Syntheses, crystal structures and Raman spectra of Ba(BF4)(PF6), Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4); the first examples of metal salts conta

Article abstract of DOI:10.1016/j.jssc.2009.08.004

In the system BaF₂/BF₃/PF₅/anhydrous hydrogen fluoride (aHF) a compound Ba(BF₄)(PF₆) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF₄

Full text of DOI:10.1016/j.jssc.2009.08.004

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Journal of Solid State Chemistry 182 (2009) 2897–2903
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Syntheses, crystal structures and Raman spectra of Ba(BF4)(PF6),
Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4); the first examples of metal salts
containing simultaneously tetrahedral BFꢀ4 and octahedral AF6ꢀ anions
a
a,
Ã
b
a
ˇ
ˇ
ˇ a
ˇ
Matic Lozinsek , Tina Bunic , Evgeny Goreshnik , Anton Meden , Melita Tramsek ,
a
a,
Ã
ˇ
ˇ
Gasper Tavcar , Boris Zemva
a
ˇ
Department of Inorganic Chemistry and Technology, Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
b
ˇ
ˇ
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, SI-1000 Ljubljana, Slovenia
a r t i c l e i n f o
a b s t r a c t
Article history:
In the system BaF2/BF3/PF5/anhydrous hydrogen fluoride (aHF) a compound Ba(BF4)(PF6) was isolated
and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF4)(PF6)
Received 22 April 2009
Received in revised form
24 July 2009
crystallizes in a hexagonal P62m space group with a ¼ 10.2251(4) A, c ¼ 6.1535(4) A, V ¼ 557.17(5) A3 at
200 K, and Z ¼ 3. Both crystallographically independent Ba atoms possess coordination polyhedra in the
shape of tri-capped trigonal prisms, which include F atoms from BFꢀ4 and PF6ꢀ anions. In the analogous
system with AsF5 instead of PF5 the compound Ba(BF4)(AsF6) was isolated and characterized. It
˚
˚
˚
Accepted 3 August 2009
Available online 8 August 2009
Keywords:
˚
˚
crystallizes in an orthorhombic Pnma space group with a ¼ 10.415(2) A, b ¼ 6.325(3) A, c ¼ 11.8297(17)
BFꢀ4
3
˚
˚
A, V ¼ 779.3(4) A at 200 K, and Z ¼ 4. The coordination around Ba atom is in the shape of slightly
distorted tri-capped trigonal prism which includes five F atoms from AsFꢀ6 and four F atoms from BFꢀ4
anions. When the system BaF2/BF3/AsF5/aHF is made basic with an extra addition of BaF2, the compound
AsFꢀ6
PFꢀ6
H3Fꢀ4
Ba2(BF4)2(AsF6)(H3F4) was obtained. It crystallizes in
a hexagonal P63/mmc space group with
Ba salts with different anions
Crystal structures
3
˚
˚
˚
a ¼ 6.8709(9) A, c ¼ 17.327(8) A, V ¼ 708.4(4) A at 200 K, and Z ¼ 2. The barium environment in the
shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BFꢀ4 , three AsF6ꢀ and three
H3Fꢀ4 anions. All F atoms, except the central atom in H3F4 moiety, act as
3-D structural network.
m2-bridges yielding a complex
& 2009 Elsevier Inc. All rights reserved.
1. Introduction
perfluorinated anions, i.e. perfluorinated analogues of the natural
alumosilicates.
The crystallisation of the compounds of the type Mn(AF6)n (M is
a metal in an oxidation state n and A is P, As, Sb, Bi, Nb, Ta, etc.)
from anhydrous HF (aHF) solutions frequently yields coordination
compounds in which neutral HF molecule(s) are coordinated to
the metal center. In the cases when Fꢀ anions are also present in
aHF solution they could react with HF molecules yielding different
(poly)hydrogen-fuoride anions, such as HFꢀ2 , H2F3ꢀ and H3F4ꢀ, e.g.
M2(H2F3)(HF2)2(AF6) (M ¼ Ca, A ¼ As; M ¼ Sr, A ¼ As, P) [1] and
Ba(H3F4)2 [2]. Recently we have reported on the synthesis and X-
ray crystal structure investigations of mixed-anion compounds of
the type Ba4F4(HF2)(PF6)3 and Pb2F2(HF2)(PF6) [3] where (poly)-
hydrogen-fluoride anions and Fꢀ anions are found besides
octahedral anions. Nevertheless, there were no examples of
compounds containing simultaneously tetrahedral and octahedral
In this paper we are describing the isolation and characteriza-
tion of the compounds Ba(BF4)(PF6), Ba(BF4)(AsF6) and Ba2(B-
F4)2(AsF6)(H3F4) which contain BFꢀ4 and AF6ꢀ (A ¼ P and As,
respectively) anions, while the third compound has an additional
H3Fꢀ4 anion. To our knowledge, these are the first examples of the
metal salts containing simultaneously tetrahedral BFꢀ4 and
octahedral AFꢀ6 anions.
