The new ZIF named UZAR-S13 is formed by Zn2+ and 4(5)-(hydroxymethyl) imidazolate. UZAR-S13 has two distinct phases according to SEM and XRD: amorphous spheres and sheet crystals. UZAR-S13 and byproducts, with no N-2 adsorption, rendered a notable CO2 uptake (up to 3.8 mmol g(-1) at 30 bar and 0 degrees C), approaching values of known ZIFs. The most promising materials were included as fillers in mixed matrix membranes based on copolyimide 6FDA-DAM to study the separation of CO2/CH4, CO2/N-2, H-2/CO2 and H-2/CH4 mixtures. The pore blocking hindered the gas flow of bulky molecules (CH4, N-2 and CO2). The high CO2 adsorption on sheet crystals also contributed to the decrease in the permeability of CH4, N-2 and CO2, giving poor selectivities. In contrast, the MMMs improved both the H-2/CH4 selectivity (8.9-12.7 vs. 7.2) and permeability of H-2 (544-597 vs. 505 Barrer) of the bare 6FDA-DAM membrane. This emphasizes the potential application of the fillers in the separation by molecular sieving of gas mixtures without CO2.