Solid state dehydration condensation of potassium tetrakis(μ-pyrophosphito-P,P′)diplatinate(II) accompanied by the red shift of the luminescence peak

Yellow crystals of K₄[Pt₂(pop)₄]·2H₂O (pop^2- = pyrophosphite(2-)) change their color to orange upon dehydration in vacuo or at elevated temperatures with concomitant change in the emission color from green (emission peak at 515 nm) to orange (emission peaks at 520, 570, 670 nm). Thermogravimetric, ³¹P CP-MAS NMR, electronic and infrared absorption spectral studies indicate that the dehydration is not a simple loss of crystalline waters but involves dehydration condensation between the neighboring complex anions. The original green emission is recovered on dissolving the orange solid in water. Emissions from the dehydrated orange solid are of phosphorescence type (τ_em ≤ 6 μs). Relative intensity of the three emission peaks depends significantly on dehydration conditions, exciting wavelength and temperature. The orange solid seems to contain various species with different extent and type of condensation. Red shift of the emission peak on dehydration was discussed on the basis of the ligand field theory.