Synthetic and structural studies of piperidine carboxamide uranyl ion complexes

Article abstract of DOI:10.1016/j.poly.2014.05.037

New piperidine based ligands of the type [C₅H ₁₀NCONR₂] (where R = CH₃ (L1), C ₂H₅ (L2) and ⁱC₃H₇ (L3)) have been prepared and characterized. The complex ch

Full text of DOI:10.1016/j.poly.2014.05.037

Accepted Manuscript
Synthetic and structural studies of piperidine carboxamide uranyl ion complexes
D. Das, B.G. Vats, S. Kannan, Mukesh Kumar, M.K. Sureshkumar
PII:
S0277-5387(14)00353-2
DOI:
http://dx.doi.org/10.1016/j.poly.2014.05.037
POLY 10751
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
17 February 2014
13 May 2014
Please cite this article as: D. Das, B.G. Vats, S. Kannan, M. Kumar, M.K. Sureshkumar, Synthetic and structural
studies of piperidine carboxamide uranyl ion complexes, Polyhedron (2014), doi: http://dx.doi.org/10.1016/j.poly.
2
014.05.037
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Synthetic and structural studies of piperidine carboxamide uranyl ion
complexes.
a
D. Das , B.G. Vats , S. Kannan *, Mukesh Kumar* and M. K. Sureshkumar
b
b
c
a
a
Fuel Reprocessing Division Bhabha Atomic Research Centre, Mumbai, India- 400085.
Fuel Chemistry Division, Bhabha Atomic Research Centre, Mumbai, India- 400085.
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, India- 400085.
b
c
ABSTRACT
New piperidine based ligands of the type [C
5
H
10NCONR
2
] (where R = CH
(L3)) have been prepared and characterized. The complex chemistry of these
ligands with uranyl chloride, bromide, nitrate and β-diketonates has been studied using IR and
NMR spectroscopic methods. Crystal structures for the complexes [UO Cl (L3) ] (1),
UO Br (L3) ] (2) [UO (NO (L3) ] (5) and [UO (C SCOCHCOCF (L3)] (8) have been
3
(L1), C
2
H
5
i
(
L2) and C
3
H
7
2
2
2
[
2
2
2
2
3
)
2
2
2
4
H
3
)
3 2
determined by the X-ray diffraction method. The structures of 1 and 2 show that the uranyl ion is
surrounded by two of the ligands and two halogen atoms in an octahedral geometry. The
structure of 5 shows that the uranyl group is surrounded by two nitrate groups and two ligands in
a hexagonal bipyramidal geometry. The structure of 8 shows that the uranyl group is surrounded
by two β-diketonates and one ligand in a pentagonal bipyramidal geometry. The structures show
that the carboxamide ligands are strongly bonded to the uranyl group, showing a near linear
geometry for the U-O-C bond (angle 150-159°). The prepared chloro and bromo compounds are
air and moisture stable and show good solubility in normal organic solvents.
Keywords: Piperidine carboxamide, Uranyl Chloride, Bromide, Nitrate, β-Diketonate, Structures

*
Corresponding author: Email : skannan@barc.gov.in (S. Kannan) and mukeshk@barc.gov.in
(
Mukesh Kumar)
1
. Introduction
Actinide separation from high level liquid waste emanating from the back end fuel cycle
of the nuclear industry is very challenging [1]. Study of actinide coordination chemistry with
various extractants containing different functional groups is very much essential to develop the
technologies for the reprocessing of the irradiated fuel and safe handling of the actinides [2-6].
N-substituted amides are proposed to be very promising extractants for the solvent extraction
removal of actinides from other fission products in nitric acid medium [7-11]. Their ease of
synthesis, complete incinerability and high stability constants with actinides make them very
good competitors with respect to tributyl phosphate. Moreover, the solvent extraction ability of
uranium(VI) from acidic medium can be enhanced by using a mixture of β-diketone and neutral
ligands [12]. Previously, we reported the chemistry of isobutyramide based ligands with
uranium(VI) ions and showed that the ligands selectively separate the uranium(VI) ion from a
large excess of thorium and lanthanide ions [13]. This property indicates their applicability as
2
33
suitable extractants for the selective partitioning of U in AHWR spent fuel reprocessing [14].
In addition, isobutyramide based ligands form air and moisture stable uranyl halide compounds
and these compounds are used as synthetic precursors for making uranyl halide compounds [15].
In continuation of our interest in the chemistry of the uranyl ion with newly synthesized ligands,
we report herein the synthesis, characterization and complex chemistry of piperidine based
carboxamide ligands with uranyl chloride, bromide, nitrate and β-diketonates.

