Coordination Polymers Particles (CPPs) with catechol functionalities hold promise for applications such as contrast agents or platforms for drug delivery. However, the characterisation of their coordination environment remains a challenge, in part due to their lack of a crystalline structure. This study explores the synergy of computational and spectroscopic techniques for elucidating the structures of iron-based CPPs.

We have synthesised CPPs based on ligands with catechol-catechol and catechol-pyridine as iron chelating moieties. To characterise these compounds, we employed UV-Vis, IR and Raman spectroscopies in combination with DFT to understand their coordination environment. These calculations were performed using B3LYP-D3BJ and the def2-TZVPP(Fe), TZVP(O,N) and SVP(C,H) methodology on simplified models of the CPPs.

The DFT model revealed different coordination environments and effectively reproduced the key features observed in the experimental spectra. The catechol-catechol complex showed a four-centre coordination with two catechol ligands bound to the iron, whereas the catechol-pyridine complex exhibited octahedral coordination, incorporating the pyridine rings into the coordination sphere. These findings were supported by the characteristic bands observed in the UV-Vis, centred at λ_max = 550nm, and IR and Raman spectra with catechol ring, Fe-O and Fe-N vibrations.

The computational proposed model effectively describes the key features observed in the synthesised polymers, demonstrating the power of combined experimental and computational approaches for elucidating the coordination environment in analogous CPPs systems.