Scandium and Yttrium

1 Scandium and Yttrium.- Fluoroscandium complexes have been 

Chemical Studies.—Mixed ligand complexes of scandium have been obtained containing edta and either Tiron, sodium 2,3-dihydroxynaphthalene-6-sulphonate, or pyrocatechol. These mixed complexes are generally more stable than their yttrium analogues, but are more susceptible to hydrolysis. The stability of tartrate complexes has also been investigated.  

Reaction of sodium with yttrium in liquid ammonia in the molar ratios 3 1 and 1 1 under pressure and at moderate temperatures gave Na3[Y(NH2) ] and Na[Y(NH2)4 ]. Y(NH2)3 was obtained from Na[Y(NH2)4,] and NH I, or from YI3 and KNH2 in liquid ammonia. Reaction of Y metal with ammonia under conditions different to those above gave YN. 

The enthalpy and entropy of vaporization of ScFj fell in the range 88.50 88.57 ( 2.50) kcal mol and 48.05—48.06 cal gm mol at 298.25 K. Studies of the phase diagrams of ScXj—Sc (X = Cl or Br) revealed the existence of SC2X3, and SC2CI3 could also be prepared by the reaction of Sc vapour with 

48(0) Nine-co-ordinate, rectangular face centred trigonal prism 

ScClji SCjXj is isomorphous with GdjCIj. The heats of formation of YOGI and TbOCl were found to be — 238.6 and — 234.0 kcal mol (at 298 K). 

The electronic configuration of scandium can be expressed as [Ar] 3d 4s leading to oxidation states of 3+ (most common), 2+, and 1+. Its oxide is therefore given as SC2O3. Scandium is considered a rare earth element, but this is firstly because it was discovered together with several other lanthanides. Secondly, scandium resembles yttrium and the rare earth elements more than it resembles aluminium or titanium (Hammond 2015). On the other hand, it also much resembles the ferromagnesian transition elements, although in aqueous systems it behaves more like the REE (see Chap. 1, and McLennan 2012). 

The electronic configuration of yttrium can be expressed as [Kr] 4d 5s leading to an oxidation state of 3+. Its oxide is given as Y2O3 

---

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

The lanthanides are congeners of the Group IIIA metals scandium and yttrium, with the +3 oxidation state usually being the most stable. These ions are strong oxyphilic Lewis acids and catalyze carbonyl addition reactions by a number of nucleophiles. Recent years have seen the development of synthetic procedures involving lanthanide metals, especially cerium.195 In the synthetic context, organocerium... 

The strangest section of the periodic chart comes in the first transition subgroup. Under scandium and yttrium (marked with stars on the periodic chart) fall two long horizontal lists of elements so much alike that they are squeezed into two squares of the chart. Elements with the atomic numbers 57-71 are called the lanthanides. The actinides are elements with the atomic numbers 89-103, and they are all radioactive. These transition elements are as follows ... 

The preparations of rare-earth trihalides can be found in various books (2-8) and in Taylor s review (2 ). This review, however, did not include the preparation of scandium and yttrium trihalides, and only covered the preparation of the trifluorides very briefly. We have reviewed the preparation of all the trihalides (including scandium and yttrium) from Taylor s review up to June 1979 and have also included some methods and references missed by Taylor. Although we have mentioned all the methods available for the preparation of the trihalides, emphasis has been placed on the methods used since Taylor s review, and these have been referenced fully, whereas for the other methods, Taylor s review is recommended as a source of references. 

The 3rd group of the Periodic Table (the 1st column within the block of the transition elements) contains the metals scandium, yttrium, lanthanum, and actinium. Lanthanum (atomic number 57) may be considered the earliest member of the family of metals, called lanthanides (general symbol Ln), forming, inside the principal transition series, an inner transition series (up to atomic number 71). Scandium and yttrium together with the lanthanides are also called rare earth metals (general symbol R). 

