Crystal structure of the dimeric 1:2 addition complex of tricarbonylmesitylenemolybdenum with mercury(II) chloride

Abstract

Crystals of the title compound [{(C₆H₃Me₃)(CO)₃Mo(HgCl₂)₂}₂] are monoclinic, space group C2/c, a= 17.049(4), b= 13.599(3), c= 17.249(7)Å, β= 102.54°, Z= 8. The structure was determined from diffractometer data by the heavy-atom method and refined by full-matrix least-squares to R 0.035 (on F) for 1 598 reflections. The structure consists of centrosymmetric dimers in which the tricarbonylmesitylenemolybdenum groups are bonded to mercury [Mo–Hg 2.745(1)Å]; the central Hg₂Cl₂ four-membered ring has one molybdenumu bonded to each mercury. All the mercury atoms are four-co-ordinate; the mercury atoms not bonded to molybdenum are halogenbridged to the four-membered ring, extending the mercury–halogen network. The mercury–chloride distances range widely from 2.317(5) to 3.038(5)Å.

The upwards shift of 58 cm^–1 of the averaged i.r. CO stretching frequencies on complex formation is due to this Lewis acid–base bonding.