Unprecedented Oxo-Titanium Citrate Complex Precipitated from Aqueous Citrate Solutions,Exhibiting a Novel Bilayered Ti_80_(10)Structural Core

摘要

Aqueous titanium citrate solutions were prepared from the reaction of citric acid with titanium 2-propoxide in a range of molar ratios.Solutions containing two or fewer citrates per titanium resulted in the slow crystallization of an insoluble titanium oxo-citrate complex.Single-crystal X-ray analysis identified the species as Ti_80_(10)(citrate)4-(H_2O)_(12)(center dot)14H_2O(center dot)3HOPr~i,crystallized in the tetragonal space group /4_1/a,with a=30.775(7)A,c=14.528(7)A,V=13 759(8)A~3,and Z=8.The trianionic citrate ligands supply both carboxylate and alkoxide coordination and stabilize the structure using simultaneous chelating and bridging modes of attachment.The compound is a neutral species,exhibiting titanium in three contrasting environments.Laser Raman microscopy and ~(13)C CPMAS solid-state NMR data were consistent with those of the X-ray crystal structure.When exposed to air,the crystals rapidly lost water and became a powder.The dehydrated powder was noncrystalline to X-rays and insoluble,but ~(13)C NMR results demonstrated retention of the carboxylate linkages.