Ammonium scandium tetrafluoride

Article abstract of DOI:10.1107/S0108270106044520

The title compound, NH₄ScF₄, is an addition to the AMF₄ family of layered perovskite-like structures. The structure consists of a two-dimensional array of corner-sharing ScF₆ octahedra, which produces anionic sheets of stoichiometry [ScF₄]^- stacked along the c axis. The layers are separated by charge-balancing ammonium cations, which hydrogen bond to the apical F atoms of adjacent layers. This structure may be viewed as a 'single-layer' fluoride analogue of the Dion-Jacobson family of oxides.

Full text of DOI:10.1107/S0108270106044520

inorganic compounds
Acta Crystallographica Section C
Crystal Structure
situ breakdown of the organic template (see Experimental). It
is related to several other layered ¯uorides of stoichiometry
Communications
AMF and may also be regarded as an n = 1 Dion±Jacobson
4
ISSN 0108-2701
phase (Dion et al., 1981).
The asymmetric unit (Fig. 1) contains one unique Sc site on
a general position, having quite regular octahedral symmetry
(Table 1). There are ®ve crystallographically independent F
sites and two N sites, both on mirror planes.
Ammonium scandium tetrafluoride
Fig. 2 shows that (I) is built from puckered layers of vertex-
sharing octahedra, typical of layered perovskites. The layers
are eclipsed relative to each other with respect to the a axis,
but staggered by b/4 along b. Extensive hydrogen bonding
occurs between adjacent layers, mediated by the ammonium
cations (Table 2). The only NÐHÁ Á ÁF hydrogen bonds are
those between ammonium cations and the `apical' F atoms
that project into the interlayer space. This hydrogen bonding
ful®lls bond-valence requirements around the apical F atoms
F2 and F3, as shown in Table 3.
Nicholas F. Stephens and Philip Lightfoot*
School of Chemistry, University of St Andrews, Fife KY16 9ST, Scotland
Correspondence e-mail: pl@st-and.ac.uk
Received 27 September 2006
Accepted 24 October 2006
Online 22 November 2006
The title compound, NH ScF , is an addition to the AMF
4
4
4
family of layered perovskite-like structures. The structure
consists of a two-dimensional array of corner-sharing ScF6
octahedra, which produces anionic sheets of stoichiometry
�
[
ScF ] stacked along the c axis. The layers are separated by
4
charge-balancing ammonium cations, which hydrogen bond to
the apical F atoms of adjacent layers. This structure may be
viewed as a `single-layer' ¯uoride analogue of the Dion±
Jacobson family of oxides.
Comment
The title compound, NH ScF , (I), was produced during our
4
4
exploratory studies in the hydrothermal chemistry of organi-
cally templated scandium ¯uorides (Stephens et al., 2004;
Stephens & Lightfoot, 2006). This compound arises from an in
Figure 1
The asymmetric unit of (I), with displacement ellipsoids drawn at the 50%
1
1
probability level [symmetry code: (i) � x, y + , � z + ].
2
2
Figure 2
(a) A projection along [100], showing staggered octahedra. (b) A projection along [010], showing eclipsed octahedra.
Acta Cryst. (2006). C62, i103±i105
DOI: 10.1107/S0108270106044520
# 2006 International Union of Crystallography i103

