Abstract
Treatment of MoO~3~ with butan‐1‐amine (BuNH~2~) or pyrrolidine (PyrNH~2~) results in the formation of (BuNH~3~)~8~[(Mo~7~O~24~)(MoO~4~)]·3H~2~O (1; BuNH~3~ = butan‐1‐aminium) or (PyrNH~2~)~6~[(Mo~7~O~24~]·2H~2~O (2; PyrNH~2~ = pyrrolidinium), respectively. On irradiation with sunlight, compound 1, which is an organic heptamolybdate [Mo~7~O~24~]^6–^ that contains a cocrystallized monomolybdate [MoO~4~]^2–^ in the same compound, is transformed to an oxido‐bridged diheptamolybdate (BuNH~3~)~10~[(Mo~7~O~22~)(μ~2~‐O)~2~(Mo~7~O~22~)]·5.5H~2~O (1b). The [Mo~7~O~24~]^6–^ units in 1 and 2 are made up of edge‐sharing [MoO~6~] octahedra, whereas the central unit in 1b is a bis(μ~2~‐O)‐bridged heptamolybdate dimer. Hydrogen bonding among the lattice water molecules in 1 results in the formation of a water octamer, whereas hydrogen bonding between the lattice water molecules and [Mo~7~O~24~]^6–^ in 2 results in the formation of a one‐dimensional water‐linked heptamolybdate chain. Supramolecular structures, photochemistry, and thermal properties of 1, 1b, and 2 are reported. For comparison of photochemical behavior, two more polyoxomolybdates, (PrNH~3~)~6~[Mo~7~O~24~]·3H~2~O (3; PrNH~3~ = propan‐1‐aminium) and (PentNH~3~)~6~[Mo~7~O~24~]·3H~2~O (4; PentNH~3~ = pentan‐1‐aminium), were prepared and characterized.