摘要:
J . CHEM. SOC. DALTON TRANS. 1995 3433Equilibria and Thermodynamic Quantities for the Reactionsof Molybdenum(vi) and Tungsten(v1) with Mandelate(a-Hydroxybenzeneacetate) tJohannes J. Cruywagen" and Elisabeth A. RohwerDepartment of Chemistry, University of Stellenbosch, 7600, South AfricaThe complex formation of molybdate and tungstate with mandelate [PhCH (OH)CO,-] have beeninvestigated in the range pH, 7.5-1.5 by potentiometric, spectrophotometric and enthalpimetrictitrations at 25 "C in 1.0 mol dm-3 NaCI. The potentiometric data were treated with the computerprogram SUPERQUAD taking into account the side-reactions of molybdate and tungstate withhydrogen ions. For both systems the 'best' reaction model comprises only one major complex and anumber of minor complexes.Thermodynamic quantities have been determined for each of the majorcomplexes. For the molybdenum(vt) complex [MOO,(C,H,O,),]~-. log p, = 15.93, AH" = -78.2 andTAS" = 12.7 k J mo1-l respectively and for the tungsten(v1) complex, [W02(C6HS03)2]2-, log p, =17.59, A H = -86.3 and TAS" = 14.1 k J mol-l. The equilibrium constant and the enthalpy change forthe protonation of mandelate have also been determined, log K = 3.1 5 and AH = -0.05 k J mot l. Theenergetics of complexation is discussed in terms of the thermodynamic quantities.Investigations of the reactions of molybdenum(v1) andtungsten(v1) with different a-hydroxycarboxylates have shownthat complexes with various metal-to-ligand ratios, e.g. 1 : I ,2 : 2 and 1 : 2, can occur in For those ligands havingonly one hydroxy and one carboxylic group the preferredstoichiometry appears to be 1 :2.2,395 Only a few of thesecomplexes have been isolated in the solid state and theirstructures determined by single-crystal X-ray analysis.Valuable structural information has been obtained on thecomplexes in solution by NMR analysis and in some cases goodestimates of formation constants were d e d ~ c e d .~ . ~ However,depending on the co-ordination characteristics of the ligand,quite often series of complexes can occur in successiveoverlapping equilibria rendering these systems exceedinglyc~mplicated.~ The relative concentrations of the complexes canvary in a complicated manner with variation in pH and/or totalconcentrations of both metal and ligand.A complete picture ofthe complexation behaviour under varying conditions cantherefore only be established if reliable formation constants areavailable. Also, the interpretation of calorimetric data dependsheavily on the correct quantitative description of the particularsystem. Previous studies of molybdenum(v1) and tungsten(vr)complexation have shown that systems of this nature can beunravelled by computer treatment of high-quality potentio-metric data provided all the side-equilibria with respect touncomplexed molybdate, tungstate and carboxylate are takeninto consideration. 3,4We now report the results of a potentiometric, spectrophoto-metric and calorimetric investigation of the complexation ofmandelate [a-hydroxybenzeneacetate, PhCH(OH)CO,-] withmolybdenum(v1) and tungsten(v1).Mandelate was chosenbecause of its expected similar co-ordination behaviourtowards molybdenum and tungsten when compared to that oflactate [MeCH(OH)CO, -1. Lactate forms one major complexwith each of these metals, i.e. [MoO~(C,H~O,)~]~- and[W0,(C3H40,)2]2-, as well as several minor c~mplexes.~Formation constants for all the complexes have beendetermined as well as thermodynamic quantities for the majorspecies. No such information is available for mandelate ast Molybdenum(v1) and Tungsten(v1) Complex Formation. Part 9.'ligand except for an approximate value (log K = 14.8 k 0.6)for the formation constant of the molybdenum complex[MoO~(C,H,O,),]~ - obtained from NMR data.Severalearlier reports indicated the existence of such a 1 :2 complexfor both molybdenum and tungsten.' Thermodynamic data forthe complexation of these closely related carboxylates withmolybdenum and tungsten should be particularly usefulbecause the predominance of a single major species shouldallow more meaningful comparisons to be drawn than in otherrelatively complicated systems.ExperimentalReagents and Solutions.