Thermoanalytical and spectroscopic studies on hydrazinium lighter lanthanide complexes of 2-pyrazinecarboxylic acid

Article abstract of DOI:10.1007/s10973-009-0117-1

The new hydrazinium lanthanide metal complexes of 2-pyrazinecarboxylic acid (HpyzCOO) of the formulae (N₂H₅)₂[Ln(pyzCOO) ₅] ? 2H₂O (1), where Ln = La or Ce and (N ₂H₅)₃

Full text of DOI:10.1007/s10973-009-0117-1

J Therm Anal Calorim (2010) 100:725–732
DOI 10.1007/s10973-009-0117-1
Thermoanalytical and spectroscopic studies on hydrazinium
lighter lanthanide complexes of 2-pyrazinecarboxylic acid
Thathan Premkumar Æ Subbiah Govindarajan
Received: 26 March 2009 / Accepted: 21 May 2009 / Published online: 3 July 2009
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract The new hydrazinium lanthanide metal com-
plexes of 2-pyrazinecarboxylic acid (HpyzCOO) of the
formulae (N2H5)2[Ln(pyzCOO)5] ꢀ 2H2O (1), where Ln =
La or Ce and (N2H5)3[Ln(pyzCOO)4(H2O)] ꢀ 2NO3 (2),
where Ln = Pr, Nd, Sm or Dy have been synthesized
and characterized by physico-chemical methods. The IR
absorption bands of N–N stretching at 960 cm-1 unam-
biguously prove the existence of N2H5? ions. The bonding
parameters b, b1/2, % d and g, have been calculated from
the electronic spectroscopic (hypersensitive) bands of
Pr(III) and Nd(III) complexes. All the complexes undergo
endothermic followed by exothermic decomposition to
leave the respective metal oxides as the end products.
However, the DTA of the complexes 2 demonstrate rather
sharp peak than the complexes 1, owing to overwhelming
exothermicity, which may be due to the loss of both
hydrazine and nitrate moieties in the same step. The X-ray
powder diffraction studies reveal the existence of isomor-
phism among the member complexes.
Introduction
The nitrogen containing heteroaromatic carboxylic acids are
being intensely studied because of their varied ligational
modes towards metal ions and manifestation of novel
structural features of the metal complexes [1–3]. Among
these acids, pyrazinecarboxylic acids are known to form
many structurally important complexes [4, 5]. Further,
among the pyrazinecarboxylic acids, the 2-pyrazinecarb-
oxylic acid (HpyzCOO) is the simplest one and it acts as
bidentate ligand through the nitrogen atom and the uniden-
tate carboxylate group [5, 6]. The HpyzCOO forms coordi-
nation compounds with divalent 3d metal ions [6] and uranyl
ion [7], in which the central ion is chelated by two HpyzCOO
ligands via their (N, O) moieties consisting of a hetero-ring
nitrogen atom and an oxygen atom belonging to the nearest
monodentate carboxylic group. Similar monomeric mole-
cules have been found in the crystals of calcium and stron-
tium [8] pyrazinecarboxylate. Although the interaction of 2-
pyrazinecarboxylate with various divalent metals [5–9] has
been carried out and the structures of these complexes have
been studied, no work has been done with trivalent metals in
general, trivalent lanthanides in particular, except our recent
work on the lanthanum 2-pyrazinecarboxylate hydrate [10].
Our interest in the chemistry of hydrazine lanthanide
complexes with O, N donor ligands come from their
interesting thermal behaviour. Hydrazine is, in fact, a
substrate [11, 12] as well as a product of functioning
nitrogenase and has been isolated by quenching the enzyme
[13, 14]. Furthermore, the coordination chemistry of
hydrazine and substituted hydrazines present some aspects
of interest, including the influence that the ancillary ligands
and central metal may have in determining the different
coordination modes, of hydrazine ligand and understanding
of the properties that coordination to a metal fragment may
Keywords Chemical synthesis ꢀ Lanthanides ꢀ
Oxides ꢀ Thermal properties ꢀ Thermogravimetric
analysis (TGA)
T. Premkumar (&) ꢀ S. Govindarajan (&)
Department of Chemistry, Bharathiar University,
Coimbatore 641046, India
e-mail: thathanpremkumar@gmail.com
S. Govindarajan
e-mail: drsgovind@yahoo.co.in
Present Address:
T. Premkumar
Department of Materials Science and Engineering,
Gwangju Institute of Science and Technology,
1 Oryong-dong, Buk-gu, Gwangju 500-712, South Korea
123

726
T. Premkumar, S. Govindarajan
Preparation of ligand solution
include on an NH2NH2 or RNHNH2 molecule towards
deprotonation reactions.
