Quadruple bonds ligand substitution

While certain reactions of complexes which contain the M2L8 skeleton, and M-M quadruple or triple bonds (i.e. molecules of classes (a) and (B), vide supra), resemble those of dimers of classes (C) and (D), other aspects of their chemical reactivity are noticeably different. They resemble dimers (c) and (D) in undergoing ligand substitution reactions(2.), Lewis base associations (particularly in the case of carboxylate-bridged dimers of the type M2(02CR)u)( ) and dimer to cluster transformations, recent examples of the latter being M2 -----M3 (triangular)(15., 16),... 

Mo2(H20)8+ is one of only three dimeric aqua ions with no bridging ligands (Hgf and Rh are the others). The structure 5 is eclipsed with 6-bond formation and quadruple metal-metal bonding. A rapid pre-equilibrium involving substitution of anion into the axial (end) waters. 

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