Synthesis and Raman spectra of [Nd (XeF2)n](AsF6)3 (n = 3, 2.5) and crystal structure of [Nd (XeF2)2.5](AsF6)3

Article abstract of DOI:10.1006/jssc.2001.9280

The reaction between Nd(AsF₆)_3(solv) and excess of XeF_2(solv) in anhydrous HF (aHF) yields compounds of the type [Nd(XeF₂)_n](AsF₆)₃ (n = 3, 2.5). The first compound is very soluble in aHF while the latter crystallizes from the saturated solution in aHF. Pink needles [Nd(XeF₂)_2.5] (AsF₆)₃ crystallize in the space group C2/m with a = 3463.7(8) pm, b = 586.3(2) pm, c = 1010.7(2) pm, β = 103.53(2)°, V = 1.9955(9) nm³, Z = 4, R₁ = 0.0379, wR₂ = 0.0910, 5341 reflections collected, 2318 independent reflections. The Nd center is coordinated by a tricapped trigonal prism of nine fluorine atoms. The rectangular faces are capped by three coordinated XeF₂ molecules. The regular trigonal prisms are formed by six different edge-bridging AsF₆ octahedra, connecting the Nd centers to infinite chains. Two of such chains are interconnected by one of the XeF₂ molecules forming a double chain.

Full text of DOI:10.1006/jssc.2001.9280

Journal of Solid State Chemistry 162, 243}249 (2001)
doi:10.1006/jssc.2001.9280, available online at http://www.idealibrary.com on
Synthesis and Raman Spectra of [Nd (XeF2)n](AsF6)3 (n ؍ 3, 2.5) and
Crystal Structure of [Nd (XeF2)2.5](AsF6)3
M. Tramsek,* E. Lork,- R. Mews,- and B. Zemva*ꢁꢀ
*Department of Inorganic Chemistry and Technology, Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia; and - Institute of Inorganic and Physical
Chemistry, University of Bremen, Leobener Strasse, NW 2, Postfach 330440, D-28359 Bremen, Germany
Received March 2, 2001; revised May 30, 2001; accepted June 12, 2001; published online August 22, 2001
IN HONOR OF PROFESSOR PAUL HAGENMULLER ON THE OCCASION OF HIS 80TH BIRTHDAY
chemistry of this new class of compounds is given for the
"rst time. While a large number of Xe(II) compounds with
anhydrous HF (aHF) yields compounds of the type binary metal and nonmetal #uorides is known (7),
The reaction between Nd(AsF6)3(solv) and excess of XeF2(solv) in
[Nd(XeF )n] (AsF6)3 (n ؍ 3, 2.5). The 5rst compound is very
[Nd(XeF ) ] (AsF ) represents the "rst fully described
Xe(II) compound in the lanthanoid series and only the
2
ꢅ ꢅꢆꢃ
ꢄ ꢂ
soluble in aHF while the latter crystallizes from the saturated
solution in aHF. Pink needles [Nd(XeF2)2.5] (AsF6)3 crystallize
in the space group C2/m with a ؍ 3463.7(8) pm, b ؍ 586.3(2) pm,
c ؍ 1010.7(2) pm, b ؍ 103.53(2)3, V ؍ 1.9955(9) nm3, Z ؍ 4,
R1 ؍ 0.0379, wR2 ؍ 0.0910, 5341 re6ections collected, 2318 inde-
pendent re6ections. The Nd center is coordinated by a tricapped
trigonal prism of nine 6uorine atoms. The rectangular faces are
capped by three coordinated XeF2 molecules. The regular trig-
onal prisms are formed by six di4erent edge-bridging AsF6
octahedra, connecting the Nd centers to in5nite chains. Two of
second example where XeF is acting as a ligand toward
ꢅ
a metal ion (8).
