Different ways to distort a tetracapped tetrahedron on route to forming anE4M4 cubane: The case of [E-4(Pd(PPh2Me)(2))(4)][Ph2EX2](2) (E = Sb, X = Cl; E = Bi, X = Br)

Tetrakis(diphenylmethylphosphine)palladium reacts with diphenylantimony chl oride or diphenyl-bismuth bromide to give [E-4(PdL2)(4)][Ph2EX2](2) (L = PP h2Me, 1: E = Sb, X = Cl; 2: E = Pi, X = Br) which have been characterized s pectroscopically and by single-crystal X-ray diffraction for [Sb-4(PdL2)(4) ][Ph2SbCl2](2). 0.5THF and [Bi-4(PdL2)(4)][Ph2BiBr2](2). These compounds ar e electron-rich based on electron counting formalisms. The additional clust er electrons can be rationalized by the ability of group 15 elements to sho w hypervalency, particularly those elements such as Sb and Pi which show mo re metal character. The electronic structure of the compounds and of relate d species has been examined by EHT and DFT calculations. Relationships to o ther cubane-derived structures are derived, and the stability of structural ly related M4E4 hypothetical clusters is discussed. Compounds 1 and 2 decom pose thermally to give Bi2Pd and SbPd.