Synthesis, characterization of 2-(bis-dibutylcarbamoylmethylamino)-N,N-dibutyl-acetamide (L) lanthanide picrate complexes (Ln = Nd, Eu, Tb) and the crystal structure of [Tb(pic) 3L]

Article abstract of DOI:10.1016/S0022-2860(03)00368-5

Solid complexes of lanthanide picrate with the ligand 2-(bis-dibutylcarbamoylmethyl-amino)-N, N-dibutyl-acetamide (L), [Ln(pic) ₃L] (Ln = Nd, Eu, Tb), have been prepared and characterized by elemental analysis, conductivity measurements, DTA and TGA analysis, IR and ¹H NMR spectra. For the terbium complex, X-ray measurements show that Tb(III) ion is 9-coordinated by three oxygen atoms and one nitrogen atom of L and five oxygen atoms of picrate groups. Molecule B has a clockwise structure due to the screw coordination arrangement of the tripod-type ligand.

Full text of DOI:10.1016/S0022-2860(03)00368-5

Journal of Molecular Structure 657 (2003) 177–183
www.elsevier.com/locate/molstruc
Synthesis, characterization of 2-(bis-dibutylcarbamoylmethyl-
amino)-N, N-dibutyl-acetamide (L) lanthanide picrate
complexes (Ln ¼ Nd, Eu, Tb) and the crystal
structure of [Tb(pic)3L]
a
Nan Yang , Jiangrong Zheng , Weisheng Liu , Ning Tang , Kaibei Yu
a
a,
a
b
*
aCollege of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China
bChengdu Center of Analysis and Measurement, Academia Sinica, Chengdu 610041, China
Received 15 January 2003; revised 27 May 2003; accepted 30 May 2003
Abstract
Solid complexes of lanthanide picrate with the ligand 2-(bis-dibutylcarbamoylmethyl-amino)-N, N-dibutyl-acetamide (L),
[Ln(pic)3L] (Ln ¼ Nd, Eu, Tb), have been prepared and characterized by elemental analysis, conductivity measurements, DTA
and TGA analysis, IR and 1H NMR spectra. For the terbium complex, X-ray measurements show that Tb(III) ion is 9-
coordinated by three oxygen atoms and one nitrogen atom of L and five oxygen atoms of picrate groups. Molecule B has a
clockwise structure due to the screw coordination arrangement of the tripod-type ligand.
q 2003 Elsevier B.V. All rights reserved.
Keywords: Lanthanide picrate; Complex; Tripod-type; Crystal structure; Cavity-like structure
1. Introduction
complexes and their extraction studies of these
types of compounds have been reported, among
which 2-{2-[bis-(2-diethylcarbamoylmethoxy-ethyl)-
amino]-ethoxy}-N,N-diethyl-acetamide shows a high
extractability to lanthanide. This extractability mostly
depends on cavity-like coordination structure and
terminal group effects [6–8]. As a subsequent study of
such ligands, in order to design better extractors and
further explore the relationship between structure and
extractability, we give here the synthesis, character-
ization of 2-(bis-dibutylcarbamoylmethyl-amino)-N,
N-dibutyl-acetamide (L) lanthanide picrate com-
plexes [Ln(pic)3L] (Ln ¼ Nd, Eu, Tb), and the crystal
structure of [Tb(pic)3L].
Amide-base tripod-type compounds have been
widely studied in the extraction of lanthanide or
some actinide ions, and in ion-selective electrodes
[1–5]. The tripod-type ligands containing amide
groups possess suitable molecular structure: a chain
with flexible terminal groups. Therefore, they are
excellent reagents for activating ion-selective electro-
des and extracts of rare earth ions. Rare earth
*
Corresponding author. Tel.: þ86-9318911809; fax: þ86-
9318912582.
E-mail address: liuws@lzu.edu.cn (W. Liu).
0022-2860/03/$ - see front matter q 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-2860(03)00368-5

