Tetracarbon Metallacarboranes 9

Alternative Title

New types of nido cage geometry. Crystal and molecular structures of [(C₆H₅)₂PCH₂]₂Ni(CH₃)₄C₄B₈H₈ (Isomer 1) and (η⁵-C₅H₅)Co(CH₃)₄C₄B₇H₇ (isomer 2)


The structures of the title compounds have been determined by single-crystal X-ray diffraction and consist, respectively, of a 13-vertex nido NiC4B8 and a 12-vertex nido CoC4B7 cage framework. The NiC4B8 cluster resembles a 14-vertex closo polyhedron (bicapped hexagonal antiprism) from which one vertex has been removed and is the first example of a 13-vertex nido cage. The CoC4B7 geometry is also unprecedented and consists of an irregular basket-shaped framework with one carbon atom bridging three framework atoms across the open top of the basket. The two compounds are structurally related, since one can formally convert a CoC4B8 cage (analogous to the NiC4B8) to the observed CoC4B7 species by removal of one BH unit and linkage of two carbon atoms. Such a mechanism is proposed to account for the structure of the CoC4B7 cage. Both species are (2n + 4)-electron frameworks and are formally nido, in agreement with their gross geometries. Crystal data for [(C6H5)2PCH2]2Ni(CH 3)4C4B8H8: mol wt 659.9, space group Pbca, Z = 8; a = 16.666 (2), b = 17.666 (1), c = 24.00 (2) Å; V = 7066 Å3; R = 0.042 for 3144 independent reflections having Fo 2 > 3σ(Fo 2). Crystal data for (η5-C5H5)Co(NH3) 4C4B7H7: mol wt 314.9, space group P21/b (unique axis a), Z = 4; a = 7.930 (3), b = 14.151 (6), c = 14.809 (5) Å; α = 101.2°; V = 1631 Å3; R = 0.047 for 1542 independent reflections having Fo 2 > 3σ(Fo 2). © 1980 American Chemical Society.



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© 1980 American Chemical Society (ACS), All rights reserved.