Dioxouranium complexes with acetylpyridine benzoylhydrazones and related ligands

Article abstract of DOI:10.1002/zaac.200400024

Acetylpyridine benzoylhydrazone and related ligands react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu₄] ₂[UO₂Cl₄] to form air-stable complexes. Reactions with 2,6-diacetylpyridinebis(benzoylhydrazone) (H₂L ^1a) or 2,6-diacetylpyridinebis(salicylhydrazone) (H₂L ^1b) give yellow products of the composition [UO₂(L ¹)]. The neutral compounds contain doubly deprotonated ligands and possess a distorted pentagonalbipyramidal structure. The hydroxo groups of the salicylhydrazonato ligand do not contribute to the complexation of the metal. The equatorial coordination spheres of the complexes can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting deep-red complexes have hexagonal-bipyramidal coordination environments with the oxo ligands in axial positions. The sterical strains inside the hexagonal plane can be reduced when two tridentate benzoylhydrazonato ligands are used instead of the pentadentate 2,6-diacetylpyridine derivatives. Acetylpyridine benzoylhydrazone (HL²) and bis(2-pyridyl)ketone benzoylhydrazone (HL³) deprotonate and form neutral, red [UO ₂(L)₂] complexes. The equatorial coordination spheres of these complexes are puckered hexagons. X-ray diffraction studies on [UO ₂(L^1a)(pyridine)], [UO₂(L^1b)(DMSO)], [UO₂(L²)₂] and [UO₂(L ³)₂] show relatively short U-O bonds to the benzoylic oxygen atoms between 2.328(6) and 2.389(8) A. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U-N bond lengths: 2.588(7)-2.701(6) A).

Full text of DOI:10.1002/zaac.200400024

Dioxouranium Complexes with Acetylpyridine Benzoylhydrazones and Related
Ligands
C. C. Gatto, E. Schulz Lang
Santa Maria/Brazil, Department of Inorganic Chemistry of the University of Santa Maria
A. Kupfer, A. Hagenbach, D. Wille, U. Abram*
Berlin, Institut für Chemie der Freien Universität Berlin
Received February 2nd, 2004.
Abstract. Acetylpyridine benzoylhydrazone and related ligands
react with common dioxouranium(VI) compounds such as uranyl
nitrate or [NBu4]2[UO2Cl4] to form air-stable complexes. Reactions
with 2,6-diacetylpyridinebis(benzoylhydrazone) (H2L1a) or 2,6-di-
acetylpyridinebis(salicylhydrazone) (H2L1b) give yellow products of
the composition [UO2(L1)]. The neutral compounds contain
doubly deprotonated ligands and possess a distorted pentagonal-
bipyramidal structure. The hydroxo groups of the salicylhydrazon-
ato ligand do not contribute to the complexation of the metal. The
equatorial coordination spheres of the complexes can be extended
by the addition of a monodentate ligand such as pyridine or
DMSO. The uranium atoms in the resulting deep-red complexes
have hexagonal-bipyramidal coordination environments with the
oxo ligands in axial positions.
pentadentate 2,6-diacetylpyridine derivatives. Acetylpyridine ben-
zoylhydrazone (HL2) and bis(2-pyridyl)ketone benzoylhydrazone
(HL3) deprotonate and form neutral, red [UO2(L)2] complexes. The
equatorial coordination spheres of these complexes are puckered
hexagons.
X-ray
diffraction
studies
on
[UO2(L1a)(pyridine)],
[UO2(L1b)(DMSO)], [UO2(L2)2] and [UO2(L3)2] show relatively
short UϪO bonds to the benzoylic oxygen atoms between 2.328(6)
˚
and 2.389(8) A. This suggests a preference of these donor sites of
the ligands over their imino and amine functionalities (UϪN bond
˚
lengths: 2.588(7)Ϫ2.701(6) A ).
Keywords: Uranium; Benzoylhydrazonato ligands, Actinides,
The sterical strains inside the hexagonal plane can be reduced when
two tridentate benzoylhydrazonato ligands are used instead of the
Uranyl chelates; Structure analysis
Dioxouranium-Komplexe mit Acetylpyridinbenzoylhydrazon und verwandten Liganden
Inhaltsübersicht. Acetylpyridinbenzoylhydrazon und davon abgelei-
tete Liganden reagieren mit Uranylnitrat oder [NBu4]2[UO2Cl4]
unter Bildung luftstabiler Dioxouranium(VI)-Komplexe. Bei Reak-
tionen mit 2,6-Diacetylpyridinbis(benzoylhydrazon) (H2L1a) und
Die sterische Belastung der äquatorialen Koordinationsebene kann
verringert werden, wenn anstelle der fünfzähnigen H2L1-Liganden
dreizähnige Benzoylhydrazonato-Liganden verwendet werden.
