Five Diverse Multidimensional Polycarboxylate–Based Mixed–Ligand Coordination Polymers with Different N,N′–Donor Ligands: Synthesis, Characterization and Their Sorption Study

Abstract Five mixed ligand coordination polymers (CPs) explicitly {[Cu 2 (btp)(2,5‐pyrdc) 2 H 2 O] . 4H 2 O} n (1) , {[Cu(bte) 0.5 (2,5‐pyrbdc)H 2 O] . 1.5H 2 O} n (2) , {[Cu(bte)(1, 2,4,5‐btc) 0.5 (H 2 O)] . 3H 2 O} n (3) , {[Co(4‐bpdh)(1, 2,4,5‐btc) 0.5 (H 2 O)(MeOH)]} n (4) , and {[Co(4‐bpdb) 1.5 (1,2,4,5‐btc)(H 2 O) 4 ] . 4H 2 O(MeOH)} n (5) have been synthesized by using two polycarboxylates 2,5‐pyridinedicarboxylate (2,5‐pyrdc 2– ), 1,2,4,5‐benzenetetracarboxylate (1,2,4,5‐btc 4– ) and four differently polar N–donor ligands. Here, two different transition metals Cu(II) and Co(II) have been used and slow diffusion technique has been followed for crystallization process at room temperature. Single crystal X‐ray diffraction analysis, powder X‐ray diffraction (PXRD), infrared spectroscopy (IR), elemental analysis and thermo gravimetric analysis (TGA) techniques have been used to characterize all the five compounds 1–5 . Compound 1 exhibits a 2D bilayer; fabricated by the N,N‘–donor 1,3‐bis(1,2,4‐triazol‐1‐yl)propane (btp) and 2,5‐pyrdc 2– ligands with the Cu(II) metal center; whereas compound 2 shows a wavy 2D sheet structure by only variation of N–donor ligand to 1,2‐bis(1,2,4‐triazol‐1‐yl)ethane (bte). Compound 3 features a 3D MOF built by 2D metal carboxylate sheet of Cu(II) and 1,2,4,5‐btc 4– pillared by bte spacer. Compound 5 displays two fold interpenetrated 3D framework containing two distorted octahedral Co(II) metal centers; formed by the 1,2,4,5‐btc 4– and 1,4‐bis‐(4‐pyridyl)‐2,3‐diaza‐1,3‐butadiene (4‐bpdb) ligands whereas compound 4 attains a 1D chain only by variation of N–donor linker to 2,5‐bis‐(4‐pyridyl)‐3,4‐diaza‐2,4‐hexadiene (4‐bpdh). For the compounds 1–5 , different sorption study has been carried out. The dehydrated framework of compound 5 shows selective CO 2 adsorption at 195 K over N 2 (at 77 K) which has been explained in terms of the strong interaction of CO 2 molecules with polar moiety of the dehydrated framework of 5 . Compound 1 and 2 exhibit both CO 2 and N 2 adsorptions but the presence of non‐polar, long chain ligands in the frameworks decreases the extent of sorption for both the cases; whereas 3 and 4 only give suitable result for N 2 sorption.