We examine the bonding possibilities of the bis(phenalenyl) MP2 sandwich complexes of the divalent metals M = Be, Mg, Ca, Sr, Ba, Zn, Cd, and Hg, at the B3LYP level of theory. The outcome is an extraordinarily diverse class of low symmetry bis(phenalenyl)metal complexes in which bonding preferences and binding enthalpies differ dramatically. The lowest energy group 2 metal MP2 complexes include an intriguing η1,η3 BeP2 structure, and bent η6,η6 systems for M = Ca, Sr, and Ba. The group 12 bis(phenalenyl) complexes are thermodynamically unstable η1,η1 slip-sandwich structures. To better understand changes in the structural preferences going from the (η6,η6) group 2 to the (η1,η1) group 12 complexes, we explored the bonding in the bis(phenalenyl) complexes of transition metals with stable +2 oxidations states between Ca and Zn in period 4. The computed binding enthalpies are large and negative for nearly all of the minimum energy bis(phenalenyl) complexes of the group 2 and the transition metals; they are tiny for MgP2, and are quite positive for the group 12 systems. The structural preferences and stability of the complexes is a subtle negotiation of several influences: the (un)availability of (n - 1)d and np, orbitals for bonding, the cost of the rehybridization at carbon sites in the phenalenyl rings in preparation for bonding to the metals, and the (P—P) interaction between the phenalenyl radicals.
Copyright © 2009 American Chemical Society. This article first appeared in Inorganic Chemistry 48:13 (2009), 5810-5819.
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Craciun, Smaranda, and Kelling J. Donald. "Radical Bonding: Structure and Stability of Bis(Phenalenyl) Complexes of Divalent Metals from across the Periodic Table." Inorganic Chemistry 48, no. 13 (2009): 5810-5819. doi:10.1021/ic900058q.