Abstract
The elucidation of formation mechanisms is mandatory for understanding and planning of synthetic routes. For (bio-)organic and organometallic compounds, this has long been realized even for very complicated molecules, whereas the formation of ligand-free inorganic molecules has widely remained a black box to date. This is due to poor structural relationships between reactants and products and the lack of structurally related intermediates—due to the comparably high coordination flexibility of involved atoms. Here we report on investigations of the stepwise formation of multimetallic clusters, based on a series of crystal structures and complementary quantum-chemical studies of (Ge2As2)2−, (Ge7As2)2−, [Ta@Ge6As4]3−, [Ta@Ge8As4]3− and [Ta@Ge8As6]3−. The study makes use of efficient quantum-chemical tools, enabling the first detailed screening of the energy hypersurface along the formation of ligand-free inorganic species for a semi-quantitative picture. The results can be generalized for an entire family of multimetallic clusters.
Highlights
The elucidation of formation mechanisms is mandatory for understanding and planning of synthetic routes
In some cases, intermediate complexes have been isolated that allowed for some understanding of the stepwise release of organic ligands from the used transition metal complexes17–21, but it was not possible to trace back the complicated re-arrangement processes of the smaller Zintl anions in the presence of transition metal atoms
The only difference from previous procedures was the application of a somewhat higher maximum temperature, 950 °C instead of 600 °C at the fusion step, which we initially chose in regard of the higher melting temperature of germanium as compared with those of tin or lead, and which turned out to be necessary to gain Ta atoms from the bulk
Summary
The elucidation of formation mechanisms is mandatory for understanding and planning of synthetic routes. The evaluation of reaction mechanisms is useful and essential for understanding, planning and optimizing chemical reactions in a reasonable and efficient and economical way In organic chemistry, this is a highly common procedure that allowed for the development of the retro-synthetic approach for systematic access of complex target molecules from simpler precursor fragments in the 1980s The design of such clusters has appeared to be very challenging, since for reactions in condensed matter, the very first steps in the formation starting out from atomic, molecular or solid state precursors have essentially remained unexplored so far It would be of great benefit to elucidate these processes to make such particles more generally available. In some cases, intermediate complexes have been isolated that allowed for some understanding of the stepwise release of organic ligands from the used transition metal complexes, but it was not possible to trace back the complicated re-arrangement processes of the smaller Zintl anions in the presence of transition metal atoms
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