Mixed Sandwich Systems

For the bis-benzene complexes and the mixed sandwich systems however the spectroscopic information is not really adequate to establish reliable values of these quantities although it is consistent again with the one-electron sequence ig-... 

Consequently, in Figures 5-11 are shown the appropriate Tanabe-Sugano type diagrams for dx systems (x = 2 — 8) in pseudo-axial, CmV, symmetry, the parameters DtjDs = 0.55 and C/B = 4.0 being adopted throughout. As indicated above this parameteri-sation is most appropriate for the metallocenes, for which the d-d spectra are now considered in more detail. Thereafter a brief survey is made of the limited data relating to bis-arene species, and to various mixed sandwich complexes. 

In principle it should be possible to determine the anisotropy of the paramagnetic susceptibility for some systems of pseudo-axial symmetry, but apart from the citation (74) of a private communication regarding the ferricenium cation, no experimental data are available for metal sandwich complexes. Such measurements should however be possible for at least some metallocenes and mixed sandwich complexes since these are found to crystallise in either a monoclinic (Fe(Cp)2 (6)) or orthorhombic (Ru(Cp)2, (Cp)V(Ch),... 

Interestingly, the structural parameters for the individual pz and porphyrin subunits of the mixed sandwich complex are indistinguishable. Selected bond lengths and angles for sandwich compounds (29), the heteroleptic system (30), and the homoporphyrin analogue are listed in Table VI (33). 

The chemistry of the larger cage lanthanacarboranes, predominantly the C2B9 and C2Bk) systems, has also been extensively studied full-, half-, and mixed-sandwich have been described. Xie has summarized much of this work in several recent reviews. - The straightforward syntheses of the lanthanacarboranes are complicated in many... 

With regards to actinides, Summerscales et al. [105] have also reported the reductive disproportionation of C02 to carbonate and squarate products, using COTR/ CpR mixed-sandwich U(III) complexes (COT = cyclooctatriene, Cp = cyclopenta-dienyl, R = Si Pr3, R = H, Me). U(III) systems have been shown previously to reduce C02 to a linear Tl -O-coordinated mono-anion [63], and to doubly reduce to give O2- salts plus CO [75, 76]. In this case, the reactions can be considered... 

The low spin Ee /Ee redox couple was initially proposed by Lever et al. [23, 24, 31] as the most appropriate standard for sandwich complexes bearing two cyclopentadienyl (Cp) or derived ligands, as such compounds are known in a large number and exhibit metal-based reversible or quasi-reversible redox processes that are fairly independent of the solvent/electrolyte system. Eor homoleptic complexes the value for the El parameter would be given by Eq. 50.6 and for mixed sandwich species, [EeLL ], Eq. 50.7 should be applied [31]. For the Cp ligand itself, an El value of 0.33 V was thus proposed [31]. 

Such a system can be realized by a sandwich system consisting of a stack of layers Figure 2 shows the arrangement of the modules of the stack The mixing unit is placed at the top, the detector unit at the bottom of the system... 

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