LANTHANIDE COMPLEXES
549
added, and refluxed for 1 h, cooled, and the resultant yellowish
Magnetic Susceptibility
white precipitate of 4-amino 3-mercapto-1,2,4-triazine-5-one
The magnetic susceptibility values show that all the lan-
thanide nitrate complexes are paramagnetic in nature except
La(III) and Y(III) complexes. The results are as shown in the
Table 1. The observed magnetic values were compared with
that of theoretical spin-orbit coupling values (of the respective
lanthanide ions and they agree each other with the exception
of Sm and Eu complexes.[12] However it is found that the ex-
perimental values of all the complexes including those of Sm
and Eu agree with the theoretical values calculated from the
Van Vleck formula. The discrepancies in the case of Sm and Eu
complexes may be attributed to the fact that the first excited J
states of Sm3+ and Eu3+ are sufficiently close to their ground
states so that these states mix each other even at room temper-
atures causing increase in the magnetic moments. This is the
reason for the breakdown of the spin-orbit coupling models for
Sm and Eu complexes. The Van Vleck treatment is more refined
since the method takes into account of the excited states also and
leads to a closer agreement between the theoretical and experi-
mental values. The fact is that the observed magnetic moments,
from the Van Vleck values, suggest the non-participation of 4f
electrons in the bond formation.
was filtered, dried, and recrystallized.[11]
In the second step, to a solution of 0.1 mol of 4–amino-
3-mercapto-1,2,4-triazine-5-one in 10 mL of ethanol, and 0.1
mol of 5-bromosalicylaldehyde was refluxed for 4 h, cooled,
filtered, washed with water, dried, and then recrystallized from
absolute alcohol, The yellow-colored 5-bromosalicylidene-4-
amino-3-mercapto-1,2,4-triazine-5-one (BrSAMT) was dried in
a desiccator. The ligand was characterized using elemental anal-
ysis, IR spectroscopy, and NMR spectroscopy.
For Ligand, Yield: 60%; Anal. Calcd. for C10H6BrN4O2S: C,
36.4; H 2.1; N, 17.0; S 9.7. Found: C, 36.5, H, 2.1, N, 17.2, S, 9.7;
IR (KBr, cm−1): 1690 s (–C O stretching of –CO in triazole
group), 1650 (C N– stretching of azomethine group), 1550,
1270, 900, and 800 cm−1 (thioamide bands I, II, III, and IV);
1HNMR (200 MHz, DMSO-d6, δ/ppm): 11.24 (1H, s, –SH), 8.1
(1H, s, CH = N), 6.24–8.76 (3H, m, aromatic, J = 7.8 Hz).
Synthesis of Complexes
A hot solution of the ligand BrSAMT (4 mmol) in 25 mL of
ethanol was added to boiling solution of lanthanide nitrate (2
mmol) in 10 mL ethanol. The resulting solution was refluxed for
about 2 h. Colored solid separated was filtered and washed with
ethanol followed by ether. The complex was dried in a desic-
cator. La(III), Ce(III), Nd(III), Eu(III), Dy(III), Y(III), Tb(III),
Pr(III), and Sm(III) metal ions were used.
Molar Conductance
The molar conductivities of lanthanide nitrate complexes in
DMF are presented in Table 1. The molar conductance values
reveal that the complexes are non electrolytes.[13] Therefore,
one nitrate ion is coordinated to the metal ion and hence the
nitrate complexes may be formulated as [Ln(BrSAMT)(ONO2)
Biological Tests
All the complexes were screened for their in vitro antibac- (H2O)2].
terial activity against pathogenic strains of bacteria such as
Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi,
Electronic Spectra
The electronic spectrum of the ligand showed n–π∗ and
π−π∗ transitions at 33333 and 37364 cm−1, respectively. Com-
plex formation with metal ions resulted in a hypsochromic shift
of these bands. The absorption bands of Ln(III) in the UV and
visible region appear due to transitions from the ground levels
Bacillus subtilis, and Shigella flexneri using plate technique.
The bacteria were cultured (15 mm dia) in a previously ster-
ilized Mueller Hinton agar medium in a Petri dish and used
as inoculum for the study. The components to be tested were
dissolved in DMF to a final concentration of 0.5% and 1% and
soaked in filter paper discs of 5 mm diameter and 1 mm thick-
ness. These discs were placed on the previously seeded plates
and incubated at 35 2◦C for 24 h. The diameter (mm) of the
inhibitory zone around each disc was measured after 24 h.
4
6
3H4, I9/2, and H5/2, respectively, to the excited J levels of 4f
configuration.[14] The sharp bands due to f–f transition origi-
nating within the 4fn configuration of lanthanide ions are only
slightly affected by the immediate surroundings of the metal
ion, and this is commonly attributed to the shielded nature of
the 4f orbitals by the overlying 5s2 and 5p6 orbitals. However,
the shift to lower frequency region can be concluded as due to
complex formation.[15]
RESULTS AND DISCUSSION
Analytical
The results show that the complexes of BrSAMT with La(III).
Ce(III), (Pr(III) Nd(III), Sm(III), Eu(III), Tb(III), Dy(III), and
Y(III) nitrates are of ML type with coordinated water molecules
Infrared Spectra
The ligands shows infrared band at 2900 cm−1, indicating the
having the molecular formula [Ln(L)(ONO2)(H2O)2]. All these absorptions ν(C-H). The ligand also shows the presence of four
complexes are non-hygroscopic with varying colors. Conclusive thioamide bands, I, II, III, and IV, at 1550, 1270, 900, and 800
evidences for all theprevious typeof complexes andits geometry cm−1, respectively, indicating the presence of thioamide moiety
comes from the spectral data. Analytical data are shown in in the ligand molecule. In the spectra of lanthanum complexes,
Table 1.
the thioamide band IV, at around 800 cm−1 has been shifted
Ramasubramanian
