Synthesis, structure and non-covalent interactions of trans-[2-(HCF 2 (CF 2 ) 3 CH 2 OCH 2 ) 2-py-PdCl 2 ] complex: Rare C-F•••F-C halogen bonds and blue-shifting C-H•••X hydrogen bonds

The sp 3-based C-F center dot center dot center dot F- C halogen bonds (XBs) and blue-shifting C-H center dot center dot center dot X (X = F , Cl) hydrogen bonds (HBs) are a relatively unusual phenomenon in chemistry, due to their uncommonness and the challenges associated with their direct observations. To investigate these interactions, a novel fluorinated trans-[2-(HCF2(CF2)3CH2OCH2)2- py-PdCl2], abbreviated as 2-(8FH-py)2PdCl2 complex, has been synthesized and structurally characterized. The incorporation of a fluorinated ponytail on the pyridyl ring in the 2-(8FH-py)2PdCl2 complex allows us to explore rare sp3-based type II C9-F4 center dot center dot center dot F6-C10 and C8-F2 center dot center dot center dot F6-C10 XBs dimers. These findings suggest, for the first time, the formation of halogen bonding dimers through C-F center dot center dot center dot F-C interactions, to our knowledge. Additionally, the 2-(8FH-py)2PdCl2 reveals interesting blue-shifting C-H center dot center dot center dot X hydrogen bonding interactions in the crystal packing. These C-H center dot center dot center dot F interactions connect adjacent molecules in a head-to-tail manner, resulting in the continuation of R22(9) synthons along the crystallographic a-axis. These hydrophobic interactions, which are expected to be very different from the typical hydrophilic interactions, play a crucial role in enhancing the self- assembly and stability of the crystal structure. In addition, the presence of blue-shifting C-H center dot center dot center dot X hydrogen bonding interactions affirmed by the FT-IR studies. Furthermore, the high positive values of electron density (rho) and Laplacian density (O2 rho) from quantum theory of atoms in molecule (QTAIM) analyses suggest the presence of electrostatic and weak interactions between atoms. We believe that this discovery will open up new opportunities for exploring and utilizing fluorinated complexes in various scientific fields, fluoro-pharmaceuticals and crystal engineering.