Synthesis and characterization of hydrated alkali metal calcium nitrates ACa(NO 3 ) 3 ·2H 2 O (A = NH 4 , Rb, Cs) as short ultraviolet birefringent materials

Three isostructural ACa(NO 3 ) 3 ·2H 2 O (A = NH 4 , Rb, Cs) compounds were synthesized by the water evaporation method, composed of [CaO 9 ] polyhedra and [NO 3 ] − units with enhanced optical properties. RbCa(NO 3 ) 3 ·2H 2 O is a representative example.