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Comparison of Hydrogen Elimination from Molecular Zinc and Magnesium Hydride Clusters
Author(s) -
Intemann Julia,
Sirsch Peter,
Harder Sjoerd
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201402141
Subject(s) - hydride , chemistry , zinc , crystallography , inorganic chemistry , magnesium hydride , cluster (spacecraft) , magnesium , hydrogen bond , molecule , metal , organic chemistry , computer science , programming language
In analogy to the previously reported tetranuclear magnesium hydride cluster with a bridged dianionic bis‐β‐diketiminate ligand, a related zinc hydride cluster has been prepared. The crystal structures of these magnesium and zinc hydride complexes are similar: the metal atoms are situated at the corners of a tetrahedron in which the vertices are bridged either by dianionic bis‐β‐diketiminate ligands or hydride ions. Both structures are retained in solution and show examples of H − ⋅⋅⋅H − NMR coupling (Mg: 8.5 Hz; Zn: 16.0 Hz). The zinc hydride cluster [ NN ‐(ZnH) 2 ] 2 thermally decomposes at 90 °C and releases 1.8 equivalents of H 2 . In contrast to magnesium hydride clusters, there is no apparent relationship between cluster size and thermal decomposition temperature for the zinc hydrides. DFT calculations reproduced the structure of the zinc hydride cluster reasonably well and charge density analysis showed no bond paths between the hydride ions. This contrasts with calculations on the analogous magnesium hydride cluster in which a counter‐intuitive H − ⋅⋅⋅H − bond path was observed. Forcing a reduced H − ⋅⋅⋅H − distance in the zinc hydride cluster, however, gave rise to a H − ⋅⋅⋅H − bond path. Such weak interactions could play a role in H 2 desorption. The presumed molecular product after H 2 release, a Zn(I) cluster, could not be characterized experimentally but DFT calculations predicted a cluster with two localized ZnZn bonds.