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

The geometries, electronic structures and bonding of early actinide-noble gas complexes are studied computationally by density functional and wavefunction theory methods, and by ab initio molecular dynamics. AcHe 18 3+ 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 Th 4+ and Th 3+ . For Pa and U in their group valences of 5 and 6 respectively, the largest number of coordinated He atoms is 17. For AnHe 17 q + (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 → An q + charge transfer. The interatomic exchange-correlation term V xc obtained 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 AcHe 17 3+ to UHe 17 6+ . The correlation energy in AnHe 16 3+ obtained from MP2 calculations decreases in the order Pa > Th > U > Ac, the same trend found in V xc . The most stable complexes of Ac 3+ with the heavier noble gases Ar-Xe are 12 coordinate, best described as Ng 12 cages encapsulating an Ac 3+ ion. There is enhanced Ng → Ac 3+ charge transfer as the Ng gets heavier, and Ac-Ng covalency increases. Computational quantum chemical techniques are used to explore charged actinide-noble gas compounds, including new Th-He systems with record coordination number.