Predicting speciation in the multi-component equilibrium self-assembly of a metallosupramolecular complex

A practical method to predict the speciation in a multi-component equilibrium self-assembly process has been developed and applied to the formation of the square macrocyclic complex formed from (ethylenediamine)Pd(II) and 4,4'-bipyridyl. The method is based on an additive free energy approach that derives the cumulative formation constants of all 56 species at equilibrium from a set of five pair-wise interactions. Estimates for the required values of the pair-wise interactions were derived from potentiometric titration of (ethylenediamine) Pd(II) and 3-phenylpyridine, and from (diethylenetriamine) Pd(II) and 4,4'-bipyridyl systems. The method calculates the equilibrium speciation as a function of reactant concentrations and pH and produces a map of the range of compositions in which the square complex and competing species are dominant. The predictions of the method closely correlate with available experimental data.