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11) The of Artificial and Radioelements (1)

Radioactive elements in the

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11) The Chemistry of Artificial and Radioelements (2)

Technetium ( 43)

- first artificial element - discovered in 1939 by deuteron bombardment of a plate) 94Mo (d,n) 95mTc, 95Mo (d,n) 97mTc!!!!!! - named in 1947 according "technetos“ (Greek, „The Artificial“) - nearly no natural resources (only ultra-trace amounts due to of 238U (1 per 1012 in uranium ) - but one of the main products of - available in kg-amounts (prize: 1 g ≈ 100 $ )

Technetium Chemistry

- typical transition - oxidation states from „0“ to „+7“ - - most stable oxidation states +4 and +7,most stable compounds TcO2, TcO4 - rich coordination chemistry (stabilisation of the different oxidation states depends on the reducing conditions and the supplied) - rich cluster chemistry 131

1 11) The Chemistry of Artificial and Radioelements (3)

Technetium coordination chemistry with

- TcO4

conc. HCl, CO, conc.HCl, NaN3, reflux BH3, reflux conc.HCl RT

conc.HCl, VI - reflux I 2- [Tc NCl4] conc.HCl, [Tc (CO)3Cl3]

Nitrido-Core NH2OH, RT Tricarbonyl-Core

V - [TcII(NO)Cl ]- [Tc OCl4] 4 Oxo-Core Nitrosyl-Core IV 2- [Tc Cl6] 132

11) The Chemistry of Artificial and Radioelements (4) Technetium coordination chemistry

+6 +4 +2 ±0

- reduction oxydation Tc metal TcO4

+7 +5 +3 +1

2

133

2 11) The Chemistry of Artificial and Radioelements (5)

Technetium cluster chemistry

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11) The Chemistry of Artificial and Radioelements (6)

Promethium chemistry

- discovery in 1947 (last gap in the Periodic Table was closed) - between 136Pm and 154Pm, longest half-life 140Pm: 17.7 a - typical element - chemistry is comparable with that of its neighbours Nd and Sm - commercial use of 147Pm in batteries: direct photovoltaic process !!!

Energy of Pm2O3: 0,333 W/g

p-n transition of a

Radiovoltaic battery 135

3 11) The Chemistry of Artificial and Radioelements (7)

Polonium

- heaviest Element of the VI. - in it is exclusively available as 210 Po as a member of the uranium decay family (in pitchblend up to 0.1 mg per , 10-4 ppm) 210 β − ,22.3a 210 β − ,5.01d 210 α ,138.38d 206 82 Pb→ 83 Bi→ 84 Po→ 82 Pb

- discovery in 1898 by Marie by its radioactivity - use as α-emitter in sources

Chemistry - marked metal character (similar to ) - frequent oxidation states +2 and +4

- typical compounds: PoCl2 (rubin-red), PoCl4 (yellow), PoO2

- more alkaline than the homologes: Po(NO3)4, Po(SO4)2 are stable - no compound with organic ligands (strong would decompose the compound) 136

11) The Chemistry of Artificial and Radioelements (8)

Astatine - heaviest element of main group VII - practically no occurance in nature (At in natural decay series have half-lifes < 10 sec) - discovered in1940 by Corson, Mackenzie and Segre - artificial synthesis by bombardment of 209Bi with α-particles - longest half-life 210At: 8.1 h

Chemistry - behaviour similar to , but preference to cationic species - oxidation states: -1, 0, +1, +3, +5 , +7 -At+ cations form complexes with und „“ compounds

+ H N NH NH2 2 2 + + SC C S At S C At 2 10 6 H N NH NH2 2 2 + - - At + 2 Cl → [AtCl2] 137

4 11) The Chemistry of Artificial and Radioelements (9)

Radon - heaviest without stable isotopes - occurs in all natural decay series - main source of natural radioactivity - isotopes from 200Rn to 226Rn - longest half-life 222Rn: 3.8 days - synonyms: triton, thoron, actinon, emanation - main source: 226Ra (1g Ra yields 0,64cm3 Rn in 3 weeks)