2. Experimental
Caution: Anhydrous hydrogen fluoride, BF3, AsF5 and PF5 must
be handled in a well-ventilated hood and protective clothing must
be worn at all times! The experimentalist must become familiar
with these reagents and the hazards associated with them. Fresh
tubes of calcium gluconate gel should always be on hand for the
fast treatment of skin exposed to these reagents. For treatment of
HF injuries see Ref. [4].
Ã
Corresponding authors. Fax: +38614773155
E-mail addresses: evgeny.goreshnik@ijs.si (E. Goreshnik).
ˇ
boris.zemva@ijs.si (B. Zemva).
0022-4596/$ - see front matter & 2009 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2009.08.004

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2.1. General experimental procedures
2.3.2. Synthesis of Ba(BF4)(AsF6)
The compound Ba(BF4)(AsF6) was prepared by the reaction
between equimolar quantities of Ba(BF4)2 and Ba(AsF6)2. The
latter compound was prepared as follows. BaF2 (0.180 g,
1.03 mmol) was weighed into the reaction vessel inside the dry
box. The reaction vessel was cooled with liquid nitrogen, and aHF
was added at ꢀ196 1C. Then the reaction vessel was warmed up to
room temperature and weighed. The vessel was cooled again to
ꢀ196 1C, and an excess of AsF5 (1.76 g, 10.36 mmol) was added. The
vessel was kept at room temperature for at least 24 h, and the
reaction mixture was stirred continuously. Anhydrous HF and
excess of AsF5 were pumped off at room temperature. The weight
of the product Ba(AsF6)2 was 0.543 g (1.05 mmol). Ba(BF4)2
(0.033 g, 0.106 mmol) and Ba(AsF6)2 (0.052 g, 0.100 mmol) were
weighed into the wider part of the crystallization vessel inside the
dry box. The wider part of the crystallization vessel was cooled
with liquid nitrogen, and aHF was added at ꢀ196 1C. Then the
crystallization vessel was warmed up to room temperature. The
solution was decanted into the narrower part of the reaction
vessel, which was left at room temperature while the wider part
was slightly cooled to generate a small temperature gradient. The
obtained crystals were isolated by pumping off aHF at room
temperature. Further procedure was performed as described in
Section 2.3.1.
A nickel vacuum line and Teflon vacuum system were used as
previously described [5]. Volatile materials, such as anhydrous HF,
PF5, AsF5, BF3, were manipulated in an all-Teflon vacuum line
equipped with Teflon valves. Non-volatile materials, sensitive to
traces of moisture, were handled in a dry box with maximum
content of 0.1 ppm of water vapor (Mbraun, Garching, Germany).
A FEP reaction vessel equipped with a Teflon valve and a Teflon-
covered mixing bar was used for the syntheses. A T-shaped FEP
reaction vessel constructed from one large FEP tube (16 mm i.d.)
and a smaller FEP tube (4 mm i.d.) joint at a right angle and
equipped with Teflon valve was used for crystallization.
2.2. Reagents
BaF2 (Alfa Aesar, 99.99%), BF3 (Union Carbide, 99.5%) and
fluorine (Solvay, 99.98%) were used as purchased. PF5 was
prepared by fluorination of P2O5 powder under high-pressure of
fluorine as previously described [6]. AsF5 was synthesized by
fluorination of As2O3 by elemental fluorine in a closed system [7].
Its purity was checked by IR spectroscopy. Anhydrous HF (Fluka,
purum) was treated by K2NiF6 (Ozark-Mahoning, 99%) for several
days prior to use.
2.3.3. Synthesis of Ba2(BF4)2(AsF6)(H3F4)
Ba(BF4)2 (0.124 g, 0.40 mmol), Ba(AsF6)2 (0.104 g, 0.20 mmol)
and BaF2 (0.037 g, 0.21 mmol) were weighed into the wider part of
the crystallization vessel inside the dry box and aHF was added at
ꢀ196 1C. Then the crystallization vessel was warmed up to room
temperature and the obtained solution was decanted into the
narrower part of the reaction vessel, which was left at room
temperature while the wider part was slightly cooled to generate
a small temperature gradient. Further procedure with the crystals
was the same as described in Section 2.3.1.
2.3. Synthesis
2.3.1. Synthesis of Ba(BF4)(PF6)
At first, the reaction was performed with equimolar mixture of
BaF2, BF3 and PF5 in aHF as a solvent. After crystallization only
already known compounds Ba(H3F4)2 [2] and Ba(BF4)2 [8] were
found.
The successful synthetic procedure yielding Ba(BF4)(PF6) was
performed in the following way. At first Ba(BF4)2 was prepared.
