Complexation thermodynamics and structural studies of trivalent actinide and lanthanide ...

12 Pages·2013·0.33 MB·English

Radiochim.Acta101,221–232(2013)/DOI10.1524/ract.2013.2018 T
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©byOldenbourgWissenschaftsverlag,München is
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Complexation thermodynamics and structural studies of trivalent c
te
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actinide and lanthanide complexes with DTPA, MS-325 and b
y
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HMDTPA e
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By P.Thakur1, ,#, J.L.Conca2, C.J.Dodge3, A.J.Francis3,4 and G.R.Choppin1 y
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ig
h
1 FloridaStateUniversity,DepartmentofChemistry&Biochemistry,Tallahassee,FL32306,USA t la
2 CenterforLaboratorySciences,RJLeeGroup,Inc.2710N20thAvePasco,WA99301,USA w
3 BrookhavenNationalLaboratory,Upton,NewYork11973,USA . Y
4 DivisionofAdvancedNuclearEngineering,PohangUniversityofScienceandTechnology,Pohang,Korea ou
m
(ReceivedSeptember27,2011;acceptedinfinalformAugust14,2012) ay
(PublishedonlineFebruary25,2013) co
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DTPA/HMDTPA/MS-325/Lanthanides/Actinides actinidescontinuestobeamajorareain f-elementscoordi- d
is
nationchemistry. tr
ib
DTPA is a potentially octadentate ligand and forms u
Summary. The protonationconstantsofDTPA(diethylene- complexes with larger stability constant of the type te th
tdriipahmeinnyelpecnytcalaocheetixcyal-cpidh)oaspnhdotwnyol-dmereitvhaytlivedsieotfhDylTenPeAn,t1ri-aRm(i4n,4e-- Min(sDolTidPA(L)(nH=2Ol)a2n−t.hTanhiedcersy)s[t2al,l3o]garanpdhtihcedlautmaoinfeLsnc(eDncTePlAif)e2-− is ar
cpttreoeinanmtmtiapoialmnecexeepettirescincoatafctiaitAdcrae(mttMiioc3+Sn,a-c3iCni2dm50)3(.+1HanMMadnD(dNRTaL)P-CnhAl3yO+)d4rwc.oaeTxtriyheomendsefeotthwerymrimlt-hadtiniitoehentedhsyoeblfeyt1nhper:eon1e-- ttoihrmedienparmetiseoeannscuserpehmoeferenotnsoefinLwnas(toDelruTtoPiofAn)h2y[−4d.,rA5at]diodanirteioinncoatlnhlsyei,sitDnennTtePrAwciotihs- ticle for yo
a promising chelating agent in lanthanide and actinide sep- u
ligandswereinvestigatedbypotentiometrictitrationwithcom- r
petition by ethylenediaminetetraacetic acid (EDTA) and the arations [6]. In the nuclear fuel cycle, DTPA is used in the pe
r
solvent extraction method in aqueous solutions of I =0.10M separation of trivalent actinides and lanthanides because of so
n
NmainCeldOb4.yTthheettehmerpmeoradtyunreamdeicpednadtaenocfecoofmtphleexstaatbioilnitwyecroendsteatnetrs- trheelairtivlaergteortsheaptaoraftitohneflaacnttohrasnfiodreasc-DtinTiPdAes.-DThTePATAcoLmSPpEleAxeKs al u
s
and by calorimetry. The complexation is exothermic and be- (Trivalent Actinide-Lanthanide Separation by Phosphorous e o
>cstormMeneSgs-th3w2oe5fa.ktEheuers3w+e/ilCtihgmai3nn+cdrsleufamosleilnoiewnscsteetnmhcepeeo,rrEadXteurAr:eFD.STTh(PEeAxct≈oenmHdpeMldexDXaT-tirPoaAny EacxttiBrnaeicdsteiadsneatssnedafnfldeacnAttihqvaeuneciodhueesslaKitsionbmgaspaelgedexonentss)tihsneisplaafonrauthtniaodnnaitdoioef-ntarc[iv7tia,nl8ied]n.et nly. Oth
AbsorptionFine Structure) andDFT(DensityFunctional The- e
ory) calculations suggest that all three ligands are octadentate separation,DTPAisalsousedasadecontaminationagentin r u
s
ainndthHeMcoDmTpPleAx)..ITnhteheMc3o+mbpilnedxs, Mvia(Lfi)2v−e(cLar=boDxyTlPaAte,sMoxSy-3g2e5n indTivhideucaolsmwplheoxehsavoeflianngtehsatnedidreasdwioiathctiDveTPmAataenridalists. deriva- e is o
atoms,threenitrogenatoms,andthecomplexcontainsonewater tives are also very important, because of their use in mag- nly
ofhydration. netic resonance imaging (MRI) as a contrast agent [9]. a
Complexes of Gd3+ with MS-325 have also received atten- llow
tion as potential contrast agent for MRI currently under- ed
1. Introduction going clinical trials [10]. It possesses a lipophilic diphen- w
Aminocarboxylates complexes of lanthanides and actinides lycyclohexyl group which provides a strong non-covalent ith w
atureranloptroopnelyrtiienst,erbeusttitnhgeybehcaavuesaenoifmthpeoirrtacnhtempliaccaelianndthsetrhuics-- bseinrudmingalibnutmerianct(iHonASw)i.thHMtheDTblPoAodwpaslasamlsoa dperositgeninedhuumsinagn ritten
tory of the lanthanides and actinides separation chemistry. the Gd(DTPA)(H2O)2− (magnevist) core which has an ex- pe
r
Early experiments on separation of lanthanides were car- cellent human safety record [11,12]. It was expected that m
riedoutintracerscaleusingcitratecomplexes,butattention substitution on the ethylene backbone would not adversely iss
soon turned to the aminocarboxylates because EDTA and affect the thermodynamic stability nor kinetic interness of ion
related ligands were found to be more effective [1]. Now, thecomplex. by
morethanhalfacenturyafterthefirstuseofaminocarboxy- Since the properties of f-cation complexes are deter- th
e
lates, the study of their complexation with lanthanides and mined principally by ionic and steric effects, comparison c
o
ofthe complexation ofDTPA,MS-325andHMDTPAwith p
y
r
*Authorforcorrespondence(E-mail:[email protected]). these cations canprovide insight into whether theintroduc- ig
h
#Current address: Carlsbad Environmental Monitoring and Re- tion of functional groups in the ethylenediamine backbone t h
searchCenter,1400UniversityDr.,Carlsbad,NM88220,USA enhances the complexation and, also, how the steric dif- old
e
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.
