Fluosilicic acid reacts with solutions of N , N -di-tert-butylurea (DTBU) in methanol or acetone to form crystalline compounds 2DTBU · H 2 SiF 6 and 2DTBU · H 2 SiF 6 · å 2 ëé , which were characterized by the IR and 19 F NMR spectra and mass spectroscopy supplemented by theoretical calculations. According to the data of IR and 19 F NMR spectra, the complexes are hexafluorosilicates of O-protonated DTBU. They undergo hydrolysis in organic media with water traces; their solubility in water is very low (0.10 and 0.14 wt %, respectively). In the DTBU structure, two independent ligand molecules are joined by hydrogen bonds NH···O (N···O) 2.888(5)-2.944(5) Å).