ルテチウム

解説Lu．原子番号71の元素．電子配置[Kr]4f 145d16s2の周期表3族ランタノイド元素．希土類元素イットリウム族の一つ．原子量174.967(1)．天然に質量数175(97.41(2)％)と176(2.59(2)％)の同位体が存在するが，176Luは半減期3.76×1010 y の β－ 崩壊核種．このほか，150から184の放射性核種が知られている．希土類分離の難しさから，1843年のC.G. Mosanderの鉱石イットリア中のイッテルビウムが，次々に新しい元素に分割され，最終的に1907年，C.F.Auer von Welsbach(ウェルスバッハ)とG. Urbain(ユルバン)が独立に，新元素として分離した．発表が早かったユルバンがパリのラテン語名Lutetiaから命名した．当初はluteciumであったが，1949年，IUPACがlutetiumと決定した．地殻中の存在度0.3 ppm．希土類中で人工元素Pmを除いて存在度がもっとも低い．銀白色の金属．六方晶のα，体心立方のβの2変態がある．融点1663 ℃，沸点3395 ℃．密度9.84 g cm－3(25 ℃)．第一イオン化エネルギー5.426 eV．酸化数3．つねに LuⅢで化合物をつくる．酸化物，フッ化物は無色で水に不溶，塩化物，臭化物，硫酸塩，硝酸塩も無色で，水に可溶．塩の溶液も無色．Lu3＋ の電子配置は4f殻充満の4f 14で反磁性である．石油クラッキング用触媒，アルキル化，重合触媒などに使えるが，希少金属で高価であるため，ほとんど用いられない．[CAS 7439-94-3]森北出版「化学辞典（第2版）

用途新素材研究用。

天然物の起源Lutetium is the 60th most abundant element on Earth, and it ranks 15th in the abundanceof the rare-earths. It is one of the rarest of the lanthanide series. It is found in monazite sand(India, Australia, Brazil, South Africa, and Florida), which contains small amounts of all therare-earths. Lutetium is found in the concentration of about 0.0001% in monazite. It is difficultto separate it from other rare-earths by the ion-exchange process. In the pure metallicform, lutetium is difficult to prepare, which makes is very expensive.

来歴In 1907, Urbain described a process by which Marignac’s ytterbium (1879) could be separated into the two elements, ytterbium (neoytterbium) and lutetium. These elements were identical with “aldebaranium” and “cassiopeium,” independently discovered by von Welsbach about the same time. Charles James of the University of New Hampshire also independently prepared the very pure oxide, lutecia, at this time. The spelling of the element was changed from lutecium to lutetium in 1949. Lutetium occurs in very small amounts in nearly all minerals containing yttrium, and is present in monazite to the extent of about 0.003%, which is a commercial source. The pure metal has been isolated only in recent years and is one of the most difficult to prepare. It can be prepared by the reduction of anhydrous LuCl3 or LuF3 by an alkali or alkaline earth metal. The metal is silvery white and relatively stable in air. While new techniques, including ion-exchange reactions, have been developed to separate the various rare-earth elements, lutetium is still the most costly of all rare earths. It is priced at about $100/g (99.9%). 176Lu occurs naturally (97.41%) with 175Lu (2.59%), which is radioactive with a very long half-life of about 4 × 1010 years. Lutetium has 50 isotopes and isomers that are now recognized. Stable lutetium nuclides, which emit pure beta radiation after thermal neutron activation, can be used as catalysts in cracking, alkylation, hydrogenation, and polymerization. Virtually no other commercial uses have been found yet for lutetium. While lutetium, like other rare-earth metals, is thought to have a low toxicity rating, it should be handled with care until more information is available.