The crystal structure of Mg,EDTA l 9H,O has been determined using 2102 independent reflections measured by a single crystal counter diffractometer (CuKcu radiation). The general conclusions are similar to those of an independent determination using film data [2] but the present investigation is very much more accurate, and all the hydrogen atoms have been located. The crystals are orthorhombic, space group
Pbcn, with a = 11.617(1)A, b = 9.495(l)& c = 19.238(2)1% The structure was refined to a conventional R of 0.048 and WR of 0.037. Standard deviations in bond distances are 0.0024.003A for C-C and C-0 bonds and 0.03-0.
04A for C-H and O-H bonds. The structure consists of a cation, Mg(HZO)z', which is very close to regular octahedral geometry, and an anion, (MgEDTA OHZ)?-in which the Mg atom is heptacoordinated by four 0 and 2 N atoms of the EDTA and one water molecule. The anion coordination sphere is close to pentagonal bipyramidal geometry and the details of the structure are discussed in comparison with other heptacoordinated EDTA complexes. One water molecule is not included in either the cation or the anion, and the whole structure is linked by a tight network of hydrogen bonds, utilizing every proton of the water molecules.