Novel multifunctional porous coordination polymers from pre-synthetically modified organophosphorus ligands
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Phosphine-based Porous Coordination Polymers (PCPs) have shown promising results as gas storage, gas separations, and molecular sensing materials due the versatility of the P(III)/P(V) chemistry, coupled with the inherent 3-dimensionality of the ligands. A variety of pre-synthetically modified organophosphine linkers have been reacted with alkali earth metals, early transition metals, and lanthanides to produce a series of Phosphine Coordination Materials (PCMs) with a wide array of topologies and pore functionalities. A p-carboxylated triphenylphosphine oxide linker, tctpoH₃, has been reacted with Mg(II) to form the thermally robust PCM-11, which possesses superior room-temperature CO₂ adsorption capacity at 12 bar. A new tetrahedral phosphonium salt, tctp⁺H₃, has been synthesized by the Pd(II)-catalyzed reaction of p-carboxylated triphenylphosphine with 4-iodobenzoic acid to produce a zwitterionic monophosphine precursor. Upon examination of its crystal structure, it was found that tctp⁺H₃ possesses a high degree of hydrogen-bonding between neighboring carboxylic acid groups, which causes it to polymerize into a porous, metal-free, ionically-bonded coordination polymer, iPCM-1. This phosphonium linker has been reacted with a series of Ln(III) precursors to form an isostructural set of PCMs that exhibit characteristic lanthanide luminescence properties. Several PCPs have been developed from a new bis(phosphine)MCl₂ (M = Pd, Pt) complex upon reaction with early transition metals. Zn(II)-based PCM-18 exhibits unusual and fully reversible H₂ adsorption at 150 °C, as well as post-synthetic reactivity inside the pores of the material. Co(II)-based PCM-24 also displays similar high-temperature H₂ sorption behavior, along with a reversible pink to blue color change upon activation, indicative of a symmetry transformation from O [subscript h] to T [subscript d] about the metal node.