Atmosphere-Controlled Solvatomorphic Transitions of Ternary Copper(II) Coordination Compounds in Solid State

Reactions of copper(II) sulfate with 2,2′-bipyridine (bpy) and l-serine (l-Hser) were investigated using different solution-based and mechanochemical methods. Four new ternary coordination compounds were obtained by solution-based synthesis, and three of them additionally via the liquid-assisted mechanochemical method: α-[Cu(l-Ser)(H2O)(bpy)]2SO4 (1a-α), β-[Cu(l-Ser)(H2O)(bpy)]2SO4 (1a-β), [Cu(l-Ser)(H2O)(bpy)]2SO4·6H2O (1a∙6H2O), and [Cu(l-Ser)(bpy)(CH3OH)]2SO4·2CH3OH (1b∙3CH3OH). The compounds were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, and thermal analysis. Structural studies revealed two polymorphs (1a-α and 1a-β) and two solvatomorphs (1a∙6H2O and 1b∙3CH3OH). To investigate the stability of the compounds, crystalline samples were exposed to different conditions of relative humidity (RH) and an atmosphere of methanol vapours. Successful solid-state transformation of 1a∙6H2O into 1a-α was established at lower RH values, and vice versa at higher RH values, while both compounds partially transitioned to 1a-β in the atmosphere of methanol vapours. Compound 1b∙3CH3OH decomposed spontaneously into 1a-α by standing in the air. All of the investigated structural transformations were underpinned with proposed mechanisms. Additionally, 1a-α showed moderate in vitro antiproliferative activity toward a human breast cancer cell line (MCF-7), a human colon cancer cell line (HCT116), and a human lung cancer cell line (H460).