2-Acetylpyridinbenzoylhydrazon (HL2) und Bis(2-pyridyl)keton-
benzoylhydrazon (HL3) bilden unter einfacher Deprotonierung
neutrale Komplexe der Zusammensetzung [UO2(L)2]. Die hexago-
nalen Grundflächen der gebildeten Bipyramiden sind in diesen
Produkten deutlich gewellt.
2,6-Diacetylpyridinbis(salicylhydrazon) (H2L1b
) entstehen gelbe
Pulver der Zusammensetzung [UO2(L1)]. Die Koordination des
Uranatoms in den Neutralkomplexen mit doppelt deprotonierten
organischen Liganden ist verzerrt pentagonal-bipyramidal. Die
Hydroxosubstituenten des Salicylhydrazonato-Liganden [L1b 2Ϫ
]
Kristallstrukturanalysen von [UO2(L1a)(Pyridin)], [UO2(L1b)-
(DMSO)], [UO2(L2)2] und [UO2(L3)2] zeigen relativ kurze Bindun-
gen zwischen den Uranatomen und den Benzoylgruppierungen
sind an der Komplexierung des Metallatoms nicht beteiligt.
Reaktionen von [UO2(L1)]-Komplexen mit monodentaten Ligan-
den wie Pyridin oder DMSO führen zur Aufweitung der äquatoria-
len Koordinationssphäre und zur Bildung von tiefroten, kristalli-
nen Verbindungen mit einer verzerrten, hexagonal-bipyramidalen
Koordination um die Uranatome.
˚
(2.328(6)Ϫ2.389(8) A). Das legt eine bevorzugte Bindung an die
Sauerstoffatome der Liganden nahe, während die UranϪStickstoff-
˚
Bindungen deutlich länger sind (2.588(7)Ϫ2.701(6) A).
Introduction
lished a report on the structural chemistry of thiosemicar-
bazonato complexes of uranium(VI) [1]. The formation of
complexes with medium stability was observed with acetyl-
pyridine thiosemicarbazone in which the pyridine nitrogen
atom provides an additional donor site to the metal atoms.
More stable complexes are expected with ‘harder’ donor
atoms such as oxygen, as is provided by semicarbazones or
hydrazones. A number of studies have been undertaken with
both ligand systems and the formation of chelates with vari-
ous compositions have been suggested on the basis of spec-
As a part of our systematic studies of the coordination
chemistry of the early actinide elements, we recently pub-
* Prof. Dr. Ulrich Abram
Freie Universität Berlin
Institut für Chemie
Fabeckstraße 34Ϫ36
D-14195 Berlin
Email: abram@chemie.fu-berlin.de
Z. Anorg. Allg. Chem. 2004, 630, 735Ϫ741
DOI: 10.1002/zaac.200400024
 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
735

C. C. Gatto, E. Schulz Lang, A. Kupfer, A. Hagenbach, D. Wille, U. Abram
troscopic data [2]. Some of the compounds have been pro-
data in dependence on the solvents and the uranium start-
ing materials used [5b]. The only compound in this report
which has been characterized by X-ray crystallography,
however, is a neutral dioxouranium(VI) complex with a
doubly deprotonated organic ligand in which the uranium
atom is seven-coordinate.
posed for the spectrophotometric determination of metal
ions including UO22ϩ [3], but less is known about the com-
position of the coordination environment of the metal. First
structural reports performed with 2,6-diacetylpyri-
dinebis(2Ј-pyridyl)hydrazones [4] and benzoylhydrazones [5]
describe uranyl complexes having pentagonal bipyramidal
or hexagonal-bipyramidal coordination spheres at the
uranium atoms. The reasons for the respective composition
of the equatorial coordination spheres and the influence of
substituents are not yet clear. In the present paper, we de-
scribe the reactions of uranyl nitrate and [NBu4]2[UO2Cl4]
with 2,6-diacetylpyridinebis(benzoylhydrazone) (H2L1a),
2,6-diacetylpyridinebis(salicylhydrazone) (H2L1b), 2-acetyl-
pyridine benzoylhydrazone (HL2) and bis(2-pyridyl)ketone
benzoylhydrazone (HL3), Scheme 1, and the solid state
structures of the products.
