in the range 93.07–87.31° and sides
,
from 2.969–3.266 A. The two square faces are essen-
tially parallel and the angle between them is 0.92(12)°.
The angle N(10A)ꢁEr(1)ꢁN(10B) is 178.04(11)° slightly
distorted from the ideal value of 180°. Similar coordi-
nation geometry was found in other ten-coordinate
lanthanides, e.g. in tetraaquatri(nitrato)yttrium(III) di-
hydrate [33] and HLa(EDTA)·7H2O [34].
The ErꢁO distances range between 2.361(3) and
,
2.465(3) A. Similarly the ErꢁN distances range between
,
2.535(3) and 2.603(3) A. These distances are consider-
ably shorter than the corresponding distances observed
in the analogous Ce-complex: [Ce(NO3)3(PBH)2]·
CH3COCH3·2H2O [22]. The CeꢁO distances range be-
,
tween 2.528(3) and 2.759(4) A and the CeꢁN distances
,
range between 2.725(4) and 2.848(4) A. In both PBH
ligands coordinated with erbium the benzene and pyri-
dine rings have normal dimensions. The dihedral angles
between the mean planes of the pyridine and phenyl
rings is 9.2(3)° in the coordinated PBH molecule A and
13.4(3)° in B, respectively.
In each nitrate group the non coordinated O-atom is
,
closer to N [1.203(10) and 1.212(7) A] than the other
,
two [1.237(5)–1.293(5) A] and the metal bound OꢁNꢁO
angles [115.34(46) and 116.57(30)°] are significantly
smaller than the other OꢁNꢁO angles [118.75(40)–
124.68(36)°], which is a common property of all biden-
tate nitrate groups [35].
Fig. 3. (a) The coordination polyhedron around each Er3+ ion. (b)
The coordination polyhedron around each Er3+ ion. Dimensions of
,
the edges are in A.

2634
D.G. Paschalidis et al. / Polyhedron 19 (2000) 2629–2637
the nitrate group increases for monodentate to biden-
tate and/or bridging. The magnitude is used to establish
the type of nitrate coordination. In our complexes
Dwꢀ170 cm−1 and is typical of bidentate bonding of
nitrates [37]. The band at 1384 cm−1 is characteristic
for ionic nitrates (D3h symmetry, free NO−3 ion). The
data indicate that the chelates contain both coordinated
bidentate and ionic nitrate groups.
3.5. Electronic spectral studies
The electronic spectral data of the lanthanide(III)
complexes both in the solid state (Nujol) and in solu-
tions of DMF are similar (Table 8). The assignments
are made by comparison with Carnall’s data on
aqueous solutions [38]. This suggests that the complexes
seem to maintain the same stereochemistry in solid and
solution phases. The electronic spectral data of the
complexes and the PBH recorded in methanol (Table 9)
and Nujol (Table 10) and they are almost identical. The
ligand shows an intense absorption band at 44 444
(methanol solution), 40 322 cm−1 (Nujol) which shifts
to a higher wavelength with increasing solvent polarity
and is assigned to p“p* transition of the rings [17]. A
red shift is observed for this transition when the nitro-
gen of the pyridine ring is metal coordinated [17]. The
position of the maximum varies between the chelates of
different lanthanides (38 000–45 000 cm−1). Another
intense absorption band in the region ꢀ33 000 cm−1
in the spectrum of the free ligand is attributed to
intraligand transition of p“p* type located mainly on
the CꢀN group [17]. This band also occurs in the
spectra of the complexes, but is shifted toward higher
frequencies, a fact which further supports the coordina-
tion of the hydrazones via azomethine nitrogen atom.
A third intense band appears in the 24 000–29 000
cm−1 region which is assigned to an n“p* transition
located on the carbonyl group. Complex formation
through the carbonyl group should cause a blue shift of
Fig. 4. View of the hydrogen bond network of Er-complex.
served at 1657 and 1600 cm−1, respectively. The shifts
of the w(CꢀO) and w(CꢀN) vibrations of the bonds
toward lower wave numbers on complexation indicate
that carbonyl oxygen and azomethine nitrogen coordi-
nate to the metal [36]. The low energy pyridine ring
in-plane and out-of-plane vibrations observed in the
spectrum of the ligand at 625 and 406 cm−1, respec-
tively, whereas the corresponding bands for the com-
plexes are shifted to higher frequencies at 633–634 and
415–422 cm−1, respectively, which is a good indication
of the coordination of the heterocyclic nitrogen [37]
(Table 7).