222 P.Thakuretal. Th
is
a
ferences between the flexible DTPA and HMDTPA, and rtic
the rigid MS-325 affect the complexation properties. There le
havebeenafewstudies onthecomplexation oflanthanides is p
and actinides with DTPA but only at or near 25◦C [13– ro
17]. Thermodynamic constants of their complexation with tec
An3+/Ln3+arestillveryscarce.Although,thecomplexation ted
ofDTPAwithlanthanides andactinides hasbeenstudiedin by
thepast,thesystematicstudiesonthecomplexationofother G
e
twoligandswithlanthanidesandactinideshavenotbeenin- rm
a
vestigated. There is only one report in the literature on the n
complexationstudyofMS-325withGd3+,Eu3+,Fe3+,Ca2+, co
p
Cu2+,andZn2+ at25◦Cin0.1MNaClO .Therefore,inthe y
present study, we initiated a systematic 4study on complex- righ
ation of Am3+, Cm3+, and Ln3+ with DTPA, MS-325, and t la
w
HMDTPA.Ligandsprotonationconstantsandtheirstability . Y
constants withLn3+ were measured bypotentiometric titra- o
u
tionmethod(directpHtitrationandcompetitionwithEDTA, m
a
respectively),whilesolventextractiontechniquewasusedto y
determine thestability constants withAm3+ andCm3+.The co
p
associated thermodynamic data of these complexes were y
a
measuredeitherbymicro-calorimeter orbytemperaturede- n
d
pendence of stability constants data using van’t Hoff linear d
is
plot. Luminescence lifetime measurements and the (X-ray tr
ib
absorptionFineStructureSpectroscopy(EXAFS)wereused u
te
to reveal information about the hydration number and the th
coordinationmodesoftheseligandsinthecomplex.Inadd- is
ition, DFT calculation with La3+ was used to evaluate the ar
effectiveness of the B3LYP/LANL2DZ basis set in struc- ticle
turalelucidationofthesecomplexesinsolution. fo
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y
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2. Experimental er
s
o
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HThCelONa,CNlOa4OaHn,dDanTdPAHCwle,rebpouthrchsoaslieddfarnodmsAtalnddriacrhd,wsohliule- al u
4 s
tions were obtained from Fisher Scientific. MS-325 and e o
HMDTPA were gifted from Mallinckrodt Medical. The nly
structure oftheligands usedinthis studyisgiveninFig.1. Fig.1.StructuresofDTPA,MS-325,andHMDTPAusedinthisstudy. . O
Ligand MS-325 (C H N O ·H O) was synthesized as the th
33 44 3 14 2 e
R isomer and is a chemically stable and moderately hygro- such that a 10.0μL of the solution has a count rate of ca. r u
scopicwhitepowder.Todetermineifthesolidhadabsorbed 60000cpm. The activities of 241Am, 244Cm, and 152,154Eu se
additional moisture since the time of elemental analysis, were measured in a Beckman Liquid Scintillation Counter is o
aKarlFischertitration wasperformedonthesolidimmedi- (LSC) using Ecolite cocktail (ICN, Research Product Divi- n
ly
atelypriortouseinthisstudy.Thenewanalysisgaveawater sion).248Cmusedfortheluminescence studies waspurified a
content of 4.13% which would give C33H44N3O14·2.5H2O by passage through a column of Dowex-1 anion exchange llow
wthiethligaannedfsfeDcTtivPAe,mMolSe-c3u2l5ar,awnedigHhMt oDfT7P8A3.w13e.reSporleuptiaornesdoinf roersaitnedinto7.d5ryMneHssNaOn3d.Treh-edicsosolllevcetdedinC0m.0f0r1acMtioHnCwlaOs e.vTahpe- ed w
0.10M(NaClO4)andtheir concentrations weredetermined concentrationoftheCm3+stocksolutionwasdetermin4edby ith w
bypPHer-cthitlroartaiotenswtoitchkstsaonludtairodnsNaoOf HLn. O (except Pm) were α-sApecccturommeett9ry50an(dFilsihqeuridSsccieinnttiilfilact)iopnHcomuentteinrgw.as used for ritte
2 3 n
prepared by dissolving a known amount of the oxide in pH measurements. Solution of pH 4.00±0.01 and 7.00± p
e
a slight excess of perchloric acid (60%, Fisher Scientific) 0.01 buffers were used to calibrate the electrode system. rm
anddiluting toaknown volume. Their concentrations were Solutions ofbaseswerestandardized bypotassiumacidph- iss
determined by complexometric titration with EDTA in the thalate,KHP,titration.Priortouse,KHPwasdriedat100◦C ion
presenceofxylenolorangeindicator[18].Di-(2-ethylhexyl) for at least 2h and cooled in the dessicator over silica gel. by
phosphoric acid, (D2EHPA, Sigma-Aldrich) and heptane The electrode was calibrated before each titration by per- th
e
(FisherScientific,ACS)wereusedasreceived. formingtitrationofaknownamountofstandardizedHClO c
4 o
The radioactive tracers 241Am, 244Cm and 152,154Eu (Oak with standardized NaOHsolution at0.1M(NaClO )asthe p
4 y
r
Ridge National Laboratory) were purified and their purity background electrolyte. A plot of mV (measured) vs. pH ig
checked by α- and/or γ-spectrometry. The working stock (calculated) gave a working slope and intercept so that pH ht h
ofeach tracer was prepared in HClO solution of pH∼3.0 couldbereadas−log[H+]directly. o
4 ld
e
r
.
ComplexationthermodynamicsandstructuralstudiesoftrivalentactinideandlanthanidecomplexeswithDTPA,MS-325andHMDTPA 223 T
h
is
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2.1Solventextractionprocedure oftheligand.ThenvaluesusedforthepHcorrectionswere rtic
2.89–2.78forAm3+,2.80–2.65forCm3+ and2.82–2.69for le
cTohnecdenisttrraitbiuotnisonofrathtieo,mDe,tailsidoenfisniendaansotrhgeanraictioanodfathneaqtoutea-l Eu3+. This correction usually did not exceed 5–10% of the is p
D value for single sample. The error limits for the stabil- ro
o2u5s, 3p5haasned, a4n5d◦Cw.asFodreteearcmhineexdtrabcytisoonlveexnpteerixmtreanctt,io3n.0atm0L, ictoynafinddenpcroetolinmaittisonbacsoendstuanptosnartweoexoprremssoerdeidnetteerrmmsinoafti9o5n%s. tected
ofthe aqueous phase and the organic phase were shaken in To allow comparison in different temperatures, the stabil- by
a water bath (Cole-Parmer Inst. Co, Polystat Model 1200- ityconstants values inmolarity wereconverted tovalues in G
00 circulator) at 180rpm for 1h at pH=3.60±0.05. Ki- molalityaccordingtoequation[19]. erm
netic measurements indicated that equilibrium was attained a
