Synthesis, crystal structure and calcination of three novel complexes based on 2-aminopyridine and polyoxometalates

Three novel complexes based on 2-aminopyridine and polyoxometalates (POMs) formulated as (C5N2H7)5H[P2Mo5O23], 1, (C5N2H7)6(H2O)2[V10O28], 2, (C5N2H7)12(H2O)2(CH3OH)[PMo12O40]4, 3, were hydrothermally synthesized and structurally characterized by elemental analysis, IR, UV, TG and single crystal X-ray diffraction. Compounds 1, 2 and 3 consist of 2-aminopyridine cations together with different POMs, [P2Mo5O23]6−, [V10O28]6− and [PMo12O40]3−, respectively. 2-Aminopyridine cations in 1 orderly link [P2Mo5O23]6− like ribbons via alternating N–H⋯O and C–H⋯O hydrogen bonding interactions and compound 1 exhibits one dimensional empty channel. It is resulted from that the weak interactions between [P2Mo5O23]6− leave equal sized cavities in which 2-aminopyridine just fits. Whereas the varying distances between POMs in compounds 2 and 3 caused by their different interactions between POMs lead to the disorder of 2-aminopyridine. Heating compounds 1 and 3 at 600 °C in air for 2 h yielded nanometer or micrometer-scale MoO3. Their different morphologies result from the different POMs and molecular arrays in their precursors.