Solvothermal synthesis, structure and characterization of 1D chain and 2D layered rare earth sulfates in the presence of cyclic diamines

Three new rare earth sulfates were solvothermally synthesized and characterized by X-ray diffraction, elemental analysis, thermogravimetric, and photoluminescent studies. Compounds [(NH4)(C6N2H12)][Ln(SO4)3] (Lndouble bond; length as m-dashEu, 1; Gd, 2) were synthesized in the solvent of DMA with 1,4-diazabicyclo-[2,2,2]-octane (DABCO) as a structure-directing agent (SDA), which are isomorphous and adopt a two-dimensional layered structure with 8-membered rings made of LnO8 polyhedra and SO4 tetrahedra. The protonated DABCO molecules lie between the layers while the ammonium cations are located within the layers. Compound [(C4N2H12)1.5][Er(SO4)3(H2O)] (3) was synthesized in the mixed solvent of water and ethanol with piperazine (PIP) as a SDA. The structural analyses showed that 3 is constructed from ErO9 polyhedra and SO4 tetrahedra to form a one-dimensional chained structure with edge-sharing 4-membered rings. The protonated PIP molecules and coordination H2O molecules form extensive intra- and inter-chain hydrogen bonding to generate a 3-dimensional supramolecular network. The three compounds exhibit good thermal stability. Compound 1 exhibits intense red luminescence upon excitation owing to the Eu3+ ion.