Metal-involving halogen bond Ar–I⋯[dz2PtII] in a platinum acetylacetonate complex†
A combined XRD and theoretical study for 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 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⋯[dz2PtII] (where the positively charged PtII center acts as a nucleophile toward an iodine σ-hole), while three-center bifurcated XB I⋯η2(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⋯η2(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.