Uranyl(VI) complexes with a diaminobisphenol from eugenol and N-(2-aminoethyl)morpholine: Syntheses, structures and extraction studies

Article abstract of DOI:10.1016/j.poly.2010.11.012

The syntheses and structural studies of an [O,N,O,N′]-type phenolic ligand [(N',N'-bis(2-hydroxy-3-methoxy-5-(propen-2-yl)benzyl)-N-(2-aminoethyl) morpholine), (H₂L) and two new uranyl complexes of this ligand are described. The reaction betwee

Full text of DOI:10.1016/j.poly.2010.11.012

Polyhedron 30 (2011) 477–485
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Uranyl(VI) complexes with a diaminobisphenol from eugenol
and N-(2-aminoethyl)morpholine: Syntheses, structures and extraction studies
⇑
Oula Wichmann , Kari Ahonen, Reijo Sillanpää
Department of Chemistry, University of Jyväskylä, P.O. Box 35, FIN-40014 Jyväskylän yliopisto, Finland
a r t i c l e i n f o
a b s t r a c t
The syntheses and structural studies of an [O,N,O,N0]-type phenolic ligand [(N’,N’-bis(2-hydroxy-3-meth-
oxy-5-(propen-2-yl)benzyl)-N-(2-aminoethyl)morpholine), (H2L) and two new uranyl complexes of this
ligand are described. The reaction between uranyl nitrate hexahydrate and H2L in a 1:2 M ratio (M to H2L)
results in a uranyl complex of the formula [UO2(HL)(NO3)(H2O)] (1). In the presence of a base (triethyl-
amine), with the same molar ratio, the uranyl complex [UO2(HL)2]ꢀ2CH3CN (2) is formed. The molecular
structures H2L, 1 and 2 were verified by X-ray crystallography. Both uranyl complexes are zwitterions
with a neutral net charge. A comprehensive NMR-structural analyses of all compounds were performed
in CDCl3, DMSO-d6 and pyridine-d5. Complex 2 dissociates in all the studied NMR-solvents, forming a 1:1
complex and free ligand, but according to the spectra the formed complexes are not alike. The results of
the ability of the ligand to extract the uranyl ion from water into dichloromethane are also presented.
Ó 2010 Elsevier Ltd. All rights reserved.
Article history:
Received 21 July 2010
Accepted 9 November 2010
Available online 19 November 2010
Keywords:
Uranyl complex
Uranyl extraction
Phenolate ligands
Crystal structures
Eugenol derivate
1. Introduction
by forming neutral complexes. One of the aims of this work is to
prepare new phenolic ligands which are usable in biological sys-
Although actinide elements are primarily associated with en-
ergy production or war technology, modern applications of these
elements exist also in civil areas and medicine. Despite their wide
use, our knowledge about the coordination chemistry of these me-
tal ions is fairly limited, compared, for instance, to d-transition me-
tal ions [1]. The uranyl ion ([UO2]2+) is found to be the most stable
species of uranium in aqueous solutions in vivo [2]. The unique lin-
ear structure of the uranyl cation with an overall +2 charge pre-
vents the use of effective chelating ligands that target spherical
ions in three dimensions (e.g. EDTA, DTPA, etc.) [3]. It was noted re-
cently that ‘‘no effective chelating agent is available for uranium,
which should be considered a matter for some concern’’ [4]. So,
finding an effective ligand to bind uranyl ions has a practical goal:
the extraction of uranium from various media, even selectively
[5–7]. For example Raymond et al. have made a series of extraction
studies with carboxylate type ligands [8]. Recently the uranyl ion
was encapsulated in order to improve its extraction [9]. Many good
uranyl extractors contain a phenolate oxygen, which is a typical
hard Lewis base and has a good affinity towards the hard uranyl
ion [10]. Earlier [11] we have studied uranyl complexes with
[O,N,O,N0]-type ligands, and the ability of these ligands to extract
uranyl ions from water into dichloromethane. Our approach to this
subject includes flexible bisphenolate ligands with nitrogen do-
nors, as these ligands are capable of coordinating to uranyl ions
tems. Eugenol (C10H12O2) is an allyl chain-substituted guaiacol,
i.e. 2-methoxy-4-(2-propenyl)phenol. This biological compound
has several uses in health care and cosmetics [12]. A new ligand,
H2L (Scheme 1), was prepared from eugenol, formaldehyde and
N-(2-aminoethyl)morpholine, and its coordination and extraction
potential with uranyl ions were studied. N-(2-aminoethyl)morpho-
line brings to the ligand two nitrogen atoms as possible donors. In
this work we report the preparation of the ligand H2L and two of its
uranyl complexes. The compounds are characterized by elemental
analysis, NMR-spectroscopy and X-ray diffraction. Uranyl ion
extractions tests were also performed.
2. Experimental
2.1. General information
N-(2-aminoethyl)morpholine (Aldrich), eugenol (Aldrich), tri-
ethylamine (Riedel), 37% formaldehyde (Riedel) and uranyl nitrate
hexahydrate (Merck) were used as supplied. The ligand H2L was
synthesized by mainly following the procedure described by Burke
et al. [13,14]. Details of the syntheses are described below.
Liquid-state 1H, 13C and 2 D PFG 1H–13C HMQC and HMBC NMR
spectra were recorded in CDCl3 at 30 °C with a Bruker Avance DRX
500 spectrometer equipped with a 5 mm diameter broad band in-
verse detection probe head operating at 500.13 MHz in 1H, and
125.77 MHz in 13C experiments. Spectra in pyridine-d5 were re-
corded with a Bruker AVANCE DPX 250 FT NMR spectrometer.
⇑
Corresponding author. Tel.: +358 14 260 2676; fax: +358 14 260 2501.
E-mail address: oula.wichmann@jyu.fi (O. Wichmann).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.11.012

478
O. Wichmann et al. / Polyhedron 30 (2011) 477–485
25
24
O
28
14
10
26
12
HO
O
N
22
20
17
16
18
N
O
9
Et3N
Ethanol, 323K
+ 2 H2O
+ 2 HCHO
N
8
2
+
7
O
5
NH2
31
HO
OH
1
3
29
O
32
33
H2L
Scheme 1. The synthesis route to H2L and the numbering system used.
1H and 13C NMR spectra were recorded either in CDCl3, DMSO-d6 or
in pyridine-d5 at 30 °C and chemical shifts are reported in ppm rel-
ative to CDCl3 (d 7.26, 1H NMR), DMSO-d6 (d 2.50, 1H NMR; 39.51,
13C NMR) or pyridine-d5 (d 8.74, 1H NMR; 150.35, 13C NMR).
