Selective recognition and reversible encapsulation of tetrameric alcohol clusters via hydrogen bonds using a perfluorinated dinuclear nickel(ii) complex

Abstract

Perfluorinated dinuclear metal complexes, [M₂L₂] (M = Ni²⁺ (1), Cu²⁺ (2), and H₂L = 1,5-dihydroxy-1,5-bis(pentafluorophenyl)-1,4-pentadien-3-one), were examined as host crystals to encapsulate alcohol molecules. Complex 1 was crystallized from EtOH and MeOH to give unique single crystals 1·2EtOH·2H₂O and 1·8MeOH, respectively, showing a unique hydrogen bonded motif of solvent molecules due to the hydrophobic crystalline cavities surrounded by the pentafluorophenyl moieties on the dinuclear Ni²⁺ sites. This open and specific cavity on the metals is not suitable for EtOH or H₂O in the crystallization process whereas MeOH, a physiologically harmful substance used in industry, is effectively and selectively encapsulated. The encapsulated MeOH molecules form tetrameric clusters that are stabilized by hydrogen bonding. Vapor adsorption of the powder samples shows reversible and accelerated recognition of alcohol only for the perfluorinated complex 1, while two coordination solvates were observed for 2.