Alkaline earth metal complexes of the edta-type with a six-membered diamine chelate ring: crystal structures of [Mg(H2O)(6)] [Mg(1,3-pdta)] center dot 2H(2)O and [Ca(H2O)(3)Ca(1,3-pdta)(H2O)] center dot 2H(2)O: comparative stereochemistry of edta-typ

摘要

Starting from Ba[Ba(1,3-pdta)] (.) 2H(2)O (where 1,3-pdta is the 1,3-propanediaminetetraacetate ion) two new hexadentate complexes: [Mg(H2O)(6)][Mg(1,3-pdta)] (.) 2H(2)O (1) and [Ca(H2O)(3)Ca(1,3-pdta)(H2O)] (.) 2H(2)O (2) have been prepared and characterized. The complexes differ in coordination numbers and geometry, and in coordinative bond distances. They also display dramatically different packing patterns: while the structural units of (1) consist of discrete [Mg(1,3-pdta)](2-) and [Mg(H2O)(6)](2+) octahedra arranged in the solid-state in a close packed fashion, the crystals of (2) are composed of one-dimensional chains of ligand-bridged coordination complexes, such that no discrete complex units exist. The calcium(II) ion (Ca1), coordinated with the 1,3-pdta ligand and two symmetry-related water molecules, forms an irregular square-anti prismatic structure, which is not common for the M-1,3-pdta system. The coordination polyhedron formed around the counter ion (Ca2) can best be described as a dodecahedron. Six-membered diamine chelate rings in complexes (1) and (2) are found to be in twist-boat and distorted chair conformations, respectively. Infrared and solid-state C-13 NMR spectra of Ba-, Mg- and Ca-1,3-pdta complexes have also been presented. (C) 2004 Elsevier Ltd. All rights reserved.