New heptafluorozirconates and -hafnates AIBIIZr(Hf) F7 (AI = Rb, Tl; BII = Ca, Cd) - Synthesis, structures, and structural relationships

Article abstract of DOI:10.1002/zaac.200700465

Four new ABZrF₇ heptafluorozirconates (A = Rb, Tl; B = Ca, Cd) and their homologous heptafluorohafnates, all colorless, orthorhombic Cmcm (n°63), Z = 4, have been synthesized by heating stoichiometric mixtures of RbF or TlF, CaF₂ or CdF₂ and ZrF₄ (HfF ₄) in sealed platinum tubes at temperature ranging from 550°C (Tl) to 600°C (Rb). The crystal structures of both RbCdZrF₇ and TlCdZrF₇ have been solved from single-crystal X-rays diffraction data. Rietveld refinements were performed from X-rays powder patterns for RbCaZrF₇ and TlCaZrF₇. In this series of heptafluorides, both B²⁺ and Zr⁴⁺ cations exhibit a pentagonal bipyramidal 7-coordination. Their structural relationships with other heptafluorozirconates A^IB^IIZrF₇ as well as β-KYb ₂F₇ are discussed. RbCaZrF₇: a = 6.863(1) A, b = 11.130(1) A, c = 8.485(1) A; TlCaZrF₇: a = 6.868(1) A b = 11.165(1) A, c = 8.486(1) A; RbCdZrF ₇: a = 6.780(1) A, b = 11.054(4) A, c = 8.420(4) A; TlCdZrF₇: a = 6.784(3) A b = 11.099(2) A, c = 8.424(9) A.

Full text of DOI:10.1002/zaac.200700465

DOI: 10.1002/zaac.200700465
New Heptafluorozirconates and -hafnates AIBIIZr(Hf)F7 (AI ؍ Rb, Tl; BII ؍
Ca, Cd) ؊ Synthesis, Structures, and Structural Relationships
Lynda Meddar, Malika El-Ghozzi*, and Daniel Avignant
`
´
´
Aubiere/France, Universite Blaise Pascal, Laboratoire des Materiaux Inorganiques, UMR CNRS 6002
Received August 6th, 2007.
Abstract. Four new ABZrF7 heptafluorozirconates (A ϭ Rb, Tl;
B ϭ Ca, Cd) and their homologous heptafluorohafnates, all color-
less, orthorhombic Cmcm (no63), Z ϭ 4, have been synthesized by
heating stoichiometric mixtures of RbF or TlF, CaF2 or CdF2 and
ZrF4 (HfF4) in sealed platinum tubes at temperature ranging from
550 °C (Tl) to 600 °C (Rb). The crystal structures of both
RbCdZrF7 and TlCdZrF7 have been solved from single-crystal
X-rays diffraction data. Rietveld refinements were performed from
X-rays powder patterns for RbCaZrF7 and TlCaZrF7. In this series
of heptafluorides, both B2ϩ and Zr4ϩ cations exhibit a pentagonal
bipyramidal 7-coordination. Their structural relationships with
other heptafluorozirconates AIBIIZrF7 as well as β-KYb2F7
are discussed. RbCaZrF7: a ϭ 6.863(1) A, b ϭ 11.130(1) A,
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
c ϭ 8.485(1) A; TlCaZrF7: a ϭ 6.868(1) A, b ϭ 11.165(1) A,
c ϭ 8.486(1) A; RbCdZrF7: a ϭ 6.780(1) A, b ϭ 11.054(4) A,
c ϭ 8.420(4) A; TlCdZrF7: a ϭ 6.784(3) A, b ϭ 11.099(2) A,
˚
c ϭ 8.424(9) A.
Keywords: Zirconium fluoride; Hafnium fluoride; Heptafluoro-
zirconates; Crystal structure
Introduction
tained with a lot of single-crystals extracted from the
batches. This paper deals with the crystal structures deter-
mination and refinements from single-crystal and powder
X-rays diffraction data for Cd and Ca compounds, respec-
tively. Then, as zirconium and hafnium are chemically very
similar, their crystal chemical properties are considered as
being identical and it is therefore easy to transpose results
obtained with the less expansive zirconium tetrafluoride to
the hafnium ones. The crystal chemical characteristics of
the homologous fluorohafnates have been determined and
are given in the present report.
