Structural characterization of Sr–Ti and Ba–Ti catecholate complexes: single source precursors for SrTiO3 and BaTiO3 binary oxides Original Research Article

Titanium catecholate complex H2Ti(cat)3 (1) is synthesized from the direct reaction of Ti(OiPr)4 with catechol (H2cat). Treatment of 1 with NEt3 gives ionic complex (HNEt3)2[Ti(cat)3] (2). Reactions of 1 with SrCO3 or with BaCO3 afford the corresponding catecholate complexes with approximate composition Sr[Ti(cat)3]radical dot3H2O (3) and Ba[Ti(cat)3]radical dot3H2O (4), of which the formula was proposed according to the previous literature report and microanalytical data. Water soluble crystalline materials [Sr(H2O)5]2[Ti2O2(cat)4]radical dot6H2O (5) and [Ba(H2O)4(C3H6O)]2[Ti2O2(cat)4]radical dot2C3H6O (6) are isolated in low yields by repeated recrystallization of 3 and 4 from a mixture of water and acetone at room temperature. The single crystal X-ray diffraction studies reveal that they fail to show the discrete Ti(cat)32− unit as suggested previously, but they contain a dimeric [Ti2O2(cat)4]4− fragment with two bridging oxo ligands and two chelating catecholate ligands associated with each Ti atom. The latter is further linked to the hydrated Sr2+ or the Ba2+ counter cations through axial oxygen atoms of the catecholate ligands and the unique bridging oxo ligand. Crystal data for 5: a=7.8251(1), b=11.3739(2), c=11.4980(2) Å, α=91.942(1), β=100.441(1), γ=103.061(1)° with Z=1 in space group P1̄. For complex 6: a=9.6450(3), b=10.2092(3), c=13.3098(4) Å, α=18.192(1), β=85.876(1), γ=73.475(1)° with Z=1 in space group P1̄. Conversion to the respective SrTiO3 and BaTiO3 phases by calcination under oxygen atmosphere is confirmed by TG analysis and X-ray powder analysis.