Pyrazine carboxylic acid (620 mg, 5 mmol) was added to a
solution of 10% hydrazine hydrate (2 mL, 4 mmol) in
25 mL of water with constant stirring. The mixture was
heated at 80 °C for 30 min. The pH of the resulting clear
solution was raised from 4 to 7 by careful addition of 10%
hydrazine hydrate. This resulting clear solution (pH = 7)
was heated over a water bath for about 10 min and allowed
to stand for 1 h at room temperature.
The coordination chemistry of lanthanides, the hard
acids, was limited initially to strong chelating ligands with
oxygen as donor atoms. The notion that neutral nitrogen
bases precipitate the hydrous oxide or hydroxide of lan-
thanides [15] hindered the progress of the coordination
chemistry of the lanthanides. Nevertheless, with the
development of new synthetic techniques, some complexes
of lanthanides (La–Nd, Sm, Dy, Er and Lu) with hydrazine
and anions like halides, carbonate, nitrate, sulphate and
perchlorate have been reported [16]. However, complexes
with carboxylate anions have not been studied except for
acetate [17], oxalate [18] and phthalate [19]. The structures
of these complexes have been inferred by chemical analysis
and IR spectra. The complexes of the type N2H5Ln(SO4)2
H2O (Ln is La–Tb, except Pm) have been characterized by
spectral, magnetic, thermal and X-ray structural studies [20,
Preparation of the complexes
Millimole samples of respective metal oxides were dis-
solved in 5 mL of 4 N nitric acid and evaporated to dryness
and the residue dissolved in 25 mL of distilled water. The
metal nitrate solution (25 mL, pH = 2.5) obtained was
added to the prepared ligand solution with constant stirring.
The pH of the resulting solution was adjusted to 5 by adding
a few drops of 10% N2H4 ꢀ H2O and concentrated over a
steam bath to one half of its volume and was allowed to
crystallize at 5 °C. The crystalline solids formed after a
week was filtered off, washed with ice-cold water and
ethanol and dried in air, which corresponds to lanthanide 2-
pyrazinecarboylate hydrate compounds [10, 30]. Then, the
filtrate was allowed to evaporate slowly at 5 °C. The needle
crystals of the complexes of type 1 and 2 suitable for X-ray
analysis were formed after 45 days, which were isolated,
washed with ice-cold absolute alcohol and dried in vacuo
over CaCl2 in a desiccator (yield 50–53%).
?
21]. In these complexes, N2H5 ion is coordinated. There
?
have been two cases where N2H5 does not participate in
the coordination sphere of UO2(II) [22] but counterbalances
the [(UO2)(C2O4)5(H2O)2]6- anion.
The coordination chemistry of carboxylates with trivalent
lanthanide metals in the presence of hydrazine has received
rather scant attention, contrary to various divalent metals for
which their complexes are known. Our research group has
long been involved in the study of hydrazine carboxylate
system [19, 22–24] and we have recently reported thermal
behaviour of several hydrazine metal carboxylates, which
act as precursors for various metal oxides [25–29]. In this
study we wanted to investigate thermal behaviour of the
lanthanide compounds of hydrazine with hyterocyclic
nitrogen containing carboxylate ligands and to study their
coordination behavior. To the best of our knowledge, no
work has been done on the thermal property of hydrazinium
lanthanide metal complexes of HpyzCOO. Hence, in this
paper we report for the first time the preparation, spectro-
scopic and thermal studies on hydrazinium trivalent
lanthanide metal complexes of HpyzCOO.
Pysico-chemical studies
The hydrazine content of the complexes was determined
volumetrically using a standard KIO3 solution (0.025 M)
under Andrews’ condition [31]. The metals after destroying
the organic part and hydrazine by treatment with concen-
trated HNO3 and evaporating the excess HNO3, were
determined volumetrically by EDTA titration [31]. Ele-
mental analyses were performed on Perkin Elmer-240 B
CHN analyzer. The solid-state absorption spectra of the
samples were recorded on a JASCO V-530 UV–Visible
spectrophotometer in the range 300–800 nm by dispersing
the solid samples in nujol mull. IR spectra were recorded as
KBr pellets with a Shimadzu FTIR 8000 model spectro-
photometer in the range 4000–400 cm-1. Simultaneous
TG-DTA measurements were carried out on a STA 1500
thermal analyzer. The experiments were carried out in air
using platinum cups as sample holders with 5–10 mg of the
samples at the heating rate of 10 °C min-1. X-ray powder
diffraction patterns of the compounds were recorded on a
Seimens D-5005 X-ray diffractometer using Cu-Ka radia-
tion with nickel filter.