-All reagents were of analyticalgrade (Merck and BDH) and solutions were prepared withwater obtained from a Millipore Milli-Q system. Sodiummolybdate and sodium tungstate stock solutions were preparedfrom the recrystallized salts Na2[Mo04].2H20 and Na2-[W0,]-2H20 and standardized gravimetrically as describedpreviously.Hydrochloric acid was standardized indirectlyagainst potassium hydrogenphthalate by titration with sodiumhydroxide. Sodium chloride was purified as describedpreviously.* Mandelic acid was used as received but its puritywas checked by titration with sodium hydroxide. Mandelatesolutions were prepared by accurate neutralization of mandelicacid.Potentiometric Titrationx-Mixtures of sodium molybdateand sodium mandelate (80 cm3) were titrated (mostly induplicate) with hydrochloric acid at 25 "C using a Metrohm 636Titroprocessor. All solutions were made 1.0 mol dm-3 withrespect to chloride ions by addition of the appropriate amountof recrystallized sodium chloride. To exclude carbon dioxidefrom the system, a stream of purified nitrogen was passedthrough 1.0 mol dm-3 NaCl and then bubbled slowly throughthe titration solution.The initial concentrations (mol dm-3) ofmolybdate and mandelate were as follows: 0.005, 0.05; 0.01,0.05; 0.01,O.Ol; 0.01,0.005; 0.02,0.05; 0.05,0.05 and 0.10,O.lO.The protonation constant of mandelate was determined bytitration of a mandelic acid solution (0.05 mol dm 3, withsodium hydroxide. Mixtures of sodium tungstate and sodiummandelate were titrated with hydrochloric acid as describe34341.0J. CHEM. SOC. DALTON TRANS. 1995-above except that a Metrohm Dosimat was used for theaddition of the acid. By manually controlling the addition ofacid and monitoring the stability of pH readings the absence ofslow equilibria can be verified. The initial Concentrations (moldrn-,) of tungstate and mandelate were as follows: 0.001,0.005;0.005, 0.05; 0.005, 0.015; 0.005, 0.025; 0.01, 0.05; 0.01, 0.025and 0.02, 0.100.The free hydrogen-ion concentration, h, was determined bymeasuring the potential, E, to 20.2 mV using a Rosscombination electrode (Orion) with a 3.0 mol dm-3 KCl bridgesolution.Equation (1) was used to calculate h from theE = E" + 59.1610gh + Ej (1)measured potential at each titration point. Values for E" and E j ,the liquid junction potential, were determined from titrationsof 1 .O mol dm-, NaCl with HCl as described by Rossotti.' Forbrevity, -log h is denoted by pH,. The value for Ej was foundto be -24.5 h mV and becomes significant only at pH, 5 2.Spectrophotometric Titrutionx-A GBC 920 UV/VISdouble-beam spectrophotometer equipped with a Peltierthermocell was used for absorption measurements.Thesolution in the titration cell, kept in a thermostatted water-bathat 25 O C , was stirred with a non-electric immersion magneticstirrer. Absorbances were measured in the wavelength range219-250 nm using quartz cuvettes of path lengths 0.5 and1.0 cm depending on the concentrations of the solutions;the composition of the reference solution was that of the ionicmedium, i.e. 1.0 mol dm-3 NaCl. The concentrations ofmolybdate and mandelate in the reaction vessel were 0.2 and 1 .Ommol dm-, for the first titration and 0.02 and 0.8 mmol dm-3for the second. The titrant solution contained in addition tohydrochloric acid and sodium chloride (0.01 and 0.99 moldrn-,) also molybdate and mandelate at the same concentrationas those in the test solution.The hydrogen-ion concentration ofthe solution was measured as described for the potentiometrictitrations. Spectra were recorded at pH, intervals of ~ 0 . 1 . Asimilar titration of mandelic acid (0.08 mmol drn-,) withsodium hydroxide was carried out from which the protonationconstant of mandelate was calculated using the programSQUAD. The individual spectra obtained for mandelate andmandelic acid were supplied to the program for the treatment ofthe absorbance data pertaining to complexation.Calorimetric Titrations. -An isothermal calorimeter, Tronacmodel 1250, was used for the enthalpy measurements. Solutionscontaining molybdate (or tungstate) and mandelate (25.0 cm3)were titrated with hydrochloric acid from a precisionmicroburette (2.5 cm3).The data were collected automaticallyby means of a personal computer using software supplied