Crystal and molecular structure of Sr2(Edta) . 5H2O, Sr2(H2Edta)(HCO3)2 . 4H2O, and Sr2(H2Edta)Cl2 . 5H2O strontium ethylenediaminetetraacetates

Three Sr2+ compounds with the Edta4- and H2Edta2- ligands-Sr2(Edta) . 5H2O (I), Sr2(H2Edta)(HCO3)2 . 4H2O (II), and Sr2(H2Edta)Cl2 . 5H2O (III)-are synthesized, and their crystal structures are studied. In I, the Sr(1) atom is coordinated by the hexadentate Edta4- ligand following the 2N + 4O pattern and by two O atoms of the neighboring ligands, which affords the formation of zigzag chains. The Sr(2) atom forms bonds with O atoms of five water molecules and attaches itself to a chain via bonds with three O atoms of the Edta4- ligands. The Sr(1)-O and Sr(2)-O bond lengths fall in the ranges 2.520(2)-2.656(3) and 2.527(3)-2.683(2) A, respectively. The Sr(1)-N bonds are 2.702(3) and 2.743(3) A long. In II and III, the H2Edta2- anions have a centrosymmetric structure with the trans configuration of the planar ethylenediamine fragment. The N atoms are blocked by acid protons. In II, the environment of the Sr atom is formed by six O atoms of three H2Edta ligands, two O atoms of water molecules, and an O atom of the bicarbonate ion, which is disordered over two positions. In III, the environment of the Sr atom includes six O atoms of four H2Edta2- ligands and three O atoms of water molecules. The coordination number of the Sr atoms is equal to 8 + 1. In II and III, the main bonds fall in the ranges 2.534(3)-2.732(2) and 2.482(2)-2.746(3) A, whereas the ninth bond is elongated to 2.937(3) and 3.055(3) A, respectively. In II, all the structural elements are linked into wavy layers. The O-H-O interactions contribute to the stabilization of the layer and link neighboring layers. In III, hydrated Sr2+ cations and H2Edta- anions form a three-dimensional [Sr2(H2Edta)(H2O)3]n2n+ framework. The Cl- anions are fixed in channels of the framework by hydrogen bonds with four water molecules. In II and III, the N-H groups form four-center N-H-O3 hydrogen bonds, which include one intermolecular and two intramolecular components. PACS numbers: 61.66.Hq