Experimental section
Materials
All the manipulations were performed under aerobic con-
ditions using 2-pyrazinecarboxylic acid (Aldrich Co),
metal oxide (99%) of La-Sm except Pm and Dy (Indian
Rare Earth Ltd.), hydrazine hydrate of 99–100% purity
(Glaxo Indio Ltd.) as received. All chemicals and solvents
used were pure analytical grade and the solvents were
distilled before use.
123

Thermoanalytical and spectroscopic studies on hydrazinium
Results and discussion
727
carboxylate hydrates. It was observed that the filtrate on
evaporation at room temperature also resulted in the same
compounds, 1 and 2 in 30 days, but with crystals of inferior
quality.
Synthesis
Compounds of composition (N2H5)2[Ln(pyzCOO)5] ꢀ 2H2O
(1), where Ln = La or Ce and (N2H5)3[Ln(pyzCOO)4
(H2O)] ꢀ 2NO3 (2), where Ln = Pr, Nd, Sm or Dy have
been prepared for which the results of the analyses are
given in Table 1. The compounds of the type 1 and 2 are
soluble in water probably due to their ionic and monomeric
nature of the complexes and are insoluble in most of the
common organic solvents such as alcohol, chloroform,
acetone etc. All of these complexes are hydrated and stable
in air. Combining appropriate mole ratio of HpyzCOO and
metal nitrate solutions alone (without hydrazine) yielded
only crystalline solid products, not single crystals. It is also
noteworthy that the reverse addition of metal and ligand
solution leads to immediate formation of insoluble metal
Attempt to synthesize similar type of hydrazinium com-
plexes of lanthanides using the related 2-pyridinecarboxylic
acid (picolinic acid), instead of 2-pyrazinecarboxylic acid,
was unsuccessful. The reason for this could be, picolinic acid
is rather a weak acid (pKa = 4.66) than the 2-pyrazine-
carboxylic acid (pKa = 2.92) [32]. Further, the additional N
atom present in the aromatic ring of the HpyzCOO makes it
more acidic facilitating not only the complex formation but
also hydrogen bonding leading to the stability of the crystal.
IR spectra
The infrared spectroscopic results of the complexes are
presented in Table 2. The respective sets of complexes
Table 1 Analytical data of the complexes
Compound
D.pt.
(°C)
Yield Colour
(%)
Found (calculated) (%)
Hydrazine
Metal
C
N
H
(N2H5)2[La(pyzCOO)5] ꢀ 2H2O
(N2H5)2[Ce(pyzCOO)5] ꢀ 2H2O
(N2H5)3[Pr(pyzCOO)4(H2O)] ꢀ 2NO3 136
(N2H5)3[Nd(pyzCOO)4(H2O)] ꢀ 2NO3 140
(N2H5)3[Sm(pyzCOO)4(H2O)] ꢀ 2NO3 146
(N2H5)3[Dy(pyzCOO)4(H2O)] ꢀ 2NO3 143
68
60
53
51
50
51
52
52
White
Yellow
Green
Purple
7.24 (7.47) 15.83 (16.22) 34.87 (35.03) 22.09 (22.89) 3.28 (3.39)
7.31 (7.46) 15.93 (16.34) 34.53 (34.97) 22.17 (22.85) 3.32 (3.38)
10.54 (10.98) 15.34 (16.12) 26.97 (27.45) 25.08 (25.62) 3.19 (3.32)
10.57 (10.94) 16.07 (16.43) 26.92 (27.34) 25.01 (25.52) 3.28 (3.31)
Dull white 10.68 (10.86) 16.59 (17.01) 26.87 (27.16) 25.21 (25.35) 3.20 (3.28)
Dull white 10.67 (10.72) 17.89 (18.14) 26.57 (26.79) 24.50 (25.00) 3.19 (3.24)
Table 2 Infrared and electronic spectral data
Compound IR Spectra (cm-1
)
Electronic spectral data
mO–H (H2O) mN–H masyCOO msyCOO Ring vibration mN–N
Band max (cm-1
)
Assignment
Parameters
La
Pr
3380 b
3340 b
3082 1629
3069 1629
1392 b 1459
1394 s 1459
962 m
–
–
–
1
961 m 16,610
20,576
3H4 ? D2
3P0
3P1
b = 0.9958
b1/2 = 0.0457
% d = 0.4218
g = 0.0021
21,276
22,421*
3P2
4
2
Nd
3355 b
3084 1631
1392 s 1458
960 m 12,490
13,485
4I9/2 ? F5/2, H9/2 b = 0.9911
4F7/2
4F9/2
b1/2 = 0.0044
% d = 0.8908
g = 0.0044
14,690
2
17,170*
4G7/2, G7/2
19,040
4G7/2
19531
4G9/2
Sm
Dy
Ce
3478
3422
3347
3321 1626
3120
1385 s 1458
1394 s 1458
1396 s 1458
961 m
961 m
960 m
–
–
–
–
–
–
–
3093 1627
2924
–
–
3163 1636
3110
123

728
T. Premkumar, S. Govindarajan
have identical infrared spectra. The IR spectra of all the
