Journal
MOLECULES
Volume 25, Issue 8, Pages -Publisher
MDPI
DOI: 10.3390/molecules25081907
Keywords
phosphinic acids; phosphoric acids; hydrogen bond; heterodimers; heterotrimers; heterotetramers; H/D isotope effects; NMR
Funding
- RSF [18-13-00050]
- Russian Science Foundation [18-13-00050] Funding Source: Russian Science Foundation
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Hydrogen-bonded heterocomplexes formed by POOH-containing acids (diphenylphosphoric 1, dimethylphosphoric 2, diphenylphosphinic 3, and dimethylphosphinic 4) are studied by the low-temperature (100 K) H-1-NMR and P-31-NMR using liquefied gases CDF3/CDF2Cl as a solvent. Formation of cyclic dimers and cyclic trimers consisting of molecules of two different acids is confirmed by the analysis of vicinal H/D isotope effects (changes in the bridging proton chemical shift, delta H, after the deuteration of a neighboring H-bond). Acids 1 and 4 (or 1 and 3) form heterotrimers with very strong (short) H-bonds (delta H ca. 17 ppm). While in the case of all heterotrimers the H-bonds are cyclically arranged head-to-tail, center dot center dot center dot O=P-O-H center dot center dot center dot O=P-O-H center dot center dot center dot, and thus their cooperative coupling is expected, the signs of vicinal H/D isotope effects indicate an effective anticooperativity, presumably due to steric factors: when one of the H-bonds is elongated upon deuteration, the structure of the heterotrimer adjusts by shortening the neighboring hydrogen bonds. We also demonstrate the formation of cyclic tetramers: in the case of acids 1 and 4 the structure has alternating molecules of 1 and 4 in the cycle, while in case of acids 1 and 3 the cycle has two molecules of 1 followed by two molecules of 3.
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