Metal-involving Halogen Bond Ar–I∙∙∙[dz2PtII] in the Platinum Acetylacetonate Complex
Combined XRD and theoretical study for the two adducts, [Pt(acac)2]∙2(1,3,5-FIB) and [Pd(acac)2]∙1,3,5-FIB (Hacac = acetylacetone; 1,3,5-FIB = 1,3,5-triiiodotrifluorobenzene), reveals that differences in types of the formed halogen bond (XB) depend on identity of a metal center. Only [Pt(acac)2] forms rare two-center metal-involving XB Ar–I∙∙∙[dz2PtII] (where the positively charged PtII center acts as a nucleophile toward an iodine -hole), while three-center bifurcated XB I∙∙∙2(O,O) was detected in both adducts. The observed linkage Ar–I∙∙∙[dz2PtII] provides an experimental argument favoring the previously established (by a kinetic study) XB-formation step upon oxidative addition of I2 to [Pt(acac)2]. The variable temperature XRD study of [Pt(acac)2]∙2(1,3,5-FIB) (100–300 K; five XRD experiments) demonstrates that the I∙∙∙Pt and I∙∙∙O contacts weaken simultaneously on heating that allows the consideration of the Pt1–O2 bond as an integrated XB acceptor. Appropriate DFT calculations (M06/DZP-DKH level of theory) performed by single-point “quasi-solid state” calculations with topological analysis of the electron density distribution within the framework of the Bader theory (QTAIM method), confirmed the existence of the two-center metal-involving XB I∙∙∙Pt in the structure of [Pt(acac)2]∙2(1,3,5-FIB) and three-center I∙∙∙2(O,O) bifurcated XB for both adducts. All these interactions exhibit noncovalent nature with estimated energies in the range 2.1–4.3 kcal/mol.