Synthesis and characterization of peroxo complexes of uranium(VI) with some Mannich base ligands

Article abstract of DOI:10.1007/s00706-011-0587-2

Uranium(VI) peroxo complexes of composition [UO(O₂)L-L(NO ₃)₂], where L-L are the Mannich base ligands morpholinobenzyl urea, piperidinobenzyl urea, morpholinobenzyl thiourea, piperidinobenzyl thiourea, mor-pholinomethyl thiourea, piperidinomethyl thiourea, or morpholinomethyl urea, are reported. The synthesized complexes were characterized by use of a variety of physi-cochemical techniques, viz. elemental analysis, molar conductivity, magnetic susceptibility measurements, IR, electronic, mass, H NMR, and C NMR spectroscopy, and TGA/DTA studies. These studies revealed that the complexes are both non-electrolytic and diamagnetic in nature. The ligands are bound to the metal in a bidentate mode through carbonyl oxygen or thiocarbonyl sulfur and the ring nitrogen. Mass spectra confirm the molecular mass of the complexes. The antifungal activity of the complexes is greater than that of the corresponding free ligands.

Full text of DOI:10.1007/s00706-011-0587-2

Monatsh Chem (2012) 143:91–99
DOI 10.1007/s00706-011-0587-2
ORIGINAL PAPER
Synthesis and characterization of peroxo complexes
of uranium(VI) with some Mannich base ligands
•
Balgar Singh Simpy Mahajan Haq N. Sheikh
•
•
•
Mohita Sharma Bansi L. Kalsotra
Received: 26 June 2010 / Accepted: 16 July 2011 / Published online: 19 August 2011
Ó Springer-Verlag 2011
Abstract Uranium(VI) peroxo complexes of composition
[UO(O2)L–L(NO3)2], where L–L are the Mannich base
ligands morpholinobenzyl urea, piperidinobenzyl urea,
morpholinobenzyl thiourea, piperidinobenzyl thiourea, mor-
pholinomethyl thiourea, piperidinomethyl thiourea, or
morpholinomethyl urea, are reported. The synthesized
complexes were characterized by use of a variety of physi-
cochemical techniques, viz. elemental analysis, molar
conductivity, magnetic susceptibility measurements, IR,
electronic, mass, 1H NMR, and 13C NMR spectroscopy, and
TGA/DTA studies. These studies revealed that the com-
plexes are both non-electrolytic and diamagnetic in nature.
The ligands are bound to the metal in a bidentate mode
through carbonyl oxygen or thiocarbonyl sulfur and the ring
nitrogen. Mass spectra confirm the molecular mass of the
complexes. The antifungal activity of the complexes is
greater than that of the corresponding free ligands.
organic and inorganic substrates [13–17], and are of bio-
chemical relevance [18–25]. They are widely used, for
example, in the oxidation of thioanisole [26, 27], methyl-
benzenes [28], tertiary amines, alkenes, alcohols [29, 30],
and bromide [31], and also in olefin epoxidation [32–36].
Peroxo complexes of molybdenum and tungsten are
attracting interest as oxidants in organic synthesis [37].
Because uranium somewhat resembles the group 6B ele-
ments, it was of interest to discover whether it would form
analogous peroxo complexes which contain organic moie-
ties. The ubiquity of the UO2 group distinguishes uranium
from molybdenum and tungsten, however, and this factor
may have hitherto prevented the generation of peroxo com-
plexes from uranyl salts and organic reagents. A variety of
peroxo complexes of uranium with organic ligands have
been reported [38]. The coordination numbers for metal
chelates of Th(IV) and UO2(VI) have been reported [39, 40].
Metal complexes of Mannich bases have been of vital
importance in the development of coordination chemistry
[41, 42]. There has been much interest in the synthesis and
characterization of transition metal complexes containing a
Mannich base, because of their varied pharmaceutical
properties [43–47]. Synthesis of N-(morpholinobenzyl)urea
and thiourea and their complexation with molybdenum and
tungsten has been reported [22, 23, 25]. In this manuscript
we describe the synthesis and characterization of peroxo
complexes of uranium(VI) with some formaldehyde and
benzaldehyde-based Mannich base ligands. The structures
of ligands are given in Scheme 1.
