Nature of Guest Species within Alkaline Earth—Ammonia Intercalates of Titanium Disulfide

Alkaline earth-ammonia intercalated compounds of lamellar titanium disulfide have been investigated using thermogravimetric analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy, evolved gas analysis, and inelastic neutron-scattering spectroscopy. Two energetically distinguishable molecular ammonia species, one weakly bound and the other complexed with alkaline earth cations, were found to coexist with metal and ammonium cations. The energies required to deintercalate these species are 13, 19, and 22 kcal/mol, respectively. Vibrational motions associated with complexed ammonia were observed in addition to those from uncomplexed ammonia. The weakly bound NH₃ exhibited vibrational bands at 290 and 345 cm⁻¹. The most prominent vibrational modes for the complexed ammonia were the NH₃ torsion and rock whose frequencies were 167 and 470 cm⁻¹, respectively, in the calcium intercalates. A change in the cation from Ca²⁺ to Sr²⁺ to Ba²⁺ resulted in a shift of the NH₃ rocking mode frequency from 470 to 460 to 425 cm⁻¹, respectively. In this work the nature of the guest species in TiS₂ has been thoroughly characterized, and strong evidence is presented for the existence of distinct molecular ammonia species.