n
in these experiments in about 1h. The organic solutions logβ =logβ +Σν logθ (7) co
(D2EHPA in heptane, 5×10−4 for Cm3+ and Am3+ and m M r r p
y
2×10−4MforEu3+)werepre-equilibrated withthe0.10M where (β ) and (β ) are the stability constants in molarity rig
M m h
t6caNhon.ae0mdC×rpleHOla1eMc40xt−iiDano7tgTnMpPamH.AgAie3xnw.t26utes00r.re–epT3wrvh0ieaoeμrrreicLeto0odvn.1ocui0nelsuneMm.ttrhaTeeNthiooarefanCntaslhgqOeoeu4fer,oaoDwdfuiTsio1tPha.sA0coot×l,iruvMtwe1io0Sitnt−r-has73oc2oeuto5rft lfimaasonlerdipttdroymiiscfitoftoceilvaormeeleinftofyfitol,camrrireeiettnshdypteieafopcofatrrinotvhdtdeheulecycro,tesnsθapcceaietcsninoidttfihnrcanesteiirMogoanant3its+ioic.v+oeΣmfLrfeνto5hdr−reiiuts⇔vhmatehlMueareen(sasdLtcoo)tviaf2ca−nhmrtii(soeoν)s--,r t law. You ma
y
stroifluutgieodnfworas3–a5ddmedin,to0.e5a0c–h1.v0iaml.LAofftedrupthliecavtiealssamwpelreescwenas- which gives avalue ofΣrνr of−1forthe complexation re- cop
action. y
takenfrombothphasesforcounting.Theremainingaqueous a
n
phasewasusedformeasurementoftheequilibriumpH. d d
2.3Potentiometrictitrations is
tr
2.2Dataanalysis Potentiometeric titrations were conducted to determine the ibu
M-Lsystem protonation constants of the ligands and the 1:1 stabil- te th
ity constants of Ln3+ with these ligands using an auto- is
The extraction of M3+ (M=Am, Cm and Ln) between matedtitrationsystem.Thetitrantsolutionwasdeliveredby ar
the aqueous phase 0.10M (NaClO4) and the organic phase aMetrohmDosimat665motor-drivenpistonburette.Nitro- ticle
(D2EHPA,representedasthedimerH2A2)canbeexpressed gengaswasbubbledthroughthetitrationsolutiontoremove fo
as: thedissolvedcarbondioxide.Thetitrations wereperformed r y
o
with stirring on a Corning model PC420 stirrer/hot plate. u
M3+(a)+3H2A2(o)⇔M(HA2)3(o)+3H+(a) (1) Thesystemwasinterfaced toacomputerthatoperatedsoft- r pe
r
ware prepared in the laboratory to control burette additions s
where(a)and(o)representtheaqueousandorganicphases, o
n
respectively.Inthepresenceofligand(L=DTPA,MS-325 alanydbteotwreeecnortdhethreeamdiVngsrewadaisn≥g 3o0f sthteo aeslescutrreodeeq.uiTlihberiudme-. al u
andHMDTPA)intheaqueousphase,thecomplexationreac- s
tionofthemetalionscanbewrittenas: After the addition was made, the system waited a mixing e o
time,typically30s,beforerestartingthemeasurementcycle. nly
M3++L5−β⇔101M(L)2− (2) Priortoeachtitrationorcomplexationtitration,theelectrode . O
was calibrated by an acid-base titration using the standard- th
e
where β101 is the stability constant of the complex formed. ized perchloric acid and sodium hydroxide solutions at the r us
Thedistributionratioofthetrivalentmetalionsbetweenthe desired temperatures so that hydrogen ion concentrations e
D2EHPA/heptaneandtheaqueousphaseisexpressedas: couldbecalculatedfromtheemfreadingsinthesubsequent is o
titrations. n
wheDre=[M[M3+3]+]r(eo)p/r[eMse3n+t]s(a)the total metal ion concentration(3in) mtroaliSlneatdmaintpeelmedspawetretahrteuerdteietrscaiitrreecddulitanetmin3pg5emrwaLatutejraercwbkaeittthhedt(hNceeelaslisdwlaohbfi)cahuncwodnaesr- ly allowed
theorganicandaqueousphases.Thepolynomialcorrelating anatmosphereofN .Titrationadditionswereaccomplished w
Dvalueswith[L5−]andlogβ101maybewrittenas: usinga25.0mLdig2italburette(Metrohm).Fortheprotona- ith w
1/D=1/D0×1+β101[L5−] (4) toifonligcaonndstsanwtemreeatisturarteemdewntisth,1t5h.e00m.1L0o0fM0.0N0a1OtoH0o.0v0er15ampHL ritte
D0/D−1=β101×[L5−] (5) range from 2 to 11, collecting 120 data points per titration. n p
e
r
To determine the stability constants of the lanthanide com- m
wtorfahcleTitgriheoaennD.dp0.HTishetohfemtdheieasstrauiqrbeuudetioodunissrtarpithbioaustoieofnmvaerrtaiaetlidoiosvnliasglihunteltsyh,eaDaftb,esrweneecxree- pat2il.ore5naxmtsei,osL1,o.c2ofo5fm12mLp.0Lne/tM1iotLfio0N/n2.a2EtC0iDt0lrOTaMtAio.aLnnFnsdo(wrI8IitI.th)9h,em1Ec0DLommToALpfe0owt.fi1te0i1ro.e21n6p0l1e0igrMMfaonrEdHmDCteidTtlrOAaa-t, ission by th
correctedusingtheequation: 4 4 e
werecombinedinthe50mLconicalflask.15mLofthisso- c
o
logD =logD−n×(pH−pH ) (6) lution was titrated with 0.015M of ligand solutions (L = py
corr av r
DTPA,MS-325orHMDTPA).Thetitrationdatawerefitted ig
h
where pHav is the average pH for each experiment. n is the by HYPERQUAD to calculate the acid dissociation con- t h
experimental slope of the logD vs. pH plot in the absence stantsandthestabilityconstants.ThevalueofpK wasfixed o
0 w ld
e
r
.
224 P.Thakuretal. Th
is
a
at 13.78 for all analyses [20]. The stability constant values performed at the EuLIII absorption edge (6.977keV)to de- rtic
of Ln(EDTA)− complex at 0.1M NaClO were taken from terminetheassociationofEu3+withthecomplexantsDTPA, le
NISTdatabase[20]. 4 MS-325andHMDTPA.Theaqueoussamples(1.0ml)were is p
placed in heat sealed polypropylene bags and mounted on ro
an Al sample holder having geometry of 2mm (H) × tec
2.4Calorimetry(ITC) 20mm (L) with a 1.5mm thickness. Fluorescence data ted
Calorimetric titrations were conducted with an isother- were collected using a 13 element Ge detector on beam- by
malsolutioncalorimetersystem(VP-ITCmicro-calorimeter line×10CattheNationalSynchrotronLightSource(NSLS) G
e
from Micro-Cal Inc. (USA) at 25◦C). The performance of (BrookhavenNationalLaboratory).Theabsorptionedgeen- rm
a
calorimeter was tested by measuring the enthalpy of pro- ergy was calibrated using the first inflection point of the n
tonation of 2-bis(2-hydroxylethyl)amino-2-hydroxymethyl- spectrum of an Fe foil (7.112keV). The EXAFS data were co
p
propan-1,3-diol. In a typical titration, n additions of the processedusingtheprogramIfeffit[24].ThetheoreticalEX- yr
titrantweremade(usuallyn=40),resultinginnexperimen- AFSmodeling codeFEFF6wasusedtocalculate theback- igh
tal values of the total heat generated in the titration vessel scattering phase and amplitude information for individual t la
w