Due to their low phonon energies and high optical trans-
parency from mid Ϫ UV to mid Ϫ IR, fluorohafnates and
fluorozirconates in particular are well known as being good
candidates for manufacturing optical fibres with ultra low
losses for telecommunications, optical waveguides and in-
frared optoelectronic devices [1Ϫ3]. They may also enter
into glassy compositions of interest since they are doped or
codoped with rare earths for optical applications such as
optical amplifiers [4Ϫ6] or upconverted luminescence of the
Er3ϩ ion [7Ϫ14]. Fluorohafnates also are promising materi-
als for dense scintillating glasses the applications of which
are manifold such as high energy physics [15], long-wave-
length luminescence [16] or in XϪCT for industrial and
medical applications [17].
Experimental Details
Synthesis of the samples
Most of the above evoked optical properties or appli-
cations depend on the host matrices structures, even for
glassy materials where the structural approach requires a
good knowledge of the structures of the crystalline phases
of ZrF4 and HfF4 containing corresponding systems. With
the aim to found new host matrices suitable for potential
optical applications a study of the phases relationship in the
MFϪMЈF2ϪZrF4 (M ϭ Rb, Tl; MЈ ϭ Ca, Cd) systems
has been carried out using X-ray diffraction. During this
investigation new phases with formula MIMЈIIZrF7 have
been evidenced and the Cd ones could have easily been ob-
All the samples were synthesized in the solid state from stoichio-
metric mixtures of MF (M ϭ Rb, Tl), MЈF2 (MЈ ϭ Ca, Cd) and
ZrF4 (HfF4) heated at 550 °C (Tl) or 600 °C (Rb) for three days in
sealed platinum tubes.
The rubidium fluoride was a commercial reagent grade fluoride
(Merck Selectipur) heated at 400 °C under vacuum prior to use in
order to remove any possible trace of water. The thallous fluoride
was a home made product prepared according to a process pre-
viously described [18]. Both CaF2 and CdF2 difluorides were com-
mercial reagent grade products (Merck (Ca), Serlabo (Cd)). The
zirconium tetrafluoride has been prepared from zirconium oxide
(Aldrich < 5 microns) by attack by a boiling solution of hydroflu-
oric acid at 40 %, followed by a slow evaporation on a sand bath
yielding ZrF4, H2O as dry residue. Then this dry residue has been
heated 12 h at 500 °C under a pure fluorine gas flow, resulting in
a well crystallized monoclinic zirconium tetrafluoride β-ZrF4. The
same process has been applied to prepare HfF4 from HfO2
(Strem chemicals).
* Dr. Malika El-Ghozzi
´
Laboratoire des Materiaux Inorganiques, UMR CNRS 6002
´
Universite Blaise Pascal
`
Aubiere/France
e-mail: malika.el-ghozzi@univ-bpclermont.fr
Z. Anorg. Allg. Chem. 2008, 634, 565Ϫ570
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
565

L. Meddar, M. El-Ghozzi, D. Avignant
a)
Table 1 Details of data collections, data processing and refinements for TlCdZrF7 and RbCdZrF7
.
