Reversible solid to solid transformation in a crystalline state gas–solid reaction under ambient conditions: Fe–N(pyridine) bond formation at the expense of Fe–OH₂ bond breaking and vice versa

The non-porous crystalline state of a trinuclear iron cluster containing compound [Fe₃(μ₃-O)(μ₂-CH₃COO)₆(C₅H₅NO)₂(H₂O)]ClO₄·3H₂O (1) demonstrates a series of crystalline state reactions that can be stimulated by an external substrate, such as methanol or pyridine. This simple trinuclear {μ₃-O} cluster [Fe₃(μ₃-O)(μ₂-CH₃COO)₆(C₅H₅NO)₂(H₂O)]¹⁺ exhibits reversible gas–solid reactions driven by the ligand exchange at one of its metal centres that involve Fe–OH₂ bond breaking and Fe–N(pyridine) bond formation in the solid state in a reversible crystal to crystal transformation. The gas–solid interface reactions have been confirmed by IR spectroscopy and powder X-ray diffraction studies. A classical trinuclear iron {μ₃-O} cluster with a slight modification in its basic molecular structure opens up new possibilities that can find applications in the development of multi-functional materials. The reversible solid to solid transformations in the present article have been established by various spectroscopic arguments.