Multinuclear systems complexes

Linear multinuclear metal complexes are attracting attention in the context of molecular electronics due to their projected use as molecular wires. 01igo(pyridyl)amido ligands are efficient scaffolds for lining up several Ni11 ions like a string. The first structurally characterized trinickel complex of this type, [Ni3(dpa)4Cl2] (dpa = bis(2-pyridyl)amide), showed a nearly linear Ni3 unit with Ni—Ni distances of around 244 pm.209 Penta-, hepta-, and nonanuclear systems have... 

The most active system to date for the Cu-catalyzed oxidation of cyclohexane has only recently been reported. Reaction of triethanolamine with Cu(N03)2 in the presence of NaOH and different types of aromatic carboxy-lates, NaNs or NaBp4 yielded a family of multinuclear copper complexes with different structural characteristics, including 6 and 7. These systems showed... 

Multinuclear hydrolysis species usually are not observed during dissolution of the most stable modification of the solid hydroxide or oxide they are formed, however, by oversaturating a solution with respect to the solid phase. Such polynuclear species, even if thermodynamically unstable, may be of significance in natural water systems. Many multinuclear hydroxo complexes may persist as metastable species for years. 

We now turn our attention to molecular hysteresis which has two essential factors. One is that a system can be expressed a double square scheme diagram (or ladder scheme diagram ) [5], as shown in Fig. 17a. A, A, A", B, B, and B" are chemical species or states. These series of A and B vary reversibly with one another under an external perturbation such as potential, pH, ion concentration, light, etc. With A and B more stable than B" and A", respectively, A" and B" can be rapidly converted to B and A. Hence we will obtain a scheme as shown in Fig. 17b. The other important thing is that the conversion is slow between A and B. The slow rate produces a bistability, A and B, which depends on the direction of an external perturbation. This is molecular hysteresis. Some binuclear or multinuclear metal complexes with the double square scheme diagram have been reported [31]. However, because they were not designed to exhibit molecular hysteresis, their hysteresis behaviors in redox are insufficient. 

Outside the scope of coverage of this contribution are Zn(II)-promoted carboxy-ester hydrolysis reactions involving multinuclear zinc complexes or systems wherein the first step involves transesterification.98,100-102,105,109-114... 

It is hoped that the above examples provide an indication of the role metal NMR can play in characterizing certain organometallic and inorganic complexes. In favorable cases, it may be seen that metal NMR provides the most direct insight to the structural details of multinuclear systems, and to the dynamics and mechanism of exchange processes occurring around the metal center. 

Redox-Based Functionalities of Multinuclear Metal Complex Systems... 

REDOX-BASED FUNCTIONALITIES OF MULTINUCLEAR METAL COMPLEX SYSTEMS... 

H. Nishihara, Redox-based functionalities of multinuclear metal complex systems in A. S. Abd-El-Aziz and I. Manners (Eds.), Frontiers in Transition Metal-Containing Polymers, Wiley, Chichester, 2007. 

I) of 5/2. For a mononuclear system, six hyperfine lines are predicted. However, for a multinuclear system containing n Mn ions, as many as 6" lines may be observed. This gives rise to a rich EPR spectroscopy among polynuclear manganese complexes, which has been used extensively in the study of biological manganese systems and model complexes. 

The aromatic moiety in phenylboranes and phenylb-orates may serve as a 6-electron tt donor ligand to transition-metal complexes. Half-sandwich complexes of chromium, Mes2[B( -Mes)Cr(CO)3] (56), MesB[jj -MesCr(CO)3]2 (57), and B[ -MesCr(CO)3]3 (58), containing trimesitylborane as a ligand have been prepared and structurally characterized. The Cr(CO)3 moieties interact weakly in the multinuclear systems (57) and (58) as shown by... 

Metal centers may be introduced into metallodendrimers and metallostars at a number of conceptually different sites. A convenient classification has been introduced by Balzani and co-workers and is used here in a slightly modified form. Conceptually, the simplest site for metal ion incorporation is at the center of the complex. In principle, a mononuclear complex with dendron-functionalized ligands could be regarded as a metallodendrimer, although this chapter concentrates upon multinuclear systems. 

An additional level of complexity can be added to multinuclear systems by moving from homonuclear to heteronuclear systems. Two such approaches that can be used to generate these mixed metal systems are the self-assembly of two preformed complexes through ternary complex formation via a free site on one or both of the complexes and careful ligand design to allow two distinct binding sites where each metal center is selectively bound to a particular set of coordinating atoms. Both approaches will be briefly discussed with appropriate examples for the formation of both heterometallic 4f and heterometallic mixed 3d-4f systems. 

Takeda H, Ishitani O (2010) Development of efficient photocatalytic systems for CO2 reduction using mononuclear and multinuclear metal complexes based on mechanistic studies. Coord Chem Rev 254 346-354... 

As described in the introduction, natural biological systems utilize Zn + as structural, catalytic, and co-catalytic factors at the appropriate sites under appropriate conditions. This review summarizes some of the methodologies for constructing supramolecular complexes, sensors, and catalysts by the synergistic and cooperative molecular assembly of multinuclear Zn + complexes with organic molecules and/ or other metal compounds in which Zn + ions are used as structural, catalytic, and anion recognition factors. 

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