Europium-hydrogen bond distances in saline metal hydrides by neutron diffraction

Europium-hydrogen bond distances in saline metal hydrides have been refined from neutron powder diffraction data on the magnesium-based ternary deuter ides EuMg2D6, EuMgD4, Eu2MgD6, Eu6Mg7D26 and Eu2Mg3D10. Absorption effects were attenuated by choosing neutron energies close to the minimum absorptio n cross section of natural isotope mixtures of europium and by using annula r sample holders on high-flux neutron diffractometers, Some structures requ ired joint refinements of neutron and synchrotron diffraction data. The Eu- D distances found for the various coordination numbers of europium range be tween 237-276 pm (CN=9), 220-287 pm (CN=10). 239-287 pm (CN=11) and 228-299 pm (CN=12). They are closely similar to, but shorter by about 4 pm than th e corresponding Sr-D distances in strontium analogues, thus underlining the analogy between the europium and alkaline-earth hydride chemistry.