Selenium heterocubanes

Both sodium atoms have a coordination number of six. Na2 is bonded to four selenium atoms, an oxygen atom of a carbonyl group and a THF molecule. Unlike Na2, Nal is coordinated by three selenium atoms and three THF molecules. The THF molecules bonded to Nal have a bridging function. This leads to a ribbon like arrangement of the heterocubane dimers along the crystallographic c axis (Fig. 4). 

In analogy to 6 the heterocubane units consist of a 812804 fragment and two iron atoms. Formally, 7 can be derived from 6 by the substitution of the sodium atoms by half the number of Fe cations. As a consequence of the linking of die heterocubane units, the iron atoms in the comers of the 8i28e4Fo2 units are coordinated by six selenium atoms. If only the central Fej8e24 framework is viewed, the stmcture of 7 can be derived from six edge shared FeSe octahedra. 

Organometallic derivatives of the less electron rich transition metals have been used by several investigators as precursors to polynuclear complexes. Cp-substi-tuted transition metal halides, for example, have been allowed to react with M2E, (M = Li, Na E = S, Se x = 1,2) or elemental sulfur or selenium. [251-254] S(SiMe3)2 and Se(SiMe3)2 have also been used successfully. Thus, the reaction of [CpCrCl2(P Bu3)] with Se(SiMc3)2 furnishes the heterocubane cluster [Cp4Cr4Se4]. [255]... 

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