Controllable congregating of homochiral and achiral coordination polymers: cadmium(II) pyridine-2,4,6-tricarboxylate species with double-helical strand and molecular building block structures

Abstract

Three kinds of three-dimensional (3D) cadmium(II) pyridine-2,4,6-tricarboxylate (L) coordination polymers, L-[Cd(L)](NH₂Me₂) (1a), R-[Cd(L)]NH₂Me₂) (1b), [Cd₃(L)₂(H₂O)₄] (2), and [Cd₄(L)₂(OH)₂(H₂O)₃](H₂O)(3), have been hydro/solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction. The variations of reaction medium and temperature not only led to an occurrence of spontaneous chiral resolution but also afforded two achrial molecular building block structures. Complexes 1a and 1b crystallize in trigonal P3₁21 and P3₂21 space groups with homochiral left- and right-handed double-helical strand arrays, while 2 and 3 self-assemble into two kinds of achiral coordination polymers with molecular building block structures. Complexes 2 and 3 remain intact after removal of the coordinated water molecules, which indicates that their dehydrated frameworks possess guest-free metal coordination sites. Complexes 1–3 also display strong fluorescent emissions at 638, 594, and 604 nm in the solid state.