The solid-state NMR measurements were recorded with a Bru-
3.70 (t, 4H, –CH2–O–CH2–), 3.80 (s, 6H, Ar-O–CH3), 5.03 (m, 4H,
CH@CH2), 5.90 (m, 2H, CH@CH2), 6.50 (s, 2H, ArC5–H), 6.59 (s,
2H, ArC3–H).
1H NMR (250 MHz, pyridine-d5): 2.31 (t, 4H, morpholine ring –
CH2–N–CH2–), 2.55 (t, 2H, N–CH2–CH2–N), 2.78 (t, 2H, N–CH2–
CH2–N), 3.38 (d, 4H, Ar-CH2–CH@), 3.78 (t, 4H, –CH2–O–CH2–),
3.78 (s, 6H, Ar-O–CH3), 3.96 (s, 4H, Ar-CH2–N–CH2–Ar), 5.12 (m,
4H, –CH@CH2), 6.09 (m, 2H, –CH@CH2), 6.86 (s, 4H, aryl H).
1H NMR (500 MHz, DMSO-d6): 2.23 (t, 4H, morpholine ring –
CH2–N–CH2), 2.48 (t, 4H, N–CH2–CH2–N), 3.23 (d, 4H, Ar-CH2–
CH@), 3.55 (t, 4H, –CH2–O–CH2–), 3.57 (s, 4H, Ar-CH2–N–CH2-Ar),
3.74 (s, 6H, Ar-O–CH3), 5.02 (m, 4H, –CH@CH2), 5.92 (m, 2H, –
CH@CH2), 6.52 (s, 2H, ArC5–H), 6.66 (s, 2H, ArC3–H).
ker Avance 400 spectrometer using 4.0 mm (50 ll) HRMAS-rotors
at a 10 kHz spinning rate. The contact times for CP/MAS experi-
ments for 13C and 15N were 2 and 3 ms, and the relaxation delays
4 and 5 s, respectively. For the non-quaternary suppression (NQS)
experiments, the dephasing delay was set to 50
ls and for the
short CP experiments, the contact time was set to 50
ls. Spinal-
64 heteronuclear decoupling was used in all solid-state NMR
experiments. The 13C and 15N chemical shifts were calibrated using
carbonyl (at 176.03 ppm) and amine (at ꢁ347.4 ppm) resonances
of glycine as an external standard.
Mass spectrometric measurements were performed using a
Micromass LCT time of flight (TOF) mass spectrometer with elec-
trospray ionization (ESI-MS). Elemental analyses were done using
a VarioE1 III elemental analyzer. Single crystal X-ray measure-
ments were performed using an Enraf Nonius Kappa CCD diffrac-
tometer. The uranyl extraction samples were analyzed with
inductively coupled plasma optical emission spectrometry (ICP-
13C NMR (126 MHz, CDCl3): 39.53 (Ar-CH2–CH@), 48.77
(N–CH2–CH2–N(8)), 53.45 (morpholine ring –CH2–N–CH2–),
53.45 (Ar-CH2–N–CH2–Ar), 55.52 (N–CH2–CH2–N(8)), 55.73 (Ar-
O–CH3), 66.30 (–CH2–O–CH2–), 111.3 (ArC3), 115.2 (–CH@CH2),
121.9 (ArC5), 122.5 (ArC6), 130.2 (ArC4), 137.6 (–CH@CH2), 143.9
(ArC1), 147.3 (ArC2).
13C NMR (63 MHz, pyridine-d5): 40.54 (Ar-CH2–CH@), 49.96
(N–CH2–CH2–N(8)), 54.37 (morpholine ring –CH2–N–CH2–), 55.25
(Ar-CH2–N–CH2-Ar), 56.18 (N–CH2–CH2–N(8)), 56.57 (Ar-O–CH3),
67.30 (–CH2–O–CH2–), 113.1 (ArC3), 115.8 (–CH@CH2), 124.3
(ArC5), 125.0 (ArC6), 130.8 (ArC4), 139.2 (–CH@CH2), 146.4
(ArC1), 149.1 (ArC2).
OES) at 385.958 nm using
instrument.
a Perkin–Elmer Optima 4300DV
13C NMR (126 MHz, DMSO-d6): 39.16 (Ar-CH2–CH@), 48.52
(N–CH2–CH2–N(8)), 53.02 (morpholine ring –CH2–N–CH2–), 53.25
(Ar-CH2–N–CH2–Ar), 54.61 (N–CH2–CH2–N(8)), 55.69 (Ar-O–CH3),
65.78 (–CH2–O–CH2–), 111.7 (ArC3), 115.2 (–CH@CH2), 121.7
(ArC5), 123.4 (ArC6), 129.4 (ArC4), 138.0 (–CH@CH2), 144.0
(ArC1), 147.4 (ArC2).
2.2. Ligand synthesis
Ligand H2L was prepared by dissolving eugenol (2.46 mL,
16 mmol) in ethanol (20 mL) in a round bottom flask. N-(2-amino-
ethyl)morpholine (1.04 mL, 8.0 mmol), 36% formaldehyde water
solution (6.0 mL, 79 mmol) and triethylamine (2.16 mL, 16.0
mmol) were added to the reaction mixture (Scheme 1). The reac-
tion flask was placed in a water bath (50 °C) and the progress of
the reaction was followed by HPLC. After 24 h, the solvent was
evaporated in a rotary evaporator and the remaining brown syrup
was dissolved in a small amount of ethanol (precipitation occurs in
a hexane–acetone 3:2 mixture, but the resulting crude product re-
quires further purification). The product was purified by silica gel
chromatography (silica 60, hexane–acetone 3:2 v/v), recrystallized
from ethanol four times and air dried. Yield 0.88 g (23%).
13C NMR (126 MHz, CP/MAS): 40.33 (Ar-CH2–CH@), 46.14 (N–
CH2–CH2–N(8)), 51.00–54.00 (morpholine ring –CH2–N–CH2– and
Ar-CH2–N–CH2-Ar), 53.39, 56.05 (Ar-O–CH3), 65.78 (–CH2–O–
CH2–), 58.47 (N–CH2–CH2–N(8)), 108.9, 111.9 (ArC3), 113.7,
115.9 (–CH@CH2), 120.8, 124.9 (ArC5), 123.2 (ArC6), 129.2 (ArC4),
137.7, 139.9 (–CH@CH2), 145.5, 146.3 (ArC1), 148.8 (ArC2).
ESI-MS m/z: 483.29 [H2L+H]+.
2.3. Syntheses of the uranyl complexes
Elemental Anal: Calc. for C28H38N2O5: C, 69.7; H, 7.9; N, 5.8.
Found: C, 69.8; H, 7.3; N, 5.5%.