Keywords Antifungal activity ꢀ Coordination chemistry ꢀ
Mannich bases ꢀ 13C NMR ꢀ Peroxo complexes
Introduction
Studies on peroxo complexes have received substantial
encouragement in recent years, because of their application
as oxidants in synthetic organic chemistry [1–12]. Many
peroxo complexes are a source of active oxygen atoms and
can be used as catalysts of oxygen-insertion reactions with
B. Singh ꢀ S. Mahajan ꢀ H. N. Sheikh (&) ꢀ M. Sharma ꢀ
B. L. Kalsotra
Results and discussion
Department of Chemistry, University of Jammu,
Jammu 1800 06, India
e-mail: hnsheikh@rediffmail.com
The analytical and physical data of the complexes are listed
in Table 1. The analytical data are in good agreement with
123

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B. Singh et al.
the general molecular formula proposed for the complexes,
[UO(O2)L–L(NO3)2] (where L–L is morpholinobenzyl urea
(MBU), piperidinobenzyl urea (PBU), morpholinobenzyl
thiourea (MBT), piperidinobenzyl thiourea (PBT), mor-
pholinomethyl thiourea (MMT), piperidinomethyl thiourea
(PMT), or morpholinomethyl urea (MMU)). The isolated
solid complexes are stable to air and light and are insoluble
in common organic solvents but soluble in DMSO and
DMF. All the complexes are yellowish coloured. All com-
plexes decompose on heating and do not have sharp melting
points.
O
H
N
H
N
N
O
N
O
NH2
NH2
Conductance and magnetic measurements
The molar conductivity K of the complexes measured in
DMF solution lies in the range 14–19 S cm2 mol-1, which
indicates the non-electrolytic nature of these complexes
(Table 1) [48]. Moreover, magnetic studies show that all
the complexes are diamagnetic as expected for the d0
system of uranyl(VI) peroxo complexes.
MBU
PBU
O
H
N
H
N
N
S
N
S
IR spectral studies
NH2
NH2
The characteristic IR absorption of the ligands and com-
plexes, and their assignments, are given in Table 2. The IR
spectra of all the complexes contain bands characteristic of
coordinated oxo and peroxo groups and the ligand mole-
cule. The metal peroxo group gives rise to three IR active
vibrational modes of v(O–O), vasym(UO2), and vsym(UO2).
These characteristic vibration modes appear around
MBT
PBT
O
875–905, 712–750, and 630–674 cm-1
, respectively.
H
N
H
N
N
S
N
S
These bands confirm the g2-coordination of the peroxo
group [49]. In all the complexes, an additional sharp band
around 995–1,002 cm-1 has been assigned to the v(U=O)
mode [18, 38]. Thus, IR the spectra confirm the presence of
the [UO(O2)]2- moiety in these complexes.
NH2
NH2
MMT
PMT
To study the mode of binding of the Mannich base
ligands with uranium in the peroxo complexes, the IR
spectra of the free ligands were compared with those of
corresponding metal complexes (Table 2). In the spectra of
the ligands MBU, PBU, and MMU a sharp band assigned to
v(C=O) of the amide group and another band assigned to
v(C–N–C) of the morpholine/piperidine ring undergo nega-
tive shift in the respective complexes. Also, bands assigned to
O
H
N
N
O
NH2
MMU
Scheme 1
Table 1 Analytical data and some physical properties of uranium(VI) peroxo complexes
Complex
Empirical formula (MW/g mol-1
)
Colour
Dec. temp/°C
K/S cm2 mol-1
[UO(O2)MBU(NO3)2]
[UO(O2)PBU(NO3)2]
[UO(O2)MBT(NO3)2]
[UO(O2)PBT(NO3)2]
[UO(O2)MMT(NO3)2]
