title: Porous lanthanide-organic frameworks: synthesis, characterization, and unprecedented gas adsorption properties.
abstract: The reactions of Ln(NO(3))(3) (Ln = La, Er) with 1,4-phenylendiacetic acid (H(2)PDA) under hydrothermal conditions produce isostructural lanthanide coordination polymers with the empirical formula [Ln(2)(PDA)(3)(H(2)O)] x 2H(2)O. The extended structure of [Ln(2)(PDA)(3)(H(2)O)] x 2H(2)O consists of Ln-COO triple helices cross-linked through the [bond]CH(2)C(6)H(4)CH(2)[bond] spacers of the PDA anions, showing 1D open channels along the crystallographic c axis that accommodate the guest and coordinated water molecules. Evacuation of [Er(2)(PDA)(3)(H(2)O)] x 2H(2)O at room temperature and at 200 degrees C, respectively, generates [Er(2)(PDA)(3)(H(2)O)] and [Er(2)(PDA)(3)], both of which give powder X-ray diffraction patterns consistent with that of [Er(2)(PDA)(3)(H(2)O)] x 2H(2)O. The porosity of [Er(2)(PDA)(3)(H(2)O)] and [Er(2)(PDA)(3)] is further demonstrated by their ability to adsorb water vapor to form [Er(2)(PDA)(3)(H(2)O)] x 2H(2)O quantitatively. Thermogravimetric analyses show that [Er(2)(PDA)(3)] remains stable up to 450 degrees C. The effective pore window size in [Er(2)(PDA)(3)] is estimated at 3.4 A. Gas adsorption measurements indicate that [Er(2)(PDA)(3)] adsorbs CO(2) into its pores and shows nonporous behavior toward Ar or N(2). There is a general correlation between the pore size and the kinetic diameters of the adsorbates (CO(2) = 3.3 A, Ar = 3.40 A, and N(2) = 3.64 A). That the adsorption favors CO(2) over Ar is unprecedented and may arise from the combined differentiations on size and on host-guest interactions.
authors.affiliation: Department of Chemistry, University of Colorado at Denver, Campus Box 194, P.O. Box 173364, Denver, Colorado 80217-3364, USA.
authors.forename: Long
authors.initials: L
authors.lastname: Pan
authors.forename: Kristie M
authors.initials: KM
authors.lastname: Adams
authors.forename: Hayden E
authors.initials: HE
authors.lastname: Hernandez
authors.forename: Xiaotai
authors.initials: X
authors.lastname: Wang
authors.forename: Chong
authors.initials: C
authors.lastname: Zheng
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Hattori
authors.forename: Katsumi
authors.initials: K
authors.lastname: Kaneko