An extended MM3(96) force field for complexes of the group 1A and 2A cations with ligands bearing conjugated ether donor groups

Abstract

Structural requirements for strain-free metal ion complexation by a conjugated ether group are investigated through the use of both electronic structure calculations and molecular mechanics calculations. Hartree-Fock calculations on simple model complexes, [M(anisole)] n+ and [M(1,2-dimethoxybenzene)] n+ , reveal a preference for trigonal planar oxygen geometry when conjugated ether oxygens are coordinated to alkali and alkaline earth cations. Potential energy surfaces from the Hartree-Fock calculations are used, in part, to develop MM3(96) force field parameters for calculation on complexes of ligands bearing conjugated ether donor atoms with the alkali (Li to Cs) and alkaline earth (Mg to Ba) cations. The extended MM3(96) model reproduces the experimental crystal structures of 42 complexes of multidentate ether ligands with the alkali and alkaline earth cations. A novel feature of the MM3(96) program is reported which facilitates the treatment of metal-centered bond angles in complexes where there are greater than six donor atoms.