Energetic Ordering of Hydrogen Bond Strengths in Methanol-Water Clusters: Insights via Molecular Tailoring Approach |
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Authors: | Deepak Patkar Mini Bharati Ahirwar Dr. Milind M. Deshmukh |
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Affiliation: | Department of Chemistry, Dr. Harisingh Gour Vishwavidyalaya, A Central University), Sagar, 470003 India |
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Abstract: | In this work, we examine the strength of various types of individual hydrogen bond (HB) in mixed methanol-water MnWm, (n+m=2 to 7) clusters, with an aim to understand the relative order of their strength, using our recently proposed molecular tailoring-based approach (MTA). Among all the types of HB, it is observed that the OM−H…OW HBs are the strongest (6.9 to 12.4 kcal mol−1). The next ones are OM−H…OM HBs (6.5 to 11.6 kcal mol−1). The OW−H…OW (0.2 to 10.9 kcal mol−1) and OW−H…OM HBs (0.3 to 10.3 kcal mol−1) are the weakest ones. This energetic ordering of HBs is seen to be different from the respective HB energies in the dimer i. e., OM−H…OM (5.0 to 6.0 kcal mol−1)>OW−H…OM (1.5 to 6.0 kcal mol−1)>OM−H…OW (3.8 to 5.6 kcal mol−1)>OW−H…OW (1.2 to 5.0 kcal mol−1). The plausible reason for the difference in the HB energy ordering may be attributed to the increase or decrease in HB strengths due to the formation of cooperative or anti-cooperative HB networks. For instance, the cooperativity contribution towards the different types of HB follows: OM−H…OW (2.4 to 8.6 kcal mol−1)>OM−H…OM (1.3 to 6.3 kcal mol−1)>OW−H…OW (−1.0 to 6.5 kcal mol−1)>OW−H…OM (−1.2 to 5.3 kcal mol−1). This ordering of cooperativity contribution is similar to the HB energy ordering obtained by the MTA-based method. It is emphasized here that, the interplay between the cooperative and anti-cooperative contributions are indispensable for the correct energetic ordering of these HBs. |
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Keywords: | methanol-water clusters hydrogen bond strengths cooperativity molecular tailoring-based approach |
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