Similar complexes are obtained when the ligands H2L1a
or H2L1b are heated with UO2(NO3)2 · 6 H2O or [NBu4]2-
[UO2Cl4] in boiling methanol. The reaction is faster when
a supporting base such as triethylamine is added, but this
is not mandatory. Yellow precipitates are formed upon cool-
ing, which have been isolated and characterized by elemen-
tal analysis, IR and NMR measurements showing that the
products formed from the different uranium precursors
were identical. The UϭO double bonds show characteristic
IR bands between 900 and 905 cmϪ1. This value is in ac-
cord with the neutral uranyl complexes in ref. [5b], whereas
anionic derivatives absorb in the range between 920 and
950 cmϪ1. The proton NMR spectra prove the absence of
the NH protons of the organic ligands, whereas an OH sig-
nal for the complex with ligand [L1b]2Ϫ was observed at
12.9 ppm. This is in the same position as in H2L1b, which
suggests that the hydroxylic group of the salicylhydrazone
does not contribute to the coordination of the metal atom.
No evidence was found for the coordination of methanol
or water. This allows the conclusion that complexes of the
composition [UO2L1] have been formed. These complexes
possess the same coordination sphere at the metal atoms as
the uranyl complex with 2,6-diacetylpyridine bis(methoxy-
benzoylhydrazone), which shows distorted pentagonal-bi-
pyramidal coordination of the metal atom [5b]. No evi-
dence could be found for anionic uranyl complexes with
non-deprotonated or monodeprotonated ligands. The bond
angles between neighbouring atoms inside the equatorial
coordination sphere are approximately 63° (4 times) and
107° (between the oxygen atoms of the benzoyl groups) [5b]
(see also Table 1 and Fig. 4), which suggests the possibility
of the extension of the coordination number by the addition
of an appropriate monodentate ligand. This has been pro-
ven by heating the [UO2(L1)] complexes in coordinating sol-
vents such as DMSO, pyridine or THF. The yellow solids
slowly dissolve in these solvents and the colour changes to
red. A reaction sequence resulting in the formation of neu-
tral [UO2(L1)(solvent)] complexes can be derived (see
Scheme 2). The products can be isolated in crystalline form
by the slow evaporation of the solvents (THF and pyridine)
or addition of a small amount of water and slow cooling
(DMSO). The UϭO stretching vibrations are shifted to
Scheme 1
Results and Discussion
UO2(NO3)2 · 6H2O as well as [Bu4N]2[UO2Cl4] react with
the benzoylhydrazone or salicylhydrazone ligands
H2L1ϪHL3 in boiling methanol under complete substi-
tution of the equatorial coordination sphere of the metal
atom. Under these conditions, complete deprotonation of
the ligands is observed independent of the uranium precur-
sor used, and neutral dioxouranium complexes are formed.
No evidence has been found for the formation of complexes
with non-deprotonated or semi-deprotonated (H2L1) hydra-
zone ligands as has been observed for related semicarb-
azones of chromium(III) [6] and other highly charged metal
ions including the uranyl ion [7]. A complicated coordi-
nation pattern has also been described for products ob-
tained from reactions of uranyl salts and 2,6-diacetylpyri-
dine bis(p-methoxybenzoylhydrazone), where different
structures have been assigned on the basis of spectroscopic
Scheme 2
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Z. Anorg. Allg. Chem. 2004, 630, 735Ϫ741

Dioxouranium Complexes
formed by the atoms U, N21, O18, N2, N1 N2Ј and O18Ј:
˚
0.201(3) A for O18 and O18Ј, r.m.s. 0.1455). The XϪUϪY
angles (X and Y are neighbouring equatorial donor atoms)
range from 59.34 to 61.39°. The torsion angle between the
pyridine ring and the hexagonal plane is 61.4(1)°, which
minimises steric hindrance between the pyridine ligand and
the benzoylhydrazonato arms of the pentadentate ligand
and the two oxo oxygen atoms. The extension of the coordi-
nation number of uranium causes lengthening of the UϪN
bonds to the chelating ligand as can be seen from a com-
parison with the corresponding data in the seven-coordi-
nate complex [UO2(L1c)] [5b]. Selected bond lengths and
angles of this compound are included in Table 1; the atomic
numbering has been adopted to fit the labelling scheme ap-
plied in the present paper. No significant change can be
derived for the bonding situation inside the hydrazonato
ligands, which are doubly deprotonated in all complexes de-
scribed in this paper. Whereas the double bond between C7
and N2 is almost localised, a delocalisation of the electron
density of the C17ϪO18 double bond can be concluded,
which results in a significant shortening of the C17ϪN3
bond as a consequence of complex formation. This situ-
ation can best be described by the bonding scheme re-
presented in I, irrespective of the coordination number of
the uranium atom. It has also been found in
[UO2(L1b)(DMSO)], which has been prepared by heating of
[UO2(L1b)] in DMSO.
