Effect of water and light on the stability of pyridine pillared 2D transition metal nitroprussides

The 3D transition metal nitroprussides have been extensively studied considering their interesting coordination chemistry, and physical and functional properties. Related to the electronic configuration of the nitrosyl group, these materials show certain instability in the presence of water under light, which we have recently documented. Their 2D analogs with organic molecules as pillars between adjacent layers are anhydrous solids and, in principle, could have higher stability under the light. Under this hypothesis, in this contribution we are reporting the results of a study of T(pyridine)₂[Fe (CN)₅NO] with T = Mn, Fe, Co, Ni, Cu, and Zn, for polycrystalline samples (powders) suspended in water, both in the darkness and exposed to white light. Such a study was conducted monitoring the suspension pH, and characterizing the recovery solid fractions using IR and Mössbauer spectroscopies, and XRD powder patterns. Although all samples show photodegradation, the extension and the mechanistic path are highly dependent on the polarizing power of the cation. For the metals (T) with low polarizing power, the pyridine loss triggers the formation of the 3D nitroprussides as intermediate species, while for those with high polarizing power, the unbound axial CN ligand is the key factor in promoting degradation.