Crystal engineering on layered zirconium phosphonates. Crystal structure (from X-ray powder data) and non-covalent interactions on the layered zirconium compound of 4-[bis(phosphonomethyl)amino]butanoic acid

Abstract

A new layered zirconium diphosphonate fluoride, ZrHF(O₃PCH₂)₂NHC₃H₆CO₂, has been prepared by the reaction of zirconyl chloride with 4-[bis(phosphonomethyl)amino]butanoic acid in the presence of HF. Its structure has been determined “ab initio” by X-ray powder data. It crystallizes in the monoclinic space group P2₁/c (No. 14), with a = 12.9640(3) Å, b = 8.9900(4) Å, c = 10.7924(4) Å, β = 101.854(4)°, and Z = 4. Both of the phosphonic groups of each diphosphonate building block are bonded to zirconium atoms on the same side of the layers. Only one organic residue is associated with two phosphonate tetrahedra. The packing of layers creates an interdigitated arrangement of organic groups in the interlayer region. Two strong non-covalent interactions are present in the structure. One of them involves neighbouring P–OH and amino groups, while the other interaction engages terminal carboxylic groups and fluorine atoms belonging to adjacent layers. Thermal treatment at 240 °C causes the loss of one mole of HF per mole of zirconium, with the formation of a stable compound in which carboxylate groups probably coordinate to the zirconium atoms belonging to adjacent layers. Preliminary experiments of intercalation with ammonia and short alkylamines are also reported.