Scandium compounds

Experimental thermodynamic information is not available about solid scandium selenides, but Mills [74M1L] has estimated thermodynamic properties for ScSe(cr) and Sc2Se3(cr). The former selenide has been reported as non-existent in [65ELL]. 

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The first compound of this series, CeSI, was reported by Carter (68) in 1961, and later discussed by Dagron (93). It was obtained by the reaction of iodine with cerium sulfide at 430 C, or by direct synthesis from the elements at 500°C. This was the start of a detailed investigation of this group of compounds mainly by Dagron and co-workers. The present situation is presented in Table VII. No scandium compounds are known thus far, and the same is true for selenium and tellurium halides of these elements. 

In metals the electrons lose their association with individual atoms and the number of valence electrons is often used in rationalization schemes. Estimated enthalpies of formation for equi-atomic alloys, MM, of two elements of the first transition metal series are given as a function of the difference in number of valence electrons in Figure 7.13 [8], Compounds of a given common metal are given a specific symbol. For example, the scandium compounds ScM where M = Ti, V, Cr, Mn, Fe, Co, Ni and Zn, are given by open circles. The metal M of the compound MM is... 

I2 vapor is extremely corrosive while scandium compounds are moisture-sensitive and very expensive. In addition, these reactions are carried out in an environmentally unfriendly solvent, CH2CI2. We have reported the bismuth triflate-catalyzed synthesis of substituted dihydro-2//-1-benzopyrans by the condensation of substituted salicylaldehydes with 2,2-dimethoxypropane (Scheme 3) [22]. 

The scandium compound, containing the constrained geometry dianionic ligand 12,... 

Scandium compounds are not heavily studied. Its oxide, Sc203 is used in the manufacture of high-in tensity electric lamps and its iodide, Scl3, is used in lamps to produce light having color similar to sunlight. 

When Mendeleev produced his original Periodic Table in 1869, he left a space for a metallic element of atomic mass 44 preceding yttrium. The first fairly pure scandium compounds were isolated by Cleve in 1879, but it was not until 1937 that the element itself was isolated. Although a relatively abundant element, it is fairly evenly distributed in the earth s crust and has no important ores, though it is the main component of the rare ore thortveitite (Sc2Si207), thus being relatively expensive. In fact, it is mainly obtained as a by-product from uranium extraction. 

Sc(THF)3Cl3 is a very useful synthon (starting material) for other scandium compounds. It can conveniently be prepared using thionyl dichloride as a dehydrating agent ... 

Scandium is still a neglected element. It is the most expensive metal in its period (caused by the fact that its even distribution in the earth means that there are no rich ores) and its chemistry is virtually exclusively that of the +3 oxidation state, so that it is not classed as a transition metal and is often silent to spectroscopy and not amenable to study by many of the usual spectroscopic tools of the coordination chemist. Chemists have often either tended to assume that complexes of Sc are just like those of the tripositive ions of the transition metals or that they resemble lanthanide complexes. Neither of these assumptions is correct—how incorrect we are now realizing. Scandium chemistry is starting to exhibit characteristics all of its own, and possibly the burgeoning use of scandium compounds in organic synthesis may drive a real expansion of scandium chemistry. 

It should be noted that there are organometallic compounds involving polyhapto ligands that contain linkages such as Sc— Te that are not found in coordination compounds. In addition, a number of recent reviews on the organometallic chemistry of the lanthanides include reference to scandium compounds. ... 

A few examples are known of crystal structures based on more complex nets. Borocarbides MB2C2 are formed by scandium and the rare-earth metals, and they consist of layers of composition B2C2 interleaved with metal atoms. In the compounds of the 4f metals the layer is the 4 8 layer, the pattern of atoms being similar to that of Fig. 3.27(b), the open and shaded circles now representing B and C atoms. The scandium compound is of special interest as the only example at present known of the layer consisting of equal numbers of 5-gons and 7-gons. 

Both scandium and yttrium form borohydride complexes [M(BH4)3(thf) ] with thf coordinated to the metal.53 In each compound two borohydride groups are bound through three hydride bridges and one borohydride is bound through two hydride bridges. The scandium compound is... 

The tetraphenylporphyrin scandium complexes were previously reported and now crystal structures have been determined for the p-toly derivatives (ttp). Both scandium and yttrium form (ttp)MCl complexes150,151 but whereas the scandium compound is five-coordinate the yttrium compound coordinates solvent molecules forming seven or eight-coordinate complexes. Reaction of (ttp)ScCl with water forms an oxide dimer [Sc(ttp)]20,151 whereas for yttrium the cation [Y(ttp)(H20)3]+ has been observed.152 The structure of [Sc(ttp)]20 is shown in Figure 7, the bridging oxygen is disordered over two sites with 50% occupancy of each site. The reaction of... 

The compound CsScCl3 has the 2H (hexagonal perovskite) structure of CsNiCl3, space group P63/mmc, a = 7.350(2) A, c = 6.045(3) A, and represents the first example of a scandium(II) compound, although many more reduced metal-metal bonded phases are known.4 The material is black in color in bulk and blue when ground. The material is relatively stable to moisture for a reduced scandium compound but still readily reacts with water with the evolution of hydrogen gas. 

Solid-state divalent scandium compounds are well documented (Meyer and Jongen, 2006 Poeppelmeier et al., 1980) and there are also some monovalent scandium compounds such as ScCl in which Sc-Sc bonds are present (Poeppelmeier and Corbett, 1977). So scandium opened the possibility to find monovalent molecular compounds, similarly to the well-known Al coordination chemistry, and since scandium looks like aluminium in some respects. Indeed, low-valent scandium molecular compounds have been found both in the monovalent and in the divalent state. 

Marusin et al. (1985a, b) reported the existence of the scandium compounds ScFeC2, ScCoCj and ScNiC2, which belong to PbFCl-type or UCoC2-type (Li and Hoffmann 1989). The lattice parameters were determined to be a = 3.3344(7) A, c = 7.292(2) A and Z = 2 for SCC0C2. 

Cyclooctatetraenyl derivatives of the rare earths were synthesized shortly after the characterization of uranocene first for europium and ytterbium in the oxidation state R by Hayes and Thomas (1969a). But one year later, Mares et al. (1970) prepared complexes of the type K[R(Cj,Hg)2], where R = Ce, Pr, Nd, Sm, and Tb. The corresponding yttrium, lanthanum and gadolinium derivatives are described by Hodgson et al. (1973) and the scandium compound was made by Westerhof and De Liefde Meijer in 1976 ... 

Some of the first reactions of soluble metal complexes with methane occurred by a-bond metathesis. Like the first examples of oxidative addition of alkyl C-H bonds, the first examples of a-bond metathesis with alkyl C-H bonds were intramolecular. Yet, the lute-tium- and yttrium-methyl complexes, Cp MMe (M = Lu and Y) were shown by Watson to react intermolecularly with C-labeled methane to form the labeled methyl complexes and unlabeled methane at 70 °C (Equation 6.51). Related scandium compounds have now been shown to undergo similar reactions with alkanes, and a thoracyclobutane... 

The scandium compounds (C5Me5)2ScCl, (CsMes)2ScC1(THF) and (C5Me5)2ScI have also been made (58). The oxidation of (CsMes)2Yb-(dme) with [(C5H5)2Fe][PFg] affords purple crystals of (CsMes)2YbPF6 (dme)... 

The analogous scandium compound is formed in a solvent-free state from C8H8ScC1(THF) and NaCsHs as a yellowish, air-sensitive powder... 

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