2. EXPERIMENTAL SECTION
2.1. Apparatus, Techniques, and Reagents
A nickel vacuum line and Te#on vacuum system were
used as previously described (9). Nonvolatile materials,
such chains are interconnected by one of the XeF2 molecules which were very sensitive to traces of moisture, were han-
forming a double chain. ( 2001 Elsevier Science
Key Words: XeF2 as ligand; synthesis; crystal structure; Raman
spectrum; Nd(AsF6)3.
dled in the dry argon atmosphere of a glove box with
a maximum content of 0.1 ppm of water vapor (Mbraun,
Garchig, Germany). PFA reaction vessels equipped with
Te#on valves and Telfon-covered stirring bars were used for
the syntheses. T-shaped PFA reaction vessels constructed
from a large PFA tube (16 mm i.d.) and a smaller PFA tube
(4 mm i.d.) jointed at a right angle and equipped with Telfon
1. INTRODUCTION
Lanthanoid tri#uorides (LnF ) dissolve at room temper- valves were used for crystallization. NdF was used as
ꢂ
ꢂ
ature in anhydrous hydrogen #uoride (aHF) acidi"ed with purchased (Johnson Matthey, Alfa Products, 99.9%), and
AsF , yielding stable solutions of Ln(AsF ) (1). The lan- aHF (Praxair, 99.9%) was treated with K NiF for several
ꢃ
ꢄ ꢂ
ꢅ
ꢄ
thanoid metal centers in Ln(AsF ) are almost &&naked'' and days prior to use. AsF was prepared by high-pressure
ꢄ ꢂ
ꢃ
interact with various, even weak, ligands (¸) to form com- #uorination of As O , a procedure previously described for
ꢅ ꢂ
plex compounds of the type [Ln(¸) ](AsF ) (¸"SO (2), PF (10). XeF was prepared by the photochemical reaction
L
ꢄ ꢂ
ꢂ
ꢅ
ꢃ
ꢅ
CH CN (3), HF (4), AsF (5), NSF , and OPF (6)). Recently between Xe and F at room temperature (11).
ꢂ
ꢂ
ꢂ
ꢅ
we brie#y reported that even XeF can be introduced as
ꢅ
a ligand in the reactions of Ln(AsF ) dissolved in aHF.
ꢄ ꢂ
2.2. X-Ray Crystallography
During this study [La(XeF ) ] (AsF ) was isolated and its
ꢅ ꢅꢆꢃ
ꢄ ꢂ
crystal structure determined (5).
Crystal data were collected on a Siemens P4 di!rac-
In the present paper with the synthesis and Raman tometer (details: u-2h scans; re"nement based on Fꢅ; R "
ꢀ
ꢅ
ꢅ
ꢅ
spectra of [Nd(XeF ) ](AsF ) (n"3, 2.5) and the crystal +""F "!"F ""/+"F "; wR "++ [w(F !F )/+ [w(F )ꢅ],ꢀꢇꢅ).
ꢅ L
ꢄ ꢂ
ꢀ
#
ꢀ
ꢅ
ꢀ
A
ꢀ
structure of [Nd(XeF ) ] (AsF ) , a detailed report on the An absorption correction using the program DIFABS (12)
ꢅ ꢅꢆꢃ
ꢄ ꢂ
was applied. Further details on the data collection and the
basic crystallographic data are given in Table 1. Programs
SHELX-97 (13) and DIAMOND (14) were used.
ꢀ To whom correspondence should be addressed. Fax:#38 61 423 21 25;
E-mail: boris.zemva@ijs.si.
243
0022-4596/01 $35.00
( 2001 Elsevier Science
All rights reserved.

244
TRAMSEK ET AL.
