Abstract: Reaction of η⁵-cyclopentadienylchromium tricarbonyl sodium with methylmercuric chloride in diglyme at room temperature for 12 h gave bis(η⁵-cyclopentadienylchromium tricarbonyl) mercury [η⁵-C₅H₅Cr(CO)₃]₂Hg in₅₈% yield. Its structure was fully confirmed by combustion analysis, IR, ¹HNMR, MS and X-ray diffraction methods. The crystal belongs to monoclinic space group P2₁/c. Cell parameters are a=8. 023 (2)Å, b=20. 843(9)Å, c=10. 331 (2)Å; β=96. 00(3)°, V=1718. 2ų; Z=4. The average Cr-Hg bond length is 2. 655Å. Mercury atom is approximately co-linear with two chromium atoms (<Cr(1)HgCr(2)=171. 12°). Each chromium atom can be viewed as being on the common apex of the pentagonal pyramid constructed from cyclopentadienyl pentagon bottom and the square-based pyramid with the bottom of three carbonyls and one mercury atom.

Key words: η⁵-Cyclopentadienylchromium tricarbonyl sodium, Methylmercuric chloride, Single crystal structure