NMR and FTIR studies of coordinate-bonding and intramolecular and intermolecular hydrogen bonding in zinc(II)(3,5-diisopropylsalicylate)₂

Abstract

Carboxylate and salicylic OH coordinate bonding as well as intramolecular and intermolecular hydrogen bonding of bis-3,5-diisopropylsalicylatozinc(II), [Zn^II(3,5-DIPS)₂], with Lewis bases were studied to determine mechanisms accounting for antioxidant reactivity of Zn^II(3,5-DIPS)₂. Apparent thermodynamic parameters: K _eq, ΔS ⁰, ΔH ⁰, and ΔG ⁰ were determined for these equilibria with bonding of two molecules of dimethyl sulfoxide-d₆ (DMSO) or ethyl acetate-d₈ (EA) to the Zn^II using NMR and FTIR. We conclude that addition of two equivalents of DMSO or EA to non-polar solutions of Zn^II(3,5-DIPS)₂ results in bonding of DMSO or EA to Zn^II via sulfoxide or ester carbonyl oxygen atoms with ternary complex formation, leading to weakening of carboxylate and salicylic OH coordinate bonding to Zn^II and strengthening intramolecular hydrogen bonding between protons of salicylic OH groups and carboxylate oxygens. Subsequent addition of two or three additional equivalents of DMSO or EA leads to intermolecular hydrogen bonding between protons of salicylic OH groups.

Keywords:

• Bis-3,5-diisopropylsalicylatozinc(II)
• NMR
• FTIR
• Coordinate bonding
• Intramolecular and intermolecular hydrogen bonding

Acknowledgements

NMR studies were supported by the NFSAT (Armenia) fund (Grant LTTG 2003/06) and FTIR studies were supported by ANSEF (US) fund (grant) and the Armenian Ministry of Science and Education (Grant N 1-22-1292). We thank Essential Metalloelement Analyses Laboratory (USA), and Dr. Garik Martirosyan, Dr. Alexander Schahchatuni, and Dr Henrik Panosyan, Molecular Structure Research Center NAS of Armenia, for their practical assistance.