Self-Assembly of Hydrogen-Bonded Cage Tetramers of Phosphonic Acid

Abstract

The self-association of phosphonic acids with general formula RP(O)(OH)2 in solution state remains largely unexplored. The general understanding is that such molecules form multiple intermolecular hydrogen bonds, but the stoichiometry of self-associates and the bonding motifs are unclear. In this work, we report the results of the study of self-association of tert-butylphosphonic acid using low temperature liquid-state 1H and 31P NMR spectroscopy (100 K; CDF3/CDF2Cl) and density functional theory (DFT) calculations. For the first time, we demonstrate conclusively that polar aprotic medium tert-butylphosphonic acid forms highly symmetric cage-like tetramers held by eight OHO hydrogen bonds, which makes the complex quite stable. In these associates. each phosphonic acid molecule is bonded to three other molecules by forming two hydrogen bonds as proton donor and two hydrogen bonds as proton acceptor. Though the structure of such cage-like tetramers is close to tetrahedral, the formal symmetry of the self-associate is C2.

Self-association of diphenylpnictoginic acids in solution and solid state: covalent vs. hydrogen bonding

“…Due to the more flexible geometry and non-planarity of a POOH group compared to carboxylic acids, phosphinic and phosphonic acids are also able to form various cyclic associates in a polar aprotic solution – trimers and tetramers with hydrogen bonds. 15,16…”

“…8,11 Another example of a compound with the XOOH group and ability to participate in hydrogen bonding as the hydrogen bond donor and hydrogen bond acceptor is phosphinic acids R 1 R 2 POOH, which have been actively researched during the past decades. [15][16][17][18][19][20][21] It was found that similar hydrogen-bonded selfassociates of phosphinic acids are stronger than that of carboxylic acids. For example, the dimerization enthalpy of the dimethylphosphinic acid Me 2 POOH is about 23-24 kcal mol À1 19,22 and it is almost twice the enthalpy measured for acetic acid dimers.…”

“…Due to the more flexible geometry and non-planarity of a POOH group compared to carboxylic acids, phosphinic and phosphonic acids are also able to form various cyclic associates in a polar aprotic solution -trimers and tetramers with hydrogen bonds. 15,16 At the moment, the ability of R 2 XOOH acids, with X being arsenic (X = As), the next element of the XVth group, to participate in hydrogen bonding is poorly explored. In early works, it was proposed that self-associates formed by dimethylarsinic acid (R = Me, also known as cacodylic acid) are stronger bonded than diethylarsinic acid ones based on the difference in their melting points.…”

Theoretical Study of closo-Borate Anions [BnHn]2− (n = 5–12): Bonding, Atomic Charges, and Reactivity Analysis

“…Currently, many useful methods focused on structure and reactivity analysis have been described. The quantum theory of atoms in molecules (QTAIM) analysis gives clear information about covalent and non-covalent interactions [28][29][30]. Previously, several closo-borate anions have been calculated by QTAIM analysis [31,32].…”

Modeling of the Response of Hydrogen Bond Properties on an External Electric Field: Geometry, NMR Chemical Shift, Spin-Spin Scalar Coupling

“…Appropriate theoretical calculations make it possible to fully understand the relationship between different parameters of the system under study and to facilitate the search for optimal correlations [27][28][29][30][31]. Such calculations are often the only method for studying weak non-covalent interactions [32][33][34][35][36] or molecular systems with competing interactions [37][38][39][40][41][42]. However, often these calculations require a very careful selection of the systems to be examined.…”