2
. Experimental
2
.1 Materials and methods
All the chemicals were purchased from commercial source and used without further
purification. Infrared spectra were recorded using a JASCO-610 FITR spectrometer as KBr
-1
pellets in the range 400-4000 cm . NMR spectra were recorded on a Brucker AMX-300
spectrometer using CDCl as the solvent.
3
2
.2 Synthesis of L1
To a solution of N,N-dimethyl carbamoyl chloride (10.75 g, 0.1 mol) in (50 mL)
benzene, a solution of piperidine (8.52 g, 0.1 mol) and triethyl amine (12.1 g, 0.12 mol) in
benzene (50 mL) was added slowly with stirring. The reaction mixture was refluxed for 2 hours
and treated with 100 ml. of 5% HCl solution. The organic layer was separated, dried over
anhydrous sodium sulfate and filtered. The solution on evaporation yielded a colorless liquid.
Yield: 62%. Anal. Found: C, 60.5; H, 10.1; N, 17.5. Calcd. for C
8
H
16
N
2
O: C, 61.5; H,10.25; N,
1
1
1
7.9 % . H NMR (CDCl
3
, 25 °C) δ: 2.85 (br, 4H, 2,6-piperidyl CH
2
), 2.50 (s, 6H, N(CH ),
3 2
)
−
1
.26 (br, 6H, piperidyl CH ). IR (cm ) ν: 1653 (C=O).
2
2
.3 Synthesis of L2
This was prepared similarly to L1 in 76% yield by taking N,N-diethyl carbamoyl
chloride. Anal. Found: C, 64.5; H, 10.3; N, 15.5. Calcd. for C10
H
20
N
2
O: C, 65.2; H, 10.9; N, 15.2
and N(C CH ), 1.55 (br, 6H,
). IR (cm ) ν: 1622 (C=O).
1
%
. H NMR (CDCl
3
, 25 °C) δ: 3.15 (8H, 2,6-piperidyl CH
2
2
H
5
)
2
2
-
1
3
,4,5-piperidyl CH
2
), 1.09 (t, J = 7.0 Hz, 6H, N(C CH
2
H
5
)
2
3

2
.4 Synthesis of L3
This was prepared similarly to L1 in 94% yield by taking N,N-diisoproyl carbamoyl
chloride. Anal. Found: C, 66.6; H, 10.7; N, 13.0. Calcd. for C12 O: C, 67.9; H, 11.3; N, 13.2
) CH), 2.91 (br, 4H, 2,6-piperidyl CH ), 1.44
). IR (cm ) ν: 1651 (C=O).
H
24
N
2
1
i
%
. H NMR (CDCl
3
, 25 °C) δ: 3.48 (m, 2H, N( Pr
2
2
i
-1
(
br, 6H, 3,4,5-piperidyl CH
2
), 1.15 (d, J = 6.6 Hz, 12H, N( Pr
2
) CH
3
2
.5 Synthesis of 1
Solid UO
3
(300 mg) was dissolved in 4 mL of concentrated HCl and the volume of the
solution was reduced completely to dryness on a hot plate. The orange colored solid thus
obtained was dissolved in 10 mL of methanol to give a clear solution. To this solution N,N-
diisopropylpiperidine-1-carboxamide was added and heated for 2 min. The volume of the
solution was reduced to 2mL, and 20 mL of diethyl ether was added into it with stirring. The
yellow product formed was filtered, washed with ether and dried in air. This product was
recrystallized from a chloroform/isooctane mixture to give a crystalline solid. Yield 89%. Anal.
-1
Found: C, 37.2; H, 6.0; N, 7.2. Calcd. for C24
H
48
N
4
O
4
Cl U: C, 37.6; H, 6.3; N, 7.3 %. IR (cm )
2
ν: 1524 (C=O), 924 (U=Oassy).
2
.6 Synthesis of 2
This was synthesized similar to 1, by taking concentrated HBr instead of HCl. Yield
5%. Anal. Found: C, 33.2; H, 5.2; N, 6.2. Calcd. for C24 Br U: C, 33.7; H, 5.6; N, 6.6
8
H
48
N
4
O
4
2
-1
%
. IR (cm ) ν: 1525 (C=O), 928 (U=Oassy).
2
.7 Synthesis of 3

