Crystal structures of calcium, strontium, and barium aqua(ethylenediaminetetraacetato(3-))cobaltate(II) tetrahydrates, M '[CoHEdta(H2O)](2)center dot4H(2)O (M ' = Ca2+, Sr2+, Ba2+)

The M'[Co(II)HEdta(H2O)](2). 4H(2)O complexes, where Edta(4-) is the ethyle nediaminetetraacetate ion, M' = Ca2+ (I) and Sr2+ (II), were synthesized an d examined by X-ray diffraction analysis. The orthorhombic crystals of I an d II are isostructural, space group Pbcn, Z = 4; for I: a = 7.745, b = 14.9 55, c = 26.621 Angstrom, V = 3083.2 Angstrom(3), R = 0.046; for II: a = 7.8 00, b = 15.073, c = 26.619 Angstrom, V = 3129.6 Angstrom(3), R = 0.060. The structures of these complexes consist of sandwich layers that are formed b y the complex anion fragments [CoHEdta(H2O)](-) linked together by the M' a toms. The coordination sphere of the Co(II) atom (octahedron) involves the donating atoms of the HEdta(3-) ligand (2N and 3O) and the O-w(1) atom of t he water molecule. The average bond lengths in complexes I and II are: Co-O -lig 2.073(3) and 2.064(7) Angstrom; Co-N, 2.238(4) and 2.230(9) Angstrom; and Co-O-w(1), 2.072(4) and 2.088(8) Angstrom, respectively. The interlayer M' cations are located on the two-fold axes. The polyhedron of the M' atom s (tetragonal antiprism) is made up of two atoms O(1) and O(2) of the same carboxylate branch of the initial anion, the O(4) atom of another anion, th e O-w(2) atom of the water molecule, and the oxygen atoms symmetrically bou nd to them. The Ca-O-lig,distances in structure I change from 2.400(3) to 2 .672(4) Angstrom, Sr-O-lig in structure II, from 2.508(7) to 2.797(7) Angst rom, and the Co-O-w(2) and Sr-O-w(2) distances are equal to 2.369(4) and 2. 547(9) Angstrom, respectively. The structural formula of the compounds unde r study is (M'(H2O)(2)[CoHEdta(H2O)](2))(2 infinity). 2H(2)O.