BaF2 (0.261 g, 1.49 mmol) was weighed into the reaction vessel
inside the dry box. The reaction vessel was cooled with liquid
nitrogen, and aHF was added at ꢀ196 1C. Then the reaction vessel
was warmed up to room temperature and weighed. The vessel
was cooled again to ꢀ196 1C and an excess of BF3 (1.84 g,
27.13 mmol) was added. The reaction vessel was kept at room
temperature for 24 h and the reaction mixture was continuously
stirred. Anhydrous HF and excess of BF3 were pumped off at room
temperature. The yield of the product Ba(BF4)2 was 0.473 g
(1.52 mmol).
2.4. Crystal structure determination
For all three compounds the data were collected on Rigaku
AFC7R diffractometer equipped with Mercury CCD area detector
using graphite monochromated MoK
Ba(BF4)(AsF6) compound has been first measured on Nonius
Kappa CCD diffractometer at 150 K. For more accurate comparison
of interatomic distances with previously measured at 200 K
another two described in this article compounds another crystal
of Ba(BF4)(AsF6) has been later measured on Rigaku AFC7R
machine at 200 K. The data were corrected for Lorentz and
a radiation at 200 K. The
polarization effects.
A multi-scan absorption correction was
For the further reaction the crystallization vessel was modified
so that both parts of the vessel (A and B) were separated by a
Teflon valve. Inside the dry box the previously synthesized
product, Ba(BF4)2 (0.132 g, 0.42 mmol) was weighed into the
vessel A and BaF2 (0.075 g, 0.43 mmol) into the vessel B. Then the
vessels A and B were cooled with liquid nitrogen and aHF was
added at ꢀ196 1C to both of them. The valve between A and B was
closed. In the vessel B an excess of PF5 (0.339 g, 2.69 mmol) was
added. The reaction vessel B was warmed up to the room
temperature and the solution of Ba(PF6)2 in aHF, still under the
pressure of an excess of PF5, was decanted into the vessel A and
stirred for one day. The crystals of Ba(BF4)(PF6) were isolated by
pumping off aHF and an excess of PF5 at room temperature. Inside
the dry box, the crystals were put in perfluorinated oil (ABCR,
FO5960). Than outside the dry box crystals, immersed in
perfluorinated oil, were selected under a microscope, and quickly
applied to all data sets. All structures were solved by direct
methods using SIR-92 [9] program implemented in program
package TeXsan [10] and refined with SHELXL-97 [11] software
(program packages TeXsan and WinGX [12]). The figures were
prepared using DIAMOND 3.1 software [13]. The crystal data and
the details of the structure refinement for all three compounds
are given in Table 1, selected distances and bond lengths in
Tables 2–4, respectively.
2.5. Raman spectroscopy
Raman spectra of the powdered samples in sealed quartz
capillaries and crystals covered by perfluorinated oil were taken
on a Renishaw Raman imaging microscope system 1000 with the
exciting line at 632.8 nm of a He–Ne laser. Geometry for all the
Raman experiments was 1801 back scattering with laser power
25 mW.
transferred into
a cold nitrogen stream of the CryoSystem
installed on the X-ray diffractometer.

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2899
˚
from the metal atom (Ba1–F12 distance of 2.900(9) A is noticeably
3. Results
˚
longer than Ba1–F13 ones 2.748(5) A). The P1–F12–Ba1 angle is
1801, whereas P1–F13–Ba1 ones are equal to 1661. Basing on
rather large U values for F21 and F22 atoms one may assume also
frequently observed disordering of BF4ꢀ unit.
3.1. Description of the crystal structure of Ba(BF4)(PF6)
The structure of Ba(BF4)(PF6) contains two crystallographically
independent barium atoms. The coordination sphere of the atom
Ba1 (Fig. 1) consists of nine F atoms, belonging to six BFꢀ4 and
three PFꢀ6 anions. Six F atoms from six BF4 moieties are located on
the corners of a trigonal prism. Three F atoms from three PF6ꢀ
anions complete metal surrounding in the shape of tri-capped
The chemical formula of Ba1 surrounding is Ba(BF4)6/4(PF6)3/5
The environment of Ba2 can be described as Ba(BF4)3/4(PF6)6/5
.
.
Because the molar ratio between Ba1 and Ba2 in the unit cell is
1:2 the overall formula appears to be Ba3(BF4)12/4(PF6)15/5, i.e.
simply Ba(BF4)(PF6). Owing to the bridging function of the cations
and both anions a complex 3-D network appears in the structure
(Fig. 2).
