Co-Crystallization and Structural Studies of Benzophenone Recognized by Positively Shifted ESPs of Perfluorinated β-Diketonate Complexes (M = Cu, Pd, Pt)

Abstract

Benzophenone was encapsulated in molecular crystals of fully fluorinated coordination complexes, [ML2] [1, M = Cu2+ and Pd2+, L = bis(pentafluorobenzoyl)-methanido−], forming a unique chiral co-crystal with a ratio of [ML2]:benzophenone = 2:3, while no encapsulation was observed in the corresponding non-fluorinated complexes [M(dbm)2] (dbm = dibenzoylmethanido−). Notable π-hole···π and metal(M)···π interactions were detected between the complex and the adapted orientation of benzophenone in the co-crystals. Analyses from crystal structures and thermogravimetric (TG) results indicated that the encapsulation and thermal stability of benzophenone in these molecular crystals correlate well with the electrophilic characteristics shown by the electrostatic potential (ESP) at the metal centers, which is enhanced by fluorination: Cu2+ > Pd2+ >> Pt2+. The recognition of benzophenone is driven by π-holes created by the electron-withdrawing nature of fluorine atoms and the electron-deficient metal ion enhanced by the aromatic fluorine, demonstrating that the effect of electrostatic molecular recognition is as significant as oxygen coordination, as shown in comparative studies with 1,1-diphenylethylene.

Keywords

• benzophenone
• co-crystal
• DFT calculations
• fluorine effect
• π-hole