Infrared spectroscopy of Ca(NH3) complexes

Mg(II) and Ca(II) Microsolvation by Ammonia: Born–Oppenheimer Molecular Dynamics Studies

“…The signals in the spectra below 1000 cm –1 correspond to the metal–NH 3 modes; for both cations, these modes begin to blur into one broad band as the cluster size increases. As mentioned before, no experimental IR spectra have been reported for [Ca­(NH 3 ) n ] 2+ dicationic species; however, it is worth noting that the experimetal IR spectra of [Ca­(NH 3 ) n ] + are consistent with a octacoordinated structure with Ca + as the central atom, which is the same type of structure found for Ca 2+ in our BOMD simulations.…”

“…On the other hand, our results agree with the proposed structure for the [Ca­(NH 3 ) 5 ] 2+ cluster . However, it is important to keep in mind that the experimental assignment of a coordination arrangement is done indirectly, usually by comparing the experimental infrared (IR) spectrum with that obtained from DFT calculations on some low-energy candidate isomer. ,,, Using this approach to identify a coordination pattern can be a very difficult task given that different isomers with different HB networks may exist, besides the fact that anharmonicities in the calculated spectra are not taken into account. In this sense, the dynamical results from BOMD simulations can be of great help in interpreting the experimental results.…”

“…A broad band can be observed between approximately 3300 and 3700 cm –1 for both dications, and these bands correspond to the N–H stretching modes; a slight blue shift is observed in this band as the cluster size increases and the NH 3 molecules populate the second solvation shell. Similar behavior was observed for the Ca­(NH 3 ) 0,+ species . The two peaks due to the H–N–H wagging and H–N–H scissoring modes (located at around 1470 and 1700 cm –1 when n = 2, respectively) begin to separate from one another when n increases; the former is red-shifted as the cluster size increases until the band is located at approximately 1200 cm –1 and the latter remains almost unchanged.…”

“…The vibrational frequencies are helpful in identifying isomers and the arrangement of solvated ion clusters. In this sense, gas-phase infrared (IR) spectroscopy has been employed along with DFT calculations to derive structural information on solvated ions in the gas phase. ,,, To the best of our knowledge, experimental IR spectra have been reported only for the neutral and cationic Mg­(NH 3 ) + and Ca­(NH 3 ) n 0,+ species, , thus a direct comparison with our theoretical predictions was not possible. The calculated spectra are shown in Figures and .…”

Scandium in Neutral and Positively Charged Ammonia Complexes: Balancing between Sc2+ and Sc3+

“…It should be mentioned that lithium–SEPs, their anions, and their dimers are all present in intermediate concentrations of lithium–ammonia solutions, while saturated metal–ammonia solutions produce the poorly studied liquid metal materials . Our results provide deeper understanding of such materials and assist future spectroscopic studies on isolated (gas-phase) metal–ammonia complexes, such as the ones appeared very recently in the literature on calcium and chromium ammonia complexes, , which indicates the increasing interest in these systems.…”