Formula
RbCdZrF7
TlCdZrF7
Mw /g·molϪ1
Symmetry, space group
Unit cell parameters /A
422.08
486.68
orthorhombic, Cmcm (no63)
orthorhombic, Cmcm (no63)
˚
6.780(1)
11.054(4)
8.420(4)
631.1(6)
4
4.442
294
MoKα (λ ϭ 0.71073 A)
12.746
Ϫ
6.784(3)
11.099(2)
8.424(9)
634.3(8)
4
5.665
294
MoKα (λ ϭ 0.71073 A)
30.339
γ-scan
3
˚
V /A
Z
Calculated density /g·cmϪ3
Temperature /K
˚
˚
Radiation
Absorption coefficient μ /mmϪ1
Absorption correction
(Tmin ϭ 0.6115, Tmax ϭ 0.9935)
ω-2θ
Scan mode
ω-2θ
Scan width
Scan aperture /mm
Angular domain
0.80 ϩ 0.35 tanθ
2.70 ϩ 0.40 tanθ
1 Յ θ Յ 40
0 Յ h Յ 12
0 Յ k Յ 19
0 Յ l Յ15
3600s, σ ϭ 0.02
2254
0.80 ϩ 0.35 tanθ
2.70 ϩ 0.40 tanθ
1 Յ θ Յ 40
0 Յ h Յ 12
0 Յ k Յ 20
0 Յ l Յ15
3600s, σ ϭ 0.02
1133
Intensity control
Number of measured reflections
Number of unique reflections with I > 4σ(I)
Rint (I/FO) (Friedel pairs merged)
Number of refined parameters
Weighting scheme
528
610
Ϫ
0.027/0.022
36
36
2
2
ω ϭ 1 / [σ2 FO ϩ (0.017 x P)2]
ω ϭ 1 / [σ2 FO ϩ (0.0485 x P)2]
P ϭ Max (FO2, 0) ϩ 2 x FC2) / 3
P ϭ Max (FO2, 0) ϩ 2 x FC2) / 3
R1
wR2
0.0268
0.0598
0.0341
0.0956
Goodness of fit
Δρmax.,min. /(e / A )
0.940
1.003
3
˚
1.30, Ϫ1.44 close to F(4)
3.74, Ϫ2.29 close to Tl
a) Further details of the crystal structure investigation are available from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-
Leopoldshafen (Germany), on quoting the depository numbers CSD-xxxx, CSD-xxxx or on request from the authors.
Table 2 Atomic coordinates and anisotropic displacement para-
Table 3 Atomic coordinates and anisotropic displacement para-
meters for RbCdZrF7.
meters for TlCdZrF7.
2
2
˚
˚
Atoms
Sites
x
y
z
Ueq./A
Atoms
Sites
x
y
z
Ueq./A
Rb
Cd
Zr
F(1)
F(2)
F(3)
F(4)
4b
4c
4c
4c
8g
8g
8f
0.5
0.0
0.5
0.5
0.3213(8)
0.2037(7)
0.5
0.0
0.0
0.25
0.25
0.25
0.25
0.25
0.0143(7)
0.029(1)
0.010(1)
0.007(1)
0.063(2)
0.025(1)
0.023(1)
0.038(1)
Tl
Cd
Zr
F(1)
F(2)
F(3)
F(4)
4b
4c
4c
4c
8g
8g
8f
0.5
0.0
0.5
0.5
0.3213(7)
0.2037(6)
0.5
0.0
0.0
0.25
0.25
0.25
0.25
0.25
0.0137(5)
0.033(1)
0.010(1)
0.007(1)
0.050(1)
0.027(1)
0.024(1)
0.039(2)
0.1905(1)
0.3087(1)
0.4904(8)
0.1518(3)
0.3586(3)
0.2961(4)
0.1905(1)
0.3094(1)
0.4910(6)
0.1542(4)
0.3589(4)
0.2991(8)
Atoms
U11
U22
U33
U12
U13
U23
Atoms
U11
U22
U33
U12
U13
U23
Tl
Cd
Zr
F(1)
F(2)
F(3)
F(4)
0.0530(3)
0.0070(3)
0.0076(4)
0.021(3)
0.012(2)
0.013(2)
0.039(3)
0.0189(2)
0.0111(4)
0.0076(5)
0.017(4)
0.013(2)
0.016(2)
0.072(5)
0.0269(2)
0.0104(3)
0.0069(4)
0.111(9)
0.054(3)
0.044(3)
0.006(2)
0.0
0.0
0.0
0.0
Ϫ0.001(1)
0.004(1)
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Ϫ0.0019(3)
0.0
0.0
0.0
0.0
Rb
Cd
Zr
F(1)
F(2)
F(3)
F(4)
0.0511(4)
0.0082(5)
0.0066(6)
0.020(2)
0.013(2)
0.011(2)
0.038(2)
0.0181(3)
0.0108(4)
0.0089(6)
0.010(3)
0.010(2)
0.020(2)
0.071(3)
0.0177(3)
0.0105(5)
0.0064(6)
0.160(7)
0.051(3)
0.038(2)
0.005(2)
0.0
0.0
0.0
0.0
0.003(1)
0.004(2)
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Ϫ0.0018(8)
0.0
0.0
0.0
0.0
0.0
0.003(2)
0.0
0.003(2)
The form of the anisotropic displacement parameters is:
The form of the anisotropic displacement parameters is:
exp[Ϫ2π2{U11(ha*)2 ϩ U22(kb*)2 ϩ U33(lc*)2 ϩ 2U12hka*b* ϩ 2U13hla*c* ϩ 2U23klb*c*}].
