Synthesis and characterisation of cis and trans isomers of the mixed chalcogen clusters Cp2Mo2Fe2(CO)(8)(mu(3)-S)(mu(3)-Se) and Cp2Mo2Fe2(CO)(8)(mu(3)-S)(mu(3)-Te)

The reaction of Fe-2(CO)(6)(mu-SSe) and Cp2Mo2(CO)(4) in benzene at room te mperature for 2 h, yielded the new isomeric mixed-metal, mixed-dichalcogeni de clusters trans-Cp2Mo2Fe2(CO)(8)(mu(3)-S)(mu(3)-Se) (1) and cis-Cp2Mo2Fe2 (Co)(8)(mu(3)-S)(mu(3)-Se) (4). The new mixed-metal clusters 1 and 4 could also be obtained when Fe-3(CO)(9)(mu(3)-S)(mu(3)-Se) and Cp2Mo2(CO)(6) were heated at 65 degrees C in benzene for 36 h. Similarly, the room-temperatur e reaction of Fe-2(CO)(6)(mu-STe) with Cp2Mo2(CO)(4) in benzene for 2 h and the thermolytic reaction of Fe-3(CO)(9)(mu(3)-S)(mu(3)-Te) with Cp2Mo2(CO) (6) in benzene for 36 h afforded the new isomeric clusters trans-Cp2Mo2Fe2( CO)(8)(mu(3)-S)(mu(3)-Te) (9) and cis-Cp2Mo2Fe2(CO)(8)(mu(3)-S)(mu(3)-Te) ( 11). The new clusters have been characterised by IR and by H-1-, Se-77-, Te -125-NMR spectroscopy. Clusters 1 and 4 have also been structurally charact erised by single-crystal X-ray diffraction methods. (C) 1999 Elsevier Scien ce S.A. All rights reserved.