Liquid-mediated mechanosynthesis of Zn-BDC coordination polymers via ball milling and twin-screw extrusion

Abstract Mechanochemical synthesis methods can offer a low cost, low waste route to prepare metal–organic materials (MOMs); however, the influence of liquid additives on phase formation remains understudied. In this work, the mechanosynthesis of Zn-BDC (BDC = benzene-1,4-dicarboxylate) coordination polymers (CPs) was systematically investigated using water, N,N-dimethylformamide (DMF), and their mixtures as additives for liquid-assisted ball milling (BM) and twin-screw extrusion (TSE) reactions. Neat BM of ZnO or Zn 5 (CO₃)₂(OH)₆ with H₂BDC or Na 2 BDC resulted in no observable reaction, whereas water-assisted BM selectively yielded the 1D CP [Zn(BDC)(H₂O)₂]ₙ. In contrast, DMF-assisted BM promoted formation of the 2D metal-organic framework {[Zn(BDC)(H₂O)]·DMF}ₙ (MOF-2) along with a competing 2D layered phase {[Zn₃(BDC)₃(H₂O) 2 ]·4DMF}ₙ. By tuning the DMF/H₂O ratio, phase selectivity was controlled and phase-pure MOF-2 was obtained at the following molar ratio of Zn: BDC: DMF: H₂O = 1:1:2:2. N 2 (77 K) and CO 2 (195 K) adsorption measurements indicated that the mechanochemically synthesized MOF-2 exhibited gas uptake capacities and surface areas consistent with those of the solution-synthesized sample and reported literature values. These findings highlight the importance of liquid composition in directing mechanochemical reaction pathways and structural dimensionality in Zn–BDC systems to provide an effective method for the phase-selective synthesis of Zn–BDC MOMs.