(Qex,j, j=1ton).Forprotonation heat,ligandsolution(L) neighboringatoms[25].Thephaseandamplitudefunctions . Y
wasloadedintothesamplecell(1.44ml),andtheacidsolu- were determined using the crystal structure for europium o
u
tionloadedintotheinjector(240μl),whichwastitratedwith terephthalate[26].Fourscanswerecollectedpersampleand m
approximately 40 aliquots of 6μl HClO into the cell. The thedatawereaveraged.Theamplitudereductionfactor(S0) ay
4 2 c
syringe is tailor-made such that the tip acts as a blade-type wasfixedat1.0forallofthefits.Fittingdataforthesamples o
p
stirrer to ensure an optimum mixing efficiency at 400rpm. wereobtainedbycomparisonwiththestandards. y a
Theheatevolvedorabsorbedbyeachinjectioninthecourse nd
of titration is directly measured by the ITC unit, producing d
is
therawheatsignal,alsoknownascell feedback (CFB).In- 3. Resultsanddiscussion tr
ib
tegration of each CFB gives the differential enthalpy curve u
3.1Complexationthermodynamics te
for the titration. The observed heat changes were corrected th
faorartteheruhnesa.tFsoorfcdoilmutpiolenxa(Qtiodnil,jh)ethata,tswoleurteiodnesteormf Linne3d+i(nLsnep=- TtohneatpiorontoonfatLion(Lan=d tDheTPthAe,rmMoSd-y3n2a5miacnsdofHsMteDpwTPisAe)parore- is ar
Nd,EuandDy)(1.44mL)wereplacedinthetitrationvessel summarized in Tables1 and 2. The ligands MS-325 and ticle
andtitratedwithL.Multipletitrationswithdifferentconcen- HMDTPA, behave similarly to DTPA in term of protona- fo
r
trations of Eu3+ were performed to reduce the uncertainty. tion constants. However,the first twoprotonation constants y
o
Thesevalues were corrected forthe heats of dilution of the aresignificantlydepressedforMS-325,whileforHMDTPA u
r
tΔttiaotirQnaoenrb,dtjt.adfiTranohtamethwneteahtesenraetdnhaiaafclfltyepiozryeenndchchweeaa:intthQgaetar,tjfPho=Cer pQjth-rteoehxg,jtpra−aormgiQnet‘tdL(ilr,Qeejt.aar,cTgjt)rhioowepnas’.se[Tt2oh1boe-]f tcdbhorienamwdfipiinarngsrgtisoeopffnrfsoeottcoodtniDouafmTtitoPhiAneon.pcThionohnissMsptahcSnoo-tud3li2sdeh5so.bteweTrhsemeitahopeirseroltityagonhnotaertliaienonccntrereoncanohsnaewnsdtciatehnidn-t personal u
s
measurementsforeachsystemwererepeatedatleasttwice. valuesdeterminedinthepresentinvestigationagreewiththe e o
valuesreportedintheliteraturefortheDTPA.Thereisonly nly
one reported work by Choppin etal., [27] in which proto- . O
2.5Luminescencemeasurementstudies nation constants of MS-235 as well as their complexation th
e
TheEu3+ andCm3+ lifetimemeasurementstudieswerecar- constants with Gd3+, Fe3+, Ca2+, and Mg2+ were measured r u
s
riedoutfor1.0×10−4MEu3+ and2.0–4.0×10−6MCm3+ and to the best of our knowledge there is no reported pro- e
at room temperature in 1.00cm quartz fluorimeter cells tonationconstants valueforHMDTPAintheliterature. The is o
using an instrumental setup similar to that in Ref. [22]. protonation constants of all three ligands decreased signifi- nly
SEoul(uCtiloOns) oofrt2h48eCcmomanpdlextheescworerreesppornepdainregdlibgyanmdisxoilnugtiothnes cfoarntHlyMasDtThPeAte,mTpaebrlaetu1r)e, swuagsgiensctirnegasethda(tetxhceepptrolotognKat4iovnaluoef allow
in 0.104M3 (NaClO ). The pH of the solutions was varied theseligandsareweakenedathighertemperatures. ed
tcfNeroorHnm2msOtao=3nl.e6t1ci–.un01l5em3ks.s0oba[ssw2−s3oit]0ch4.wi7adet0ier,ldeuwtuwehseieHtrdheCttkolhOoebcs4aEiloscurut3h+lNaetacleOuotmmHheip.nlnTeeusxhcm.eeFbneoecqrreuoCadftmeiwoc3ana+ys-, btchryoeTcmeahnlieotchrreiaomnlcpteahitlearosylrpiymoafreoetfpryrapolrltoaotrnnoeeangtaisaothtinioovwned,neotcfeiorntmnhseiTinssaeetbedlnlietgd2aiwrn.edictFshtolymrthebDeaysTguPmerAenid--, with written
thecorrelation N =0.65k −0.88[5]wasusedtocalcu- eral trends that all protonation constants decrease as the pe
latethenumberoHf2bOoundwatoebrs molecules.Anuncertaintyof temperature is increased. The large negative enthalpies of rm
±0.5isassignedfor N inthesemeasurements[23]. protonationsuggestthatthefirsttwoprotonationstepsprob- iss
H2O ably occur onthe nitrogen atoms and zwitterions similar to ion
thosereportedforEDTA[19]formintheprotonated DTPA by
2.6ExtendedX-rayabsorptionfinestructure species.ForMS-325andHMDTPA,thefirstthreeprotona- th
(EXAFS) tion steps (HL4−,H L3− and H L2−)are negative, while the e c
2 3 o
Three solutions, (1) Eu:DTPA1:2 pH=9.0, (2) Eu:MS- lasttwoprotonationsteps(H L−,H L)areeitherpositiveor p
4 5 y
325,1:2,pH∼9.0(3)Eu:HMDTPA,1:2,pH∼9.0were slightlynegative(Table2). rig
used for the EXAFS experiments. The concentration of Fig.2 shows speciation diagrams for the Am3+ with ht h
[Eu3+] was ∼0.015M in all solutions. The analysis was three ligands studied. The protonated complex was not ob- o
ld
e
r
.
ComplexationthermodynamicsandstructuralstudiesoftrivalentactinideandlanthanidecomplexeswithDTPA,MS-325andHMDTPA 225 T
h
is
a
Table1.ProtonationconstantsofDTPA,MS-325andHMDTPAat I=0.10M(NaClO4); T=0–45◦C(Hn−1L+ rtic
H⇔HnL;n=1–5). le is
p
Ligands T(e◦mCp). logK1 logK2 logK3 logK4 logK5 rote
c
te
d
b
DTPA 0 10.27±0.05 8.95±0.05 5.06±0.06 3.22±0.10 2.18±0.08 y
25 10.17±0.03 8.75±0.02 4.52±0.04 2.84±0.03 2.12±0.07 G
e
25a 10.42 8.76 4.42 2.56 1.79 rm
25b 10.49 8.60 4.28 2.64 2.00 a
n
20c 10.55 8.60 4.26 2.41 2.08 c
35 9.80±0.05 8.63±0.04 4.44±0.06 2.79±0.08 2.07±0.06 op
45 9.83±0.05 8.42±0.04 4.23±0.08 2.78±0.08 2.04±0.05 yr
ig
MS-325 0 10.02±0.05 8.92±0.04 4.72±0.05 3.03±0.05 2.62±0.08 h
25 9.64±0.05 8.57±0.05 4.46±0.06 2.87±0.13 2.41±0.12 t la
25d 9.56±0.09 8.31±0.09 4.41±0.09 2.92±0.03 2.43±0.15 w
35 9.60±0.04 8.46±0.02 4.57±0.03 2.82±0.03 2.19±0.05 . Y
o
45 9.58±0.03 8.38±0.02 4.51±0.01 2.76±0.02 2.14±0.02 u
m
HMDTPA 0 10.83±0.06 8.52±0.07 4.98±0.04 2.84±0.11 2.21±0.10 a
25 10.71±0.07 8.47±0.07 4.64±0.09 2.82±0.12 2.22±0.11 y c
35 10.11±0.08 8.42±0.04 4.40±0.05 2.81±0.09 2.24±0.07 o
p
45 9.80±0.05 8.38±0.06 4.35±0.09 2.85±0.11 2.07±0.10 y
a
n
ba::00..11MMKKNClOf3rofrmomReRf.ef[.4[42]0;b]; d dis
