Hexaiododiplatinate(ii) as a useful supramolecular synthon for halogen bond involving crystal engineering

Abstract

Hexaiododiplatinates(II) bearing ammonium and phosphonium cations, [R₄N]₂[Pt₂(μ-I)₂I₄] {R = Et (1) and n-Bu (2)} and [R₃PR¹]₂[Pt₂(μ-I)₂I₄] {R = n-Bu and R¹ = n-Bu (3); R = Ph and R¹ = Ph (4); R = Ph and R¹ = CH₂Ph (5)}, were synthesized and characterized by high resolution ESI-MS, ¹H, ¹³C{¹H}, ³¹P{¹H}, and ¹⁹⁵Pt NMR spectroscopy, Fourier transform infrared and Raman spectroscopy, X-ray diffraction (XRD), X-ray powder diffraction, and also 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 with two, three, and even four Pt–I_terminal ligands. The results of Hirshfeld molecular surface analysis and density functional theory (DFT) calculations (the 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⁻¹.