[UO(O2)PMT(NO3)2]
[UO(O2)MMU(NO3)2]
C12H17N5O11U (645.32)
C13H19N5O10U (643.33)
C12H17N5O11SU (661.37)
C13H19N5O9SU (659.39)
C6H13N5O10SU (585.27)
C7H15N5O9SU (583.30)
C6H13N5O11U (569.21)
Lt. yellow
Yellow
[300
[280
[290
[300
[295
[310
[313
18
15
19
14
16
19
17
Yellow
Lt. yellow
Lt. yellow
Yellow
Yellow
123

Synthesis and characterization of peroxo complexes of uranium(VI)
93
Table 2 Selected FT-IR data (cm-1) for ligands and uranium(VI) peroxo complexes
Compound
v(NH)
v(C–N–C)
v(C=O)
v(C=S)
v(U=O)
v(O–O)
v
asym(UO2)
v
sym(UO2)
MBU
2,952
2,940
2,949
2,947
2,962
2,929
2,960
2,924
2,923
2,920
2,934
2,945
2,923
2,949
1,137
1,117
1,144
1,152
1,154
1,119
1,164
1,105
1,111
1,125
1,151
1,125
1,116
1,123
1,630
1,631
–
–
–
–
–
–
PBU
–
–
–
–
–
MBT
853
855
845
866
–
–
–
–
–
PBT
–
–
–
–
–
MMT
–
–
–
–
–
PMT
–
–
–
–
–
MMU
1,601
1,625
1,629
–
–
–
–
–
[UO(O2)MBU(NO3)2]
[UO(O2)PBU(NO3)2]
[UO(O2)MBT(NO3)2]
[UO(O2)PBT(NO3)2]
[UO(O2)MMT(NO3)2]
[UO(O2)PMT(NO3)2]
[UO(O2)MMU(NO3)2]
–
995
1,001
984
1,002
1,000
989
998
892
891
905
875
901
898
901
722
720
719
719
712
734
750
674
668
669
658
630
655
670
–
789
740
790
786
–
–
–
1,631
v(N–H) stretching of ligands appear at lower frequencies
in the corresponding complexes [UO(O2)MBU(NO3)2],
[UO(O2)PBU(NO3)2], and [UO(O2)MMU(NO3)2], indicating
bonding of the ligands through the carbonyl oxygen and ring
nitrogen of morpholine/piperidine. Ring nitrogen atoms of
alicyclic amines in a variety of ligands have been reported to
coordinate metal ions [50].
and [UO(O2)PBT(NO3)2] in an atmosphere of air and
nitrogen, respectively, at a heating rate of 10 °/min.
The TG curve (Fig. 1) for the complex [UO(O2)M-
BU(NO3)2] in an air atmosphere shows, initially, a sharp
weight loss starting from 23 to 500 °C which corresponds
to a weight loss of 14.1%. This weight loss approximates to
loss of peroxo and nitrate groups (theoretical weight loss
14.3%). The DTA curve of the complex contains an exo-
thermic peak at 173 °C, confirming loss of the peroxo
group as free dioxygen. Further heating up to 1,000 °C
shows a gradual weight loss of 2.6% (theoretical weight
loss 2.4%) attributable to loss of an oxo group. A broad
exothermic curve all along indicates oxidation of the
ligand.
In the spectra of the ligands MBT, MMT, PMT, and PBT a
sharp band assigned to v(C=S) of the thioamide group and a
band assigned to v(C–N–C) of the morpholine and piperidine
rings are shifted to lower frequencies in the corresponding
complexes [UO(O2)MBT(NO3)2], [UO(O2)MMT(NO3)2],
[UO(O2)PMT(NO3)2], and [UO(O2)PBT(NO3)2] (Table 2).
Another band assigned to v(N–H) stretching is also shifted to
lower position in complexes compared with the free ligands.
The shift of these characteristic bands of ligands to lower
frequencies after complexation indicates their coordination to
the metal.
The TG curve (Fig. 2) for the complex [UO(O2)PBT
(NO3)2] in nitrogen atmosphere shows initially a sharp
weight loss starting from 25 to 500 °C which is observed to
be 12.9%. This weight loss approximates to loss of nitrate
and a peroxo group (theoretical weight loss 14.3%). Further
heating up to 1,000 °C shows weight loss of 3.1% attrib-
utable to loss of an oxo group (theoretical weight loss
2.4%). A broad exothermic curve all along indicates oxi-
dation of the ligand.
