Two new octahedral/pyramidal frameworks containing both cation channels and lone-pair channels: Syntheses and structures of Ba2Mn IIMn2III(SeO3)6 and PbFe2(SeO3)4

Article abstract of DOI:10.1016/j.jssc.2004.07.057

The hydrothermal syntheses, single crystal structures, and some properties of Ba₂Mn^IIMn₂^III(SeO ₃)₆ and PbFe₂(SeO₃)₄ are reported. These related phases contain three-dimensional frameworks of vertex (FeO₆) and vertex/edge linked (MnO₆) octahedra and SeO₃ pyramids. In each case, the MO₆/SeO₃ framework encloses two types of 8 ring channels, one of which encapsulates the extra-framework cations and one of which provides space for the Se^IV lone pairs. Crystal data: Ba₂Mn₃(SeO₃) ₆, M_r=1201.22, monoclinic, P2₁/c (No. 14), a=5.4717 (3) A, b=9.0636 (4) A, c=17.6586 (9) A, β=94.519 (1)°, V=873.03 (8) A³, Z=2, R(F)=0.031, wR(F ²)=0.070; PbFe₂(SeO₃)₄, M _r=826.73, triclinic, P1^- (No. 2), a=5.2318 (5) A, b=6.7925 (6) A, c=7.6445 (7) A, α=94.300 (2)°, β=90.613 (2)°, γ=95.224 (2)°, V=269.73 (4) A³, Z=1, R(F)=0.051, wR(F²)=0.131. Polyhedral view of the structure of the mixed valence barium manganese selenite Ba ₂Mn₃(SeO₃)₆ projected onto (100).

Full text of DOI:10.1016/j.jssc.2004.07.057

ARTICLE IN PRESS
Journal of Solid State Chemistry 177 (2004) 4680–4686
www.elsevier.com/locate/jssc
Two new octahedral/pyramidal frameworks containing both cation
channels and lone-pair channels: syntheses and structures of
Ba2MnIIMn2III(SeO3)6 and PbFe2(SeO3)4
Ã
Magnus G. Johnston, William T.A. Harrison
Department of Chemistry, University of Aberdeen, Meston Walk, Aberdeen, Scotland AB24 3UE, UK
Received 13 January 2004; received in revised form 18 May 2004; accepted 14 July 2004
Abstract
The hydrothermal syntheses, single crystal structures, and some properties of Ba2MnIIMn2III(SeO3)6 and PbFe2(SeO3)4 are
reported. These related phases contain three-dimensional frameworks of vertex (FeO6) and vertex/edge linked (MnO6) octahedra
and SeO3 pyramids. In each case, the MO6/SeO3 framework encloses two types of 8 ring channels, one of which encapsulates the
extra-framework cations and one of which provides space for the SeIV lone pairs. Crystal data: Ba2Mn3(SeO3)6, Mr=1201.22,
monoclinic, P21/c (No. 14), a=5.4717 (3) A, b=9.0636 (4) A, c=17.6586 (9) A, b=94.519 (1)1, V=873.03 (8) A3, Z=2,
2
R(F)=0.031, wR(F )=0.070; PbFe2(SeO3)4, Mr=826.73, triclinic, P1 (No. 2), a=5.2318 (5) A, b=6.7925 (6) A, c=7.6445 (7) A,
¯
a=94.300 (2)1, b=90.613 (2)1, g=95.224 (2)1, V=269.73 (4) A3, Z=1, R(F)=0.051, wR(F2)=0.131.
r 2004 Elsevier Inc. All rights reserved.
Keywords: Hydrothermal synthesis; Crystal structures; Selenites
1. Introduction
In this paper, we report the hydrothermal syntheses,
single-crystal structures, and some properties of Ba2MnII
Mn2III(SeO3)6 and PbFe2(SeO3)4. These related phases
demonstrate a self-containment effect [4] in which the
SeIV lone pairs of electrons are directed into otherwise
empty, infinite, one-dimensional 8-ring channels of
significant size. A similar effect has recently been
demonstrated for the phase Tb2O(SeO3)2, in which the
selenite moieties arrange themselves so that their lone
The structures of extended inorganic networks
incorporating the [SeO3]2– selenite ion are of interest
due to the asymmetric coordination polyhedron adopted
by this species, as described in the extensive, recent
review of Verma [1]. The effect can be rationalized in
terms of the stereochemically active lone pair of
electrons associated with SeIV, which are always directed
away from the three O atoms, as predicted by VSEPR
theory [2], leading to pyramidal coordination for the
selenite species. It has been suggested that this inherently
asymmetric geometry for SeIV may lead to a tendency
for selenites to crystallize in noncentrosymmetric
structures with consequent interesting physical proper-
ties [3], such as second harmonic generation (SHG).