complexes show strong bands in the range of 3545–
3320 cm-1 assignable to m(OH) stretching vibrations of
lattice and/or coordinated water molecules [33]. The dif-
ference in this region between complexes of the types 1
and 2 is consistent with the different water content and
this is further substantiated by the results of elemental and
18
17
16
15
14
13
12
11
10
9
a
8
7
6
thermal analyses. In contrast to the free acid (m(CO)
:
1721 cm-1), the complexes show C–O absorption bands
between 1635 and 1610 cm-1 indicating the presence of
coordinated –COO- group. The bands due to the ring
vibrations [33] of the pyrazine molecule are found to
move to higher frequency and the band due to the car-
boxyl group which moves to a lower frequency, in the
compounds, suggests that the nitrogen atoms in the aro-
matic ring and the oxygen of the carboxyl groups are
coordinated to the metal atom [34, 35]. The N–N
stretching vibration of complexes 1 and 2 is seen at
5
4
3
2
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm-1
)
42
40
38
36
34
32
30
28
26
24
22
20
18
16
14
12
10
8
b
960 cm-1 and is consistent with the existence of N2H5
?
ions [16].The IR spectra of parent acid, La and Nd
complexes are shown in Fig. 1a–c, respectively, as
examples.
6
4
4000
3500
3000
2500
2000
1500
1000
500
Electronic spectra
Wavenumbers (cm-1
)
The electronic spectra of the lanthanides, constituting
mainly Laporte-forbidden 4f-transitions, are not much
influenced by the ligand environment, as in the case of
d-block metal complexes. The spectral data along with the
various calculated bonding parameters are given in
Table 2. The absorption band associated with nearly
c
56
54
52
50
48
46
44
42
40
38
36
34
32
4
2
degenerate I9/2 ? G7/2,
4G5/2 transitions of Nd3? is
known to exhibit strong hypersensitive behaviour [36],
making it especially suitable for probing the coordination
environment around the Nd3? ion. The spectral profile of
the above transition in the present Nd3? complex resemble
those of the nine-coordinated complexes [37]. All the
bands show a weak perturbation due to complexation and
an increase in intensity compared to the aquo ion [38],
presumably due to nephelauxetic effect [39, 40]. Various
spectral parameters, viz., nephelauxetic ratio (b), bonding
parameter (b1/2), Sinha’s covalency parameter (% d) and
covalency angular overlap parameter (g), were calculated
[41, 42] from the electronic spectra of the complexes.
Depending upon the ligands, the values of d may either
be positive (covalent bonding) or negative (ionic bond-
ing). All these parameters suggest a weak covalent
interaction between the lanthanide and the ligand. The
electronic spectra of the Pr and Nd complexes of 2, are
shown in Fig. 2a and b, respectively, as representative
examples.
30
28
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm-1
)
Fig. 1 IR spectra of a HpyzCOO, b (N2H5)2[La(pyzCOO)5] ꢀ 2H2O
and c (N2H5)3[Nd(pyzCOO)4(H2O)] ꢀ 2NO3
Thermal decomposition of hydrazinium compounds
(1 and 2)
The thermal decomposition characteristics of the com-
plexes are summarized in Table 3. The simultaneous TG
and TDA results of the La and Ce complexes are similar as
are those of Pr, Nd, Sm and Dy. Both the set of compounds
undergo three-step decomposition to give the respective
metal oxide as the final products. The first stage weight loss
123

Thermoanalytical and spectroscopic studies on hydrazinium
729
Fig. 2 Electronic spectra of
a (N2H5)3[Nd(pyzCOO)4
(H2O)] ꢀ 2NO3 and
b (N2H5)3[Pr(pyzCOO)4
(H2O)] ꢀ 2NO3
Table 3 Thermal dataa
Compound
DTA Peak
temperature (°C)
Thermogravimetry (TG)
Intermediates/end products
TG temperature
range (°C)
Mass loss (%)
Obsd.
