Hexaiododiplatinate(II) as a Useful Supramolecular Synthon for Halogen Bond Involving Crystal Engineering

Abstract

The hexaiododiplatinates(II) bearing ammonium and phosphonium cations, [R₄N]₂[Pt₂(μ-I)₂I₄] {R = Et (1), n-Bu (2)} and [R₃PR¹]₂[Pt₂(μ-I)₂I₄] {R = n-Bu, R¹ = n-Bu, (3); R = Ph, R¹ = Ph (4); R = Ph, R¹ = CH₂Ph (5)}, were synthesized and characterized by high resolution ESI-MS, ¹H, ¹³C{¹H}, ³¹P{¹H}, ¹⁹⁵Pt NMR spectroscopies, Fourier transform infrared and Raman spectroscopies, X-ray diffraction (XRD), X-ray powder diffraction, and also by the electrostatic surface potential calculations. Complexes 1–3 were cocrystallized with halogen bond (XB) donors based on organic iodides featuring electron withdrawing groups {R^EWGIs: 1,3,5-triiodotrifluorobenzene (1,3,5-FIB), iodopentafluorobenzene (IPFB), 1,4-diiodotetrafluorobenzene (1,4-FIB), and tetraiodoethylene (C2I4)} to give crystalline adducts 1•2(1,3,5-FIB), 1•2IPFB, 2•2(1,4-FIB), and 3•C2I4. Inspection of the XRD data of the obtained adducts revealed the presence in all four structures of intermolecular R^EWGI•••I–Pt XBs between the iodine centers of R^EWGIs and the terminal iodide ligands of [Pt₂(μ-I)₂I₄]^2– anions, where the latter act as rectangular XB-accepting synthons forming XBs by two, three, and even four Pt–I_terminal ligands. Results of the Hirshfeld molecular surface analysis and density functional theory (DFT) calculations (M06/DZP-DKH level of theory) followed by topological analysis of the electron density distribution within the framework of Bader’s approach (QTAIM) confirmed the existence of the detected XBs, and their estimated energies vary from 2.2 to 4.7 kcal/mol.