Uncovering the Individual Hydrogen Bond Strengths and Cooperativity in Pure (H2S)n and Mixed (H2O)m(H2S)n (m + n = 2 to 8) Clusters

The present investigation deals with the estimation individual hydrogen bond (HB) energ¬¬y in pure (H2S)n (n = 3 to 8) and mixed (H2O)m(H2S)n (m + n = 2 to 8) clusters. A deeper understanding of individual interactions in these clusters are brought out in terms of energetics. Such a knowledge from the experimental studies is difficult. Therefore, the present investigation is important. The calculated results show that the hydrogen bonding strengths in these clusters range from 0.10 to 11.06 kcal mol-1 at the MP2(full)/aug-cc-pVTZ level. The O-H…O HB being the strongest (0.10 to 11.06 kcal mol-1), followed by O-H…S HB (1.36 to 6.89 kcal/mol), S-H…O HB (1.08 to 6.39 kcal mol-1), and S-H…S HB (1.35 to 4.23 kcal mol-1) being the weakest. The hydrogen bonding energies in dimers follow the same rank ordering, with lower energies due to the loss of cooperativity. Thus, cooperativity contributions in the hydrogen bonding range from 0.83 to 5.96 kcal mol-1. The HB energies in pure (H2S)n clusters are similar but slightly smaller compared to those in mixed (H2O)m(H2S)n (m + n = 2 to 8) clusters. These results provide important insights into the structure and energetics of hydrogen bonding in pure and mixed clusters, and sheds light on the various interactions in chemical and biological systems. Such a profound knowledge of individual energetics is missing from the literature.