Selenourea-Ca²⁺ reactions in gas phase. Similarities and dissimilarities with urea and thiourea

The gas-phase reactions between Ca²⁺ and selenourea were investigated by means of electrospray/tandem mass spectrometry techniques. The MS/MS spectra of [Ca(selenourea)]²⁺ complexes show intense peaks at m/z 43, 121, 124, and 146 and assigned to monocations produced in different coulomb explosion processes. The structures and bonding characteristics of the stationary points of the [Ca(selenourea)]²⁺ potential energy surface (PES) were theoretically studied by DFT calculations carried out at the B3LYP/6-311+G(3df,2p)// B3LYP/6-311+G(d,p) level. The analysis of the topology of this PES allows identification of H₂NCNH⁺, CaSeH ⁺, selenourea^+. and CaNCSe⁺ ion peaks at m/z 43, 121, 124, and 146, respectively. The reactivity of selenourea and the topology of the corresponding potential energy surface mimic that of thiourea. However, significant dissimilarities are found with respect to urea. The dissociative electron-transfer processes, not observed for urea, is one of the dominant fragmentations for selenourea, reflecting its much lower ionization energy. Similarly, the coulomb explosions yielding CaXH⁺ + H ₂NCNH⁺ (X = O or Se), which for urea are not observed, are very favorable for selenourea. Finally, while in urea the loss of NH ₃ competes with the formation of NH₄⁺, for selenourea the latter process is clearly dominant.