TABLE 1
CrystalData andStructureRe5nement for [Nd(XeF2)2.5](AsF6)3
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
As F NdXe
ꢂ ꢅꢂ
ꢅꢆꢃꢈ
1134.25
173(2) K
71.073 pm
Monoclinic
C2/m
Unit cell dimensions
a"3463.7(8) pm
b"586.3(2) pm
c"1010.7(2) pm
b"103.53(2)3
1.9955(9) nmꢂ
4
Volume
Z
Density (calculated)
Absorption coe$cient
F(000)
3.775 Mg/mꢂ
11.905 mm\ꢀ
2004
Crystal size
Theta range for data collection
Index ranges
0.50;0.30;0.20 mmꢂ
2.633 to 27.513
!444h444, !14k47,
!124l412
5341
Re#ections collected
Independent re#ections
2318 [R(int)"0.0397]
Completeness to theta"27.513 91.7%
Max. and min. transmission
Re"nement method
Data/restraints/parameters
Goodness-of-"t on Fꢅ
0.1993 and 0.0660
Full-matrix least-squares on Fꢅ
2318/0/162
FIG. 1. Weight-loss versus time of pumping curve in the course of the
synthesis of [Nd(XeF ) ](AsF ) .
1.099
ꢅ ꢂ
ꢄ ꢂ
Final R indices [I'2p(I)]?ꢁ@
R "0.0379, wR "0.0910
ꢀ
ꢅ
R indices (all data)?ꢁ@
R "0.0486, wR "0.0957
ꢀ
ꢅ
by pressure}volume measurements and by weight, were
added to the suspension of NdF in aHF until the molar
ratio of 1:3 was reached (total amount 4.35 mmol). The
reaction was carried out at room temperature for 24 h until
all NdF dissolved to give a clear pink solution of
Nd(AsF ) . An excess of XeF (10.14 mmol) was then added
by sublimation from 295 K to the solution of Nd(AsF )
kept at 77 K. The reaction was carried out for 48 h at room
temperature. The solution remained clear and no precipitate
Extinction coe$cient
Largest di!. peak and hole
0.00016(6)
1.755 and !2.269 e A\ꢂ
ꢂ
Note. w"1/[pꢅ(Fꢅ)#(0.0502P)ꢅ#14.2171P]; P"[2Fꢅ#Max(Fꢅ, 0)]/3.
ꢀ
#
ꢀ
? R "+ #F "!"F #/+"F ".
ꢀ
ꢀ
#
ꢀ
@ wR "++[w(Fꢅ!Fꢅ)ꢅ]/+ [w(Fꢅ)ꢅ],ꢀꢇꢅ.
ꢂ
ꢄ ꢂ
ꢅ
ꢀ
#
ꢀ
ꢅ
ꢄ ꢂ
2.3. Raman Spectroscopy
was observed. Anhydrous HF and the excess of XeF were
pumped o!. The weight-loss versus time of pumping curve
was recorded (Fig. 1). At the end of pumping a pink solid
Raman spectra of powdered samples and crystals were
measured in sealed quartz capillaries on a Renishaw Raman
Imaging Microscope System 1000, with the existing line at
632.8 nm of a He}Ne laser.
ꢅ
with the composition [Nd(XeF ) ] (AsF ) with n"3.14
ꢅ L
ꢄ ꢂ
determined by mass balance was obtained. Chemical analy-
sis of the bulk of the sample gave a molar ratio Nd:As:F
ꢁ
close to 1:3:24. Anal Calcd. for [Nd(XeF ) ] (AsF ) :
F(total), 37.4; F(free), 9.4; As, 18.5; Nd, 11.8. Found: F(total),
37.0; F(free), 8.4; As, 21.1; Nd, 11.8.
2.4. Chemical Analysis
ꢅ ꢂ
ꢄ ꢂ
Free and total #uoride ion contents were determined with
an ion selective electrode (15, 16). Nd was determined by
complexometric titration (17), arsenic by the ICP method
(18).
2.6. Preparation of Single Crystals
A small portion of [Nd(XeF ) ] (AsF ) (approx. 400 mg)
ꢅ ꢂ
ꢄ ꢂ
was transferred into the T-shaped PFA reaction vessel.
