Molar-Ratio-Dependent Coordination Assembly of Organoiridium(III)-Octatungstate Complexes in Aqueous Solution.

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 Na 2 WO 4 in varying molar ratios. 1 H nuclear magnetic resonance (NMR) spectroscopy revealed the formation of three distinct Cp*Ir-polyoxotungstate species in the reaction solution, and they were isolated as Na 4 [(Cp*Ir) 2 (μ-OH) 3 ] 2 [(Cp*Ir) 2 H 2 W 8 O 30 ] ( 1 ), [(Cp*Ir) 2 (μ-OH) 3 ] 2 [(Cp*Ir) 2 {Cp*Ir(OH 2 )} 2 H 2 W 8 O 30 ] ( 2 ), and [(Cp*Ir) 2 {Cp*Ir(OH 2 )} 2 {Cp*Ir(OH 2 ) 2 } 2 H 2 W 8 O 30 ](NO 3 ) 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 [H 2 W 8 O 30 ] 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, (CH 3 NH 3 ) 10 [H 2 W 12 O 42 ], and was isolated as a methylamine-coordinated complex (CH 3 NH 3 ) 2 [(Cp*Ir) 2 {Cp*Ir(NH 2 CH 3 )} 2 H 2 W 8 O 30 ] ( 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(NC 5 H 5 )} 2 (μ-OH) 2 ][(Cp*Ir) 2 {Cp*Ir(NC 5 H 5 )} 2 H 2 W 8 O 30 ] ( 5 ).