The crystalline forms of tris(pyridin-2-yl)phosphoric triamide, OP[NH-²Py]₃ were investigated using single crystal X-ray diffraction, both as a metal complex [Co{(O)P[NH-²Py]₂[NH-²PyH]}₂]Cl₃, compound 1, and as the purely organic pseudopolymorphs, the pure/anhydrate OP[NH-²Py]₃, 2, monohydrate 2OP[NH-²Py]₃·H₂O, 3 and solvate 2OP[NH-²Py]₃·2DMF·H₂O, 4, respectively. An improved model of the metal organic framework (MOF) structure of Cu(II)O₆ {[Cu(OCHO)₃][(CH₃)₂NH₂]}_n, 5 is also reported. Compound 1 is the first example of a discrete chelate phosphoric triamide (PT) complex with an [N]₃P(O)-based backbone which in the PT compound acts as a flexible tridentate ligand. The structures 1, 3 and 4 crystallize in the monoclinic space group P2₁/n, while the anhydrous form 2 crystallizes in the R trigonal space group. 5 which was obtained as a byproduct of the synthesis process of coordination compounds of OP[NH-²Py]₃, crystallizes in the monoclinic space group I2/c. Hydrogen bonding pattern analysis for the different solid state forms of OP[NH-²Py]₃ (2–4) shows a 2D sheet of the N–H⋯N linked molecules for 2, and a 1D chain and a ten-membered ring motif, both formed via the hydrogen bonds N–H⋯O, N–H⋯N and O–H⋯O, for 3 and 4, respectively. Of note is the unusual absence of the expected hydrogen bond interaction N–H⋯OP of PT compounds and also a lack of any significant π interactions in structure 2. The role of the solvent/hydrate and substituent (aminopyridine) in the formation of the expected hydrogen bond interactions in the studied solid state forms is also investigated. For these structures, crystal packing analysis using 3D Hirshfeld surface (HS), 2D fingerprint plot (FP) and enrichment ratio (E) calculations confirm a competition between the pyridinyl nitrogen and phosphoryl oxygen atoms as H-bond acceptors to construct the N–H⋯N or N–H⋯O contacts. Moreover, the significant differences between the anhydrous form of OP[NH-²Py]₃, 2, and the monohydrate and solvate forms, 3 and 4, can be correlated to the pseudo-infinite (in 2) versus finite values (in 3 and 4) for the upper values of d_e and d_i on the related full FPs.