MOMEC

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. 

MOMEC is a force field for describing transition metal coordination compounds. It was originally parameterized to use four valence terms, but not an electrostatic term. The metal-ligand interactions consist of a bond-stretch term only. The coordination sphere is maintained by nonbond interactions between ligands. MOMEC generally works reasonably well for octahedrally coordinated compounds. 

MOMEC a molecular mechanics force field with a semiempirical term for describing transition metals... 

Within MM, a POS or ligand-ligand repulsion scheme removes the angle-bend term at the metal and thus reference 9q values are not required. This approach has been adopted by Hambley and Comba in their MOMEC program (17) and we have followed suit (18). 

The repulsion increases exponentially, and it is steeper than the bond length deformation potential. The attractive force is usually modeled by a 1/r6 term, while various possibilities exist for the repulsion. The functions used in modem programs include, apart from the Morse potential (Eq. 2.13), the Lennard-Jones potential (Eq. 2.25)[401 (e.g., AMBER1411), the Buckingham potential (Eq. 2.26)[421 (e.g., MOMEC[81), or a modification thereof, the Hill potential (Eq. 2.27) (e.g., MM2, MM3[1,2,231). 

Comba, P Hambley, T. W. Okon, N. MOMEC, A Strain Energy Minimization Package Adapted to HyperChem , Altenhoff Schmitz, Dortmund Germany (1995). 

Comba, P. Hambley, T.W. Okon, N. Lauer, G. MOMEC - A Molecular Modeling Package for Inorganic Compounds. CVS Heidelberg, 1997. 

Momec[521 is a molecular mechanics program which was designed specially for coordination and inorganic compounds. It has been adapted for use with HyperChem[511. 

Another way to demonstrate this effect is shown in three sample calculations using the MOMEC force fieldt52-57 58 96 99-124-140 155) jn Table 3.5 the experimental M-N distances (r(obs)), the calculated bond lengths (r(calc)), the corresponding force constants (k) and ideal bond lengths (r0) are shown for some sample calculations of some hexaamminemetal complexes. 

The tutorial has been written for the full, commercially available programs MOMEC and HyperChem but most tutorials can be completed with the MOMEClite/Hinview set of programs provided on the CD. Readers who have li-... 

Save the structure by selecting the Save option under the File menu of HyperChem. When saving the file choose the path that you want to use in your MOMEC calculations. 

---