˚
trigonal prism. Ba1–FB distances of 2.636(6) A are shorter than
˚
Ba–FP distances of 2.900(9) A. The coordination polyhedron of Ba2
is also tri-capped trigonal prism with six F atoms from six PF6ꢀ
anions located on the corners of a trigonal prism while the three F
atoms which are capping the trigonal prism are belonging to three
3.2. Description of crystal structure of Ba(BF4)(AsF6)
˚
BF4 units. Distances Ba2–FB are 2.588(8) A, and Ba2–FP bond
The coordination sphere of Ba atom (Fig. 3) consists of nine F
atoms, belonging to four BFꢀ4 and five AsFꢀ6 anions. Four F atoms
from four AsFꢀ6 moieties and two F atoms from two BFꢀ4 moieties
ꢀ
˚
lengths are 2.748(5) A. PF6 anions have five bridging F atoms
which are bonded to five metal centers while one F atom is
terminal. P–F distance for the terminal F atom (1.51(1) A) is much
˚
˚
shorter as for the bridging F atoms (1.591(5)–1.605(9) A). All F
atoms in BF4 units act as 2-bridges which results in a very similar
Table 3
m
˚
Interatomic distances (A) in Ba(BF4)(AsF6) at 200 K (regular font) and 150 K (italic).
˚
B–F distances of 1.348(11)–1.350(9) A. The shape of fluorine atoms
thermal ellipsoids indicates weak rotational disordering of PF6
moiety with an axe of rotation Ba1–F12–P1–F11 (Fig. 1).
Interesting, that the F12 atom appears to be markedly removed
Ba1—F1i, Ba1—F1ii
Ba1—F4iii
2.603(7)
2.593(5)
2.618(9)
2.591(8)
2.624(8)
2.605(8)
2.749(8)
2.745(7)
2.773(6)
2.765(5)
2.810(6)
2.799(5)
As2—F8
1.678(9)
1.685(7)
1.713(6)
1.713(5)
1.716(7)
1.718(5)
1.725(8)
1.717(7)
1.366(12)
1.367(8)
1.352(17)
1.335(13)
1.35(2)
As2—F7, As2—F7viii
As2—F9, As2—F9viii
As2—F5
Ba1—F3
Ba1—F5iv
Table 1
Crystal data and structure refinement for Ba(BF4)(PF6), Ba(AsF6)(BF4) and
Ba2(AsF6)(BF4)2(H3F4) compounds.
Ba1—F9, Ba1—F9v
Ba1—F7vi, Ba1—F7vii
B12—F1, B12—F1v
B12—F3
Empirical formula
Ba B F10
369.11
200
P
As B2 Ba2 F18 H3
716.22
As B Ba F10
413.07
Fw
B12—F4
T (K)
200
200
1.383(14)
150
Space group
P63/mmc (no.194)
Pnma (no. 62)
P62m (no.189)
Symmetry codes: (i) ꢀx+3, y+1/2, ꢀz+1; (ii) ꢀx+3, ꢀyꢀ1, ꢀz+1; (iii) xꢀ1/2, ꢀyꢀ1/2,
ꢀz+1/2; (iv) ꢀx+2, ꢀy, ꢀz+1; (v) x, ꢀyꢀ1/2, z; (vi) x+1/2, yꢀ1, ꢀz+1/2; (vii) x+1/2,
ꢀy+1/2, ꢀz+1/2; (viii) x, ꢀy+1/2, z; (ix) x+1/2, ꢀyꢀ1/2, ꢀz+1/2; (x) xꢀ1/2, ꢀy+1/2,
ꢀz+1/2.
10.2251(4)
6.8709(9)
10.415(2)
˚
a (A)
10.3638(3)
6.325(3)
˚
b (A)
6.3305(2)
6.1535(4)
557.17(5)
17.327(8)
708.4(4)
11.8297(17)
˚
c (A)
11.7736(3)
3
779.3(4)
˚
Volume (A )
Table 4
772.44(4)
4
˚
Interatomic distances (A) in Ba2(BF4)2(AsF6)(H3F4).
Z value
3
2
Dcalculated (g cmꢀ3
)
3.3
3.358
3.521
3.552
Ba1—F22
2.640(11)
2.682(6)
2.738(4)
2.825(6)
1.700(6)
Ba1—F21i, Ba1—F21ii, Ba1—F21
Ba1—F1, Ba1—F1i, Ba1—F1ii
Ba1—F11iii, Ba1—F11iv, Ba1—F11v
As1—F11, As1—F11vi, As1—F11iii
As1—F11vii, As1—F11x, As1—F11ix
B2—F21x, B2—F21xi, B2—F21xii
B2—F22
0.71069
5.698
0.71069
8.036
0.71069
˚
l
m
(A)
(mmꢀ1
)
9.44
9.524
R1a; wR2
0.0334; 0.0718
1.167
0.0435; 0.0969
1.155
0.061; 0.147
0.0356; 0.0967
1.15
1.355(8)
1.44(2)
GOF
1.391
Symmetry codes: (i) ꢀy+1, xꢀy, z; (ii) ꢀx+y+1, ꢀx+1, z; (iii) y+1, ꢀx+y+1, ꢀz; (iv)
ꢀx+1, ꢀy, ꢀz; (v) xꢀy, x, ꢀz; (vi) ꢀx+2, ꢀy, ꢀz; (vii) ꢀy+1, xꢀyꢀ1, z; (viii) xꢀy, xꢀ1,
ꢀz; (ix) ꢀx+y+2, ꢀx+1, z; (x) ꢀx+1, ꢀy+1, ꢀz; (xi) y, ꢀx+y, ꢀz; (xii) xꢀy+1, x, ꢀz.
