Editing Promethium (section)

===Chemical properties and compounds===
[[File:Promethium(III) nitrate hydrate.jpg|thumb|150px|left|Promethium nitrate]]
[[File:Promethium-147 solution.jpg|thumb|150px|Solution containing Pm<sup>3+</sup> ions]]
Promethium belongs to the [[cerium group]] of lanthanides and is chemically very similar to the neighboring elements.{{sfn|Lavrukhina|Pozdnyakov|1966|p=120}} Because of its instability, chemical studies of promethium are incomplete. Even though a few compounds have been synthesized, they are not fully studied; in general, they tend to be pink or red in color.{{sfn|Emsley|2011|p=429}}<ref name="brit">[http://www.britannica.com/EBchecked/topic/478714/promethium promethium]. Encyclopædia Britannica Online</ref> In May 2024, a promethium coordination complex with neutral PyDGA ligands was characterized in aqueous solution.<ref>{{Cite journal |last1=Driscoll |first1=Darren M. |last2=White |first2=Frankie D. |last3=Pramanik |first3=Subhamay |last4=Einkauf |first4=Jeffrey D. |last5=Ravel |first5=Bruce |last6=Bykov |first6=Dmytro |last7=Roy |first7=Santanu |last8=Mayes |first8=Richard T. |last9=Delmau |first9=Lætitia H. |last10=Cary |first10=Samantha K. |last11=Dyke |first11=Thomas |last12=Miller |first12=April |last13=Silveira |first13=Matt |last14=VanCleve |first14=Shelley M. |last15=Davern |first15=Sandra M. |date=May 2024 |title=Observation of a promethium complex in solution |journal=Nature |language=en |volume=629 |issue=8013 |pages=819–823 |doi=10.1038/s41586-024-07267-6 |pmid=38778232 |issn=1476-4687|pmc=11111410 |bibcode=2024Natur.629..819D }}</ref> Treatment of acidic solutions containing {{chem2|Pm(3+)}} ions with [[ammonia]] results in a gelatinous light-brown sediment of hydroxide, [[Promethium hydroxide|{{chem2|Pm(OH)3}}]], which is insoluble in water.{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} When dissolved in [[hydrochloric acid]], a water-soluble yellow salt, [[Promethium(III) chloride|{{chem2|PmCl3}}]], is produced;{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} similarly, when dissolved in nitric acid, a nitrate results, [[Promethium(III) nitrate|{{chem2|Pm(NO3)3}}]]. The latter is also well-soluble; when dried, it forms pink crystals, similar to [[Neodymium(III) nitrate|{{chem2|Nd(NO3)3}}]].{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} The electron configuration for {{chem2|Pm(3+)}} is [Xe] 4f<sup>4</sup>, and the color of the ion is pink. The ground state term symbol is <sup>5</sup>I<sub>4</sub>.<ref>{{cite book|title=Chemistry of the f-block elements| author=Aspinall, H. C.|year= 2001| page=34, Table 2.1|publisher=Gordon & Breach|isbn=978-9056993337}}</ref> The sulfate is slightly soluble, like the other cerium group sulfates. Cell parameters have been calculated for its octahydrate; they lead to conclusion that the density of {{chem2|Pm2(SO4)3*8H2O}} is 2.86&nbsp;g/cm<sup>3</sup>.{{sfn|Lavrukhina|Pozdnyakov|1966|p=122}} The oxalate, {{chem2|Pm2(C2O4)3*10H2O}}, has the lowest solubility of all lanthanide oxalates.{{sfn|Lavrukhina|Pozdnyakov|1966|p=123}}

Unlike the nitrate, the [[promethium oxide|oxide]] is similar to the corresponding samarium salt and not the neodymium salt. As-synthesized, e.g. by heating the oxalate, it is a white or lavender-colored powder with disordered structure.{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} This powder crystallizes in a cubic lattice upon heating to 600&nbsp;°C. Further annealing at 800&nbsp;°C and then at 1750&nbsp;°C irreversibly transforms it to [[monoclinic]] and [[Hexagonal crystal system|hexagonal]] phases, respectively, and the last two phases can be interconverted by adjusting the annealing time and temperature.<ref name="PmO" />

