Facile room-temperature synthesis of layered transition metal phosphonates via hitherto unknown alkali metal tert-butyl phosphonates

Abstract

A facile room-temperature synthetic method is presented to produce alkali metal salts of tert-butyl phosphonic acid. The reaction between equimolar amounts of alkali metal carbonates and tert-butyl phosphonic acid in methanol results in the formation of [(^tBuPO₃H)Li(H₂O)₃·(H₂O)] (1), [(^tBuPO₃)Na₂(H₂O)₄]_n (2), and [(^tBuPO₃H)K(H₂O)]_n (3). Solid-state structures of these compounds have been confirmed by single-crystal X-ray diffraction studies and further validated using numerous spectroscopic and analytical techniques. Compounds 1–3 are polymeric solids that are predominantly made up of a 1-D polymeric metal phosphonate chain. This synthetic approach leads to the formation of network structures/polymers in the solid state that otherwise are absent in solution due to the ionic nature of the interaction between the alkali metal ions and phosphonate anions. Apart from the multidentate nature of the phosphonate ligands, additional hydrogen bonding interactions involving water molecules, free P–OH groups, and PO moieties allow these chains to be propagated into 2-D sheets. We have further utilized the completely metalated sodium phosphonate 2 to synthesize layered metal phosphonates [(^tBuPO₃)Ca(H₂O)]_n (4), [(^tBuPO₃)Mn(H₂O)]_n (5) and [(^tBuPO₃)Co(H₂O)]_n (6) via a simple metathesis reaction.