Sequential transformations in assemblies based on octamolybdate clusters and 1,2-bis(4-pyridyl)ethane

Abstract

The new hybrid inorganic–organic solids [Mo₈O₂₆][H₂bpe]₂ (1), {[Mo₈O₂₆(μ-bpe)][H₂bpe]₂}_n (2), [Mo₈O₂₆(Hbpe)₂][H₂bpe] (3), and {[Mo₈O₂₆][H₂bpe]₂}_n (4) were synthesized under hydrothermal conditions. The crystal structure of 1 contains the discrete octamolybdate β-isomer, whereas in 3 the inorganic building unit is a functionalized octamolybdate of general formula [Mo₈O₂₆X₂]⁽²ⁿ⁺⁴⁾. A similar building unit is found in 2 and 4, but forming part of polymeric 1D-arrays. In 2 the polymer is constructed from [Mo₈O₂₆(μ-bpe)]⁴⁻, and the functionalization of the anionic cluster in 4 occurs through Mo–O–Mo bonds. The sequential hydrothermal 2/3 → 1 and 1 → 4 transformations were observed at 145 and 180 °C, respectively. However, thermal studies of 1 and 4 revealed that both materials do not suffer any phase transitions below 340 °C for 1 or <350 °C for 4, indicating that such transformations are possible only under the hydrothermal conditions. An XRPD study as a function of the temperature of 1 also demonstrated the negligible structural changes before 330 °C.