Figure
1
Ellipsoid presentation [13] of [UO2(L1a)(pyridine)].
Thermal ellipsoids represent 50 per cent probability.
1a
˚
Table 1 Selected bond lengths /A and angles/° in [UO2(L )-
(pyridine)], [UO2(L1b)(DMSO)] and [UO2(L1c)].
[UO2(L)1a(pyridine)] [UO2(L)1b(DMSO)] [UO2(L)1c a)
]
UϪO10
UϪO20
UϪO18
UϪN2
1.774(2)
Ϫ
1.77(1)
1.777(9)
2.389(8)
2.613(9)
2.65(1)
2.527(9)
1.28(1)
1.32(1)
1.38(1)
1.31(1)
1.45(1)
1.49(1)
1.77
1.77
2.356(3)
2.630(3)
2.685(8)
2.68(1)
1.280(5)
1.293(5)
1.398(5)
1.284(4)
1.455(6)
1.502(6)
2.32/2.30b)
2.47/2.49b)
2.52
UϪN1
UϪN21/O30
O18ϪC17
C17ϪN3
N3ϪN2
N2ϪC7
C7ϪC6
Ϫ
1.26/1.30b)
1.33/1.30b)
1.41/1.40b)
1.31/1.31b)
1.50/1.48b)
1.50/1.51b)
C7ϪC8
O18ϪUϪN2
N2ϪUϪN1
O18ϪUϪN21/O30 61.39(7)
60.07(9)
59.34(7)
60.3(3)
59.8(2)
61.8(2)
63.5/63.3b)
63.3/63.3b)
Ϫ
O18ϪUϪO18Ј
122.8(1)c)
119.2(4)d)
106.8
Scheme 3
N1···N2
N2···O18
2.631(5)
2.507(4)
2.62/2.63
2.52/2.52
[UO2(L1b)(DMSO)] crystallizes as large red blocks, and
the results of an X-ray structure analysis confirm the spec-
troscopic conclusion that the hydroxylic group of the
salicylhydrazone is not involved in the coordination of the
metal atom. The structure of the complex is illustrated in
Figure 2. The OH substituents of the salicylic groups are
disordered. The occupation of the two positions is about
0.8/0.2 with a preference of the position on C16 (Figure 2)
which allows intramolecular hydrogen bonds to O18 and
O30. The overall bonding pattern in [UO2(L1b)(DMSO)] is
similar to that in [UO2(L1a)(pyridine)], with the uranium
atom in an almost regular hexagonal-bipyramidal coordi-
nation environment. Only small deviations from planarity
can be found for the hexagonal plane (maximum deviation:
a) Values taken from ref. [5b] and adopted to the atomic labelling schemes
given in Figures 1 and 2. b) Two values since there is no intramolecular
symmetry in this complex. c) Symmetry operation: 1Ϫx, Ϫy, z. d) Symmetry
operation: x, Ϫ0.5Ϫy, z.
higher frequencies compared with the values in the
[UO2(L1)] complexes and occur between 914 and 920 cmϪ1
.
Similar changes in the position of the uranyl bands in de-
pendence on the coordination number of the metal atom
have been observed previously [5b].
