Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
For the final structure refinement of Pb7O4(SeO4)2(TeO3) and
ion resulting in an identifiable void: the lone electron pair is
Pb5(SeO4)2(TeO4)(CO3), oxygen atoms were refined with isotropic
displacement parameters, whereas for refinement of Pb3(SeO4)(TeO3)2
and Pb2(SO4)(TeO3) they were refined with anisotropic displacement
parameters. Numerical data of the data collections and structure refine-
ments are summarized in Table 2 and selected bond lengths are listed
in Table 3. A complete list of bond length including symmetry codes
to generate symmetry-related sites is given as Supporting Information.
For the four structure models bond valence sum calculations[14] were
performed by using values of R0 = 1.963, B = 0.49 for Pb–O interac-
said to be “stereochemically active”. According to Shimoni-
Livny et al., the coordination environment around lead(II) can
be classified into two categories, viz. holodirected, in which
the bonds to the ligands are directed throughout the surface of
an encompassing sphere, and hemidirected, in which the bonds
are directed throughout only a part of the encompassing
sphere, leading to an identifiable void or gap.[18] The distinc-
tion whether the coordination sphere around a Pb2+ cation is
tions,[15] as well as R0 = 1.624, B = 0.37 for S–O, R0 = 1.788, B = considered to be holo- or hemidirected is not unproblematic
0.37 for Se–O, R0 = 1.917, B = 0.37 for Te–O and R0 = 1.390, B =
0.37 for C–O interactions;[16] results of the calculations are compiled
in Table 3. Drawings of structural details were produced using the pro-
gram ATOMS.[17]
and clearly depends on the radius of the defined coordination
sphere (or the respective coordination number of the central
atom). It appears obvious that for large coordination spheres
the tendency for a holodirected coordination increases (then
accompanied with higher coordination numbers and a disparate
bond lengths distribution), whereas for only small coordination
spheres the tendency for hemidirected coordination prevails.
However, since the coordination number is somewhat subjec-
tive,[19] in particular for large ions, the threshold for the radius
of the first coordination sphere is not clearly definable.
Our approach for the definition of the first coordination
sphere of the Pb2+ cation in the title structures is based (a) on
the sum of the van der Waals radii of Pb and O (2.02 and
1.52 Å, respectively)[20] and (b) on bond valence calculations.
A Pb–O bond of 3.5 Å still accounts for 2.2% of the overall
bond valence sum (BVS). Therefore Pb–O interactions up to
3.55 Å were considered for BVS calculations, in agreement
with the sum of the van der Waals radii given above. Based
on the Pb–O bond length distributions (Table 3), “short” Pb–
O bonds might be considered for distances less than 2.80 Å
and consequently “long” bonds greater than this boundary.
However, from the BVS calculations it is obvious that “long”
Pb–O bonds (Ͼ 2.80 Å) significantly contribute to the valence
sum of an individual lead atom. Inclusions of these “long”
bonds raise the bond valence sums at some of the lead and
oxygen atoms to much more reasonable values, cf. Table 3. For
the sake of clarity, crystal structure plots (Figure 2, Figure 5,
Figure 8, Figure 10) in this communication include only Pb–O
bonds up to 2.80 Å, whereas individual [PbOx] polyhedra for
each structure are shown with all relevant Pb–O contacts, dis-
tinguishing short Pb–O distances with filled and long Pb–O
distances with open bonds, respectively (Figure 1, Figure 3,
Figure 6, Figure 9).
Further details of the crystal structures investigations may be obtained
from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-
Leopoldshafen, Germany (Fax: +49-7247-808-666; E-Mail:
crysdata@fiz-karlsruhe.de,
deposited-data.html) on quoting the depository numbers CSD-
432394 [Pb3(SeO4)(TeO3)2], CSD-432395 [Pb7O4(SeO4)2(TeO3)],
CSD-432396
[Pb5(SeO4)2(TeO4)(CO3)],
and
CSD-432397
[Pb2(SO4)(TeO3)].
Supporting Information (see footnote on the first page of this article):
Detailed list of selected bond lengths and angles including symmetry
codes.
Results and Discussion
Formation
As previously pointed out,[2] multi-phase formation of hy-
drothermally synthesized products is a common observation
and also applies for the present PbII/XVI/TeIV/O/(C) (X = S and
Se) systems. All experiments resulted in the formation of
multi-phase products; representative batches with reagents
used and product phases determined are compiled in Table 1.
Just like in the related systems MII/XVI/TeIV/O, where lead is
replaced by divalent metals of comparable size (M = Ca, Sr,
Cd, Hg[1,2]), in the present study compounds containing both
tellurium and sulfur/selenium are minority products, whereas
compounds containing tellurium as the only chalcogen are ma-
jority products. Likewise, formation of Te- and S/Se-contain-
ing phases becomes more successful at basic conditions (pH
9–11), which also explains the formation of the “basic” com-
pound Pb7O4(SeO4)2(TeO3) (for a discussion of “basic” fea-
tures in this compound, see below). One batch using basic lead
carbonate PbCO3·Pb(OH)2 as the lead source resulted in an
incorporation of carbonate (pH of the resulting solution was
ca. 6), whereas for other lead sources [lead(II)-acetate or
-nitrate] under similar conditions an incorporation of the re-
spective anion was not observed.
All four title structures are centrosymmetric and contain tet-
2–
rahedral XO4 anions (X = Se and S). The observed bond
lengths (average 1.63 Å for the three selenate structures and
1.48 Å for the sulfate structure) and angles are characteristic
for selenate and sulfate groups.[21,22] In three out of four struc-
tures, the oxotellurate(IV) anion has a trigonal-pyramidal con-
figuration, representing the most frequently observed shape of
isolated oxotellurate(IV) anions.[23] The mean Te–O distances
and O–Te–O angles in the three structures are very similar
(Pb3(SeO4)(TeO3)2 1.87 Å, 95°, Pb7O4(SeO4)2(TeO3) 1.85 Å,
97°, Pb2(SO4)(TeO3) 1.89 Å, 92°) and conform with literature
Crystal Structures – Common Features
2–
data.[23,24] In all of the four structures, the XO4 (X = S and
The lone electron pair situated at the Pb2+ cation is associ-
ated with a non-spherical charge distribution which, in the ma- Se) anions and the oxotellurate(IV) anions are separated from
jority of cases, causes a disposition of ligands around the cat- each other.
Z. Anorg. Allg. Chem. 0000, 0–0
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© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Weil, Matthias
