Studies of metal carbonate equilibria. Part 15. The beryllium(II)–water–carbon dioxide(g) system in acidic 3.0 mol dm–3 perchlorate media
The complex-formation equilibria in the system BeII–H2O–CO2(g) have been studied by e.m.f. techniques in 3.0 mol dm–3(Na)ClO4 at 25 °C in the range 2.0 ⩽ log h⩽ 6.2, where h is the free hydrogen-ion concentration. The total metal concentration, B, has been varied from 1 to 80 mmol dm–3 and the partial pressure of CO2 from 0.1 to 0.97 atm. The e.m.f. data obtained can be explained by assuming, in addition to previously proposed hydrolytic species, the temary equilibria (i)–(iv). The stability constants of the mixed complexes are as follows: log β331=–8.90 ± 0.02, 3Be2++ 3H2O + CO2(g)⇌[Be3(OH)3(CO2)]3++ 3H+(i), 5Be2++ 6H2O + CO2(g)⇌[Be5(OH)6(CO)2]4++ 6H+(ii), 6Be2++ 9H2O + 2CO2(g)⇌[Be6(OH)9(CO2)2]3++ 9H+(iii), Be2++ 2H2O + CO2(g)⇌ Be(OH)2(CO2)+ 2H+(iv) log β561=–17.24 ± 0.04, log β692=–29.46 ± 0.06, and log β121=–10.4 ± 0.1. The Raman spectra of concentrated solutions containing the different mixed complexes have been recorded. From these results tentative structures for the mixed hydroxo–carbonato complexes are proposed and discussed. The (1,2,1), (3,3,1), and (5,6,1) complexes are suggested to possess stoicheiometries BeCO3,[Be3(OH)2(HCO3)]3+, and [Be5(OH)4(CO3)]4+ respectively.