A New Switchable Zr12 Oxocluster Based Large Pore Metal-Organic Framework Functionalized With Spin Crossover Complexes for Acetic Acid Colorimetric Sensing.

Acetic acid sensing is a critical and challenging subject in the industrial, chemical, cultural heritage, and health sectors. While metal-organic Frameworks (MOFs) offer new opportunities for the capture of this type of compound, colorimetric detection is rare, and a chemically stable material that presents both selective adsorption and colorimetric chemosensing potential under environmental conditions is almost non-existent. We present here the synthesis and crystal structure of a new Zr12 oxocluster carboxylate-based MOF, MIP-216(Zr) ([Zr12(μ3-O)8(μ3-OH)8(μ2-OH)6 (formate)6(L1)6], L1: 4,4'-(hexafluoroisopropylidene)bis(benzoic acid). MIP-216(Zr) features specific properties such as a dual pore system with hydrophobic microporous large channels and hydrophilic small pores leading to an unprecedented ability to capture traces of acetic acid under ambient conditions. Its pores were then loaded with the crossover iron complex [FeII(L2)2] (L2: 4-amino-, 2-(2-pyridinylmethylene)hydrazide) (1), leading to the (1)⊂MIP-216(Zr) compound that presents a pronounced solvatochromic effect upon acetic acid vapor sorption, associated with the spin-state change of the encapsulated complex. We finally illustrate the high potential of this compound for acetic acid colorimetric sensing at low concentrations, demonstrating a rapid, visible, and selective response under ambient conditions that highlights its relevance for real-world monitoring applications.