Synthesis, reactivity and structures of hafnium-containing homo- and
hetero- (bi- and tri-) metallic alkoxides based on edge- and
face-sharing bioctahedral alkoxometalate
ligands
Abstract
Using
[{Hf(OPr
i
)
4
(Pr
i
OH)}
2
] as a building-block precursor, a series of homo- and
hetero-metallic alkoxides of hafnium has been prepared and characterised
using elemental analyses, infrared, multinuclear (
1
H,
7
Li,
13
C and
113
Cd) NMR and
single-crystal X-ray diffraction studies. The solid-state structure of
[Hf
2
(OPr
i
)
8
(Pr
i
OH)
2
] 1 reveals an edge-shared bioctahedral structure with the
co-ordinated alcohol forming a hydrogen bridge across the dinuclear
unit. The reactions of 1 with other nitrogen- or oxygen-containing
donors gave monosubstituted products of the general formula
[Hf
2
(OPr
i
)
8
(Pr
i
OH)L]
(L = C
5
H
5
N 2 or
C
4
H
8
O
2
3) which retain the dinuclear
edge-sharing bioctahedral structure as determined for 2 by X-ray
crystallography. Compound 1 reacted (1:2) with
LiBu
n
or LiOPr
i
to afford dimeric
[{LiHf(OPr
i
)
5
}
2
] 4. The
molecular structure of 4 can be conceived as a dianionic
[Hf
2
(OPr
i
)
10
]
2-
unit
that binds two Li
+
one on each side of the Hf–Hf
vector which are additionally co-ordinated by the bridging
OPr
i
groups to display a trigonal-pyramidal geometry at the
lithium atoms. The Hf
2
O
6
Li
2
core in 4
comprises two analogous seconorcubane subunits sharing a common face
defined by a Hf
2
O
2
ring. Equimolar reaction of
CuCl
2
and [KHf
2
(OPr
i
)
9
]
afforded the monomeric halide heterobimetallic derivative
[CuHf
2
Cl(OPr
i
)
9
] 5. Compound 5 is
paramagnetic and follows Curie law behaviour as inferred by a
variable-temperature
1
H NMR study. In the solid state its
molecular geometry could be formally seen as a tetradentate interaction
of the distorted confacial bioctahedron
[Hf
2
(OPr
i
)
9
]
-
with a
CuCl
+
fragment. Each Hf is six-co-ordinated; Cu is
five-co-ordinated and displays a distorted trigonal-bipyramidal
geometry. The reaction (1:1) of
[CdHf
2
I(OPr
i
)
9
] with
KSr(OPr
i
)
3
produced a new heterotermetallic
derivative
[{[Cd(OPr
i
)
3
]Sr[Hf
2
(OPr
i
)
9
]}
2
] 6. This involves the switching
of central metal atoms between the two precursors and the
Hf
2
(OPr
i
)
9
unit in 6 binds to Sr rather
than Cd as anticipated. The centrosymmetric dimeric form of 6 is made up
of a
[Sr(µ-OPr
i
)
2
Cd(µ-OPr
i
)
2
Cd(µ-OPr
i
)
2
Sr]
2+
spirocyclic
unit capped at both the ends by
[Hf
2
(OPr
i
)
9
]
-
moieties.
:2) with
LiBu
n
or LiOPr
i
to afford dimeric
[{LiHf(OPr
i
)
5
}
2
] 4. The
molecular structure of 4 can be conceived as a dianionic
[Hf
2
(OPr
i
)
10
]
2-
unit
that binds two Li
+
one on each side of the Hf–Hf
vector which are additionally co-ordinated by the bridging
OPr
i
groups to display a trigonal-pyramidal geometry at the
lithium atoms. The Hf
2
O
6
Li
2
core in 4
comprises two analogous seconorcubane subunits sharing a common face
defined by a Hf
2
O
2
ring. Equimolar reaction of
CuCl
2
and [KHf
2
(OPr
i
)
9
]
afforded the monomeric halide heterobimetallic derivative
[CuHf
2
Cl(OPr
i
)
9
] 5. Compound 5 is
paramagnetic and follows Curie law behaviour as inferred by a
variable-temperature
1
H NMR study. In the solid state its
molecular geometry could be formally seen as a tetradentate interaction
of the distorted confacial bioctahedron
[Hf
2
(OPr
i
)
9
]
-
with a
CuCl
+
fragment. Each Hf is six-co-ordinated; Cu is
five-co-ordinated and displays a distorted trigonal-bipyramidal
geometry. The reaction (1:1) of
[CdHf
2
I(OPr
i
)
9
] with
KSr(OPr
i
)
3
produced a new heterotermetallic
derivative
[{[Cd(OPr
i
)
3
]Sr[Hf
2
(OPr
i
)
9
]}
2
] 6. This involves the switching
of central metal atoms between the two precursors and the
Hf
2
(OPr
i
)
9
unit in 6 binds to Sr rather
than Cd as anticipated. The centrosymmetric dimeric form of 6 is made up
of a
[Sr(µ-OPr
i
)
2
Cd(µ-OPr
i
)
2
Cd(µ-OPr
i
)
2
Sr]
2+
spirocyclic
unit capped at both the ends by
[Hf
2
(OPr
i
)
9
]
-
moieties.
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