Metal-involving halogen bond Ar-I•••[dz2PtII] in a platinum acetylacetonate complex

A combined XRD and theoretical study for two adducts, [Pt(acac)(2)]center dot(1,3,5-FIB) and [Pd(acac)(2)]center dot 1,3,5-FIB (Hacac = acetylacetone; 1,3,5-FIB = 1,3,5-triiiodotrifluorobenzene), reveals that differences in the type formed halogen bond (XB) depend on the identity of the metal center. Only [Pt(acac)(2)] forms rare two-center metal-involving XB Ar-I center dot center dot center dot[d(z2)Pt(II)] (where the positively charged Pt-II center acts as a nucleophile toward an iodine sigma-hole), while three-center bifurcated XB I center dot center dot center dot eta(2)(O,O) was detected in both adducts. The observed linkage Ar-I center dot center dot center dot[d(z2)Pt(II)] provides an experimental argument favoring the previously established (by a kinetic study) XB-formation step upon oxidative addition of I-2 to [Pt(acac)(2)]. The variable temperature XRD study of [Pt(acac)(2)]center dot 2(1,3,5-FIB) (100-300 K; five XRD experiments) demonstrates that the I center dot center dot center dot Pt and I center dot center dot center dot 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 center dot center dot center dot Pt in the structure of [Pt(acac)(2)]center dot 2(1,3,5-FIB) and three-center I center dot center dot center dot eta(2)(O,O) bifurcated XBs for both adducts. All these interactions exhibit a non-covalent nature with estimated energies in the range of 2.1-4.3 kcal mol(-1).