Unraveling NMR signal splitting in dinuclear platinum(II) complexes

Three binuclear platinum(II) complexes containing dicarboxylate bridging ligands were synthesized and characterized by IR, multinuclear NMR (^1H, ^13C, and ^195Pt), and high-resolution ESI(+)-FT-MS. The spectroscopic analyses confirmed the proposed structures and revealed an unusual splitting pattern for the ^1H NMR signals of the bridging ligand, contrasting with the singlet resonances commonly reported for analogous systems. To elucidate this behavior, a systematic density functional theory (DFT) investigation was performed on a series of binuclear platinum complexes considering five-membered (5T) and sixmembered (6T) pseudo-chelate coordination modes. Several functionals and basis sets were evaluated, with the M06 and M06-2X functionals providing the best agreement with experimental structures. Calculated NMR chemical shifts demonstrated that the 5T and 6T conformations exhibit distinct spectroscopic signatures, indicating that conformational effects, particularly variations in ligand dihedral angles and terminal-ligand arrangements, govern the observed NMR signal splitting.