Coordination assembly of helicate and mesocate with two-armed carbohydrozine ligand: Synthesis, structure and fluorescence

Two-armed carbohydrozine ligand, H2L1 and its cobalt(III) and zinc(II) complexes (1 and 2) have been synthesized and characterized by single-crystal X-ray diffraction analysis. In the solid state, compound 1 has double-strand helicate structure involving ligand that twists to the central metal ions. Abundant π…π stacking interaction extended in the crystallographic bc plane. However, compound 2 has mesocate structure with a side-by-side arrangement of two ligands. The structure of zinc(II) compound 2 can be described as plane-symmetry one with symmetry plane perpendicular to the metal linker. The π…π stacking interaction existed in the crystallographic ac plane of compound 2. Weak intermolecular interactions play dominant roles in shaping the extended two-dimensional structures for all the molecules in the solid state. In solution, zinc(II) compound 2 exhibited strong ligand-based π*–π fluorescent emissions that can be tuned by the attached proton, a potential proton probe model.