To a solution of N,N-dimethylpiperidine-1-carboxamide (200 mg, 1.29 mmol) in
chloroform, solid UO (NO .6H O (300 mg, 0.59 mmol) was added with stirring. The solution
2
3
)
2
2
was allowed to stir until all the uranyl nitrate dissolved to give a clear solution. This solution was
filtered and layered with isooctane. This solution on slow evaporation yielded a yellow
crystalline solid. This was filtered, washed with hexane and air dried. Yield: 89%. Anal. Found:
1
C, 26.7; H, 4.2; N, 11.5. Calcd. for C16
H
32
N
6
O
10U: C, 27.2; H, 4.5; N, 11.9 %. H NMR (CDCl
3
,
2
5 °C) δ: 3.55 (br, 4H, 2,6-piperidyl CH
2
), 3.14 (s, 6H, N(CH
3
2
) ), 1.63 (br, 6H, 3,4,5-piperidyl
-1
CH
2
). IR (cm ) ν: 1525 (C=O), 925 (U=Oassy).
2
.8 Synthesis of 4
This was prepared similarly to 3 by taking UO
2
(NO
3
)
2
.6H O (300 mg, 0.59 mmol) and
2
N,N-diethylpiperidine-1-carboxamide (240 mg, 1.3 mmol). Yield 86%. Anal. Found: C, 31.1; H,
1
4
3
6
.8; N, 10.7. Calcd. for C20
H
40
N
6
O
10U: C, 31.5; H, 5.2; N, 11.0 %. H NMR (CDCl
3
, 25 °C) δ:
), 1.26 (s,
.52 (br, 8H, 2,6-piperidyl CH
2
and N(C
2
H
5
)
2
CH
2
), 1.63 (br, 6H, 3,4,5-piperidyl CH
2
-
1
H, N(C
2
5
H )
2
CH
3
). IR (cm ) ν: 1521 (C=O), 928 (U=Oassy).
2
.9 Synthesis of 5
This was prepared similarly to 3 by taking UO
2
(NO
3
)
2
.6H O (300 mg, 0.59 mmol) and N,N-
2
diisopropylpiperidine-1-carboxamide (270 mg, 1.27 mmol). Yield 85%. Anal. Found: C, 35.1; H,
1
5
3
1
.8; N, 10.1. Calcd. for C24
H
48
N
6
O
10U: C, 35.2; H, 5.9; N, 10.2 %. H NMR (CDCl
3
, 25 °C) δ:
),
i
.90 (br, 2H, N( Pr
2
) CH), 3.40 (br, 4H, 2,6-piperidyl CH
2
), 1.56 (br, 6H, 3,4,5-piperidyl CH
2
i
-1
.41 (d, J = 6.0 Hz, 12H, N( Pr
2
) CH
3
). IR (cm ) ν: 1522 (C=O), 932 (U=Oassy).

2
.10 Synthesis of 6
To a dichloromethane solution of N,N-dimethylpiperidine-1-carboxamide (70 mg, 0.44
mmol), solid UO (C S) .2H O (300 mg, 0.4 mmol) was added and refluxed for 2 hours
2
8
H
5
F
3
O
2
2
2
with constant stirring. This solution was filtered and layered with isooctane. This solution on
slow evaporation yielded bright yellow colored needle shaped crystals in 94% yield. Anal.
1
Found: C, 32.8; H, 2.7; N, 3.1. Calcd. for C24
H
24
N
2
O
7
F
6
S
2
U: C, 33.2; H, 2.8; N, 3.2 %. H NMR
(
CDCl
3
, 25 °C) δ: 8.26 (s, 2H, thiophene CH), 7.83 (t, J = 6.6 Hz, 2H, thiophene CH), 7.28 (q, J
4.5 Hz, 2H, thiophene CH), 6.79 (s, 2H, TTA CH), 3.59 (br, 4H, piperidyl CH ), 3.22 (s, 6H,
). IR (cm ) ν: 1618 (C=O, TTA), 1540 (C=O, L1), 919
=
2
-1
N(CH
3
)
2
), 1.63 (br, 6H, piperidyl CH
2
(
U=Oassy).
2
.11 Synthesis of 7
This was prepared similarly to 6 in 89% yield by taking [UO
2
(C
8
H
5
F
3
O
2
S)
2
.2H O] (300
2
mg, 0.4 mmol) and N,N-diethylpiperidine-1-carboxamide (80 mg, 0.43 mmol). Anal. Found: C,
1
3
2
4.6; H, 2.9; N, 3.0. Calcd. for C26
H
28
N
2
O
7
F
6
S
2
U: C, 34.8; H, 3.1; N, 3.1 %. H NMR (CDCl
3
,
5 °C) δ: 8.26 (br, 2H, thiophene CH), 7.84 (br, 2H, thiophene CH), 7.28 (d, J = 4.7 Hz, 2H,
and N(C CH ), 1.61 (br,
). IR (cm ) ν: 1591 (C=O, TTA), 1539 (C=O,
thiophene CH), 6.79 (s, 2H, TTA CH), 3.52 (br, 8H, piperidyl CH
2
2
H
5
)
2
2
-1
6
H, piperidyl CH
2
), 1.23 (br, 6H, N(C
2
H
5
)
2
CH
3
L2), 922 (U=Oassy
)
2
.12 Synthesis of 8
This was prepared similarly to 6 in 88% yield by taking [UO
mg, 0.4 mmol) and N,N-diisopropylpiperidine-1-carboxamide (90 mg, 0.42 mmol). Anal. Found:
2
(C
8
H
5
F
3
O
2
S)
2
.2H O] (300
2

