Engineering metal site behavior: electrophilic-nucleophilic dualism in square-planar platinum(ii) through geometry-controlled switching

Abstract

This study reveals a fundamentally new mechanism for controlling metal site behavior in supramolecular chemistry and crystal engineering: geometric control of platinum(II) centers’ electrophilic–nucleophilic switching. Using the dithiocarbonato complex [Pt(S₂COEt)₂] (1) and three iodo-substituted perfluoroarenes as coformers—1,3-diiodotetrafluorobenzene (1,3-FIB), 1,4-diiodotetrafluorobenzene (1,4-FIB), and 2,2′,3,3′,5,5′,6,6′-octafluoro-4,4′-diiodo-1,1′-biphenyl (FIBiPh)—we demonstrate for the first time that organic tecton geometry alone can control the directionality and type of metal-involving noncovalent interactions, independent of electronic factors. X-ray diffraction studies establish that the platinum(II) site exhibits unprecedented dual reactivity: it functions as a weak electrophile in 1·2(1,4-FIB) and 1·FIBiPh through {p_z-Pt}⋯S semicoordination, while acting as a nucleophile in 1·2(1,3-FIB), forming I⋯{d_z²-Pt} halogen bonds. This geometric control represents a significant advance over previous methods that relied on electronic modification through metal selection or ligand environment changes. Comprehensive DFT calculations, including electron localization function analysis and electron density/electrostatic potential profiling, confirm the noncovalent nature of these interactions and illuminate the electronic factors controlling this amphiphilic behavior. The calculations reveal that halogen bond donor geometry and the resulting supramolecular assembly determine whether the platinum(II) site manifests its electrophilic nature via {p_z-Pt}⋯S semicoordination or its nucleophilic character through I⋯{d_z²-Pt} halogen bonding. This discovery of geometry-controlled switching between bonding modes represents both a fundamental advance in understanding of metal-involving noncovalent interactions and a new strategic approach for controlling supramolecular assembly through the manipulation of metal-involving interactions.