Structural, magnetic and photoluminescence properties of new hybrid hypophosphites: discovery of the first noncentrosymmetric and two cobalt-based members.

Hybrid organic-inorganic perovskites comprising hypophosphite ligands are emerging functional materials exhibiting magnetic, photoluminescence, negative thermal expansion and negative linear compressibility behaviours. This work reports five novel hypophosphite perovskites, [A]M(H 2 POO) 3 (A = pyrrolidinium (PYR + ), guanidinium (GUA + ) and imidazolium (IM + ); M = Cd 2+ and Co 2+ ). [GUA]Cd(H 2 POO) 3 , [IM]Cd(H 2 POO) 3 , [GUA]Co(H 2 POO) 3 and [IM]Co(H 2 POO) 3 belong to the centrosymmetric trigonal R 3̄ c , monoclinic P 2 1 / c , monoclinic I 2/ m , and orthorhombic Pbca space groups, respectively, while [PYR]Cd(H 2 POO) 3 crystallizes in the noncentrosymmetric orthorhombic space group Aea 2. The polar order of PYR + cations was confirmed by observation of moderate second harmonic generation (SHG) activity. Magnetic studies reveal that [GUA]Co(H 2 POO) 3 and [IM]Co(H 2 POO) 3 are weak ferromagnets with the ordering temperatures higher compared to their manganese analogues. Upon ultraviolet excitation, the cadmium counterparts exhibit purplish-blue emissions at low temperatures, which decrease on heating. Analysis of the photoluminescence data reveals that the emission quenching decreases with decreasing distortion of the cadmium-hypophosphite framework. Discovery of the new hypophosphites exhibiting magnetic or polar order and photoluminescence properties shows that hypophosphite perovskites offer a promising platform for generating new functional materials, including those that are light emitting, ferroelectric and multiferroic.