1
C, 35.8; H, 3.0; N, 3.0. Calcd. for C28
H
32
N
2
O
7
F
6
S U: C, 36.4; H, 3.5; N, 3.0 %. H NMR
2
(
CDCl
3
, 25 °C) δ: 8.25 (t, 2H, thiophene CH), 7.82 (d, 2H, thiophene CH), 7.29 (br, 2H,
i
thiophene CH), 6.79 (s, 2H, TTA CH), 3.91 (s, 2H, N( Pr
2
i
) CH), 3.46 (s, 4H, piperidyl CH ),
2
-1
1
.56 (s, 6H, piperidyl CH
2
), 1.46 (d, J = 6.6 Hz, 12H, N( Pr
2
) CH
3
). IR (cm ) ν: 1618 (C=O,
TTA), 1540 (C=O, L3), 922 (U=Oassy).
2
.13 Synthesis of 9
To a solution of N,N-dimethylpiperidine-1-carboxamide (80 mg, 0.51 mmol) in
dichloromethane, solid UO (C COCHCOC .2H O (350 mg, 0.47 mmol) was added and
2
6
H
5
6
H
5
)
2
2
the resulting mixture was refluxed for 2 hours with constant stirring. The solution was filtered
and layered with dodecane. This on slow evaporation yielded an orange red crystalline solid
product in 92% yield. Anal. Found: C, 51.8; H, 3.9; N, 3.0. Calcd. for C38
H
38
N
2
7
O U: C, 52.3; H,
1
4
.4; N, 3.2 % . H NMR (CDCl
3
, 25 °C) δ: 8.46 (d, 8H, Ph, DBM), 8.0 (d, 4H, Ph, DBM), 7.58
), 3.14 (br, 6H,
). IR (cm ) ν: 1591 (C=O, DBM), 1542 (C=O, L1), 907
(
br, 8H, Ph, DBM), 7.24 (s, 2H, CH, DBM), 3.53 (br, 4H, piperidyl CH
2
-1
N(CH
3
)
2
), 1.55 (br, 6H, piperidyl CH
2
(
U=Oassy).
2
.14 Synthesis of 10
This was
(C COCHCOC
prepared
.2H
similarly
to
9
in
94%
yield
by
taking
[
UO
2
6
H
5
6
H
5
)
2
2
O] (350 mg, 0.47 mmol) and N,N-diethylpiperidine-1-
carboxamide (90 mg, 0.49 mmol). Anal. Found: C, 52.8; H, 4.5; N, 3.0. Calcd. for C40
H
42
N
2
7
O U:
1
C, 53.3; H, 4.7; N, 3.1 %. H NMR (CDCl
3
, 25 °C): δ 8.49 (br, 8H, DBM Ph), 8.0 (d, 4H, DBM
and N(C
Ph), 7.58 (s, 8H, DBM Ph), 7.25 (s, 2H, DBM CH), 3.53 (br, 8H, piperidyl CH
2
2
H )
5 2

-1
CH
2
), 1.52 (s, 6H, piperidyl CH
2
), 1.23 (t, J = 6.6 Hz, 6H, N(C
2
5
H )
2
CH ). IR (cm ) ν: 1591
3
(
C=O, DBM), 1542 (C=O, L2), 905 (U=Oassy).
2
.15 Synthesis of 11
This was
(C COCHCOC
prepared
.2H
similarly
to
9
in
89%
yield
by
taking
[
UO
2
6
H
5
6
H
5
)
2
2
O] (350 mg, 0.47 mmol) and N,N-diisopropylpiperidine-1-
carboxamide (105 mg, 0.5 mmol). Anal. Found: C, 53.9; H, 4.5; N, 2.8. Calcd. for C42
H
46
N
2
7
O U:
1
C, 54.3; H, 4.9; N, 3.0 %. H NMR (CDCl
3
, 25 °C) δ: 8.61 (br, 4H, DBM Ph), 8.40 (br, 4H,
DBM Ph), 8.0 (d, 4H, DBM Ph), 7.59 (s, 8H, DBM Ph), 7.27 (s, 2H, DBM CH), 3.94 (s, 2H,
i
i
-1
N( Pr
2
) CH), 3.42 (s, 4H, piperidyl CH
2
), 1.49 (s, 18H, piperidyl CH
2
and N( Pr
2
) CH ). IR (cm )
3
ν: 1592 (C=O, DBM), 1541 (C=O, L3), 901 (U=Oassy).
2
.16 Crystallography
Crystal data for 1, 2, 5 and 8 were measured on an Agilent SuperNova system equipped
with a Titan CCD detector at 293(2) K using CuK radiation (λ = 1.5418 Å). The crystals were
α
positioned 101 mm from the CCD. 1008, 643, 1750 and 1016 frames were measured respectively
for compounds 1, 2, 5 and 8 with a counting time of 1s. Data analysis was carried out with the
CrysAlis program [16a]. The structures were solved using direct methods with the Shelxs97
program [16b]. All non-hydrogen atoms were refined with anisotropic thermal parameters. The
hydrogen atoms bonded to carbon atoms were included in the geometric positions and given
thermal parameters equivalent to 1.2 times those of the atoms to which they were attached.
Empirical absorption corrections were carried out using the ABSPACK program [16c]. The

