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

摘要

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)(OH2)(4)]center dot 2DMF center dot 2H(2)O 1, a two-dimensional coordination polymer, contains aqua-and carboxylato-bridged trinuclear NiII 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-[Zn2L]center dot 2DMF center dot 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)]center dot 3DMSO center dot 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)]center dot DMSO center dot 3H(2)O 4 was prepared under similar synthetic conditions by including the 1,2-bis(4pyridyl) 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 CO2 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.