Ab initio study of the structure of the hydrogen maleate anion

Abstract

The hydrogen maleate ion was studied by ab initio methods with complete optimization at the 3-21G, 6-31G, 6-31G**, and 6-31+G(2d,1p) levels. To study the influence of electron correlation, MP2 calculations have been done for the 6-31G** geometry. All calculations at the HF level predicted an asymmetric hydrogen bond with a double minimum potential governing transfer between the two equivalent structures. Moreover, both asymmetry and proton transfer barrier increase systematically with the power of the basis set used, with calculated barrier heights of 0.12 (3-21G), 1.59 (6-31G), 1.64 (6-31G**), and 2.00 kcal/mol (6-31+G). Only the introduction of the electron correlation at the MP2 level seems to predict a single minimum potential.

Excited State Intramolecular Proton Transfer in Anionic Analogues of Malonaldehyde

“…The last three columns in Table 4 refer to the proton transfer barriers computed at the MP2 level, using geometries optimized by CIS. Consistent with prior findings, 29,30 electron correlation lowers these transfer barriers. This lowering is particularly large in the case of the nπ* states.…”

“…Of particular relevance, the geometric aspects of the intramolecular H-bond in the various electronic states of 4 -are very similar when compared amongst the 6-31+G*, 6-31+G**, and 6-311+G** basis sets. Analogously, a previous study of the ground state of hydrogen maleate 30 (similar to 6 -) compared basis sets ranging from 3-21G to 6-31+G and 6-31G**; all yielded qualitatively similar conclusions. One may conclude, then, that the results described above for the 6-31+G** basis set would probably not be altered in any important way by further refinements of the basis.…”

Theoretical Study of the Low-Barrier Hydrogen Bond in the Hydrogen Maleate Anion in the Gas Phase. Comparison with Normal Hydrogen Bonds

“…Anyway, it is noteworthy that MP2 D-A distances are shorter than the corresponding Hartree-Fock ones, especially in the maleic monoanion ( 1a ). The O−O distance calculated for this molecule (2.41 Å) is in very good agreement with the corresponding experimental measurements for different salts of hydrogen maleate (2.40−2.44 Å) 2 Most Relevant Geometrical Parameters of the Minimum Energy Structures at the MP2/6-31+G(d,p)//MP2/6-31+G(d,p) Level a D−AD−HA−HD−H−A 1a 2.41 1.12 1.30 178.09 1b 0.97 1c 2.65 0.99 1.67 169.61 1d 0.95 3a 2.64 1.04 1.63 163.19 3b 1.01 1a + H 2 O (A) 2.45 1.06 1.39 176.95 a The labels are defined in Schemes and .…”

“…These changes demonstrate the effect of the environment. Until now, theoretical calculations have shown that the hydrogen bond in the maleic monoanion is asymmetrical with a double well at the Hartree−Fock level using different basis sets, ,, although the introduction of electron correlation at MP2 level, keeping the Hartree-Fock optimized geometries frozen, seems to predict a single well. , However our MP2 results still yield two minima, although geometrically much closer than our two Hartree-Fock minima. That is, the interconversion between the two minima involves a hydrogen jump of about 0.49 Å at Hartree-Fock level, but of only 0.18 Å at MP2 level.…”

Probing the Low-Barrier Hydrogen Bond in Hydrogen Maleate in the Gas Phase: A Photoelectron Spectroscopy and ab Initio Study

“…One system that has been widely studied for LBHB is the maleic/fumaric acid monoanion ( cis -/ trans -HO 2 CCHCHCO 2 - ), ,− due to the existence of a LBHB in the maleic acid monoanion (hydrogen maleate). Several experimental and theoretical studies have been designed to measure the hydrogen bond strength in hydrogen maleate. − The reported values cover a rather wide energy range.…”