CREATED USING THE RSC COMMUNICATION TEMPLATE (VER. 2.0) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS
Communication
[JOURNAL NAME HERE] | www.rsc.org/[JOURNAL]
The first crystal structure of an actinide complex of the macrocyclic
ligand DOTA: a two dimensional uranyl-organic framework
Pierre Thuéry
5
10
15
20
25
30
35
40
45
50
Receipt/Acceptance Data [DO NOT ALTER/DELETE THIS TEXT]
Publication data [DO NOT ALTER/DELETE THIS TEXT]
DOI: 10.1039/b000000x [DO NOT ALTER/DELETE THIS TEXT]
Reaction of excess uranyl nitrate with DOTA (H4L) under
hydrothermal
conditions
gave
the
complex
[(UO2)2(H2L)(C2O4)(H2O)2]·6H2O 1, in which the oxalato ligand
was generated in situ. Each H2L2– ligand is bound to four uranyl
groups, further oxalato-bridging giving rise to corrugated layers.
This result shows the interest of DOTA as a square assembler.
The macrocyclic ligand DOTA (1,4,7,10-tetraazacyclododecaneN,N',N",N"'-tetraacetic acid), denoted H4L hereafter, is an armed
cyclen which has been much investigated for the exceptional
stability and properties of its complexes with calcium and
lanthanide ions.1,2 In particular, its Gd(III) complex is one of the
most powerful contrast agents in Magnetic Resonance Imaging
(MRI).3,4 The crystal structures of the DOTA complexes with
Ca(II),5 3d-block transition metal ions [Fe(III), Ni(II), Cu(II),
Zn(II)],4,6 Ga(III),7 Bi(III)8 and rare-earth ions spanning the whole
ion size range4,9 are reported in the Cambridge Structural Database
(CSD, Version 5.28)10 and the recent literature. In all cases, the
ligand chelates the cation through the four nitrogen atoms and two
or three (3d-block transition metals, Ga(III)) to four (all other
cases) carboxylic oxygen atoms. Although the complexation of
Th(IV) and U(IV) by the larger, related macrocycle HEHA
(1,4,7,10,13,16-hexaazacyclooctadecane-N,N',N",N"',N"",N""'hexaacetic acid) has been studied in solution,11 no crystal structure
of an actinide complex of DOTA was ever reported. In particular, a
completely different complexation mode of DOTA can be expected
in the case of the linear uranyl ion UO22+, which has strong
stereochemical requirements and cannot be chelated by the four
nitrogen atoms since larger macrocycles, such as hexacyclen
(1,4,7,10,13,16-hexaazacyclooctadecane), are required for that.12
Uranyl-based metallamacrocycles can be obtained from
tetracarboxylic acids sufficiently rigid and with the right geometry,
such as (2R,3R,4S,5S)-tetrahydrofurantetracarboxylic acid,13 but
DOTA appears too flexible and maladapted to that. In contrast, it is
a promising ligand for the synthesis of uranyl-organic frameworks
(UOFs) by hydrothermal methods,14 as illustrated herein.
Isolation of the uranyl complex of DOTA proved a difficult task,
and succeeded only with a large excess of uranyl and in the absence
of a base,† yielding a crystalline material which was characterized
as [(UO2)2(H2L)(C2O4)(H2O)2]·6H2O 1.‡ Heating at 180°C resulted
in partial decomposition of the ligand and formation of oxalic acid
in situ, as previously reported for different acids such as orotic,15
3,5-pyrazoledicarboxylic,16 2-pyrazinecarboxylic,17 L(+)-tartaric18
and L-pyroglutamic acids.19 Oxalate formation is likely the result of
acid decarboxylation followed by CO2 coupling.19 The crystal
CEA/Saclay, DSM/DRECAM/SCM (CNRS URA 331), Bât. 125, 91191
Gif-sur-Yvette, France. E-mail: pierre.thuery@cea.fr
This journal © Royal Society of Chemistry
structure of 1 is represented in Fig. 1. The asymmetric unit contains
two uranyl ions, one zwitterionic H2L2– ligand, in which the four
carboxylic acid groups are deprotonated, but two ammonium
groups are formed, two oxalato halves and eight water molecules.