a
R1 ¼
S
||Fo|ꢀ|Fc||/
S
|Fo|, wR2 ¼ [w(Fo2ꢀFc2)2)/
S
w(Fo2)2]1/2, GOF ¼ [
S
w(Fo2ꢀF2c)2)/
NoꢀNp)]1/2, where No ¼ no. of reflns and Np ¼ no. of refined parameters.
Table 2
˚
Interatomic distances (A) in Ba(BF4)(PF6).
Ba1—F21i, Ba1—F21ii, Ba1—F21iii, Ba1—F21iv, Ba1—F21, Ba1—F21v
Ba2—F13x, Ba2—F13ix, Ba2—F13, Ba2—F13xi, Ba2—F13xii, Ba2—F13vi
Ba1—F12vi, Ba1—F12vii, Ba1—F12viii
2.636(6)
2.748(5)
2.900(9)
2.588(8)
1.591(5)
Ba2—F22, Ba2—F22vi, Ba2—F22ix
P1—F13, P1—F13iii, P1—F13xiii, P1—F13xiv
P1—F11
B2—F21, B2—F21x
1.511(10)
1.350(9)
P1—F12
B2—F22vi, B2—F22xvi
1.605(9)
1.348(11)
Symmetry codes: (i) ꢀx+y, ꢀx, z; (ii) ꢀy, xꢀy, ꢀz+1; (iii) x, y, ꢀz+1; (iv) ꢀx+y, ꢀx, ꢀz+1; (v) ꢀy, xꢀy, z; (vi) ꢀx+y+1, ꢀx+1, z; (vii) ꢀy, xꢀyꢀ1, z; (viii) xꢀ1, y, z; (ix) ꢀy+1, xꢀy, z;
(x) x, y, ꢀz; (xi) ꢀy+1, xꢀy, ꢀz; (xii) ꢀx+y+1, ꢀx+1, ꢀz; (xiii) xꢀy, ꢀy, z; (xiv) xꢀy, ꢀy, ꢀz+1; (xv) x+1, y, z; (xvi) y, xꢀ1, z.

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2900
Fig. 1. Coordination environment of crystallographically independent Ba1 and Ba2 atoms in the structure of Ba(BF4)(PF6). The thermal ellipsoids are drawn at 40%
probability.
Fig. 2. Packing diagram of Ba(BF4)(PF6).
Fig. 4. Packing diagram in the structure of Ba(BF4)(AsF6).
AsFꢀ6 anions, similarly to PF6ꢀ in Ba(BF4)(PF6), have five bridging
F atoms which are bonded to five metal centers while one F atom
˚
is terminal. As–F distance for the terminal F atom 1.678(9) A is
shorter as the distances for ꢀthe bridging F atoms (1.713(6)–
˚
1.725(8) A). All F atoms in BF4 anions are bridging with a very
˚
similar B–F distances of 1.35(2)–1.37(1) A thus forming a complex
3-D network (Fig. 4). The AF6ꢀ anion, similarly as in Ba(BF4)(PF6),
demonstrate weak rotational disordering. Also enlarged
(especially in the case of F3 atom) the displacement ellipsoids
may indicate small disordering of BF4 moiety.
Fig. 3. Coordination environment of Ba atom in the structure of Ba(BF4)(AsF6). The
thermal ellipsoids are drawn at 40% probability.
3.3. Description of crystal structure of Ba2(BF4)2(AsF6)(H3F4)
are located on the corners of a slightly distorted trigonal prism.
Two F atoms from two BFꢀ4 anions and one F atom from AsFꢀ6 anion
complete metal surrounding in the shape of tri-capped trigonal
The metal atom, located at 4f Wyckoff position with local 3m
symmetry, is surrounded by 10 F atoms. Three pairs of F atoms,
ꢀ
belonging to two BF4ꢀ, two AsF6ꢀ and two H3F4 anions respec-
˚
prism. Ba–FB distances from 2.603(7)–2.624(8) A are shorter than
tively, form distorted trigonal prism. Two rectangular planes are
capped by F atoms belonging to H3F4 and BF4 moieties while the
third rectangular plane is bi-capped by F(BF4) and F(AsF6) species
(Fig. 5). The Ba–F bond lengths clearly depend on the anion’s
˚
Ba–FP (2.749(8)–2.810(6) A) distances (these values relate to the
data collected at 200 K for correct comparison with the other two
structures).

