Coordination polymers from a highly flexible alkyldiamine-derived ligand: structure, magnetism and gas adsorption studies

Studies into a series of coordination polymers from a new diamine polycarboxylate ligand reveal an interplay between flexibility and material properties. The synthesis and structural, magnetic and gas adsorption properties of a series of coordination polymer materials prepared from a new, highly flexible and internally functional tetrakis-carboxybenzyl ligand H4L derived from 1,2-diaminoethane have been examined. The compound poly-[Ni 3 ( HL ) 2 (OH 2 ) 4 ]·2DMF·2H 2 O 1 a two-dimensional coordination polymer, contains aqua- and carboxylato-bridged trinuclear Ni II clusters, the magnetic behaviour of which can be well described through experimental fitting and ab initio modelling to a ferromagnetically coupled trimer with a positive axial zero-field splitting parameter D . Compound poly-[Zn 2 L ]·2DMF·3H 2 O 2 a three-dimensional coordination polymer displaying frl topology, contains large and well-defined solvent channels, which are shown to collapse on solvent exchange or drying. Compound poly-[Zn 2 ( L )(DMSO) 4 ]·3DMSO·3H 2 O 3 a highly solvated two-dimensional coordination polymer, displayed poor stability characteristics, however a structurally related material poly-[Zn 2 ( L )( bpe )(DMSO) 2 ]·DMSO·3H 2 O 4 was prepared under similar synthetic conditions by including the 1,2-bis(4-pyridyl)ethylene bpe co-ligand. Compound 4 containing small one-dimensional solvent channels, shows excellent structural resilience to solvent exchange and evacuation, and the evacuated material displays selective adsorption of CO 2 over N 2 at 273 K in the pressure range 0–1 atm. Each of the coordination polymers displays subtle differences in the conformation and binding mode of the ligand species, with switching between two distinct conformers (X-shaped and H-shaped), as well as a variable protonation state of the central core, with significant effects on the resulting network structures and physical properties of the materials.