55
60
65
Fig. 1 View of complex 1. Carbon-bound hydrogen atoms and
uncoordinated water molecules have been omitted. Displacement
ellipsoids are drawn at the 50% probability level. Symmetry codes: ' = 1 –
x, y – ½, ½ – z; " = 1 – x, –y, –z; # = 1 – x, –y, 1 – z; * = 1 – x, ½ + y, ½ –
z. Selected bond lengths (Å) and angles (°): U1–O1 1.771(4), U1–O2
1.778(4), U1–O5 2.312(5), U1–O9' 2.293(5), U1–O13 2.459(5), U1–O14
2.450(5), U1–O15 2.411(5), U2–O3 1.770(4), U2–O4 1.767(4), U2–O7
2.310(5), U2–O16 2.439(5), U2–O17 2.451(4), U2–O11' 2.291(5), U2–
O18 2.467(4), O1–U1–O2 179.1(2), O5–U1–O9' 77.59(16), O9'–U1–O13
73.63(16), O13–U1–O14 65.20(15), O14–U1–O15 67.63(16), O15–U1–
O5 76.26(17), O3–U2–O4 180.0(3), O7–U2–O16 74.06(16), O16–U2–
O17 66.16(15), O17–U2–O11' 73.69(16), O11'–U2–O18 73.25(16), O18–
U2–O7 72.83(15).
70
75
80
85
Each uranyl ion is bound to two oxygen atoms from the bridging
oxalato ligands, two oxygen atoms from two H2L2– moieties and
one water molecule, which results in the usual pentagonal
bipyramidal uranium coordination geometry. The average U–
O(H2L), U–O(C2O4) and U–O(water) bond lengths of 2.302(10),
2.450(7) and 2.44(3) Å, respectively, are unexceptional. The
average equatorial planes of the two uranyl ions (rms deviations
0.072 and 0.003 Å) define a dihedral angle of 6.87(8)° and are thus
nearly parallel. The oxalato bridges are located on inversion centers
and they are bis-chelating with each uranium atom bound to an
oxygen atom from each acid group, as usually observed.18,19
The bis-deprotonated DOTA molecule assumes the so-called
[3333] square conformation, with carbon atoms at the corners and
nitrogen atoms along the sides, as in most other complexes,5–9 and
the four monodentate acetate arms are located on the same side of
[JOURNAL], 200X, 00, 0000 | 1
CREATED USING THE RSC COMMUNICATION TEMPLATE (VER. 2.0) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS
Communication
90
95
100
105
the ring. The three torsion angles in each C–N–C–C–N–C fragment
assume average values of 81(4), 57(2) and –164(1)°, similar to
those in the complexes in which the four nitrogen atoms are
chelating, this being probably due to the presence of two NH···N
intramolecular hydrogen bonds (NH···O hydrogen bonds are
observed in diprotonated DOTA,9f and result in preorganization for
complexation). Two uncoordinated oxygen atoms in 1 (O6 and
O10) are involved in hydrogen bonds with one of the water ligands
(O18). Successive carboxylate groups are approximately
perpendicular to one another, with the coordinated oxygen atoms
directed outwards, thus giving the ligand a C4 pseudo-symmetry.
The H2L2– conformation is thus very close to that in the complexes
in which the chelated metal is bound to the four nitrogen and four
oxygen atoms with a distorted square antiprismatic
environment,5,8,9 but the ligand is connected here to four different
metal centres, each of them part of an oxalato-bridged dimer. The
strongly chelating ligand DOTA thus becomes a square uranyl
assembler. A similar situation arises with the nitrilotriacetato
ligand, usually chelating, but turned into a trigonal node by the
peculiar geometric requirements of uranyl, and which is also
complexed in its zwitterionic form.20
www.rsc.org/[JOURNAL] | [JOURNAL NAME HERE]
120
125
130
resulting in sheets parallel to the bc plane. The H2L2– moieties are
located alternately above and below the sheet plane along the b
axis, which results in severe sheet corrugation and interpenetration
along the a axis. Whereas the layers are very tightly packed when
viewed down the c axis, channels are formed down the a and b
axis. These channels are occupied by the uncoordinated (and partly
disordered) water molecules which are involved in hydrogen bonds
with the coordinated water molecule directed towards the channel
cavity (O15) and with one another. The size of the largest channels,
directed along the a axis and of quite irregular shape, is
approximately 5  8 Å (Fig. 3), whereas those directed along b
have the same largest dimension, but a width of about 3 Å only
between oxo groups.