Single
crystals
of
[UO2(L1a)(pyridine)]
and
[UO2(L1b)(DMSO)] have been studied by X-ray crystal-
lography, showing that the complexes possess eight-coordi-
nate uranium atoms. An ellipsoid representation of the mo-
lecular structure of [UO2(L1a)(pyridine)] is shown in Figure
1. Selected bond lengths and angles are summarised in
Table 1. The coordination environment of the uranium
atom can be described as an almost perfect hexagonal bi-
pyramid with a planar equatorial coordination sphere
(maximum deviation from a mean least-square plane
˚
0.170(4) A for O30, r.m.s. 0.1459), and the bond angles are
very close to 60°. The corresponding values and selected
bond lengths are listed in Table 1. It is interesting to note
that the increase in coordination number and the observed
lengthening of the uranium-nitrogen bonds are not related
to an increase of the bite angles of the binding sites, which
Z. Anorg. Allg. Chem. 2004, 630, 735Ϫ741
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C. C. Gatto, E. Schulz Lang, A. Kupfer, A. Hagenbach, D. Wille, U. Abram
Figure
2
Ellipsoid presentation [13] of [UO2(L1b)(DMSO)].
Thermal ellipsoids represent 50 per cent probability.
Figure 3 Ellipsoid presentation [13] of [UO2(L2)2]. Thermal
ellipsoids represent 50 per cent probability.
can be estimated by the intramolecular distances between
the donor atoms N1 and N2 or N2 and O18. The corre-
sponding values are also listed in Table 1.
More distortions from an ideal hexagonal bipyramid are
found in the structures of the complexes [UO2(L2)2] and
[UO2(L3)2], which also possess coordination number 8 at
the uranium atoms. The compounds are formed during re-
actions of uranyl nitrate or [NBu4]2[UO2Cl4] with an excess
of the ligands in boiling methanol. They precipitate as
orange-red solids directly from the reaction mixtures and
recrystallisation from hot methanol or CHCl3/methanol
mixtures results in red crystals. The IR spectra show the
expected ν(UO2) bands at 912 cmϪ1 ([UO2(L2)2]) and
911 cmϪ1 ([UO2(L3)2]). The absences of NH bands indicates
deprotonation of the hydrazones; the coordination of the
benzoyl group is strongly suggested by the shift of the corre-
sponding ν(CϭO) bands to lower frequencies. A shift of the
band at 990 cmϪ1 in the spectra of the proligands, which
can be assigned to the breathing motion of the pyridine
ring, to higher frequencies indicates the coordination of the
pyridyl groups and, thus, a tridentate, monoanionic bond-
ing scheme is expected for both of these hydrazones, irres-
pective of the possible binding mode of HL3 as a bidentate,
neutral bipyridine analogue, which has been observed re-
cently for a rhenium() tricarbonyl complex [8].
The coordination environments of the uranium atoms in
the molecular structures of [UO2(L2)2] (Fig. 3) and
[UO2(L3)2] (Fig. 4) are similar and can best be described
as a strongly distorted hexagonal bipyramid. Selected bond
lengths and angles of both complexes are summarized in
Table 2. For [UO2(L2)2], the atomic labelling scheme of
[UO2(L3)2] has been applied, with the exception that the
second [L2]Ϫ ligand is symmetry-generated in [UO2(L2)2]
since the atoms O10, U and O20 are situated on a 2-fold
crystallographic axis. The UϪN bond lengths in both com-
plexes are in the same range as has been found in [UO2(L1)-
(solvent)] complexes with 8-coordinate uranium atoms and
are accordingly longer than the values in [UO2(L1c)]. This
is another indication that the observed bond lengthening is
due to steric overcrowding of the equatorial coordination
spheres in the compounds with coordination number 8 at
the metal atoms.
Figure 4 Ellipsoid presentation [13] of [UO2(L3)2]. Thermal
ellipsoids represent 50 per cent probability.
The six equatorial atoms in [UO2(L2)2] and [UO2(L3)2]
form puckered hexagons in which the five-membered che-
late rings are almost planar and angles between 13° and 18°
are established between them. This allows for the minimis-
ation of steric interaction. Figure 5 shows a comparison of
the coordination spheres of [UO2(L1c)], [UO2(L1a)-
(pyridine)] and [UO2(L3)2] containing uranium atoms with
the coordination numbers seven and eight. Particularly the
side views indicate that the sterical hindrance inside the
equatorial coordination sphere is reduced by the coordi-
nation of two tridentate ligands rather than a 5ϩ1 coordi-
nation as is established in [UO2(L1a)(pyridine)] or
[UO2(L1b)(DMSO)]. The views along the uranyl units, how-
ever, show almost regular hexagons for the equatorial coor-
dination spheres of both structural types.
The present study shows that acetylpyridine benzoyl-
hydrazones and related ligands are well suited for the for-
mation of stable complexes with dioxouranium(VI) units.
