Calculation of boron-isotope fractionation between B(OH)(3)(aq) and B(OH)(4)(-)(aq)

Journal Article · Sat May 15 00:00:00 EDT 2010 · Geochimica et Cosmochimica Acta, 74(10):2843-2850

DOI:https://doi.org/10.1016/j.gca.2010.02.032· OSTI ID:985001

Rustad, James R; Bylaska, Eric J; Jackson, Virgil E; Dixon, David A

Density functional and correlated molecular orbital calculations (MP2) are carried out on B(OH)3-nH2O clusters (n = 0, 6,32), and B(OH)-4.nH20 (n = 0, 8, 11, 32) to estimate the equilibrium distribution of 10B and 11B isotopes between boric acid and borate in aqueous solution. For the large 32-water clusters, multiple conformations are generated from ab initio molecular dynamics simulations to account for the effect of solvent fluctuations on the isotopic fractionation. We provide an extrapolated value of the equilibrium constant x34 for the isotope exchange reaction 10B(OH)3(aq) + 11B(OH)-4 (aq) = 11B(OH)3(aq) + 11B(OH)-4 (aq) of 1.026-1.028 near the MP2 complete basis set limit with 32 explicit waters of solvation. With some exchange-correlation functionals we find potentially important contributions from a tetrahedral neutral B(OH)3.H2O Lewis acid-base complex. The extrapolations presented here suggest that DFT calculations give a value for 103lnx34 about 15% higher than the MP2 calculations.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 985001
• Report Number(s): PNNL-SA-72955; GCACAK; 25713; 20900; 3563; KC0303020; TRN: US201016%%1649
• Journal Information: Geochimica et Cosmochimica Acta, 74(10):2843-2850, Vol. 74, Issue 10; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BORON HYDROXIDES
AQUEOUS SOLUTIONS
FRACTIONATION
DENSITY FUNCTIONAL METHOD
MOLECULAR ORBITAL METHOD
ISOTOPIC EXCHANGE
SOLVATION
HYDRATES
BORON 10
BORON 11
BORATES
BORIC ACID
MOLECULAR DYNAMICS METHOD
calculation
boron-isotope
fractionation
MP2
water clusters
DFT
Environmental Molecular Sciences Laboratory