Cacld.
(N2H5)2[La(pyzCOO)5] ꢀ 2H2O
68 (?)
50–75
6.50
4.20
(N2H5)2[La(pyzCOO)5]
[La(pyzCOO)3]
253 (-)b
411 (-)
468 (-)
60 (?)
75–325
40.00
40.66
325–745
45–70
80.00
6.00
80.98
4.19
La2O3
(N2H5)2[Ce(pyzCOO)5] ꢀ 2H2O
(N2H5)2[Ce(pyzCOO)5]
[Ce(pyzCOO)3]
CeO2
253 (-)
403 (-)s
136 (?)b
263 (-)s
419 (-)sh
439 (-)
448 (-) t
459 (-)
137 (?)
240 (-)s
430 (-)
450 (-)
128 (?)
146 (?)d
256 (-)s
417 (-)
456 (-)s
147 (?)
253 (-)
449 (-)
509 (-)
70–340
340–410
105–145
145–270
39.00
75.00
2.00
40.59
79.93
2.06
(N2H5)3[Pr(pyzCOO)4(H2O)] ꢀ 2NO3
(N2H5)3[Pr(pyzCOO)4] ꢀ 2NO3
[Pr(pyzCOO)3]
43.00
41.64
270–595
75–155
80.00
2.00
80.53
2.05
Pr6O11
(N2H5)3[Nd(pyzCOO)4(H2O)] ꢀ 2NO3
(N2H5)3[Nd(pyzCOO)4] ꢀ 2NO3
[Nd(pyzCOO)3]
155–250
41.00
41.49
250–590
75–155
78.00
2.00
80.83
2.04
Nd2O3
(N2H5)3[Sm(pyzCOO)4(H2O)] ꢀ 2NO3
(N2H5)3[Sm(pyzCOO)4] ꢀ 2NO3
155–260
40.00
41.19
[Sm(pyzCOO)3]
260–640
100–175
175–300
79.00
2.00
80.27
2.01
Sm2O3
(N2H5)3[Dy(pyzCOO)4(H2O)] ꢀ 2NO3
(N2H5)3[Dy(pyzCOO)4] ꢀ 2NO3
[Dy(pyzCOO)3]
39.00
40.60
300–610
77.00
79.18
Dy2O3
a
b Broad, s sharp, sh shoulder, d doublet, t triplet
of the complexes 1 occurs in the range 50–75 °C, whereas
complexes 2 show in the range 105–150 °C, and is attrib-
uted to the loss of water molecules. This loss observed as
an endotherm at around 65 and 140 °C, respectively,
confirms the presence of lattice water in the former and
coordinated water in the latter complexes. In the second
step, the anhydrous hydrazinium compounds undergo an
exothermic decomposition between 250 and 265 °C to give
123

730
T. Premkumar, S. Govindarajan
Fig. 3 Simultaneous TG-DTA of a (N2H5)2[La(pyzCOO)5] ꢀ 2H2O, b (N2H5)3[Pr(pyzCOO)4(H2O)] ꢀ 2NO3, and c (N2H5)3[Sm(pyzCOO)4
(H2O)] ꢀ 2NO3
the isomeric lanthanide 2-pyrazinecarboxylate intermedi-
ate. The DTA of the complexes 2 show rather sharp peak
than the complexes 1, due to overwhelming exothermicity,
which may be due to the loss of both hydrazine and nitrate
moieties in the same step. Final step weight loss corre-
sponds to the decomposition of the intermediates to metal
oxides. This loss is observed as a sharp exothermic peak for
Ce compound (may be due to the oxidative decomposition
to form CeO2 as the final product) and two successive
exotherms for La, Nd, Sm and Dy, and exothermic multi-
plets for Pr compound. The metal oxide formation is sig-
nificantly low. The simultaneous TG and DTA curves of
the La, Pr and Sm complexes are given in Fig. 3 (a, b and
c), respectively, as examples. Our effort, to isolate the
intermediates was unsuccessful due to their continuous
decomposition as evident from the TG. Hence, we have
tried to assign the possible intermediates as observed from
the TG mass losses, which are in agreement with the
calculated mass losses.
not bonded to the central metal ion. However, in order to
confirm this assignment unambiguously it was considered
to determine the crystal structure of these compounds.
