Sc complex

At this stage, the important (but still not well-understood) role of solvent in SCO compounds properties should be pointed out indeed, the nonsolvated [Fe(qsal)2] [Ni(dmit)2] compound was reported 2 years later [103]. The latter does not exhibit any cooperative spin-transition, probably due to the lack of n-interactions observed in its structural arrangement. Therefore, it seems that, whatever the counter-ion, the control of Ji-stacking is one of the key points to enhance cooperativity in SC complexes. 

As described earlier, the reactivity of photoinduced electron transfer is remarkably enhanced by the complexation of excited states with metal ions. Even if there is no direct interaction between excited states and metal ions, however, metal ions can enhance the reactivity of photoinduced electron transfer when the radical anion produced in photoinduced electron transfer binds with metal ions [11,12,25]. For example, although there is no direct interaction between the triplet excited state of Ceo ( Ceo ) and Sc(OTf)3, an efficient electron transfer occurs from Ceo to p-chloranil (CI4Q) to produce Ceo" and the p-chloranil radical anion CUQ -Sc complex [135]. In contrast to the facile reduction of Ceo,... 

Fig. 9. Possible one- and two-site intermediates of reactions involving SC complexes.

In the Cp3Ln complexes (i) increase in volatility and (ii) decrease in Ln-Cp bond energy with increasing atomic number have been observed. X-ray crystal structure determinations show monomeric structures in the case of Er, Tm and Yb complexes and polymeric structures in the case of La, Pr, Sm, Lu and Sc complexes. The two forms of Cp3La with different crystal packing are shown in Fig. 6.1. One form has short La-C contacts between adjacent molecules in the form of ij5-(C Hs jjL M [i-r]5 -CsHs) units [23] and the other in the form of i]5-(CsU )2La.(/i-i]5 i] -C Ks) with one La-C short contact for the bridging C5H5 to the adjacent molecule [24],... 

When 3 equiv of hexamethylphosphoric triamide (HMPA) ligand is added to the (BNA)2—O2—Sc system, the O2 /Sc complex becomes significantly stable and the ESR spectrum of the O2 -Sc (HMPA) complex can be detected even at 60°C under irradiation with light (78). The lanthanide complexes of radical anions of aromatic ketones are stabilized by the presence of HMPA ligand (79, 80). Oxygen enriched in can provide valuable information about the inequivalency... 

The dependence of the observed second-order rate constant (Atet) on [Sc +] for ET from (AcrH)2 to TolSQ at 233 and 298 K is affected by the formation of TolSQ Sc and TolSQ —(Sc )2 depending on Sc " " concentration. The A et value increases with increasing Sc concentration exhibiting a saturated behavior at low concentrations of Sc + ([Sc ] < 5.0 x 10 M) at both 233 and 298 K, as shown in Fig. 43 (a and b), respectively (115). Such saturated dependence of Atet on [Sc ] is ascribed to a 1 1 complex formation between TolSQ and Sc " " (TolSQ Sc ), which enhances the electron-acceptor ability of TolSQ. The formation constants (ATi) of the TolSQ Sc " " complex at 298 and 233 K were determined from UV-Vis spectral changes of TolSQ in the presence of... 

An early example of a hydride with pronounced H donor character is [Cp2ZrHCl] , which attacks ketones, aldehydes, esters, epoxides, and even CO2, as shown in Scheme 1. Cp 2ScH is so active that it even attacks nitriles to give Cp Sc(N=CHR) the resulting imine complexes react with H2 to give amines, and the Sc complex is a nitrile hydrogenation catalyst. ... 

The 02 -Sc + complex can be stabilized by complexation with 3 equiv. of HMPA ligand as reported for the case of the fluorenone radical anion-Sm +... 

The electronic difference between benzene and borazine is further supported by the properties of compounds of the type (R<,BjN j)Cr(CO)j. Although the.se are formally analogous to (rj< -QRf,)Cr(CO)j. the bonding is not nearly so strong in the borazine complex—its ring-metal dissociation energy appears to be about one-half that of the arene complex. In addition, there is considerable evidence that the borazine molecule is puckered in the.sc complexes. The actual structure appears to be intermediate between a true tt complex and the extreme rr-only model ... 

The base-free dimethyl Sc complex 121 was a highly active catalyst precursor for ethylene polymerization under B(C6F5)3, trityl borate, or methylaluminoxane (MAO)-type activation. The catalytic activity of 121 was similar to those observed of Group 4 metallocene complexes [81]. Generally, cationic scandium complexes are believed to be the active species. Activation of the catalyst was studied by reacting 120 and 121 with various equivalences of B(C6F5)3. The monomeric bulky rBu-substituted dimethyl complex 121 reacted with 1 equiv of B(C6F5)3... 

An examination of the data in Figure 4 indicates that a pH of about 2 should be appropriate for Sc complexation. An estimate of the logarithmic values of at pH 2 for EDTA complexes of the elements of interest is given in Table V. 

The data indicate that, at a pH of 2, divalent Mn and Fe have much lower conditional stability constants than Sc, and therefore Sc would be complexed preferentially, even in the presence of larger concentrations of these ions. However, the Kml- of die ferric ion is larger than that of Sc, and it is thus mandatory to keep all iron in the solution in the ferrous state in order to achieve selective Sc complexation and, if this model is reasonable, selective retention on the ion exchange column. The data for Th and Ca are presented to illustrate the effect of other ions Ca presents no problem as it is not complexed at this pH with EDTA, while Th would be coextracted at a comparable rate with Sc. The assumptions of this model have been proven valid, as shown by the data below (Table VI) which demonstrate the selective extraction of Sc on the ion exchange column with iminodiacetic acid functionality in the presence of a large excess of Mn and Fe. 

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