Monomer and Dimer of Mono‐titanium(IV)‐Containing α‐Keggin Polyoxometalates: Synthesis, Molecular Structures, and pH‐Dependent Monomer–Dimer Interconversion in Solution

Powder and crystalline samples of the monomer (Et 2 NH 2 ) 5 [α‐PW 11 TiO 40 ] · 2H 2 O (EtN‐ 1 ) and a crystalline sample of the μ‐oxo dimer (Et 2 NH 2 ) 8 [(α‐PW 11 TiO 39 ) 2 O] · 6H 2 O (EtN‐ 2 ) of mono‐titanium(IV)‐containing α‐Keggin polyoxometalates (POMs) were prepared and characterized by elemental analysis, thermogravimetry/differential thermal analysis (TG/DTA), FTIR, single‐crystal X‐ray crystallography, and solid‐state cross‐polarization magic angle spinning (CPMAS) 31 P NMR and solution ( 31 P and 183 W) NMR spectroscopy. The molecular structure of the dimeric polyoxoanion with a μ‐oxo group in 2 was determined for the first time. The monomer–dimer equilibrium in solution was clarified by pH‐varied 31 P NMR spectroscopy.