Selective Sensing of Phosphates by a New Bis‐heteroleptic RuII Complex through Halogen Bonding: A Superior Sensor over Its Hydrogen‐Bonding Analogue

Abstract The selective phosphate‐sensing property of a bis‐heteroleptic Ru II complex, 1 [PF 6 ] 2 , which has a halogen‐bonding iodotriazole unit, is demonstrated and is shown to be superior to its hydrogen‐bonding analogue, 2 [PF 6 ] 2 . Complex 1 [PF 6 ] 2 , exploiting halogen‐bonding interactions, shows enhanced phosphate recognition in both acetonitrile and aqueous acetonitrile compared with its hydrogen‐bonding analogue, owing to considerable amplification of the Ru II ‐center‐based metal‐to‐ligand charge transfer (MLCT) emission response and luminescence lifetime. Detailed solution‐state studies reveal a higher association constant, lower limit of detection, and greater change in lifetime for complex 1 in the presence of phosphates compared with its hydrogen‐bonding analogue, complex 2 . The 1 H NMR titration study with H 2 PO 4 − ascertains that the binding of H 2 PO 4 − occurs exclusively through halogen‐bonding or hydrogen‐bonding interactions in complexes 1 [PF 6 ] 2 and 2 [PF 6 ] 2 , respectively. Importantly, the single‐crystal X‐ray structure confirms the first ever report on metal‐assisted second‐sphere recognition of H 2 PO 4 − and H 2 P 2 O 7 2− with 1 through a solitary C−I⋅⋅⋅anion halogen‐bonding interaction.