Europium Oxalate Ion Association in Water

Abstract

IASSINGd [ilres Brcln( 11, Depnrttr~ent of ilFi'iltes atld Tecl~r~zcc~l Sl~wcys, Ottawa, C(~nada Received March 4, 1066 .-iRSTRACT The partitioning of radiotracer 1"1151fC~~ between aqueous sodium osalate (3a.L) solutions and toluene solutio!ls of thenoyltritluoroaceto~le (HTTz1) has been studied as a function of the oxalate concentrat~on. The pl-I of the aqLleoLrs phase was controlled by Incans of sodiunl acetate -acetic acid ~nixtures and the ionic strength (I) by NaCl or NaCIO.,. The magnit~~des of the stepwise stability constant ratios are disc~~sscd. INTRODUCTIONRare earth -oxalate complexing in solution has been studied extensively by Croutha~llel and Martin (1) and by Seliine (2). The absolute magnitudes of the stability constants of the complexes cannot be compared directly because of the vastly dilierent ionic strengths used in these worlis. However, the ratios of the stepwise stability coilstants are clearly a t variance (Table I). The stepwise stability constallt is defined a s where L is the ligand. Bjerrunl (3) has sho\\.n that for siinple conlplexes where S is a statistical factor and T is a llleasure of the work done in bringing a charged ligand from infinity to its equilibrium position in the 1:2 complex against the repulsive force exerted by already bound ligands. For singly charged ligands that bind to rare earth or transition metal ions it has been shown that T = 1.6 (4, 5). If the cation has Navailable sites and if, for example, the ligand is monodentate,The factor of 2 arises because the probability of a ligand's leaving the 1:2 complex is twice that of a ligand's leaving the 1 : l . The R factor, termed the rest effect, covers those contributions to P that are neitller statistical nor electrostatic. R w-ill be an inlportant entity in stepwise reactions where, for example, the cation coordinatioll number changed.Steric hindrance and metal-ligand covalency are other obvious contributors to R. The nlagnitudes of the ratios of the stepwise stability constants are discussed later in this paper. The solvent extraction -radiotracer technique has proved useful in the study of rare earth ion association reactions in solution (6). The method is particularly applicable in the

Indicator ligands in metal complexation studies: role of 4-(2-pyridylazo)resorcinol in europium carbonate equilibrium investigations

“…However, since the results obtained by using our B1 and S2 data differ by more than a factor of two, a few contrasting features of the two methods should be noted: We suspect that the quality of our B1 results should be somewhat greater than the quality of our B2 results due to the considerably smaller absorbance signal in that portion of our data most responsible for defining B2. We note additionally that, in conjunction with the estimates log ox3i = 4.9 (3,(15)(16)(17)(18)(19) and log ß ~5.86 (2, 3), calculations with eq 20 and 21 are in excellent accord. The values of B0 implied by eq 14 and our 0 2 results are 575 at pH 7.6 and 1230 at pH 8.0.…”

“…log oxB2 + log ß2 (15) and we note that previous analyses, through a variety of methods (3,(15)(16)(17)(18)(19), provide the oxalate formation constant result appropriate to our conditions, log 0 32 = 8.7 ± 0.05.…”

In Situ Analysis of Europium Calcium Oxalate Crystallization Using Luminescence Microspectroscopy

“…Differences in the ionic equilibrium properties of Ca 2+ and Eu 3+ should also be considered. Eu 3+ hydrolyzes water more effectively, is more strongly hydrated, and forms more stable complexes with both OH - and C 2 O 4 2- . , …”

“…Eu 3+ hydrolyzes water more effectively, is more strongly hydrated, and forms more stable complexes with both OHand C 2 O 4 2-. 19,20 The inhibitory effect of trace metal ions on ionic crystal growth is well established and has been linked to the large dehydration energy and low dehydration frequency of the impurity metal. 21,22 The fact that Eu 3+ ions are strongly hydrated in aqueous solution is thus consistent with their inhibitory behavior in our experiments.…”

“…It is reasonable to conclude that a partially hydrated Eu 3+ ion or complex strongly adsorbs at active growth sites, inhibiting growth. Strong adsorption is inferred from the fact that Eu 3+ exhibits high affinity for oxalate anions 20 and forms stable, innersphere complexes in solution. We also observe strong 5 D 0 f 7 F 2 emission bands in our LMS experiments, indicating that the Eu 3+ site symmetry has been broken, most likely by replacing one or more coordinating waters with an anionic ligand at the surface.…”