Nucleophilic addition reaction in coordinated non-linear pseudohalides: experimental charge density analysis in trans-bis(cyanamidonitrato-N:O)bis-(imidazole-N 3)copper(II) complex

The experimental crystal charge density of the complex [Cu(iz)2(can)2] (I) (where iz = imidazole, can = cyanamidonitrate anion), [Cu(C3H4N2)2(CN3O2)2], crystallizing in centrosymmetric space group P21/c, has been determined at 120.0 (2) K, using Hansen and Coppens' aspherical atom multipole model. The central Cu atom is pseudo-octahedrally coordinated by four N atoms in an equatorial plane [two from iz molecules, 1.9660 (4) Å, two from can anions, 2.0273 (5) Å] and by two O atoms (from two adjacent molecules) in axial positions [2.5566 (5) Å]. The d-orbital population analysis shows that the oxidation state for the copper is +2 with the d 9 configuration and that there is a hole in the d_{x^2 - y^2} orbital, located in the plane of the four nitrogen-ligating atoms. Electron lone pairs of these four N atoms are pointing into these regions of depleted electron density. In accordance with the medium-length Cu—O axial bonds, the d z2 orbital is almost fully occupied [1.79 (3) electrons]. The non-bonding d xy orbital is fully occupied [2.05 (3) electrons]. Analysis of the atomic charges does indicate a deficit of +0.35 (4) e− on the nitrile carbon, which provides evidence of β-carbon activation for a possible nucleophilic addition reaction. This reaction has been indirectly confirmed experimentally.