Mimicking cellular phospholipid bilayer packing creates predictable crystalline molecular metal–organophosphonate macrocycles and cages

Abstract

We report a novel mechanism to create a predictable molecular metal–organophosphonate cage [Zn₂(2,2′-bpy)₂(H₂ODP)₂(H₄ODP)]·2H₂O (1·2H₂O) (H₄ODP = 1,8-octanediphosphonic acid) and a macrocycle [Cu₂(2,2′-bpy)₂(H₂-1,4-NDPA)₂(H₂O)₂]·H₂O (2) (H₄-1,4-NDPA = 1,4-naphthalene diphosphonic acid). The structures were solved using single crystal X-ray diffraction. The photoluminescence properties of 1·2H₂O, investigated both in solution and in the solid-state at room temperature, indicated that the tighter zinc binding in the solid state leads to the augmentation of fluorescence. The ORCA molecular structure optimization calculations for 1·2H₂O suggest a slight opening of the cage structure in non-polar solvents while in polar solvents the cage is tightened. Toxicity analysis with Caco-2 cells indicates that the molecule is readily tolerated by intestinal cells.