Mixed halide/oxoanion-templated frameworks

A tetrahedral tetra-amidinium compound 1⁴⁺ was crystallised in the presence of a range of anions (Cl^-, Br^-, NO₃^-, oxalate^2-) giving a range of interesting solid state structures assembled through amidinium⋯anion hydrogen bonding interactions. Mixing the chloride or bromide salts of 1⁴⁺, i.e.1·4Cl or 1·4Br, and inorganic oxalate salts in water gave crystals of ordered three-dimensional network structures containing both oxalate and halide anions. These interesting "mixed anion" frameworks exhibit high thermal stability to heat and hydrolysis but are not significantly porous. Importantly, these materials are significantly more robust than the analogous terephthalate-containing framework materials.