Recognition of the pi-hole donor ability of iodopentafluorobenzene - a conventional sigma-hole donor for crystal engineering involving halogen bonding

摘要

Iodopentafluorobenzene (IPFB or (PhI)-I-F) was co-crystallized with tetra(n-butyl) ammonium tetraiodo-mu,mu'-diiododiplatinate(II), [n-Bu4N]2[Pt-2(mu-I-2)I-4] (1), to give the adduct 1 center dot 2IPFB. The XRD experiment revealed that 1 center dot 2IPFB displays previously unreported C center dot center dot center dot I-Pt anion-p interactions formed along with the expected Ph-F-I center dot center dot center dot I-Pt-II halogen bond (XB); these two interactions join two complexes and two IPFBs in a heterotetrameric cluster. Processing of the available CSD data revealed only one structure (CSD code: IKIYAE) with a heterotetrameric cluster bearing simultaneous two Ph-F-I center dot center dot center dot X (X = I-PtIV, N) XBs and C center dot center dot center dot I lp.I)-pi contacts between the two IPFBs. Results of the DFT calculations (M06/DZP-DKH level of theory) followed by the topological analysis of the electron density distribution within the framework of Bader's approach (QTAIM) for both 1 center dot 2IPFB and IKIYAE confirmed the availability of these (anion/lp)-pi weak interactions. The estimated energies of the observed (anion/lp)-pi and XBs contacts are in the 0.9-1.3 kcal mol(-1) and 1.3-5.3 kcal mol(-1) ranges, respectively. p-Hole donor ability of IPFB was additionally confirmed by theoretical calculations of the molecular surface electrostatic potential for the optimized equilibrium structure of IPFB.