Thermally and hydrolytically unstable di-tert-butyl phosphate (dtbp-H) has been used as synthon to prepare discrete or polymeric calcium phosphates which are convenient single-source precursors for a range of calcium phosphate ceramic biomaterials. The reaction of Ca(OMe)2 with dtbp-H in a 1:6 molar ratio in petroleum ether forms mononuclear calcium hexa-phosphate complex [Ca(dtbp)2(dtbp-H)2)4] (1), while the change of calcium source to CaH2, in a 1:2 molar ratio under otherwise similar reaction conditions, yields the calcium phosphate polymer, [Ca(µ-dtbp)2)2(H2O)2.H2O]n (2). Compounds 1 and 2 have been extensively characterized by various spectroscopic and analytical techniques. The solid-state structures of both 1 and 2 have been determined by single-crystal X-ray diffraction studies. Solid-state thermolysis of bulk 1 in air leads to the exclusive formation of calcium metaphosphate β-Ca(PO3)2 in the entire temperature range of 400–800 oC. Thermal decomposition of polymer 2 however can be fine-tuned to produce either α-Ca(PO3)2 or β-Ca(PO3)2 depending on the thermolysis conditions employed. While the sample sintered at 600 oC produces exclusively α-form, the sample annealed 800 oC or above produces β-form. Additional forms of ceramic phosphates have been prepared by solvothermal conditions owing the highly labile nature of the tert-butoxy groups of dtbp in 1 and 2. Solution decomposition of either 1 or 2 in boiling toluene at 140 oC in a sealed tube produces calcium dihydrogen phosphate [Ca(H2PO4)2.H2O] as the only product in the form of single crystals. Solution thermolysis of 2 in protic solvents such as water and methanol can be biased to produce other calcium phosphate biomaterials such as of hydroxyapatite [Ca10(PO4)6(OH)2] and calcium monohydrogen phosphate [Ca(HPO4)] in the presence of additional calcium precursors such as CaO and Ca(OMe)2, respectively.

Di-tert-butylphosphate derived thermolabile calcium organophosphates: Precursors for Ca(H2PO4)2, Ca(HPO4), α-/β-Ca(PO3)2, and nanocrystalline Ca10(PO4)6(OH)2

ACS Spring Meeting 2021

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