1D chains and an open 3D network from poly(diethylamidinium) cations and polycarboxylate anions

Abstract

New monotopic, ditopic, and tetratopic diethylamidinium building blocks were prepared and their interactions with (poly)carboxylates studied in solution and by crystallisation to give hydrogen-bonded networks. Crystallisation of the bis(diethylamidinium) tecton with terephthalate or biphenyldicarboxylate gave 1D hydrogen-bonded chains where the diethylamidinium groups adopted E/E conformations allowing for R²₂(8) hydrogen bonding with the anion. In contrast, 3D networks had E/Z diethylamidinium conformations, limiting hydrogen bonding to single-point interactions. Despite this, an open network structure was formed where approximately half of the unit cell volume was occupied by disordered solvent molecules. A survey of the Cambridge Structural Database revealed that both E/E and E/Z arrangements are common, while DFT calculations suggest that the E/E conformation is ∼13 kJ mol⁻¹ higher in energy than the E/Z conformation for both dimethylamidiniums and diethylamidiniums in the gas phase. Factors that contribute to the favourability of E/E and E/Z arrangements in the solid state are discussed, specifically with reference to the design of open networks.