exp[Ϫ2π2{U11(ha*)2 ϩ U22(kb*)2 ϩ U33(lc*)2 ϩ 2U12hka*b* ϩ 2U13hla*c* ϩ 2U23klb*c*}].
the first one Friedel’s pairs were collected and no absorption cor-
rection was made, whereas for the latter only an asymmetrical unit
has been recorded to save time as the structure was found to be
centric and an empirical absorption correction based on γ-scans
was applied. Data reduction were performed with the SDP package
[19] and refined with SHELXL-97 software [20] implemented in
the program package WinGX [21]. Details of the single-crystal data
collections, data processing and refinements are given in table 1.
The atomic coordinates and the anisotropic displacement param-
Colorless translucent single-crystals of TlCdZrF7 and RbCdZrF7
were extracted from the batches and were subsequently used for
the crystal structures determination.
X-rays diffraction
Single-crystals data for RbCdZrF7 and TlCdZrF7 were recorded at
room temperature with an Enraf Nonius CAD4 diffractometer. For
566
www.zaac.wiley-vch.de
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 565Ϫ570

New Heptafluorozirconates and -hafnates AIBIIZr(Hf)F7 (AI ϭ Rb, Tl; BII ϭ Ca, Cd)
Table 4 Main interatomic distances in RbCdZrF7
ZrIV polyhedron [CN7]
CdII polyhedron [CN7]
RbIpolyhedron [CN8 ϩ 2]
Zr Ϫ F(4)i,iii
Zr Ϫ F(1)I
x 2
1.989(6)
2.009(9)
2.084(5)
2.115(5)
Cd Ϫ F(1)i
2.212(8)
2.220(1)
2.230(6)
2.316(4)
Rb Ϫ F(2)i,ii,v,vi
Rb Ϫ F(3)i,ii,v,v
Rb Ϫ F(4)i,ii
x 4
x 4
x 2
2.952(3)
2.963(3)
3.276(5)
Cd Ϫ F(2)i,vi
Cd Ϫ F(4)ii,iv
Cd Ϫ F(3)i,vi
x 2
x 2
x 2
Zr Ϫ F(3)i,vi
Zr Ϫ F(2)i,vi
x 2
x 2
˚
˚
˚
d < Zr Ϫ F> ϭ 2.055 A
d < Cd Ϫ F> ϭ 2.249 A
d < Rb Ϫ F> ϭ 3.021 A
˚
˚
˚
d
ϭ 2.11 A
d
ϭ 2.36 A
d
ϭ 2.99 A
Shannon
Shannon
Shannon
Symmetry code: (i) x, y, z; (ii) x, Ϫy, Ϫz; (iii) x, y, 1/2Ϫz; (iv) x, Ϫy, 1/2ϩz; (v) Ϫx,ϪyϪz; (vi) Ϫx, y, z; (vii) Ϫx, Ϫy, 1/2ϩz; (viii) Ϫx, y, 1/2Ϫz.
Table 5 Main interatomic distances in TlCdZrF7.
ZrIV Polyhedron [CN7]
CdIIPolyhedron [CN7]
TlI Polyhedron[CN8 ϩ 2]
Zr Ϫ F(4)i,iii
Zr Ϫ F(1)i
x 2
1.994(5)
2.015(8)
2.084(5)
2.106(5)
Cd Ϫ F(1)i
2.214(7)
2.217(5)
2.225(5)
2.325(5)
Tl Ϫ F(3)i,ii,v,vi
Tl Ϫ F(3)i,ii,v,v
Tl Ϫ F(4)i,ii
x 4
x 4
x 2
2.966(3)
2.972(3)
3.322(9)
Cd Ϫ F(2)i,vi
Cd Ϫ F(4)ii,iv
Cd Ϫ F(3)i,vi
x 2
x 2
x 2
Zr Ϫ F(3)i,vi
x 2
x 2
Zr Ϫ F(2)i,vi
d < Zr Ϫ F> ϭ 2.055 A
˚
˚
˚
d < Tl Ϫ F> ϭ 3.040 A
d < Cd Ϫ F> ϭ 2.250 A
˚
˚
d
ϭ 2.11 A
d
ϭ 2.36 A
Shannon
Shannon
Symmetry code: (i) x, y, z; (ii) x, Ϫy, Ϫz; (iii) x, y, 1/2Ϫz; (iv) x, Ϫy, 1/2ϩz; (v) Ϫx,ϪyϪz; (vi) Ϫx, y, z; (vii) Ϫx, Ϫy, 1/2ϩz; (viii) Ϫx, y, 1/2Ϫz.
