Preparation and structures of complexes of titanium(IV) and 8-hydroxyquinoline: TiQ 2(Opr i) 2 and [TiQ 2(μ-O)] 4·6H 2O

Abstract

The reaction between Ti(OPr i ) 4 and 8-hydroxyquinoline (HQ) resulted in TiQ 2(OPr i ) 2, 1 in 90% yield. Further reaction of 1 with water yielded [TiQ 2(μ-O)] 4· nH 2O, 2·nH 2O, n=2 or 6 depending on whether the sample was dried. The structures of 1 and 2·6H 2O were determined by X-ray diffraction method. In 1 and 2 the bonding situations around the pseudo-octahedrally coordinated Ti(IV) are very similar. The two oxygen atoms from Q − ligands are trans to each other, while the two nitrogen atoms are cis to each other and trans to the other two oxygen atoms of OPr i in 1 and μ-O in 2. The [Ti(μ-O)] 4 eight-membered ring is puckered. There is extensive hydrogen bonding of four water molecules with [TiQ 2(μ-O)] 4, two on each side of the eight-membered ring of [Ti(μ-O)] 4. The two water molecules on the same face of the eight-membered ring are further hydrogen bonded to another water molecule. A novel feature in 2 is that the plane of each Q − ligand is parallel to that of another Q − ligand coordinated to a neighboring Ti(IV) in an eclipsed conformation. The average distance between the corresponding atoms in the parallel Q − ligands is 3.6 Å. It is an indication that there is a strong non-bonding interaction between each pair of parallel Q − ligands. The hydrogen bonds and the non-bonding interactions lead to the most severely distorted plane of the [Ti(μ-O)] 4 eight-membered ring.