A magnetic Ni-based metal-organic framework with interesting transformation dynamics

Abstract

Herein, a flexible system composed of two Ni(II)-based coordination compounds: a 3D framework of {[Ni(μ-3isoani)2]·DMF}n (1) formula and a 0D monomeric [Ni(3isoani)2(H2O)4] (2) complex (where 3isoani = 3-aminoisonicotinato and DMF = dimethylformamide) which show mutual solvent-induced reversible transformations into each other is reported. The system shows reversible 1 ↔ 2 transformations upon the exposure of one compound to the solvent present in the other, that is, the MOF (1) in water and the monomer (2) in DMF. The process is easily followed by the naked eye because it involves a colour change from green (1)-to-brownish green (2), making the process traceable as previously observed for the Co(II)-based system. Moreover, these compounds present very different magnetic properties since 1 shows field-induced single-molecule magnet (SMM) behaviour, which corresponds to one of the few Ni(II)-based compounds showing single-ion behaviour (being Ni(II) the unique spin carrier), whereas 2 behaves as a regular paramagnet, all of which is explained according to a careful study of the magnetic properties by means of experimental direct-current (dc) and alternating-current (ac) measurements. Obtained experimental results are well supported by active space self-consistent field (CASSCF) calculations that allow understanding the slow relaxation occurring in the Ni(II) ion.