Assessing the strategic preparation of CPPs: a computational analysis of the impact of different catechol-based ligands

Catechol derivatives are promising for functional materials due to their metal-chelating ability, making them excellent ligands for generating Coordination Polymer Particles (CPPs). They self-assemble into CPPs from metal ions and polydentate organic ligands, up till now polymeric structure characterization remains challenging. Predicting CPPs properties (morphology, size, stability) in diverse environments is essential for their applications.

In this context, by employing DFT calculations on an iron/catechol-derivatives system, the study aims to investigate the effect on the structure of CPPs materials based on: (a) the utilization of Fe²⁺ and Fe³⁺ in high and low spin states; (b) the type of chelating groups in catechol derivatives and their geometries; and (c) the distance between two chelating groups in a model polydentate ligand.

Geometry optimizations were performed with the BP86 functional. SP Energy calculations with wB97X-D3BJ and the def2 TZVPP(Fe), TZVP(O,N) and SVP(other) basis sets. Iron complexes were modelled with simplified representative ligands: [Fe(catechol_n)]_n=2,3 and [Fe(cat₂)L₂] (L=2-vynilpyridine(pyr), methanethiolate). Fe³⁺ complexes in high-spin had the lowest formation energy. The trans-[Fe(cat)₂(pyr)₂] octahedral complex emerged as the most stable, followed by the tetrahedral [Fe(cat₂)]. 3-((5-mercaptoalkyl)thio)benzene-1,2-diol was employed as the model ligand with a methylene chain (C2-C8) between the chelating groups. The length and conformation of this chain could significantly affect CPPs formation, as it may precipitate as a stable monomer, inhibiting polymer growth. Calculation indicated that monomer formation required a minimum of three methylene units in the chain, with the cis conformation being preferred. Longer chains were favored for the dimers formation, with C4 being most stable.