All hydrazone units of the ligands are deprotonated in the
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Z. Anorg. Allg. Chem. 2004, 630, 735Ϫ741

Dioxouranium Complexes
2
˚
Experimental
Table 2 Selected bond lengths/A and angles/° in [UO2(L )2] and
[UO2(L3)2].
HL1a, HL1b, HL2 and HL3 were prepared by refluxing equivalent
amounts of 2,6-diacetylpyridine (ALDRICH), 2-acetylpyridine
(ALDRICH) or di(2-pyridine)ketone (ACROS) with equivalent
amounts of benzoylhydrazine (ACROS) or salicylhydrazine
(ACROS) in ethanol and recrystallized from ethanol/water [8,10].
[NBu4]2[UO2Cl4] was prepared following a standard procedure
from uranyl nitrate, aqueous HCl and tetrabutylammonium chlo-
ride. Infrared spectra were recorded for KBr pellets on a Shimadzu
[UO2(L2)2]
[UO2(L3)2]
UϪO10
UϪO20
UϪO18
UϪN2
UϪN1
UϪN31
UϪN4
UϪO58
C7ϪN2
N2ϪN3
C17ϪO18
C37ϪN4
N4ϪN5
C51ϪO58
1.725(9)
1.727(9)
2.371(6)
2.612(7)
2.701(6)
2.701(6)a)
2.612(7)a)
2.371(6)
1.30(1)
1.771(6)
1.756(6)
2.328(6)
2.610(7)
2.635(7)
2.670(7)
2.588(7)
2.355(6)
1.28(1)
1.376(9)
1.29(1)
1.31(1)
1.385(9)
1.27(1)
FT IR spectrometer between 4000 and 400 cmϪ1
.
[UO2(L1a)]. HL1a (440 mg, 1.1 mmol) was partially dissolved in
about 5 ml methanol and added to a solution of UO2(NO3)2 · 6
H2O (502 mg, 1 mmol) in 3 ml methanol. After heating the mixture
to reflux, a clear yellow solution was formed, from which a bright
yellow powder began to precipitate after about 15 min. After an
overall reflux time of 2 h, the mixture was cooled to room tempera-
ture and the yellow solid was filtered off.
The reaction rate can be increased by the addition of two drops of
triethylamine. In this case, the precipitation of the solid is complete
after 30 min. The solid is almost insoluble in alcohols. Yield:
633 mg (95%). Elemental analysis, Found: C, 41.2; H, 2.7; N,
10.5%; Calcd. for C23H19N5O4U: C, 41.4; H, 2.8; N, 10.5%. IR
(νmax/cmϪ1): 1590 (CϭN), 900 (OϭUϭO).
1.377(9)
1.28(1)
1.30(1)a)
1.377(9)a)
1.28(1)a)
O18ϪUϪN2
N2ϪUϪN1
N1ϪUϪO18Ј/O58
O58ϪUϪN4
N4ϪUϪN31
O18ϪUϪN1Ј/N31
O10ϪUϪO20
60.0(2)
59.5(2)
65.3(2)b)
60.0(2)a)
59.5(2)a)
65.3(2)a
180
59.9(2)
59.1(2)
64.8(2)
61.0(2)
59.4(2)
67.1(2)
177.3(3)
a) Symmetry-related bond lengths or angles due to an intramolecular
2-fold axis. b) Symmetry operation: 1Ϫx, y, 0.5Ϫz. d) Symmetry operation:
x, Ϫ0.5Ϫy, z.
The same procedure can be applied when the reaction is performed
with [NBu4]2[UO2Cl4] instead of uranyl nitrate.
[UO2(L1b)]. The complex was prepared following the procedure
given above for [UO2(L1a)] starting from UO2(NO3)2 · 6 H2O
(502 mg, 1 mmol) and HL1b (517 mg, 1.2 mmol). Yellow, sparingly
soluble solid. Yield: 629 mg (90%). Elemental analysis, Found: C,
39.2; H, 2.7; N, 10.3%; Calcd. for C23H19N5O6U: C, 39.5; H,
2.7; N, 10.0%. IR (νmax/cmϪ1): 3209 (OH), 1591 (CϭN), 902
(OϭUϭO).
The same procedure can be applied when the reaction is performed
with [NBu4]2[UO2Cl4] instead of uranyl nitrate.
