High coordination number actinide-noble gas complexes; a computational study

Abstract

The geometries, electronic structures and bonding of early actinide-noble gas complexes are studied computationally by density functional and wavefunction theory methods, and byab initiomolecular dynamics. AcHe183+is confirmed as being an 18-coordinate system, with all of the He atoms accommodated in the primary coordination shell, and this record coordination number is reported for the first time for Th4+and Th3+. For Pa and U in their group valences of 5 and 6 respectively, the largest number of coordinated He atoms is 17. For AnHe17q+(An = Ac,q= 3; An = Th,q= 4; An = Pa,q= 5; An = U,q= 6), the average An-He binding energy increases significantly across the series, and correlates linearly with the extent of He → Anq+charge transfer. The interatomic exchange-correlation termVxcobtained from the interacting quantum atoms approach correlates linearly with the An-He quantum theory of atoms-in-molecules delocalization index, both indicating that covalency increases from AcHe173+to UHe176+. The correlation energy in AnHe163+obtained from MP2 calculations decreases in the order Pa > U > Ac, the same trend found inVxc. The most stable complexes of Ac3+with the heavier noble gases Ar-Xe are 12 coordinate, best described as Ng12cages encapsulating an Ac3+ion. There is enhanced Ng → Ac3+charge transfer as the Ng gets heavier, and Ac-Ng covalency increases.