178
N. Yang et al. / Journal of Molecular Structure 657 (2003) 177–183
2. Experimental
2.1. Materials
precipitated solid complex was filtered, washed with
ethanol three times and dried in vacuo over P4O10 for
48 h. Single crystal of the terbium picrate complex
grew from methanol/acetone by slow evaporation at
room temperature. After about a month, transparent
yellowish crystals formed from the solution.
The lanthanide picrate [9] and L [10] were
prepared according to literature methods. All com-
mercially available chemicals were of reagent grade
and were used without further purification.
2.4. Chemical and physical measurements
2.2. Synthesis of ligand
The metal ions were determined by EDTA titration
using xylenal orange as an indicator. C, N and H were
determined using an Elementar Vario EL. IR spectra
were recorded on a Nicolet AVATAR 360 FTIR
instrument using KBr discs in the 400–4000 cm21
region, 1H NMR spectra were measured on a Brucker
AC 200 spectrometer in CDCl3 solution with TMS as
internal standard. Conductivity measurements were
carried out with a DDSJ-308 type conductivity bridge
using 1 £ 1023 mol/l solutions in acetone at 25 8C.
Scheme 1 shows the synthesis of ligand L. Oxalyl
chloride (15.0 ml) was added dropwise to the mixture
of (bis-carboxymethyl-amino)-acetic acid (1.5 g,
7.85 mmol, in 20 ml benzene) with one drop of
DMF as catalyst. After the mixture had been stirred
under 30 8C for 6 h, the benzene and extra oxalyl
chloride were removed by decompress distillation
under 50 8C. Dibutyl-amine (6.1 g, 47.29 mmol, in
30 ml benzene) was added and the mixture was heated
to 40 8C. After being stirred for about 8 h, the
precipitated solid was filtered, and the solvent was
removed by decompress distillation. The crude
product was chromatographed on silica gel (pet-
roleum/CH3COOC2H5, 5:1 (v/v)) to afford pure
product as brown oil in 50% yield.
2.5. X-ray crystallography
For the terbium complex, X-ray measurements
were performed on a P4 four-circle diffractometer
with graphite monochromatized Mo Ka radiation at
291(2) K using the v=2u scan mode. Lorentz and
polarization corrections were applied, and empirical
absorption correction was made. A summary of
crystallographic data and details of the structure
refinements are listed in Table 1. The structure was
solved by direct methods and refined by full-matrix
least-square techniques with all non-hydrogen atoms
treated anisotropically. All calculations were
2.3. General preparation of the complexes
A solution of L (0.2 mmol, in 10 ml of ethanol)
was added dropwise to a solution of lanthanide picrate
(0.2 mmol, in 5 ml of ethanol). The mixture was
stirred at room temperature for 8 h. The yellowish
Scheme 1. The Synthesis of ligand L.