inorganic compounds
Figure 3
A view of a single layer along [001], showing (a) the Pmcn model with the additional c axis tilt mode and (b) the Amma model, with b = b/2.
0
Both the raw diffraction data and the derived model display
a signi®cant degree of pseudosymmetry (e.g. the bond lengths
involving F1/F4 and F2/F3). An alternative model in space
together with a small amount of ScF
1
3
. Compound (I) was heated to
073 K at a rate of 5 K min under N gas. Thermogravimmetric
�
1
2
analysis shows a single-step weight loss of 19.6% from 573 to 698 K
(20% calculated). Powder X-ray diffraction of the residue shows that
0
group Amma, with b = b/2, was also considered. However, our
3
this decomposition product is ScF .
re®nements con®rm that the chosen model is correct; re®ne-
ments in the higher-symmetry model lead to anomalously
elongated ellipsoids for the `in-plane' F atoms, transverse to
the ScÐFÐSc linkages. In fact, the pseudosymmetry is due to
Crystal data
NH
4
ScF
4
Z = 8
x
D = 2.151 Mg m
Mo Kꢀ radiation
ꢁ = 1.67 mm
T = 93 (2) K
Prism, colourless
0.10 Â 0.03 Â 0.02 mm
�
3
M
r
= 139.00
Orthorhombic, Pmcn
`
octahedral tilting', and the difference between the two models
Ê
� 1
a = 7.862 (2) A
Ê
b = 8.088 (2) A
c = 13.503 (4) A
Ê
V = 858.6 (4) A
is clari®ed in Fig. 3. In addition to the tilting relative to the b
axis, shown in Fig. 2(b), there is a second tilt mode around the
c axis, which is allowed in the correct Pmcn model but
forbidden in the approximate Amma model. The two models
Ê
3
Data collection
are analogous to those in KFeF (Lapasset et al., 1986), which
4
Rigaku/MSC CCD area-detector
diffractometer
5191 measured re¯ections
847 independent re¯ections
587 re¯ections with I > 2ꢂ(I)
undergoes a structural phase transition from KFeF (III) to
4
!
scans
Absorption correction: multi-scan
SADABS; Bruker, 1999)
min = 0.825, Tmax = 0.970
KFeF (II) at 368 K, corresponding to Pmcn to Amma. We
4
R
int = 0.026
have not explored the possibility of such a phase transition in
the present case.
In comparison with other compositionally related AMF4
ꢀ
(
T
ꢃmax = 25.3
Re®nement
compounds, (I) is isotypic with KGaF (Courbion et al., 1989).
4
2
2
2
2
Re®nement on F
2
w = 1/[ꢂ (F ) + (0.0519P)
o
2
Interestingly, however, more precisely similar compositions
have different structure types; for example, NH FeF (Leblanc
R[F > 2ꢂ(F )] = 0.028
wR(F ) = 0.102
S = 1.11
847 re¯ections
75 parameters
Only H-atom coordinates re®ned
+ 0.1485P]
where P = (Fo + 2F )/3
2
2
2
c
4
4
�
(Á/ꢂ)max = 0.005
et al., 1985) has the same type of layer as (I), but the [ScF4]
sheets are eclipsed along both a and b, whereas KScF , has a
Ê
� 3
Áꢄmax = 0.40 e A
Áꢄmin = � 0.40 e AÊ �
3
4
unique `corrugated sheet' structure containing both cis- and
trans-vertex-sharing octahedra (Champarnaud-Mesjard &
Frit, 1992).
Table 1
Selected geometric parameters (A, ).
Ê
ꢀ
Experimental
ScÐF2
ScÐF3
ScÐF1
1.9904 (12)
1.9919 (12)
2.0272 (7)
ScÐF4
ScÐF5
ScÐF5
2.0273 (7)
2.0320 (19)
2.0325 (19)
i
Scandium oxide (0.138 g), water (5 ml) and a 40% aqueous solution
of HF (0.5 ml) were heated in a Te¯on-lined steel autoclave for 1 h
at 463 K. To this, ethylene glycol (5 ml) and 1,3-diaminopropane
ii
Sc ÐF1ÐSc
F2ÐScÐF3
F1ÐScÐF4
179.61 (9)
179.82 (7)
179.713 (18)
151.46 (10)
151.82 (10)
168.48 (8)
iii
Sc ÐF4ÐSc
(0.4 ml) were added, and the resulting mixture was heated at the
i
F5 ÐScÐF5
iv
Sc ÐF5ÐSc
same temperature for four days. The product was ®ltered off, washed
with water and allowed to dry at room temperature overnight.
Powder X-ray diffraction revealed predominantly (I) as the product,
1
2
1
2
1
2
1
2
Symmetry codes: (i) � x; y ‡ ; � z ‡ ; (ii) � x � ; y; z; (iii) � x ‡ ; y; z; (iv) � x,
1
2
1
2
y � ; � z ‡ .
ꢁ
i104 Stephens and Lightfoot
NH ScF
4 4
Acta Cryst. (2006). C62, i103±i105

