Comparison of structure and reactivity of bis(2-aminoethyl)amine- and bis(2-aminoethyl)amido-chlorogold(III) complexes

Abstract

The crystal and molecular structures of the title compounds, [AuCl{NH(CH₂CH₂NH₂)₂}]Cl[ClO₄](1) and [AuCl{N(CH₂CH₂NH₂)₂}][ClO₄](2) have been determined by Patterson and Fourier methods. Compound (1) crystallizes in the monoclinic space group P2₁/n with four molecules in a cell of dimensions: a= 8.590(6), b= 12.745(8), c= 12.256(8)Å, and β= 113.6(1)°. Compound (2) crystallizes in the orthorhombic space group P2₁2₁2₁, with four molecules in a unit cell of dimensions: a= 12.976(8), b= 10.029(7), and c= 8.171(6)Å. Anisotropic least-squares refinement has reduced R to 0.119 and 0.103 for (1) and (2) respectively. In both compounds the co-ordination about the gold atom is approximately square planar but two atoms of the counter ions are about 3.1 Å from the metal along the axial co-ordination sites. In compound (1) the four donor atoms are essentially in a plane and the gold atom is displaced from this by 0.063 Å; in compound (2), instead, there is a pronounced tetrahedral distortion of the co-ordination geometry. Moreover, the pyramid about the central nitrogen of the tridentate ligand is much flatter in (1) than in (2). The Au–Cl bond is longer in the amido- than in the amino-complex [2.273(8) and 2.330(10)Å in (1) and (2) respectively] suggesting a greater trans influence of N^– as compared with NH. The reactivity of these substrates towards chloride substitution by bromide has been re-examined.