2.3.1. [UO2(HL)(NO3)(H2O)] (1)
1H NMR (500 MHz, CDCl3): 2.35 (t, 4H, morpholine ring –CH2–
N–CH2–), 2.54 (t, 2H, N–CH2–CH2–N(8)), 2.61 (t, 2H, N–CH2–CH2–
N(8)), 3.25 (d, 4H, Ar-CH2–CH@), 3.66 (s, 4H, Ar-CH2–N–CH2–Ar),
UO2(NO3)2ꢀ6H2O (0.050 g, 0.10 mmol) and H2L (0.10 g,
0.21 mmol) were dissolved separately in 1 mL CH3CN. The solu-
tions were combined and an immediate colour change from yellow

O. Wichmann et al. / Polyhedron 30 (2011) 477–485
479
to red was observed. The reaction tube was kept at room temper-
ature for two days and at 5 °C for another two days. The resulting
dark red crystals of 1 were filtered off, washed once with diethyl
ether (5 mL) and then air dried. Yield 0.077 g (77%).
Elemental Anal. Calc. for C28H39N3O11U: C, 40.4; H, 4.7; N, 5.1;
Found: C, 40.5; H, 4.6; N, 5.0%.
1H NMR (250 MHz, pyridine-d5), (coordinated ligand): 2.24 (t,
4H, morpholine ring –CH2–N–CH2–), 2.91 (t, 2H, N–CH2–CH2–N),
3.44 (t, 4H, –CH2–O–CH2–), 3.56 (d, 4H, Ar-CH2–CH@), 3.69 (s,
6H, Ar-O–CH3), 3.76 (t, 2H, morpholine ring N–CH2–CH2–), 3.76
(t, 2H, N–CH2–CH2–N), 4.52, 5.41 (d, 4H, Ar-CH2–N–CH2-Ar), 5.13
(m, 4H, –CH@CH2), 6.10 (m, 2H, –CH@CH2), 7.06 (s, 1H, ArH5),
7.11 (s, 1H, ArH3); (uncoordinated ligand): 2.30 (t, 4H, morpholine
ring –CH2–N–CH2–), 2.55 (t, 2H, morpholine ring N–CH2–CH2–),
2.78 (t, 2H, morpholine ring N–CH2–CH2–), 3.38 (d, 4H, Ar-CH2–
CH@), 3.76 (t, 4H, –CH2–O–CH2–), 3.78 (s, 6H, Ar-O–CH3), 3.96 (s,
4H, Ar-CH2–N–CH2–Ar), 5.13 (m, 4H, –CH@CH2), 6.10 (m, 2H, –
CH@CH2), 6.86 (s, 2H, ArH5 and ArH3).
1H NMR (250 MHz, pyridine-d5), (coordinated ligand): 1.95 (t,
4H, morpholine ring –CH2–N–CH2–), 2.49 (t, 2H, N–CH2–CH2–
N(8)), 3.51 (d, 4H, Ar-CH2–CH@), 3.61 (t, 2H, N–CH2–CH2–N(8)),
3.63 (s, 6H, –O–CH3), 3.68 (t, 4H, –CH2–O–CH2–), 4.36, 5.61 (d,
4H, Ar-CH2–N–CH2-Ar), 5.15 (m, 4H, –CH@CH2), 6.10 (m, 2H, –
CH@CH2), 6.93 (s, 2H, ArH5), 7.01 (s, 2H, ArH3).
1H NMR (500 MHz, DMSO-d6), (coordinated ligand): 2.01 (t, 4H,
morpholine ring –CH2–N–CH2–), 2.55 (t, 2H, N–CH2–CH2–N(8)),
3.01 (t, 2H, N–CH2–CH2–N(8)), 3.27 (t, 4H, –CH2–O–CH2–), 3.37
(d, 4H, Ar-CH2–CH@), 3.89 (s, 6H, Ar-O–CH3), 5.03 (m, 4H, –
CH@CH2), 5.96 (m, 2H, –CH@CH2), 6.77 (s, 1H, ArH5), 6.85 (s, 1H,
ArH3); (uncoordinated ligand): 2.22 (t, 4H, morpholine ring –
CH2–N–CH2–), 3.25 (d, 4H, Ar-CH2–CH@), 3.52 (t, 4H, –CH2–O–
CH2–), 3.76 (s, 6H, Ar-O–CH3), 5.02 (m, 4H, –CH@CH2), 5.92 (m,
2H, –CH@CH2), 6.58 (s, 1H, ArH5), 6.72 (s, 1H, ArH3).
1H NMR (500 MHz, DMSO-d6), (coordinated ligand): 2.00 (t, 4H,
morpholine ring –CH2–N–CH2–), 2.54 (t, 2H, N–CH2–CH2–N(8)),
2.99 (t, 2H, N–CH2–CH2–N(8)), 3.27 (4H, –CH2–O–CH2–), 3.37 (d,
4H, Ar-CH2–CH@), 3.90 (s, 6H, Ar-O–CH3), 4.11, 4.66 (4H, Ar-CH2–
N–CH2-Ar), 5.06 (m, 4H, –CH@CH2), 5.97 (m, 2H, –CH@CH2), 6.77
(s, 1H, ArH5), 6.84 (s, 1H, ArH3); (uncoordinated ligand): 2.23 (t,
4H, morpholine ring –CH2–N–CH2–), 2.48 (t, 4H, N–CH2–CH2–N),
3.23 (d, 4H, Ar-CH2–CH@), 3.55 (t, 4H, –CH2–O–CH2–), 3.57 (s,
4H, Ar-CH2–N–CH2-Ar), 3.74 (s, 6H, Ar-O–CH3), 5.02 (m, 4H, –
CH@CH2), 5.92 (m, 2H, –CH@CH2), 6.52 (s, 1H, ArH5), 6.66 (s, 1H,
ArH3).
13C NMR (63 MHz, pyridine-d5), (coordinated ligand): 40.30 (Ar-
CH2–CH@), 51.80, 53.38 (N–CH2–CH2–N(8)), 53.95 (morpholine
ring –CH2–N–CH2–), 56.17 (Ar-O–CH3), 62.03 (Ar-CH2–N–CH2-Ar),
66.84 (–CH2–O–CH2–), 114.1 (ArC3), 115.82 (–CH@CH2), 122.3
(ArC6), 129.4 (ArC4), 139.6 (–CH2–CH@CH2), 152.9 (ArC1), 160.1
(ArC2).
