A pseudo-merohedrally twinned rare-earth sulfate: K6[Ce(HSO 4)2(SO4)4]·-H2O, a novel structure type

Article abstract of DOI:10.1107/S010827010700875X

A novel structure type of an acidic rare-earth sulfate, hexa-potassium cerium dihydrogensulfate tetra-sulfate monohydrate, is reported. The crystal is twinned, mimicking tetra-gonal symmetry. The Ce^IV atom is nine-coordinate, connecting to one corner-sharing and four edge-sharing sulfate groups. One of the potassium ions is disordered over two general positions. The compound is unique as it contains rare-earth monomers, [Ce(HSO4)(SO4)4] ^5-. The structure is composed of these monomers, water mol-ecules, discrete hydrogensulfate ions and potassium ions held together by ionic inter-actions. There are two types of alternating layers in the structure, with compositions [K4Ce(HSO4)(SO4)4]^- and [K2(HSO4)(H2O)]⁺. International Union of Crystallography 2007.

Full text of DOI:10.1107/S010827010700875X

inorganic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
dominate, while for the larger monovalent ions the tetra-
hydrates prevail. Anhydrous as well as hydrated ternary
+
3+
sulfates with A :M compositions other than 1:1 are not well
characterized, although a number of phases are supposed to
exist (Wickleder, 2002). Nearly all the structurally character-
ized sulfates with an A:M ratio not equal to 1 are described as
non-centrosymmetric (Wickleder, 2002). Five hydrated alkali
cerium sulfates have been structurally characterized to date,
ISSN 0108-2701
A pseudo-merohedrally twinned rare-
earth sulfate: K [Ce(HSO ) (SO ) ]Á-
6
4 2
4 4
IV
viz. one Ce compound, K Ce(SO ) ÁH O (Iskhakova et al.,
2
4 3
2
H O, a novel structure type
III
1988), and four Ce compounds, ACe(SO ) ÁH O [A = Li
2
4
3
2
(
Iskhakova et al., 1987), Na (Blackburn & Gerkin, 1995), K
Jemmali et al., 2005) and Rb (Robinson & Jasty, 1998)].
a
b
(
Ternary rare-earth sulfates with
Barbara M. Casari * and Vratislav Langer
a composition ratio
a
Department of Chemistry, Inorganic Chemistry, G oÈ teborg University, SE-412 96
b
G oÈ teborg, Sweden, and Environmental Inorganic Chemistry, Department of
Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96
G oÈ teborg, Sweden
Correspondence e-mail: casari@chem.gu.se
Received 8 January 2007
Accepted 21 February 2007
Online 17 March 2007
A novel structure type of an acidic rare-earth sulfate,
hexapotassium cerium dihydrogensulfate tetrasulfate mono-
hydrate, is reported. The crystal is twinned, mimicking
IV
tetragonal symmetry. The Ce atom is nine-coordinate,
connecting to one corner-sharing and four edge-sharing
sulfate groups. One of the potassium ions is disordered over
two general positions. The compound is unique as it contains
5�
rare-earth monomers, [Ce(HSO )(SO ) ] . The structure is
4
4 4
composed of these monomers, water molecules, discrete
hydrogensulfate ions and potassium ions held together by
ionic interactions. There are two types of alternating layers in
�
the structure, with compositions [K Ce(HSO )(SO ) ] and
4
4
4 4
+
K (HSO )(H O)] .
[
2 4 2
Figure 1
Comment
The atom-numbering scheme for the title compound. One of the
potassium ions (K6A and K6B) is disordered, occupying 50% of two
general positions. Displacement ellipsoids are shown at the 30%
probability level.
The chemistry of the lanthanides has expanded rapidly; the
interest in their complexes is driven by their promising utili-
zation as a result of their low toxicity. Among the lanthanide
materials, cerium compounds have attracted attention owing
to their applications as ion conductors, catalysts, and magnetic
and ¯uorescence materials. Recently, during investigations of
rare-earth frameworks, advances in the syntheses of new
inorganic materials with interesting applications have been
achieved (Yu et al., 2004; Perles et al., 2005; He et al., 2005). A
comprehensive review of the lanthanide compounds with
complex inorganic anions was presented by Wickleder (2002),
covering the structurally characterized compounds to that
time. These materials are intriguing because of the complexity
of their structural arrangements with high coordination
numbers and a variety of coordination geometries.
There exists structural information on anhydrous ternary
+
rare-earth sulfates, AM(SO ) , with all alkali ions (A ) for
4
2
Figure 2
Hydrogen-bonding contacts between hydrogensulfate and sulfate groups,
nearly the whole lanthanide series (Wickleder, 2002). The
most common hydrated ternary rare-earth sulfates are mono-
+
and tetrahydrates; for the smaller A ions the monohydrates
i
forming dimers of cerium sulfate complexes. The O12Á Á ÁO51 distance is
Ê
2.878 (8) A. [Symmetry code: (i) � x + 1, � y, � z + 1.]
Acta Cryst. (2007). C63, i25±i27
DOI: 10.1107/S010827010700875X
# 2007 International Union of Crystallography i25

