Linear I···I contacts in a platinum(IV)-diiodo porphyrin: Emergent type III halogen–halogen interactions
Year: 2026
Type: preprint
Abstract: This study presents experimental and theoretical evidence for unusual intermolecular I···I interactions between axially coordinated iodide ligands in a Pt(IV) porphyrin. Single-crystal X-ray diffraction reveals that PtI2T[3,5-diOMe]PP, where T[3,5-diOMe]PP is the 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)porphyrinato dianion, crystallises in the uncommon P4/n space group, in contrast to the I4/m space group frequently observed for related metalloporphyrins, and adopts an eclipsed columnar packing arrangement, with co-crystallised dichloromethane (DCM) molecules occupying the space between successive porphyrin layers. The iodide ligands form linear I···I contacts that propagate into a one-dimensional supramolecular network. Comparison with the axial-iodide-free PtT[3,5-diOMe]PP and the related OsI2T[2,4,6-triMe]PP, where T[2,4,6-triMe]PP is the 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphyrinato dianion, demonstrates how axial iodide coordination, peripheral substitution, and the local solvent environment influence the resulting crystal packing and macrocyclic conformation. Molecular surface electrostatic potential (MESP), quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO), and Hirshfeld surface analyses were employed to investigate the nature of the intermolecular contacts. QTAIM analysis identifies the I···I contacts as weak, closed-shell interactions, while NBO analysis reveals a significant donor–acceptor component involving iodide lone pairs and neighbouring Pt–I or Os–I antibonding orbitals. The magnitude and distribution of these interactions depend on the local supramolecular environment, with co-crystallised DCM contributing additional C–H···I contacts and altering the electronic environment of these ligands. Together, these results demonstrate that the I···I interactions cannot be considered in isolation, but instead form part of a broader network of cooperative intermolecular contacts that governs the crystal packing of the Pt(IV) porphyrin.
Source: ChemRxiv
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
Award: G1636584653
OpenAlex ID: W7213912578