¯
pairs occupy channels in a manner that reflects the 4
symmetry of other parts of the structure [5].
2. Experimental
Syntheses: Ba2Mn3(SeO3)6 was prepared by a hydro-
thermal reaction, as follows: 0.395 g (2 mmol) BaCO3,
0.209 g (1 mmol) MnCl2 ꢀ 4H2O, 0.536 g (2 mmol)
Mn(CH3CO2)3 ꢀ 2H2O, 0.666 g (6 mmol) SeO2 and
15 ml H2O were sealed in a 23 ml capacity, teflon-lined
Ã
Corresponding author. Fax: +44-1224-272-921.
E-mail address: w.harrison@abdn.ac.uk (W.T.A. Harrison).
0022-4596/$ - see front matter r 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2004.07.057

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M.G. Johnston, W.T.A. Harrison / Journal of Solid State Chemistry 177 (2004) 4680–4686
4681
stainless steel bomb. The bomb was heated to 140 1C for
4 days, followed by cooling to room temperature over a
few hours. The solid product, consisting of a mass of
brown rods and needles, was recovered from the
supernatant liquors by vacuum filtration and washing
with water and acetone. Powder XRD (see below)
indicated the presence of a small (visual estimate,
based on peak heights, of perhaps 2%) quantity of
MnIIMnI2IIO(SeO3)3. This phase [6] also crystallizes as
brown needles, making phase separation extremely
difficult.
PbFe2(SeO3)4 initially arose from a very surprising
reaction: 2 g MgSO4 ꢀ 7H2O (BDH Analar), 5 g SeO2
(Lancaster Synthesis), and 15 ml deionised H2O were
sealed in a 23 ml hydrothermal bomb and heated to
200 1C for two days, followed by cooling to room
temperature over a few hours. The solid product,
consisting of a tiny yield (o1 mg) of yellow–green,
faceted, chunks of PbFe2(SeO3)4 was recovered by
vacuum filtration and washing with water and acetone.
This reaction is reproducible. No lead or iron com-
pounds had been recently prepared using the hydro-
thermal bomb in question; thus, presumably, impurities
in the starting material(s) reacted to form the PbFe2
(SeO3)4 product. This is supported by trace-elemental
analysis results: the Lancaster SeO2 sample contained
4.24 (9) mg/kg Pb whereas the lead content of the
magnesium nitrate heptahydrate was negligible (below
detection limits). The iron probably arose from the
Analar MgSO4 ꢀ 7H2O [Fe content=9.37 (11) mg/kg]
whereas the Lancaster SeO2 contained negligible Fe (at
or below detection limits).
EDX indicated the presence of Pb, Fe, and Se in the
crystalline chunks, which was confirmed in the crystal-
structure study described below. A rational hydrother-
mal synthesis started from 0.662 g (2 mmol) Pb(NO3)2,
1.616 g (4 mmol) Fe(NO3)3 ꢀ 9H2O, 0.888 g (8 mmol)
SeO2 (BDH Analar with negligible Pb content as
determined by trace element analysis) and 15 ml H2O,
which were sealed in a 23-ml bomb and heated to 200 1C
for 2 days, followed by cooling to room temperature
over a few hours. Product recovery as above led to a
mixture of tiny (o0.02 mm) yellow cuboids of PbFe2
(SeO3)4 accompanied by brown whiskers and needles of
Fe2O(SeO3)4 [7] (identified on the basis of its unit cell
parameters), in about a 50:50 ratio (visual estimate).
