Scandium complexes properties

While the lanthanide series is due to the successive filling of the 4f orbitals, it is generally assumed that they do not contribute significantly to bonding due to their limited radial extension and the shielding from the valence shell by the filled 5s and 5p orbitals. However, these f-orbitals (filled or empty) should be able to modulate some electronic properties of the metal center. In the ubiquitous oxidation state 3+, the lanthanide ions reach an inert gas core configuration by the loss of one 4f electron. It is for this reason that yttrium and scandium complexes are included in discussions of lanthanide chemistry i.e., in their predominant 3+ oxidation states, these elements have an inert gas core configuration ([Kr] and [Ar], respectively) and empty d orbitals. Indeed, due to the lanthanide contraction, the size of Y + falls between Ho and Er +, whereas scandium is considerably smaller than the lanthanides. 

This chapter consists of a description of the ions formed in aqueous solutions by the transition elements - the d-block elements - and a discussion of the variations of their redox properties across the Periodic Table from Group 3 to Group 12. There is particular emphasis on the first transition series from scandium to zinc in the fourth period, with summaries of the solution chemistry of the second (Y to Cd) and third (Lu to Hg) series. The d-block ions in solution are those restricted solely to aqua complexes of cations, e.g. [Fe(H20)f,]" +, and the various oxocalions and oxoanions formed, e.g. V02+ and MnCXj". Oxidation states that are not well characterized are omitted or referred to as such. 

Sc(OEP)C>2CMe is 0.4 s, which is the longest for any porphyrin, while the fluorescent yield of 0.2 is very high. The radiative properties are explained in terms of covalent interactions between the metal and the ring as modified by the probable location of the metal ion above the porphyrin plane.24 Scandium OEP complexes are reduced to the a, y-dihydro derivatives on reduction with sodium anthracenide and methanol.25 The redox potentials of Sc(OEP)OH have been determined by cyclic voltammetry to be ligand oxidation in PrCN, 1.03 and 0.70 ligand reduction in DMSO, —1.54 (Ey2 values in V vs. SCE) no metal redox wave was observed.26... 

Like the hydroxides of the Rare earth, scandium hydroxide, Sc(OH)3, is precipitated by addition of alkalies to solutions of scandium salts however, the latter is precipitated at pH 4.9, while the former require pH 6.3 or more, a property which is utilized in one method of separation. Upon heating the hydroxide (or certain oxyatid salts), scandium oxide. Sc>C>3 is produced. Scandium hydroxide is less acidic than aluminum hydroxide, requiring boiling KOH solution to form the complex potassium compound, K2[Sc(OH)5 H 0] 3H 0. 

Lanthanide elements (referred to as Ln) have atomic numbers that range from 57 to 71. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). With the inclusion of scandium (Sc) and yttrium (Y), which are in the same subgroup, this total of 17 elements are referred to as the rare earth elements (RE). They are similar in some aspects but very different in many others. Based on the electronic configuration of the rare earth elements, in this chapter we will discuss the lanthanide contraction phenomenon and the consequential effects on the chemical and physical properties of these elements. The coordination chemistry of lanthanide complexes containing small inorganic ligands is also briefly introduced here [1-5]. 

The series of ten elements from scandium to zinc is known as the First Transition Series. Most of these show distinctive properties such as variable valency, coloured compounds, and complex ion formation. 

Scandium.- The complex Cp2Sc(BH ) has been synthesised and Its properties have been compared with those of related complexes such as Cp2Zr(BH )2. ... 

The zinc ion is colourless. Zinc shows some catalytic properties and does form complex ions, although this property is not unique to transition metals. Scandium shows some similarities to zinc but is classified as a transition element because it can exist in multiple oxidation states +3 (common), +2 (rare) and +1 (rare). 

Transition metals are those that either have incompletely filled d subshells or form ions with incompletely filled d subshells (Figure 22.1). Incompletely filled d subshells give rise to several notable properties, including distinctive colors, the formation of paramagnetic compounds, catalytic activity, and the tendency to form complex ions. The most common transition metals are scandium through copper, which occupy the fourth row of the periodic table. Table 22.1 lists the electron configurations and some of the properties of these metals. 

In general, the ionic radii give an indication of the expected coordination number in a rare earth complex, though this is more apparent in aqueous solutions than in the solid state, where bulky ligands and different coordination modes may result in unexpected CNs. Scandium with its smaller ionic size has a significantly lower average coordination number than the other rare earths. The properties of scandium and yttrium, which are partly due to the ionic radii, are discussed in relation to those of the lanthanides in section 1.3.4. 

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