Magnetic and Photoluminescent Sensors Based on Metal-Organic Frameworks Built up from 2-aminoisonicotinate

In this work, three isostructural metal-organic frameworks based on first row transition metal ions and 2-aminoisonicotinate (2ain) ligands, namely, {[M(μ-2ain)]·DMF} [M = Co (1), Ni (2), Zn (3)], are evaluated for their sensing capacity of various solvents and metal ions by monitoring the modulation of their magnetic and photoluminescence properties. The crystal structure consists of an open diamond-like topological 3D framework that leaves huge voids, which allows crystallizing two-fold interpenetrated architecture that still retains large porosity. Magnetic measurements performed on 1 reveal the occurrence of field-induced spin-glass behaviour characterized by a frequency-independent relaxation. Solvent-exchange experiments lead successfully to the replacement of lattice molecules by DMSO and MeOH, which, on its part, show dominating SIM behaviour with low blocking temperatures but substantially high energy barriers for the reversal of the magnetization. Photoluminescence studied at variable temperature on compound 3 show its capacity to provide bright blue emission under UV excitation, which proceeds through a ligand-centred charge transfer mechanism as confirmed by time-dependent DFT calculations. Turn-off and/or shift of the emission is observed for suspensions of 3 in different solvents and aqueous solutions containing metal ions.
This work has been funded by Red Guipuzcoana de Ciencia, Tecnología e Innovación (OF218/2018), University of the Basque Country (GIU 17/13), Gobierno Vasco/Eusko Jaurlaritza (IT1005-16, IT1291-19, IT1310-19), Junta de Andalucía (FQM-394) and the Spanish Ministry of Science, Innovation and Universities (MCIU/AEI/FEDER, UE) (PGC2018-102052-A-C22, PGC2018-102052-B-C21, MAT2016-75883-C2-1-P). The authors thank for technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF). Dr. Iñigo López Arbeloa and Dr. Virginia Martínez Martínez are greatly acknowledged for their generous collaboration with quantum yield measurements.