ISSN:
1434-1948
Keywords:
Genetic Algorithms
;
Force field calculations
;
Refinement of force field parameters
;
Tripod metal compounds
;
Conformational analysis
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Force field parameters used to describe the conformation of coordination compounds involving transition metals are generally derived by a trial-and-error procedure, until a somehow satisfying agreement between the calculated and observed conformations of a few members of a class of related compounds is reached. It is shown in this paper that a more general and less biased alternative is available, applicable to many structures at a time. Genetic Algorithms will effectively optimize force field parameters in an automatic way, on the basis of a potentially exhaustive set of all the structural data available for a given class of compounds. The feasibility of this procedure has been demonstrated by the derivation of force field parameters describing the conformational behaviour of tripod-Mo(CO)3 compounds [tripod= RCH2C(CH2X)(CH2Y)(CH2Z), X,Y,Z = PR′R′′)] by simultaneous optimization based on the structure of ten individual molecules. With the force field parameters relevant to the organic part of these compounds taken from MM2*, the parameters involving contributions from the Mo center were refined. The agreement between observed and calculated structures is characterized by an rms deviation of around 0.3 Å for the ten structures contained in the data base. To assess the validity of this approach, the conformational space of CH3C(CH2PPh2)3Mo(CO)3 was explored exhaustively. A contour diagram representing the relative energy of the molecule with respect to the rotational positions of its phenyl groups was found to effectively reproduce the scatter of these conformational parameters as earlier derived from an analysis of 82 relevant compounds. - As a further assessment, the conformational space of CH3C[CH2P(o-Tol)2]3Mo(CO)3, which was not included in the data base, has been analyzed. It is found that the structure corresponding to the global energy minimum corresponds to that observed in the crystal with an rms deviation of only 0.3 Å. The novel approach to problems of this type - Genetic Algorithms had not previously been applied in this context - thus appears promising.
Type of Medium:
Electronic Resource