Radon Chemistry - heaviest noble gas → easiest polarisation - should be more reactive than - heaviest alkaline metal without stable isotopes - discovered in 1939 (Margueritte Perey) - occurrence in natural decay family - overall amount in crust: about 15 g - isotopes: 201Fr to 229Fr (longest half-life 212Fr: 24 min) 138

11) The Chemistry of Artificial and Radioelements (10)

Radium - heaviest alkaline element, key element for the development of

- discovered in 1898 by Pierre and (isolation of RaCl2 from several of pitch blend (uranium ) - occurs on earth together with uranium (): 1 mg Ra per 3 kg U - isotopes: 206Ra to 230Ra - longest half-life 226Ra (1600a)

Actinium - element of the third group without stable isotopes - discovered in 1899 (A. Debierne) in uranium minerals - natural Ac (227Ac) is a ß- emitter (half-life: 21.77 a) with highly γ- products (hard to handle) - pure Ac-metal emits light in the dark

Actinium Chemistry - typical : „+3“ - chemistry is similar to that of lanthanium 139

5 11) The Chemistry of Artificial and Radioelements (11) - element of the series without stable isotopes - chemically related to the lanthanide elements (natural occurance in ) - discovered in 1828 by Berzelius in (Norwegian mineral) -thoriumisotopesfrom213Th to 236Th (longest half-life 232Th: 1.4 x 1010 a) - application in special ceramics

Thorium Chemistry - typical oxidation state „+4“

- well-established ‚‘ (ThO2, ThCl4, Th(NO3)4) and coordination chemistry due to the ready availability of the long-living isotope 232Th from natural sources - large with high charge Æ chemistry of high coordination numbers

Strongly distorted e.g. icosahedron 2- 12 in [Th(NO3)6]

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11) The Chemistry of Artificial and Radioelements (12)

Protactinium A part of the Uranium family series is important for the laboratory course:

- 238U (99.27% ) decays into 234Th (Half-life: 4.4 x 109 y, α-decay) - 234Th is radioactive itself and forms 234 Pa (Half-life 24.1 d, ß-decay) - this disintegration passes a transient state with a certain half-life ( the metastable 234mPa which is a γ -emitter) -Thisγ -emitter is the radioactive substance of almost all measuring experiments in the lab course

234m 91 Pa short half-life γ

α β - β - 238 234 234 234 α 230 90 92 U 9 91 92 90 4.47 10 a Th 24.1 d Pa 6.7 h U 2.44 105 a Th α 7.7 104 a

141 Uranium family family

6 11) The Chemistry of Artificial and Radioelements (13)

Uranium

- Most important actinide element - discovered in 1789 by Klaproth from the mineral pitch blend - element with the highest naturally occuring (with the exception of its disintegration products Np and Pu) - isotopes 225U to 242U (longest half-life 238U: 4.4 x 108 a) - great importance as „“ in stations

- uranium chemistry - frequently occuring oxidation states: „+3“, „+4“, „+5“ and „+6“ - complicated coordination chemistry with various species and changes in the oxidation states

- halides: UF6 (colourless, volatile compound with importance for the isotope separation by means of gas diffussion), UCl6 (green), UCl5 (brown), UCl4 (green), UF3 (violet) 2+ - complexes with linear U(VI)O2 - remarkable tendency to form multinuclear aggregates by condensation

via O-, OH- or OH2 bridging units

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Reaction:

Calculated species contribution: Species concentration:

143 pH

7 11) The Chemistry of Artificial and Radioelements (15)

Reaction: CH N C 3 UO2(NO3)2 x 6 H2O + N in(in Methanol / /water Wasser) NH C S NH without addition of a supporting 2 addition of NEt3

same reaction starting from (NBu4)[UO2Cl4]

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