Computational Study of Very High Spin Actinyl Peroxide Matryoshka Nanoclusters

Generalised gradient approximation and hybrid density functional theory is used to study the geometries, electronic structures and spin state energetics of a series of high symmetry multi-layer “Matryoshka” actinyl peroxide manganese nanoclusters “E@Mn12@An20n+” (An = U, Np, Pu; E = S, Se, Te, n = 2; E = Br, n = 3; E = Xe, n = 4). These systems are all highly open shell, with up to 100 unpaired electrons in the case of the highest spin state plutonyl complexes. Very strong linear correlations are found in all cases between the number of unpaired electrons and the energies of the complexes, with the highest spin states being much the most stable. We confirm a key conclusion from our previous work in this area (Chemistry, A European Journal 24 (2018) 347) i.e. that the highest spin states of the chalcogen-centred systems are the ground states only when the chalcogen is present; removal of the central group 16 element causes lower spin states to become the most stable. The compositions of the molecular orbitals associated with the changing spin states are studied in detail, and the relative energies of the highest and next highest spin states of the E-free uranyl and plutonyl clusters rationalized on the basis of the characters of the orbitals whose occupation changes between the different spin states.