Table 6 Details of data collections and Rietveld refinements of
Table 8 Atomic coordinates and isotropic displacement parame-
TlCaZrF7 and RbCaZrF7.
ters for TlCaZrF7.
2
˚
Atoms
Sites
x
y
z
Biso. /A
Chemical formula
RbCaZrF7
TlCaZrF7
Mw /g·molϪ1
Symmetry
Space group
349.77
468.68
Tl
Ca
Zr
F(1)
F(2)
F(3)
F(4)
4 b
4 c
4 c
4 c
8 g
8 g
8 f
0.5
0
0.5
0.5
0.3229(15)
0.221(2)
0.5
0.0
0.0
0.25
0.25
0.25
0.25
0.25
0.0092(16)
3.5(1)
0.8(2)
1.3(1)
1.8(3)
1.4(3)
5.0(5)
3.4(3)
0.1908(9)
0.3076(4)
0.492(1)
0.1511(12)
0.3598(15)
0.3001(8)
orthorhombic
orthorhombic
Cmcm (no63)
Cmcm (no63)
˚
Unit cell parameters /A
a
b
c
6.863(1)
11.130(1)
8.485(1)
648.10(1)
4
6.868(1)
11.165(1)
8.486(1)
650.69(1)
4
3
˚
V (A )
Z
Calculated density /g·cmϪ3 3.585
4.784
Wavelength incident
radiation /A
Profile function
Rietveld refinements were performed using the program FULLP-
ROF [22]. Details of the data collections and refinements are given
in table 6. Figure 1 displays the final fit between calculated and
observed X-ray diffraction patterns of the TlCaZrF7 fluoride. The
atomic coordinates and isotropic displacement parameters of
RbCaZrF7 and TlCaZrF7 are gathered in tables 7 and 8 respec-
tively. The main interatomic distances are given in tables 9 and 10.
˚
1.54056
Pseudo-Voigt
Thompson-Cox Hastings Thompson-Cox Hastings
RP ϭ 9.67, Rwp ϭ 11.6 RP ϭ 15.0, Rwp ϭ 17.1
Rexp ϭ 2.89
1.54056
Pseudo-Voigt
R factors (%)
Rexp ϭ 3.12
RF ϭ 6.16, RB ϭ 7.19
RF ϭ 5.12, RB ϭ 5.56
Table 7 Atomic coordinates and isotropic displacement parame-
ters for RbCaZrF7.
The homologous heptafluorohafnates have been synthesized and
their crystal chemical characteristics are gathered in table 11.
2
˚
Atoms
Sites
x
y
z
Biso. /A
Rb
Ca
Zr
F(1)
F(2)
F(3)
F(4)
4 b
4 c
4 c
4 c
8 g
8 g
8 f
0.5
0
0.5
0.5
0.3226(7)
0.2085(7)
0.5
0.0
0.0
0.25
0.25
0.25
0.25
0.25
0.0144(6)
3.48(4)
1.95(8)
1.82(3)
5.2(2)
3.02(2)
2.82(1)
4.91(1)
Structures Description and Discussion
0.1898(3)
0.3062(1)
0.4989(9)
0.1514(4)
0.3563(4)
0.3005(4)
In all of these heptafluorozirconates ABZrF7 (A ϭ Rb, Tl;
B ϭ Ca, Cd) there are nearly regular pentagonal bipyrami-
dal 7-coordination of B2ϩ and Zr4ϩ cations and all the
bond distances in all of these 7-coordination polyhedra
(tables 4, 5, 9 and 10) are shorter than the Shannon’s dis-
tances i.e. the sum of the Shannon ionic radii [23], apart
the ZrϪF(2) distance which is equal within the e. s. d. to
the Shannon ones. However these distances are in good
agreement with equivalent distances reported in the litera-
ture [24Ϫ26].
eters are gathered in tables 2 and 3. The main interatomic distances
are given in tables 4 and 5.
