Crystal and molecular structure of aquoethylenediaminetetra-acetatoruthenium (III) and its extraordinary lability towards substitution

Abstract

The crystal and molecular structure of [Ru(HEDTA) (H₂O)] (<strong>2</strong>), was determined using single crystal X-ray diffraction techniques. The complex crystallizes with 4 molecules in the space group <em>P</em>2₁/<em>c </em>with the unit cell dimensions <em>a </em>= 8.414(1)Ǻ, <em>b =</em> 8.835(1)Ǻ, <em>c= </em>17.610(4)Ǻ, β = 99.64*. The structure has been solved taking advantage of the fact that the complex is isomorphous with the analogous Rh(III) complex. The</p> structure is refined to an R value 0.033 (Rw = 0.043) for 5983 observed reflections. Ru occurs as a distorted octahedron. Ethylenediaminetetraacetic acid is a pentadentate ligand, with one free carboxylate group.</p> Water approaches the coordination sphere <em>trans </em>to one of the nitrogens of the ethylenediamine moiety. Ring R2 is planar, while rings R₁ and G are envelopes. Ring E occurs as a half-chair. The structure is held in three-dimensional space by an elaborate network of hydrogen bonds. Water exchange rate constants show that the complex is labile. An attempt is made to rationalize the unusual lability of the complex.