Metal clusters unique feature

Figure 4.1 clearly illustrates the modular construction of MOFs, with ligands used as pillars and metal clusters as node points. One unique feature of MOFs seems to be the possibihty to systematically modify their lattice. For instance, by replacing the terephthalate ligands of MOF-5 (Figure 4.1) with different dicarboxylate ligands, a family of isoreticular metal-organic frameworks (known in literature as the... 

As the names of the component proteins imply, iron-containing redox groups are essential to nitrogenase function. These clusters are of the Fe S type, but they exhibit many unique features that are not present in simpler protein and model systems. A brief summary of the properdes of the nitrogenase proteins, with emphasis on the metal clusters, follows. 

In large part, the reactivity of a metal cluster is the same as that of the individual metal fragments. The unique features of cluster reaction chemistry involve the bridging of ligands between two or more metal atoms, ligand migration between metal atoms, and metal-metal bond cleavage and formation. 

Iron is counted as the only major bioelement of the transition elements, or as the most important trace element. This importance is based on a unique feature of iron depending on the species and distance of the ligands of this metal in complex compounds, high- or low-spin complexes with a broad variety of redox potentials can be formed, namely iron- sulfur clusters and heme compounds. Therefore, iron forms the most electron-transferring prosthetic groups in the cell, enabling respiration and other important redox reactions. 

In urease, the active site with a pair of nickel ions is unique. A large number of esterases and phosphatases contain dinuclear clusters of zinc and/or iron, and in these a metal-bound hydroxide or water molecule is a common feature [170], In urease the active site is rather rigid and designed to favor binding of urea over that of solvent water, and for this purpose nickel may be preferable to zinc, which has more flexible coordination geometry. 

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