13C NMR (126 MHz, CDCl3), (dinuclear complex): 39.47 (C26),
39.68 (C31), 46.58 (C16), 50.71 (C17), 54.16 (C19/C23), 55.81
(C33), 60.05 (C9), 61.47 (C7), 64.25 (C25), 66.88 (C20/C22), 112.4
(C3), 114.9 (C13), 115.2 (C29), 116.1 (C28), 121.9 (C5), 124.8
(C10), 126.1 (C6), 127.5 (C11), 129.8 (C4), 131.2 (C12), 137.4
(C30), 138.8 (C27), 150.3 (C2), 151.3 (C14), 152.9 (C15),
156.2(C1); (uncoordinated ligand): 39.72 (Ar-CH2–CH@), 48.99
(N–CH2–CH2–N(8)), 53.67 (morpholine ring –CH2–N–CH2–), 55.15
(Ar-CH2–N–CH2-Ar), 55.74 (N–CH2–CH2–N(8)), 55.96 (Ar-O–CH3),
66.54 (–CH2–O–CH2–), 111.5 (ArC3), 115.4 (–CH@CH2), 122.1
(ArC5), 122.6 (ArC6), 130.5 (ArC4), 137.8 (–CH@CH2), 144.1
(ArC1), 147.5 (ArC2).
13C NMR (126 MHz, DMSO-d6), (coordinated ligand): 46.10 (N–
CH2–CH2–N(8)), 50.12 (N–CH2–CH2–N(8)), 53.74 (morpholine ring
–CH2–N–CH2–), 55.80 (Ar-O–CH3), 59.44 (Ar-CH2–N–CH2-Ar),
65.94 (–CH2–O–CH2–), 113.0 (ArC3), 114.7 (–CH@CH2), 122.1
(ArC5), 125.8 (ArC4), 139.0 (–CH@CH2), 149.9 (ArC2), 156.8
(ArC1); (uncoordinated ligand): 48.54 (N(18)–CH2–CH2–N), 52.71
(morpholine ring –CH2–N–CH2–), 53.34 (Ar-CH2–N–CH2–Ar),
55.76 (Ar-O–CH3), 65.57 (–CH2–O–CH2–), 112.1 (ArC3), 115.4
(–CH@CH2), 129.9 (ArC4), 137.9 (–CH@CH2), 143.8 (ArC1), 147.4
(ArC2).
13C NMR (63 MHz, pyridine-d5), (coordinated ligand): 40.52 (Ar-
CH2–CH@), 48.90 (N–CH2–CH2–N(8)), 52.00 (N–CH2–CH2–N(8)),
55.12 (morpholine ring –CH2–N–CH2–), 56.54 (Ar-O–CH3), 60.91
(Ar-CH2–N–CH2-Ar), 67.48 (–CH2–O–CH2–), 114.3 (ArC3), 115.4
(–CH@CH2), 127.4 (ArC6), 128.8 (ArC4), 140.1 (–CH@CH2), 151.4
(ArC2), 158.3 (ArC1); (uncoordinated ligand): 40.52 (Ar-CH2–
CH@), 49.96 (N–CH2–CH2–N(8)), 54.35 (morpholine ring –CH2–N–
CH2–), 55.24 (Ar-CH2–N–CH2-Ar), 56.15 (N–CH2–CH2–N(8)), 56.54
(Ar-O–CH3), 67.28 (–CH2–O–CH2–), 113.1 (ArC3), 115.8
(–CH@CH2), 125.0 (ArC6), 130.7 (ArC4), 139.2 (–CH@CH2), 146.4
(ArC1), 149.1 (ArC2).
Molecular ion species were not observed by ESI-MS.
2.3.2. [UO2(HL)2]ꢀ2CH3CN (2)
UO2(NO3)2ꢀ6H2O (0.050 g, 0.10 mmol) and H2L (0.10 g,
0.21 mmol) were dissolved separately in 1 mL CH3CN. The solu-
tions were combined and triethylamine (20 lL, 0.15 mmol) was
added to the solution. An immediate colour change was observed
and the red solution was kept at room temperature for two days
and at 5 °C for another two days. The resulting orange crystals of
2 were filtered off, washed once with diethyl ether (5 mL) and then
air dried. Yield 0.095 g (76%).
13C NMR (126 MHz, DMSO-d6), (coordinated ligand): 39.06
(Ar-CH2–CH@), 46.04 (N–CH2–CH2–N(8)), 50.07 (N–CH2–CH2–
N(8)), 53.76 (morpholine ring –CH2–N–CH2–), 55.76 (Ar-O–
CH3), 59.57 (Ar-CH2–N–CH2-Ar), 66.01 (–CH2–O–CH2–), 113.0
(ArC3), 114.6 (–CH@CH2), 122.2 (ArC5), 125.8 (ArC6), 125.9
(ArC4), 139.1 (–CH@CH2), 149.8 (ArC2), 156.7 (ArC1); (uncoordi-
nated ligand): 39.06 (Ar-CH2–CH@), 48.54 (N–CH2–CH2–N(8)),
53.03 (morpholine ring –CH2–N–CH2–), 53.27 (Ar-CH2–N–
CH2-Ar), 54.61 (N–CH2–CH2–N(8)), 55.71 (Ar-O–CH3), 65.79
(–CH2–O–CH2–), 111.7 (ArC3), 115.2 (–CH@CH2), 121.8 (ArC5),
123.4 (ArC6), 129.4 (ArC4), 138.0 (–CH@CH2), 144.0 (ArC1),
147.4 (ArC2).
Elemental Anal. Calc. for C56H74N4O12U: C, 54.5; H, 6.0; N, 4.5.
Found: C, 54.3; H, 6.1; N, 4.7%.
1H NMR (500 MHz, CDCl3), (dinuclear complex): 2.22 (m, 4H,
morpholine ring –CH2–N–CH2–), 2.80, 2.89 (m, 2H, N–CH2–CH2–
N), 3.51 (t, 4H, –CH2–O–CH2–), 3.52 (d, 2H, Ar-C(26)H2–CH@),
3.57 (d, 2H, Ar-C(31)H2–CH@), 4.04 (s, 3H, free Ar-O–CH3), 4.38
(d, 1H, Ar-C(9)H2–N–), 4.50 (d, 1H, Ar-C(7)H2–N–), 5.03–5.20 (m,
4H, –CH@CH2), 5.43 (s, 3H, coordinated Ar-O–CH3), 5.49 (d, 1H,
complex Ar-C(9)H2–N–), 5.52 (d, 1H, complex Ar-C(7)H2–N–),
6.05 (m, 2H, –CH@CH2), 6.95 (s, 1H, ArC5–H), 7.02 (s, 1H, ArC3–
H), 7.10 (s, 1H, ArC11–H), 7.42 (s, 1H, ArC13–H); (uncoordinated
ligand): 2.38 (t, 4H, morpholine ring –CH2–N–CH2–), 2.58 (t, 2H,
N–CH2–CH2–N(8)), 2.63 (t, 2H, N–CH2–CH2–N(8)), 3.27 (d, 4H,
Ar–CH2–CH@), 3.69 (s, 4H, Ar–CH2–N–CH2–Ar), 3.73 (t, 4H, –CH2–
O–CH2–), 3.83 (s, 6H, Ar-O–CH3), 5.03–5.20 (m, 4H, –CH@CH2),
5.93 (m, 2H, –CH@CH2), 6.51 (s, 2H, ArC5(/11)–H), 6.61 (s, 4H,
ArC3(/13)–H).