c:0.1MfromRef.[20b];and tr
ib
d:fromRef.[27]. u
te
th
is
Table2.ThermodynamicdataforstepwiseprotonationofLat25◦C; a
r
I=0.10M(NaClO4). ticle
Ligands ΔG ΔH ΔS fo
r
(kJmol−1) (kJmol−1) (JK−1mol−1) y
o
u
r
DHT+PLA=(HH5LL) −58.03±0.17 −35.15±2.56 77±9 pers
o
HL+L=H L −49.93±0.11 −13.09±0.58 123±2 n
H2L+L=H23L −25.79±0.23 −4.21±0.06 72±1 al u
HL+L=H L −16.20±0.17 −0.80±0.13 52±1 s
3 4 e
HM4SL−+32L5=(HH5L5L) −12.1±0.40 −0.70±0.32 38±2 only
H+L=HL −55.00±0.29 −26.62±1.34 95±5 . O
HL+L=H2L −48.90±0.17 −10.06±0.41 130±2 th
HL+L=H L −26.93±0.34 −1.51±0.09 85±2 e
H2L+L=H3L −16.38±0.74 −0.48±0.04 53±2 r u
3 4 s
HL+L=H L −13.75±0.68 3.21±0.70 57±3 e
HM4 DTPA(H5L) is
H+L=HL 5 −61.10±0.40 −35.8±3.99 85±13 on
HL+L=H L −48.33±0.40 −12.53±1.34 120±5 ly
HH2LL++LL==HH23LL −−2166..4089±±00..5618 −42..0121±±01..736 6715±±35 allow
3 4
H4L+L=H5L −12.67±0.63 1.20±0.06 46±2 ed
w
ith
w
shearsvebdeeunndreerpotrhteedcofnodritGiodnHs(eDmTpPlAoy)−e,dEinuHth(DisTsPtAud)−y, abnudt ritte
n
NdH(DTPA)− [27,28]. Linear curves of 1/D vs. [L]5− p
corr e
for Am3+, Cm3+ and Eu3+ (Fig.3, representative graph for rm
Am3+,Cm3+andEu3+forMS-325at25◦C)indicatethefor- iss
mationofonly1:1complexes.Thestabilityconstantsofthe ion
Ln3+withtheseligandsdeterminedbycompetitiontitrations by
are summarized in Table3, while those with Am3+, Cm3+ th
e
andEu3+ at different temperatures measured bysolvent ex- c
o
traction are listed in Table4. Representative potentiometric p
y
r
titration curvesfortheformationofGd-DTPA,Yb-MS-325 ig
h
andLu-MS-325areshowninFig.4.Thebestfitofthedata Fig.2. Speciation diagrams for Am3+ with DTPA, MS-325 and t h
by the Hyperquad program indicates that only monomeric HMDTPA,drawnat[M]=[L]=1mM. old
e
r
.
226 P.Thakuretal. Th
is
a
Table3.StabilityconstantsofLn3+,Am3+andCm3+withDTPA,MS- rtic
3(M253+a+ndLH5−M=DMTPLA2−a)t. I=0.1M(NaClO4);T=25◦Cforthereaction le is
p
r
M3+ DTPA MS-325 HMDTPA Method ote
c
te
PLra 2119..2326±±00..0096 1198..6927±±00..0076 2119..2462±±00..0078 ppoott d by
Nd 21.45±0.08 20.41±0.11 21.46±0.09 pot G
e
Sm 21.58±0.07 20.85±0.10 21.48±0.08 pot rm
Eu 22.49±0.11 21.58±0.09 22.58±0.09 pot a
n
Gd 22.63±0.08 21.82±0.07 22.70±0.12 pot c
Tb 22.72±0.09 22.02±0.12 22.78±0.08 pot op
Dy 22.79±0.10 22.15±0.12 22.81±0.11 pot yr
Ho 22.75±0.10 22.18±0.08 22.76±0.12 pot igh
TEmr 2222..7723±±00..1100 2222..1120±±00..1102 2222..7754±±00..1121 ppoott t law
Yb 22.61±0.11 22.09±0.09 22.69±0.09 pot . Y
Fig.3. The variationof 1/Dcorr for Am3+, Cm3+ and Eu3+ as a func- Lu 22.53±0.06 21.78±0.09 22.54±0.07 pot ou
tionof[MS-3255−];I=0.1M(NaClO)andT=25◦C;[D2EHPA]= Am 22.57±0.14 21.65±0.13 22.63±0.14 sx m
4
5.0×10−4MforAm3+ andCm3+ and2.0×10−4MforEu3+. Cm 22.64±0.13 21.77±0.15 22.60±0.15 sx ay
Eu 22.56±0.14 21.65±0.13 22.58±0.16 sx c
o
p
complex,MLformduringthetitration.Forcomparisonpur- pot=potentiometric,sx=solventextraction. y a
pose,theliteraturestabilityconstantsvaluesfortheseligand Theuncertaintieslistedarethestandarderrorsprovidedbythestatistics n
d
are also included in Table4. The values at 0.1M from this ofthenon-linearregressionanalysisofindividualdatasetsascarried d
outbytheHYPERQUADprogram. is
workAm-DTPA(22.57),Cm-DTPA(22.64),andEu-DTPA tr
ib
(22.56) are in fair agreement with the values of Am-DTPA u
te
(22.92), Cm-DTPA (22.99) and Eu-DTPA (22.40) reported creasesbetweenEuandGd,andthenslowlyincreasesforTb th
Gbyd-BMaySb-3a2rz5a=t 02.21.6M3NisHsl4iCghlOtly4 [h1i4g]h.eHrothwaenvtehre, ovuarluveamlueeaos-f atrnedndDiys,aonftdenfinoabllsyerdveecdreianseLsnf-raomminEoprotolyLcaur.bSouxcyhlatsetabciolmity- is ar
uredbyChoppinetal.,forGd-MS-325=22.11atthesame plexes,ifthenumberofdonoratomsissevenormore[30]. ticle
ionic strength [27]. The stability constants values for other For instance, the stability constant values increase mono- fo
r
membersofthelanthanide seriesarenotreported,whilefor tonically across the Ln-series for the ligands with fewer y
o
actinidesnosuchvaluesareavailableintheliterature. coordinationsites(e.g.,EDTA,CDTA(trans-1,2diaminocy- u
r
The stability constant values of our three ligands vary clohexanetetraacetic acid)andTMEDTA(1,4dinitrobutane p
e
r
non-monotonically across the Ln-series. Fig.5 shows the tetraacetic acid)) [31], while stability trend similar to those s
o
plot of free energy of complexation (ΔG) vs. lanthanide observed in this study were reported for the heptaden- na
ionic radius for the MS-325 and HMDTPA complexes tate Ln-TEDTA(thiobis(ethylenediamine tetraacetic acid)), l u
s
(values of ionic radii were taken from Ref. [29] for CN= Ln-DEATA(N,N-bis (2-aminoethyl)aniline tetraacetic acid e o
9).TheΔG gradually increases fromLatoSm,weaklyde- (BEATA)) [30], and octadentate Ln-DTPA-MA (DTPA-N- nly
. O
th
e
Table4.StabilityconstantsofEu3+,Am3+andCm3+withDTPA,MS-325andHMDTPAatI=0.1M(NaClO4);T=0–45◦C. r u
s
e
0 25 35 45 Ref. is
o
n
Eu3++DTPA5−=Eu(DTPA)2− 22.97±0.14 22.56±0.14 22.31±0.15 22.11±0.16 Thiswork ly a
22.40±0.07a [14] llo
22.39±0.08b [15] w
20.87±0.07c [45] ed
22.77±0.04 [46] w
21.00±0.08d [28] ith
20.97±0.19d [28] w
r
Am3++DTPA5−=Am(DTPA)2− 22.98±0.15 22.57±0.14 22.30±0.15 22.02±0.14 Thiswork itte
22.92±0.02a [14] n p
21.14c [17] e
r
m
Cm3++DTPA5−=Cm(DTPA)2− 23.01±0.15 22.64±0.13 22.31±0.16 22.04±0.14 Thiswork is
22.99±0.01a [14] s
21.26c [17] ion
Eu3++MS-325=Eu(MS-325)2− 21.99±0.16 21.65±0.13 21.58±0.15 21.40±0.16 Thiswork by
Am3++MS-325=Am(MS-325)2− 22.04±0.16 21.77±0.13 21.56±0.14 21.46±0.15 Thiswork th
Cm3++MS-325=Cm(MS-325)2− 22.02±0.14 21.65±0.15 21.56±0.16 21.41±0.16 Thiswork e c
Eu3++HMDTPA=Eu(HMDTPA)2− 23.01±0.15 22.58±0.13 22.18±0.16 21.86±0.15 Thiswork op
Am3++HMDTPA=Am(HMDTPA)2− 23.09±0.17 22.63±0.15 22.32±0.14 22.01±0.15 Thiswork yr
Cm3++HMDTPA=Cm(HMDTPA)2− 23.05±0.16 22.60±0.14 22.32±0.15 21.95±0.15 Thiswork igh
t h
a:0.1NH ClO ;b:0.1KNO ,c:0.5NaClO;d:1.0MNaClO . o
4 4 3 4 4 ld
e
r
.