The infrared spectra of the complexes demonstrate
the presence of coordinated and ionic nitrates. The two
strong bands associated with the asymmetric stretch
(C26 symmetry, coordinated NO−3 group) appear at
1473–1478 and 1284–1311 cm−1. The separation of
the nitrate stretching fundamentals at ꢀ1400 and ꢀ
1300 cm−1 (Dw) has been used as a criterion to distin-
guish between the degree of covalency of the nitrate
coordination [37]. Dw increases as the coordination of
Table 6
,
Hydrogen bonds (A) and angles (°) for [Er(C13H11N3O)2(NO3)2]NO3·1.5H2O
DꢁH···A
d(DꢁH)
d(H···A)
d(D···A)
B(DHA)
N(9A)ꢁH(9A)···O(2W)
N(9A)ꢁH(9A)···O(1C)
N(9B)ꢁH(9B)···O(1W)
0.90
0.90
0.90
0.96
1.94
1.94
2.04
2.47
2.47
2.798(9)
2.818(10)
2.894(6)
3.234(6)
157.9
164.4
157.6
136.0
a
C(14B)ꢁH(14B)···O(1B) b
C(16B)ꢁH(16B)···O(3B) a
O(1W)…O(1A) c
0.96
3.296(5)
144.4
3.157(7)
3.036 (14)
2.927 (11)
2.900 (12)
O(2W)···O(2D)
O(1W)···O(1W) d
O(2W)···O(2W) d
2.684 (17)
3.267 (12)
2.986 (18)
O(1W)···O(3C)
O(1W)···O(1D)
O(1W)···O(2D)
a Symmetry transformations used to generate equivalent atoms: −x+1/2, y+1/2, −z+1/2.
b Symmetry transformations used to generate equivalent atoms: x, −y+1, z+1/2.
c Symmetry transformations used to generate equivalent atoms: −x+1/2, −y+1/2, −z+1.
d Symmetry transformations used to generate equivalent atoms: −x+1, y , −z+3/2.

D.G. Paschalidis et al. / Polyhedron 19 (2000) 2629–2637
2635
Table 7
Infrared spectral data (cm−1) for the PBH ligand and its lanthanide(III) chelates
Compound
w(O–H) water w(N–H) w(CꢀO) w(CꢀN) w4(NO3−
)
w3(NO−3
)
w1(NO−3
)
Pyridine a
In plane
Out-of-plane
PBH·H2O
[Y(NO3)2(PBH)2]NO3·2H2O
[Nd(NO3)2(PBH)2]NO3·0.5H2O 3445
[Eu(NO3)2(PBH)2]NO3·1.5H2O 3420
[Gd(NO3)2(PBH)2]NO3·H2O
[Tb(NO3)2(PBH)2]NO3·H2O
[Dy(NO3)2(PBH)2]NO3·1.5H2O 3441
[Ho(NO3)2(PBH)2]NO3·1.5H2O 3440
[Er(NO3)2(PBH)2]NO3·1.5H2O
[Yb(NO3)2(PBH)2]NO3·2H2O
3459
3450
3186
3200
3192
3196
3220
3191
3191
3193
3200
3192
1657
1611
1608
1610
1610
1610
1610
1610
1611
1612
1600
1570
1567
1568
1568
1568
1569
1569
1570
1572
625
633
633
633
633
633
633
634
634
634
406
420
415
418
418
419
420
420
422
420
1478
1476
1477
1478
1478
1477
1478
1473
1477
1384
1384
1384
1384
1384
1384
1384
1384
1384
1284
1308
1311
1306
1307
1305
1309
1305
1302
3447
3490
3452
3420
a Low energy pyridine ring vibrations.
Table 8
Electronic spectral data of the lanthanide(III) chelates for DMF solutions and Nujol mull spectra (t=20°C) in the visible region
Compound
DMF solution
Nujol
Assignments
Frequency (cm−1
)
log m
Frequency (cm−1
)
[Nd(NO3)2(PBH)2]NO3·0.5H2O
11 507
12 531
13531
0.46
0.94
0.84
11 481
12 531
13 568
14 727
17 271
18 975
19 493
20 964
10 267
10 881
12 515
13 315
15 600
18 691
20 661
10 288
15 408
19 305
4I9/2“4F3/2
4I9/2“4F5/2
4I9/2“4F7/2
4I9/2“4F9/2
,
3S3/2
2G7/2
17 182
19 047
19 531
0.98
0.63
0.42
4I9/2“4G5/2
4I9/2“4G7/2
4I9/2“4G9/2
,
4I9/2“4G11/2
[Dy(NO3)2(PBH)2]NO3·1.5H2O
6H15/2“6H5/2
6H15/2“6F7/2
6H15/2“6F5/2
6H15/2“6F3/2
5H8“5F5
11 001
12 391
0.37
0.25
[Ho(NO3)2(PBH)2]NO3·1.5H2O
[Er(NO3)2(PBH)2]NO3·1.5H2O
15 528
18 587
20 618
10 298
15 337
19 194
0.64
0.72
0.29
0.05
0.35
0.98
5H8“5F4
5H8“5F3
4I15/2“4I11/2
4I15/2“4F9/2
4I15/2“2H11/2
4G11/2
,
20 534
10 235
0.39
0.66
20 576
10 256
4I15/2“4F7/2
2F7/2“2F5/2
[Yb(NO3)2(PBH)2]NO3·2H2O
the n“p* transition. In our complexes this band is
shifted by 1000–2000 cm−1. The electronic spectral
data of the complexes further support the coordination
of the ligand to the lanthanide through the carbonyl
oxygen, azomethine nitrogen and pyridine nitrogen.