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Fig. 7. {[Ba2(AsF6)(BF4)2]n}n+ double layer in Ba2(AsF6)(BF4)2(H3F4). Ba atoms in the
upper layer are shown as ‘‘octants’’ and Ba atoms in the lower layer are represented
as ‘‘solid’’.
Fig. 5. Coordination environment of Ba atom in the structure of
Ba2(AsF6)(BF4)2(H3F4). The thermal ellipsoids are drawn at 40% probability. Some
fluorine atoms are omitted for clarity.
ꢀ
Fig. 6. Coordination behavior of H3F4 anion in Ba(H3F4)2 (left) and in the
structure of Ba2(AsF6)(BF4)2(H3F4) (right).
˚
ꢀ
nature: the distances Ba–F(BF4) of 2.640(11)–2.682(6) A appear to
Fig. 8. Connection of two double layers with H3F4
anions in
be the shortest, medium values were found for Ba–F(H3F4)
Ba2(AsF6)(BF4)2(H3F4).
˚
contacts of 2.738(4) A, and Ba–F(AsF6) bonds are the longest
˚
(2.825(6) A). Such differences are in an agreement with the
In Ba2(BF4)2(AsF6) (H3F4) the shape of thermal ellipsoids of F
atoms in H3F4 anions agrees well with their trigonal surrounding.
In the case of terminal F1 the longest axe is oriented perpendi-
cularly to the plane formed by two Ba and one H atoms. The
thermal ellipsoid of central F4 atom is elongated in direction
perpendicularly to the plane of whole H3F4 unit. Flattening of
fluorine thermal ellipsoids roughly corresponds to the bridging
role of F atoms in AsF6 anion, i.e. the principal axe of ellipsoid
oriented along As–F–Ba directions appears to be the shortest.
Similar flattening is also observed for F atoms of BFꢀ4 anion.
effective negative charge on the F atoms in these species. All F
atoms in BFꢀ4 and AsFꢀ6 anions act as
m
2-bridges—i.e. each BF4 unit
is bound to four and each AsF6 moiety—to six metal atoms. The
(poly)-hydrogen-fluoride anion H3Fꢀ4 demonstrates
more
a
complex bridging role. Each terminal F atom connects a pair of
Ba atoms, similarly as observed in Ba(H3F4)2 compound [2]. In the
structure of Ba(H3F4)2 the Ba atoms connected to one H3F4 anion
lie in a common plane and form nearly regular hexagon while in
this structure six Ba atoms form trigonal prism (Fig. 6). The double
layer, containing Ba atoms, BFꢀ4 and AsF6ꢀ anions, is shown in Fig. 7.
In this double layer each BFꢀ4 anion is connected to the three Ba
atoms in ‘‘the lower part’’ and to the forth one in ‘‘the upper part’’
of the same double layer, whereas AsFꢀ6 moiety is linked to the
three metal centers in ‘‘the upper part’’ and to the three Ba atoms
in ‘‘the lower part’’ of the same double layer. H3Fꢀ4 anions, located
between mentioned double layers, are bonded to the three barium
atoms in ‘‘the upper double layer’’ and to the three Ba atoms in
‘‘the lower double layer’’ what results in a complicated 3-D
network (Fig. 8). Similarly to that in Ba(H3F4)2, each pair of Ba
atoms from the closest double layers is bound via three F bridges
belonging to three H3Fꢀ4 anions.
3.4. Raman spectra
The Raman spectra of the investigated compounds, recorded
on the powdered samples in quartz capillaries, were not very
illustrative. The Raman spectrum of the compound Ba(BF4)(PF6)
is showing only two peaks at 743 and 770 cmꢀ1. To record
the Raman spectra of the compounds Ba(BF4)(AsF6) and
Ba2(BF4)2(AsF6)(H3F4) a new technique was used. The spectra
were obtained directly on the corresponding crystal, which
was protected against the moisture in the air by covering it

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M. Lozinsek et al. / Journal of Solid State Chemistry 182 (2009) 2897–2903
Fig. 9. Raman spectrum of Ba(BF4)(AsF6).
should be all the time maintained under pressure of PF5 in order
Table 5
to prevent its decomposition to BaF2 and PF5. The formation of
Ba(BF4)(PF6) is favored by its low solubility in aHF.
Raman frequencies, intensities and tentative assignments for Ba(BF4)(AsF6) and
Ba2(BF4)2(AsF6)(H3F4).
The synthesis of the analogous compound Ba(BF4)(AsF6) is
simple because both starting compounds are stable in aHF at
room temperature. Ba(BF4)2 and Ba(AsF6)2 were dissolved in aHF
and left to react in the mole ratio 1:1.
