Preparation, thermal stability and crystal structure of a new ruthenium(V) oxide containing peroxide ions: Ba5Ru2O9(O2). Structural relationships to thehexagonal-type perovskite
Abstract
The compound Ba
5
Ru
2
O
11
has been
synthesized by solid state reactions at 980 °C and 1 atm oxygen
pressure. The crystal structure has been determined on a single crystal
(R
1
=0.027, wR
2
=0.058). The
symmetry is hexagonal (P6
3
/mmc) with the
cell parameters a=5.9470(5) Å, c=18.0428(10)
Å, Z=2. Perpendicular to the c-axis, the structure
is built up by the periodic stacking of three hexagonal close packed
[BaO
3
] layers separated by a layer of composition
[Ba
2
O
2
] containing
(O
2
)
2-
peroxide ions. The detailed formula is
then Ba
5
Ru
2
O
9
(O
2
) if we
emphasize the formation of peroxide ions in the phase. The ruthenium(v)
ions occupy the octahedral sites formed between the [BaO
3
]
layers (hexagonal perovskite slabs) and then constitute isolated
[Ru
2
O
9
] pairs.
Ba
5
Ru
2
O
9
(O
2
) belongs to a new
family of compounds, generically formulated as
[A
2
(O
2
)][A
n
B
n
-1
O
3n
] wheren represents the
number of [AO
3
] successive layers in the hexagonal perovskite
slabs. Each member of the series is an intergrowth of
[A
2
(O
2
)] and hexagonal perovskite layers;
n=3 corresponds to
Ba
5
Ru
2
O
9
(O
2
). The
isostructural phase has been observed when ruthenium is replaced by
niobium. The n=4 member and the intergrowth between the
n=3 and n=4 members of this family has been observed in
the Ba–Nb(Ta)–S ternary systems. The former proposed formula
for the ternary barium sulfides is discussed in the light of the framework
of this new family.
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