Zn(ii) and Co(ii) coordination polymers based on semi-rigid bis-pyridyl-bis-amide and angular dicarboxylate ligands: synthesis, structures and properties

Abstract

Hydro(solvo)thermal reactions of N,N′-di(3-methylpyridyl)oxalamide (L¹) and N,N′-di(4-methylpyridyl)oxalamide (L²) with angular dicarboxylic acids and Zn(II) and Co(II) metal salts afforded six coordination polymers (CPs), namely, [Zn(L¹)_0.5(FIPBB)·H₂O]_n [H₂FIPBB = 4,4′-hexafluoroisopropylidenebis(benzoic acid)] (1), [Zn(L²)(OBA)·CH₃OH]_n [H₂OBA = 4,4′-oxybis(benzoic acid)] (2), [Co(L²)_0.5(FIPBB)·0.25CH₃OH]_n (3), [Co(L¹)(OBA)·2H₂O]_n (4), [Co(L¹)_0.5(FIPBB)]_n (5), and [Co₂(L¹)₂(FIPBB)₂(H₂O)₅·4H₂O]_n (6), which have been structurally characterized by using single-crystal X-ray diffraction. CPs 1 to 6 form a two-dimensional (2D) net with the bey, a polycatenated 2D net with the sql, a three-dimensional (3D) framework with the 6T9, a 2D net with the 3,5L2, 2D net with the bey and a one-dimensional (1D) looped chain with the 2,2,2,4C10 topologies, respectively. The distinct topological switch between 5 and 6 in the presence and absence of coordinated/cocrystallized water molecules was triggered under various temperatures through coordination and breakage of Co–O bonds. CPs 1 and 2 exhibit sustained porosities indicated by CO₂ adsorption and exhibit high selectivity toward detection of pesticides such as 2,6-dichloro-4-nitroaniline (2,6-DCNA) and 4-nitroaniline (4-NA) with low detection limits and good recyclability up to five cycles. Integrating 1-octadecene with a long alkyl chain into 1–5 to modify the surface wettability induces hydrophobicity, which was verified by the measurement of water contact angles.