3-1 Lecture 3: Actinium Chemistry Lecture notes from Radiochemistry of the Rare Earths, Scandium, Yttrium, and Actinium Chemistry of actinides §Metals §Soluble and insoluble salts §Complex ions and chelate compounds §Organic compounds §Separations

3-2 Actinium Isotopes

3-3 Actinium Isotopes and fundamental data Ac is trivalent §Very similar chemistry to lanthanides and Y §Trivalent chemistry §electropositive 227 Ac §From 235 U decay §Beta emitter 225 Ac has been proposed for nuclear medicine §Ac from 229 Th parent àAlpha emitting therapeutic agent §Use of 225 Ac to produce 213 Bi Chemistry of Ac basis of use as radiopharmaceutical §Use of Ac in delivery to tumor based on fundamental chemical interactions §Separation of Bi daughter from Ac parent Atomic radius §195 pm Ionic radius §126 pm §6-coordinate

3-4 Redox Trivalent is predominant state Divalent state postulated based on similarities to Ac behavior with divalent Eu and Sm §Reinfored with polarogram data àTwo waves in HClO 4, pH *Ac 2+ +2e - +Hg  Ac(Hg) *Ac 3+ +3e - +Hg  Ac(Hg) §Other experiments failed to find divalent state

3-5 Ac Metal Preparation of metals difficult §Tendency to form oxides and hydroxides in water § Formation in electrolytic reduction àMolten salt systems §Reduction of fluoride salts by metallic Ca §Need to melt both CaF 2 and resulting metal Metal oxidizes in air §4Ac + 3O 2 → 2Ac 2 O 3 §Useful starting material for synthesis àAc 2 O 3 + 3H 2 S  Ac 2 S 3 + 3H 2 O Density §10.07 g/mL Melting point §1050 °C Boiling Point §3300 °C Crystal structure §fcc

3-6 Ac preparation and purification Separation from U ores §Ores also contain a fair amount of lanthanides, require separation Nuclear reactions and generators §Irradiation of 226 Ra  226 Ra(n,  ) 227 Ra, beta decay to 227 Ac  227 Ac   =762 barns § 225 Ac from 229 Th generator àStart with 233 U from neutron activation of 232 Th

3-7 Ac purification: solvent extraction Extration with TTA pH control of extraction §Ac extracts well above pH 6 àHydrolysis in this range §Synergist extraction with 0.1 TTA in 0.1 M TBP àAbove pH 4 Keto Enol Hydrate

3-8 Ion exchange Cation exchange §Separation of 227 Ac from 227 Th and 223 Ra §Strong cation exchange àDOWEX 50 Organic stationary phases §Trioctylamine §Bis(2-ethyl- hexyl)phosphoric acid (HDEHP) §TBP §TTA Inorganic §MnO 2

3-9 Preparation of gram quantities of Ac Irradiation of multigram quantities of 226 Ra §Forms both 227 Ac and 228 Th § 222 Rn daughter from 226 Ra Irradiation of RaCO 3 §Dissolved in dilute HNO 3 àRa(NO 3 ) 2 precipitated *Recycle for further Ac production àTh and Ac remain in solution §5 M HNO 3, anion exchange àTh strongly absorbed, Ac only slightly §Oxalate precipitation of Ac àCalcination after precipitation àUsed to form Ac 2 O 3

3-10 Ac salts Salts are soluble in most acids §Some salt are insoluble and used in separations based on precipitation Most data from one study §Each compound prepared from less than 10 µg §Purified by TTA Hydroxides §pK 1h =9.4 §Described by electrostatic model of hydrolysis §Linearity of log K 1h versus 1/ionic radius àFor trivalent metal ions, actually related to charge density àHydrolyzes less than trivalent lanthanides or actinides *More basic than lanthanides Ac hydrolysis paper

3-11 Ac salts Fluorides §AcF 3 §Density g/mL §Formation of AcF 3 àAc(OH) 3 + 3HF  AcF 3 + 3H 2 O Oxalate §Oxalates used in precipitation of metal ions §Oxalate salt of actinium used to form oxide §Ac precipitated as an oxalate by the addition of an oxalic acid §Oxalates are destroyed by boiling concentrated HNO 3 or HClO 4 §In 0.1 M HNO M oxalic acid àAc oxalate solubility 24 mg/L

3-12 Ac salts Chloride §Melting point: 1051°C (sublimes) §Density: g/mL §Formation reaction à4Ac(OH) 3 + 3CCl 4  4AcCl 3 + 3CO 2 + 6H 2 O Bromide §Melting point: 1051°C §Boiling point: 3198°C §Density: g/mL §Formation reaction àAc 2 O 3 + 2AlBr 3  2AcBr 3 + Al 2 O 3 §For Iodide àAc 2 O 3 + 2Al + 3I 2  2AcI 3 + Al 2 O 3

3-13 Solubility and complexation Generally co-precipitation with insoluble salts from cation §Fluorides, hydroxides of metal ion §Ac precipitated by Pb sulfate Solubility of oxalates evaluated §Effects of radiolysis àLa solubility half of Ac solubility àK sp around 5E-27 *Large decrease in pH due to radiolysis from 227 Th *Purified Ac did not show large pH decrease Resembles lanthanum in complexation §Generally lower for Ac Determined in tracer experiments §Solvent extraction Compared to ionic radius to some evaluated constants §HDEHP

3-14 Radiocolloid Separation of 227 Ac from 227 Th and 223 Ra §Formation of colliods àAc goes into solution, Th remains in solid phase §Sorption of Ac onto filter increases with pH and time àAbove pH 5 filter separation of Ac by centrifuge Analytical chemistry of Ac §Radiation detection §Neutron activation for 227 Ac à1E-17 g level §Activity used to determine to 1E-20 g

3-15 Actinium uses Heat sources § 227 Ac multiCi amount §5 alpha particles Neutron sources  ,n source using 227 Ac Nuclear medicine §Medical use based on ligand  Bone treatments (polyphosphonate ) § 225 Ac suitable isotope àDecay series produces alpha and beta *No hard gammas §Ac bound by marcocyclic compounds §HEHA incorporates Ac  1,4,7,10,13,16-hexaazacyclohexadecane-N,N′,N′,N′,N′,N′-hexaacetic acid Geotracer §Compare 231 Pa with 227 Ac àAc higher than Pa in deep seawater àAc as a tracer for deep seawater circulation

3-16 Review Actinide isotopes §Lifetimes, production Actinium data §X-ray, radii, density Redox §Oxidation states Preparation and purification §Solvent extraction and ion exchange Compounds and properties Uses of actinium

3-17 Questions What is the longest lived Ac isotope? What are two different ways to obtain actinium §Provide the isotopes What Ac oxidation state can be found in solution? How is Ac separated from U Which Ac species are insoluble? What are some uses of Ac?

3-18 Pop Quiz Describe a method for separating Ac from the lanthanides.