DFT study of the tetranuclear lutetium and yttrium polyhydride cluster complexes [(C5Me4SiMe3)4Ln4Hs8] (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)(4)Ln(4)H(8)] (Ln = Lu, Y). In contrast with the previously described X-ray analysis of (C5Me4SiMe3)(4)LU4H8, which suffered from a serious disorder problem and showed a C-2v-symmetrical structure with one body-centered mu(4)-H, two face-capped mu(3)-H, and five edge-bridged mu(2)-H atoms, the present DFT studies indicated that the optimized Ln(4)H(8) core prefers a pseudo-C-3v-symmetrical structure with one body-centered mu(4)-H, one face-capped mu(3)-H, and six edge-bridged mu(2)-H atoms. Metal-metal orbital interactions via the hydride bridges were also observed in these complexes. The,mu(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 (C5Me4SiMe3)(4)Y4H8, which was solved without suffering from the disorder problems, showed excellent agreement with the theoretical calculations.