X-rays powder diffraction patterns for TlCaZrF7 and RbCaZrF7
were recorded with a Siemens D501 powder diffractometer using
the Cu Kα 1, 2 radiation.
Z. Anorg. Allg. Chem. 2008, 565Ϫ570
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
567

L. Meddar, M. El-Ghozzi, D. Avignant
Table 9 Main interatomic distances in RbCaZrF7
ZrIV polyhedron [CN7]
CaII polyhedron [CN7]
RbI polyhedron [CN8 ϩ 2]
Zr Ϫ F(4)i,iii
Zr Ϫ F(1)i
x 2
2.000(5)
2.034(10)
2.077(5)
2.110(5)
Ca Ϫ F(1)i
2.236(11)
2.246(5)
2.255(5)
2.341(5)
Rb Ϫ F(2)i,ii,v,vi
Rb Ϫ F(3)i,ii,v,v
Rb Ϫ F(4)i,ii
x 4
x 4
x 2
2.970(3)
3.017(13)
3.347(4)
Ca Ϫ F(4)i,vi
Ca Ϫ F(2)ii,iv
Ca Ϫ F(3)i,vi
x 2
x 2
x 2
Zr Ϫ F(3)i,vi
Zr Ϫ F(2)i,vi
x 2
x 2
˚
˚
˚
d < ZrϪF> ϭ 2.058 A
d < CaϪF> ϭ 2.274 A
d < RbϪF> ϭ 3.064 A
˚
˚
˚
d
ϭ 2.11 A
d
ϭ 2.40 A
d
ϭ 2.99 A
Shannon
Shannon
Shannon
Symmetry code: (i) x, y, z; (ii) x, Ϫy, Ϫz; (iii) x, y, 1/2Ϫz; (iv) x, Ϫy, 1/2ϩz; (v) Ϫx,ϪyϪz; (vi) Ϫx, y, z; (vii) Ϫx, Ϫy, 1/2ϩz; (viii) Ϫx, y, 1/2Ϫz.
Table 10 Main interatomic distances in TlCaZrF7.
ZrIV polyhedron [CN7]
CaII polyhedron [CN7]
TlI polyhedron[CN8 ϩ 2]
Zr Ϫ F(3)i,vi
Zr Ϫ F(4)i,iii
Zr Ϫ F(1)i
x 2
x 2
2.003(14)
2.045(14)
2.060(1)
Ca Ϫ F(4)ii,iv
Ca Ϫ F(1)i
x 2
2.202(14)
2.220(1)
2.261(11)
2.422(17)
Tl Ϫ F(2)i,ii,v,vi
Tl Ϫ F(3)i,ii,v,v
Tl Ϫ F(4)i,ii
x 4
x 4
x 2
2.971(9)
3.042 (11)
3.352 (9)
Ca Ϫ F(2)i,vi
Ca Ϫ F(3)i,vi
x 2
x 2
Zr Ϫ F(2)i,vi
x 2
2.129(13)
˚
˚
˚
d < ZrϪF> ϭ 2.059 A
d < CaϪF> ϭ 2.284 A
d < TlϪF> ϭ 3.076 A
˚
˚
d
ϭ 2.11 A
d
ϭ 2.40 A
Shannon
Shannon
Symmetry code: (i) x, y, z; (ii) x, Ϫy, Ϫz; (iii) x, y, 1/2Ϫz; (iv) x, Ϫy, 1/2ϩz; (v) Ϫx,ϪyϪz; (vi) Ϫx, y, z; (vii) Ϫx, Ϫy, 1/2ϩz; (viii) Ϫx, y, 1/2Ϫz.
with two adjacent(BF7)5 or (ZrF7)3Ϫ pentagonal bipyra-
Table 11 Crystal chemical characteristics of heptafluorohafnates
ABHfF7
mids and three corners with three other (BF7)5 or (ZrF7)3Ϫ
pentagonal bipyramids involving one equatorial F(1) and
two apical F(4) fluorine atoms (figure 2).
