Internal Electric Field-Induced Formation of Exotic Linear Acetonitrile Chains

Abstract

The application of external electric and magnetic fields is a powerful tool for aligning molecules in a controlled way, if the thermal fluctuations are small. Here we demonstrate that the same holds for internal electric fields in a molecular cluster. The electric field of a single molecular dipole, HCl, is used to manipulate the aggregation mechanism of subsequently added acetonitrile molecules. As a result, we could form exotic linear acetonitrile (CH3CN) chains at 0.37 K, as confirmed by infrared spectroscopy in superfluid helium nanodroplets. These linear chains are not observed in the absence of HCl and can be observed only when the internal electric field created by an HCl molecule is present. The accompanying simulations provide mechanistic insights into steric control, explain the selectivity of the process, and show that non-additive electronic polarization effects systematically enhance the dipole moment of these linear chains. Thus, adding more CH3CN monomers even supports further quasi-linear chain growth.

Cooperativity between Intermolecular Hydrogen and Carbon Bonds in ZY···CH3CN/CH3NC···HX Trimers (ZY = H2O, H2S, HF, HCl, HBr, NH3, and H2CO; HX = HF, HCl, and HBr)

“…49 explored the positive and negative cooperativity effects in ternary complexes formed by two imidazole and F 2 TO (T = C, Si, and Ge) molecules. In a high-resolution infrared spectroscopic study, Mani et al 60 Given the importance of the hydrogen-bonding and carbonbonding interactions, a comprehensive understanding of the trends of cooperativity between these two interactions is needed. This prompted us to undertake the current study, in which we have chosen 42 trimeric complexes to study this phenomenon.…”

“…explored the positive and negative cooperativity effects in ternary complexes formed by two imidazole and F 2 TO (T = C, Si, and Ge) molecules. In a high-resolution infrared spectroscopic study, Mani et al found a positive cooperativity between carbon and hydrogen bond in CH 3 CN···CH 3 CN···HCl and HCl···CH 3 CN···HCl trimers, which was reflected in the observed redshifts in the stretching frequencies of the hydrogen-bonded HCl in the trimers as compared to that in the hydrogen-bonded CH 3 CN···HCl dimer.…”

“…The geometries of all the complexes under investigation were optimized at Mo̷ller-Plesset perturbation (MP2) (full) level of theory using 6-311++G(2d,2p) basis sets using Gaussian16 software suite . We note that the calculated vibrational spectra for (CH 3 CN) m (HCl) n complexes ( m = 1–3, n = 1–2), using this level of theory, were close to the experimentally observed spectra for these complexes . Harmonic vibrational frequency analysis for each of the complexes was also performed which verified that all optimized complexes are true minima, as confirmed by the absence of any imaginary frequency.…”

“…69 We note that the calculated vibrational spectra for (CH 3 CN) m (HCl) n complexes (m = 1−3, n = 1−2), using this level of theory, were close to the experimentally observed spectra for these complexes. 60 Harmonic vibrational frequency analysis for each of the complexes was also performed which verified that all optimized complexes are true minima, as confirmed by the absence of any imaginary frequency. The interaction energy of each complex was calculated by subtracting the sum of the energies of optimized individual monomers from the energy of the complex.…”

“…Another rationale for choosing these complexes is that these should be accessible experimentally under ultracold conditions provided by superfluid helium nanodroplets , and thus can be studied using techniques such as high-resolution infrared spectroscopy. The ultracold helium nanodroplets (temperature 0.4 K) facilitate stepwise growth of molecular aggregates, and at such low temperatures, the aggregation of polar molecules is predominantly governed by electrostatic steering, which can lead to the formation of such local minimum structures. ,− …”