DFT calculations have been carried out on the organometallic clusters [(η-C 5 H 5 )TiN] 4 and [Cl 3 MoN] 4 with the aim of comparing the energies and the electronic structures of the cubane and planar forms for these two clusters. Calculations indicate for the titanium cluster that the cubane conformation is much more stable than the structure in which the four metals and the four nitrogens are in the same plane, whereas the square planar structure is preferred for the molybdenum complex. The octahedral coordination of the metal in the cubane-like form implies an important reorganization of the [Cl 3 MoN] unit. The high cost of this reorganization explains the relative stability of the square planar conformation in that case. Metal-metal interactions have been characterized in the vanadium cubanes [(η-C 5 H 5 )V(µ 3 -X)] 4 , X ) N, P, and As. The distortion of the cage observed in some cubanes is discussed in relation to the metal-metal bonding interactions evidenced in these clusters.

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