Solvatomorphs of (Bu4N)2[{Ag(N2-py)}2Mo8O26]: structure, colouration and phase transition

Abstract

Self-assembly of (Bu₄N)₄[β-Mo₈O₂₆], AgNO₃ and N₂-py (N₂-py = 2,6-diaminopyridine) in DMF solution results in a (Bu₄N)₂[β-{Ag(N₂-py)}₂Mo₈O₂₆] complex which crystallises as two phases: one (OP) is orange in colour and consists of [β-{Ag(N₂-py)}₂Mo₈O₂₆]²⁻ monomers and [β-{Ag(N₂-py)}₂Mo₈O₂₆]_n²ⁿ⁻ polymeric chains in the crystal structure; the other (YP) is yellow in colour and built only with [β-{Ag(N₂-py)}₂Mo₈O₂₆]²⁻ monomers. Both complexes were characterised by single crystal X-ray diffraction (SCXRD), X-ray powder diffraction (XRPD), diffuse reflectance (DR), infrared spectroscopy (IR), elemental analysis, and quantum chemical calculations. According to differential scanning calorimetry (DSC) and DR, OP demonstrates a complicated phase transition at 130 K. Comprehensive SCXRD studies of the crystal structure change show rearrangement of the Ag⁺ coordination sphere related with the dominant Ag–N bond distance change. TGA of both complexes confirms formation of silver nanoparticles (Ag-NPs), MoO₃ and Ag₂Mo₄O₁₃ upon thermal decomposition. The Ag-NPs were studied by SEM. Exfoliation of the resulting mixture in water gives a Ag-NP and MoO₃ mixed colloid system studied by TEM.