3
˚
˚
˚
˚
Compounds a /A
b /A
c /A
V /A
Dcal. /g·cmϪ3
RbCaHfF7
TlCaHfF7
RbCdHfF7
TlCdHfF7
6.850(1) 11.111(1) 8.472(1) 644.81(2) 4.504
6.855(1) 11.148(1) 8.472(1) 647.44(2) 5.706
6.757(1) 11.058(1) 8.404(1) 627.89(1) 5.562
6.780(1) 11.092(1) 8.427(1) 633.68(2) 6.588
Figure 1 Final Rietveld plot of TlCaZrF7 from X-ray powder
diffraction data: observed (full circles) and calculated (solid line)
patterns, difference (observed minus calculated, lower solid line)
and Bragg reflections (vertical markers).
Figure 2 View of the crystal structure of ABZrF7 heptafluoro-
zirconates projected along [0 0 1].
Thus, by sharing F(2)-F(3) edges, alternating (ZrF7)3Ϫ
and (BF7)5Ϫ pentagonal bipyramids form infinite zigzag
chains running along the a direction. These chains are
further linked together by sharing F(1) corners alternatively
Each pentagonal bipyramid, either (ZrF7)3Ϫ or (BF7)5Ϫ
shares two edges involving F(2) and F(3) fluorine atoms
,
568
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 565Ϫ570

New Heptafluorozirconates and -hafnates AIBIIZr(Hf)F7 (AI ϭ Rb, Tl; BII ϭ Ca, Cd)
from side to side to form BZrF11 (M2X11) layers. These
tioned exhibit a 3D framework built of layers further linked
layers are perfectly plane insofar as all atoms Zr, B ϭ Ca,
together by corner-sharing only and characterized by the
presence of pseudo-hexagonal channels. They can be di-
vided in three different structural types (since KVZrF7 is
isotypic with KPdZrF7), the characteristic building layers
of which, although being quite different, have the same for-
mula. The main differences arise from the respective coordi-
nations of the B2ϩ and Zr4ϩ cations and therefore from the
polyhedra connection modes within the layers. For example,
in the AMnZrF7 fluorides as well as in the title compounds,
both B2ϩ and Zr4ϩ cations are 7-coordinated by the fluor-
ide ions whereas in KPdZrF7 the Pd2ϩ cations have an octa-
hedral coordination and the Zr4ϩ ones a 7-coordination.
However, in KPd(Hf)ZrF7 (figure 4c) we can still dis-
tinguish infinite zigzag chains built of trans corner-sharing
binuclear (PdZrF11)5Ϫ structural units, running along the [1
1
Cd, F(1), F(2) and F(3) lie in the z ϭ
/ mirror plane.
4
Further corner-sharing between these layers involving only
F(4) fluorine atoms gives the 3D framework of the struc-
ture.
This 3D polyhedral string delimits pseudo hexagonal
channels running along the c direction and accommodating
the Rbϩ or Tlϩ ions (figure 2). These last ones are located
at half distance between the M2X11 layers, in the average
plane of the F(4) fluorine atoms.
A similar polyhedral linking has been found in the high
temperature form β of KYb2F7 [27] and in the heptafluoro-
indate KIn2F7 [28]. This suggests that two Yb3ϩ ions might
easily be substituted for the couple B2ϩ-Zr4ϩ (B ϭ Ca, Cd)
without any charge compensation. This may be envisaged
in three different ways:
¯
0 1] and [1 0 1] directions and joined together by corner-
i) The two Yb3ϩ ions may be substituted for the couple
B2ϩ-Zr4ϩ in the dimeric structural unit [BZrF12]6Ϫ built of
edge sharing between (ZrF7)3Ϫ and (BF7)5Ϫ pentagonal bi-
pyramids (figure 3a).
