Synthetic, Structural, and Theoretical Investigations of Alkali Metal Germanium Hydrides—Contact Molecules and Separated Ions

The preparation of a series of crown ether ligated alkali metal (M=K, Rb, Cs) germyl derivatives M(crown ether) n GeH 3 through the hydrolysis of the respective tris(trimethylsilyl)germanides is reported. Depending on the alkali metal and the crown ether diameter, the hydrides display either contact molecules or separated ions in the solid state, providing a unique structural insight into the geometry of the obscure GeH 3 − ion. Germyl derivatives displaying MGe bonds in the solid state are of the general formula [M([18]crown‐6)(thf)GeH 3 ] with M=K ( 1 ) and M=Rb ( 4 ). The compounds display an unexpected geometry with two of the GeH 3 hydrogen atoms closely approaching the metal center, resulting in a partially inverted structure. Interestingly, the lone pair at germanium is not pointed towards the alkali metal, rather two of the three hydrides are approaching the alkali metal center to display MH interactions. Separated ions display alkali metal cations bound to two crown ethers in a sandwich‐type arrangement and non‐coordinated GeH 3 − ions to afford complexes of the type [M(crown ether) 2 ][GeH 3 ] with M=K, crown ether=[15]crown‐5 ( 2 ); M=K, crown ether=[12]crown‐4 ( 3 ); and M=Cs, crown ether=[18]crown‐6 ( 5 ). The highly reactive germyl derivatives were characterized by using X‐ray crystallography, 1 H and 13 C NMR, and IR spectroscopy. Density functional theory (DFT) and second‐order Møller–Plesset perturbation theory (MP2) calculations were performed to analyze the geometry of the GeH 3 − ion in the contact molecules 1 and 4 .