New halogen-bonded complexes of diiodine with 1,3,5-triaza-7-phosphaadamantane chalcogenides: a structural and computational investigation

Whilst the coordination chemistry of 1,3,5-triaza-7-phosphaadamantane-7oxide (PTA=O) and -sulfide (PTA=S) towards transition metals is widely established, examples involving bonding to main-group elements such as halogens are relatively rare. In the presented work, the interaction of PTA=O and PTA=S with diiodine has been studied in solution and solid state. UV-visible spectroscopy indicates that in the solution phase iodine bonds with PTA=O via a nitrogen whereas with PTA=S the iodine bonds to the donor ligand via the sulfur. In contrast, crystallographic studies of the complexes show that in the solid state the diiodine interacts with a nitrogen atom of the adamantane cage in both PTA=O.I2 and PTA=S.I2, with near linear N-I-I units, and both compounds are halogen-bonded charge-transfer adducts. Contributions to crystal packing have been delineated through Hirshfield surface analysis. The nature of the charge-transfer interaction in both compounds has been investigated by computational methods with DLPNO-CCSD(T), and further wavefunction analysis techniques.