13C NMR (126 MHz, CP/MAS), (coordinated ligand + acetoni-
trile): 1.911 CH3CN, 40.81 (Ar-CH2–CH@), 50.85 (N–CH2–CH2–N),
53.37 (morpholine ring –CH2–N–CH2–), 54.84, 56.78 (Ar-O–CH3),
61.83 (Ar–CH2–N–CH2–Ar), 66.14 (–CH2–O–CH2–), 113.0 (ArC3),
113.7 (–CH@CH2), 119.5, 121.7 (CH3CN), 120.4 (ArC5), 127.6
(ArC6 and ArC4), 139.4, 140.4 (–CH@CH2), 153.1, 153.9 (ArC2),
160.1 (ArC1).
Molecular ion species were not observed by ESI-MS.

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O. Wichmann et al. / Polyhedron 30 (2011) 477–485
2.4. Uranyl extraction
fixed distances using fixed displacement parameters from their
host atoms while other H atoms were refined using fixed displace-
ment parameters. Structure figures were drawn using ORTEP-3 for
Windows [21].
A two phase extraction study was performed to determine the
uranyl cation uptake from a water layer to a CH2Cl2 layer. To the
bottom of a test tube was placed 3 mL of dichloromethane with
the ligand diluted in it (0.10 g, 0.210 mmol). To the top of this layer
was added 2 mL water with uranyl nitrate (c(U) = 6.25 mg/mL,
n(U) = 0.0525 mmol). This led to a ratio of uranium to ligand of
1:4. For control purposes, a similar test tube was prepared without
the ligand dissolved in the organic layer. The samples for ICP
3. Results and discussion
3.1. Syntheses of the ligand and the uranyl complexes
The synthesis of the ligand is a simple condensation reaction,
but due to the complexity of the reaction mechanism it is very sen-
sitive to the reaction conditions. We have found several factors
which directly affect the progress and yield of the reaction.
Most important among these is the solvent system used: wet
polar solvents like alcohols are suitable for the reaction [11]. How-
ever this synthesis was performed in ethanol without added water
because it gave the best yield, but this is an exception in the series
of similar type syntheses [11,22–24]. Another important factor is
that the reaction does not go to completion and after a certain
reaction time it can even reverse direction. It seems that among
the intermediates, the one with only one phenolic moiety attached
to the amine is quite stable. The isolation process of the product
was also difficult due to similar solubilities of eugenol, the reaction
intermediates and the product. The mixture of hexane and acetone
proved to give the best results in the efforts to precipitate the
product from the reaction mixture. The same solvent mixture
was used in further purification of H2L with silica gel column
chromatography.
(V = 50 ll, diluted to 10 mL with water) were taken from the water
layer over three days. One final sample was taken after three
months from the beginning to find out the long term behaviour
of the extraction process. The samples were analyzed with ICP-
OES at 385.985 nm using
instrument.
a Perkin–Elmer Optima 4300DV
2.5. X-ray crystallography
Crystals suitable for single crystal X-ray measurements were
obtained directly from the reaction tubes before filtration. This
was necessary because the crystals of compound 2 readily decom-
posed by losing solvent molecules. The crystal data for compounds
H2L, 1 and 2, along with other experimental details, are summa-
rized in Table 1. The crystallographic data were collected at
123 K or 173 K on an Enraf Nonius Kappa CCD area detector diffrac-
tometer using graphite monochromatized Mo
K
a
radiation
(k = 0.71073 Å). Data collection was performed with
u
and scans
x
and the data were processed using DENZO-SMN v0.95.373 [15,16].
SADABS [17] absorption correction was applied to the data. The
structures were solved by direct methods using the SHELXS-97 [18]
or SIR-97 [19] programs and full matrix least squares refinements
on F2 were performed using the SHELXL-97 [20] program. The heavy
atoms were refined anisotropically, except for the disordered car-
bon atoms in the side chains of the aromatic rings of 2, which were
refined isotropically. The CH hydrogen atoms were included at
Complex formation was studied in five different reactions by
varying the stoichiometry of the reactants. The amounts of uranyl
ions and solvent (acetonitrile) were kept constant, while the
amounts of the ligand and the base (triethylamine) were varied
(Table 2).
The possible reaction in tests 1 and 2 can be described by the Eq.
(1):
½UO2ðNO3Þ2ðH2OÞxꢂ þ 2H2L ! ½UO2HLðNO3ÞðH2OÞꢂðsÞ
þ H3Lþ þ NO3ꢁ þ ðx ꢁ 1ÞH2O
ð1Þ
Table 1
Summary of the crystallographic data for H2L, 1 and 2.
Compound
H2L
1
2
H2L formed only mononuclear 1:1 complexes if no extra base
was added to the reaction mixture. A complexation reaction oc-
curred also in test 3 (notable colour change), but no crystals or sol-
ids were obtained. Under similar reaction conditions, it is possible
to form a dinuclear complex, as was found earlier [22]. If this hap-
pened with H2L, the complex must be diphenoxo-bridged.
If triethylamine is added to the reaction mixture, as was done in
tests 4 and 5, an acetonitrile adduct of the 1:2 complex is formed,
according to the reaction Eq. (2) (x is probably 4).
