A research paper co-authored by Dr Brijesh Kumar Mishra, Associate Professor, Chemistry, SIAS titled Cluster-size-dependent cooperativity in sulfur-centred hydrogen bonds: ethane-1,2-dithiol with HF, H2O, and NH3 has been published in Physical Chemistry Chemical Physics (PCCP).
Abstract
Ethanedithiol (EDT) complexed with one to three solvent molecules (HF, H2O, and NH3) was computationally investigated systematically to elucidate how hydrogen-bond donor identity and cluster size govern the structure, energetics, and spectroscopic signatures of sulfur-centred hydrogen bonds (SCHBs). All clusters were optimised at the MP2/aug-cc-pVTZ level and confirmed as true minima by harmonic frequency calculations, while accurate interaction energies were obtained from high-level coupled-cluster single-point calculations.
DLPNO-CCSD(T)/aug-cc-pVQZ interaction energies were employed as a uniform reference for all cluster sizes (n = 1–3). These were benchmarked against CCSD(T)/aug-cc-pVQZ calculations for monomer and dimer systems (n ≤ 2), showing very good agreement, with deviations typically within ∼0.1–0.7 kcal mol−1. The most stable assemblies predominantly adopt cyclic or quasi-cyclic hydrogen-bonding networks featuring bifunctional binding, in which the solvent donates X–H…S and may also accept S–H…X interactions. Interaction energies increase monotonically with cluster size and establish a clear stability hierarchy, EDT–(HF)n > EDT–(H2O)n > EDT–(NH3)n, with the most stable trimers bound by approximately 19.2, 18.4, and 12.1 kcal mol−1, respectively, at the DLPNO-CCSD(T)/aug-cc-pVQZ level. Vibrational analysis revealed direct spectroscopic evidence of hydrogen-bond strengthening and cooperativity with an exceptionally large red shift (up to ∼513 cm−1) exhibited by the H–F stretching mode, and a moderate red shift shown by the O–H and N–H stretching modes. Complementary atoms-in-molecules (AIM) analysis identified F–H…S as the strongest hydrogen bond through elevated electron densities at the bond critical points (up to ∼0.033 a.u.), providing quantitative benchmarks for solvent-dependent SCHB cooperativity and clarifying how hydrogen-bonding motifs govern the stability and spectroscopic response of EDT–solvent clusters.