2.5. Synthesis of [Nd(XeF2)3] (AsF6)3
After addition of 4}5 ml of aHF a clear pink solution was
NdF (1.44 mmol) was weighted into a PFA vessel in obtained. This solution was decanted into the narrower arm
ꢂ
a glove box. The aHF was added by condensation at 77 K. of the reaction vessel, which was left at room temperature
The suspension of NdF in aHF was allowed to warm to while the wider arm was cooled with running water. By this
ꢂ
room temperature. Small portions of AsF gas, monitored method a small temperature gradient of 6 K was achieved.
ꢃ

NEW COORDINATION COMPOUNDS [Nd(XeF ) ](AsF )
245
ꢅ L
ꢄ ꢂ
The crystallization proceeded for several days. Pink needles #uorines of the XeF ligands. During evaporation of the
ꢅ
were obtained in the narrower tube of the reaction vessel solvent the concentration of the solvated [Nd(XeF ) ]ꢂ>
ꢅ ꢂ
after all of the aHF was removed. Crystals were immersed in cations increases and leads to the interaction between
Kel-F oil in the glove box, selected under the microscope, solvated cations, yielding a less soluble compound with
and transferred into the cold nitrogen stream of the a polymeric double-chain structure which precipitates out
di!ractometer.
of solution. During the formation of the double chain one
XeF molecule is liberated per two connected cations. This
ꢅ
ꢅ
XeF is probably not free but it is coordinated in still
3. RESULTS AND DISCUSSION
dissolved [Nd(XeF ) ]ꢂ> cations increasing a number of
ꢅ ꢂ
3.1. Synthesis of [Nd(XeF2)3] (AsF6)3
XeF ligands around the Nd center. The compounds
ꢅ
[Nd(XeF ) ](AsF ) (n"3, 2.5) can be kept inde"nitely in
A solution of Nd(AsF ) in aHF was prepared by the
ꢅ L
ꢄ ꢂ
ꢄ ꢂ
ꢃ
evacuated quartz or PFA reaction vessels or in a dry argon
or nitrogen atmosphere but they decompose immediately
on contact with traces of moisture.
reaction of NdF with AsF :
ꢂ
295 K
\
NdF #nAsF
[Nd(HF) ]ꢂ>#3AsF
&&"
ꢂ
ꢃ
V
ꢄ
aHF
3.2. Crystal Structure of [Nd(XeF ) ] (AsF )
ꢅ ꢅꢆꢃ
ꢄ ꢂ
#(n!3)AsF .
n53
[1]
ꢃ
Atomic coordinates, equivalent isotropic displacement
Nd (AsF ) is stable in neutral or AsF -acidi"ed aHF. When parameters, and selected bond distances and angles are
aHF and excess of AsF are removed under vacuum given in Tables 2 and 3. The Nd atoms are coordinated by
Nd(AsF ) starts losing AsF to give the pink solid nine #uorine atoms in the form of a tricapped trigonal prism
NdF(AsF ) as the stable "nal product. If this solid is (Fig. 2). The regular trigonal prisms are formed by the
ꢄ ꢂ
ꢃ
ꢃ
ꢄ ꢂ
ꢃ
ꢄ ꢅ
dissolved again in aHF the compound partly solvolises, #uorine atoms of six di!erent edge-bridging AsF oc-
yielding some NdF , which precipitates while the remaining tahedra, connecting the Nd centers to in"nite chains. The
ꢄ
ꢂ
Nd is present in solution as Nd(AsF ) (1). Pure Nd}XeF
ꢄ ꢂ
ꢅ
complexes can be prepared only if no excess of AsF is
