Tetraammine Tetrafluorido Cerium(IV) Ammonia (1/1), [CeF 4(NH3)4] · NH3

Article abstract of DOI:10.1515/znb-2011-0815

The synthesis and crystal structure of the first ammine complex of a cerium fluoride, tetraammine tetrafluorido cerium(IV) ammonia (1/1), [CeF ₄(NH₃)₄] · NH₃, are presented. The compound crystallizes in the form of colorless, block-shaped single crystals in the tetragonal space group P4/ncc with a = 9.03215(9), c = 10.96404(17) A , V = 894.443(19) A³, and Z = 4. The compound contains discrete [CeF₄(NH₃)₄] molecules interconnected by N-H·F hydrogen bonds.

Full text of DOI:10.1515/znb-2011-0815

868
Note
Table 1. Selected bond lengths and angles of the [CeF4-
(NH3)4] moleculea.
Tetraammine Tetrafluorido Cerium(IV)
Ammonia (1/1), [CeF4(NH3)4] · NH3
˚
Atoms
Ce(1)–F(1)
Ce(1)–N(1) 2.586(2)
N(1)–H(1A) 0.66(3)
N(1)–H(1B) 0.84(3)
Distance (A)
Atoms
Angle (deg)
2.1586(14)
F(1)#1-Ce(1)–F(1)#2 146.05(8)
F(1)#1-Ce(1)–F(1)#3 104.98(8)
Florian Kraus and Sebastian A. Baer
F(1)#1-Ce(1)–F(1)
84.95(8)
72.62(7)
AG Fluorchemie, Department Chemie,
Technische Universita¨t Mu¨nchen, Lichtenbergstraße 4,
85747 Garching, Germany
F(1)#1-Ce(1)–N(1)#1
N(1)–H(1C) 0.84(3)
a
F(1)#2-Ce(1)–N(1)#1 140.62(7)
Symmetry operations as in Fig. 1.
Reprint requests to PD Dr. Florian Kraus.
Fax: +49-89-289-13762. E-mail: fluorchemie@mytum.de
Table 2. Hydrogen bond parameters of the title compound
˚
(A, deg).
Z. Naturforsch. 2011, 66b, 868 – 870;
received June 24, 2011
D–H
H···A
2.35(3)
2.24(3)
2.60(3)
D···A
∠DHA
160(4)
177(3)
144(2)
N(1)–H(1A)···F(1)#4
N(1)–H(1B)··· F(1)#5
0.66(3)
0.84(3)
0.84(3)
2.975(3)
3.075(3)
3.315(4)
The synthesis and crystal structure of the first ammine
complex of a cerium fluoride, tetraammine tetrafluorido
cerium(IV) ammonia (1/1), [CeF4(NH3)4] · NH3, are pre-
sented. The compound crystallizes in the form of colorless,
block-shaped single crystals in the tetragonal space group
N(1)–H(1C)··· N(2)#6
a
Symmetry transformations for the generation of equivalent atoms:
#4
#5
#6
−x + 1, y + 1/2, −z; x − 1, −y + 1/2, z; −x + 1, y − 1/2,
−z+1/2.
˚
P4/ncc with a = 9.03215(9), c = 10.96404(17) A, V =
3
˚
894.443(19) A , and Z = 4. The compound contains discrete
[CeF4(NH3)4] molecules interconnected by N–H···F hydro-
gen bonds.
Key words: Cerium, Fluoride, Ammine, Crystal Structure,
Liquid Ammonia
Fig. 1. The [CeF4(NH3)4] molecule at 123 K. Displacement
ellipsoids are shown at the 70 % probability level, hydrogen
atoms with arbitrary radii. Symmetry transformations for the
generation of equivalent atoms: #1 −x+1, −y+1, −z+1/2;
Introduction
Metal fluorides dissolve only sparingly in liquid
ammonia and their chemistry is therefore little ex-
plored [1]. Biltz and coworkers used hydrates of flu-
orides to lower the lattice energy and hence to improve
their solubility in liquid ammonia [2]. The ammoni-
ates obtained in this way were analyzed using volume-
pressure measurements [3]. In our own investigations
on the reactions of fluorides with anhydrous ammo-
nia, we discovered that fluorides of the β-ZrF4 struc-
ture type, which is also known for the tetrafluorides
of the elements Hf, Ce, Th, U, Np, Pu, and Cm [4 – 7]
show appreciable solubility and form the isotypic com-
pounds [MF4(NH3)4] · NH3 (M = Zr, Hf, U) [8, 9]. To
our knowledge, the reaction of CeF4 with liquid am-
monia has not been investigated and we present here
the first structural evidence for the existence of ammine
complexes of cerium fluorides.