(SeO3)6 showed two distinct weight losses (–39.8%
occurring between 350 and 700 1C and –14.4% between
800 and 1200 1C). The overall weight loss of 54.2%
correlates reasonably well with that calculated (55.4%)
for the decomposition scheme Ba2Mn3(SeO3)6 (s)-
Ba2Mn3O6 (s)+6 SeO2 (g), allowing for the presence of
a small quantity of Mn3O(SeO3)3. The identity of the
intermediate decomposition stage at 700 1C is not
known. There was insufficient amount of pure sample
of PbFe2(SeO3)4 to perform similar measurements. The
temperature ranges for the decomposition steps reported
here for Ba2Mn3(SeO3)6 are wide (up to 400 1C), but
similar sluggish decompositions have been seen for other
selenites [1].
The diffuse reflectance spectrum (reference standard
BaSO4) of Ba2Mn3(SeO3)6 was recorded on a Shimadzu
UV-3100 spectrometer at room temperature and con-
verted according to the Kubelka Munk method. It
shows a broad, relatively weak absorbance (ꢀ ꢁ 5)
centered at about 500 nm (20,000 cm–1), which probably
5
corresponds to a nominal Eg-5T2g transition [8] for
Mn3+ (i.e., promotion of an electron from a t2g-like
state to an eg-like state assuming approximate octahe-
dral symmetry). Any spin-forbidden d–d transitions
associated with Mn2+ are expected to be up to two
orders of magnitude weaker [8].
2.2. Structure determinations
The structures of Ba2Mn3(SeO3)6 (brown rod,
ꢂ0.04 Â 0.04 Â 0.37 mm3) and PbFe2(SeO3)4 (yellow–
green chunk, ꢂ0.082 Â 0.045 Â 0.045 mm3) were deter-
mined by standard X-ray methods using data collected
on a Bruker SMART CCD diffractometer (MoKa
(
radiation, l ¼ 0:71073 A; T=2572 1C). In each case, a
hemisphere of data was collected using o scans (0.31
slices) with the aid of the SMART and SAINT
programs [9], and empirical absorption corrections
(min./max. transmission coefficients=0.053/0.515 and
0.181/0.329 for Ba2Mn3(SeO3)6 and PbFe2(SeO3)4,
respectively) was made with SADABS [10] during data
reduction. The systematic absences for Ba2Mn3(SeO3)6
indicated space group P21/c (No. 14) which was
assumed for the remainder of the refinement. For
PbFe2(SeO3)4, the situation is somewhat less clear cut.
¯
Structure solution and refinement in space group P1
(No. 2) resulted (see below) in a generally satisfactory
answer, except for excessively large anisotropy of the
lead atom displacement parameters [Umax/Umin=7.7].
Thus, a model involving positional disorder of the Pb
species over two adjacent sites related by inversion
symmetry was developed [refined d(PbyPbi)=0.449
(3) A; symmetry code (i)=–x, Ày, –z; Umax/Umin=2.9].
A refinement was also performed in space group P1
(No. 1), but this also led to disorder over two adjacent,
nonsymmetry-related sites [d(PbyPb)=0.495 (5) A] and
2.1. Characterization
Powder XRD (Bruker D8 diffractometer, CuKa
(
radiation, l ¼ 1:5418 A; T=201 C) on a well-ground
sample of Ba2Mn3(SeO3)6 yielded a pattern in good
agreement with a simulation based on the single crystal
structure accompanied by a few weak lines correspond-
ing to Mn3O(SeO3)3 [6]. TGA (Mettler Toledo Star
system; ramp at 10 1C/min under argon) for Ba2Mn3

ARTICLE IN PRESS
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4682
Table 1
Crystallographic parameters