The compound Ba2(BF4)2(AsF6)(H3F4) is the best prepared from
the mixture of the compounds Ba(BF4)2, Ba(AsF6)2 and BaF2 in the
mole ratio 2:1:1 in aHF. BaF2 is providing Fꢀ anions which are
making the solution basic and forming H3Fꢀ4 anions. Stable
anions BFꢀ4 , AsF6ꢀ and H3Fꢀ4 present in the right mole ratio in the
solution combine with Ba2+ cations yielding the final product
Ba2(BF4)2(AsF6)(H3F4). Its low solubility is again essential for the
synthesis of this compound.
Ba(BF4)(AsF6)
Ba2(BF4)2(AsF6)(H3F4)
Raman frequencies
Raman frequencies
Assignments
Assignments
1050(6)
800(21)
737(11)
689(100)
574(22)
562(32)
532(15)
n3 BFꢀ4
n1 BFꢀ4
786(40)
733(4)
n1 BFꢀ4
n1 AsFꢀ6
n2 AsFꢀ6
696(100)
576(28)
n1 AsFꢀ6
n2 AsFꢀ6
n4 BFꢀ4
534(5)
n4 BFꢀ4
523(15)
366(18)
349(10)
365(20)
359(18)
n5 AsFꢀ6
n2 BFꢀ4
n5 AsFꢀ6
n2 BFꢀ4
4.2. Crystal structures
with perfluorinated oil. The Raman spectra of the compounds
Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4) recorded in this way are
shown in Fig. 9. The frequencies, intensities and tentative
assignments are presented in Table 5.
In all studied structures the bond distances Ba–F(BF4) are
much shorter than the bond distances Ba–F(PF6) or Ba–F(AsF6).
There are at least two main reasons for this. First, the volume of
the tetrahedral BFꢀ4 anion is much smaller than the volumes of the
octahedral AF6ꢀ anions (PF6ꢀ:BF4 ¼ 1.49; AF6ꢀ:BF4 ¼ 1.51) [15].
Second, it appears that on the average the charge on the F ligand
in the BFꢀ4 anion is larger than the average charge on the AFꢀ6 anion
ligands (A ¼ P, As). Of course, the lower ligand number in the BF4ꢀ
anion is a major contributor to this.
ꢀ
ꢀ
4. Discussion
4.1. Syntheses
The fluoride ion affinities of the Lewis acids AsF5, PF5 and BF3
are 105.9, 94.9 and 83.1 kcal molꢀ1, respectively [14]. Although PF5
has higher fluoride ion affinity as BF3 and in principle it should
replace BF3 in the fluoroborates, the reaction between equimolar
mixtures of BaF2, BF3 and PF5 in a solvent aHF did not proceed in
the desired direction. BF3 and PF5 interacted with BaF2 yielding
stable Ba(BF4)2 and unstable Ba(PF6)2. The formation and the
stability of the latter compound require an overpressure of PF5.
Besides, BaF2 dissolved in aHF yielded Fꢀ anions which further
reacted with solvated [Ba2+(HF)x] cations yielding the compound
Ba(H3F4)2. Therefore the products obtained in this system were
only Ba(BF4)2 and Ba(H3F4)2.
There are two crystallographically different Ba atoms in the
structure of the compound Ba(BF4)(PF6). The bond distances Ba–FB
are not significantly different in both cases, being on the average a
little shorter in the case of Ba2 because of only three BF4 ligands in
comparison with Ba1 with six BF4 ligands. The main difference is
in the case of PFꢀ6 ligands. The bond distance Ba1–FP is
˚
significantly longer (3 ꢁ 2.901 A) as the bond distance Ba2–FP
˚
(6 ꢁ 2.748 A) because the positive charge on Ba2 cation is higher
as on the Ba1 cation as a consequence of lower number of BF4
˚
ligands on Ba2. Ba1–FB distances of 2.636(6) A and Ba2–FB
˚
distances of 2.588(8) A are shorter than in the Ba(BF4)2 compound
˚
(2.690–2.886 A) [8], what is probably the consequence of higher
The best synthetic route for the preparation of the compound
Ba(BF4)(PF6) is to pour together the solutions of Ba(BF4)2 and
Ba(PF6)2 in aHF in the mole ratio 1:1. The compound Ba(PF6)2
coordination number of Ba (CN 14) in the latter case. The distance
˚
Ba–F in Ba(BF4)(PF6) is even shorter than in BaF2 (2.683 A) [16]
despite the lower coordination number of barium (CN 8) and the

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M. Lozinsek et al. / Journal of Solid State Chemistry 182 (2009) 2897–2903
2903
smaller volume of Fꢀ anion in comparison with BF4ꢀ or PFꢀ6 . The
compound Ba(BF4)(PF6) represents the first example of the metal
salt containing BF4ꢀ and PFꢀ6 anions simultaneously.
between four Ba atoms. Therefore they do not possess Oh
symmetry and are deformed.
The Raman spectrum of the compound Ba2(BF4)2(AsF6)(H3F4)
is showing the bands which could be expected for the anions BF4ꢀ
and AsFꢀ6 (see Table 5 and Fig. 9). The vibrations of the H3Fꢀ4 anion
were not detected.
