Anhydrous neodymium(III) acetate

Article abstract of DOI:10.1002/zaac.200700407

Anhydrous neodymium(III) acetate, Nd(OAc)₃ was obtained as light purple single crystals by direct oxidation of neodymium metal with malonic acid in a glass ampoule at 180 °C. It crystallizes with the monoclinic space group P2₁/a (no. 14) with a = 2201.7(2), b = 1850.0(1), c = 2419.0(3) pm, β = 96.127(8)°, V = 9796.8(1) · 10⁶ · pm³, Z = 40 [Nd(OAc)₃], R₁ = 0.0430 [I ₀ > 2σ(I₀)]. Most of the Nd³⁺ cations are coordinated by nine (or eight) oxygen atoms of acetate ligands which bridge these polyhedra to slightly waved layers which are stacked in the [010] direction.

Full text of DOI:10.1002/zaac.200700407

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DOI: 10.1002/zaac.200700407
Anhydrous Neodymium(III) Acetate
Sonia Gomez Torres and Gerd Meyer*
Köln, Institut für Anorganische Chemie der Universität
Received August 17th, 2007.
Abstract. Anhydrous neodymium(III) acetate, Nd(OAc)3 was ob-
tained as light purple single crystals by direct oxidation of neo-
dymium metal with malonic acid in a glass ampoule at 180 °C. It
crystallizes with the monoclinic space group P21/a (no. 14) with
a ϭ 2201.7(2), b ϭ 1850.0(1), c ϭ 2419.0(3) pm, β ϭ 96.127(8)°,
V ϭ 9796.8(1)·106 ·pm3, Z ϭ 40 [Nd(OAc)3], R1 ϭ 0.0430
[I0 > 2σ(I0)]. Most of the Nd3ϩ cations are coordinated by nine
(or eight) oxygen atoms of acetate ligands which bridge these
polyhedra to slightly waved layers which are stacked in the [010] di-
rection.
Keywords: Neodymium; Acetate; Crystal structure
Anhydrous rare-earth acetates may be obtained from acetic-acid
solutions or from their hydrates by careful dehydration, usually as
powders. Single crystals are obtained from acetic-acid solutions to
which, for example, caesium acetate is added [1] or from an am-
monium acetate melt in a closed system [2, 3]. An alternative only
recently explored route to anhydrous rare-earth(III) acetates is the
oxidation of the respective rare-earth metal with glacial acetic acid
in a sealed ampoule at temperatures slightly above its boiling point.
Thereby, the crystal structure of anhydrous europium(III) acetate
was recently confirmed [4].
Table 1 Anhydrous rare-earth acetates, M(OAc)3: Molar volumes
Vm, coordination numbers CN, shortest (d1), longest (dn; n ϭ CN)
and mean (<d>) M-O distances
M
Vm/cm3molϪ1
CN
d1-dn/pm
247-279
<d>/pm
261.5
Ref.
La(OAc)3 type: network
La 138.8*
10
10
[3]
[3]
Ce
Pr(OAc)3 type: network
Pr 147.4
136.0
10
9
9
241-306
244-263
239-287
261.1
253.5
255.6
[2]
So far the crystal structures of the anhydrous acetates of lanthanum
through praseodymium, samarium through lutetium, yttrium and
scandium are known [1Ϫ4, 5], Table 1. Missing are those of neo-
dymium and promethium. We herein report the synthesis [6] and
the crystal structure [7] of anhydrous neodymium(III) acetate,
Nd(OAc)3, the last one not yet analyzed structurally which can be
handled in a normal laboratory.
Nd(OAc)3 type: layer
Nd 147.5
9
8
235-267
235-251
250.1
245.7
this work
Ho(OAc)3 type: chain
Sm 146.2
Eu 145.9 / 145.1
8
8
8
8
8
8
8
8
8
8
[1]
[4, 1]
229-257
231-256
242.5
242.2
Gd 144.7
Tb 144.0
Dy 143.6
[1]
[1]
[1]
[1]
[1]
Y
143.4
Ho 142.6 / 142.6
227-252
224-256
237.0
238.1
Results and Discussion
Instead of acetic acid (HOAc), malonic acid (H2Mal) was used as
the Liebig acid [8] for the oxidation of neodymium metal. Malonic
acid is solid under ambient conditions and easier to handle under
anhydrous conditions. It decarboxylates upon heating to 140-
150 °C to acetic acid [9]. As our reaction was carried out at 180 °C,
it must be assumed that acetic acid was actually the reactant.
Er 141.0
[1]
Lu(OAc)3 type: chain
Tm 144.9 / 144.1
Yb 144.0 / 143.7
Lu 143.2 / 141.7
Sc(OAc)3 type: chain
Sc 144.7
7
7
7
222-244
219-243
220-242
228.5
228.6
227.5
[10]
[10]
[1]
6
208.4(1)
208.4
[5]
* Bold: from single crystal data; other values are from powder diffraction
