Structural characterization of Sr–Ti and Ba–Ti catecholate complexes: single source precursors for SrTiO 3 and BaTiO 3 binary oxides

Abstract

Titanium catecholate complex H 2Ti(cat) 3 ( 1) is synthesized from the direct reaction of Ti(O i Pr) 4 with catechol (H 2cat). Treatment of 1 with NEt 3 gives ionic complex (HNEt 3) 2[Ti(cat) 3] ( 2). Reactions of 1 with SrCO 3 or with BaCO 3 afford the corresponding catecholate complexes with approximate composition Sr[Ti(cat) 3] 3H 2O ( 3) and Ba[Ti(cat) 3] 3H 2O ( 4), of which the formula was proposed according to the previous literature report and microanalytical data. Water soluble crystalline materials [Sr(H 2O) 5] 2[Ti 2O 2(cat) 4] 6H 2O ( 5) and [Ba(H 2O) 4(C 3H 6O)] 2[Ti 2O 2(cat) 4] 2C 3H 6O ( 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) 3 2− unit as suggested previously, but they contain a dimeric [Ti 2O 2(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 Sr 2+ or the Ba 2+ 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 SrTiO 3 and BaTiO 3 phases by calcination under oxygen atmosphere is confirmed by TG analysis and X-ray powder analysis.