Hydrothermal synthesis, characterization and crystal structures of two new zinc(ii) phosphonates: Zn2[(O3PCH2)2NHCH2CO2] and Zn2[HO3PCH2NH(CH2PO3)2]

Abstract

The hydrothermal reaction of zinc(II) acetate with N,N-bis(phosphonomethyl)aminoacetic acid [(H₂O₃PCH₂)₂NCH₂CO₂H, H₅L¹] and nitrilotris(methylenephosphonic acid) [N(CH₂PO₃H₂)₃, H₆L²] at 180 °C afforded two new zinc coordination polymers with a similar 3D network structure. Zn₂[(O₃PCH₂)₂NHCH₂CO₂] (complex 1) is hexagonal, P6₁, with a = 8.0677(12), c = 27.283(6) Å, u = 1537.9(5) ų, Z = 6. In complex 1, the Zn(II) atoms are tetrahedrally coordinated by three phosphonate oxygen atoms and one carboxylate oxygen atom from four ligands. The ZnO₄ tetrahedra are further interconnected through bridging phosphonate and carboxylate groups into a three dimensional network. Zn₂[HO₃PCH₂NH(CH₂PO₃)₂] (complex 2) is also hexagonal, P6₁ with a = 8.3553(8), c = 26.657(4) Å, u = 1611.6(3) ų, Z = 6. The structure of complex 2 features a 3D network built from ZnO₄ tetrahedra linked together by bridging phosphonate groups. One zinc and three phosphonate oxygen atoms are disordered. The two zinc atoms in the asymmetric unit are tetrahedrally coordinated by four phosphonate oxygen atoms of four ligands. Each ligand connects with eight zinc atoms. The effect of the extent of deprotonation of phosphonic acids and substitution groups on the type of complexes formed are discussed.