data.
In the crystal structures of the anhydrous rare-earth acetates,
M(OAc)3, coordination numbers range from 10 (M ϭ La) to 6
(M ϭ Sc) and M-O coordination polyhedra are connected via car-
boxylate groups to network (M ϭ La-Pr [2, 3]) or to chain struc-
tures (M ϭ Sm-Lu, Y, Sc [1, 5]). In La(OAc)3 and isotypic
Ce(OAc)3 the M3ϩ cations are ten-coordinate [2], in Pr(OAc)3 coor-
dination numbers are 10 and 9 (twice) [3]. The Ho(OAc)3-type of
structure represents the acetates with M ϭ Sm-Er, Y with CN ϭ 8.
Lu(OAc)3 with CN ϭ 7 is isotypic with M(OAc)3 (M ϭ Tm-Lu)
[1]. These two structure types are closely related to the crystal struc-
ture of Sc(OAc)3 [5], CN ϭ 6, a structure which is adopted from
all acetates M(OAc)3 with M ϭ Sm-Lu, Y at elevated temperatures
[1]. Table 1 gives an overview.
* Prof. Dr. G. Meyer
Institut für Anorganische Chemie
Universität zu Köln
Greinstraße 6
D-50939 Köln
www.gerdmeyer.de
Z. Anorg. Allg. Chem. 2008, 634, 231Ϫ233
 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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S. Gomez Torres, G. Meyer
Table 2 Internuclear Nd-O distance ranges d1-dn/pm (n ϭ CN)
and averaged distances <d> for Nd(OAc)3 (<<d>> is the average
of the averaged distances)
CN
d1-dn/pm
<d>/pm
Nd1-O
Nd2-O
Nd3-O
Nd4-O
Nd5-O
Nd6-O
Nd7-O
Nd8-O
Nd9-O
Nd10-O
9
8
9
9
9
8
9
9
9
9
244.6(9)-255.9(9)
236.6(10)-251.0(9)
237.2(8)-261.7(10)
245.4(10)-260.6(10)
240.9(10)-266.6(9)
236.6(10)-251.3(10)
237.3(9)-259.5(10)
235.0(10)-255.2(9)
240.6(9)-265.6(10)
241.8(10)-254.8(10)
252.1
245.9
250.6
251.1
248.8
245.5
249.2
249.5
249.4
250.1
Nd-O
<<d>>
249.2
Fig. 2 Two layers stacked in the [010] direction in the crystal
structure of Nd(OAc)3 (above) and a superposition of these two
layers (without methyl groups) exhibiting the offset of about 1/4a
(below).
The large unit cell of Nd(OAc)3 contains 40 such formula units
with 10 symmetry-independent neodymium atoms. Eight of these
are nine-coordinate, the remaining two eight-coordinate. Nd-O dis-
tances are summarized in Table 2. Distances range from 235 to
267 pm, averaged distances from 246 to 252 pm, and the average of
the averaged distances is 249.2 pm. This mean Nd-O distance in
Nd(OAc)3 for a coordination number of almost CN ϭ 9, lies in
between the mean Pr-O distance in Pr(OAc)3 (256.7 pm) and the
mean Eu-O distance in Eu(OAc)3 (242.4 pm), for which single-crys-
tal structure analyses were carried out. For further details see
Table 1.
The ten symmetry-independent Nd-O polyhedra are connected to
layers roughly parallel (010), space group P121/a1, Figure 1. Al-
though the connection modes are complicated in detail (bidentate-
bridging, tridentate-chelating and-bridging as well as tetradentate-
chelating), these layers consist of ten-membered rings attached to
each other, Figure 1. The methyl rings of the acetate anions are
oriented towards the open space within the rings (Fig. 1) and be-
tween the layers which are stacked in the [010] direction, see Figure
2. The layers are somewhat waved and shifted against each other
by roughly one quarter in the [100] direction, thereby avoiding open
space through the creation of channel structure, Figure 2.
Fig. 1 The connection of ten-membered Nd-O rings in one layer
of the crystal structure of Nd(OAc)3 (above) and projection of
Nd-O polyhedra of one such layer with methyl groups onto (010)
(below).
The crystal structures of the anhydrous acetates M(OAc)3 with
M ϭ Nd and Pm were elusive. Surprisingly, the now-determined
crystal structure of anhydrous neodymium(III) acetate, Nd(OAc)3,
represents the missing link, a layer structure.
Acknowledgements. This work was generously supported by the
State of Nordrhein-Westfalen and the Universität zu Köln.
232
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 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 231Ϫ233