Formula
Mr
Crystal system
Space group (No.)
a (Å)
C28H38N2O5
C28H39N3O11
831.65
monoclinic
P21/c (14)
11.0770(2)
U
C60H80N6O12
1315.33
triclinic
P1 (2)
11.7999(2)
11.9321(3)
12.5360(3)
68.009(2)
82.047(2)
65.444(2)
1488.28 (7)
1
173
1.468
2.778
21419
0.056
6473
362
0.043 (0.041)
U
482.60
monoclinic
C2/c (15)
49.7208(9)
7.62060(10) 16.0070(3)
13.8123(2)
90
92.8290(10) 100.4630(10)
90 90
5227.13(14) 3127.94(10)
8
123
1.226
0.084
10660
0.0289
5709
ꢀ
b (Å)
c (Å)
17.9394(3)
90
a
(°)
b (°)
c
(°)
V (Å3)
½UO2ðNO3Þ2ðH2OÞ2ꢂ ꢀ xH2O þ 2H2L þ 2Et3N
Z
4
173
! ½UO2ðHLÞ ꢂ ꢀ 2CH3CNðsÞ þ 2½Et3NHꢂþ þ 2NO3ꢁ þ ð2 þ xÞH2O
Temperature (K)
2
Dcalc (g cmꢁ3
)
1.766
5.251
35248
0.057
6810
) (mmꢁ1
)
ð2Þ
l
(Mo K
a
Collected reflections
Rint
Refined reflections
Parameters
324
397
0.046 (0.031)
a
Table 2
R1
0.0604
(0.0467)b
0.1081
(0.1012)
0.221,
ꢁ0.203
Summary of the performed reactions and the isolated uranyl complexes. The U:H2L:B
ratio refers to the ratio of uranyl ion, ligand and base (B = triethylamine).
c
wR2
0.061 (0.057)
0.078 (0.077)
Reaction
U:H2L:B
Isolated complex
Largest difference in peak
0.706, ꢁ0.806 1.009, ꢁ0.557
and hole (e Åꢁ3
)
1
2
3
4
5
1:1:0
1:2:0
1:1:1
1:2:1
1:2:2
[UO2(HL)(NO3)(H2O)] (1)
[UO2(HL)(NO3)(H2O)] (1)
red solution
a
b
c
R1
=
R
||Fo| ꢁ |Fc||/
R|Fo|.
Values in parentheses for reflections with I > 2.0
r(I).
[UO2(HL)2]ꢀ2CH3CN (2)
[w(Fo ꢁ Fc2)2]/
R r
[w(Fo2)2]}1/2 and w = 1/[ 2(Fo2) + (aP)2 + bP)], where
2
wR2 = {
R
[UO2(HL)2]ꢀ2CH3CN (2)
P = (2Fc2 + Fo2)/3.

O. Wichmann et al. / Polyhedron 30 (2011) 477–485
481
Scheme 2. Route (a) describes the formation of the uranyl complexes in this work. In H2L (Route a) R1 = OMe, R2 = CH2CH@CH2. Route (b) is the one found in Ref. [11] using
the H2L ligand shown in 10 with R3 = R4 = Me.
If the amount of water in the reaction mixture is reduced by
using a drying agent, the reaction can lead to product 10, presented
in Scheme 2 (Route b). These reactions for Route b were found in
the experiments made by Sopo et al. [11] using N,N-bis(2-hydro-
ton at N18 (route b) is formed as a minor component, but it stays in
solution.
Complex 1 is quite soluble in polar solvents like alcohols and
DMSO but its solubility is poor in slightly polar or non-polar sol-
vents. Complex 2 is also quite soluble in slightly polar solvents like
chloroform and dichloromethane. However both complexes (1 and
2) decompose on dissolving. This will be discussed in the NMR part
of this chapter.
xy-3,5-dimethylbenzyl)-N0,N0-dimethylethylenediamine as
a li-
gand, which has an [O,N,O,N0]-donor set similar to H2L in this
work. Several experiments were made to achieve a complex of type
10 for H2L, but they were not successful.
In complexes 1 and 2, HLꢁ is in a zwitterionic form: the nitrogen
(N8) is protonated while both phenolic oxygens bear a negative
charge. The net charge in both complexes is zero. The colour of
the reaction mixtures remained red in all cases after the isolation
of the crystals formed, indicating that the crystallization was
incomplete. Thus it is also possible that a 1:1 complex with a pro-
3.2. Structural studies of the ligand and its uranyl complexes
The molecular units of H2L, 1 and 2 are presented in Figs. 1–3.
Selected bond lengths and angles of 1 and 2 are presented in Table
3. The structure of H2L is normal for a diaminobisphenol in which
Fig. 1. The molecular structure of H2L. The intramolecular H bonds between H(O1) and N8, and H(O2) and N18 are shown by dashed lines. Thermal ellipsoids have been
drawn at the 20% probability level.

482
O. Wichmann et al. / Polyhedron 30 (2011) 477–485
Fig. 2. The molecular structure of [(UO2(HL)(NO3)(H2O)] (1). Thermal ellipsoids have been drawn at the 20% probability level. The CH hydrogen atoms have been omitted for
clarity. The CH2CH@CH2 groups at C4 and C14 are disordered over two positions in about a 1:1 ratio. Only the atoms in part a are shown.
Table 3
Selected bond lengths (Å) and angles (°) for 1 and 2.
Complex 1
Complex 2
Bond lengths
U(1)–O(1)
U(1)–O(2)
U(1)–O(3)
U(1)–O(4)
U(1)–O(5)
U(1)–O(6)
U(1)–O(8)
C(1)–O(3)
C(15)–O(4)
1.788(3)
1.782(3)
2.196(3)
2.179(2)
2.545(3)
2.533(3)
2.488(3)
1.337(4)
1.335(4)
U(1)–O(1)
U(1)–O(1)i
U(1)–O(2)
U(1)–O(3)
1.795(2)
1.795(2)a
2.270(2)
2.287(2)
C(1)–O(2)
C(15)–O(3)
1.333(4)
1.333(4)
Bond angles
O(1)–U(1)–O(2)
O(1)–U(1)–O(3)
O(1)–U(1)–O(4)
O(2)–U(1)–O(3)
O(2)–U(1)–O(4)
O(3)–U(1)–O(4)
O(3)–U(1)–O(8)
O(4)–U(1)–O(5)
O(5)–U(1)–O(6)
O(6)–U(1)–O(8)
C(1)–O(3)–U(1)
C(15)–O(4)–U(1)
174.12(13)
93.81(13)
92.32(12)
90.22(13)
92.20(12)
86.38(10)
73.48(10)
84.39(10)
50.38(9)
O(1)–U(1)–O(1)i
O(1)–U(1)–O(2)
O(1)–U(1)–O(2)i
O(1)–U(1)–O(3)
O(1)–U(1)–O(3)i
O(2)–U(1)–O(3)
O(2)–U(1)–O(3)i
180
88.95(10)
91.05(10)
92.72(10)
87.28(10)
82.51(9)
97.49(9)
65.57(10)
161.5(3)
159.6(3)
C(1)–O(2)–U(1)
C(15)–O(3)–U(1)
137.2(2)
140.4(2)
55.3(2)
b
s1 versus s2
47.2(2)
a
Fig. 3. The molecular structure of [UO2(HL)2]ꢀ2CH3CN (2). Thermal ellipsoids have
been drawn at the 30% probability level. The CH hydrogen atoms and the
acetonitrile molecules have been omitted for clarity. Symmetry operation: 2 ꢁ x,
1 ꢁ y, ꢁz.
