High-throughput microwave-assisted discovery of new metal phosphonates

Abstract

A systematic study was carried out to investigate the influence of linker geometry, metal ionic radius as well as the nature of the counter ions on the structure formation of metal tetraphosphonates. Two tetraphosphonic acids p- and m-(H₂O₃PCH₂)₂N-CH₂-C₆H₄-CH₂-N(CH₂PO₃H₂)₂, six metal ions (Ca²⁺, Mn²⁺, Co²⁺, Ni²⁺, Zn²⁺, and Cd²⁺) and two different counter ions (Cl⁻ and NO₃⁻) were employed using high throughput methods. Microwave (MW)-assisted heating led to the discovery of ten new metal-phosphonates which crystallize in three different crystal structures. The combination of direct methods and force field calculations allowed us to establish the crystal structures. The counter ion and the ionic radii of the metal ions have a profound influence on the crystallinity and the formed crystal structure. All compounds were characterized in detail by thermogravimetric analyses, IR spectroscopy and magnetic susceptibility measurements. The proton conductivity of two selected compounds is also reported.