The novel metalloligand [Fe(bppd)3] (bppd = 1,3-bis(4-pyridyl)-1,3-propanedionate) for the crystal engineering of heterometallic coordination networks with different silver salts. Anionic control of the structures

Abstract

The crystal engineering of heterometallic coordination networks based on the novel tris-chelate metalloligand [Fe^III(bppd)₃] (bppd = 1,3-bis(4-pyridyl)-1,3-propanedionate) is reported here. The building block [Fe(bppd)₃] crystallizes with a balanced packing of the Δ and Λ forms and exhibits distorted octahedral chiral structure with six exo-oriented pyridyl donor groups suitable for networking via interactions with external metal ions. It was reacted with many silver salts AgX (X = BF₄⁻, ClO₄⁻, PF₆⁻, AsF₆⁻, SbF₆⁻, NO₃⁻, CF₃SO₃⁻, tosylate) giving polymeric products with structures depending on the nature of the counter-anions X⁻. With pseudo-spherical anions (such as BF₄⁻, ClO₄⁻, PF₆⁻, AsF₆⁻ and SbF₆⁻) 2D polymeric species [Fe(bppd)₃Ag](X) are obtained showing sql topology, because the metalloligands use only four, out of the six pyridyl donors, to bind silver ions. The reaction with Ag(CF₃SO₃) affords a quite different type of [Fe(bppd)₃Ag]⁺ 2D polymeric frame, with the metalloligands that again employ only four pyridyl groups for networking, i.e. a double layered species comprised of two superimposed honeycomb sheets, exhibiting a (4³.6³) topology. By using AgNO₃ a 3D framework, [Fe₂(bppd)₆Ag₃](NO₃)₃, is obtained that, interestingly, consists of double layers like those of the previous species connected viaAg bridges on both sides to produce a binodal 5,4-connected 2-fold interpenetrated network. The reaction with silver p-toluenesulfonate produces the complex 3D nanoporous network [Fe₃(bppd)₉Ag₅](tosylate)₅ with 6-connected metalloligands and 3- and 4-connected silver ions. An interesting rationalization of this network is that it is comprised of 1D parallel nanotubular motifs of hexagonal section with square-meshed walls; these nanotubes are laterally interconnected by Ag triple-bridging atoms to generate the whole 3D array. We observe that in these species the metalloligands use a variable number of pyridyl donors for networking, i.e. four, five and six, leading to frames of increased complexity and dimensionality that are strongly dependent on the anionic shape and nature. The reactions of the analogous metalloligand [Al^III(bppd)₃] with the same AgX salts under similar conditions produce polycrystalline materials that in the cases of silver triflate and tosylate are isostructural with the corresponding iron containing species, as evidenced by their X-ray powder diffraction spectra.