Neutron Diffraction Studies on a 4-Coordinate Hydrogen Atom in an Yttrium Cluster

A four-coordinate hydrogen atom has been unambiguously located, by single-crystal neutron
diffraction for the first time, in the center of the tetrahedral metal complex Y4H8(Cp‘)4(THF) [Cp‘=C5Me4(SiMe3)]. The core of the molecule consists of a tetranuclear cluster with one interstitial, one face-bridging,
and six edge-bridging hydride ligands. The compound was prepared via the reaction of YCp‘(CH2SiMe3)2(THF) with gaseous H2. Neutron data were collected on a 4 mm3 crystal at the Quasi-Laue diffractometer
VIVALDI at ILL (Grenoble)1a and on an 8 mm3 crystal at the SXD diffractometer at ISIS (Didcot). The final
agreement factor is R = 8.9% for 4171 reflections. The existence of 4-coordinate hydrogen now completes
the series of high-connectivity hydride ligands located in the interstitial cavities of molecular cluster
complexes. We had previously reported the existence of 6-coordinate hydrogen in the octahedral cavity of
[HCo6(CO)15]- in 1979, and 5-coordinate hydrogen in the square pyramidal cavities of [H2Rh13(CO)24]3- in
1997, also via single-crystal neutron analyses.