In these complexes three additional bands which are not
present in the spectra of free ligands are observed. Of these, a
band appearing around 1,025–1,040 cm-1 is assigned to the
bending (m2) mode of the NO3 group. Two more bands in the
regions 1,425–1,465 and 1,350–1,390 cm-1 are assigned as
the m4 and m1 modes, respectively, of the coordinated nitrato
group. A difference in frequencies between the higher-energy
bands (Dm (m4 - m1) & 75 cm-1) suggests unidentate coor-
dination of the nitrato group [51, 52]. For bidentate
coordination of a nitrato group the difference should be in the
range of 120–180 cm-1 [53].
The TG/DTA curves of complexes of the same family,
although studied in different atmospheres, show almost the
same pattern of weight loss, indicating stability of the
complexes.
ESI mass spectral studies
TGA/DTA studies
ESI mass spectra were recorded for the complexes
[UO(O2)MBU(NO3)2] (1) and [UO(O2)PBT(NO3)2] (2).
Extensive fragmentation was observed for both complexes,
and only the most abundant fragment ions (with relative
TGA and DTA thermograms were recorded up to 1,000 °C
for two representative complexes [UO(O2)MBU(NO3)2]
123

94
B. Singh et al.
Fig. 1 TGA/DTA thermogram of [UO(O2)MBU(NO3)2]
Fig. 2 TGA/DTA thermogram of [UO(O2)PBT(NO3)2]
123

Synthesis and characterization of peroxo complexes of uranium(VI)
95
Table 3 Mass spectral data for uranium(VI) peroxo complexes
m/z (%)
M - 3* (%)
M* (%)
M ? 1* (%)
M ? 2* (%)
Complex 1
[UO(O2)C12H17N5O8] (645.32 g mol-1
[UO(O2)C12H17N5O8]?
[UOC12H17N5O8]?
[UOC12H17N4O5]?
[UOC12H17N3O2]?
[UC12H17N3O2]?
)
644.32 (10.07)
613.32 (28.56)
551.32 (0.53)
489.32 (0.89)
473.32 (0.35)
387.32 (3.57)
282.32 (100)
0.70
0.70
0.70
0.70
0.70
0.70
0.70
100
100
100
100
100
100
100
15.4
15.4
14.8
14.4
14.3
9.5
3.4
2.9
2.3
1.6
1.4
0.6
0.2
[UC8H9N2O]?
[UCH2NO]?
1.5
Complex 2
[UO(O2)C13H19N5O6S] (659.39 g mol-1
[UO(O2)C13H19N5O6 S]?
[UOC13H19N5O6 S]?
[UOC13H19N4O3 S]?
[UOC13H19N3S]?
[UC13H19N3 S]?
[UC8H9N2 S]?
[UCH2NS]?
)
658.39 (2.78)
627.39 (2.22)
565.39 (5.00)
503.39 (12.5)
487.39 (5.20)
403.39 (4.44)
298.39 (100)
0.70
0.70
0.70
0.70
0.70
0.70
0.70
100
100
100
100
100
100
100
17.2
17.2
16.7
16.2
16.1
10.3
2.3
7.8
7.3
6.7
6.0
5.8
5.0
4.5
2-
isotopic abundance) are given in Table 3. The molecular
ion peak for complex 1 was at m/z = 644.32 for the frag-
ment [UO(O2)C12H17N5O8]?; that for complex (2) was at
m/z = 658.39 for fragment [UO(O2)C13H19N5O6S]?.
Masses of the fragment ions listed in Table 3 were calcu-
lated using the uranium atomic mass equal to 238.05 amu.
For complex 1 the base peak appears at m/z = 282.32
corresponding to [UCH2NO]? and for complex 2 it appears
at m/z = 298.39 corresponding to [UCH2NS]?.
LMCT, p O2 ? U [48, 54]. There was no evidence of
any d–d transition. This result is consistent with the pres-
ence of the uranium(VI) system in the complexes.
