High-throughput ultrasonic synthesis and in situ crystallisation investigation of metal phosphonocarboxylates

Abstract

High-throughput reactions of aqueous solutions of 4-(phosphonomethyl)benzoic acid (H₃PMBC) with metal salts were carried out using, for the first time, ultrasonication as well as the previously described conventional heating. On screening the influence of 12 divalent metal ions, two new compounds ([Ca(H₂O)₂(H₂PMBC)₂] and [Ni(H₂O)₄(H₂PMBC)₂]) were discovered. Their formation fields were established by systematically studying the systems Ni²⁺ or Ca²⁺/H₃PMBC/KOH. Both compounds crystallise in the space group P ([Ca(H₂O)₂(H₂PMBC)₂]: a = 4.6806(9) Å, b = 6.1340(12) Å, c = 17.932(4) Å, α = 83.84(3)°, β = 89.03(3)°, γ = 85.65(3)°; [Ni(H₂O)₄(H₂PMBC)₂]: a = 4.7713(10) Å, b = 6.8621(14) Å, c = 16.598(3) Å, α = 83.42(3)°, β = 89.71(3)°, γ = 83.50(3)°) and contain MO₆-octahedra linked to form chains by hydrogen bonded (H₂PMBC⁻)₂-dimers formed between the carboxylate groups. The formation of [Ni(H₂O)₄(H₂PMBC)₂] was studied by in situ EDXRD and in situ IR spectroscopy. The increased formation rate of [Ni(H₂O)₄(H₂PMBC)₂] under ultrasonic irradiation as compared to conventional heating could be unequivocally attributed to the faster dissolution of the ligand H₃PMBC.