ComplexationthermodynamicsandstructuralstudiesoftrivalentactinideandlanthanidecomplexeswithDTPA,MS-325andHMDTPA 227 T
h
is
a
r
tic
le
is
p
r
o
te
c
te
d
b
y
G
e
r
m
a
n
c
o
p
y
r
ig
h
t la
w
. Y
o
FLiug-.M4.S-P3o2t5enatnimdeYtrbic-MtiStr-a3t2io5ncocumrpvleexfeosr,tIhe=f0o.r1mMatiNonaColfOG.d[-MD3T+P]A=, Fig.6. Variation of the stability constant, logβ101, of some Gd com- u m
0.005M,[L]=0.015M,[EDTA]=0.04M. 4 plexeswithDTPAderivativesligands. ay
c
o
p
the number of groups in the carboxylates arms decrease y
a
the stability values by ca. three to six log units. For ex- n
d
ample, DTPA-BMA (DTPA-bis(methoxyethylamide)), Gd d
is
(DTPA-BMA)=16.84±0.28[33],DTPA-MMEA(DTPA- tr
bis(methylmethoxyethylamide)), Gd(DTPA-MMEA) = ibu
17.69±0.21 [32], DTPA-HEMEA (DTPA-bis(hydroxy- te th
ethylmethoxyethylamide)), Gd(DTPA-HEMEA)=17.49± is
0.14 [33], DTPA-BIPA (DTPA-bis(iso-propylamide)), ar
Gd(DTPA-BIPA) = 17.07±0.04 [34], DTPA-BTBA ticle
(DTPA-bis(tert-butylamide)), Gd(DTPA-BTBA)=17.15± fo
0.03 [34], DTPA-BBA (DTPA-bis(benzylamide)), Gd r y
o
(DTPA-BBA) = 16.48±0.05 [34], in all these cases two u
r
of the terminal carboxylate groups of DTPA are replaced p
e
r
by amide functionalities result in complexes with lower s
o
n
stability than DTPA. This is because of weaker donor a
ability of the amide group and the lower basicity of the l u
s
Fig.5.VariationofstabilityconstantofLn-HMDTPAandLn-MS-325 terminal nitrogen atoms. Similar decrease in stability is e o
complexes with ionic radii along the lanthanide series. Ionic radius alsoreportedforDTPA-BGAM(logβGd-DTPA-BGAM=16.02± nly
correspondstoaCN=9. 0.05) [35] and DTPA-BP ((N,N(cid:8))-bis(2-pyridylmethyl-di- . O
ethylenetriaminetriaacetic acid)) (logβ =16.83± th
Gd-DTPA-BP e
0.11, I =0.1MNaCl)[36]inwhichtwoterminalcarboxy- r u
s
monomethylamide) complexes [32]. This is either because late groups of DTPA are replaced by sugar and pyridyl- e
of the change in hydration number from 9 to 8 with de- methyl groups, respectively. The decrease in stability is is o
creasing ionic radii or the steric hindrance imposes by not only restricted to terminally substituted DTPA lig- n
ly
various donor groups upon complexation. Acomparison of ands. The middle substituted DTPA ligands i.e., DTPA- a
the stability constants of the complexes demonstrates the MA (DTPA-monoamide), DTPA-MP (N(cid:8)-2-pyridylmethyl- llow
order: DTPA≈HMDTPA>MS-325, indicating that intro- diethylenetriaminetetraacetic acid) and DTPA-HP (N-2- ed
duction of phosphodiester groups on the ethylenediamine hydroxypropyl-diethylenetriaminetetraacetic acid) in which w
backbone of DTPA decreases the stability constant of the amiddle carboxylate group ofDTPAis replaced by amide, ith w
Min(MtheS-3st2a5b)i2l−itycocmonpslteaxn.tOvnaluthees ootfheHrMhaDnTd,PAtheansdimDilaTrPitAy palysroidyrlempoetrhteydl otrohfyodrrmoxywlperaokpeyrl gcoromupplse,xeressptehcatniveDlyTaPrAe ritte
n
withthesecations implies that theincorporation ofhydrox- (logβ =19.9±0.048 at I =0.1M KCl [32], p
Gd-DTPA-MA e
ymethyl groups has not significantly altered the nature and logβ =21.59±0.07 [36], and logβ = rm
tthheessttreernicgtehffoefctthoefcothmepbleuxlkaytiosnu.bTsthitiusemntasycboenestxrpalianiinnegdtbhye m18o.4d8iGfi±dc-Da0TtPi.Ao0-n5MsP[o3f6t]haetDIT=PA0.l1igManMdsed4oNnNoOts3)ig.nHifiowcGaednv-DtelTyrP,Aa-tHfhfPeescet ission
ligandsintoachelationintheMS-325complex. thecoordinationgeometryaboutthecentralmetalcations. by
Fig.6 shows the stability constant plot of some Gd- Fig.7 shows representative calorimetric titration curve th
e
complexes with several closely related DTPA ligands. of the three successive protonation steps of DTPA (H L2−, c
3 o
All these ligands are, like the parent ligand DTPA, oc- H L−, H L). Using the data from multiple titrations with p
4 5 y
r
tadentate. An increase in the steric constraints of the differentreagentconcentrations inconjunction withthesta- ig
h
polyaminocarboxylate ligand either by increasing the num- bility constants obtained by potentiometer and extraction t h
ber of groups in the ligand backbone or by increasing experiments, the enthalpies of complexation at 25◦C were o
ld
e
r
.