135
140
145
150
155
Fig. 3 CPK representation of a sheet parallel to the bc plane showing the
largest channels. Uncoordinated water molecules and hydrogen atoms are
omitted. Yellow: U, red: O, violet: N, blue: C.
Polymeric frameworks involving DOTA have previously been
obtained, resulting from bridging carboxylic/ate groups and often
involving alkali or alkaline-earth metal ions located outside the
cavity,4,5,9d,g but, to the best of our knowledge, complex 1 is the first
example of the use of DOTA as a square assembler. This result
opens new perspectives for the synthesis of UOFs, which are
presently under investigation.
Notes and references
160
165
170
110
Fig. 2 Projections of the framework in 1 down the a (top), b (middle) and
c (bottom) axis. The coordination polyhedra of uranium are represented
and the other atoms are shown as spheres of arbitrary radii.
Uncoordinated water molecules and hydrogen atoms are omitted.
175
115
The framework thus formed in 1 is two-dimensional, as shown
in Fig. 2. The oxalato-bridged dimers [(UO2)2(C2O4)(H2O)2]2+ are
arranged in rows along the three cell axis and these rows are
connected to one another by H2L2– bridges along the b and c axis,
2 | [JOURNAL], 200X, 00, 0000
180
† Synthesis of 1. DOTA (14 mg, 0.035 mmol), a fourfold excess of
UO2(NO3)2·6H2O (70 mg, 0.139 mmol) and demineralized water (1 mL)
were placed in a 15 mL tightly closed glass vessel and heated at 180°C
under autogenous pressure (ca. 1.1 MPa), yielding light yellow crystals of
complex 1 within 24 hours (11 mg, 27% yield on the basis of the acid).
Anal. calcd. for C18H42N4O24U2: C, 18.41; H, 3.60; N, 4.77. Found: C,
18.26; H, 3.57; N, 4.63%. Reaction of DOTA with a stoichiometric
amount of uranyl nitrate and/or in the presence of a base (NaOH, amines)
never gave any crystalline material in these experimental conditions.
‡ Crystal data for 1: C18H42N4O24U2, M = 1174.62, monoclinic, space
group P21/c, a = 6.7056(3), b = 18.3989(10), c = 27.4530(17) Å,  =
92.523(4)°, V = 3383.8(3) Å3, Z = 4, T = 100(2) K. Refinement of 466
parameters on 6413 independent reflections out of 136783 measured
reflections (Rint = 0.047) led to R1 = 0.033, wR2 = 0.078, S = 1.029, min
= –1.51, max = 1.72 e Å–3. Data were collected on a Nonius Kappa-CCD
area-detector diffractometer and processed with HKL2000.21 Absorption
effects were corrected with the program SCALEPACK.21 The structure
was solved by Patterson map interpretation and refined by full-matrix
least-squares on F2 with SHELXTL.22 All non-hydrogen atoms were
refined with anisotropic displacement parameters, with restraints for the
badly resolved water solvent molecules. The hydrogen atoms bound to
nitrogen and coordinated water oxygen atoms were found on Fourier-
This journal © Royal Society of Chemistry
CREATED USING THE RSC COMMUNICATION TEMPLATE (VER. 2.0) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS
[JOURNAL NAME HERE] | www.rsc.org/[JOURNAL]
185
difference maps and the carbon-bound hydrogen atoms were introduced at
calculated positions. All were treated as riding atoms with an isotropic
displacement parameter equal to 1.2 times that of the parent atom. The
drawings were done with SHELXTL,22 Balls & Sticks23 and ORTEP3/POVRay.24
CCDC
reference
number.
See
http://www.rsc.org:suppdata/cc for crystallographic data in CIF format.
1
190
2
3
4
195
5
6
200
7
8
205
9
210
215
220
10
11
12
13
225
14
15
230
235
Communication
16
17
18
19
20
21
22
240
23
24
H. Stetter and W. Frank, Angew. Chem., Int. Ed. Engl., 1976, 15,
686.
J. F. Desreux, Inorg. Chem., 1980, 19, 1319.
R. B. Lauffer, Chem. Rev., 1987, 87, 901.
C. A. Chang, L. C. Francesconi, M. F. Malley, K. Kumar, J. Z.
Gougoutas, M. F. Tweedle, D. W. Lee and L. J. Wilson, Inorg.
Chem., 1993, 32, 3501.
O. P. Anderson and J. H. Reibenspies, Acta Crystallogr., Section C,
1996, 52, 792.
