ELECTRON-SPIN-RESONANCE AND OPTICAL SPECTRAL STUDIES OF A TITANIUM(III) COMPLEX FORMED WITH NITRILOTRIACETIC ACID

On adding more than two moles of nitrilotriacetic acid (NTA) to a solution of Ti(III) at pH 4 to 10 containing 10-20 M tartaric acid, a solution is obtained that exhibits a rather sharp ESR absorption signal (g0 = 1.963 +/- 0.001, the linewidth DELTA-H(p-p) = (0.30 +/- 0.05) mT). A constant maximum signal level is observed under basic conditions: pH 4 to 10. Measurement of the integrated intensity of the maximum signal indicated that (90 +/- 10) % of Ti(III) is in the complex. The variation and mole ratio methods based on the measurement of the ESR signal and optical absorption maximum (at nu approximately = 14 000 cm-1), respectively, for determining the composition of this complex ion indicate that the concentration ratio Ti(III) to NTA is 1:2. The experimental g-tensor components (g(x) = 1.946 +/- 0.001, g(y) = 1.959 +/- 0.001, and g(z) = 1.997 +/- 0.001) derived from the frozen solution ESR spectrum of this Ti(NTA)2 paramagnetic species are consistent with an axially elongated octahedral structure with an equatorial rhombic distortion through bidentate NTA ligands. Significant in-plane sigma and pi bonding is indicated in this octahedron of the D2h symmetry. It is proposed that there is at least one axial hydroxide ligand.