Generated by inversion.
Dihedral angle between the planes of the phenyl rings: C1,. . ., C6 and C10,. . .,
b
C15.
two intramolecular hydrogen bonds (O1–H1Oꢀ ꢀ ꢀN8 and O2–
H2Oꢀ ꢀ ꢀN18) control the conformation of the ligand [22,25].
In 1 the coordination sphere around U is pentagonal bipyrami-
dal and in 2 it is compressed octahedral. In both complexes the li-
gands behave in a zwitterionic manner with the protons at N(8).
Only this nitrogen in the ligand is geometrically available for coor-
dination, as in the 1:1 uranyl complex of N,N-bis(2-hydroxy-3,5-
dimethylbenzyl)-N0,N0-dimethylethylenediamine [11], but now it
is protonated and thus coordination is not possible. This feature
is somewhat surprising because the charge balance could also be
achieved by protonation of N(18) instead, which this would enable
the coordination of N(8) to the uranyl ion. The U–O(phenolato)
bonds in 1 are approximately 0.30 Å shorter than the U–O bonds
to the coordinated nitrate ions and water molecules [26]. This
can be understood because the O atoms in the nitrate ions and
water molecules are weak donor atoms.
There is also a difference between the lengths of the U–O(phe-
nolato) bonds of complexes 1 and 2. These bonds are approxi-
mately 0.1 Å shorter in 1 compared to those in 2. This indicates
that the phenolato donors in 1 (a 1:1 complex) bond more strongly
to the uranyl ion than in 2. In a way this explains why the 1:2 com-
plexes are not very stable in strongly coordinating solvents. This is

O. Wichmann et al. / Polyhedron 30 (2011) 477–485
483
discussed in the section on NMR studies. The C–O–U bond angles
are closer to linearity in 1 than in 2; in 1 they are about 20° bigger
than in 2. The linearity of the C–O–U angles is another indication of
stronger U–O(phenolato) bonds in 1.
The morpholine moiety attached to the ligand does not form
any bonds with the uranium atom. This is partly expected when
one considers the Lewis basicity of the phenolate oxygens versus
the nitrogen and oxygen atoms in the morpholine moiety. The lin-
ear structure of the uranyl ion also limits the coordination of the
ligands to only the equatorial positions of the metal, and combin-
ing these facts there is hardly any available coordination space for
the heteroatoms of the morpholine group.
In the solid state, the morpholine moiety is folded on top of the
complex in 1 (Fig. 2), forming a cup-like structure. In 2, two similar
cup-like structures (Fig. 3) are also formed on both sides of the
coordination sphere, resulting for the whole molecule a structure
in which the uranyl ion is inside of a capsule. The main reason
for these structural arrangements is the intramolecular N8–
H8ꢀ ꢀ ꢀN18 hydrogen bond. Another reason for this arrangement
can be that in this way the oxygen and nitrogen atoms of the mor-
pholine units are brought into a more polar environment. In com-
pound 1, one of the H atoms of the water molecule forms an
intramolecular hydrogen bond to O24, and another to O1 in the
neighbouring molecule, forming H-bonded dimeric units which
pack together via weak van der Waals interactions (Fig. 4).
These observations give some evidence about the importance
and strength of the internal hydrogen bonds in the conformation
of the complex. Although the ligand is flexible enough to enable
the coordination of N(8) to the uranyl ion, this would lead to a dif-
ferent conformation for the complex, as the hydrogen bonding be-
tween the nitrogens would be prevented and the morpholine
moiety would most likely point away from the uranyl centre.
Structural comparisons between complexes 1 and 2 and two
other complexes with a similar [O,N,O,N0]-donor set ligand (Sopo
et al. [11]) reveal almost parallel structural properties between
the complexes. Also two uranyl azacalixarene (p-methyl-N-benzyl-
tetrahomodiazacalix[4]arene) compounds with an [O,N,O,O,N,O]-
donor set ligand presented by Thuéry et al. [27,28] have structural
similarities with the previous complexes.
tallized out, in which the coordination sphere around the U(VI)
ion is pentagonal bipyramidal. In two 1:1 uranyl calixarene com-
plexes [27], only half of the possible four O donors are coordinated
to the uranyl ion, and two nitrogens are protonated. The ligand is
bonded ‘‘externally’’ to the uranyl ion and two nitrate ions fulfil
the coordination sphere around the uranyl ion.
In the presence of an extra base, the ligand H2L used in this
work and the one mentioned in Ref. [11] form zwitterionic 1:2
(U to L) complexes with an octahedral coordination geometry
around the uranyl ion. Also azacalixarene forms a similar complex
in the presence of base [28]. Now all four phenolate oxygens of the
calixarene ligand bond to the uranyl ion and both nitrogen donors
of the ligand are protonated. Positively charged nitrogen atoms in
close proximity to uranium seem not to hinder the formation of the
complex, and the uranyl ion is placed inside the calixarene ring. On
the other hand, in 2 the proton is not transferred to other nitrogen
atom, which is further away from the uranyl ion, although this pos-
sibility is provided by the ligand.
3.3. NMR studies
Compounds H2L and 2 are very soluble in chloroform and this
allows the measurement of their 1H NMR spectra in CDCl3, but as
1 had a low solubility in CHCl3 the NMR spectra of all compounds
(H2L, 1 and 2) were recorded in DMSO-d6 and pyridine-d5, in which
all the substances readily dissolved. The NMR spectra of all the
compounds in DMSO were analyzed with 1H, 13C, DEPT, HMQC
and HMBC techniques in order to explain satisfactorily all the
chemical shifts in the spectra. The proton and carbon spectra were
also recorded in pyridine-d5 to find out if there are signals under
the solvent residual peaks of DMSO. The peak interpretation of
the NMR spectra is described in Chapters 2.2.–2.3.
DMSO has good solvating properties with strong coordinating
and H bonding properties. In the 1H NMR spectra of H2L in CDCl3
and DMSO-d6 there is a notable difference; in CDCl3 it appears that
the conformation with an intramolecular H bond (the one found in
the solid state) remains in solution, but in DMSO-d6 the intermo-
lecular H bonds dominate, causing another conformation for H2L.
For the complexes dissolved in DMSO, one can clearly see the
partial dissociation of the ligand from the uranyl ion. For example,
in the 1H NMR spectra of 1 and 2 (in DMSO) the same peaks are
seen that are found in the spectra of the free ligand H2L, but also
a similar battery of peaks that can be identified as the uranyl com-
plex is present. In 1 the amount of free ligand is 30% and in 2 it is
50%. These spectral data suggest that both 1:1 and 1:2 complexes
in DMSO decompose to a similar 1:1 complex.