N. Yang et al. / Journal of Molecular Structure 657 (2003) 177–183
179
Table 1
Table 2
Crystal data and structure refinement for the complex [Tb(pic)3L]
Analytical data for the complexes (calculate values in parentheses)
Empirical formula
Temperature (K)
Crystal color
C48H66N13O24Tb
Complex Analysis (%)
291(2)
C
H
N
Ln
Yellow
Crystal size (mm3)
Formula weight
Crystal system
Space group
0.56 £ 0.48 £ 0.46
1368.06
Nd(pic)3L 42.77(42.60) 5.09(5.08) 12.92(13.45) 10.13(10.67)
Eu(pic)3L 41.96(42.36) 4.53(4.89) 13.16(13.38) 11.35(11.17)
Tb(pic)3L 41.88(42.14) 5.10(4.86) 13.40(13.31) 11.24(11.63)
Monoclinic
P21/c
Unit cell
dimension
˚
a (A)
˚
b (A)
indicate that all the three picrate groups coordinate
to Ln(III) in each complex [12].
23.123(5)
19.794(4)
29.112(6)
90
˚
c (A)
3.2. 1H NMR spectra
a (degree)
b (degree)
g (degree)
112.61(2)
90
The spectrum of the ligand exhibits four multiples
at 0.92, 1.31, 1.50 and 3.28 ppm assigned to –CH3,
CH3–CH2–, CH3–CH2–CH2– and –CH2–N, and
one single peak at 3.67 ppm to N–CH2 –CyO
protons, respectively (Table 4).
3
˚
V (A )
12300(4)
8
Z
Density (calculated,
g/cm3)
1.477
Fð000Þ
5616
Radiation, graphite
0.71073
˚
monochromatized, l (A)
m (Mo Ka) (cm21
3.3. IR spectra
)
5.67
Reflections collected
Independent reflections
u range for data
collection
23,676
21,662
1.52–25.00
Free L shows band at 1642 cm21 which may be
assigned to n(CyO). In the IR spectra of the
lanthanum complexes, the disappearances of free
picrate acid n(O–H) characteristic frequency
(3445 cm21) indicate that the O–H groups take part
in coordination and the hydrogen atoms are sub-
stituted by lanthanide ions.
Index range
0 # h # 27; 0 # k # 23;
234 # l # 31
Goodness-of-fit on F2
R½I . 2sðIÞꢀ
0.777
R1 ¼ 0:0541; wR2 ¼ 0:1116a
R1 ¼ 0:1625; wR2 ¼ 0:1377a
0.539, 21.065
R (all data)
Largest difference peak and
23
In the IR spectra of complexes, the bands of
n(CyO) of free L shift about 30 cm21 towards lower
wave number, indicating the CyO groups take part in
coordination to the metal ions. The larger band shifts
for n(C–O) (62 cm21) in the spectra of complexes
suggest that the Ln–O (phenol) bonds are stronger
than Ln–O (carbonyl) ones [13]. Furthermore, the
characteristic frequencies (1342, 1555 cm21) of free
˚
hole [e A
]
a
2
2
w ¼ 1=½s2ðFoÞ þ ð0:0337pÞ ꢀ where p ¼ ðFo2 þ Fc2Þ=3:
performed on an Eclipse S/140 computer with the
program package SHELXTL [11] version 5.10.
3. Results and discussion
Table 3
3.1. Properties of the complexes
Conductivity of complexes (concentration of complexes:
1 £ 1023 mol/l, temperature: 25 8C)
Analytical data for the complex conform to
1:3:1 metal-to-picrate-to-L stoichiometry
a
Compounds
Conductivity (Lm)
[Ln(pic)3L] (Table 2). All complexes are soluble
in DMSO, DMF, THF, CHCl3, CH3CN, methanol
and acetone, and sparingly soluble in benzene, Et2O
and cyclohexane. Conductivity measurements for
these complexes in acetone solution (Table 3)
Acetone
0.7 S cm2 mol21
48.2 S cm2 mol21
47.3 S cm2 mol21
45.7 S cm2 mol21
Nd(pic)3L
Eu(pic)3L
Tb(pic)3L

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N. Yang et al. / Journal of Molecular Structure 657 (2003) 177–183
Table 4
The 1H NMR spectrum of ligand (ppm)
Compound
L
d–CH3
dCH3–CH2–
dCH3–CH2–CH2–
d–N–CH2–
d–N–CH2–CyO
0.92
1.31
1.50
3.28
3.67
Table 5
The relevant characteristic IR bands (cm21
)
n(CyO)
n(O–H)
n(C–O)
nas(–NO2)
nas(–NO2)
Ligand (L)
Picrate acid
Nd(pic)3L
Eu(pic)3L
Tb(pic)3L
1642
3445
1213
1275
1275
1275
1555
1342
1611
1613
1613
1574, 1545
1576, 1544
1576, 1545
1360, 1324
1362, 1324
1362, 1325
picrate were divided into two double peaks (about
1362, 1325 and 1576, 1545 cm21, respectively),
indicating that the picrate groups coordinate to the
metal ions as bidentate ligands [14] (Table 5).
3.5. X-ray crystal structure
Fig. 2 shows the structure and the atomic
numbering schemes of the terbium complex. Fig. 3
shows the stacking pattern along y-axis in the unit cell.
Selected bond lengths and angles are given in Table 6.
In the complex, L acts as a tetradentate ligand; two
bidentate and one-unidentate picrate groups to give 9-
coordination occupy the remaining coordination sites.
Upon coordination, L gives two different arrangements
around Tb(III) ions. In structure A, the torsion angles of
Tb(1)–N(1)–C(1)–C(2), Tb(1)–N(1)–C(11)–C(12)
3.4. DTA and TGA analysis
In the DTA and TGA spectra of complex
[Tb(pic)3L], a heat-absorb peak appeared at about
80 8C without any loss of weight indicating that the
melting point of the complex is 80 8C. As the
temperature rising, the heat-emission bands appeared,
beginning at 250 8C, with successive weight loss. At
the 500 8C, the complex completely convert into
Tb4O7 and the weight become stable (Fig. 1). The
experimental total weight-loss value (85.67%) is
similar to the calculated one (86.25%).
The DTA and TGA spectra of [Nd(pic)3L] and
[Eu(pic)3L] are similar to that of [Tb(pic)3L]. All
the complexes begin to lose weight at about 250 8C,
and completely convert into oxide (Nd2O3, Eu2O3
and Tb4O7) after 500 8C. The differences among
them are the melting point and the total weight-loss
value. For complex [Nd(pic)3L], the melting point
is 69 8C and the experimental total weight-loss
value is 86.61% (87.56%, calculated). The melting
point for complex [Eu(pic)3L] is 73 8C and the
experimental total weight-loss value is 86.79%
(87.06%, calculated).
Fig. 1. The DTA and TGA spectra of [Tb(pic)3L].