inorganic compounds
+
3+
A :M > 3 are very rare and only one structure has been
described, viz. (NH ) [Ce (SO ) ]Á4H O (Shan & Huang,
sulfate ion, six potassium ions and one water molecule, with
two of the sulfate ions monoprotonated. From a chemical
point of view, we expect the highly electronegative cerium
complex to be protonated. From a structural point of view, we
assume that one of the H atoms is situated between O51 and
4
8
2
4 8
2
1
998).
The structure of K [Ce(HSO ) (SO ) ]ÁH O is presented
6
4 2
4 4
2
here. Crystals are pseudo-merohedrally twinned, mimicking
tetragonal symmetry (see Experimental for details). There are
six potassium ions, one Ce atom, two hydrogensulfate groups,
four sulfate groups and one water molecule in the asymmetric
unit (Fig. 1). One of the potassium ions (K6A and K6B) is
disordered, occupying 50% of two general positions. The Ce
atom is coordinated by nine O atoms, belonging to one corner-
sharing (S1) and four edge-sharing sulfate groups (S2±S5)
i
O12 , forming dimers (symmetry code as in Fig. 2). However,
since there is no clear evidence present in the sulfur±oxygen
bond lengths, the location of this H atom may be disordered
between the S1 and S5 sulfate groups. The other H atom may
be located on the S6 sulfate group and attached to O61. The
Ê
S6ÐO61 bond length is 1.525 (6) A, while the remaining S6Ð
Ê
O bond lengths average 1.475 (7) A. The distance between the
(
Fig. 1). The cerium coordination polyhedron is a monocapped
tetragonal antiprism. Ninefold coordination is not as frequent
donor O61 atom and the acceptor water molecule (O1) is
ꢀ
Ê
2.680 (8) A and the S6ÐO61ÐO1 angle is 109.2 (3) (Fig. 3).
The water molecule, in contact with one potassium ion (K5),
IV
as eightfold coordination for the Ce ion. The CeÐO
Ê
distances average 2.41 (4) A (Table 1). The bond-valence sum
is 3.84 valence units [using parameters from Trzesowska et al.
ii
iv
forms hydrogen-bonding contacts to O12 , O22 and O61
(Fig. 3). Hence, the two water H atoms and the hydro-
gensulfate H atom could be disordered among these three
contacts; however, we believe that the water molecule acts as
hydrogen-bond acceptor from O61 and as hydrogen-bond
(2006)]. The potassium ions are in contact with seven or eight
O atoms at distances ranging between 2.714 (6) and
3
one potassium ion, while the terminal sulfate O atoms are in
contact with two or three potassium ions. The SÐO distances
Ê
within the six sulfate groups average 1.48 (2) A (Table 1) and
the edge-sharing groups (S2±S4) show a departure from the
ideal tetrahedral symmetry, with angles ranging from 100.6 (2)
Ê
.294 (8) A. The bridging sulfate O atoms are in contact with
ii
iv
donor to O12 and O22 (symmetry codes as in Fig. 3).
Several structures (Wickleder, 1998a,b, 1999, 2000) of acidic
rare-earth sulfates have been described since the ®rst structure
of a lanthanide hydrogensulfate, Gd(HSO ) (Hummel et al.,
4
3
ꢀ
to 113.5 (3) . It is dif®cult to discern, analyzing the SÐO bond
lengths, which two of the six sulfate groups are protonated.
6
The structural units present are a [Ce(SO ) ] unit, one
�
4
5
Figure 4
The packing of the title compound, with the water molecules shown as
Figure 3
Hydrogen-bonding contact possibilities for the hydroxide group (O61)
dark spheres (red in the electronic version of the paper) and the
potassium ions shown as light-grey spheres. (a) View along the b-axis
ii
ii
iv
5�
and the water molecule (O1). The O61Á Á ÁO1Á Á ÁO12 , O12 Á Á ÁO1Á Á ÁO22
direction; the structure consists of Ce[(HSO
discrete hydrogensulfate groups, potassium ions and water molecules.
4
)(SO
4
)
4
]
monomers,
iv
ꢀ
and O22 Á Á ÁO1Á Á ÁO61 angles are 98.6 (2), 121.8 (2) and 90.60 (19) ,
ii
iv
respectively, and the O1Á Á ÁO12 , O1Á Á ÁO22 and O1Á Á ÁO61 distances are
(b) View along the c-axis direction; there are two types of alternating
Ê
.642 (7), 2.865 (6) and 2.680 (8) A, respectively. [Symmetry codes: (ii)
�
2
�
4 4 4 4
layers, parallel to the ac plane, with compositions [K Ce(HSO )(SO ) ]
+
and [K (HSO )(H O)] .
2 4 2
3
1
3
1
1
1
x + , y + , � z + ; (iii) x + , � y + , z + ; (iv) x, y, z + 1.]
2
2
2
2
2
2
ꢁ
i26 Casari and Langer
K
6
[Ce(HSO
4
)
2 4
(SO )
4
2
]ÁH O
Acta Cryst. (2007). C63, i25±i27