sharing alternatively from side to side. Contrary to the title
compounds where each (ZrF7)3Ϫ pentagonal bipyramid is
linked to three (BF7)5Ϫ pentagonal bipyramids by sharing
two edges and one equatorial corner, in KPd(Hf)ZrF7 each
(ZrF7)3Ϫ pentagonal bipyramid is linked to three octahedra
(PtF6)4Ϫ by sharing two equatorial corner and one edge
also delimited by two other equatorial corners. Thus, to
compensate for the loss of one fluoride ion due to the
change of the coordination of the B cations from pentag-
onal bipyramidal to octahedral a corner is substituted for
one shared edge out of two within the zigzag chains. In the
KCuZr(Hf)F7 (figure 2b) fluoride the coordination num-
bers of the Cu2ϩ (B cation) and Zr4ϩ cations are 6 and 8,
respectively. But contrary to the title compounds where the
B2ϩ and Zr4ϩ cations regularly alternate, these cations are
now gathered together in pairs. This comes down to substi-
ii) The two Yb3ϩ ions may be substituted for the couple
B2ϩ-Zr4ϩ in the [BZrF13]7Ϫ structural entity built of corner
sharing between (ZrF7)3Ϫ and (BF7)5Ϫ involving the equa-
torial F(1) corner (figure 3b).
iii) This substitution may take place in the [BZrF13]7Ϫ
structural entity resulting of the corner-sharing between
both (ZrF7)3Ϫ and (BF7)5Ϫ involving the F(4) apical corner
(figure 3c).
A number of fluorozirconates with the AIBIIZrF7 general
formula have been reported for different combinations of
the BII and ZrIV cations, namely AMnZrF7 (A ϭ Rb, Tl)
[29], KPdZrF7 [30], KCuZrF7 [31], KVZrF7 [32], KSnZrF7
[33] (see also figure 4). Apart for this last one which is a
special case with a very distorted coordination polyhedron
of the Sn2ϩ ion, all the other fluorozirconates afore-men-
tute in the title compounds polyhedral string (figure 4a) a
10Ϫ
new structural unit (BZrF11)2
built of edge sharing
between an octahedron (BF6)2Ϫ, two square antiprisms
Figure 3 Different ways to conceive the selection of the pair B2ϩ-Zr(Hf)4ϩ for the substitution of 2 Ln3ϩ for this pair.
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Z. Anorg. Allg. Chem. 2008, 565Ϫ570
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
569

L. Meddar, M. El-Ghozzi, D. Avignant
Figure 4 Structural relationships between the AIBIIZrF7 heptafluorozirconates (a) AIBIIZrF7 (AI ϭ Rb, Tl; BII ϭ Ca, Cd), (b) KCuZrF7
and (c) KPd(V)ZrF7.
(ZrF8)4Ϫ and another octahedron for two (BZrF12)6Ϫ struc-
[15] P. R. Hobson, D. C. Imrie, T. Price, S. Sheikh, K. W. Bell, R.
M. Brown, D. J. A. Cockerill, P. S. Flower, G. H. Grayer, B.
W. Kennedy, A. L. Lintern, P. W. Jeffreys, M. Sproston, K. J.
tural units (figure 4c) within the zigzag chains. This lead to
the doubling of the unit cell parameter in the b direction
McKinlay, J. M. Parker, D. L. Bowen, T. Cliff, R. Stewart-
along which the zigzag chains are running. These chains
Hannay, R. Hammond-Smith, J. Non-Cryst. Solids 1997,
are linked together by corner-sharing between the (CuF6)2Ϫ
213Ϫ214, 147.
octahedra and by edge-sharing between (ZrF8)4Ϫ square
[16] I. Kamenskikh, V. Mikhailin, D. Spassky, S. Batygov, L.
antiprisms. It is also worth noting that in this KCuZr(Hf)F7
Dmitruk, L. Moiseeva, N. Vinogradova, M. Kirm, G.
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Zimmerer, Nucl. Instr. Methods Phys. Res. 2002, A 486, 288.
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between themselves whereas the (ZrF8)4Ϫ square antiprisms
Bull. 2007, in press.
[18] D. Avignant, I. Mansouri, R. Chevalier, J. C. Cousseins, J.
only share edges between themselves. These ABZrF7 com-
pounds thus illustrate three ways of attaining both F: B and
F: Zr ratios of 7: 1 with coordination numbers of 6 and 7
for the B atoms and 7 and 8 for the Zr ones.
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