[Eu(NO3)2(PBH)]+ cation, which are formed from the
expulsion of the −NO3 and after the [PBH] radical
’
’
from the molecular ion of the complex. The fragment
due to {[Y(NO3)2(PBH)]NO3}+ radical cation is
’
’
formed from the expulsion of the [PBH] radical from
the molecular ion of the complex (Fig. 5). The spectra
of Y and Dy complexes show fragments due to
[Y(PBHan)]2+ and [Dy(PBHan)]2+, respectively (PBHan
represents the anionic form of the PBH). The
major peaks of the spectra of all complexes can be
explained following the fragmentation path of the PBH
(Fig. 6).
3.6. Mass spectral studies
The electron impact mass spectra of all the com-
plexes and the PBH are summarized in the Table 11.
The mass spectrum of the Eu complex shows fragments
due to [Eu(NO3)2(PBH)2]+ radical cation and
’

2636
D.G. Paschalidis et al. / Polyhedron 19 (2000) 2629–2637
Table 9
Electronic spectral data of the PBH ligand and its lanthanide(III) chelates for methanol solutions (t=20°C)
Compound
Assignments
p“p*
p“p*
n“p*
Frequency (cm−1
)
log m (max)
Frequency (cm−1
)
log m (max)
Frequency (cm−1
)
log m (max)
PBH·H2O
[Y(NO3)2(PBH)2]NO3·2H2O
[Nd(NO3)2(PBH)2]NO3·0.5H2O 45 662
[Eu(NO3)2(PBH)2]NO3·1.5H2O 45 454
[Gd(NO3)2(PBH)2]NO3·H2O
[Tb(NO3)2(PBH)2]NO3·H2O
[Dy(NO3)2(PBH)2]NO3·1.5H2O 45 662
[Ho(NO3)2(PBH)2]NO3·1.5H2O 44 444
[Er(NO3)2(PBH)2]NO3·1.5H2O 44 444
44 444
39 370
3.92
4.33
4.40
4.22
4.39
4.46
4.42
4.23
4.30
4.19
32 787
34 602
33 112
33 112
33 112
33 783
33 112
34 722
34 602
33 112
4.23
4.34
4.51
4.49
4.49
4.57
4.58
4.30
4.32
4.44
27 397
27 397
27 397
27 397
27 397
27 397
27 472
27 397
27 174
27 322
3.73
4.48
4.32
4.05
4.35
4.38
4.37
4.52
4.55
4.06
45 871
45 454
[Yb(NO3)2(PBH)2]NO3·2H2O
45 662
Table 10
Electronic spectral data of the ligand PBH and its lanthanide(III) chelates from Nujol mull spectra (solid state, t=20°C)
Compound
Assignments
p“p*
p“p*
n“p*
Frequency (cm−1
)
Frequency (cm−1
)
Frequency (cm−1
)
PBH·H2O
40 322
40 816
40 650
40 816
39 062
38 168
38 610
38 910
40 650
40 486
33 445
33 222
33 333
33 557
33 222
33 112
33 112
33 222
33 333
33 333
29 239
27 777
24 691
24 691
26 809
24 272
27 777
26 455
24 691
24 875
[Y(NO3)2(PBH)2]NO3·2H2O
[Nd(NO3)2(PBH)2]NO3·0.5H2O
[Eu(NO3)2(PBH)2]NO3·1.5H2O
[Gd(NO3)2(PBH)2]NO3·H2O
[Tb(NO3)2(PBH)2]NO3·H2O
[Dy(NO3)2(PBH)2]NO3·1.5H2O
[Ho(NO3)2(PBH)2]NO3·1.5H2O
[Er(NO3)2(PBH)2]NO3·1.5H2O
[Yb(NO3)2(PBH)2]NO3·2H2O
Table 11
Relative abundances (%) of the ions in the EI mass spectra of the PBH ligand and its complexes
m/z
Assignments
Relative abundances (%)
PBH
Y
Nd
Eu
Gd
Tb
89
87
89
Dy
Ho
Er
Yb
51
77
78
93
VIII
IV
VII
V
50
50
51
72
50
65
48
9
65
47
47
47
25
44
24
55
66
69
68
33
69
29
71
36
37
39
37
32
31
67
32
100
69
72
37
62
23
4
7
5
3
4
2
105
119
121
147
223
224
225
314
388
500
501
726
III
VI
II
16
15
7
100
11
33
13
8
I
15
45
60
17
65
[PBH]+ −H2
100
12
13
23
55
72
47
60
’
’
’
[PBH]+ −H
2
5
21
20
’
[PBH]+
28
[Y(PBH)]2+
19
[Dy(PBH)]2+
11
{[Y(NO3)2(PBH)]NO3}+
[Eu(NO3)2(PBH)]+
5
’
5
3
[Eu(NO3)2(PBH)2]+
’

D.G. Paschalidis et al. / Polyhedron 19 (2000) 2629–2637
2637
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