Metal-Dependent Self-Selection of Solvent Guests as “Molecular Pillars” in Manganese(II) and Zinc(II) 2,2′-Bipyridine–Chloranilate One-Dimensional Coordination Polymers

Metal ions influence the self-assembly behavior of crystallization solvents within low-dimensional coordination polymers, thereby determining pore geometry and (ir)reversibility. In this study, we investigate two isomorphous one-dimensional (1D) chain compounds, {[Mn(2,2′-bpy)(CA)]·2EtOH} (1) and {[Zn(2,2′-bpy)(CA)]·5H2O} (2) (2,2′-bpy = 2,2′-bipyridine; CA2– = chloranilate), crystallized from the same EtOH/H2O mixed solvent. Notably, these compounds selectively incorporate EtOH in 1 and H2O in 2 as continuous hydrogen-bonded “molecular pillars.” Single-crystal X-ray diffraction analysis revealed π-stacked −M–(μ2-CA)–M– chain columns that form molecular-pillar-stabilized 1D channels. Thermal and vacuum desolvation induced an irreversible transformation to a distinct phase, and resoaking in the original solvent failed to restore the initial diffraction pattern. Attenuated total reflectance infrared analysis using an area-normalized band ratio confirmed the selective attenuation of guest bands after desolvation with limited recovery upon resoaking. Combined thermogravimetric analysis and differential scanning calorimetry further quantified guest-retention energetics, yielding ΔH per guest of approximately 20 kJ mol–1 for EtOH in 1 and 5 kJ mol–1 for H2O in 2. Gas and vapor sorption measurements exhibited negligible uptake after activation, consistent with pore collapse in the guest-free state. These findings establish crystallization solvents as integral structural components that dictate metastable porosity and irreversible structural fixation in 1D coordination polymers.