Pentaguanidinium monohydrogendiphosphopentamolybdate(VI) 2.5‐hydrate, (CH6N3)5[HP2Mo5O23]·2.5H2O: hydrogen bonding and π‐stacking in guanidinium cations

The asymmetric unit of the title compound consists of two crystallographically independent, but structurally identical, HP₂Mo₅O₂₃]^5? anions, ten guanidinium cations and five water molecules. Each singly protonated diphosphopentamolybdate(VI) anion retains the typical geometry of a ring of five edge‐sharing MoO₆ octahedra Mo...Mo = 3.3265 (8)–3.4029 (10) Å], except for one corner‐sharing link Mo...Mo = 3.6642 (7) and 3.6826 (8) Å]. Two capping PO₄ tetrahedra share corners with the five octahedra. Despite being surrounded by an extensive network of hydrogen bonds, predominantly from the guanidinium cations, short P—O—H...O=P contacts O...O = 2.519 (7) and 2.457 (7) Å] associate the anions into infinite columns generated by the c‐glide. In addition to their heavy involvement in hydrogen bonding, with all N—H donors being utilized, the guanidinium cations assemble into extensive π‐stacked columns with an average interplanar spacing of 3.53 Å.