byTronac. The initial concentrations of molybdate (or tungstate)and mandelate were 0.02 and 0.10 mol drn-,.Separate titrations of mandelate (0.10 mol drn-,) withhydrochloric acid (1 .O mol drn-,) were carried out to determinethe heat involved in the protonation of mandelate. All solutionswere made 1 .O mol dmP3 with respect to chloride by addition ofthe appropriate amount of recrystallized sodium chloride. Ablank titration of acid into sodium chloride was done to correctfor the heat of dilution (endothermic) which amounted tox 1.1% of the heat of complexation per mol of acid added.Theheat of protonation of mandelate, however, is so small that itamounts to only about 10% of the heat of dilution. Titrationswere carried out in duplicate.p[Mo0,12- + qPhCH(OH)C02- +rH+[c~mplex](~P + q -r) - (2)mostly be described in terms of the stoichiometric coefficients ofthe reactants, for example [ 1,0,1] - for hydrogen molybdate. Inthe treatment of the data all side-equilibria involving thereaction of protons with mandelate, molybdate and tungstatehave to be taken into account. The protonation constant ofmandelate was determined in separate titrations of mandelicacid with sodium hydroxide. The value obtained, log poll =3.15 2 0.01 (error limits 30), can be compared with thatdetermined in 1 .O mol dm-, KNO,, namely 3.14 2 0.01.l 1For the equilibria involving uncomplexed molybdate thespecies [HMoO,] -, [MoO,(H,O),], [MoO,(OH)(H,O),] +,[H,Mo,O2,l3-, [Mo8O2,l4- and [HMo20,] + were takeninto account using previously determined equilibrium constantspertaining to a 1 mol dm-, NaCl medium at 25 OC.', In thecase of tungstate, acidification up to 2 x 1.2 (2 = degreeof protonation) results in the formation of the followingpolyanions of which formation constants for the conditionsin question have been reported,', namely [W,020(OH),]6-,~ 7 0 2 , ] 6 - , [HW702,]5- and [H2W,20,2]10-. At 2 2 1.2slow equilibria occur and conditions were chosen to preventthese reactions, i.e. relatively low tungstate concentration and asufficient excess of mandelate.In the treatment of the data theequilibrium constants of the above species were supplied to theprogram to check whether the concentrations of polyanionswere indeed negligible.The results of some representative titrations are shown inFigs. 1 and 2 as plots of Fagainst pH,. For these protonationcurves the function F represents the fraction of the totalnegative charge neutralized due to protonation where H , B andC are the analytical concentrations of acid, molybdate (ortungstate) and mandelate [equation (3)]. An F value of 1.0[HMo207]-, [Mo7024l6-, [HMo702415-, [H2Mo7024l4-,F = ( H - h)/(2B + C ) (3)Results and DiscussionPotentiometric Investigation.-The various protonation,condensation and complexation reactions that can take placewhen a solution of molybdate (or tungstate) and mandelate isacidified are represented by the general equation (2).Forbrevity, species with overall formation constants ppqr will8 6 4 2PHCFig. 1 Plots of function F versus pH, for some representativepotentiometric titrations. Initial concentrations (molybdate, mandel-ate): (a) 0.05, 0.05; (6) 0.01, 0.05; (c) 0.005, 0.05 and ( d ) 0, 0.05 rnoldm-J. CHEM. SOC. DALTON TRANS. 1995 34351 .o0 80 6LI0 48 6 4 2PHCFig. 2 Plots of function F uersus pH, for some representativepotentiometric titrations. Initial concentrations (tungstate, mandelate):(a) 0.005,0.015; (b) 0.005,0.025; (c) 0.005,0.05 and ( d ) 0,0.05 mol dm-3therefore indicates an average charge of zero for the species insolution, e.g.for the formation of mandelic acid. The curvesshow that the complex-formation characteristics for the twosystems are very similar. Complexation starts at pH, 7-8resulting in a sharp increase in Fvalues until at low pH, theprotonation of the complexes becomes more difficult than thatof mandelate itself. The inflexions exhibited by the curvespertaining to an excess of carboxylate show that after all themolybdate or tungstate has reacted very little protonation takesplace until the pH, is low enough ( ~ 4 . 