Neutron Diffraction Studies of a Four-Coordinated Hydride in Near Square-Planar Geometry

The structure of a nanospheric polyhydrido copper cluster, [Cu₂₀(H)₁₁{S₂P­(O^<i>i</i>Pr)₂}₉], was determined by single-crystal neutron diffraction. The Cu₂₀ cluster consists of an elongated triangular orthobicupola constructed from 18 Cu atoms that encapsulate a [Cu₂H₅]^3– ion with an exceptionally short Cu–Cu distance. The 11 hydrides in the cluster display three different coordination modes to the Cu atoms: six μ₃-hydrides in a pyramidal geometry, two μ₄-hydrides in a tetrahedral cavity, and three μ₄-hydrides in an unprecedented near square-planar geometry. The neutron data set was collected for 7 days on a small crystal with dimensions of 0.20 mm × 0.50 mm × 0.65 mm using the Spallation Neutron Source TOPAZ single-crystal time-of-flight Laue diffractometer at Oak Ridge National Laboratory. The final <i>R</i>-factor was 8.63% for 16,014 reflections