Phosphite and phosphonate complexes. Part IV. trans-Influence in mercury(II) complexes. X-Ray crystal structure analysis of bis(dimethyl phosphonato)mercury(II)

Abstract

Crystals of the title compound are monoclinic, space group I2/c, with Z= 4 in a cell of dimensions: a= 8·869(13), b= 6·930(9), c= 17·797(27)Å, α=γ= 90°, β= 91° 16′(20′). The structure was determined from photographic X-ray data by Patterson and Fourier methods and refined by full-matrix least-squares techniques to R 0·116 for 804 observed reflections. The mercury atom forms strong bonds with only two phosphorus atoms, the angle P–Hg–P being 165·9°, and molecules of [Hg{(MeO)₂PO}₂] are clearly distinguishable. Two phosphoryl oxygen atoms from neighbouring molecules interact weakly with mercury (Hg ⋯ O ca. 2·54 Å) forming with the two phosphorus atoms a very distorted tetrahedral arrangement about mercury. The molecular association results in the formation of chains parallel to the a axis. Hg–P distance (2·41 Å) is significantly longer than in [HgCl{(EtO)₂PO}], which confirms that the trans-influence formalism is useful in digonal mercury(II) complexes and that effects through the metal σ electrons are dominant.