We scrutinized the speciation of Cp*Ir-containing tungsten
oxide
clusters (Cp* is pentamethylcyclopentadienyl anion) in aqueous mixtures
of [(Cp*IrCl)2(μ-Cl)2] and Na2WO4 in varying molar ratios. 1H nuclear magnetic
resonance (NMR) spectroscopy revealed the formation of three distinct
Cp*Ir–polyoxotungstate species in the reaction solution, and
they were isolated as Na4[(Cp*Ir)2(μ-OH)3]2[(Cp*Ir)2H2W8O30] (1), [(Cp*Ir)2(μ-OH)3]2[(Cp*Ir)2{Cp*Ir(OH2)}2H2W8O30] (2),
and [(Cp*Ir)2{Cp*Ir(OH2)}2{Cp*Ir(OH2)2}2H2W8O30](NO3)2 (3) from the mixtures
in which iridium concentration is less than, equal to, and more than
the tungsten concentration, respectively. These results show the octatungstate
[H2W8O30]10– anion
is the major polyoxotungstate species in the presence of {Cp*Ir}2+ cations, and it has high nucleophilicity enough to bind
up to six {Cp*Ir}2+ cations on its surfaces producing a cationic Cp*Ir–octatungstate complex. The octatungstate
anion was also generated from the reaction of [(Cp*IrCl)2(μ-Cl)2] and methylammonium paratungstate-B, (CH3NH3)10[H2W12O42], and was isolated as a methylamine-coordinated complex
(CH3NH3)2[(Cp*Ir)2{Cp*Ir(NH2CH3)}2H2W8O30] (4), indicating {Cp*Ir}2+ cations
function as a structure-directing agent that converts tungsten species
into octatungstate anions in aqueous solution. In addition, the coordination
environment of {Cp*Ir}2+ can be further modified by coordination
with pyridine forming [{Cp*Ir(NC5H5)}2(μ-OH)2][(Cp*Ir)2{Cp*Ir(NC5H5)}2H2W8O30] (5).