2
structures were refined to convergence on F using Shelxl972 [16b]. Selected crystallographic
data for 1, 2, 5 and 8 are given in Table 1 .
3
. Results and Discussion
3
.1 Synthesis of the piperidine carboxamide ligands.
Ligands L1-L3 were prepared by reacting piperidine and N,N’-dialkyl carbamoyl
chloride in presence of triethyl amine ( Scheme 1). The IR spectra of all ligands show the
1
presence of carbamoyl group in the synthesized ligands. The H NMR spectra of all the ligands
show the expected peaks and integrations.
3
.2 Synthesis of piperidine carboxamide uranyl halo compounds
The reaction of [UO ⋅nH O] (X = Cl or Br) with the ligand L3 yielded compounds 1
2
X
2
2
and 2 ( Scheme 1). However, similar reactions with L1 and L2 yielded hydroscopic products
which were therefore not characterized. C, H and N analyses of 1 and 2 revealed that the ratio of
ligand to uranyl halide is 2:1 in both compounds. The IR spectra of 1 and 2 show that the water
molecules from the starting compounds [UO
2
X
2
⋅nH O] are replaced completely by the ligand.
2
-1
The observed frequency difference for the carbamoyl group (∆νCO = 125 cm , where ∆νCO
=
ν
CO(free ligand) - νCO(coordinated)) shows that the carbamoyl group is bonded to the uranyl group
directly. This difference is comparable/greater in magnitude than those observed in
i
i
i
i
[
UO
2
X
2
{ C
3
H
7
CON( C
4
H
9
)
2
}
2
] (X = Cl or Br) [15], [[UO
2
(NO
3
)
2
{ C
3
H
7
CON( C
4
H
9
)
2
2
} ] [13]
UO (NO
2
3
)
2
(N-cyclohexyl,2-pyrrolidone)
2
] [17]
,
[UO
2
(NO
3
)
2
(1,3-dimethyl,2-imidazolidone) ]
2
i
i
[
17] and [UO
2
(NO
3
)
2
( C
3
H
7
)
2
NCOCH
2
CON( C
3
H )
7 2
] [18].
1
The H NMR spectra of 1 and 2 show the expected peaks and integrations. All the
protons are deshielded with respect to the free ligand indicating that the bonding between the

ligand and uranyl group persists in solution. It is apparent from the IR and NMR spectra that the
ligand bonds through the carbamoyl groups to the uranyl group. The structures of 1 and 2 have
been determined by the single crystal X-ray diffraction method, which confirms these spectral
results.
3
.3 Structure of 1 and 2
The structures of 1 and 2 are shown in Figures 1 and 2, respectively, and selected bond
distances and angles are given in Table 2. The structures of both 1 and 2 show a centrosymmetric
uranium(VI) ion surrounded by four oxygen atoms and two halogen atoms in an octahedral
geometry. The two uranyl oxygen atoms occupy the axial positions. Two oxygen atoms of the
two piperidine carboxamide ligands together with two halogen atoms form the equatorial square
plane.
This type of coordination is similar to that observed in the compounds of uranyl chloro or
i
i
bromo compounds such as [UO
OPPh ] [19] with monodentate ligand. The average U-O(amide) distance of 2.322(10) Å in 1
and 2.317(5) Å in 2 are comparable in magnitude with those of earlier reported uranyl halide-
2
X
2
{ C
3
H
7
CON( C
4
H
9
)
2
}
2
] (X = Cl or Br) [15] and [UO
2
Cl
2
(
)
3 2
i
i
amide compounds [UO
X = Br) [15]. The observed average U-Cl bond distance 2.683(5) Å in 1 and U-Br distance
.8073(10) Å in 2 are normal [13,19]. The angles subtended at the metal atom show that the
uranium atom has a slightly distorted octahedral geometry.
2
X
2
{ C
3
H
7
CON( C
4
H
9
)
2
}
2
] (2.3151(18) Å for X = Cl and 2.281(4) Å for
2
3
.4 Synthesis of uranyl nitrate piperidine carboxamide compounds

The reaction of ligands L1-L3 with [UO
). C, H and N analyses revealed that the ratio of ligand to uranyl nitrate is 2:1 in all the
compounds. The IR spectra of 3-5 show that the water molecules from the starting compound
UO (NO ⋅6H O] are completely replaced by the ligand and the ligand is bonded through the
carbamoyl oxygen atom to the uranyl group. The observed frequency difference for the
2
(NO
3
)
2
⋅6H
2
O] yielded compounds 3-5 (Scheme
1
[
2
3
)
2
2
-1
carbamoyl group (∆νCO = 120 cm , where ∆νCO = νCO (free ligand) - νCO(coordinated)) is consistent with
the supposition that the carbamoyl group is bonded to the uranyl group directly. This difference
is comparable in magnitude with those observed in [UO
2
(NO
] [17], [UO (NO
] [18].
3
)
2
(N-cyclohexyl,2-pyrrolidone) ]
2
i
i
[
17], [UO
2
(NO
3
)
2
(1,3-dimethyl,2-imidazolidone)
2
2
3
)
2
{ C
3
H
7
CON( C
4
H
9
)
2
2
} ] [13]
i
i
and [UO
2
(NO
3
)
2
( C
3
7
H )
2
N COCH
2
CON( C
3
H )
7 2
1
The H NMR spectra of 3-5 show the expected peaks and integrations. The protons of the
piperidine carboxamide ligands are deshielded by ca. 0.5-0.8 ppm with respect to the free ligand,
indicating that the bonding between the carbamoyl oxygen and uranyl group persists in solution.
The structure of 5 has been determined by single crystal X-ray diffraction methods and confirms
the spectral results.
3
.5 Structure of 5
The structure of 5 is shown in Figure 3, and selected bond distances and angles are given
in Table 2. The structure of 5 shows that the uranium atom is surrounded by eight oxygen atoms
in a hexagonal bipyramidal geometry. Six oxygen atoms of the two bidentate nitrate groups
together with two oxygen atoms of piperidine carboxamide ligands form the equatorial
hexagonal plane. The two uranyl oxygen atoms occupy the axial positions.

