Hydrogen bonding adducts of octamolybdate anions containing coordinately bound pyridiniumoxides

The reaction of [Mo7O24][NH4]6 with 3-hydroxypyridine (3-HOPy) and 4-hydroxypyridine (4-HOPy) in water resulted in the crystalline materials of [Mo8O26(3-OPyH)2][3-HOPyH]4 · 4H2O (1) and [Mo8O26(4-OPyH)2][4-HOPyH]4 · 4H2O (2), respectively. Crystal structures of the complexes 1 and 2 reveal that two of the OPyH moieties coordinately linked to two molybdate atoms of Mo8O26 clusters. The crystal structures of 1 and 2 are not iso-structural. However, in both cases the iso-structural Mo8O26(OPyH)2 units join together via N–H⋯O hydrogen bonds to form linear ribbons which are further joined by H2O molecules to form 2D-layers. The cavities or channels of these layers are occupied by the C–H⋯O, O–H⋯O and O–H⋯π aggregates of hydroxypyridinium cations.