inorganic compounds
Table 2
Hydrogen-bond geometry (A, ).
the convention in perovskite chemistry. H atoms were located from a
difference Fourier map and were re®ned freely; the Uiso(H) values
Ê
ꢀ
Ê
2
were ®xed at 0.018 A .
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
Data collection: CrystalClear (Rigaku/MSC, 2005); cell re®nement:
CrystalClear; data reduction: CrystalClear; program(s) used to solve
structure: SHELXS97 (Sheldrick, 1997); program(s) used to re®ne
structure: SHELXL97 (Sheldrick, 1997); molecular graphics:
DIAMOND (Brandenburg, 2001); software used to prepare material
for publication: SHELXL97.
N1ÐH1Á Á ÁF2
N1ÐH2Á Á ÁF3
N1ÐH3Á Á ÁF2
N2ÐH4Á Á ÁF3
N2ÐH5Á Á ÁF3
N2ÐH6Á Á ÁF2
0.91 (3)
0.97 (4)
0.86 (4)
0.84 (4)
0.93 (3)
0.99 (4)
1.97 (3)
2.11 (3)
2.21 (3)
2.24 (3)
1.95 (3)
2.11 (3)
2.836 (2)
2.858 (3)
2.853 (3)
2.867 (3)
2.837 (2)
2.872 (4)
159 (2)
v
132.0 (9)
131.3 (14)
132.1 (14)
158 (2)
vi
vii
viii
132.1 (9)
1
2
3
3
2
1
2
1
2
1
2
Symmetry codes: (v) � x ‡ ; � y ‡ ; z � ; (vi) x ‡ ; � y ‡ 2; � z; (vii) x � , � y ‡ 2,
1
2
1
2
�
z ‡ 1; (viii) � x � ; � y ‡ ; z ‡ .
2
We thank Professor Alex Slawin for X-ray data collection
and the University of St Andrews for funding.
Table 3
Bond valence parameters.
P
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: BC3020). Services for accessing these data are
described at the back of the journal.
Bond
s
ij
s
ij
Sc F2
Sc F3
Sc F1
Sc F4
Sc F5
Sc F5
0.54
0.53
0.49
0.49
0.48
0.48
±
±
±
±
±
±
±
References
Brandenburg, K. (2001). DIAMOND. Version 2.1. Crystal Impact GbR, Bonn,
Germany.
Brese, N. E. & O'Keeffe, M. (1991). Acta Cryst. B47, 192±197.
Bruker (1999). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.
Champarnaud-Mesjard, J. C. & Frit, B. (1992). Eur. J. Solid State Inorg. Chem.
3.00
0.97
0.54
0.53
0.97
±
F1 Sc
F2 Sc
F3 Sc
F4 Sc
F5 Sc
F5 Sc
0.49 Â 2
0.54
0.53
0.49 Â 2
29, 161±170.
0.48
0.48
Courbion, G., Randrianohavy, J. V. & Rousseau, J. J. (1989). J. Solid State
Chem. 81, 285±292.
0.96
Dion, M., Ganne, M. & Tournoux, M. (1981). Mater. Res. Bull. 16, 1429±1435.
Lapasset, J., Sciau, P., Moret, J. & Gros, N. (1986). Acta Cryst. B42, 258±262.
Leblanc, M., Ferey, G., De Pape, R. & Teillet, J. (1985). Acta Cryst. C41, 657±
Note: sij values calculated for B = 0.37; Brese & O'Keeffe (1991) extrapolated.
660.
Systematic absences were consistent with space groups Pmcn (62)
or P2 cn (33). Successful re®nement of the structure in centrosym-
Rigaku/MSC (2005). CrystalClear. Rigaku/MSC Inc., The Woodlands, Texas,
USA.
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. Release 97-2.
University of G oÈ ttingen, Germany.
Stephens, N. F. & Lightfoot, P. (2006). Solid State Sci. 8, 197±202.
Stephens, N. F., Slawin, A. M. Z. & Lightfoot, P. (2004). Chem. Commun.
pp. 614±615.
1
metric Pmcn, together with the lack of any contradictory physical
property measurements, meant that this was preferred over P2 cn.
1
Pmcn [a non-standard setting of Pnma (62)] was chosen as this
de®nes the perovskite-like layers to lie perpendicular to c, which is
ꢁ
Acta Cryst. (2006). C62, i103±i105
Stephens and Lightfoot
NH ScF
4 4
i105