228 P.Thakuretal. Th
is
a
r
tic
le
is
p
r
o
te
c
te
d
b
y
G
e
r
m
a
n
c
o
p
y
r
ig
h
t la
w
. Y
Fig.8.Van’tHoffplotofthestabilityconstantsofCm-HMDTPAand o
u
Cm-MS-325complexes,I=0.1MNaClO4. m
a
y
c
o
p
the large exothermicity of the Eu-DTPA and Eu-HMDTPA y
a
complexationsuggeststhatM–Ninteractionsarestrongeras n
d
comparedtotheM–Ninteractions inM-MS-325.Thelarge d
is
positive entropies values are responsible for the higher sta- tr
ib
bilitiesoftheseligandswith f-elementcations. u
te
th
is
3.2Luminescencelifetimemeasurements a
r
Table6 lists the luminescence lifetimes and the calculated ticle
0N.H120OMva(lNueasCflOor)t.hTehEeua3q+uaenodusCEmu33++ schoomwpslepxeeaskwatit5h7L8.9i0n for y
4 o
nmwithlifetimeof113±5and N of8.5,whileforCm3+ u
thepositionofthepeakisat396.70H2nOmwithlifetimeof64± r p
e
Fig.7. Calorimetric titrations of protonation of DTPA, t=25◦C, 3and N of9.1.Thefluorescence lifetimeofCm3+ inso- rs
NTIha=eC0luO.p14p.MerInfiNitgiauaClrelcOios4n.tchVeen0tt=rhaet1rimo.4no5sgmorafLmD; oTtiftPrAtahnet=:ti0t0r.a.00t2i0o82nM4s–.0H.0C0l5O54MinD0T.1PAM. lSuitniocentwhHea2nsOfisersvteorablsgerrvoeudpsbyhaBveeitrzepaonrdteHdetshselelrifientim19e80fo[r3t7h]e. onal us
593nm emission of Cm3+. As shown in Table6, the life- e o
timesatroomtemperatureinpureH2Omeasuredbydifferent nly
calculated. The enthalpy values as well as the entropies of groupsagreewellwitheachother(65–68μsforCm3+). . O
complexation calculated are summarized in Table5. The The excitation spectra of Eu-L at a ratio of 1:2 and th
e
stability constants of Cm-HMDTPA and Cm-MS-325 ob- pH=3.6 show a peak at 579.91nm with lifetimes and r u
s
tained at different temperatures are plotted as functions of N (Table6 and Fig.9) consistent with the formation e
1tw/eTen(Klo)gaβreanshdo1w/nTisnugFgiges.t8t.hTathtehelineeffaerctcoorfretelamtipoenrsatubree- opHfH2E1Ou3(.0L)i(nHd2icOa)t2e−s.tLheacfkormofatciohnanogfe1in:1NcHo2mOpvleaxlueosveurpthtios is on
ly
onthecomplexationcouldbeapproximatelydescribedwith pH range. Brittain etal., [38] also reported no change in a
the constant enthalpy approach in the temperature range of the hydration number for Eu(DTPA)2− up to pH of about llow
0–45◦C. From the slopes of the linear fits, the enthalpies 11.0. The lifetime value measured in various studies for ed
of complexation (in kJmol−1) for reaction 2 were calcu- the Eu(DTPA)2− species agrees with each other (Table6). w
lated (Table5).Ourenthalpy value of−32.6±1.1kJmol−1 The formation of hydrolyzed species, Eu(L)(OH)3− as re- ith w
afogrretehsewEeull-DwTitPhAthceomvapllueexs(e−le3c2tekdJimnotlh−e1 NatIS0T.1dMat)a.bFasoer 1p,o4r,t7e-dtriins(tchaerbcoaxseymofetEhuy(lD)-9T,P1A7--dDioiexno)-(1O,4H,7)−,1(0D,1T3P,A16--Dhieexna-= ritte
n
Am and Cm, no such values were recommended in the azocycloocta decane)andEu(EDTA)(OH)(H O) 2− wasnot p
2 2 e
NIST database. The complexation enthalpies are negative observedinourstudy.ThecrystalstructureofEu(DTPA)2− rm
asexpectedforstrongmetal-ligand interaction, whereasthe has been shown to be an octadentate in which DTPAbinds iss
entropy values are positive which is consistent with inner viafivecarboxylate oxygenatomsandthreeaminenitrogen ion
sphere coordination with displacement of water molecules atoms with one water of hydration remain attached to the by
fromthehydrationsphereofthemetalcations.Thisiscom- Eu3+ [39]. th
e
monforchelatingligands[29],andisobservedinthiswork. The Cm3+ also forms 1:1 complex over pH range c
o
The complexation enthalpies (ΔH) for M-DTPA and M- 3.6–13.0.However,Cm(L)2− hasaslightlylargerhydration p
y
HMDTPA complexation are ca. 15kJmol−1 more exother- number (NH2O=1.5) than that of Eu(L)2−. This can be at- righ
mic than the corresponding complexes with MS-325. The tributed to the larger total average coordination number for t h
M–N interaction strongly influences the value of ΔH and Cm3+ (9.0±0.5) as compared to that the Eu3+ (8.5±0.5) o
ld
e
r
.
ComplexationthermodynamicsandstructuralstudiesoftrivalentactinideandlanthanidecomplexeswithDTPA,MS-325andHMDTPA 229 T
h
is
a
Table5. Thermodynamic data of the 1:1 complexes of Ln, Am and Cm with DTPA, MS-325 and rtic
HMDTPAat I=0.1M(NaClO4);T=25◦C. le is
Method ΔG ΔH ΔS Ref. pr
(kJmol−1) (kJmol−1) (JK−1mol−1) ote
c
te
DNTdPA c −122.39±0.46 −29.7±1.3 311±5 Thiswork d by
Eu c −128.32±0.63 −32.6±1.1 295±4 Thiswork G
e
sx −128.72±0.79 −30.8±7.3 328±25 Thiswork rm
c −127.75±0.4 −32 320 [20a] a
n
c −119.1±0.4a −39.8±1.5 266±5 [45] c
Dy c −130.00±0.57 −33.1±1.5 325±5 Thiswork op
Am sx −128.78±0.79 −34.1±7.2 317±24 Thiswork yr
c −120.60±0.6a −39.5±1.0 272±5 [45] igh
Cm sx −129.18±0.74 −34.7±7.2 317±24 Thiswork t la
MS-325 w
Nd c −116.46±0.63 −16.8±2.1 334±7 Thiswork . Y
o
Eu c −123.53±0.51 −18.9±1.2 351±4 Thiswork u
Eu sx −123.13±0.74 −20.7±7.7 343±26 Thiswork m
a
Dy c −126.38±0.68 −20.2±2.8 356±10 Thiswork y
Am sx −124.22±0.74 −21.6±7.6 344±20 Thiswork co
Cm sx −123.53±0.86 −22.0±7.3 341±25 Thiswork py
a
HMDTPA n
Nd c −122.45±0.51 −39.7±2.5 278±9 Thiswork d d
Eu c −128.27±0.51 −41.9±2.2 289±8 Thiswork is
Eu sx −128.84±0.91 −41.2±7.4 294±25 Thiswork trib
Dy sx −130.38±0.62 −43.6±2.7 291±9 Thiswork u
CAmm ssxx −−112289..9152±±00..8759 −−3389..94±±78..70 330021±±2262 TThhiisswwoorrkk te this
a
a:0.5M(NaClO4);pw=presentwork;sx=solventextraction;c=calorimeter. rtic
le
fo
r
Table6.LuminescencelifetimeandcalculatednumberofprimarycoordinationspherewaterforEu3+andCm3+complexes y
o
withL(I=0.10MNaClO );T=25◦C. u
4 r
p
e
Components pH/medium Peak(pnoms)itions Species Lif(μetsi)me (±NH02.O5) Ref. rson
