Metallomacrocyclic systems

Describing the cation state generated from a neutral Mn(L) metallomacrocycle is more complex than describing an oxidized organic compound. One must consider the site of oxidation, since both the central metal and the aromatic jr-system of the macrocycle can be redox active182-1841. For some metals, such as Mn, Fe, Co, and Ag, the first oxidation normally occurs at the metal ion and the process can be written... 

The two Ni(omtbp)Ix materials isolated following oxidation with iodine have very different stoichiometries, x = 1.08 0.01 and 2.9 0.3, and represent the only case to date in which a porphyrinic metallomacrocycle has yielded crystals at different levels of partial oxidation. The crystal structure for the x = 1.08125 material exhibits columns of macrocycles, as illustrated in Fig. 2 a and 20. The iodine occurs as If chains which parallel the macrocyclic columns, and which exhibit an interesting one-dimensional disorder. The iodine disorder in Ni(omtbp)I1.08 is much more severe than that found in the Ni(pc)I2) or Ni(tbp) 132 1 systems (see below). In order to solve the structure of Ni(omtbp)Ii.08, the disordered iodine atom had to be treated as a statistical distribution of electron density, with the fit for both cosine and triangle-shaped distributions being comparable (Fig. 29). 

The importance of the porphyrin macrocycle to biology can not be overstated 1-3), Heme-based enzymes and proteins, which contain iron porphyrins in their active sites, are ubiquitous in biological systems. In mammals, key metabolic and catabolic pathways are mediated by these metallomacrocycles, including oxygen transport, storage and activation, catalysis, membrane transport, electron transfer, and substrate sensing (4). In... 

Immobilization of macrocycle molecules onto SAMs on solid substrates has been widely studied because of potential applications of such systems in light harvesting and catalytic processes. An abundant scheme for macrocycle attachment is coordination binding of the metallomacrocycle molecule to a preformed SAM terminated with a suitable ligand. 

The uranyl cation, UOj, turned out to be an effective template for constructing binuclear macrocyclic systems related to those described above [108-110,112-116]. Thus, metallomacrocycles U02(L1755)(H20) to U02(L1757)(H20) were synthesised from 1,2-benzenediamine and the corresponding aldehydes in the presence of U02(CH3C00)2-2H20 in methanol/dichloromethane (Eq. 8.44) [117]. 

Other interesting systems that show catalytic activity is a variety of molecules that contain thiol groups [39 1]. Studies of the electrooxidation of thiols to give disulfides have shown that the catalytic activity of the molecular electrodes of gold. In this case, the metallomacrocycles of Co and Fe have exhibited the high activity. A very interesting case corresponds to the oxidation of L-cysteine and... 

In the bridged macrocyclic systems mentioned so far, the conduction pathway, with a few exceptions has been described as originating from w-w-overlap of the stacked metallomacrocycles which are separated by small distances. Only a minor role has been attributed to the central metal ion. 

Changing the macrocycles in the coordination polymers shown in Fig. 1 from phthalocyanine to one with an extended x-electron system, e.g. 2,3-naphthalocyanine leads to an interesting effect concerning the semiconducting properties of the corresponding bridged systems. A systematic investigation of the oxidation potentials of the metallomacrocycles used for... 

PcM(pyz)]n (M = Fe, Ru, Os) exhibit normal UV/Vis spectra with Soret-and Q-bands between 245 and 700 nm, respectivdy, but show no absorption between 1200 and 2(X)0nm. The absorption bands in the near infrared correlate well with the electrochemically estimated energy gap between the HOMOs of the different metallomacrocycles and the LUMO of f-tetrazine in all the tetrazine-bridged systems described here. The broad band observed in the absorption spectra of these complexes can be assigned to charge transfer process from the metallomacrocycle to the jr -orbital of s-tetrazine. 

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