Scandium, coordination compound

Scandium coordinates fairly readily with several other types of oxygen donors, especially those with a little negative charge on the oxygen atom, as in Ph3P— 0. It usually takes a coordination number of six, judging from the stoichiometry of the compounds formed and from structures in the limited number of cases where there are single crystal X-ray data available. 

The lanthanides, elements 58 through 71, constitute a so-called inner transition series, as do the actinides, elements 90 through 103. Scandium (21) and yttrium (39), together with the lanthanides, are traditionally referred to as the rare earth elements. The lanthanides, with 3+ ions and decreasing radii, show strong ionic bonding and weaker covalent bonding characteristics. As discussed below, the lanthanides tend to exhibit hard sphere or A-type behavior in their coordination compounds. 

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. ... 

Furthermore, these bulky aryloxide ligands played a crucial role in making the crystallographically characterized less-familiar three-coordinate compounds of scandium, yttrium, and the lanthanides (Ln), such as Ln(OC6H2-r-Bu2-2,6-R-4)3 (28) more accessible. 

The chemistries of scandium and yttrium are often reported together (although yttrium is also often grouped with the lanthanides) so in this section they will be discussed together. Reference, where appropriate, will be made to the first volume in this series, Comprehensive Coordination Chemistry The Synthesis, Reactions, Properties and Applications of Coordination Compounds (CCC, 1987). Volume 3 of CCC (1987) contained a chapter entitled Scandium, Yttrium and the Lanthanides and this chapter is designed to follow part of that chapter. The articles reviewed will cover the period 1982-2001 although earlier work may be cited. Volume 2 of CCC (1987), devoted to ligands, will also be referred to in this chapter. 

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. 

Neutral Ny is (like N5) a radical and so is likewise not expected to be reasonably stable. In an experiment of some relevance to Ny, laser-ablated scandium atoms were codeposited with argon/nitrogen at 10 K (the purpose was to study scandium nitride species) [16]. The reported IR spectra gave no indicahon of the presence of a compound with an Ny ring coordinated to scandium, a compound which has been predicted by computational methods to have a fair chance of existing [17]. 

Organolithium compounds of structure 275 can been applied as transfer agents for transition metal ions, for example, as shown in equation 54 for scandium(III) with tetrahedral coordination (276). The structure of these complexes, elucidated by XRD crystallography, shows the transition metals forming part of an anionic entity, paired to solvated lithium cations. Further structural information can be obtained from H, and "B NMR spectroscopies. ... 

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