Molecular modelling metal complexes

Another area of active research is the development of stable low molecular weight metal complexes, which could serve as SOD mimics. Fridovich has described a complex of mangsmese (III) with desferral, which can catalyse the dismutation of superoxide anion in vitro and can protect green algae against paraquat toxicity (Beyer and Fridovich, 1989). This manganese-desferral complex was evaluated in models of circulatory shock and also found to improve survival rate (de Garavilla etal., 1992). 

Kane. P. Kincaid, K. Fayne, D. Diamond. D. McKervey, M.A. Modelling metal complexes of calixarene esters and phosphine oxides using molecular mechanics. J. Mol. Model. 2000. 6. 272-281. 

The modeling of inorganic compounds in general is gaining more and more interest [25-28]. The authors of MOMEC addressed this in a monograph describing how molecular modeling techniques can be applied to metal complexes and how the results can be interpreted [29]. The current force field parameter set is available on the author s web site. 

The strength of this bonding depends on the kind of ether Simple ethers form relatively weak complexes with metal ions but Charles J Pedersen of Du Pont discovered that cer tain polyethers form much more stable complexes with metal ions than do simple ethers Pedersen prepared a series of macrocyclic polyethers cyclic compounds contain mg four or more oxygens m a ring of 12 or more atoms He called these compounds crown ethers, because their molecular models resemble crowns Systematic nomencla ture of crown ethers is somewhat cumbersome and so Pedersen devised a shorthand description whereby the word crown is preceded by the total number of atoms m the ring and is followed by the number of oxygen atoms... 

Fig. 4.13. Space-lilling molecular model depicting a metal cation complexed by 1 R-crown-6.

For Hg, the temperature coefficient of Ea=0 was determined by Randies and Whiteley78 and found to be equal to 0.57 mV K l.On the basis of a simple up-and-down molecular model for water,79 this positive value has been taken to indicate a preferential orientation, with the negative end of the molecular dipole (oxygen) toward the metal surface. While this may well be the case, the above discussion shows that the analysis of the experimental value is far more complex. 

The molecular geometry of a complex depends on the coordination number, which is the number of ligand atoms bonded to the metal. The most common coordination number is 6, and almost all metal complexes with coordination number 6 adopt octahedral geometry. This preferred geometry can be traced to the valence shell electron pair repulsion (VSEPR) model Introduced In Chapter 9. The ligands space themselves around the metal as far apart as possible, to minimize electron-electron repulsion. 

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