#2
−x+3/2, −y+1/2, z; #3 x−1/2, y+1/2, −z+1/2.
(NH3)4] · NH3 (see Table 4 for crystallographic de-
tails). As the title compound is isotypic to [MF4-
(NH3)4] · NH3 (M = Zr, Hf, U) [8, 9], a detailed struc-
tural description will not be given. The crystals con-
tain discrete [CeF4(NH3)4] molecules (Fig. 1) with
four Ce–F distances of 2.1586(14) and four U–N dis-
˚
tances of 2.586(2) A. Selected bond lengths and an-
gles are listed in Table 1. The molecules are intercon-
nected via N–H···F hydrogen bonds. These hydrogen
˚
bonds have H···F distances of 2.24(3) and 2.35(3) A
with N–H···F angles of 177(3) and 160(4)◦. Hydrogen
bonds from the ammine ligands to the nitrogen atom of
the crystal ammonia can also be inferred with an H···N
˚
distance of 2.60(3) A and an N–H···N hydrogen bond
angle of 144(2)◦. Details of the hydrogen bonds are
listed in Table 2. The coordination sphere of the cerium
atom can be described as distorted square antipris-
matic or bisphenoidal. The distance of the ammonia
molecule of solvation to the next nearest fluorine atom
Results and Discussion
Cerium(IV) fluoride dissolves sparingly in liquid
ammonia and forms the crystalline compound [CeF4-
c
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Note
869
Table 3. Comparison of bond
Zr
Hf
Ce
U
˚
lengths (A) and bond angles
M-F
M-N
2.036(2)
2.397(3)
85.08(11)
104.96(11)
145.86(11)
140.70(13)
121.31(14)
72.93(14)
2.040(5)
2.381(7)
85.0(3)
105.1(3)
145.8(3)
141.2(4)
121.0(3)
72.9(4)
2.1586(14)
2.586(2)
84.95(8)
104.98(8)
146.05(8)
141.59(11)
122.44(12)
71.34(11)
2.188(4)
2.618(5)
85.0(2)
104.4(2)
147.1(2)
141.4(3)
122.1(2)
71.7(2)
(deg) of the isotypic com-
F(1)-M-F(1)#1
F(1)-M-F(1)#2
F(1)-M-F(1)#3
N(1)-M-N(1)#1
N(1)-M-N(1)#2
N(1)-M-N(1)#3
pounds
[MF4(NH3)4]·NH3
(M = Zr, Hf, Ce, U)a.
a Symmetry operations as in Fig. 1.
Fig. 2. The unit cell of the title compound at 123 K. Dis-
placement ellipsoids are shown at the 70 % probability level,
hydrogen atoms with arbitrary radii.
Fig. 3. Plot of the shortening percentage of the H···F and
H···N distances as compared to the van der Waals radii of H,
F and N, plotted versus the deviation of the N–H···X (X =
F, N) angle from 180◦. N–H hydrogen bonds to F atoms are
shown in grey and in black to N atoms. Triangles stand for
the Zr, circles for the Hf, boxes for the Ce, and diamonds for
the U compound.
˚
is 3.061(2) A, and therefore further connectivities via
N–H···F hydrogen bonds must be assumed. Fig. 2
shows a projection of the unit cell of the title com-
pound. The extensive hydrogen bonding lends some
stability to the crystals at low temperature, but upon
warming ammonia is lost rapidly. From the chemical
analyses and thermogravimetric studies on the analo-
gous compound [UF4(NH3)4]·NH3 it can be assumed
that only the ammonia of crystallization is lost upon
warming to r. t., and that the [CeF4(NH3)4] molecule
should be stable to temperatures above 100 ◦C [9].
encountered a plot is used where the shortening per-
centage of the distance of the hydrogen atoms to the
fluorine atoms as compared to the sum of their van
der Waals radii is plotted versus the deviation of the
N–H···F angle from 180◦. Strong hydrogen bonds
with a large shortening percentage and a small de-
viation from 180◦ generally appear in the upper left,
Table 3 shows a comparison of the bond lengths and weak hydrogen bonds in the lower right corner of the
angles of the isotypic compounds [MF4(NH3)4]·NH3
plot. As can be seen from Fig. 3, the hydrogen bond
parameters are rather similar for the compounds with
(M = Zr, Hf, Ce, U) [8, 9]. While the bond angles
are essentially similar, the bond lengths differ slightly. Zr, Hf, and U, but different for Ce, as is expected
This can be attributed to the ionic radii of the tetrava- due to the different hydrogen atom treatment. How-
lent metal atoms with coordination number eight
ever, the plot clearly shows the differences of hydro-
gen bond strength for N–H···F and N–H···N hydro-
gen bonds.