ꢃ
present. XeF is a #uorobase which will neutralize all excess
ꢅ
TABLE 2
Atomic Coordinates and Equivalent Isotropic Displacement
AsF from the preparation of Nd(AsF ) to give the very
ꢃ
ꢄ ꢂ
Parameters (pm2؋ 10؊1) for [Nd(XeF2)2.5](AsF6)3
soluble Xe F AsF salt as an impurity, which cannot be
ꢅ ꢂ
separated from the main product. Therefore Nd(AsF )
ꢄ
ꢄ ꢂ
x
y
z
;(eq)
should be prepared with the exact stoichiometric amount
of the acid AsF . To a solution of pure Nd(AsF ) in
Nd(1)
F(1)
0.38358(1)
0.4456(2)
0.5000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.2959(10)
0.5000
0.5000
0.2900(12)
0.5000
0.2927(10)
0.5000
0.5000
0.20558(5)
0.3793(7)
0.5000
0.2675(7)
0.36704(7)
0.4616(9)
14(1)
29(2)
17(1)
33(2)
25(1)
54(3)
36(2)
23(1)
39(2)
33(1)
25(1)
40(2)
55(2)
52(2)
31(1)
18(1)
26(2)
30(2)
35(1)
38(1)
17(1)
31(2)
31(2)
45(2)
ꢃ
ꢄ ꢂ
neutral aHF an excess of XeF is added, yielding
ꢅ
[Nd(XeF ) ] (AsF ) ; excess XeF is removed under vac- Xe(1)
ꢅ L
ꢄ ꢂ
ꢅ
F(2)
0.3231(2)
0.27696(2)
0.2344(2)
0.3900(2)
0.41143(2)
0.4298(2)
0.3421(1)
0.32270(3)
0.3683(2)
0.3062(2)
0.2808(2)
0.3854(1)
0.36896(3)
0.3245(2)
0.4148(2)
0.3533(1)
0.4288(1)
0.46660(3)
0.4718(2)
0.4565(2)
0.5002(2)
uum. For the "nal product which has no vapor pressure at
room temperature and which is stable in a dynamic vacuum
n equals 3. The weight loss versus time of pumping curve is
shown on Fig. 1.
Xe(2)
F(3)
F(4)
!0.0158(6)
!0.19101(6)
!0.3560(7)
0.0834(5)
!0.04342(11)
!0.0840(7)
!0.1571(6)
0.0136(10)
0.3760(5)
Xe(3)
The reaction between Nd(AsF ) and XeF dissolved in F(5)
ꢄ ꢂ
ꢅ
F(6)
As(1)
F(7)
F(8)
F(9)
aHF was also monitored by recording Raman spectra of the
solution and of the solid product. It is interesting that even
at a molar ratio XeF /NdF "7 no free XeF was observed
ꢅ
ꢂ
ꢅ
in the aHF solution. This could mean that n could be 6 or
even higher but compounds of the type [Nd(XeF ) ](AsF )
are not stable at room temperature under dynamic vacuum.
F(10)
As(2)
F(11)
F(12)
F(13)
F(14)
As(3)
F(15)
F(16)
F(17)
ꢅ ꢄ
ꢄ ꢂ
0.47701(10)
0.3608(6)
0.5814(6)
0.5659(5)
0.1692(5)
0.18039(10)
0.3511(6)
0.0092(6)
They lose XeF during pumping at room temperature until
ꢅ
0.5000
the composition [Nd(XeF ) ] (AsF ) is reached.
0.2882(10)
0.2965(10)
0.5000
0.5000
0.5000
ꢅ ꢂ
ꢅ ꢂ ꢄ ꢂ
ꢄ ꢂ
When [Nd(XeF ) ] (AsF ) is dissolved in neutral aHF in
order to grow single crystals, only [Nd(XeF ) ] (AsF )
ꢅ ꢅꢆꢃ
ꢄ ꢂ
crystallizes from the saturated solution, suggesting that it is
less soluble than [Nd(XeF ) ] (AsF ) . The high solubility
ꢅ ꢂ
ꢄ ꢂ
0.2873(11)
0.1941(6)
of [Nd(XeF ) ] (AsF ) in aHF is probably due to the
ꢅ ꢂ
ꢄ ꢂ
solvated [Nd(XeF ) ]ꢂ> complex cation. The solvent mol-
Note. ;(eq) is de"ned as one third of the trace of the orthogonalized ;GH
ꢅ ꢂ
ecules interact via strong hydrogen bonding to the terminal tensor.

