Solvent-free syntheses of two pcu topological indium phosphite-oxalates with a novel butterfly motif and proton conductivity

Under solvent-free conditions, two new 3D open-framework indium phosphite-oxalates In-5(HPO3)(6)(H1.5PO3)(2)(C2O4)(2)center dot(H(2)A)(2,) where A = C5N2H12 (compound 1) and C6N2H14 (compound 2), are synthesized by using 1-methylpiperazine and 1-ethylpiperazine as the structure-directing agent, respectively. Single crystal X-ray diffraction reveals that these two compounds have the analogue inorganic framework structures, which may be viewed as the assembly of butterfly motifs and [C2O42-] groups. Interestingly, the butterfly motif is firstly reported in metal phosphite/phosphite-oxalate. By regarding the butterfly motifs as topologically equivalent 4-connected nodes and thus framework can be simplified into a uninodal pcu network with point symbol of (4(12), 6(3)). 1 and 2 are also characterized by powder X-ray diffraction, IR spectroscopy, SEM, TGA, ICPAES and elemental analyses. In addition, proton conduction was investigated by alternating-current impedance analysis and the results demonstrate that both compounds show high proton-conductive properties with the conductivity of 3.4 x 10(-3) S cm(-1) and 2.1 x 10(-3) S cm(-1) at 75 degrees C and 98% RH, respectively.