5 ) for free mandelate tobecome protonated and F increases again.The potentiometric data were treated with the programSUPERQUAD l4 to find the reaction model that would givethe best description for each of the systems.A noticeable featureof the best models is the predominance of the [ 1 ,2,212 - complexover a wide pH, range. The distribution of the complexes as afunction of pH, at concentrations chosen to illustrate thestability regions are shown in Figs. 3 and 4. A number of minorspecies also occur in the models (Table 1) of which the [1,2, I]’ -and [ 1,2,3] - molybdenum complexes and the [ 1,2,3] - tungstencomplex with relative standard deviations of 20-23% are themost uncertain; the program automatically rejects species forwhich the relative standard deviation is greater than 33%. In thecase of the tungstate system fewer minor species were identified,in particular dinuclear complexes, which would not be expectedbecause of the requirement of low tungstate concentration andexcess of mandelate as discussed above.The models now obtained are, with few exceptions regardingvery minor species, the same as those reported for complexationwith lactate.When the formation constants for the [1,2,2]’-complexes of molybdenum and tungsten are compared it is seenthat the tungsten complex is significantly more stable than themolybdenum complex, the difference being 1.66 and 1.76 logunits for the mandelate and lactate complexes respectively. Forboth molybdenum and tungsten the mandelate complex is onlyslightly more stable than the lactate complex, the differencebetween the values of the stability constants being only 0.22 and0.12 log units respectively. Apart from reflecting the consistencyof the results, these small differences show that substituting aphenyl for a methyl group has little effect on the co-ordination10080v) a,0.-Q, 60 3 c-0a0 ([Ic -QI 40 2a a,2008 6 4 2 0PHCFig.3 Distribution of species in the molybdenum(v1)-mandelatesystem as function of pH,. The total concentrations of molybdate andmandelate are 0.05 and 0.10 mol dm-3, respectively10080cna,a v)0a,c3) ([I5 40.- 60c--2a”200\ P O T - [ 1,2,2]8 6 4 2PHCFig. 4 Distribution of species in the tungsten(v1tmandelate system asa function of pH,. The total concentrations of tungstate and mandelateare 0.001 and 0.003 mol dm-3, respectivelystrength of these ligands. The structure of the lactate andmandelate complexes should be similar (Fig.5). Informationobtained from NMR spectra for a-hydroxycarboxylic acids’indicated that the carboxyl oxygens are trans to the terminaloxygens of the cis-MOO, and -WO, units similar to the situationin tartrate, malate and citrate complexes of known structure.3436 J . CHEM. SOC. DALTON TRANS. 1995Table 1 Reaction models and formation constants of the variousmolybdenum(v1) and tungsten(v1) mandelate complexesComplex MoV’ WV‘c1,2,1 i3 - 7.80 f. 0.30 -c 1 > 1 J l 2 - 6.83 2 0.12 -~c2,2,4i2 - 25.87 _+ 0.03 __[ 1,2,2]2 - * 15.93 0.01 17.59 k 0.01c1,2,31- 16.27 k 0.29 18.09 ? 0.30c1>1,21- 11.57 _+ 0.06 13.78 f 0.07- 15.33 t 0.07 c1,1,31c2,2,51- 26.86 k 0.12 -[2,1 ,312 - 19.00 k 0.15 -r2,1,41- 21.18 k 0.24 -r2, I ,51 23.00 k 0.06 -* For the corresponding lactate complexes log Plz2 = 15.71 k 0.01(Mo”) and 17.47 ? 0.01 (W”’).- 2-PhIPhFig.5or WProbable structure of the [1,2,2]’- complex where M = MoSpectrophotometric Investigation.-By choosing relativelyfavourable conditions it ought to be possible to verify theexistence of at least the major molybdenum complex byspectrophotometry (in the UV region) despite some of thelimitations imposed by the nature of the system. At the very lowconcentrations required for the absorption measurements atleast a four- to five-fold excess of mandelate is essential topromote complex formation. Although the absorption ofmandelate is weaker than that of molybdate this excess meansthat its contribution to the total absorption measured becomescomparable to that of molybdate.Fortunately this contributiondoes not change much during the titration because of therelatively small difference between the spectra of mandelate andmandelic acid (Fig. 6) which in any case had been accuratelydetermined in a separate titration experiment and could besupplied to the program in the treatment of the data. Theprotonation constant of mandelate calculated with the programSQUAD from the data of this experiment, log p o l l =3.16 k 0.01 (error limits 