[UO2(L1a)(DMSO)]. [UO2(L1a)] (333 mg, 0.5 mmol) was dis-
solved in about 1 ml hot DMSO. Large red blocks deposited upon
slow cooling of the solvent. More product could be obtained by
diffusion of water into the DMSO solution. Yield: 224 mg (60%).
Elemental analysis, Found: C, 41.2; H, 3.3; N, 9.7; S, 4.5%;
Calcd. for C25H25N5O5SU: C, 41.2; H, 3.4; N, 9.6; S, 4.4%. IR
(νmax/cmϪ1): 1585 (CϭN), 914 (OϭUϭO).
Figure 5 Representation [14] of the coordination spheres of a)
[UO2(L1c)] [5b], b) [UO2(L1a)(pyridine)] and c) [UO2(L2)2] in top
and side views with respect to the OϪUϪO axis showing the
distortions of the equatorial coordination spheres of the complexes
in dependence on the chelating ligands.
[UO2(L1a)(pyridine)]. The compound was prepared from
[UO2(L1a)] and pyridine following the procedure given for
[UO2(L1a)(DMSO)]. Yield: 60%. Elemental analysis, Found: C,
45.0; H, 3.0; N, 11.0%; Calcd. for C28H24N6O4U: C, 45.0; H, 3.2;
N, 11.3%. IR (νmax/cmϪ1): 1587 (CϭN), 912 (OϭUϭO). Single
crystals suitable for X-ray diffraction were obtained directly from
the reaction mixture.
[UO2(L1a)(THF)]. The compound was prepared from [UO2(L1a)]
and THF following the procedure given for [UO2(L1a)(DMSO)].
The large red crystals immediately decompose after removal from
the solvent. This is most probably due to the loss of solvent incor-
porated in the crystal lattice. Elemental analysis was performed
with the remaining red powder after drying in vacuum and con-
firmed the presence of coordinated THF. Yield: 80%. Elemental
analysis, Found: C, 43.8; H, 3.6; N, 9.4%; Calcd. for C27H27N5O5U:
C, 43.8; H, 3.7; N, 9.5%. IR (νmax/cmϪ1): 1594 (CϭN), 917
(OϭUϭO).
uranium complexes studied in this paper. This is in contrast
to the behaviour in some lanthanide complexes, where only
partial deprotonation of the NH groups was observed [9].
The ready extension of a pentagonal equatorial coordi-
nation sphere in the complexes of the type [UO2(L1)] indi-
cates a higher stability of the products with coordination
number 8 at the uranium atoms, despite the resulting steric
strains due to the relatively rigid pentadentate ligands,
which obviously cannot fully be compensated for by distor-
tions of the coordination sphere.
[UO2(L1b)(DMSO)]. The compound was prepared from
[UO2(L1b)] and DMSO following the procedure given for
Z. Anorg. Allg. Chem. 2004, 630, 735Ϫ741
zaac.wiley-vch.de
 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
739

C. C. Gatto, E. Schulz Lang, A. Kupfer, A. Hagenbach, D. Wille, U. Abram
Table 3 X-ray structure data collection and refinement parameters
[UO2(L1a)(pyridine)]
[UO2(L1b)(DMSO)]
[UO2(L2)2]
[UO2(L3)2]
Formula
C28H24N6O4U
746.56
C25H25N5O7SU
777.60
C28H24N6O4U
746.56
C36H26N8O4U
872.68
M /g molϪ1
Crystal system
Space group
Orthorhombic
Fdd2
Orthorhombic
Pnma
Orthorhombic
Pbcn
Monoclinic
P21/n
Unit cell a
11.191(2)
19.620(3)
24.248(3)
17.979(2)
17.716(1)
8.300(1)
14.641(2)
7.834(1)
23.163(3)
11.863(1)
15.127(2)
18.780(2)
100.72(2)
3311.3(6)
4
b
c
β
3
˚
V /A
53234(1)
8
1.863
2642(5)
4
1.955
2656.7(6)
4
1.866
Z
Dc /g cmϪ3
1.751
Measuring device and temperature /°C
Linear absorption coefficient /mmϪ1
Absorption correction
Tmin / Tmax
Measured reflections
Independent reflections / Rint
Refined parameters
R1 (F) / wR2 (F2) (I > 2σ())a)
GooF
SMART CCD / Ϫ100
6.144
SADABS
0.4601 / 0.5088
16098
4004 / 0.035
179
0.0208 / 0.0464
0.972
CAD4 / 20
6.276
Psi Scans
0.7583 / 0.9750
3148
2970 / 0.072
197
0.0626 / 0.0906
0.973
CAD4 / 20
6.156
Psi Scans
0.6754 / 0.8621
7990
3517 / 0.1076
178
0.0495 / 0.1047
0.966
CAD4 / 20
4.955
Psi Scans
0.2419 / 0.6371
8449
7201 / 0.0628
442
0.0526 / 0.0951
0.978
Deposit No.
