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

Hexaiododiplatinates(ii) bearing ammonium and phosphonium cations, [R4N](2)[Pt-2(mu-I)(2)I-4] {R = Et (1) and n-Bu (2)} and [R3PR1](2)[Pt-2(mu-I)(2)I-4] {R = n-Bu and R-1 = n-Bu (3); R = Ph and R-1 = Ph (4); R = Ph and R-1 = CH2Ph (5)}, were synthesized and characterized by high resolution ESI-MS, H-1, C-13{H-1}, P-31{H-1}, and Pt-195 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(EWG)Is: 1,3,5-triiodotrifluorobenzene (1,3,5-FIB), iodopentafluorobenzene (IPFB), 1,4-diiodotetrafluorobenzene (1,4-FIB), and tetraiodoethylene (C2I4)} to give crystalline adducts 12(1,3,5-FIB), 12IPFB, 22(1,4-FIB), and 3C(2)I(4). Inspection of the XRD data of the obtained adducts revealed the presence, in all four structures, of intermolecular (RII)-I-EWG-Pt XBs between the iodine centers of R(EWG)Is and the terminal iodide ligands of [Pt-2(mu-I)(2)I-4](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).