3a), agrees very well with the value(3.15) obtained from the potentiometric data.Under the conditions of the first titration experiment (0.2and 1 .0 mmol dm-3 molybdate and mandelate respectively)a maximum concentration of about 90% of the [1,2,212-complex is present over the range pH, 6 4 , with less than 6%of the [1,1,2]- species which had to be neglected in thecalculations.The data treated with SQUAD resulted in a goodfit between experimental and calculated absorbances with thevalue of the formation constant of the [ 1 ,2,212 - complex, logp122 7 16.01, in very good agreement with that obtained bypotentiometry (1 5.93).A second titration was done under conditions where a greaterpercentage of the [ 1,1,2] - complex (maximum = 25%) wouldbe present while the concentration of other minor complexes canbe neglected. However, under these conditions the presence of[HMoOJ and in particular [MoO,(H,O),] at pH, < 3reaches concentrations comparable to and greater than that of8000 1..- I I2000 /-200 220 2 40h/nmFig.6 Absorption spectra of mandelic acid (0) and mandelate (0)the [ 1 , I ,2] complex. The spectra and equilibrium constants ofthese two molybdenum species, known from previous work,were therefore also supplied to the program. The data of thetwo titrations were combined and in spite of the variousuncertainties involved in the procedure the value calculated forthe formation constant of the [1,1,2]- complex, log p I l 2 =11.7, agreed reasonably well with that obtained bypotentiometry ( I 1.57). The value now calculated for theformation constant of the [1,2,212- complex log p122 = 16.03was practically the same as that obtained from the data of thefirst experiment alone.The spectra of the complexes are shownin Fig. 7. The reaction model proposed for the molybdenum(v1)-mandelate system and the formation constants can therefore beaccepted with sufficient confidence to warrant a calorimetricinvestigation. Owing to the very small part of the UV spectrumof tungstate that is available for absorption measurements asimilar spectrophotometric study of tungsten(v1)-mandelatecomplex formation would not be feasible.EnthuIpimetric Investigation.-The results of the enthalpi-metric titrations are shown in Fig. 8 where the total amountof heat measured, Q, is plotted against the molar ratio of acidadded to either molybdate or tungstate. The curves show aclear break at a mole ratio of 1 : 2 which corresponds to thestoichiometry of the major complex [ 1 ,2,212 - , determined bypotentiometry and spectrophotometry.The heat evolved in theformation of the tungsten complex is greater than that for themolybdenum complex. Included in the measured heat is a verysmall contribution from the protonation of mandelate whichneeds to be present in excess to ensure complete complexationand prevent side-reactions of molybdate and tungstate withprotons. Also, under the chosen conditions minor complexspecies do not appear in measurable concentrations for most ofthe titration which simplifies the calculation of enthalpychanges. To account for the heat involved in the protonation offree mandelate the enthalpy change for the reaction wasdetermined in a separate titration. The value obtained aftercorrecting for the endothermic heat of dilution was AW =-0.05 kJ mol compared to - 1.7 kJ mol determined forlactate under the same condition^.^The values obtained for the enthalpy change for theformation of the [ 1 ,2,212 complexes of tungsten anJ.CHEM. SOC. DALTON TRANS. 1995 343725000 I20000rI 5 15000r -E"0 E . 10000 Uw50000220 230 240 250XlnmFig. 7mandelic acid (Hman) systemAbsorption spectra of various species in the molybdenum(v1)-5040307 --.020100 I I I0 1 2 3Mole ratio acid : rnolybdate (or tungstate)Fig. 8 The measured heat evolved, Q, as a function of the molar ratioof acid to molybdate (a) or tungstate (6) for the titration of 0.1 mol dm-3mandelate and 0.02 mol dm-3 molybdate and tungstate, respectivelymolybdenum are listed in Table 2.That for the tungstencomplex is about 8 kJ mol-' more favourable than for themolybdenum. The entropy changes for the two reactions areabout the same and compare well with the results previouslyobtained for complexation with lactate. The enthalpy changetherefore is the cause for the greater stability of the tungstencomplex and reflects the greater tendency of tungsten toTable 2 Thermodynamic quantities (kJ mol-') for complex formationof molybdate and tungstate with mandelate and lactate in 1 .O mol dm-3NaCl at 298.15 KMandelate (H,L) AGO AHo T A P[MoO,L,]~- -90.93 t 0.06 -78.2 t 0.5 12.7 t 0.5cWO2L,I2 - - 100.40 f 0.06 -86.3 ? 