Homoleptic Poly(nitrato) Complexes of Group 14 Stable at Ambient Conditions

Using a novel approach in homoleptic nitrate chemistry, Sn­(NO3)62− (3c) as well as the previously unknown hexanitrato complexes Si­(NO3)62− (1c), Ge­(NO3)62− (2c) were synthesized from the element tetranitrates as salt-like compounds which were isolated and characterized using 1H, 14N, and 29Si NMR and IR spectroscopies, elemental and thermal analyses, and single-crystal XRD. All hexanitrates are moderately air-sensitive at 298 K and possess greater thermal stability toward NO2 elimination than their charge-neutral tetranitrato congeners as solids and in solution. The complexes possess distorted octahedral coordination skeletons and adopt geometries that are highly symmetric (3c) or deformed (1c, 2c) depending on the degree of steric congestion of the ligand sphere. As opposed to the κ2O,O′ coordination mode reported for Sn­(NO3)4 previously, all nitrato ligands of 3c coordinate in κ1O mode. Six geometric isomers of E­(NO3)62− were identified as minima on the PES using DFT calculations at the B3LYP/6-311+G­(d,p) level of which two were observed experimentally.