1H NMR studies
1
The H NMR spectrum of the representative ligand MMU
was recorded in deuterated ethanol whereas that of com-
plex was recorded in deuterated DMF solution. The
spectrum of the ligand contains a triplet at d = 2.37 ppm
for N–CH2 of the morpholine ring and a triplet at 3.67 ppm
for O–CH2 of the morpholine ring. The methylidine pro-
tons of the H–CH–NH group appear as a doublet at 4.23
ppm. For the complex [UO(O2)MMU(NO3)2] the peaks
corresponding to the four protons of the –CH2 groups of N–
CH2 in the morpholine ring undergo a downfield shift to
2.49 ppm. This is because of coordination of the ring
nitrogen of morpholine with uranium.
In a similar way, the 1H NMR spectra of the ligand PMT
and the complex [UO(O2)PMT(NO3)2] were recorded in
deuterated ethanol and DMF solution, respectively. The
spectrum of the ligand contains a triplet at 2.24 ppm for N–
CH2 of the piperidine ring. The methylidine protons of the
H–CH–NH group appear at 3.72 ppm. For the complex
[UO(O2)PMT(NO3)2] the peaks corresponding to the four
protons of the –CH2 groups of N–CH2 in the piperidine
ring undergo a downfield shift to 2.67 ppm. This, again, is
because of coordination of the ring nitrogen of piperidine
with uranium.
Uranium has two isotopes having atomic masses of 235
and 238 amu. Their relative abundances are 0.70 and
100%, respectively. Here, the most intense isotope peak is
set to 100% and percentages for the other isotope peaks are
computed relative to this (Table 3). The molecular ion and
fragment peaks containing uranium appear as doublets at
M?* and M - 3?*, and the ratios of their relative inten-
sities confirm the presence of the U-235 and U-238
isotopes in the fragments. In addition M ? 1?* and
M ? 2?* peaks also appear because of the isotopic con-
tribution of C, H, N, O, and S atoms.
Electronic spectral studies
The electronic spectra of the metal complexes in the
UV–visible region (Table 4) were recorded in DMF solu-
tion at a concentration of 10-3 M. The spectra show three
transitions in the ranges 297–335, 345–367, and
373–398 nm ascribed to p ? p*, n ? p*, and the charge-
transfer transitions from uranyl oxygen ? uranium, i.e.
123

96
B. Singh et al.
PMT(NO3)2] the ring methylene carbon atoms linked to the
nitrogen atom are shifted downfield to 54.5 ppm. The
thiocarbonyl carbon is also shifted downfield (185.0 ppm)
because of coordination of the ligand to the metal through
the thiocarbonyl sulfur and ring nitrogen.
Table 4 Electronic spectral data (nm) of uranium(VI) peroxo
complexes
Complex
k/nm
[UO(O2)MBU(NO3)2]
[UO(O2)PBU(NO3)2]
[UO(O2)MBT(NO3)2]
[UO(O2)PBT(NO3)2]
[UO(O2)MMT(NO3)2]
[UO(O2)PMT(NO3)2]
[UO(O2)MMU(NO3)2]
297, 356, 380
324, 345, 375
335, 367, 390
321, 347, 373
320, 358, 398
331, 354, 395
315, 357, 397
Antifungal activity
Antifungal screening of the ligands and their uranium peroxo
complexes against the pathogen Fusarium vasinfectum was
carried out using potato dextrose agar (PDA) nutrient as the
medium. Zones developed on the plates were measured by
measuring the diameter of the inhibited zone in millimeters.
The zone of inhibition values are presented in Table 5. It is
evident from the table that the metal chelates are more active
than the free ligands. It is observed that on increasing the
concentration of the complexes, the colony diameter of the
fungus decreases and hence percentage inhibition increases
compared with the corresponding ligands. From these find-
ings it seems the prolonged activity of the complexes against
the chosen organism, compared with that of the free ligand,
might be because of diffusion of the metal complexes as a
whole through the cell membrane or because of the com-
bined effect of the metal and ligand. Such increased activity
of the metal chelates can be explained on the basis of
Overtone’s concept [55] and Tweedy’s chelation theory [56].
According to Overtone’s concept of cell permeability, the
membrane that surrounds the cell favours the passage of only
lipid-soluble materials which control antimicrobial activity.
