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 K(2n)[ZnCl(2)(1,3-H(2)pdta)ZnCl(2)](n) (1) and its substituted iodide [ZnI(2)(H(2)O)(1,3-H(4)pdta)](n) (2) (H(4)pdta = 1,3-propanediaminetetraacetatic acid, C(11)H(18)N(2)O(8)) were isolated. The former was obtained from the reaction of zinc chloride and H(4)pdta in pH similar to 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 [ZnCl(2)(1,3-H(2)pdta)ZnCl(2)](2-) with strong intra-molecular hydrogen bonds [N1 center dot center dot center dot O2 2.648(4); N1 center dot center dot center dot O4 2.710(4) angstrom]. In neutral complex 2, an 1,3-pdta ligand links each monomeric unit [Zn(H(2)O)I(2)] to generate an infinite 1D chain, which extents into a 3D supramolecular structure by very strong inter-molecular hydrogen bonds the [O4 center dot center dot center dot O2b 2.50 (1) angstrom, bx, y, z + 1]. 1 is soluble in water at room temperature, which is traced by (13)C NMR experiment. (C) 2011 Elsevier B.V. All rights reserved.