(Zr4+ 0.98, Hf4+ 0.97, Ce4+ 1.11, U4+ 1.14 A) [10].
˚
Comparing the hydrogen bonds of the four isotypic
compounds is problematic, as for M = Zr, Hf, U the hy-
In summary, [CeF4(NH3)4]·NH3 has been synthe-
drogen atoms were refined using a riding model. In the sized from CeF4 in liquid ammonia. In crystals of
Ce compound the hydrogen atoms of the ammine lig- this compound, the discrete [CeF4(NH3)4] molecules
ands could be located from the difference Fourier syn- are interconnected by an extensive N–H···F hydrogen
thesis. To discuss the strength of the hydrogen bonds bond system.
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870
Note
Table 4. Crystal structure data for the title compound [CeF4-
Experimental Section
(NH3)4]·NH3.
All work was carried out under argon (4.8, Westfalen
AG) using standard Schlenk techniques. Liquid ammonia
(3.8, Westfalen AG) was dried and stored over sodium metal
at −78 ◦C. CeF4 was prepared from CeF3 and a gas mixture
of 10 % F2 in Ar at 400 ◦C [4]. A reaction vessel was charged
with 94 mg (0.43 mmol) of CeF4 and, after evacuation, with
Formula
Mr
CeF4H15N5
301.29
Crystal system
Size, mm3
Space group
tetragonal
0.03×0.03×0.03
P4/ncc
9.03215(9)
10.96404(17)
894.443(19)
4
2.24
0.71073
123
5.1
0.0340 / 0.0085
721 / 37 / 0
0.0155 / 0.0256
0.0425 / 0.0443
1.162
˚
a, A
˚
c, A
◦
approximately 10 mL of liquid ammonia at −40 C. Color-
3
˚
V, A
less, block-shaped crystals suitable for the X-ray diffraction
Z
ρ
◦
calc, g/cm3
˚
experiment were obtained after storage at −40 C for three
months. The crystals are temperature-sensitive and decrepi-
tate at temperatures above −20 ◦C loosing ammonia. All
crystals were handled in a perfluorinated ether under nitro-
gen atmosphere at temperatures below −50 ◦C, and mounted
on the diffractometer using the MiTeGen MicroLoop system.
The structure was solved using Direct Methods and refined
on F2 [11, 12]. All non-hydrogen atoms were localized by
Fourier cycling methods and refined anisotropically, the hy-
drogen atoms were localized by Fourier cycling methods and
refined isotropically.
λ (A)
T, K
µ(MoKα ), mm−1
Rint / Rσ
Data / parameters / restraints
R(F)a [I ≥ 2σ(I)] / all data
wR(F2)a [I ≥ 2σ(I)] / all data
GoF (F2, all da−ta3)b
˚
∆ρmax/min, e A
0.63 / −0.34
a
2
R1(F)
=
ꢀFo| − |Fcꢀ/Σ|Fo|, wR(F2)
=
=
[Σw(Fo
−
Fc2)2/Σw(Fo2)2]1/2
,
for the compound:
w
[σ2(Fo2) +
(0.0182P)2 + 1.4973P]−1, where P = (Max(Fo2,0) + 2Fc2)/3;
b
2
GoF = [Σw(Fo −Fc2)2/(nobs −nparam)]1/2
.
Acknowledgements
Further details of the crystal structure investigation
F. K. would like to thank the Fonds der Chemischen Indus-
are available from the FachinformationszentrumKarls- trie for his stipend and Solvay Fluor for a continuous supply
of elemental fluorine. Deutsche Forschungsgemeinschaft is
acknowledged for financial support.
ruhe, D-76344 Eggenstein-Leopoldshafen (Germany),
http://www.fiz-karlsruhe.de/icsd.html, on quoting the
depository number CSD 423232 for the compound, the
name of the authors, and citation of the paper.
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