Table 2
Atomic coordinates/displacement parameters for Ba2Mn3(SeO3)6
Ba2Mn3(SeO3)6 PbFe2(SeO3)4
Ba2Se6Mn3O18 PbSe4Fe2O12
Atom
x
y
z
Ueq
Empirical formula
Formula weight
Crystal system
Crystal color, form
a (A)
Ba1
Mn1
À0.01925(4)
0.33191(3)
1
2
0.203911(14)
0
0.01187(6)
0.01221(16)
1201.26
826.73
Triclinic
0
Monoclinic
Brown rod
5.4717 (3)
9.0636 (4)
17.6586 (9)
90
Mn2
Se1
Se2
Se3
O1
O2
O3
O4
O5
O6
O7
O8
O9
0.51495(11)
0.50497(7)
0.49958(7)
0.00833(7)
0.5531(5)
0.2623(5)
0.7189(5)
0.2375(5)
0.6036(6)
0.7026(5)
0.0884(6)
0.2825(6)
À0.1398(6)
À0.00133(7)
0.14602(4)
0.29574(5)
0.86033(5)
0.3240(3)
0.0960(3)
0.0664(3)
0.3623(4)
0.1812(4)
0.4324(3)
0.6833(4)
0.9554(4)
0.8942(4)
0.16398(4)
0.31342(2)
0.04648(2)
0.06694(2)
0.28145(18)
0.25312(18)
0.26060(16)
0.07730(19)
0.1205(2)
0.01130(12)
0.01082(8)
0.01157(9)
0.01273(9)
0.0153(6)
0.0148(6)
0.0132(5)
0.0185(6)
0.0208(7)
0.0148(6)
0.0216(7)
0.0233(7)
0.0219(7)
Yellow–green chunk
5.2318 (5)
6.7925 (6)
7.6445 (7)
94.300 (2)
90.613 (2)
95.224 (2)
269.73 (4)
b (A)
c (A)
a (1)
b (1)
94.519 (1)
90
873.03 (8)
g (1)
3
(
VðA Þ
0.06780(17)
0.0792(2)
Z
Space group
2
P21/c (No. 14)
1
¯
P1(No. 2)
0.08245(19)
0.14531(18)
T (1C)
2072
0.71073
4.57
2072
0.71073
5.09
l (MoKa) (A)
rcalc ðg=cm3Þ
m ðcmÀ1
Þ
191.5
65.0
317.8
65.0
2800
Maximum 2y (1)
Reflections measured
Rint
(3) A] is essentially a regular octahedron, whereas the
Mn2 coordination [dav(Mn2–O)=2.043 (3) A] is sub-
stantially distorted from octahedral regularity, and
could also be described as an elongated tetragonal
bipyramid, although the axial O–Mn–O bond angle of
146.61 (12)1 is far removed from the nominal value of
1801. The Mn2 polyhedron can be quantified in terms of
the distance distortion [12] Doct ¼ 0:0068 and the
angular variance [13] s2oct ¼ 116:5: Bond valence sum
(BVS) calculations, using the Brown [14] formalism,
yield BVS(Mn1)=2.01, and BVS(Mn2)=3.06, strongly
suggesting that Mn1 is divalent and Mn2 is trivalent.
This presence of mixed-valence Mn2+/Mn3+ is also
consistent with the brown crystal color [15] and the
diffuse reflectance spectrum of Ba2Mn3(SeO3)6 (see
above). The distortion of the Mn2O6 octahedron can
be explained by the Jahn–Teller effect for d4 MnIII, and
the average Mn–O distance seen here is in excellent
6923
0.034
0.027
1874/1443
94
Merged/observeda reflections 3149/2657
Parameters
Coverage of unique data (%) 99.6
133
96.2
0.051
0.131
R(F)b
wR(F2)c
0.031
0.070
aI42s(I) after the merging of systematically equivalent and multiply
measured reflections.
bR=S99Fo9À9Fc 99/S9Fo9for merged data with I42sðIÞ:
cwR=[Sw(9Fo29À9Fc29)2/Sw9F2o92]1/2 for all merged data.
essentially the same residuals, and was discarded. For
both structures, direct methods using SHELXS-97 [11]
were used to locate most of the atoms, and the
remaining atoms were located from difference maps
during the full-matrix least-squares refinements using
SHELXL-97 [11]. Neither structure required charge
balancing by protons. Crystallographic data are sum-
marized in Table 1. Supplementary materials are
available from the authors by e-mail or from the
Fachinformationzentrum (FIZ), Karlsruhe, Germany
[deposition numbers CSD-414051 for Ba2Mn3(SeO3)6
and CSD-414053 for PbFe2(SeO3)4].
