The space between: Neutron diffraction studies reveal multiple hydrogen atom coordination numbers in an anionic dysprosium hydride cluster

Our single-crystal neutron diffraction results unambiguously reveal a four-coordinate H atom located in the center of a soluble organometallic tetrahedral complex [Li(THF)₄][(C₅Me₄SiMe₃)₄Dy₄(μ-Cl)(μ-H)₈]. The core of the molecule consists of a tetranuclear cluster with one interstitial, two face-bridging and five edge-bridging hydride ligands. The four Dy-H distances to the interstitial hydride ligand are 2.249(9), 2.255(9), 2.157(12) and 2.160(12) ?. The compound was prepared via the reaction of [(C₅Me₄SiMe₃)₄Dy₄(μ-H)₈(THF)₂] with LiCl. Neutron data collected on a 3 mm³ pale-yellow single crystal on the Quasi-Laue diffractometer VIVALDI at I.L.L. (Grenoble) which gave an agreement factor R = 10.1% in the final structure refinement against 6947 reflections. The existence of a four-coordinate hydrogen reinforces previous results observed with a series of high-connectivity hydride ligands located at the interstitial cavities of molecular clusters. Interestingly, this structure allows us to analyze simultaneously three different types of hydride coordination in the same molecule (M₂(μ₂-H), M₃(μ₃-H), and M₄(μ₄-H)).