On chelation, the polarity of the metal ion is substantially
reduced. This is because of overlap of the ligand orbital and
partial sharing of the positive charge of the metal ion with
donor groups. Further it increases the delocalisation of elec-
trons over the whole chelate ring and enhances the lipophilic
character of the metal complexes [57]. This increased lipo-
philicity leads to breakdown of the permeability barrier and
enables the complexes to penetrate into the lipid membrane.
13C NMR studies
The 13C NMR spectra of the representative ligand MMU
and the complex [UO(O2)MMU(NO3)2] were recorded in
deuterated ethanol and deuterated DMF solution, respec-
tively. The 13C spectrum of the ligand MMU contains four
peaks indicating four types of carbon atom. A peak at
d = 162.7 ppm is assigned to –NHCONH2 and another
peak at 65.7 ppm is attributed to –NH–CH2–N\. The
methylene carbon atoms of the morpholine ring appear at
50.4 and 66.5 ppm. In the complex [UO(O2)MMU(NO3)2]
the ring methylene carbon atoms linked to the nitrogen
atom are shifted downfield to 52.6 ppm. The carbonyl
carbon is also shifted downfield (165.1 ppm) because of
coordination of the ligand to the metal through the carbonyl
oxygen and ring nitrogen.
In a similar way the 13C NMR spectrum of the repre-
sentative ligand PMT and the complex [UO(O2)PMT
(NO3)2] were recorded in deuterated ethanol and deuterated
DMF solution, respectively. The 13C spectrum of the ligand
PMT contains five peaks indicating five types of carbon
atom. A peak at 182.6 ppm is assigned to –NHCSNH2 and
another peak at 70.8 ppm is attributed to –NH–CH2–N\.
The methylene carbon atoms of the piperidine ring appear
at 52.3, 25.6, and 25.9 ppm. In the complex [UO(O2)
Table 5 In vitro efficacy of complexes against Fusarium vasinfectum
Complex
Colony diameter
(mm) at 100 ppm
%Inhibition I = [(C - T)/C] 9 100
at 100 ppm
Colony diameter
(mm) at 200 ppm
%Inhibition I
at 200 ppm
Ligand
Complex
Ligand
Complex
Ligand
Complex
Ligand
Complex
[UO(O2)MBU(NO3)2]
[UO(O2)PBU(NO3)2]
[UO(O2)MBT(NO3)2]
[UO(O2)PBT(NO3)2]
[UO(O2)MMT(NO3)2]
[UO(O2)PMT(NO3)2]
[UO(O2)MMU(NO3)2]
48
42
49
43
41
47
45
39
35
38
36
32
37
39
36
44
35
43
45
37
40
48
53
49
52
57
51
48
37
32
36
33
35
40
39
28
25
29
26
27
22
23
51
57
52
56
53
47
48
63
67
61
65
64
71
69
Colony diameter of control C = 75 mm
123

Synthesis and characterization of peroxo complexes of uranium(VI)
97
Control
[UO(O2)MBU(NO3)2]
[UO(O2)PBT(NO3)2]
Fig. 3 Antifungal activity against Fusarium vasinfectum of complexes at 100 ppm
after decomposing the complex with concentrated nitric
acid [58]. Carbon, hydrogen, and nitrogen were analysed
microanalytically by use of a Leco model 932 CHNS
analyser; results agreed favourably with calculated values.
The total peroxide content of the complexes was deter-
mined by adding a weighed amount of the compound to a
cold solution of 1.5% (w/v) boric acid in 0.7 M sulfuric
acid (100 cm3) and then titrating with standard cerium(IV)
solution [59]. Molar conductivity of the complexes was
measured at room temperature, by use of a model 611E
digital conductivity metre with a conductivity cell with a
cell constant of 1.0 10%, using 10-3 molar solutions of
the complexes in DMF. Magnetic susceptibility measure-
ments were carried out by Gouy’s method at room
temperature using Hg[Co(NCS)4] as standard. IR spectra of
the complexes over the region4,000–400 cm-1 were recorded
on a Perkin–Elmer FT-IR model RX1 spectrophotometer,
using KBr discs. Melting points were determined on an
Analab melting point apparatus and mass spectral data were
obtained on a ESI-Esquire 3000 Bruker Daltonics spectrom-
eter. Electronic spectra over the region 200–900 nm were
recorded by use of a Systronics UV–visible single-beam
spectrophotometer, using 10-3 M DMF solutions of the
complexes. TGA/DTA studies were recorded on a Linseis
STA PT-1000 (Pyris Diamond) thermoanalyser at a heating
rate of 10°/min in atmospheres of air and nitrogen in the
temperature range 23–1,000 °C.
