Influencing the morphology and phase of calcium ceramic nanoparticles based on the calcium alkoxide precursors' characteristics

Select members of a series of structurally characterized calcium aryloxides (Ca(OAr)(2)) were found to influence the morphologies and phases of the final calcium ceramic nanomaterials produced, independent of the process route investigated. The Ca(OAr)(2) were synthesized using an amide alcohol exchange route between [Ca(mu-NR2)(NR2)](2) (R = Si(CH3)(3)) and the appropriate aryl alcohol [H-OAr = H-OC6H4(R)-2 where R = CH(CH3)(2) (H-oPP), C(CH3)(3) (H-oBP); H-OC6H3(R)(2)-2,6 where R = CH3 (H-DMP), CH(CH3)(2) (H-DIP), and C(CH3)(3) (H-DBP)] along with triphenyl silanol (H-TPS = OSi(C6H5)(3)], in toluene (tol) or tetrahydrofuran (THF). The resulting products were isolated as H+[(mu(3)-O)Ca-2(mu-oPP)(2)(oPP)(THF)(3)](2)center dot THF](-) (1), Ca(oBP)(2)(THF)(4) (2), H+[(mu(3)-O)Ca-2(mu-DMP)(2)(DMP)(THF)(3)](2)(-) (3), {2[Ca(DIP)(2)(THF)(3)]center dot Ca(DIP)(2)(THF)(4)}center dot THF (4a), [Ca(mu-DIP)(DIP)(THF)(2)](2) (4b), Ca(DBP)(2)(THF)(3) (5), [Ca(mu-DBP)(DBP)](2) (6), and Ca(TPS)(2)(THF)(4) (7). The coordination of the Ca atoms ranged from trigonal planar to octahedral, forming mono-, di-, and tetranuclear species based on the steric bulk of the ligand and coordination of Lewis basic THF. Solution NMR indicated that these compounds retain their structure in solution, except for 5, which was found to be disrupted to form a monomer. Vaterite or portlandite nanomaterials were isolated from 3 or 4a, respectively, independent of the processing route (solvothermal or solution precipitation). The morphology variations were interpreted based on the "precursor structure argument", and the phase variation was attributed to the "precursor's decomposition pathway". Full details of the synthesis and characterization of 1-7 as well as the nanomaterials generated therefrom are discussed.