Acidic 1,3-propanediaminetetraacetate zinc complexes as a probe of water soluble coordination polymers

In a very acidic solution, potassium 1,3-propanediaminetetraacetate zinc chloride K2n[ZnCl2(1,3-H2pdta)ZnCl2]n (1) and its substituted iodide [ZnI2(H2O)(1,3-H4pdta)]n (2) (H4pdta = 1,3-propanediaminetetraacetatic acid, C11H18N2O8) were isolated. The former was obtained from the reaction of zinc chloride and H4pdta in pH ∼1.5. Further substitution of 1 results in the formation of iodide 2 with the addition of potassium iodide in acidic solution of pH 0.5. Complex 1 consists of a dimeric anionic unit [ZnCl2(1,3-H2pdta)ZnCl2]2− with strong intra-molecular hydrogen bonds [N1⋯O2 2.648(4); N1⋯O4 2.710(4) Å]. In neutral complex 2, an 1,3-pdta ligand links each monomeric unit [Zn(H2O)I2] to generate an infinite 1D chain, which extents into a 3D supramolecular structure by very strong inter-molecular hydrogen bonds the [O4⋯O2b 2.50 (1) Å, bx, y, z + 1]. 1 is soluble in water at room temperature, which is traced by 13C NMR experiment.