The asymmetric unit of the title complex, [Ni(C12H8N2)3]S2O8·2C3H7NO·H2O, consists of a complex [Ni(phen)3](2+) cation and one isolated pds anion, with two DMF mol-ecules and one water mol-ecule as solvates (where phen is 1,10-phenanthroline, pds is the hexa-oxido-μ-peroxoido-di-sulf-ate dianion and DMF is dimethyl-formamide). The [Ni(phen)3](2+) cation is regular, with an almost ideal Ni(II) bond-valence sum of 2.07 v.u. The group, as well as the water solvent mol-ecule, are well behaved in terms of crystallographic order, but the remaining three mol-ecules in the structure display different kinds of disorder, viz. the two DMF mol-ecules mimic a twofold splitting and the pds anion has both S atoms clamped at well-determined positions but with a not-too-well-defined central part. These peculiar behaviours are a consequence of the hydrogen-bonding inter-actions: the outermost SO3 parts of the pds anion are heavily connected to the complex cations via C-H⋯O hydrogen bonding, generating an [Ni(phen)3]pds network and providing for the stability of the terminal pds sites. Also, the water solvent mol-ecule is strongly bound to the structure (being a donor of two strong bonds and an acceptor of one) and is accordingly perfectly ordered. The peroxide O atoms in the pds middle region, instead, appear as much less restrained into their sites, which may explain their tendency to disorder. The cation-anion network leaves large embedded holes, amounting to about 28% of the total crystal volume, which are occupied by the DMF mol-ecules. The latter are weakly inter-acting with the rest of the structure, which renders them much more labile and, accordingly, prone to disorder.