Improper ferroelastic phase transition in a hydrogen-bonded metallocyanide-based (azetidinium) 2 (H 3 O)[Co(CN) 6 ] framework.

A hydrogen-bonded metallocyanide-based (AZE) 2 (H 3 O)[Co(CN) 6 ] framework was obtained by introducing a hydronium cation to the A 2 B(1)B(2)CN 6 -type structure. Simple K + /H 3 O + substitution exchange the three-dimensional structure of the double-perovskite into two-dimensional layers containing open inorganic cages with a strongly discontinuous improper ferroelastic phase transition.