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 [(C5Me4SiMe3)4Ln4H8] (Ln = Lu, Y). In contrast with the previously described X-ray analysis of (C5Me4SiMe3)4Lu4H8, which suffered from a serious disorder problem and showed a C2v-symmetrical structure with one body-centered μ4-H, two face-capped μ3-H, and five edge-bridged μ2-H atoms, the present DFT studies indicated that the optimized Ln4H8 core prefers a pseudo-C3v-symmetrical structure with one body-centered μ4-H, one face-capped μ3-H, and six edge-bridged μ2-H atoms. Metal−metal orbital interactions via the hydride bridges were also observed in these complexes. The μ4-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 (C5Me4SiMe3)4Y4H8, which was solved without suffering from the disorder problems, showed excellent agreement with the theoretical calculations.