(a) A. Riesen, M. Zehnder and T. A. Kaden, Helv. Chim. Acta,
1986, 69, 2067 and 2074; (b) A. Riesen, M. Zehnder and T. A.
Kaden, Acta Crystallogr., Section C, 1991, 47, 531.
N. A. Viola, R. S. Rarig Jr., W. Ouellette and R. P. Doyle,
Polyhedron, 2006, 25, 3457.
E. Csajbók, Z. Baranyai, I. Bányai, E. Brücher, R. Király, A.
Müller-Fahrnow, J. Platzek, B. Radüchel and M. Schäfer, Inorg.
Chem., 2003, 42, 2342.
(a) M. R. Spirlet, J. Rebizant, J. F. Desreux and M. F. Loncin,
Inorg. Chem., 1984, 23, 359; (b) J. P. Dubost, J. M. Leger, M. H.
Langlois, D. Meyer and M. Schaefer, C. R. Séances Acad. Sci., Sér.
II, 1991, 312, 349; (c) S. Aime, A. Barge, M. Botta, M. Fasano, J.
D. Ayala and G. Bombieri, Inorg. Chim. Acta, 1996, 246, 423; (d)
S. Aime, A. Barge, F. Benetollo, G. Bombieri, M. Botta and F.
Uggeri, Inorg. Chem., 1997, 36, 4287; (e) F. Benetollo, G.
Bombieri, S. Aime and M. Botta, Acta Crystallogr., Section C,
1999, 55, 353; (f) S. Aime, A. Barge, J. I. Bruce, M. Botta, J. A. K.
Howard, J. M. Moloney, D. Parker, A. S. de Sousa and M. Woods,
J. Am. Chem. Soc., 1999, 121, 5762; (g) F. Benetollo, G. Bombieri,
L. Calabi, S. Aime and M. Botta, Inorg. Chem., 2003, 42, 148; (h)
L. Burai, E. Tóth, G. Moreau, A. Sour, R. Scopelliti and A. E.
Merbach, Chem. Eur. J., 2003, 9, 1394.
F. H. Allen, Acta Crystallogr., Sect. B, 2002, 58, 380.
V. Jacques and J. F. Desreux, Inorg. Chem., 1996, 35, 7205.
P. Thuéry, N. Keller, M. Lance, J. D. Vigner and M. Nierlich, New
J. Chem., 1995, 19, 619.
P. Thuéry, C. Villiers, J. Jaud, M. Ephritikhine and B. Masci, J. Am.
Chem. Soc., 2004, 126, 6838.
C. L. Cahill, D. T. de Lill and M. Frisch, CrystEngComm, 2007, 9,
15 and references therein.
X. Li, R. Cao, D. Sun, Q. Shi, W. Bi and M. Hong, Inorg. Chem.
Commun., 2003, 6, 815.
M. Frisch and C. L. Cahill, Dalton Trans., 2005, 1518.
B. Li, W. Gu, L. Z. Zhang, J. Qu, Z. P. Ma, X. Liu and D. Z. Liao,
Inorg. Chem., 2006, 45, 10425.
P. Thuéry, Polyhedron, 2007, 26, 101.
M. Frisch and C. L. Cahill, J. Solid State Chem., 2007, 180, 2597.
(a) M. S. Grigoriev, C. Den Auwer, D. Meyer and P. Moisy, Acta
Crystallogr., Section C, 2006, 62, m163; (b) P. Thuéry, Inorg.
Chem. Commun., 2007, 10, 423.
Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276, 307.
G. M. Sheldrick, SHELXTL, Version 5.1, Bruker AXS Inc.,
Madison, WI, USA, 1999.
T. C. Ozawa and S. J. Kang, J. Appl. Cryst., 2004, 37, 679.
L. J. Farrugia, J. Appl. Cryst., 1997, 30, 565.
This journal © Royal Society of Chemistry
[JOURNAL], 200X, 00, 0000 | 3
CREATED USING THE RSC COMMUNICATION TEMPLATE (VER. 2.0) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS
Communication
245
www.rsc.org/[JOURNAL] | [JOURNAL NAME HERE]
Graphical Abstract:
The complex formed by uranyl ions with DOTA and oxalato ligands is a two-dimensional, heavily corrugated framework which
demonstrates the interest of DOTA as a square assembler.
4 | [JOURNAL], 200X, 00, 0000
This journal © Royal Society of Chemistry