0.5 14.1 f 0.5HL- -17.98 f 0.03 -0.05 f 0.5 17.5 f 0.5Lactate (H2L)3[MoO,L,I2 - -89.67 f 0.06 -72 k 2 18 k 2IYO2L,I2 - -99.72 f 0.06 -80 2 2 20 k 2HL- -20.52 f 0.02 -1.7 k 0.2 18.8 k 0.2increase its co-ordination number from four to six.This effectis also seen in the greater stability of polyoxoanions oftungsten(v1) compared to those of molybdenum(v1) as has beendiscussed previously.The results of this investigation again demonstrate thesomewhat special co-ordination behaviour of a-hydroxycarb-oxylic acid groups towards molybdenum(vr) and tungsten(vr)in that very stable 1 : 2 rather than 1 : 1 metal : ligand complexesare formed. In the case of oxalate, for example, the 1 : 1 complex[MoO~(C,O,)(H,O)]~ - predominates at high pH,., Thisbehaviour has been explained in terms of the energy costinvolved in the ionization of the alcoholic proton when a 1 : 1complex is formed.When a 1 :2 complex is formed, however,the cost can be regained (with profit) when two protons becomeavailable to form a water molecule.ConclusionBoth molybdenum(vI) and tungsten(v1) form one predominantcomplex with mandelate, i.e. [MoO,(C,H,~,),]~- and~ 0 , ( C , H , 0 , ) , ] 2 - as well as several minor complexes. Theco-ordination behaviour of mandelate towards these metals isvery similar to that of lactate. The tungsten(v1) complexes aremore stable than those of molybdenum(v1) due to a morefavourable enthalpy change for the complexation reaction ( x 8kJ mol-') which is associated with the greater tendency oftungsten(v1) to expand its co-ordination sphere from four to six.AcknowledgementsFinancial support by the University of Stellenbosch and theFoundation for Research Development is gratefullyacknowledged.ReferencesI Part 8, J.J. Cruywagen, E. A. Rohwer and G. F. S. Wessels,2 V. M. S. Gil, Pure Appl. Chem., 1989, 61, 841 and refs. therein.3 J. J. Cruywagen, L. Kruger and E. A. Rohwer, J. Chem. Soc., DaltonTrans., 1993, 105.4 J. J. Cruywagen, J. B. B. Heyns and E. A. Rohwer, J. Chem.Soc., Dalton Trans., 1990, 1951; J. J. Cruywagen, L. Kruger andE. A. Rohwer, J. Chem. Soc., Dalton Trans., 1991, 1727.5 M. M. Caldeira, M. L. Ramos and V. M. S. Gil, Can. J. Chem., 1987,65, 827 and refs. therein.6 J. J. Cruywagen, L. J. Saayman and M. L. Niven, J. Crystullogr.Spectrosc. Rex, 1992, 22, 737; L. R. Nassimbini, M. L. Niven,J. J. Cruywagen and J. B. B. Heyns, J. Crystallogr. Spectrosc. Res.,1987,17,99; M. A. Porai-Koshits, L. A. Aslanov, G. V. Ivanova andT. N. Polynova, J. Struct. Chem. (Engl. Transl.), 1968, 9, 401;C. B. Knobler, A. J. Wilson, R. N. Hider, I . W. Jenson, B. R. Penfold,W. T. Robinson and C. J. Wilkins, J. Chem. Soc., Dalton Trans., 1983,1299; W. T. Robinson and C. J. Wilkins, Transition Met. Chem.,1986,11, 86.7 D. H. Brown, J. Chem. Soc., 1961, 4732; S. P. Banerjee and A. K.Bhattacharya, Curr. Sci., 1961,30,380; P. Souchay, Bull. Soc. Chim.Fr., 1989, 122.Polyhedron, 1995,14, 348 1343 8 J. CHEM. SOC. DALTON TRANS. 19958 J. J. Cruywagen, J. B. Heyns and R. F. van de Water, J. Chem. SOC.,9 H. S. Rossotti, Talanta, 1974, 21, 809.Dalton Trans., 1986, 1857.10 D. J. Legget, in Computational Methods for the Determination ofFormation Constants, ed. D. J. Legget, Plenum, New York, 1985,1 1 J. E. Powell and W. F. S. Neillie, J. Inorg. Nucl. Chem., 1967, 29,2371.12 J. J. Cruywagen, J. B. B. Heyns and E. F. C. H. Rohwer, J. Znorg.Nucl. Chem., 1976, 38, 2033; K.-H. Tytko, B. Baethe andp. 221.J. J. Cruywagen, Inorg. Chem., 1985,24, 3132; J. J. Cruywagen andE. A. Rohwer, unpublished work.13 J. J. Cruywagen and I. F. J. van der Merwe, J. Chem. Soc., DaltonTrans., 1987, 1701.14 P. Gans, A. Sabatini and A. Vacca, J. Chem. Soc., Dalton Trans.,1985, 1185.15 J. J. Cruywagen and J. B. B. Heyns, Znorg. Chem., 1987,26,2569.Received 1 1 th April 1995; Paper 5/02330
ISSN:1477-9226
DOI:10.1039/DT9950003433
出版商:RSC
年代:1995
数据来源: RSC