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Anhydrous Neodymium(III) Acetate
Ϫ26 Յ h Յ 25, Ϫ21 Յ k Յ 21, Ϫ28 Յ l Յ 28; ρcalc ϭ 2.179 g
cmϪ3; 78369 reflection intensities measured of which 17257
were symmetrically independent, Rint ϭ 0.1834, F(000) ϭ
6120, µ ϭ 52.95 mmϪ1. Monoclinic, P21/a (no. 14), a ϭ
2201.7(2), b ϭ 1850.0(1), c ϭ 2419.0(3) pm, β ϭ 96.127(8)°,
V ϭ 9796.8(1) 106 ·pm3, Z ϭ 40 [Nd(OAc)3]. Structure solu-
tion and refinement were carried out using the programs
SHELXS-97 and SHELXL-97 (G. M. Sheldrick, Pro-
grammsysteme, Göttingen, 1997). A numerical absorption
correction was applied after optimisation of the crystal shape
(X-RED and X-SHAPE (Stoe & Cie, Darmstadt 1999, 2001)).
R values: R1/wR2 for 6972 reflections with [I0>2σ(I0)]: 0.0430/
0.0522 and for all data: 0.1380/0.0671; Sall ϭ 0.652. Crystallo-
graphic data for the structure have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC 653325. Copies of the data can be ob-
tained, free of charge, on application to CHGC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: ϩ44 1223 336033 or
e-mail: deposit@ccdc.cam.ac.uk).
[1] A. Lossin, G. Meyer, Z. Anorg. Allg. Chem. 1993, 619, 1609.
[2] A. Lossin, G. Meyer, Z. Anorg. Allg. Chem. 1994, 620, 438.
[3] G. Meyer, D. Gieseke-Vollmer, Z. Anorg. Allg. Chem. 1993,
619, 1603.
[4] S. Gomez Torres, I. Pantenburg, G. Meyer, Z. Anorg. Allg.
Chem. 2006, 632, 1989.
[5] R. Fuchs, J. Strähle, Z. Naturforsch. 1984, 39b, 1662.
[6] Nd(OAc)3: 72.1 mg (0.5 mmol) neodymium metal (Chempur,
99.9 %) and 140.1 mg (1 mmol) of anhydrous malonic acid
(Riedel-de Haen, 99.5 %) were filled under exclusion of air/
humidity in a dry box (argon, MBraun, Garching) in a glass
ampoule. The ampoule was sealed outside the dry box at a
vacuum line with a methane/oxygen burner. The reaction was
carried out at 180 °C for two weeks in an oven. Some crystals
were selected under a microscope in a dry box and sealed in
thin-walled glass capillaries. They were transferred to a single-
crystal X-ray diffractometer (Stoe Image Plate Diffraction Sys-
tem, IPDS) to collect a complete intensity data set at ambi-
ent temperature.
[8] G. Meyer, Z. Anorg. Allg. Chem. 2008, 634,(Research Report)
[9] Beyer/Walter, Lehrbuch der Organischen Chemie, 21. Auflage,
S. Hirzel Verlag, Stuttgart, 1988, p. 324 ff.
[10] S. Gomez Torres, Dissertation, Universität zu Köln, geplant
für 2007.
[7] Nd(OAc)3: C60H90O60Nd10 (3213.72 g molϪ1); diffractometer
IPDS-II, Stoe, Darmstadt; Mo-Kα (graphite monochromator,
λ ϭ 71.073 pm); T ϭ 293(2) K; 2θmax ϭ 50.5°; 120 images, 0°
Յ ω Յ 180°, ϕ ϭ 0°; 0° Յ ω Յ 60°, ϕ ϭ 90°; ∆ω ϭ 2°; indices:
Z. Anorg. Allg. Chem. 2008, 231Ϫ233
 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
233