agreement with the relationship d(MnIII–O)=(1.994+
¯
7.08 Doct)=2.042 A established by Shannon et al. [12]
for other trivalent manganese compounds. The three
selenium atoms show their normal coordination beha-
vior [1,16] of three O atom neighbors in pyramidal
conformation [dav(Se–O)=1.704 (3) A], with the fourth
tetrahedral vertex assumed to be occupied by the SeIV
lone pair of electrons. O2 and O3 form a common edge
between the Mn2 and Se1 groups, and the other O
atoms form vertex-sharing Mn–O–Se bridges
(yav=129.51). All but O7 and O8 also bond to the
barium cation which could be described as either nine or
[if the longer Ba1–O1 bond of 3.318(3) A is included]
ten coordinate [spread of Ba–O distances=
2.729(3)–3.012(2)+3.318(3) A; mean for 9 values=
2.820 A; mean for 10 values=2.869 A] and the Ba2+
bond valence sum [14] is 2.24 (expected 2.00) indicating
that its valence requirements are satisfied in this
structure.
3. Results
3.1. Crystal structure of Ba2Mn3(SeO3)6
Atomic coordinates and displacement parameters and
selected geometrical data are presented in Tables 2 and
3, respectively. This phase contains 15 atoms (1 Ba, 2
Mn, 3 Se, 9 O) in the asymmetric unit (Fig. 1), all of
which occupy general positions, except Mn1 (site
¯
symmetry 1). Both manganese cations have six neigh-
boring O atoms; the Mn1 grouping [dav(Mn1–O)=2.194

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4683
O6v
Table 3
Selected bond lengths (A) and angles (1) for Ba2Mn3(SeO3)6
O7vi
O9ix
Se2
Ba1–O3i
Ba1–O2
2.729 (3)
2.737 (3)
2.747 (3)
2.793 (3)
2.796 (3)
2.804 (3)
2.869 (3)
2.889 (3)
3.012 (3)
3.318 (3)
2.183 (3)
2.183 (3)
2.198 (3)
2.198 (3)
2.201 (3)
2.201 (3)
1.886 (3)
1.903 (3)
1.905 (3)
2.057 (3)
2.161 (3)
2.347 (3)
1.697 (3)
1.713 (3)
1.736 (3)
1.685 (3)
1.686 (3)
1.730 (3)
1.673 (3)
1.686 (3)
1.733 (3)
O8vii
O4vi
O6
Mn1
Ba1–O4
O5
Mn2
O3
Ba1–O9ii
Ba1–O5iii
Ba1–O1iii
Ba1–O2iv
Ba1–O6iii
Ba1–O3iii
Ba1–O1
O4
O7
O8
O6iii
O3i
O1viii
O5iii
Se3
O2
O1
Ba1
Se1
Mn1–O6v
Mn1–O6iii
Mn1–O4
Mn1–O4vi
Mn1–O7vi
Mn1–O7
Mn2–O8vii
Mn2–O5
Mn2–O1viii
Mn2–O3
Mn2–O9ix
Mn2–O2
Se1–O2
O9
O3iii
O2iv
O1iii
O9ii
Fig. 1. Fragment of Ba2Mn3(SeO3)6, showing the atomic connectivity
(50% displacement ellipsoids). Symmetry codes as in Table 3.
c
b
Se1–O3
Se1–O1
Se2–O4
Se2–O6
Se2–O5
Se3–O7
Se3
Mn2
Se3–O9
Se3–O8
Se1
Se2
Se1–O1–Mn2i
Se1–O2–Mn2
Se1–O3–Mn2
Se2–O4–Mn1
Se2–O5–Mn2
Se2–O6–Mn1x
Se3–O7–Mn1
Se3–O8–Mn2xi
Se3–O9–Mn2xii
124.54 (17)
92.75 (12)
Ba1
Mn1
103.18 (13)
118.64 (17)
138.39 (19)
126.17 (16)
126.82 (19)
138.37 (19)
133.43 (19)
Fig. 2. Polyhedral view projected onto (1 0 0) for Ba2Mn3(SeO3)6
showing the network of Mn1O6, Mn2O6 octahedra (light and dark
shading, respectively) and SeO3E pseudo tetrahedra [the dummy atom
E (unshaded circle), placed 1.0 A from Se represents the lone pair of
electrons] encapsulating channels at yE0.33, zE0.20 and equivalent
locations occupied by the barium cations (shaded circles) and Se1 lone
pairs and empty lone-pair channels at y=0, z=0 and equivalent
locations occupied by the Se2 and Se3 lone pairs.
