Structures of photochemically prepared mixed-valence polyoxovanadate clusters: oblong [V18O44(N3)]14- , superkeggin [V18O42(PO4)]11- and doughnut-shaped [V12B32O84Na4]15 - anions
Abstract
Three mixed-valence polyoxovanadates,
Na
12
H
2
[V
18
O
44
(N
3
)]·30H
2
O 1,
K
8.5
H
2.5
[V
18
O
42
(PO
4
)]·19H
2
O 2 and
H
15
[V
12
B
32
O
84
Na
4
]·13H
2
O 3 have been photochemically synthesized and
characterized by X-ray single-crystal analysis and magnetic
susceptibility measurements. The
[V
18
O
44
(N
3
)]
14-
anion
has an oblong structure encapsulating a linear
N
3
-
anion with approximate
D
2h
symmetry. The extent of reduction is
different from that in
[V
18
O
44
(N
3
)]
7-
prepared by thermal decomposition of
[V
19
O
50
]
17-
in the presence of
N
3
-
at 75 °C. The
[V
18
O
42
(PO
4
)]
11-
anion
has a superkeggin structure with a PV
12
O
40
Keggin
unit capped by six VO moieties which lie above six rectangle faces of
the T
d
-distorted cuboctahedron defined by
the V atoms in the Keggin unit. The
[V
12
B
32
O
84
Na
4
]
15
-
anion contains an edge-sharing dodecagonal array of
OVO
4
square pyramids, sandwiched by two hexadecaborates to
produce a cyclic doughnut-shaped framework. The crystallographic
analysis indicates that the cavity produced by the cyclic
[V
12
B
32
O
84
]
19-
anion
is occupied by a tetragonal Na
4
4+
moiety. The
paramagnetic complexes 1–3 show the antiferromagnetic exchange
interaction which is discussed in terms of the nearest
V · · ·
V distances in the anion.
V distances in the anion.
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