LANTHANIDE(III) SCHIFF BASE COMPLEXES
621
The complexes are soluble in water, chloroform, ether, EtOH, acetone and
dimethylformamide (DMF). The colors of aqueous solutions are dependent
on the pH value. Between pH ¼ 175 yellow solutions were observed, and at
pH ¼ 677.5 colorless turbid solutions were produced. The molar con-
ductance values in methanol and in DMSO indicate that the complexes are
non-electrolytes in solution8,9, but in methanol the molar conductance
values are relatively higher than those in DMSO and this may be attributed
to methanol coordination. To confirm this result, longer time molar con-
ductance values have been examined. It was found that the change of the
molar conductance values with time increased for about 2 h at room tem-
perature and then the data become constant. These phenomena indicate that
the coordinated sphere or the coordination bond model may be changed due
to replacement by small polar molecules. The TG-DTA diagrams of all
complexes are similar and indicate that the complexes sustain weight loss in
the 1207140 ꢀC region and mass loss was observed at ca. 200 ꢀC, then the
complexes continue to decompose exothermally at 350, 520 and 630 ꢀC and
the decomposition is completed at about 780 ꢀC. Water of crystallization
(extraspheric water) is usually lost over the 707110 ꢀC range while water of
coordination (intraspheric water) is eliminated at higher temperature
(1207150 ꢀC). Together with the corresponding weight losses (water) it can
be concluded that the two water molecules in all complexes are coordinated.
Infrared Spectra
The IR spectra of the potassium salt of the ligand (KL) and its
complexes are complicated. However, attempts have been made to identify
some important bands that furnish information regarding the mode of
bonding. The main IR bands with their tentative assignments are listed in
Table II. The broad band between 3414 and 3386 cmꢁ1 due to the stretching
modes of n(OH) of the ligand remains almost unchanged but becomes
stronger in the complexes, which indicates that the hydroxyl group remains
ꢁ
uncoordinated. Two stretching vibration of CO2ꢁ, nas(CO2ꢁ) and ns(CO2
)
in the spectra of the complexes are observed at ca. 1580 and 1406 cmꢁ1 with
the difference Dn(CO2ꢁ) ¼ 174 cmꢁ1. Compared with the ligand, the two
bands at 1566 and 1400 cmꢁ1 having the difference Dn(CO2ꢁ) ¼ 166 cmꢁ1
ꢁ
suggested that the CO2 group is coordinated with the metal ion in uni-
dentate form. The band at 1625 cmꢁ1 in the ligand attributed to the
n(C¼N)stretching vibration shifts to lower frequencies at 160071605 cmꢁ1
after complexation indicating coordination of the nitrogen atom in the C¼N
group to the metal ion. Furthermore, several new bands observed in the far-
IR spectra at ca. 510, 318, 270 and 225 cmꢁ1 in the complexes are assigned