inorganic compounds
1
994), was published. These structures are built up by eight- or
Re®nement
2
2
nine-coordinate rare-earth ions held together by sulfate
groups, bridging by corner sharing. The structure of the title
compound is essentially different from these structures; it is an
acidic ternary sulfate, containing a second cation. This is
unique, as the structure contains a rare-earth monomer,
R[F > 2ꢃ(F )] = 0.033
wR(F ) = 0.089
353 parameters
H-atom parameters not de®ned
2
Ê
� 3
Áꢄmax = 1.68 e A
S = 1.01
8933 re¯ections
Áꢄmin = � 0.74 e AÊ
� 3
5�
[Ce(HSO )(SO ) ] . Usually, rare-earth sulfates form layers
or three-dimensional networks mediated by bridging sulfate
H atoms were not located. The crystal under investigation was
twinned, mimicking tetragonal symmetry because of the similarity
4
4 4
between the a and c parameters and the closeness of the ꢀ angle to
90 [twin law (001, 010, 100)]. The twin volume ratio was re®ned to
0.537 (1):0.463 (1). The highest difference peak is located close
groups. Only one structure has been described, viz.
ꢀ
(
NH ) [Ce (SO ) ]Á4H O (Shan & Huang, 1998), containing
�
2 4 8
4
8
2
4 8
2
8
distinct rare-earth dimers, [Ce (SO ) ] . The packing of the
Ê
(0.67 A) to atom K6A.
5
�
title compound is shown in Fig. 4. The [Ce(HSO )(SO ) ]
4
4 4
Data collection: SMART (Siemens, 1995); cell re®nement: SAINT
Siemens, 1995); data reduction: SAINT and SADABS (Sheldrick,
monomers, water molecules, hydrogensulfate groups and
potassium ions are held together mainly by ionic interactions.
(
2002); program(s) used to solve structure: SHELXTL (Bruker, 2003);
program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997);
molecular graphics: DIAMOND (Brandenburg, 2001); software used
to prepare material for publication: SHELXTL.
Experimental
Ce(SO
Ce(OH)
was added to a 1:2 molar mixture of Ce(OH)
solid residue was completely dissolved. An equal volume of a satu-
rated aqueous solution of K CrO was then added to the sample.
4
)
2
Á4H
was precipitated with ammonia (15 M). Sulfuric acid (9 M)
and K CrO until the
2
O (1.5 g, 3.75 mmol) was dissolved in water (10 ml) and
4
4
2
4
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FA3068). Services for accessing these data are
described at the back of the journal.
2
4
Light-yellow crystals, shaped as square plates, started to form after a
few weeks.
Crystal data
Ê
V = 2510.75 (8) A
3
K
M
6
[Ce(HSO
= 969.10
4
)
2
(SO
4
4 2
) ]ÁH O
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r
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S6ÐO63
S6ÐO64
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1.497 (4)
1.531 (4)
1.447 (4)
1.465 (5)
1.503 (4)
1.538 (4)
1.444 (4)
1.461 (5)
1.502 (4)
1.522 (4)
1.465 (7)
1.478 (6)
1.481 (6)
1.525 (6)
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2.367 (4)
2.384 (4)
2.430 (4)
2.433 (3)
2.435 (4)
2.439 (4)
2.443 (4)
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1.450 (4)
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ꢁ
Acta Cryst. (2007). C63, i25±i27
Casari and Langer
K
6
[Ce(HSO
4
)
2 4
(SO )
4
2
]ÁH O
i27