Ab Initio MO Study on the Reaction Mechanism of Reduction of Hypophosphorous Acid

Abstract

The reduction mechanism of hypophosphorous acid has been investigated by ab initio calculations at the MP2/6-311G͑d,p͒ and CBS-QB3 levels. Two mechanisms with three possible pathways have been proposed for the process. The first mechanism that can be viewed as a direct mechanism contains two possible pathways, giving H 3 PO 2 + H → P + 2H 2 O. The other, as an indirect mechanism, is H 3 PO 2 + 2H → PH 3 + 2OH − . Theoretical calculations predict four transition states with the highest barrier height of 37.7 kcal/mol in the indirect mechanism, which is the most likely pathway compared to others.To form the nickel phosphorus alloy film by electroless plating or electroplating, hypophosphite can be used as a reactant to supply the phosphorus atom. 1 The performance of the alloy film is, usually, predominated by the content of phosphorus in the coatings. [2][3][4][5] In order to control the content, it is necessary to know the details of the reduction process of hypophosphorous acid, although it is not fairly understood.The mechanism of the reduction of hypophosphorous acid has been a subject of intense debate in electrochemistry. At least two mechanisms have been proposed. One of them, referred to as a direct mechanism, considered the direct reduction of hypophosphite to phosphorus element. On the contrary, the other follows an indirect mechanism via phosphine formation, which transfers to phosphorous element. 6-10 Both cases contain the bond breakage and formation of phosphorus species.Many researches have been reported on the reactions that H and OH species react with phosphorous oxides and acids, theoretically. Homma and his co-workers 11,12 applied ab initio molecular orbital method to study oxidation of hypophosphite ion via different intermediates at the level of MP2/6-311G͑d,p͒. Mackie et al. 13,14 and Twarowski 15,16 have reported the results of quantum chemistry calculations on the recombination of H and OH catalyzed by the phosphorous oxides and acids, such as PO 2 , HOPO, and HOPO 2 . They thought phosphorous oxides and acids should be capable of undergoing reactions of addition with OH or H and subsequent decomposition of recombination products. 14 In this study, we performed theoretical investigations on the reduction of hypophosphorous acid from three possible pathways. Our purpose is to clarify the indirect mechanism in this process. To our knowledge, no experimental data regarding the details of the reaction mechanism and the possible intermediates are available so far. We attempt to give insight into the mechanism details by increasing our calculation accuracy. This work may, then, pave the way for further considering the real surroundings, including the solvent effect, electrode effect, and electric field effect. Computational MethodsTheoretical calculations were carried out with a Gaussian 03 program package. 17 The geometries of the reactants, products, intermediates, and transition states were optimized at the MP2/6-311͑d,p͒ level. Harmonic vibrational frequency calculations for zero-point ener...

Role of p-Hydroxybenzhydrazide Additive in Electrodeposition of Thin NiP Film Used as a Nonmagnetic Spacer in Laminated (CoFe/NiP) Nano Structures

“…The ab initio MO study of reduction of phosphorous acid indicates that some of the protonation steps might be the rate limiting. 26 Figure 3 shows results of the effect of the controlled electrode potential of Pt-RDE on the deposition of NiP films obtained from the plating solution containing p-HBHy organic additive. The current transients in Fig.…”