Within the lanthanides the first ones from La to Eu are the so-called light lanthanides, the other are the heavy ones. Together with the heavy lanthanides it may be useful to consider also yttrium the atomic dimensions of this element and some general characteristics of its alloying behaviour are indeed very similar to those of typical heavy lanthanides, such as Dy or Ho. An important subdivision within the lanthanides, or more generally within the rare earth metals, is that between the divalent ones (europium and ytterbium which have been described together with other divalent metals in 5.4) and the trivalent ones (all the others, scandium and yttrium included). 

The review is divided into three sections, (i) the chemistry of scandium and yttrium, (ii) the chemistry of the lanthanide elements, further subdivided into a survey of lanthanide n.m.r. shift reagents and the general chemistry of the elements, and (iii) the chemistry of the actinide elements and uranyl and related compounds. 

Analogous methyl compoimds are iU-characterized and appear to be polymeric [129). The air-sensitive phenyl derivatives when first obtained from THF are soluble in benzene, but when dried completely are no longer soluble — apparently due to pol5unerization. The homoaryl complexes of the smaller scandium, and yttrium ions form only the tris complexes Sc(CeH5)3 and Y(C6H5)3 [129) It is apparent that the structure and stabihty of the homoaryls are dependent on the metal ionic radii and the steric bulkiness of the phenyl group. 

In subsequent studies, methyl vinyl ketone (2.0 mmole) was chosen as the dienophile so as to determine the combined effect of the ionic liquid (2 mL) and the Lewis acids (0.2 and 0.5 wt%) upon the yield and selectivity. Without the Lewis acid catalyst, this system demonstrated a 52% conversion of the cyclopentadiene (2.2 mmol) in 1 h with the endojexo selectivity being 85/15. The cerium triflate-catalyzed reaction was quantitative in 5 min and the endo. exo selectivity was very good for this experiment as well (94 6, endo. exo). Also with the scandium or yttrium salts tested, reactions came to completion in a short time with high stereo-selection. Cerium, scandium and yttrium triflates are strong Lewis acids known to be quite effective catalysts in the cycloadditions of cyclopentadiene with acyclic aldehydes, ketones, quinones and cycloalkenones. These compounds are expected to act as strong Lewis acids because of their hard character and the electron-withdrawing triflate group. On the other hand, reaction times of 1 hour were required for... 

Rare-Earth Oxides, Including Scandium and Yttrium Oxides... 

The earth s crust is again a good source of lanthanides. Although the name rare earths is still used to denote the lanthanide elements, and scandium and yttrium, in the strictest sense of the word rare they are more plentiful than many of our common elements. It comes as a surprise to many people when a comparison of the relative abundance of the lanthanides and other elements in the earth s crust is made. Table 4... 

Table 1 shows the assignment of the various lanthanide elements in the numbering of the compounds in this article. As usual, scandium and yttrium have been included because of their chemical similarity with the lanthanides. Not included was the radioactive promethium for which no complex containing heteroallylic ligands has so far been reported. 

The subsequent fate of the perchlorate depends on the temperature. At relatively low temperatures it is stable and thus remains. At temperatures high enough for it to decompose, the final products are chloride and oxygen. When the metal exists in more than one oxidation state, the oxide may form. The chlorates of the rare earths, scandium, and yttrium form oxychlorides. 

The generation of reactive species by a fast pre-reaction is a well established process in kinetics, particularly in flow systems, although this technique is now being used in molecular beam sources [see (f), below]. As atoms are commonly generated by thermal or microwave dissociation (see above), reactions are mainly used to produce radicals. However, some atoms may be produced by reaction as a more convenient alternative to direct vaporisation or dissociation. Scandium and yttrium atoms have been generated [25] by the reaction... 

The known oxide fluorides of the transition metals and of scandium and yttrium are shown in Table I. 

Some properties of lanthanides along with scandium and yttrium are given in Table 2.2. 

---