Trinuclear systems

A trinuclear system, whose structure was published,555 was formed in high yield by the cyclometalation of a l,3-bis(alkylbenzimidazol-2-yl)benzene ligand, followed by the trimerization of the unit, which possesses a vacant coordination site on the palladium atom and a pendant noncoordinated benzimidazole moiety. The resulting product forms a cup-shaped trimer or tricorn, presented in Figure 46, that includes a molecule of acetonitrile in the crystal structure.556... 

A trinuclear system, formed in high yield by the cyclometalation of a l,3-bis(alkylbenzimidazol-2-... 

Cyclic trinuclear gold(I) complexes provide a novel and productive strategy for achieving supramolecular structures. While molecules of this type have been known for more than twenty years, some of their remarkable properties have only been recognized recently. Some can form liquid crystals at room temperature [41], while others lead to luminescent materials with surprising properties. We will now summarize some selected examples to illustrate the behavior of these trinuclear systems. 

Let us consider a trinuclear system the JT theorem predicts that the geometry of an equilateral triangle will be unstable unless the ground electronic state is nondegenerate. In the geometry of D3h the electronic wave functions... 

It would appear that the possibilities of obtaining photoinduced charge separation with trinuclear systems containing the Ru(bpy)22+ chromophoric unit are bound to the possibility of (i) using two bridges entailing different degrees of adiabaticity for primary recombination and secondary electron transfer (electronic... 

Triangular trinuclear systems in which the alkyne bridges two of the three metals have been prepared by reaction of preformed clusters with alkynes, as in Eq. (13),128... 

There have been far fewer studies on the reactions between tetranuclear clusters and alkynes or alkenes than have been reported for trinuclear systems. The reactions that have been investigated have largely been with alkenes. Both R H CO) 2 and Os4H4(CO)12 react with mono- and polyalkenes, and substitution of hydrides and carbon monoxide ligands is observed in most cases (180-187), as shown by Eq. (10). There are a few examples, however, where metal-metal bond cleavage does occur and trinuclear clusters are isolated (181-183,188). In contrast, when Rh4(CO)12 and Ir4(CO)12 are treated with dienes, cluster growth occurs (189-193). 

Regular and Irregular Spin State Structures in Trinuclear Systems. 342... 

Let us consider again a symmetric and linear trinuclear system ABA where the interacting centers have no orbital degeneracy and let us assume that the interaction between... 

In the case of the trinuclear systems, the important cases are those in which the X" positions of Fig. 26-D-4 are occupied by neutral ligands, L, to give molecules of the stoichiometry Re3X9L3. In the case where L = PEt2Ph this type of structure has been verified by X-ray diffraction. 

Using these expressions, the isotropic exchange Hamiltonian of a trinuclear system has the following diagonal elements... 

Some consequences of antisymmetric exchange for trinuclear systems are discussed elsewhere [6]. 

Mixed-valence trinuclear systems involve two groups ... 

Let us recapitulate the approach applied for trinuclear systems where each ket is constructed by means of its own coupling scheme depending on the localisation of the extra electron (hole). Any pair of kets is related through a recoupling formula which, for the four spins, contains the 9/-symbol, e.g. 

Based on the rational of binding modes of 18-crown-6, heterocalixarenes 185-188 were designed for RNHs" /K binding selectivity. Their synthesis involved a straightforward condensation of respective trinuclear systems 175 and 177 (R, R = H) with the dibromides 183 and 184, formed from the corresponding cyclic urea and l,3- )w(bromomethyl)benzene (2000MI2). 

Trinuclear systems are also readily prepared by analogous methods (Figure 18). 

More recently, we have developed a new method for the assembly of trinuclear systems. One of the problems with the ruthenium(II) compounds is that the Idnetically inert second row metal centre may only react sluggishly with ligands (in both the and states). Conversely, first row metal ions usually react relatively rapidly, but the complexes so... 

A significant solvent effect was reported in the Sonogashira reaction for example, dimethylsulfoxide was slightly better in terms of conversion, but also promoted an unwanted side reaction - the homocoupling of the arene. However, the combination of a trinuclear system and dimethylformamide was efficient, leading to quantitative conversion. 

As a first interesting example, Stang and Critell reported in 1990 the alkynylation of Vaska complexes 16 and 17 with alkynyliodonium triflates at room temperature in excellent yield (Scheme 9) [88]. Using bis-alkynyliodonium salts, the method could be extended to the formatiOTi of binuclear complexes such as 18 and 19, or even trinuclear systems [89-91]. These conjugated polymetallic complexes have great potential for applications in nonlinear optics, organic conductors, or liquid crystals. 

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