246
TRAMSEK ET AL.
TABLE 3
pound are in the range from 235.7(7) to 248.9(7) pm (H.
Selected Bond Length (pm) and Angles (3)
for [Nd(XeF2)2.5](AsF6)3
Borrman and M. Tramsek, private communication, 1997).
The shortest Nd}F distances are in the case of both terminal
XeF molecules being 230.0(6) pm for Xe(3) and 232.1(6) pm
for Xe(2). The longest Nd}F distance of 243.5(6) pm is in the
ꢅ
Nd}F
230.0(6)
232.1(6)
240.2(5)
242.1(5)
Nd(1)}F(4)
Nd(1)}F(2)
Nd(1)}F(6)
Nd(1)}F(10)
Nd(1)}F(14)
Nd(1)}F(1)
case of bridging XeF . In the compound Nd F(AuF ) ,
ꢅ
ꢅ
ꢉ ꢃ
where CN is also nine, the Nd}F distances are from 226.0 to
255.0 pm (21). It is known that Nd}F distances are slightly
shorter (22) than La}F distances which is in accordance
242.4(5)
243.5(6)
with the smaller radius of neodymium (r "130.3 pm) in
!,ꢊ
Xe}F
comparison with the radius of lanthanum (r "135.6 pm).
!,ꢊ
F(1)}Xe(1)
F(2)}Xe(2)
Xe(2)}F(3)
F(4)}Xe(3)
Xe(3)}F(5)
199.1(6) F(1)}Xe(1)}F(1)C2
207.9(6) Xe(2)}F(2)}Nd(1)
193.6(6) F(3)}Xe(2)}F(2)
207.3(6) Xe(3)}F(4)}Nd(1)
191.8(6) F(5)}Xe(3)}F(4)
180.0(2)
The shortest La}F bonds in LaF (CN"9) are in the range
ꢂ
167.2(4)
179.4(3)
165.1(4)
178.5(3)
from 242 to 248 pm (23).
The As}F distances for the terminal #uorines are in the
range from 168.3(8) to 172.3(8) pm, while these distances for
the bridging #uorine atoms are in the range from 175.7(5) to
176.7(5) pm (Table 3).
AsF octahedra
ꢄ
F(6)}As(1)
As(1)}F(7)
As(1)}F(8)
As(1)}F(9)
F(10)}As(2)
As(2)}F(11)
As(2)}F(12)
As(2)}F(13)
F(14)}As(3)
As(3)}F(15)
As(3)}F(16)
As(3)}F(17)
176.7(5) As(1)}F(6)}Nd(1)
160.4(3)
87.6(2)
90.6(3)
173.9(4)
160.2(3)
87.9(2)
88.7(2)
89.4(3)
167.4(3)
88.0(2)
87.8(2)
89.6(3)
The closest interactions between negatively charged #u-
172.3(8) F(7)}As(1)}F(6)
169.0(6) F(8)}As(1)}F(6)
168.3(8) F(9)}As(1)}F(7)
176.6(5) As(2)}F(10)}Nd(1)
170.4(6) F(11)}As(2)}F(10)
168.8(6) F(12)}As(2)}F(10)
169.5(5) F(13)}As(2)}F(10)
175.7(5) As(3)}F(14)}Nd(1)
169.2(6) F(15)}As(3)}F(14)
168.3(6) F(16)}As(3)}F(14)
169.0(6) F(17)}As(3)}F(14)
\
orine atoms from XeF and AsF of one double chain and
ꢅ
ꢄ
positively charged Xe atoms of the other double chains are
in the range from 326.0 to 374.5 pm. The F(Xe)}Xe distances
are shorter than the F(AsF )}Xe distances as consequence of
ꢄ
the higher charge at F in XeF being approximately !0.5
ꢅ
\
(24) in comparison to the charge at F in AsF being much
ꢄ
less. In crystalline XeF each atom is surrounded by eight
#uorine atoms from neighboring XeF molecules at the
ꢅ
ꢅ
distance of 342 pm (25).