Symmetry transformations used to generate equivalent atoms: (i) 1Àx,
y+1/2, 1/2Àz; (ii) Àx, yÀ1/2, 1/2Àz; (iii) xÀ1, y, z; (iv) Àx, y+1/2,
1/2Àz; (v) 1Àx, 1Ày, Àz; (vi) Àx, 1Ày, Àz; (vii) x, yÀ1, z; (viii) 1Àx,
yÀ1/2, 1/2Àz; (ix) x+1, yÀ1, z; (x) x+1, y, z; (xi) x, y+1, z; (xii) xÀ1,
y+1, z.
The polyhedral connectivity (Fig. 2) in Ba2Mn3
(SeO3)6 can be described as follows: twisted chains of
Mn2O6 (trivalent Mn) and Se1O3 groups, alternately
sharing edges (via O2+O3) and vertices (via O1),
propagate along [010]. The edge-sharing Mn–O–Se
bond angles are much smaller than the vertex-sharing
Mn–O–Se angles and also correlate with the very
compressed O2–Mn2–O3 octahedral [68.99 (10)1] and
O2–Se1–O3 [94.60 (14)1] pyramidal bond angles. The
Mn1O6 and Se2O3 groups form 4-ring (four polyhedral
units) chains by vertex sharing and propagate along
[1 0 0], with the manganese atoms serving to fuse the
links of the chain. Thus, each Mn1 atom is bonded to
four distinct Se2 species. Pairs of Se3O3 groups are also
attached to the Mn1 centers in trans configuration.
Cross linking between the Mn1/Se2/Se3 and Mn2/Se1
chains by way of both the Se2O3 and Se3O3 groups
results in a three-dimensional, anionic, framework in
which the Mn- and Se-centered polyhedra strictly
alternate. The [Mn3(SeO3)6]2À framework contains two
types of channels propagating along [100], both
comprised of eight polyhedral units (8 rings) alternating
between MnO6 and SeO3. The first of these (atom-to-
atom dimensions ꢂ3.40 Â 6.18 A) is occupied by the
Ba2+ species. In addition, the Se1 lone pair appears to
point into this channel. The second channel provides

ARTICLE IN PRESS
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4684
Table 4
Atomic coordinates/displacement parameters for PbFe2(SeO3)4
space for the Se2 and Se3 lone pairs and is empty of any
other chemical species, despite its atom-to-atom dimen-
sions of some 3.99 Â 5.42 A.
Atom
x
y
z
Ueq
Pb1a
Fe1
0.0387(4)
0
À0.0059(5)
À0.0105(4)
0.0254(4)
0.0092(3)
3.2. Crystal structure of PbFe2(SeO3)4
1
2
0
1
2
1
2
Fe2
0
0.0096(3)
This phase contains 12 atoms (2 Pb, 2 Fe, 2 Se, 6 O) in
the asymmetric unit (Fig. 3), with the lead species
statistically disordered over two adjacent sites (see
above) and both iron cations occupying inversion
centers. Atomic positional and displacement parameters
are listed in Table 4 and selected geometrical data are
shown in Table 5. Both iron cations have essentially
regular octahedral coordination [dav(Fe1–O)=2.002
(7) A and dav(Fe2–O)=2.035 (7) A] and bond valence
sum calculations [14] [BVS(Fe1)=3.11, BVS(Fe2)=
2.88] confirm the presence of trivalent iron. The two
distinct pyramidal selenite groups have typical geome-
trical parameters [dav(Se1–O)=1.707 (7) A, BVS(Se1)=
3.98; dav(Se2–O)=1.706 (7) A, BVS(Se2)=3.99]. The six
O atoms all form Fe–O–Se bridges (yav=126.21), thus
there is no edge-sharing in this phase, and all but O1 and
O3 also bond to the lead cation (Table 5).
The Pb2+ species in PbFe2(SeO3)4 can be described as
4+5 coordinate; with four O atom near neighbors
[d(Pb–O)o2.6 A] arranged in approximately square
planar conformation, with five more distant atoms
[d(Pb–O)42.9 A] completing an irregular coordination
with a large spread of distances of 0.714 A. The BVS [14]
for Pb1 of 1.66 (expected=2.00) for the nine nearest O
atoms suggests a significant degree of underbonding
which may correlate with the space-filling requirements
of the Pb2+ lone pair, although it is difficult to visualize
in which direction this may point. The next-nearest O
atom is over 3.5 A from the lead atom.
