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, [HP(2)Mo(5)O(23)](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 MoO(6) 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 PO(4) 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.