Metal–ligand Lability and Ligand Mobility Enables Framework Transformation via Ligand Release in a Family of Crystalline 2D Coordination Polymers

Abstract

A family of seven silver(I)-perfluorocarboxylate-quinoxaline coordination polymers, [Ag4(O2CRF)4(quin)4] 1–5 (RF=(CF2)n-1CF3)4, n=1 to 5); [Ag4(O2C(CF2)2CO2)2(quin)4] 6; [Ag4(O2CC6F5)4(quin)4] 7 (quin=quinoxaline), denoted by composition as 4 : 4 : 4 phases, was synthesised from reaction of the corresponding silver(I) perfluorocarboxylate with excess quinoxaline. Compounds 1–7 adopt a common 2D layered structure in which 1D silver-perfluorcarboxylate chains are crosslinked by ditopic quinoxaline ligands. Solid-state reaction upon heating, involving loss of one equivalent of quinoxaline, yielding new crystalline 4 : 4 : 3 phases [Ag4(O2C(CF2)n-1CF3)4(quin)3]n (8–10, n=1 to 3), was followed in situ by PXRD and TGA studies. Crystal structures were confirmed by direct syntheses and structure determination. The solid-state reaction converting 4 : 4 : 4 to 4 : 4 : 3 phase materials involves cleavage and formation of Ag−N and Ag−O bonds to enable the structural rearrangement. One of the 4 : 4 : 3 phase coordination polymers (10) shows the remarkably high dielectric constant in the low electric field frequency range.