A Simple Route to Calcium and Strontium Hydride Clusters

The first Sr hydride complex has been obtained by simply reacting Sr[N(SiMe3)2]2 with PhSiH3 in the presence of PMDTA. The Sr complex Sr6[N(SiMe3)2]3H9∙(PMDTA)3 crystallizes as an "inverse cryptand": an interstitial Hˉ is surrounded by a Sr6H84+ cage decorated with amide and PMDTA ligands. The analogue Ca complex could also be obtained and both retain their solid state structures in solution: 1H NMR spectra in C6D6 show two doublets and one nonet (4:4:1). Up till 90 °C, no coalescence is observed. The Ca cluster was investigated by DFT calculations and shows atypically low charges on Ca (+1.14) and H (-0.59) which signifies an unexpectedly low ionicity. AIM analysis shows hydride∙∙∙hydride bond paths with considerable electron densities in the bond critical point. The clusters thermally decompose in larger, undefined, metal hydride aggregates.