DFT Study of the Tetranuclear Lutetium and Yttrium Polyhydride Cluster Complexes [(C₅Me₄SiMe₃)₄Ln₄H₈] (Ln = Lu, Y) that Contain a Four-Coordinate Hydrogen Atom

DFT calculations revealed some unprecedented aspects of the structure of the tetranuclear lutetium and yttrium polyhydride complexes [(C 5 Me 4 SiMe 3 ) 4 Ln 4 H 8 ] (Ln = Lu, Y). In contrast with the previously described X-ray analysis of (C 5 Me 4 SiMe 3 ) 4 Lu 4 H 8, which suffered from a serious disorder problem and showed a C 2 v -symmetrical structure with one body-centered μ 4 -H, two face-capped μ 3 -H, and five edge-bridged μ 2 -H atoms, the present DFT studies indicated that the optimized Ln 4 H 8 core prefers a pseudo- C 3 v -symmetrical structure with one body-centered μ 4 -H, one face-capped μ 3 -H, and six edge-bridged μ 2 -H atoms. Metal−metal orbital interactions via the hydride bridges were also observed in these complexes. The μ 4 -H bonding fashion, a new bonding mode for hydrogen, was well proved by the Wiberg bond indexes and linear overlap bond orders. The X-ray structure of (C 5 Me 4 SiMe 3 ) 4 Y 4 H 8, which was solved without suffering from the disorder problems, showed excellent agreement with the theoretical calculations.