This type of coordination is similar to that observed in the compounds of monodentate
ligands with uranyl nitrate, such as [UO (NO (N-cyclohexylmethyl,2-pyrrolidone) ] [17],
] [17], [UO ] [13],
(tetrabutylglutaramide) ],
)CO(CH )NPh) ] [22]. The
2
3
)
2
2
i
i
[
[
[
UO
UO
UO
2
2
2
(NO
(NO
(NO
3
3
3
)
2
(1,3-dimethyl,2-imidazolidone)
)(DMF) [20],
(tetrabutylglutaramide) ] [21] and [UO
2
2
(NO
[UO
(PhN(CH
3
)
2
{ C
3
H
7
CON( C
4
H
9
)
}
2 2
2
]
2
(NO
3
)
2
2
)
2
2
2
(NO
3
)
2
3
3
2
U-O(amide) distance (2.378(6) Å) in 5 is comparable in magnitude with those of earlier reported
uranyl nitrate-amide compounds, such as UO (NO (N-cyclohexylmethyl,2-pyrrolidone)
(1,3-dimethyl,2-imidazolidone) (2.383(2) Å) [17],
] (2.349(6) Å) [13], [UO (NO )(DMF) ] (2.397(6) Å) [20],
(tetrabutylglutaramide) ] (2.378(6) Å), [UO (NO (dibutyldecanamide) ] (2.37(2)
(NO (PhN(CH )CO(CH )NPh) ] (2.381(2) Å) [22]. The observed average U-
) bond distance of 2.527(9) Å is normal. The angles subtended at the metal atom show
that the uranium atom has a slightly distorted hexagonal bipyramidal geometry.
2
3
)
2
2
]
(
[
[
2.374(2) Å) [17], [UO
2
(NO
3
)
2
2
]
i
i
UO
2
2
(NO
3
3
)
2
2
{ C
3
H
7
CON( C
4
H
9
)
2
}
2
2
3
2
UO
(NO
)
2
2
3
)
2
2
Å) [21] and [UO
2
3
)
2
3
3
2
O(NO
3
3
.6 Synthesis of uranyl bis( β-diketonates) piperidine carboxamide compounds
The reactions of L1-L3 with [UO (OO) .2H O] (OO = C SCOCHCOCF
COCHCOC ) yielded the compounds 6-11 ( Scheme 1). C, H and N analyses revealed
2
2
2
4
H
3
3
or
C
6
H
5
6
H
5
that the ratio of ligand to uranyl bis(β-diketonate) is 1:1 in all the compounds. The IR spectra of
-11 show that the water molecules from the starting compound [UO (OO) .2H O] are
completely replaced by the ligand and furthermore the observed frequency difference for the
6
2
2
2
-1
carbamoyl group (∆νCO = 100-120 cm , where ∆νCO = νCO (free ligand) - νCO(coordinated)) is
consistent with the supposition that the carbamoyl group is bonded to the uranyl group directly.
This
difference
is
comparable
in
magnitude
with
those
observed
in

i
i
[
[
UO
2
2
(DBM)
(NO
2
{ C
3
H
7
CON( C
3
H
7
)
2
}
2
] [13], [UO
2
(NO
3
)
2
(N-cyclohexyl,2-pyrrolidone) ] [17] and
2
UO
3
)
2
(1,3-dimethyl,2-imidazolidone)
2
] [17].
1
The H NMR spectra of 6-11 show the expected peaks and integrations. The piperidine
carboxamide protons are deshielded by ca. 0.5 ppm with respect to the free ligand, indicating that
the bonding between the ligand and uranyl group persists in solution. The structure of 8 has been
determined by the single crystal X-ray diffraction method and confirms the spectral and analysis
results.
3
.7 Structure of 8.
The structure of 8 is shown in Figure 4 together with the numbering scheme, and selected
bond distances and angles are given in Table 2. The structure shows that the uranyl group is
bonded to two C SCOCHCOCF groups and one piperidine carboxamide ligand to give a
4
H
3
3
coordination number of seven. The piperidine carboxamide ligand acts as a monodentate ligand
and is bonded through the carbamoyl oxygen to the uranyl group. Four oxygen from two
bidentate C
4
H
3
SCOCHCOCF groups and one oxygen from the piperidine carboxamide ligand
3
form the equatorial plane, which together with two oxygen atoms of the uranyl group form a
pentagonal bipyramidal geometry around the uranium(VI) ion. The thiophene ring is disordered
due to 180° rotation of this ring about the C16-C17 and C24-C25 bonds. A hybrid scattering
factor consisting of 50% sulfur and 50% carbon was used to model this disorder.
Similar structures are also observed in the compounds of phosphine oxides, sulfoxides,
ketones, N-oxides and amides with uranyl bis(β-diketoantes), viz: [UO
2
(DBM)
(TTA) (C
)] [13] . The observed U-O
2
(OPPh
3
)] [23],
[
[
UO
2
2
(DBM)
(TTA)
2
(C
6
H
5
CH
2
SOCH
3
)] [24], [UO
2
(TTA)
2
(DBA)] [25], [UO
2
2
5
H
5
NO)] [26],
i
i
UO
2
(camphor)] [27] and [UO
2
(DBM)
2
( C
3
H
7
CON{ C
3
H )
7 2