{| Class = "wikitable" style = "text-align: center"
! Formula
! symmetry
! [[space group]]
! No
! [[Pearson symbol]]
! ''a'' (pm)
! ''b'' (pm)
! ''c'' (pm)
! ''Z''
! density, <br/>g/cm<sup>3</sup>
|-
| α-Pm
| [[Close-packing of equal spheres|dhcp]]<ref name="str">{{cite journal|doi=10.1016/0022-5088(71)90101-9|title=The crystal structure of promethium|year=1971|last1=Pallmer|first1=P. G.|last2=Chikalla|first2=T. D.|journal=Journal of the Less Common Metals|volume=24|issue=3|pages=233| issn = 0022-5088}}</ref><ref name="CRCrare">{{cite book |editor=Lide, D. R. |author=Gschneidner Jr., K.A. |chapter=Physical Properties of the rare earth metals |title=CRC Handbook of Chemistry and Physics |edition=86th |location=Boca Raton, FL |publisher=CRC Press |year=2005 |isbn=978-0-8493-0486-6 |chapter-url=http://203.158.253.140/media/e-Book/Engineer/Chemistry/Handbook%20of%20Chemistry%20and%20Physics/Section%2004/04_03_86.pdf |access-date=2012-06-20 |archive-url=https://www.webcitation.org/6AlZkPuDd?url=http://203.158.253.140/media/e-Book/Engineer/Chemistry/Handbook%20of%20Chemistry%20and%20Physics/Section%2004/04_03_86.pdf |archive-date=2012-09-18 |url-status=dead }}</ref>
| P6<sub>3</sub>/mmc
| 194
| hP4
| 365
| 365
| 1165
| 4
| 7.26
|-
| β-Pm
| [[Cubic crystal system|bcc]]<ref name="CRCrare" />
| Fm{{overline|3}}m
| 225
| cF4
| 410
| 410
| 410
| 4
| 6.99
|-
| Pm<sub>2</sub>O<sub>3</sub>
| cubic<ref name="PmO" />
| Ia{{overline|3}}
| 206
| cI80
| 1099
| 1099
| 1099
| 16
| 6.77
|-
| Pm<sub>2</sub>O<sub>3</sub>
| monoclinic<ref name="PmO">{{cite journal|doi=10.1111/j.1151-2916.1972.tb11329.x|title=Polymorphic Modifications of Pm2O3|year=1972|last1=Chikalla|first1=T. D.|last2=McNeilly|first2=C. E.|last3=Roberts|first3=F. P.|journal=Journal of the American Ceramic Society|volume=55|issue=8|pages=428}}</ref>
| C2/m
| 12
| mS30
| 1422
| 365
| 891
| 6
| 7.40
|-
| Pm<sub>2</sub>O<sub>3</sub>
| hexagonal<ref name="PmO" />
| P{{overline|3}}m1
| 164
| hP5
| 380.2
| 380.2
| 595.4
| 1
| 7.53
|}

Promethium forms only one stable oxidation state, +3, in the form of ions; this is in line with other lanthanides. Promethium can also form the +2 oxidation state.<ref>{{Holleman&Wiberg|page=1704}}</ref> Thermodynamic properties of Pm<sup>2+</sup> suggests that the dihalides are stable, similar to NdCl<sub>2</sub> and SmCl<sub>2</sub>.<ref>{{cite journal | last1=Elkina | first1=Veronika | last2=Kurushkin | first2=Mikhail | title=Promethium: To Strive, to Seek, to Find and Not to Yield | journal=Frontiers in Chemistry | volume=8 | date=2020-07-10 | page=588 | issn=2296-2646 | doi=10.3389/fchem.2020.00588 | doi-access=free| pmid=32754576 | pmc=7366832 | bibcode=2020FrCh....8..588E }}</ref>

{| Class = "wikitable" style = "text-align: center"
|+Promethium halides<ref>{{cite book|author=Cotton, Simon|title=Lanthanide And Actinide Chemistry|url=https://books.google.com/books?id=SvAbtU6XvzgC&pg=PA117|year= 2006|publisher=John Wiley & Sons|isbn=978-0-470-01006-8|page=117}}</ref>
! Formula
! color
! coordination<br/>number
! symmetry
! [[space group]]
! No
! [[Pearson symbol]]
! [[melting point|m.p.]] (°C)
|-
|PmF<sub>3</sub>
|Purple-pink
|11
|hexagonal
|P{{overline|3}}c1
|165
|hP24
|1338
|-
|PmCl<sub>3</sub>
|Lavender
|9
|hexagonal
|P6<sub>3</sub>/mc
|176
|hP8
|655
|-
|PmBr<sub>3</sub>
|Red
|8
|orthorhombic
|Cmcm
|63
|oS16
|624
|-
|α-PmI<sub>3</sub>
|Red
|8
|orthorhombic
|Cmcm
|63
|oS16
|α→β
|-
|β-PmI<sub>3</sub>
|Red
|6
|rhombohedral
|R{{overline|3}}
|148
|hR24
|695
|}