If the complexation reaction of H2L with the uranyl ion is car-
ried out without an extra base, a 1:1 complex (U to L) (1) is crys-
On the contrary, in pyridine 1 is stable towards dissociation
(only very small peaks of the ligand H2L are seen in the spectra),
but 2 dissociates totally to a 1:1 complex, as seen in DMSO. The
1:1 complexes in DMSO and pyridine are not identical although
their spectra resemble each other. The reason for the small differ-
ences is the coordination of the solvent (DMSO or pyridine) as an
extra ligand to the uranyl ion.
The chemical shifts of the coordinated ligand atoms compared
to the ones of the free ligand depend on the electronic and confor-
mational changes due to the complex formation. In the studied
compounds, the shifts of the coordinated ligand atoms are gener-
ally not very different from those of the free ligand. However it
was possible to assign their origins by comparing the spectra of
the free and coordinating ligands using the spectral analysing
methods mentioned above. In this work the way to follow the con-
formational changes of the ligand is to look at the signals of the
prochiral hydrogens on carbon atoms 7 and 9.
In the 1H spectra of 1 and 2 recorded in pyridine, the hydrogens
at C7 and C9 give doublets in the lower field region, but these
hydrogens give a singlet in the spectra of the pure ligand and
Fig. 4. The water molecules form hydrogen bond bridges in 1 generating a dimeric
unit.

484
O. Wichmann et al. / Polyhedron 30 (2011) 477–485
uncoordinated ligand. The 1H NMR spectra of 1 and 2 recorded in
DMSO produce such broad signals for the hydrogens at C7 and
C9 that it is impossible to locate their exact positions.
7
6
5
4
3
2
1
0
The 1H NMR spectrum of 2 recorded in chloroform shows quite
a different behaviour. The peak pattern, especially in the aromatic
region of the spectrum, indicates that the complex is not stable in
chloroform either, but since the solvent cannot offer a donor for
coordination, a different 1:1 complex from that formed in pyridine
or in DMSO is produced. One obvious possibility is that the com-
plex is dinuclear with the formula [(UO2)2(L)2] (3). Hence one
can find the signals for a free ligand and also the signals of the ura-
nyl complex which are different from those of 2 in pyridine or in
DMSO. The formation of this new complex can be explained
according to reaction (3), in which the zwitterionic complex is bro-
ken forming complex 3 and a free ligand.
2½UO2ðHLÞ2ꢂ ! ½ðUO2Þ2ðLÞ2ꢂ þ 2H2L
ð3Þ
0
20
40
60
80
100 2000
2500
The 1H NMR data strongly support the structure of [(UO2)2(L)2]
described in Scheme 3. Especially, four different new aromatic sig-
nals and a signal for a coordinated ArOMe group at 5.43 ppm sup-
port the structure of 3. The methoxy groups from one phenolic
moiety can take the fifth coordination site around the uranyl ion
in the xy-plane. This explains why a methyl singlet of the methoxy
group at 5.43 ppm is at so low a field. More support for 3 can be
obtained from the literature: the dimerization of the uranyl com-
plex, UO2(salophen)L (L = DMF, DMSO), occurs also in non-coordi-
nating chloroform [29].
Several efforts to obtain crystals of this dinuclear complex were
not successful. One reason for this failure can be seen from spec-
trum recorded in chloroform: it seems that the complex is decom-
posed in CDCl3 by moisture. This is indirectly observed from the
increase of the integrals related to the free ligand if the spectrum
is measured as a function of time. The explanation for this phe-
nomenon is most likely that moisture causes the decomposition
and it also prevents the crystallization. If a chloroform solution
of [UO2(HL)2] (2) is evaporated to dryness and the residue (H2L
and 3) is dissolved in acetonitrile, 2 is formed again.
Time (h)
Fig. 5. The result of the uranyl extraction study.
comes to the conclusion that also in pyridine this nitrogen is coor-
dinated to the U atom. The pyridine solvent can accept a proton
from the coordinated ligand. The observed low field doublets in
the spectra, similar to those observed in chloroform, support this
assumption. In DMSO, however, the situation remains somewhat
uncertain: although broad signals from these hydrogens are ob-
served in the spectra of 1 and 2, they appear in a higher field re-
gion, and their broadness indicates conformational flexibility
around N8 and thus the presence of a proton at N8.
Because almost all NMR spectra of the complexes recorded in
solution indicated that the complexes dissociate, 13C NMR CP/
MAS spectra of H2L and 2 were also recorded. However, the chem-
ical shifts of the carbon atoms around N8 were quite similar and no
confirmation of either proton transfer or nitrogen coordination in
solution could be totally ensured.
Finally the coordination of the N8 nitrogen to the uranyl centre
in deuterated solutions of complexes 2 and 3 forms another ques-
tion of interest. The formation of the dinuclear complex 3 in chlo-
roform most likely causes N8 to coordinate to the uranyl ion. If 1H
NMR data in CHCl3 is compared to those in other solvents, one
3.4. Uranyl ion extraction studies
The result of the uranyl ion extraction study at room tempera-
ture (ca. 22 °C) is shown in Fig. 5. The experimental setup is de-
scribed in Section 2.4. With this ligand, the transfer of the uranyl
ion from the water layer to the CH2Cl2 layer was 34% in three days
and 65% in three months. At the same time, the uranium concen-
tration in the control sample was constant. The organic layer
turned from colourless to red during the test time, indicating com-
plex formation, but no crystals were obtained. The reason for the
low extraction results of H2L is found from NMR studies in chloro-
form; the 1:2 complex decomposes to the free ligand and the dinu-
clear uranyl complex, which is not very stable in moist
dichloromethane. This causes the slow and inefficient extraction
process.
O
N
O
O
O
U
O
O
U
O
N
O
O
O
O
N
4. Conclusion
O
O
In conclusion, we have found that UO2(NO3)2ꢀ6H2O reacts with
the phenolic ligand N’,N’-bis(2-hydroxy-3-methoxy-5-(propen-2-
yl)benzyl-N-(2-aminoethyl)morpholine, H2L, in CH3CN to form
two different dioxouranium(VI) complexes. The complex of the
formula [UO2(HL)2]ꢀ2CH3CN was obtained from acetonitrile when
triethylamine was added to the reaction solution; without triethyl-
amine the formed uranyl complex had the formula [UO2(HL)
(NO3)(H2O)]. Both formed complexes have a zwitterionic nature
in the solid state with bideprotonated phenol groups, but the
N
O
Scheme 3. The suggested structure of the dinuclear complex 3 in chloroform, based
on its NMR data.

O. Wichmann et al. / Polyhedron 30 (2011) 477–485
485
complexes are formally electrically neutral as their charge is bal-
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