amide bond distance (2.375(5) Å) is comparable in magnitude with that reported in
i
i
[
UO
2
(DBM)
2
( C
3
H
7
CON{ C
3
H
7
)
2
)] (2.379(5) Å) [13] .
The observed M-O(amide) bond distances ( 2.322(10), 2.317(5) and 2.376(6) Å) and M-O-
C bond angles (154.9, 155.20 and 149.3°) in the uranyl, chloro, bromo and nitrate compounds
show clearly that the piperidine based amide ligand forms relatively weaker complexes with the
uranyl ion as compared to those of the corresponding iso-butyramide based ligands (2.3151(18)
Å, 160.83(15)°, 2.281(14) Å, 171.9(6)° and 2.349(6) Å, 171.2(6)° respectively for the chloro,
bromo and nitrate compounds). Interestingly, the chloro and bromo compounds of L3 are stable
to air and moisture and are soluble in normal organic solvents, whereas those with L1 and L2 are
hydroscopic, giving insoluble products.
4
. Conclusions
In conclusion, the piperidine based amide ligands form 2:1 complexes with uranyl
chloride, bromide and nitrate and 1:1 complexes with the uranyl bis(β-diketonates). The uranyl
chloro and bromo compounds are air and moisture stable and soluble in common organic
solvents. The structures of the chloro and bromo complexes show that the uranium(VI) ion is
surrounded by two halogen, two uranyl and two amido oxygen atoms in an octahedral geometry.
The structures of the uranyl nitrate and uranyl bis( β-diketonates) complexes show hexagonal
bipyramidal and pentagonal bipyramidal geometries respectively around the uranium(VI) ion .
Acknowledgements
We wish to thank Dr. S. K. Aggarwal, Associate Director, Radiochemistry and Isotope
Group and Head, Fuel Chemistry Division for his support. We also wish to thank, Dr. V. K. Jain,

Head Chemistry Division for NMR Spectra and C,H,N analysis. D.D wishes to thank Shri. P.M.
Gandhi, Head, Fuel Reprocessing Division for his support and encouragement.
Appendix A: Supplementary data
Electronic Supplementary Information (ESI) is available. CCDC 980684, 980685 980686
and 980687 contain the supplementary crystallographic data for 1, 2, 5 and 8 respectively. These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from
the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax:
(
+44) 1233-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
References
[
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[
[
3] L.R. Morss, N.M. Edelstein, J. Fuger, J. J. Katz, The Chemistry of the Actinide and
Transactinide Elements, Springer, The Netherlands, 2006.
[
[
[
[
[
4] S. C. Bart, K. Meyer, Struct. Bond. 127( 2008 ) 119
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[
9] C. Musikas, Inorg. Chim. Acta, 140 (1987) 197.

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[
10] Z.X, Zhu, Y. Sasaki, H. Suzuki, S. Suzuki, T. Kimuta, Anal. Chim. Acta, 527
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(
11] Y. Sasaki, Y.Tsubata. Y. Kitatsuji, Y. Sugo, N. Shirasu, Y. Morita, T. Kimura, Solv.
Extr. Ion Exch. 31( 2013) 401.
[
[
[
[
[
12] V. V. Ramakrishna, S. K. Patil, Structure Bonding. 56 (1984) 35.
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(
b) G. M. Sheldrick, Shelxs97 and Shelxl97, program for crystallographic solution and
refinement, Acta Crystallogr. A64 (2008) 112.
(
c) ABSPACK (2005) Oxford Diffraction Ltd, Oxford, U.K.
17] N. Koshino, M. Harada, M. Nogami, Y. Morita, T. Kikuchi, Y. Ikeda, Inorg. Chim.
Acta, 358 (2005) 1857
[
[
[
18] G. J. Lumetta, B. K. McNamara, B. M. Rapko, R. L. Sell, R. D. Rogers, G. Broker, J. E.
Hutchison, Inorg. Chim. Acta, 309 (2000) 103.
19] (a) G. Bombieri, E. Forsellini, J. P. Day, W. I. Azeez, Dalton Trans. (1978) 677;
(
b) S. B. Akona, J. Fawcett, J. H. Holloway, D. R. Russel, I. Leban, Acta Crystallogr.
C47 (1991) 45.
[
20] J. M. Gil, F. J. M. Gil, A. Perales, J. Fayos, M. M. Ripoll, Acta Crystallogr. C39
(
1983) 44.
[
[
21] P. Charpin, M. Lance, M. Nierlich, D. Vigner, Acta Crystallogr. C42 (1986) 560.
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[
[
[
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Natarajan, Acta Crystallogr. E59 (2003) m1-m3.
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(
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[
26] S. Kannan, A. Usman, H. K. Fun, Polyhedron, 21 (2002) 2403.
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Acta, 254 (1997) 113.