Se1
Se2
O1
O2
O3
O4
O5
O6
À0.00877(13)
0.51726(13)
0.0138(11)
0.1531(10)
À0.3227(11)
0.2212(10)
0.7052(10)
0.5731(10)
0.45083(11)
0.19967(11)
0.2906(9)
0.3480(9)
0.4001(10)
0.0695(9)
0.0111(9)
0.2455(9)
0.74140(10) 0.00929(17)
0.32356(10) 0.00960(18)
0.5642(7)
0.9065(8)
0.7904(8)
0.2951(7)
0.3341(8)
0.1094(8)
0.0131(11)
0.0136(11)
0.0182(12)
0.0127(11)
0.0141(11)
0.0141(11)
aSite occupancy for Pb1 ¼ 12:
Table 5
Selected bond lengths (A) and angles (1) for PbFe2(SeO3)4
Pb1–O4
Pb1–O4i
Pb1–O2ii
Pb1–O2iii
Pb1–O6iv
Pb1–O5iv
Pb1–O5v
Pb1–O6v
Pb1–O6
Fe1–O1iii
Fe1–O1
Fe1–O5vi
Fe1–O5v
Fe1–O4iii
Fe1–O4
Fe2–O3vii
Fe2–O3viii
Fe2–O6
Fe2–O6ix
Fe2–O2x
Fe2–O2ii
Se1–O1
2.513 (7)
2.541 (6)
2.552 (6)
2.629 (6)
2.792 (6)
2.825 (6)
3.176 (6)
3.203 (6)
3.227 (6)
1.993 (6)
1.993 (6)
1.997 (6)
1.997 (6)
2.016 (5)
2.016 (5)
1.968 (6)
1.968 (6)
2.041 (6)
2.041 (6)
2.095 (5)
2.095 (5)
1.685 (6)
1.699 (6)
1.736 (6)
1.690 (6)
1.712 (6)
1.716 (5)
Se1–O3
Se1–O2
O2x
O2
O6ix
Se1
O3viii
Se2–O5
Se2–O6
Se2–O4
O3
Fe2
O1
Se2
O6
Se1–O1–Fe1
Se1–O2–Fe2xi
Se1–O3–Fe2xii
Se2–O4–Fe1
Se2–O5–Fe1xiii
Se2–O6–Fe2
140.1 (3)
117.2 (3)
127.1 (4)
121.9 (3)
126.5 (3)
124.7 (3)
O5vi
O3vii
O4iii
O4
O5
O2ii
Fe1
O6v
O5v
Symmetry transformations used to generate equivalent atoms: (i) Àx,
Ày, Àz; (ii) x, y, zÀ1; (iii) Àx, Ày, 1Àz; (iv) 1Àx , Ày, Àz; (v) xÀ1, y, z;
(vi) 1Àx, Ày, 1Àz; (vii) x+1, y, zÀ1; (viii) Àx, 1Ày, 1Àz; (ix) 1Àx,
1Ày, Àz; (x) 1Àx, 1Ày, 1Àz; (xi) x, y, z+1; (xii) xÀ1, y, z+1; (xiii)
x+1, y, z.
Pb1
O5iv
O1iii
O6iv
O2iii
O4i
The polyhedral connectivity (Fig. 4) in PbFe2(SeO3)4
consists of chains of the Fe1, Se1 and Se2-centered
moieties propagating along [100]. Each Fe1 center is
Fig. 3. Fragment of PbFe2(SeO3)4, showing the atomic connectivity
(50% displacement ellipsoids). Symmetry codes as in Table 5. The
longer (d42.75 A) Pb–O bonds are shown as open lines.

ARTICLE IN PRESS
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4685
and in the case of Ba2Mn3(SeO3)6, the presence of edge-
sharing between the polyhedral units. The irregular
nine- or ten-fold coordination of Ba2+ in Ba2Mn3
(SeO3)6 is typical whereas the nine-fold coordinated
Pb2+ species in PbFe2(SeO3)4 appears to be somewhat
under-bonded, perhaps due to its lone-pair stereoche-
mical activity [17]. These species are accommodated in
infinite channels, each surrounded by 8 polyhedral
building blocks. In both cases, a second one-dimen-
sional channel of significant size exists which is empty of
other chemical species. Based on geometrical placement,
the Se lone pairs are directed into these 8-ring channels.
