Philip L. W.
Tregenna-Piggott, Stephen P. Best, Hans U. Güdel, Høgni Weihe
and Chick C. Wilson
Influence of the Mode of Water Coordination on the Electronic
Structure of the [V(OH2)6]3+
Cation
J. Solid State Chem. 145, 460-470 (1999)
Abstract:
The correlation between the stereochemistry and electronic structure of the
[V(OH2)6]3+] cation has been examined using a
variety of physical techniques in conjunction with angular overlap model
calculations. The experimental data includes the first reported high-field,
high-frequency EPR study of a vanadium(III) complex which enables a precise
determination of the ground term spin-Hamiltonian parameters. The electronic
structure and vibrational spectrum of the
[V(OH2)6]3+ cation was studied in samples
formed from the co-crystallization of
RbV(SO4)2·12H2O and
RbGa(SO4)2·12H2O. The structural modifications
of these salts differ in terms of the orientation of the water molecules about
the tervalent cation while the MIIIO6 framework remains
approximately octahedral. The electronic structure of the
[V(OH2)6]3+ cation in samples of
Rb[Ga:V](SO4)2·12H2O is found to depend greatly
on the relative proportions of gallium(III) and vanadium(III). The experimental
data are in accordance with predictions based on the angular overlap model when
the p-bonding normal to the plane of the water molecule is dominant over
the in-plane interaction
(ep
- ep ||
ca. 930 cm–1 for trigonal planar water coordination). The
p-anisotropy results in a large trigonal field splitting of the
3T1g (Oh) ground
term in RbV(SO4)2·12H2O (1930 cm–1)
which diminishes almost to zero when
[V(OH2)6]3+ is doped into
RbGa(SO4)2·12H2O, on account of the change in
the orientation of the water molecules imposed by hydrogen bonding constraints.
This work demonstrates the strong correlation between the stereochemistry and
electronic structure of the [V(OH2)6]3+ cation
and accounts for the structural abnormalities reported for vanadium(III) salts
of this type.