Table 1. Crystal data refinement of compounds 1, 2, 5 and 8
1
2
5
8
Empirical Formula
Crystal system
Space group
a (Å)
C
24
H
48
N
4
O
4
Cl
2
U C24
H
48
N
4
O
4
Br
2
U C24
H
48
N
6
O
10
U
C
28
H
34
N
2
O
7
S
2
6
F U
Orthorhombic
Pbca
Orthorhombic
Pbca
Monoclinic
P 2 /n
Monoclinic
P 2 /n
16.0316(3)
1
1
15.2149(6)
12.2538(7)
16.9457(8)
90.0
15.2003(4)
12.3726(3)
16.9049(4)
90.0
8.9696(2)
18.2161(4)
10.2600(3)
102.403(3)
b (Å)
9.03822(19)
23.4060(4)
94.8813(18)
c (Å)
β (°)
3
V (cm )
3159.4(3)
4
3179.24(13)
4
1637.26
2
3379.16(12)
4
Z
-3
ρ
calcd (g cm )
1.610
1.785
1.661
1.822
-
1
µ (mm )
16.279
2957/1360
17.576
2981/1769
14.447
3088/2010
15.382
6283/4965
Reflections
collected/unique
Data/restrains/
parameters
2957/0/165
2981/72/165
3088/36/202
6283/138/457
2
Goodness of fit on F
1.050
1.000
1.060
1.007
Final R
1
indices
0.0798
0.0452
0.0425
0.0416
[
I > 2σ(I)]
R
1
indices (all data )
0.1308
0.0789
0.0688
0.0559
2
2
2
2
2
2
w = 1/[σ (Fo )+(0.1805P) + 0.8529P] for 1, w = 1/[σ (Fo )+(0.0646P) +1.6221P] for 2, w =
2
2
2
2
2
2
2
2
1
/[σ (Fo )+(0.0649P) ] for 5, w = 1/[σ (Fo )+(0.0643P) ] for 8, where P = (Fo +2Fc )/3

Table 2. Important bond lengths (Å) and angles (°) for 1, 2, 5 and 8
1
U1 – O1
U1 – O2
U1 – Cl1
C1 – O2
1.739(8)
2.322(10)
2.683(5)
1.262(16)
O1 – U1 – O2
O1 – U1 – Cl1
O2 – U1 – Cl1
U1 – O2 – C1
88.1(4)
90.8(3)
88.7(3)
154.9(11)
2
U1 – O1
U1 – O2
U1 – Br1
C1 – O2
1.754(6)
2.317(5)
2.8073(10)
1.263(9)
O1 – U1 – O2
O1 – U1 – Br1
O2 – U1 – Br1
U1 – O2 – C1
91.4(2)
89.99(19)
88.10(14)
155.2(5)
5
U1 – O1
U1 – O2
U1 – O3
U1 – O4
C1 – O2
1.762(6)
2.378(6)
2.517(6)
2.538(6)
1.253(9)
O1 – U1 – O2
O3 – U1 – O4
O2 – U1 – O4
U1 – O2 – C1
87.4(2)
50.0(2)
65.2(2)
149.3(6)
8
U1 – O1
U1 – O2
U1 – O3
U1 – O4
1.754(5)
1.757(5)
2.375(5)
2.387(5)
U1 – O5
U1 – O6
U1 – O7
C1 – O3
2.393(5)
2.379(5)
2.383(5)
1.256(8)

O1 – U1 – O2
O6 – U1 – O7
O4 – U1 – O3
U1 – O3 – C1
178.2(2)
70.06(17)
73.97(17)
155.6(5)
O4 – U1 – O5
O5 – U1 – O6
O3 – U1 – O7
70.29(18)
71.18(18)
74.60(17)
Figure Legends
Scheme 1. Synthesis of the ligands and their compounds
Fig 1. Molecular structure of 1
Fig 2. Molecular structure of 2
Fig 3. Molecular structure of 5
Fig 4. Structure of 8

Scheme 1
R
Et N
3
Cl
+
N
R
N
H
R
O
N
R
O
i
R = CH ( L1 ) ; R = C H ( L2 ) ; R = C H ( L3 )
2 5 3 7
3
[UO X .2L]
2 2
[
UO X .nH O] + 2L
2 2 2
X = Cl, L = L3 ( 1 ) ; X = Br, L =L3 ( 2)
UO (NO ) .2L]
[
[
UO (NO ) .6H O] + 2L
2
2
3 2
3 2
2
L = L1 ( 3 ) ; L = L2 ( 4 ); L = L3 ( 5 )
UO (TTA) .L]
[
[
UO (TTA) .2H O] + L
2
2
2
2
2
L = L1 ( 6 ) ; L = L2 ( 7 ); L = L3 ( 8 )
UO (DBM) .L]
[
[
UO (DBM) .2H O] + L
2
2
2
2
2
L = L1 ( 9 ) ; L = L2 ( 10 ); L = L3 ( 11 )

Fig 1

Fig 2

Fig 3

Fig 4

Graphical abstract