a
l u
Eu3+(aq) 2.2 578.90 − 113±5 8.5 Thiswork s
e
2.0 579.04 − 117 9.0 [47] o
n
Cm3+ (aq) 2.5 396.7 − 64±3 9.1 Thiswork ly
397 − − 9.2 [5] . O
0.1MHClO 593 − 68±3 8.7 [48] th
1MHClO 4 593.8 − 63 9.4 [48] er
0.1MHClO44/ 593 − 65±2 9.1 [48] use
1MHCl is
Eu-DTPA 3.6–11.0 579.91 Eu(DTPA)2− 650±4 0.9 Thiswork o
n
13.0 579.98 Eu(DTPA)2− 549±5 1.2 Thiswork ly
2.0–11.0 − Eu(DTPA)2− 680 0.95 [5] a
− 579.84 Eu(DTPA)2− 630 1.1 [49] llo
w
− Eu(DTPA)2− 560–638 − [28] e
d
Eu-MS-325 3.6–11.0 579.91 Eu(MS-325)2− 617±7 1.0 Thiswork w
13.0 579.90 Eu(MS-325)2− 526±8 1.3 Thiswork ith
Eu-HMDTPA 3.6–11.0 579.92 Eu(HMDTPA)2− 632±10 1.0 Thiswork wr
13.0 579.91 Eu(HMDTPA)2− 546±8 1.2 Thiswork itte
Cm-DTPA 3.6–9.0 404.20,400.32,396.51 Cm(DTPA)2− 285±6 1.4 Thiswork n p
13.0 404.20,400.20,396.51 Cm(DTPA)2− 242±8 1.8 Thiswork e
r
− Cm(DTPA)2− 257 1.65 [5] m
is
Cm-MS-325 3.6–9.0 404.05,400.32,396.51 Cm(MS-325)2− 269±6 1.5 Thiswork s
13.0 404.04,400.25,396.54 Cm(MS-325)2− 232±7 1.9 Thiswork ion
Cm-HMDTPA 3.6–9.0 404.04,400.32,396.51 Cm(HMDTPA)2− 271±7 1.5 Thiswork by
13.0 404.12,400.38,396.78 Cm(HMDTPA)2− 242±6 1.8 Thiswork th
e
c
o
p
y
inaminopolycarboxylates [5].TheDFT(density functional of Cm3+ [19]. The protonated complex of L was also not rig
h
theory) calculations are also consistent with the presence observed in the present systems as such complexes usually t h
of nine waters of hydration in the inner coordination shell formatpH<3.0[40]. o
ld
e
r
.
230 P.Thakuretal. Th
is
a
distance identifies it as being associated as a carboxylate rtic
group. The EXAFS data analysis (Table7) confirmed the le
formationofEu(DTPA)(H2O)2−withDTPAbindingviafive is p
carboxylates and three nitrogens which is consistent with ro
the crystallography analysis [2]. In the crystal structure of tec
cKr2y[sEtaul(lDogTrPaAph)y(H[23O9)]], dtheetearmveirnaegdeiEnus−oOlidbpohnadsedibstyanXce-raoyf ted by
2.41Å and Eu-N bond distance of 2.69Å were reported. G
e
Thesebonddistancesagreewellwiththosemeasuredbyso- rm
a
lution EXAFS for Eu-DTPA complex. The Eu bonding in n
the Eu:HMDTPA complex consists of 5.6±0.4 oxygens at co
p
a distance of 2.40±0.01Å, 2.9±0.4 nitrogens at 2.79± y
r
0.02Åand3.6±1.0carboxylates carbons at3.33±0.02Å. igh
These data lead to a total coordination number, CN = 8.5 t la
(1HMDTPA (5 carboxylates + 3 nitrogens)+1H2O) for w. Y
Eu3+ in Eu(HMDTPA)(H O)2−. Unfortunately, the solution o
2 u
EXAFSspectraofEu-MS-325wereveryinclusive.Despite m
a
severalattempts,wehavenotbeenabletoobtaingoodqual- y
c
ityspectrafortheEu-MS-325system. o
p
GeometryoptimizationofstructuresofLaL2−complexes y
a
were performed in aqueous solution at the DFT (level) by n
d
using LANL2DZ basis set. In these calculations second- d
is
sphere water molecules were excluded, and solvent effects tr
ib
were included by using the polarizable continuum model u
te
(PCM)[41].Theoptimized structures andthebondlengths th
are shownin Fig.11andTable8,respectively. Inthe struc- is
ture of LaL2−, the DTPA ligand is octadentate with five ar
1HFiM:g2.D,9.TpPHTAh=e(1ae1)x.5cEi;tua(:tciH)onMCmDspT:ePHcAtMr,aD1oTf:P2AE,,up31+H:2=a:n3dp.H6C;=m(b33+).c6oEmaunp:dlHe(xMde)sDT1wP:iAt2h,, otrxoyggeennataotommssfrformomthteheamcainrbeogxryoluaptes cgoroourdpisnaatnindgthtoreLean3+i-. ticle for
pH=11.5; [Eu3+]=1×10−4M, [Cm3+]=2×10−6M; I =0.10M The complex contains one water molecule in the inner co- yo
(NaClO4). norudminbaetrioonf9sp(hFeirge.1o1f)L.Ta3h+e,osaxtyisgfeyninagtotmhesftorotaml cthoeorcdairnbaotxioyn- ur p
e
r
3.3EXAFSstudies late groups and water are considerably closer to the cen- s
o
tral La atom (La−O=2.520 to 2.610Å) than the nitrogen na
The formation and the coordination environment of M3+ atoms from the amine groups (La−N=2.829 to 2.937Å). l u
s
in these complexes were further confirmed by solution Averagebondlengthsincreaseintheorder:La−Ocarboxylate < e o
EXAFS studies. Fig.10 shows the fitted and K3-weighted La−Owater <La−N, reflecting the preference of lanthanum nly
(2.0–11.0Å) LIII edge EXAFSspectra forEu:DTPA(1:2, forharddonors inthese strongly ionic bonds.This trend of . O
pH=6.0),Eu:HMDTPA(1:2,pH=9.3),andtheirFourier short M–O bonds and long M–N bonds is seen in a variety th
e
transformed spectra in de-ionized water. The spectra show of aminopolycarboxylate complexes. For Ln-EDTA com- r u
s
similarity both in phase andamplitude, supporting the sim- plex, it is seen that the average Ln–O bond is 0.0321Å e
ilarity in the bonding of carboxylates and nitrogens. The shorter than that calculated from ionic radii [42], while is o
best fit data and the corresponding Debye-Waller factors the average Ln–N bond is 0.087Å longer than calculated. n
ly
are given in Table7. The nearest neighbors of Eu in the The Ln(DTPA)2− complexes (Ln = Nd, Eu, Dy, Ho, Er a
Eu:DTPA complex are 5.8±1.0 oxygens with Eu−O dis- and Yb) also have shown to have shorter Ln–O and longer llow
tances of 2.40±0.01Å, 2.7±0.9 nitrogens at a distance Ln–N interactions than expected [43]. Using the optimized ed
of 2.81±0.02Å, and 4.2±1.5 carbons at a distance of structure of La(DTPA)2− as a starting point, the structures w
3.31±0.02Å (Table7). The presence of carbon at this of La(HMDTPA)2− were further optimized. The optimized ith w
r
itte
n
p
e
r
m
is
s
io
n
b
y
th
e
c
Fig.10.The fittedk3-weighted(2.0–12.0Å−1) op
y
(a)andFouriertransformedspectra(b).Show- r
ing association of Eu3+ with DTPA and igh
HMDTPA. Experimental data (–); fitted data t h
(---). old
e
r
.