Coexistence of Magnetic and Electric Orderings in the Metal–Formate Frameworks of [NH4][M(HCOO)3]

A family of three-dimensional chiral metal–formate frameworks of [NH4][M(HCOO)3 ] (M = Mn, Fe, Co, Ni, and Zn) displays paraelectric to ferroelectric phase transitions between 191 and 254 K, triggered by disorder–order transitions of NH4+ cations and their displacement within the framework channels, combined with spin-canted antiferromagnetic ordering within 8–30 K for the magnetic members, providing a new class of metal–organic frameworks showing the coexistence of magnetic and electric orderings.