Note. Symmetry transformations used to generate equivalent atoms:
C1, x, !y, z; C2, !x#1, !y,!z#1; C3, x, !y#1, z.
3.3. Raman Spectra of [Nd(XeF ) ] (AsF )
ꢅ L
ꢄ ꢂ
Raman spectra of the powder of [Nd(XeF ) ] (AsF )
ꢅ ꢂ
ꢄ ꢂ
rectangular faces of the trigonal prisms are occupied by and of the crystals of [Nd(XeF ) ] (AsF ) are given in
ꢅ ꢅꢆꢃ
ꢄ ꢂ
three #uorine atoms from three XeF molecules. Two of Table 4 and Fig. 4. The high polarizability of xenon usually
ꢅ
these coordinated XeF are terminal ligands, the third results in the Raman active modes of xenon #uorides and
ꢅ
bridges two Nd centers under formation of a double chain. their complexes having intense Xe}F stretching modes.
Arrangements of the chains in the structure are presented in Modes involving As}F and Nd}F vibrations are ordinarily
Fig. 3. Due to the special crystallographic position of the far less intense. The intense bands in the Raman spectra of
bridging XeF , there is only one independent Xe}F distance the 1:3 compound (Fig. 4a) at 568 cm\ꢀ and for the 1:2.5
ꢅ
(Xe(1)}F(1) 199.1(6) pm), which is not signi"cantly di!erent compound at 584 and 575 cm\ꢀ (Fig. 4b) can therefore be
from the Xe}F distance in XeF itself (200 pm) (19). As con"dently attributed to Xe}F stretching modes. The latter
ꢅ
a result of the interaction with the highly acidic Nd centers, splitting could be a consequence of the inequivalence of the
the two terminal XeF molecules are strongly distorted, the two XeF molecules coordinated singly to the Ndꢂ>, or
ꢅ
ꢅ
Xe}F bonds to the bridging #uorines are stretched to to some intermolecular coupling, as in some XeF }MF
ꢅ
ꢃ
207.3(6)}207.9(6) pm, while the terminal Xe}F distances adducts (26).
shrink to 191.8(6)}193.6(6) pm, respectively. For the Xe}F>
The totally symmetric (a ) stretching mode for XeF (27)
ꢀ'
ꢅ
cation a distance less than 190 pm is expected (20). These and symmetrical XeF in complexes such as XeF )
ꢅ
ꢅ
data suggest that the neodymium compound should be 2XeF AsF (20) is at or near 497 cm\ꢀ. When XeF is
ꢃ
ꢄ
ꢅ
considered as a XeF complex rather than a #uorine bridges distorted (and on the ionization pathway toward Xe}F>
ꢅ
Xe}F> salt.
and F\) as in the XeF ) XeF AsF (20), this band is replaced
ꢅ
ꢃ
ꢄ
The Nd}F distances to the Fs of the AsF forming the by two. The band at higher frequency is labeled as the
corners of the trigonal prism are in the range from 240.2(5) short-bond Xe}F stretch (l (Xe}F)), and that at lower fre-
ꢄ
to 242.4(5) pm while the Nd}F distances to the Fs of XeF
which are capping the trigonal prism are in the range from previously been concluded that the stretching frequency for
quency as the long-bond Xe}F stretch (l (Xe2F)). It has
ꢅ
230.0(6) to 243.5(6) pm. La}F distances in the isotypic com- (Xe}F)> should be at or higher than 600 cm\ꢀ (28).

NEW COORDINATION COMPOUNDS [Nd(XeF ) ](AsF )
247
ꢅ L
ꢄ ꢂ
FIG. 2. Coordination of Nd center in [Nd(XeF ) ](AsF ) .
