Solid and solution evidences on the temperature effect of N-chelated zinc phthalates

Progressive reactions of zinc(II) phthalate in the presence of 2,2-bipyridine result in the isolations of three complexes, [Zn(phth)(bpy)(H2O)]2·2H2O (1), [Zn(phth)(bpy)(H2O)]2 (2) and {[Zn(phth)(bpy)(H2O)][Zn(phth)(bpy)]·H2O}n (3) (bpy = 2,2-bipyridine). Heating the reaction mixture reduces the coordination numbers from distorted octahedron, trigonal–bipyramid to tetrahedron configurations. The metal configurations of the isolated complexes depend on the reaction temperature. Detailed comparisons in solid and solution NMR spectra reveal that dimers 1 and 2 show no decomposition in solution and retain their coordinated structures in solid. Obvious downfield shifts (Δδ = 3.19 and 2.31 ppm) of carboxy groups in 2 are observed compared with those of dihydrates 1 in solid and solution respectively, which are consistent with the bond strengths of their structures.

► Increase of reaction temperature decreases the coordination numbers in zinc phthalate.
► The configurations change from octahedron, trigonal-bipyramid to tetrahedron.
► The two dimers retain their structures in solution based on solid and solution NMR measurements.
► Obvious downfield shifts of carboxy groups in NMR are consistent with the bond strengths of their structures.