Structural studies of steric effects in phosphine complexes. Part XI."' Synthesis, characterization, crystal and molecular structure of the dinitrato(trimesitylarsine)mercury(II) dimer

The synthesis and crystal and molecular structure of the dinitrato(trimesitylarsine)mercury(II) dimer are reported. The compound [HgAs(mesityl)3(NO3)2]2 belongs to the monoclinic space group P21/c with a = 20.001(2), b = 17.591(5), c = 16.553(2), β = 99.991(6), and Z = 4; the asymmetric unit contains two independent half dimers. The structure was refined to a final R of 0.0458 for 2631 observed reflections measured by diffractometer with 2 < θ < 20°. The crystal structure consists of discrete centrosymmetric dimeric molecules of [HgAs(mesityl)3(NO3)2]2 separated by normal van der Waals distances. The mercury coordination in both dimers I and II is characterized by three strong, nearly coplanar bonds (in I Hg—As 2.476(3), Hg—O 2.41(2) and 2.20(2), and in II Hg—As 2.482(3), Hg—O 2.28(2) and 2.39(2), and three weaker Hg—O bonds in the range 2.55–2.90 A. Both independent trimesitylarsine ligands have the same regular propeller conformation (Hg—As—C—C torsion angles of 45 to 50°) and the largest C—As—C angles ...