Synthesis and characterization of novel tetraphosphonates as possible chelating agents with a large cavity

• Syntheses of novel phosphonate ligands with large cavities for e.g. f-elements • Simple, straightforward synthetic protocols with high yields • Full characterization via X-Ray, NMR, HRMS and ATR-IR This publication presents the synthesis and solid-state structures of two novel phosphonate chelating ligands, ethylenediaminetetrakis(ethylenephosphonate) (EDTEP) and phenylenediamine-tetrakis(ethylenephosphonate) (PhDTEP). Syntheses of each ligand were initially tested as one-step reactions under solvothermal, aqueous conditions, but resulted in unsatisfactory results. The access to the target molecules could be improved for PhDTEP by means of a two-step reaction starting with a Finkelstein-type reaction and for EDTEP via a four-step reaction using reductive amination for the construction of the backbone. Both compounds could be obtained in high yields. Structure determination by single crystal X-ray diffraction revealed double-zwitterionic states for both, EDTEP (P2 1 /n) and PhDTEP (P-1). The solid states structures are characterized by extensive hydrogen bond networks, which in the case of PhDTEP involve two water molecules per unit cell.