Zeolite-Like Sorption of Volatile Organics in β-[CuL2] (L = {CF3COCHCOC(CH3)2OCH3}-)

The β-form of the title copper(II) acetylacetonate derivative shows zeolite-like behavior, as exemplified by its ability to absorb volatile guests instantly and reversibly over a wide range of guest pressures. Sorption isotherms with methylene chloride, chloroform, carbon tetrachloride, n-pentane, acetone, tetrahydrofuran, and diethyl ether were determined at 30 °C or over a range of temperatures. For all guests tested, sorption occurred even at minimal guest pressure, indicating the presence of porosity of the host sorbent even without included species present. The nature of the isotherms as well as other characteristics suggests a physical mode of sorption on the inner hydrophobic surface of the host pores. With increasing pressure, the isotherms quickly reached plateau values corresponding to a guest/host ratio of 2/3 for compact molecules and to a lower value for n-pentane and diethyl ether. At elevated temperatures and low guest pressure, the porous β-form collapses to the dense, α-form of the complex, as does the guest-free β-form. At 70 °C, the enthalpy of the α-to-β transformation equals 1.31(5) kJ/mol as determined from DSC experiments. In the β-[CuL2]*2/3(chloroform) compound studied by X-ray diffraction, 1D channel segments of both larger and smaller widths are filled stoichiometrically with guest species, thus explaining the limiting guest−host ratio observed.