Crystallization of a solid at pH 4.0 from an aqueous acidified
Rh3+–[WO4]2−
solution resulted in the isolation of
Na9[H3W12O42]·24H
2 O, which contains the protonated paratungstate B anion
and which is likely the species identified previously as ‘acid
paratungstate’. The compound is triclinic, space group
P1– ,
a 10.603(2), b 12.134(3),
c 14.042(3) Å, α 114.78(1), β 101.84(1),
γ 108.34(1)˚, V 1432.9(5)
Å3 , Z 1, and the structure
was solved to an R1 value of
0.0404 (wR 2 0.1108) for 5997
independent observed reflections. The anion exhibits essentially the same
isopolytungstate framework as paratungstate B,
[H2W12O42]10−
, consisting of two W3O13 and two
W3O14 structural subunits linked
by shared vertices. Bond valence arguments place two of the hydrogen atoms
unequivocally in the internal cavity of the anion, with the remaining hydrogen
atom also likely located in this cavity, but disordered over several internal
oxygen atoms. The protonation of
[H2W12O42
]10− is shown to lead to species that are
electrochemically reducible. Extended-HÜckel molecular orbital
calculations confirm that protonation of paratungstate B within the internal
cavity leads to a change in composition of the LUMO, now based mainly on
electrochemically reducible W3O13
as opposed to (essentially) non-reducible
W3O14 structural subunits. This
results in species that are considerably more electrochemically active than
the unprotonated anion. The role of
[H3W12O42]9−
as an intermediate in the polymerization of
[WO4]2− to give
the solution form of ψ-metatungstate,
[H7W11O40]7−
, which crystallizes as
[H4W11O38]6−
, is also discussed.
Synthesis of perovskite type NdFeO3 nanoparticles and used as electrochemical sensor for detection of paracetamol
