Abstract: | Upon reacting SeCl4 with Me3Si–F–Al(ORF)3, the selenonium salt SeMeCl2al‐f‐al] ( 1 ) {al‐f‐al]– = FAl(OC(CF3)3)3]2]–} was obtained and characterized by NMR, IR, and Raman spectroscopy as well as single crystal XRD experiments. Despite the SeX3]+ (X = F, Cl, Br, I) and SeR3]+ salts (R = aliphatic organic residue) being well known and thoroughly studied, the mixed cations are scarce. The only previous example of a salt with the SeMeCl2]+ cation is SeMeCl2SbCl6], which was never structurally characterized and is unstable in solution over hours. Only 1H‐NMR studies and IR spectra of this compound are known. The unexpected use of Me3Si–F–Al(ORF)3 as a methylating agent was investigated via DFT calculations and NMR experiments of the reaction solution. The reaction of SeCl3al‐f‐al] with Me3Si‐Cl at room temperature in CH2Cl2 proved to yield the same product with Me3Si–Cl acting as a methylating agent. |