ꢅ ꢅꢆꢃ
ꢄ ꢂ
From the structure of the 1:2.5 compound the XeF
F ligand facing the Ndꢂ> is far from being F\. The Raman
ꢅ
molecules that are uniquely bound to Ndꢂ> are seen to be spectra clearly show that the short-bonded Xe}F compon-
distorted and on the ionization pathway. However, the ent in both complexes is far from (Xe}F)>. The slightly
FIG. 3. Arrangement of double chains in the structure of [Nd(XeF ) ](AsF ) .
ꢅ ꢅꢆꢃ
ꢄ ꢂ

248
TRAMSEK ET AL.
TABLE 4
stretch at &497 cm\ꢀ, but, as may be seen from Fig. 4 and
Table 4, the observed band at 534 cm\ꢀ is most likely to be
associated with this vibration. The enhancement of this
stretching frequency is probably associated with the high
Coulomb "eld (between two Ndꢂ>) that this semiionic
molecule is in.
Vibrational Frequencies for Raman Spectra of [Nd(XeF2)3]
(AsF6)3 and Crystals of [Nd(XeF2)2.5](AsF6)3 (in cm؊1)?
[Nd(XeF2)3](AsF6)3
[Nd(XeF2)2.5](AsF6)3
Assignment
736(0.4)
689(1.9)
606(0.1)
737(0.6)
690(2.4)
608(0.4)
584(8.9)
575(10)
l (As}F)
l (As}F)
l (As}F)
l (Xe}F)
l (Xe}F)
l (Xe}F)
The assignment of the Nd}F vibrations is di$cult on the
basis of comparison. It is possible that the band at 472 cm\ꢀ
can be assigned to the Nd}F vibration although the sym-
metry and the environment are in our case di!erent than in
the case of NdF . Raman active lattice modes in NdF have
568(10)
555(0.8)
534(1.5)
509(0.5)
ꢂ
ꢂ
been observed at 414 cm\ꢀ (29), although a recent study of
l (XeF )
ꢅ
512(0.2)
472(0.8)
l (Nd}F)
molecular geometry and vibrational frequencies of LnF
ꢂ
l (Nd}F)
l (Xe2F)
l (Xe2F)
l (Xe2F)
l (Xe2F)
l (As}F)
presume that l for NdF is at 556 cm\ꢀ (30). Stretching
ꢀ
ꢂ
461(1.0)
vibration l for a pyramidal structure of LnF should have
ꢀ
ꢂ
437(0.5)
a reasonably high Raman intensity and in the case of PrF
446(0.7)
411(0.2)
374(1.5)
356(0.4)
ꢂ
band at 526 cm\ꢀ was observed (31).
\
374(1.0)
356(0.4)
236(0.2)
The AsF octahedra are deformed due to the formation of
ꢄ
l (As}F)
strong #uorine bridges between Nd atoms via cis #uorine
atoms of AsF . The O symmetry is reduced and instead of
ꢄ
)
159(0.5)
126(0.7)
three Raman active modes more bands could be assigned to
145(0.9)
120(0.6)
Lattice modes
Lattice modes
\
AsF anions. Some bands are split and some forbidden
ꢄ
bands can appear.
? Intensities are in parentheses.
ACKNOWLEDGMENTS
higher value (Xe}F short) in the 1:2.5 compound may mean
that the ionization is a little greater in the unique XeF
ligands of that material.
The authors gratefully acknowledge the "nancial support of the Ministry
of Science and Technology of the Republic of Slovenia. One of us (B.Z.)
thanks the Alexander von Humboldt Foundation for the von Humboldt
Research Award. Support by WTZ (Wissenschaftlich-technologische
Zusammenarbeit Deutschland-Slowenien) (Project SLO-005-97) is also
gratefully acknowledged. The authors are grateful to Dr. Paul G. Watson
for helpful discussion.
ꢅ
The undistorted (bridging) XeF in the 1:2.5 compound
ꢅ
might have been expected to exhibit a symmetric XeF
ꢅ
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ꢅ L
ꢄ ꢂ

NEW COORDINATION COMPOUNDS [Nd(XeF ) ](AsF )
249
ꢅ L
ꢄ ꢂ
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