Y.-Y. Guo et al. / Inorganica Chimica Acta 391 (2012) 182–188
183
Cary 100 spectrophotometer in acetonitrile solution at 16 °C. Sin-
gle crystals data were collected on a Bruker SMART CCD diffrac-
tate, THF, but insoluble in chloroform, dichloromethane and ethyl
ether. Molar conductance data in acetonitrile indicate that all the
complexes (see Table 1) act as non-electrolytes.
tometer with graphite-monochromatized Mo
Ka radiation
(k = 0.71073 Å) at 298 2 K. The structures were solved by direct
methods and refined by full matrix least-squares techniques with
anisotropic thermal factors for all non-hydrogen atoms. Theoreti-
cal models fixed the hydrogen atoms of the compound. All calcula-
tions were performed using the program package SHELXTL 97.
Luminescence and phosphorescence spectra were obtained on a
Hitachi F-4500 fluorescence spectrophotometer. The lifetime spec-
trum was measured on an Edinburgh Instruments FLS920 Fluores-
cence Spectrometer with Nd pumped OPOLETTE laser as the
excitation source.
3.2. Thermogravimetric analyses
To examine the thermal stability of the complexes, thermo-
gravimetric analysis (TGA) was carried out on by heating the com-
plexes from 25 °C to 525 °C at a rate of 10 °C per minute Table 2.
The complexes exhibited very similar mass losses over the entire
operating range respectively. The mass losses begin at ca. 152 °C,
showing the complexes are stable in the room temperature. The
mass losses were matched with the contents of water, which is
consistent with the single crystal analysis.
2.3. Synthesis of L
3.3. IR spectra
The synthetic route for the ligand L and its lanthanide com-
plexes are shown in Scheme 1. Anhydrous K2CO3 (2.76 g, 22 mmol)
was added slowly to the DMF solution of 2-hydroxy-N-(pyridin-2-
ylmethyl)benzamide (4.56 g, 20 mmol) at 100 °C. An hour later, a
solution of 2-chloro-N,N-diisopropylacetamide (3.56 g, 20 mmol)
in 10 ml DMF was added dropwise and slowly to the mixture.
The reaction mixture was stirred at 100–120 °C for 12 h, and then
poured into 50 ml water. The orange precipitate were collected,
washed with a small amount of ethyl acetate, and then dried in
vacuum, yield: 80%. 1H NMR (200 MHz CDCl3): d 9.8 (s, 1H, –NH–
), 8.5–6.9 (m, 8H, –Ar–H), 4.9 (d, 2H, –O–CH2–), 4.8 (s, 2H, –CH2–
py), 3.9 (m, 1H, –CH–), 3.4 (m, 1H, –CH–), 1.3 (d, 6H, –CH3), 1.2
(d, 6H, –CH3).
IR spectra of the ligand and complexes are shown in Table 3. The
IR spectra of the complexes are obviously different from the ligand,
but they resemble with each other, suggesting they share a similar
coordination behavior.
The IR spectrum of the free ligand shows bands at 1644 and
1108 cmꢁ1, which may be assigned to
m
(C@O) and
respectively. In the IR spectra of the lanthanide complexes, the
(C@O) shifts by 20–29 cmꢁ1 towards lower wave numbers (red
m(Ar–O–C),
m
shift), In the IR spectra of the lanthanum complexes, the m(Ar–O–
C) shifts by 6–9 cmꢁ1 towards higher wave numbers (blue shift),
it is clear that the carboxylic group and ester carbonyl group take
part in coordination at the same time [10].
The absorption bands assigned to the coordinated nitrato
groups (C2v) were observed at about 1487–1489 cmꢁ1
(
m
1), 1318–
2) and 819–821 cmꢁ1
[11] for the complexes, respectively. In addition, the separation
2.4. Synthesis of the lanthanide complexes 1–6
1330 cmꢁ1
(m
4), 1036–1041 cmꢁ1
(m
(m3)
A solution of 0.2 mmol L in ethyl acetate (10 ml) was added
dropwise to a solution of 0.2 mmol of lanthanide nitrates (Ln = La,
Nd, Eu, Gd, Tb, Er) in ethyl acetate (10 ml). The mixture was stirred
at room temperature for 6 h. Then the precipitated solid complex
was filtered, washed with ethyl acetate and diethyl ether, recrys-
tallized from appropriate solvent, dried in vacuum, yield: 75–
85%. Single crystals of the europium, neodymium and gadolinium
complexes were grown from acetonitrile solution with slow evap-
oration at room temperature. After approximately 3 weeks, color-
less crystals (light purple for the Nd complex) were formed from
the solution.
of two strongest frequency bands |m1
–
m
4| isꢁapproximately 157–
169 cmꢁ1, clearly establishing that the NO3 groups in the solid
complexes coordinate to the lanthanide ion as bidentate ligands
[12]. No bands at 1380, 820 and 720 cmꢁ1 in the spectra of com-
plexes indicates that free nitrate groups (D3h) are absent, in agree-
ment with the results of the conductivity experiments. There is
also a strong and wide peak of m
(OH) (3418–3516 cmꢁ1) and the
in-plane and out-of-plane vibration of water at ca. 818 cmꢁ1 and
571 cmꢁ1 in all the complexes, which are associated with the
coordinated water [13].
3.4. Crystal structures of complexes 2–4
3. Results and discussion
Single-crystal X-ray diffraction investigations reveal that the
two complexes all crystallize in monoclinic with space group
P21/c of the monoclinic system and the results of the structure
analysis of the complexes [NdL(NO3)3(H2O)]ꢀCH3CN (2), [Eu-
L(NO3)3(H2O)]ꢀCH3CN (3) and [GdL(NO3)3(H2O)]ꢀCH3CN (4) show
that they have the similar coordination sphere (Table 4), thus only
the structure of the gadolinium complex is described here as an
3.1. Properties of the complexes
Analytical data for the newly synthesized complexes, listed in
Table 1, are conformed to a 1:1 metal-to-L stoichiometry for ni-
trate complex. All complexes are soluble in acetone, acetonitrile,
methanol, ethanol, DMF and DMSO, slightly soluble in ethyl ace-
Scheme 1.
Guo, Yuan-Yuan
