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(OiPr)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 R-factor was 8.63% for 16,014 reflections.