Therefore, the final proof of the coordination environ-
ment of the metal was confirmed by a single crystal
X-ray study of the compounds.
Crystal structures of (N2H5)2[La(pyzCOO)5] ꢀ 2H2O
(1a) and (N2H5)3[Nd(pyzCOO)4(H2O)] ꢀ 2NO3 (2a)
The structure of (N2H5)2[La(pyzCOO)5] ꢀ 2H2O (1a) and
(N2H5)3[Nd(pyzCOO)4(H2O)] ꢀ 2NO3 (2a) have been
determined from single crystal X-ray analysis [43]. The
crystallographic data for the compound 1a are monoclinic,
space group P21/n with a = 16.4018 (4), b = 22.8727 (6),
˚
c = 14.9608 (9) A, b = 102.660 (2)°, Z = 8 and R =
0.0592. The compound 2a crystallizes in the monoclinic
space group C2/c, with a = 10.7176(7), b = 21.7630(13),
˚
c = 14.9608(9) A, b = 104.468(4)° and Z = 4. The struc-
?
?
The aforesaid results suggest that the N2H5 ions
ture analysis shows that the 1a crystals consist of N2H5
and water molecules are not involved in coordination
and hence lanthanide ions in 1 are coordinated only by
2-pyrazinecarboylate anions. Thus, the lanthanum and
cerium complexes may have rare ten coordination by five
N, O bonding moieties. The metal ions in complex 2 are
nine coordinated by four 2-pyrazinecarboxylate anions
cations, water molecules and the [La(pyzCOO)5]2- anions.
The asymmetric unit of complex 1a contains two crystal-
lographically independent lanthanum complexes. Interest-
ingly, each lanthanum atom has ten coordination formed by
five 2-pyrazinecarboxylate (bidentate chelate) ligands, via
its N, O bonding moieties. The other pyrazine N atom
present in the ring is not involved in coordination. The
?
-
and one water oxygen. The N2H5 and NO3 ions are
123

Thermoanalytical and spectroscopic studies on hydrazinium
731
Fig. 4 X-ray powder pattern of
compounds a 1 and b 2
N2H5? ions and the water molecules are not coordinated to
the metal. It is worthwhile to mention here that, the ten
coordination of hydrazinium lanthanide complexes with
carboxylate anions have been observed for the first time
[43]. The structure is built up by lanthanum ions joined by
2-pyrazinecarboxylate groups forming two-dimensional
sheets parallel to (001) plane. Whereas the 2a is monomeric
pertinent to note that the cerium compound shows a low
temperature, distinct single exothermic peak in contrast to
other compounds, which show relatively high temperature
exothermic multiplets in their final step of decomposition.
The overwhelming exothermicity of the cerium compound
may be due to its oxidative decomposition to give CeO2
[26] as the end product as against Ln2O3 [19, 25] in other
cases. Further, it is interesting to find out that the La and
Ce compounds are ten coordinated and the latter tri-
hydrazinimum compounds are nine coordinated in addition
to having nitrate anions and this unusual behavior of
lighter lanthanides, under identical experimental condi-
tions, may be due to their difference in size, i.e., lanthanide
contraction.
?
and the structure comprises of N2H5 cations, [Nd(pyz-
COO)4(H2O)]- and NO3- anions. The coordination number
for neodymium is nine with four pyzCOO ligands, bidentate
(N, O) to the metal and the lone water molecule completes
the coordination sphere and the sheets like pattern in all are
interlinked via multiple hydrogen bonds leading to three
dimensional structure.
Acknowledgements T. Premkumar thanks the Council of Scientific
and Industrial Research, New Delhi, for the award of a Senior
Research Fellowship. The authors gratefully acknowledge Dr. Nigam
P. Rath, Department of Chemistry and Biochemistry, University of
Missouri-St. Louis, USA and Dr. J. W. Steed, Kings College, London
for helping with single crystal X-ray data collection for the
compounds.
Powder X-ray pattern
In order to ascertain the isomorphic nature of the set of
complexes, the powder diffraction patterns have been
recorded and are depicted in Fig. 4. From the patterns, it is
evident that the respective set of complexes are isostruc-
tural. The results from the IR and thermoanalytical studies
are in accordance with these isostructural groupings.
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