Vacuum-Induced Guest N,N′‑Diethylformamide Binding in a Metastable Cd₅‑Based Metal–Organic Framework

A three-dimensional (3D) metal–organic framework (MOF) of [Et₂NH₂]₂[Cd₅(BTB)₄(DEF)₂]·4.75DEF (1; H₃BTB = benzene-1,3,5-tribenzoic acid and DEF = N,N′-diethylformamide) sustained by symmetrical Z-shaped Cd₅ secondary building units (SBUs) with an intrinsically metastable host framework has been prepared and characterized. Upon gentle vacuum (800 Pa) at 50 °C, some encapsulated DEF solvates are released, leading to pore-shape changes and Cd²⁺ coordination geometry distortion. This is followed by DEF solvate migration to only one end of the SBU with concomitant symmetry breaking. Additional time under vacuum promoted further structural distortion and topology changes as authenticated by single-crystal X-ray diffraction studies. This work was initially inspired by unusual gas adsorption isotherms and points to the potentially complicated, nonspectator role of coordinative solvents such as DEF during MOF activation.