Coordination polymers from a flexible alkyldiamine-derived ligand

Abstract

A traditionally good chelating motif has been incorporated into a ligand for the synthesis of coordination polymers with vacant amine sites. A novel tetracarboxylic acid diamine ligand, isolated as N,N,N′,N′-tetra(4-carboxybenzyl)-1,3-diaminopropane dihydrochloride trihydrate (H₆L1)Cl₂·3H₂O, has been prepared, structurally characterised, and subsequently used in the formation of three new coordination polymers. Poly-[Cu₂(L1)(OH₂)₂]·6DMF·3H₂O 1 consists of (4,4) sheets formed by each L1 ligand coordinating to four copper(II) ‘paddlewheel’ dinuclear clusters. The amines of the ligand are non-coordinating. After solvent exchange and evacuation, 1 was found to adsorb approximately 23 cm³(STP) g⁻¹ of CO₂ at atmospheric pressure at 273 K. The isostructural compounds poly-[Zn(H₂L1)(OH₂)]·DMF·4H₂O and poly-[Cd(H₂L1)(OH₂)]·DMF·3H₂O 2Zn/2Cd are self-penetrating (10,3) coordination polymers containing square-shaped one-dimensional solvent channels. After solvent exchange it was found that 2Zn and 2Cd lost crystallinity, which accounts for the low N₂ and CO₂ uptakes observed.