The analogous compound Ba(BF4)(AsF6) has different crystal
structure. Ba atom is crystalographically unique with the
coordination number nine in the shape of tri-capped trigonal
prism. Five F atoms are from five AsFꢀ6 anions and four F atoms are
from four BFꢀ4 anions. The number of BFꢀ4 units is smaller as in the
case of Ba1 and greater as in the case of Ba2 atoms in the
compound Ba(BF4)(PF6). The distance Ba–FB is on the average
insignificantly shorter as in the case of the atom Ba1 while it is on
the average a little longer as in the case of the atom Ba2. The same
is valid for the distances Ba–FAs which are shorter as in the case of
the atom Ba1 and on the average a little longer as in the case of
the atom Ba2. However, the fluoroarsenate anion is a significantly
weaker Fꢀ donor than the fluorophosphate anion [17], the gaseous
ionization energies for the process AFꢀ6 -AF5+Fꢀ being 4.08
(A ¼ P) and 4.42 eV (A ¼ As). This must be a consequence of
greater effective nuclear charge at the As center than at the P
atom. It is therefore to be expected that the F ligands of the AsF6ꢀ
will bear less charge than those in the PFꢀ6 anion. The structural
details of both compounds confirm that in the case of the
compound Ba(BF4)(PF6) the anion PFꢀ6 is able to compete with BFꢀ4
for the coordination of Ba atom while in the case of the compound
Ba(BF4)(AsF6) the anion AsFꢀ6 is less able to do so.
5. Supplementary material
Further details of the crystal structure investigation(s) can be
obtained from the Fachinformationszentrum Karlsruhe, 76344
Eggenstein-Leopoldshafen, Germany, (fax: +497247 808 666;
e-mail: crysdata@fiz.karlsruhe.de) on quoting the depository
numbers CSD-420597 for Ba(BF4)(PF6), CSD-420598 for
Ba2(BF4)2(AsF6)(H3F4), CSD-420599 for Ba(BF4)(AsF6) at 150 K,
CSD-420600 for Ba(BF4)(AsF6) at 200 K.
Acknowledgment
The authors gratefully acknowledge to the Slovenian Research
Agency (ARRS) for the financial support of the Research Program
P1-0045 (Inorganic Chemistry and Technology).
The Ba2(BF4)2(AsF6)(H3F4) appears to be even more complex
compound being composed from three different anions. The
formation of H3Fꢀ4 moieties could be explained by the reaction of
Fꢀ anions with the solvent molecules. It is interesting, that the
local trigonal/hexagonal symmetry of BF4, AF6 and H3F4 moieties
and a possibility of such symmetry for Ba surrounding results in
the formation of the crystal structures in the hexagonal system.
Appendix A. Supplementary material
Supplementary data associated with this article can be found
in the online version at 10.1016/j.jssc.2009.08.004.
References
4.3. Raman spectra
ˇ
ˇ
ˇ
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[1] M. Tramsek, G. Tavcar, T. Bunic, P. Benkic, B. Zemva, J. Fluorine Chem. 126
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on the powdered sample in the quartz capillary, was not very
informative. Only two bands, at 743 and 770 cmꢀ1, were observed.
The band n1 of Oh symmetry of the PFꢀ6 anion occurs at 756 cmꢀ1
[18] therefore the band at 743 cmꢀ1 could be related to the
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band at 770 cmꢀ1 could be related to 1 of BFꢀ4 . All four F ligands in
, n1
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Fluorine Chem. 101 (2000) 151–153.
,
n
n
n
the anion BFꢀ4 are further connected to the Ba centers with
practically the same length of the B–F bonds. In this way the anion
BFꢀ4 is anchored between four Ba centers and therefore it could
not freely vibrate. Again, more bands would be expected.
The Raman spectrum of the compound Ba(BF4)(AsF6) was
recorded on the crystal. All four Raman bands expected for the
tetrahedral BFꢀ4 anion were observed. The same situation was in
the case of the AsFꢀ6 anion where all Raman bands expected for Oh
symmetry of the AsFꢀ6 anion (n1
, n2 and n5) were observed [20]
(see Table 5 and Fig. 9). Both anions are anchored between Ba
atoms, each AsFꢀ6 anion between five Ba atoms and each BFꢀ4 anion
[15] H.D.B. Jenkins, H.K. Robotton, J. Passmore, L. Glasser, Inorg. Chem. 38 (1999)
3609–3620.
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[18] A.M. Heyns, Spectrochim. Acta 33A (1977) 315–322.
[19] A.S. Quist, J.B. Bates, G.E. Boyd, J. Chem. Phys. 54 (1971) 4896–4901.
[20] G.M. Begun, A.C. Rutenberg, Inorg. Chem. 6 (1967) 2212–2216.