Unlike the case of Tb2O(SeO3)2 [5] there is no obvious
symmetry relationship between the packing of the metal-
centered octahedra and the Se lone pairs.
c
b
Se2
Se1
Fe2
Fe1
Pb1
Ba2Mn3(SeO3)6 complements various other mixed-
valence manganese selenites prepared hydrothermally
including MnIIMn2IIIO(SeO3)2 [6], KMnI4IMnIII(SeO3)6
[18], and Li5MnI4IMnIII(SeO3)8 [18]. The average
Mn–O separations in MnIIMnI2IIO(SeO3)2 (MnII–O
dav=2.192 A; MnIII–O dav=2.036 A) are very similar
to those reported above for Ba2Mn3(SeO3)6 although
the overall structures of the two materials are quite
different. The essentially regular MnII coordination in
Ba2Mn3(SeO3)6 is completely different to the highly
distorted, effectively irregular, manganese(II) environ-
ment in SrMn(SeO3)2 in which edge-sharing occurs
between the MnIIO6 and SeO3 moieties [19]. The
Fig. 4. Polyhedral view projected onto (1 0 0) for PbFe2(SeO3)4
showing the network of FeO6 octahedra and SeO3E pseudotetrahedra
[the dummy atom E (unshaded circle), placed 1.0 A from Se represents
the lone pair of electrons] encapsulating channels at y=0, z=0 and
equivalent locations occupied by the lead cations (shaded circles) and
empty lone-pair channels at y ¼ 12; z ¼ and equivalent locations.
1
2
bridged to two Fe1 neighbors by way of a pair of Se2O3
groups. The two remaining Fe1 vertices are linked to
Se1O3 groups. Crosslinking of the chains by the Fe2
groups results in a three-dimensional FeO6/SeO3 net-
work encapsulating two types of channels propagating
along [1 0 0]. The first of these at (y=0, z=0) and
equivalent locations, with maximum atom-to-atom
dimensions of 3.63 Â 7.99 A contains the lead cations
and the second at (y=1/2, z=1/2; dimensions=
3.10 Â 6.76 A), is empty, apart from the unobserved Se
lone pairs of electrons.
recently
described
[20]
manganese
selenites
Mn3(SeO3)3 ꢀ H2O and Mn4(SeO3)4 ꢀ 3H2O also possess
very distorted MnO6 groupings.
The occurrence of lone-pair channels of reasonable
size and redox-active MnII/MnIII metal centers in
Ba2Mn3(SeO3)6 suggests the possibility of redox inter-
calation in which a process schematically represented by
Ba2MnIIMnI2II(SeO3)6+Li-LixBa2Mn Mn (SeO3)6
II
1+x
III
2Àx
(0pxp2) could occur and we are now investigating this
4. Discussion
possibility further.
The new mixed-metal selenites Ba2Mn3(SeO3)6 and
PbFe2(SeO3)4 have been hydrothermally prepared as
single crystals and characterized. To the best of our
knowledge, they are the first well-characterized binary
M/M0/selenites to contain these cation combinations. A
very puzzling ‘‘impurity+impurity reaction’’ initially
prepared the lead phase, which could then be followed
up by a more rational synthesis from the appropriate
starting materials once the composition and structure
were known. However, neither material could be made
in entirely pure form by the methods tried here. Both
structures consist of three-dimensional octahedral
(MnO6, FeO6)/pyramidal (SeO3) networks encapsulat-
ing one-dimensional channels which are occupied by the
large, divalent cations. The shapes of the manganese,
iron and selenium polyhedra can be rationalized in
terms of the oxidation states of the species in question,
Acknowledgments
We thank Brian Paterson for assistance with the TGA
measurement. We thank Andrea Raab and Jorg
Feldmann (Trace Element Speciation Laboratory
Aberdeen) for their invaluable assistance with the
elemental analysis. We thank an anonymous referee
for helpful crystallographic suggestions.
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