A rare dimer of dimers having four hydride linkers joining two quadruply bonded dimolybdenum units

Hydride anions, H-, have been found to cause the assembly of dimolybdenum units Mo2(cis-DAniF)2]2+, DAniF = N,N'-di(p-anisyl)formamidinate, forming a tetranuclear complex Mo2(cis-DAniF)2]2(mu-H)4 (1) with an Mo4H4 core that may be described as an elongated tetrahedron in which the H atoms are along the four long edges of such tetrahedron and the Mo2 units are along the short edges. The two quadruply bonded dimolybdenum units, separated by only 2.718 A, are essentially orthogonal. This gives the shortest Mo2]...Mo2] distance known for complexes with multiple dimolybdenum units. DFT calculations indicate that the energy of a cuboidal isomer is only 3.8 kcal/mol above that of 1, but such an isomer has not been observed.