<p>A series of new 1,5-diaza-3,7-diphosphacyclooctanes bearing fixed N-iodophenyl substituents and variable alkyl or aryl groups at the phosphorus atoms has been synthesized and comprehensively characterized. All compounds were obtained in good yields and studied by ¹H and ³¹P NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Structural analysis reveals that the ligands belong to Type I according to the recently proposed P₂N₂ classification; however, several representatives exhibit conformations approaching those typical of Type III ligands. In particular, two distinct borderline Type I conformations were identified, differing in the orientation of the phosphorus lone electron pairs and the P···P distances. These structural variations are shown to correlate with slight changes in the endocyclic C–N–C angles, indicating a decisive role of the nitrogen atom geometry in controlling the overall geometry of the aminomethylphosphine cycle. In addition, a rare anti-isomer adopting a chair–boat conformation was observed for one compound, representing an uncommon structural motif for 1,5-diaza-3,7-diphosphacyclooctanes. The obtained crystallographic data expand the experimental basis of the P₂N₂ ligand classification and demonstrate that Type I ligands represent a structurally dual case, capable of adopting conformations preorganized for both P, P-chelating and P, P-bridging coordination modes.</p>