Alkali Metal Di- tert -butyl Phosphates: Single-Source Precursors for Homo- and Heterometallic Inorganic Phosphate Materials.

The reaction of alkali metal acetates, M(OAc)· n H 2 O (M = Li, Na, K), with thermally and hydrolytically unstable di- tert -butylphosphate (( t BuO) 2 PO 2 H, dtbp-H) in a 1:1 molar ratio in MeOH at room temperature leads to clean formation of group 1 metal phosphates [Li(μ-dtbp)] n ( 1 ), [Na(μ-dtbp)] n ( 2 ), and [K 4 (μ-dtbp) 4 (μ-H 2 O) 3 ] n ( 3 ). All three compounds are essentially M/L 1:1 complexes. Owing to the presence of larger potassium ions, additional coordinated water molecules are found in 3 , which has been further employed as a precursor for the synthesis of a mixed-metal phosphate polymer [CaK(μ-H 2 O) 3 (μ-dtbp) 3 ] n ( 4 ) by reacting 3 with Ca(OAc) 2 . Compounds 1 - 4 have been characterized by various analytical and spectroscopic techniques. Molecular structures of 1 - 4 have been established in the solid state by single-crystal X-ray diffraction studies, which reveal them to be one-dimensional polymers, where the adjacent metal centers are connected through -O-P-O- bridges formed by the dtbp ligand. These complexes are rare examples of analytically pure alkali metal alkyl phosphates bearing no additional N-donor ligands (other than dtbp ligands, only water molecules are coordinated to the metal centers). Therefore, these compounds can be employed as single-source precursors (SSPs) for nano-sized ceramic phosphates. The thermogravimetric analysis of 1 - 4 reveals the loss of thermally labile tert -butyl substituents of the organophosphate ligands to form organic-free phosphate materials in the temperature range 300-500 °C. Solvothermal decomposition of 1 - 3 in boiling toluene leads to the formation of corresponding dihydrogen phosphates M(H 2 PO 4 ) (M = Li, Na, and K). The thermal decomposition of heterometallic 4 in the temperature range 400-800 °C leads to the formation of phase-pure mixed-metal calcium potassium metaphosphate CaK(PO 3 ) 3 .