Rare-earth-metal iodide clusters centered by transition metals: synthesis, structure, and bonding of R7I12M compounds (R = Sc, Y, Pr, Gd; M = Mn, Fe, Co, Ni)
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The compounds R7I12M (M = Co, Ni for R = Sc; M = Fe, Co for R = Y; M = Mn, Fe, Co for R = Gd; M = Mn, Fe, Co, Ni for R = Pr) have been synthesized by reactions of RI3, MI2, and R metals at 750-950 C in sealed Nb or Ta containers. These compounds all adopt the Sc(Sc6Cl12B) structure (space group R3, Z = ) with a transition metal at the cluster center (in place of boron). The seventh isolated R3+ ion can be substituted by Ca2+ in several of the Pr and Gd cases. The structural details of Sc7I12Co, Y7I12Fe, and (Ca0.65Pr0.35)(Pr6I12Co) were determined by single-crystal X-ray diffraction methods (a = 14.800, 15.351, 15.777 ; c = 10.202, 10.661, 10.925 ; R = 3.3, 3.8, 3.4%; Rw = 6.7, 3.3, 3.5%, respectively). The last of these presented twinning difficulties endemic to this structure type, but these were overcome satisfactorily by an approximate separation procedure. R-M distances in the clusters are short; Pr-Co = 2.770, Y-Fe = 2.621, and Sc-Co = 2.431 . While MO theory provides some useful guides to these compounds' stability, the true breadth of the chemistry possible remains to be explored. 1988, American Chemical Society. All rights reserved.
