Cage, complexes

Data are given in Table 10-7 to illustrate certain facets of the Marcus cross relation. They refer to six reactions in which the cage complex Mn(sar)3+ is reduced or Mn(sar)2+ oxidized.34 These data were used to calculate the EE rate constant for this pair. The results of the calculation, also tabulated, show that there is a reasonably self-consistent value of fcEE for Mn(sar)3+/Mn(sar)2+ lying in the range 3-51 L mol-1 s-1. When values34 for an additional 13 reactions were included the authors found an average value of kEE = 17 L mol 1 s l. 

Techniques other than UV-visible spectroscopy have been used in matrix-isolation studies of Ag see, for example, some early ESR studies by Kasai and McLeod 56). The fluorescence spectra of Ag atoms isolated in noble-gas matrices have been recorded (76,147), and found to show large Stokes shifts when optically excited via a Si j — atomic transition which is threefold split in the matrix by spin-orbit and vibronic interactions. The large Stokes shifts may be explained in terms of an excited state silver atom-matrix cage complex in this... 

The number of metal wheels and, more generally, polynuclear cage complexes of the 3d metals has increased considerably in the last decade because of their magnetic properties, especially their behavior... 

The remarkable physical properties exhibited by the divalent macrobicyclic cage complex [Co(sep)]2+ (29) are unparalleled in Co chemistry.219 The complex, characterized structurally, is inert to ligand substitution in its optically pure form and resists racemization in stark contrast to its [Co(en)3]2+ parent. The encapsulating nature of the sep ligand ensures outer sphere electron transfer in all redox reactions. For example, unlike most divalent Co amines, the aerial oxidation of (29) does not involve a peroxo-bound intermediate. 

Figure 31 Hexanuclear Ni11 cage complex (832) with an interstitical /i6-Cl atom2033 (reproduced by permission of the Royal Society of Chemistry).

Figure 3.2 The synthesis of N3S3-donor cage complexes.

Fig. 18. The structures of the building blocks 21 and 22 and schematic representation of the structures of cage complexes 23 and 24 (131).

Wright et al. have reported two cases where LiPHCy acts as a precursor to main group phosphinidine complexes. Reaction of the primary lithium phosphide with [AlMe N(mes) ]4 gives the heterometallic cage complex Li(THF) 4[ (AlMe)(ja-PCy) 2(ju.-PCy)]2 C6H5Me (95) (Fig. 12a). Reaction of [SnNBut]4 with 6 equiv of LiPHCy yields the complex cluster [ Sn2(PCy)3 2 Li(THF) 4], 2THF (96) (Fig. 12b). 

The same strategy as for the synthesis of 40 has been employed for the preparation of the Li/Sn-mixed cluster 41. Thus, replacement of the imido groups in [Sn(NtBu)]4 with LiPHR (R = cyclohexyl) in the molar ratio of 4 6 yielded the metallacyclic cage complex 41, which has a rhombododecahedral Li4Sn4P6 core (Eq. 24) (69). The clusters 40 and 41 are isostructural, since the MeAl fragments in 40 have been replaced by the isoelectronic Sn(II) centers. 

These photoproducts are initially in an encounter cage complex" and may either recombine within this cage structure or... 

As noted, the products of electron transfer retained in the solvent cage. Benzene was used as a solvent in these experiments. The cage complex [R -O, OH, D+ ] decays either on disproportionation in the cage or dissociation. Disproportionaton leads to phosphinoxides or sulfoxides mentioned earlier. Dissociation results in the passage of radicals out of the cage into the solvent pool. 

Structures have been determined for [Fe(gmi)3](BF4)2 (gmi = MeN=CHCF[=NMe), the iron(II) tris-diazabutadiene-cage complex of (79) generated from cyclohexanedione rather than from biacetyl, and [Fe(apmi)3][Fe(CN)5(N0)] 4F[20, where apmi is the Schiff base from 2-acetylpyridine and methylamine. Rate constants for mer fac isomerization of [Fe(apmi)3] " were estimated indirectly from base hydrolysis kinetics, studied for this and other Schiff base complexes in methanol-water mixtures. The attenuation by the —CH2— spacer of substituent effects on rate constants for base hydrolysis of complexes [Fe(sb)3] has been assessed for pairs of Schiff base complexes derived from substituted benzylamines and their aniline analogues. It is generally believed that iron(II) Schiff base complexes are formed by a template mechanism on the Fe " ", but isolation of a precursor in which two molecules of Schiff base and one molecule of 2-acetylpyridine are coordinated to Fe + suggests that Schiff base formation in the presence of this ion probably occurs by attack of the amine at coordinated, and thereby activated, ketone rather than by a true template reaction. ... 

A number of cobalt(III) encapsulated cage complexes have been used as electron-transfer agents their advantage over viologens is their long-term stability in photochemical cycles. The most effective complex is [CoL] where L is l-chloro-3,6,10,13,16,19-hexaazabicyclo[6.6.6]eico-sane at a concentration of 4 x 10 mol dm , this cage exhibits a similar ability to methylviolo-gen to produce Laser flash photolysis in sodium dodecyl sulfate and sodium laurate... 

The iron solution in ethanol develops an intense black color that fades to yellow-brown within minutes. From this, the cage complex can be isolated in 80% yield. (Adapted from Venkateswara Rao et ah, 2004)... 

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