Solvent- and heat-induced polymorphic transformation with single-crystal integrity in Cu(ii) paddle wheel metal complexes

Abstract

We report the single-crystal-to-single-crystal (SCSC) transformation of the Cu(II) paddle wheel complex [Cu₂(benzoate)₄(24F-4spy)₂] involving two novel polymorphs from form II to form I driven by both through solvent induced and thermal activation. In form I, the 24F-4spy ligands are aligned in a head-to-tail fashion, leading to photoreactivity, whereas form II is photostable. Single crystals of form II gradually transform into form I at room temperature, as confirmed by single-crystal X-ray diffraction and powder X-ray diffraction. In addition, two related Cu(II) paddle-wheel complexes, [Cu₂(benzoate)₄(26F-4spy)₂] and [Cu₂(benzoate)₄(34F-4spy)₂], are also described for comparison.