H2N
HN
O
S
O
C
U
O
CH
ONO2
O2NO
N
H
Scheme 2
The antifungal activity of [UO(O2)MBU(NO3)2] and
[UO(O2)PBT(NO3)2] is shown in Fig. 3.
On the basis of analytical, IR, UV–Vis, and mass
spectral data, pentagonal bipyramidal geometry was pro-
posed.
A representative structure for the complex
[UO(O2)PMT(NO3)2] is given in Scheme 2.
Experimental
Materials and physical measurements
All reagents used were chemically pure and analytical-
reagent grade. Solvents used were purified and dried
according to standard procedures [58]. Morpholine
(Ranbaxy), piperidine (SDS), benzaldehyde (Ranbaxy),
urea (Rankem), thiourea (NICE), formaldehyde (Ranbaxy),
uranyl nitrate (SISCO), and hydrogen peroxide (Merck)
were used as supplied. Analysis of uranium was carried out
gravimetrically as uranyl oxinate UO2(C9H6ON)2C9H7ON
Preparation of ligands
The ligands MBU, PBU, MBT, PBT, MMT, PMT, and
MMU were prepared by the reported method [60]. In a
typical reaction urea/thiourea (0.1 mol) in 20 cm3 ethanol
123

98
B. Singh et al.
Antimicrobial study
was mixed with piperidine/morpholine (0.1 mol) with
constant stirring to obtain a clear solution under cooling
with ice. To the resulting solution, benzaldehyde/for-
maldehyde (0.1 mol) was added dropwise with stirring for
15–20 min under cooling with ice. The reaction mixture
was then kept at room temperature for two days. The
colourless solid obtained was filtered, washed with distilled
water, and recrystallized from ethanol. The melting points
of the ligands MBU, PBU, MBT, PBT, MMT, PMT, and
MMU were 68, 69, 74, 72, 141, 120 and 162 °C, respec-
tively. These values are identical with the values reported
for the ligands in the literature [60].
The in-vitro biological effects of the compounds against
the pathogen Fusarium vasinfectum (Table 5) were tested
by the poisoned food method using PDA nutrient as the
medium. The test solutions were prepared by dissolving the
compounds in DMF. PDA mixed with test solution was
poured into sterilized Petri dishes. After solidification, the
plates were inoculated with a seven-day-old culture of the
pathogen by placing 2-mm sample in the centre of plates.
The inoculated plates were incubated at 27 °C for 4 days.
The linear growth of the fungus on control and treated
plates was recorded for different concentrations of the
complexes. Inhibition of the growth of Fusarium vasin-
fectum compared with control was calculated in accordance
with Vincent [62]:
Preparation of uranyl peroxo complexes
The peroxo complexes were synthesized by a reported
procedure [61]. In a typical reaction 0.502 g UO2(NO3)2ꢀ
6H2O (1 mmol) was dissolved in methanol. An equimolar
(1 mmol) methanolic solution (30 cm3) of the ligand
(Mannich base) was added to the uranyl nitrate solution
followed by addition of 0.1122 g potassium hydroxide
(2 mmol). The solution was heated under reflux for 15 min,
then 10 cm3 30% H2O2 was added dropwise and heated
under reflux for another hour. After cooling, the resulting
yellow precipitates were isolated by filtration and washed
successively with methanol and ether and dried in vacuo.
%Inhibition ðIÞ ¼ ½ðC ꢁ TÞ=Cꢂ ꢃ 100
where I is percentage inhibition, C is the growth of the
fungus (mm) on control plates, and T is the growth of the
fungus (mm) on treated plates.
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