N. Yang et al. / Journal of Molecular Structure 657 (2003) 177–183
181
Fig. 2. The structure of [Tb(pic)3L], showing 50% thermal ellipsoids. Hydrogen atoms have been omitted for clarity.
Fig. 3. The structure of [Tb(pic)3L] in the unit cell. Some atoms have been omitted for clarity.

182
N. Yang et al. / Journal of Molecular Structure 657 (2003) 177–183
Table 6
˚
Selected bond lengths (A) and bond angles (degree) for [Tb(pic)3L]
distance between Tb(2) atom and oxygen atoms
˚
(CyO) is 2.332 A and the distance between Tb(2)
˚
and apex nitrogen atom is 2.695 A.
Tb(1)–O(1)
Tb(1)–O(2)
Tb(1)–O(3)
Tb(1)–O(4)
Tb(1)–O(11)
Tb(1)–O(12)
Tb(1)–O(18)
Tb(1)–O(19)
Tb(1)–N(1)
2.359(6) Tb(2)–O(25)
2.387(5) Tb(2)–O(26)
2.327(6) Tb(2)–O(27)
2.274(5) Tb(2)–O(28)
2.319(5) Tb(2)–O(29)
2.580(6) Tb(2)–O(35)
2.325(5) Tb(2)–O(36)
2.630(6) Tb(2)–O(42)
2.686(6) Tb(2)–N(14)
2.320(6)
2.296(6)
2.380(6)
2.359(5)
2.591(7)
2.292(6)
2.681(7)
2.240(6)
2.695(7)
In conclusion, amide-base tripod-type ligand L can
form stable solid complexes with lanthanide ions.
Because of its cavity-like coordination structure and
flexibility, L exhibits a stable conformation that
provides a coordination cavity. It, therefore, shows
high coordination ability and lipophilicity, both of
which could make it a useful component sensor.
Furthermore, it can be shown experimentally that the
structures and properties of the amide-base tripod-
type complexes are closely related to counter anion
and terminal group effects [15–18]. A further study
concerned with these will be reported in following
communications.
Tb(1)–N(1)–C(1)
111.4(4) Tb(2)–N(14)–C(49) 110.9(5)
Tb(1)–N(1)–C(11) 108.6(4) Tb(2)–N(14)–C(59) 108.8(5)
Tb(1)–N(1)–C(21) 107.5(4) Tb(2)–N(14)–C(69) 106.4(5)
N(1)–C(1)–C(2)
112.8(7) N(14)–C(49)–C(50) 112.1(8)
N(1)–C(11)–C(12) 107.2(7) N(14)–C(59)–C(60) 109.8(7)
N(1)–C(21)–C(22) 110.8(7) N(14)–C(69)–C(70) 107.8(8)
and Tb(1)–N(1)–C(21)–C(22) are 25.79, 35.65 and
35.378, respectively, while in structure B, the torsion
angles of Tb(2)–N(14)–C(49)–C(50), Tb(2)–
N(14)–C(59)–C(60) and Tb(2)–N(14)–C(69)–
C(70) are 24.28, 227.52 and 240.018, respectively,
which induce a chiral structure (Fig. 4).
4. Supplementary data
Crystallographic data for the structures reported in
this paper have been deposited with the Cambridge
Crystallographic data Center, CCDC no. 201065.
Copies of this information may be obtained free of
charge from the Director CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (Fax: þ44-1223-336-033;
E-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.
cam.ac.uk).
In structure A, the value of the Tb–N distance
˚
(2.686 A) is longer than the average Tb–O (CyO)
˚
bond distance (2.358 A), indicating that Tb–O (CyO)
bond is stronger than the Tb–N one. The same
situation occurs in structure B, where the average
Acknowledgements
We are grateful to the Foundation for University
Key Teacher by the Ministry of Education, and the
National Natural Science Foundation of China
(projects 29571014 and 20071015) for financial
support.
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