CCDC 229649
CCDC 229650
CCDC 229651
CCDC 229652
2
a) R1 ϭ ͉Fo Ϫ Fc͉/͉Fo͉; wR2 ϭ [w(Fo Ϫ Fc2)2/(wFo2)]Ϫ1/2
.
[UO2(L1a)(DMSO)]. Yield: 60%. Elemental analysis, Found: C,
38.5; H, 3.2; N, 8.8; S, 4.4%; Calcd. for C25H25N5O7SU: C, 38.6;
H, 3.2; N, 9.0; S, 4.1%. IR (νmax/cmϪ1): 3053 (OH), 1591 (CϭN),
914 (OϭUϭO).
Single crystals for the X-ray structure analysis were obtained by
slow diffusion of water into a DMSO solution of the complex.
X-Ray structure determinations
The X-ray diffraction data were collected on an automated single
crystal diffractometer of the type CAD4 (Enraf-Nonius, Delft) or
a BRUKER SMART CCD with Mo Kα radiation. The structures
were solved by direct methods using SHELXS-97 [11]. Subsequent
Fourier-difference map analyses yielded the positions of the non-
hydrogen atoms. Refinement was performed using SHELXL-97
[12]. The positions of the hydrogen atoms were calculated for ideal-
ised positions and treated with the ‘riding model’ option of
SHELXL-97. Crystal data and more details of the data collections
and refinements are contained in Table 3. Additional information
on the structure determinations have been deposited at the Cam-
bridge Crystallographic Data Centre. See information for Authors,
Issue No. 1.
[UO2(L1b)(pyridine)]. The compound was prepared from
[UO2(L1b)] and pyridine following the procedure given for
[UO2(L1a)(pyridine)]. Yield: 85%. Elemental analysis, Found:
C, 43.2; H, 3.0; N, 12.1%; Calcd. for C28H24N6O6U: C, 43.2; H,
3.1; N, 12.3%. IR (νmax/cmϪ1): 3005 (OH), 1588 (CϭN), 915
(OϭUϭO).
[UO2(L2)2]. HL2 (526 mg, 2.2 mmol) was dissolved in about 10 ml
methanol and added to a solution of UO2(NO3)2 · 6 H2O (502 mg,
1 mmol) in 5 ml methanol. The mixture was heated at reflux for 1
h. During this period the solution turned red. A red, crystalline
solid precipitated after reducing the volume to about 5 ml and cool-
ing to room temperature. Addition of a few drops of triethylamine
increased the rate of the reaction, but did not influence the overall
yield of the product. The red solid was filtered off, washed with a
small amount of cold methanol and dried in vacuum. Yield:
595 mg (80%). Elemental analysis, Found: C, 45.2; H, 3.3; N,
11.6%; Calcd. for C28H24N6O4U: C, 45.0; H, 3.2; N, 11.3%. IR
(νmax/cmϪ1): 1575 (CϭN), 912 (OϭUϭO).
The same procedure can be applied when the reaction is performed
with [NBu4]2[UO2Cl4] instead of uranyl nitrate.
Single crystals suitable for X-ray diffraction were obtained from
hot methanol.
[UO2(L3)2]. The compound was prepared as reported for
[UO2(L2)2] starting from HL3 (665 mg, 2.2 mmol) and UO2(NO3)2
· 6 H2O (502 mg, 1 mmol). Red blocks were deposited directly
from the reaction mixture. Yield: 785 mg (90%). Elemental analysis,
Found: C, 49.8; H, 3.3; N, 12.8%; Calcd. for C36H26N8O4U:
C, 49.5; H, 3.0; N, 12.8%. IR (νmax/cmϪ1): 1574 (CϭN), 911
(OϭUϭO).
Acknowledgements. We thank the DAAD and CAPES for providing
a travel grant in the CAPES/PROBRAL programme.
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