Modulating Magnetic and Photoluminescence Properties in 2‐Aminonicotinate‐Based Bifunctional Coordination Polymers by Merging 3d Metal Ions

• Published in: Chemistry : a European journal 2020-10, Vol.26 (59), p.13484-13498
• Main Authors: Pajuelo‐Corral, Oier, Zabala‐Lekuona, Andoni, San Sebastian, Eider, Rodríguez‐Diéguez, Antonio, García, Jose Angel, Lezama, Luis, Colacio, Enrique, Seco, Jose M., Cepeda, Javier
• Format: Article
• Language: English
• Subjects: Alternating current; Anisotropy; Antiferromagnetism; Aqueous solutions; Chemical synthesis; Chemistry; Coordination polymers; Diamagnetism; Direct current; Luminescence; Magnetic anisotropy; Magnetic permeability; Magnetic properties; Manganese; Metal ions; multifunctional materials; Nickel; Photoluminescence; Photons; Polymers; single-ion magnets; Thermal stability
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202002755

Herein, the synthesis and study of bifunctional coordination polymers (CPs) with both magnetic and photoluminescence properties, derived from a heterometallic environment, are reported. As a starting point, three isostructural monometallic CPs with the formula [M(μ‐2ani)2]n (MII=Mn (1Mn), Co (3Co) and Ni (4Ni); 2ani=2‐aminonicotinate), crystallise as chiral 2D‐layered structures stacked by means of supramolecular interactions. These compounds show high thermal stability in the solid state (above 350 °C), despite which, in aqueous solution, compound 1Mn is shown to partially transform into a novel 1D chain CP with the formula [Mn(2ani)2(μ‐H2O)2]n (2Mn). A study of the direct current (dc) magnetic properties of 1Mn, 3Co and 4Ni reveals a spin‐canted structure derived from antisymmetric antiferromagnetic weak exchanges along the chiral network (as confirmed by DFT calculations) and magnetic anisotropy of the ions, in such a way that long‐range ordering is observed with variable magnitude for the spin carriers. Moreover, compounds 3Co and 4Ni show no frequency‐dependent alternating current (ac) susceptibility curves under zero dc field; this is characteristic behaviour of a glassy state that may be partially supressed for 3Co by applying an external dc field. To overcome long‐range magnetic ordering, CoII ions are diluted in a diamagnetic ZnII‐based matrix, which enables single‐molecule magnet behaviour. Interestingly, this strategy allows a bifunctional CoxZn1−x2ani material, which is imbued with a strong photoluminescent emitting capacity, as characterised by an intense blue light followed by a green afterglow, to be obtained. Behavioural changes: The combination of 2‐aminonicotinic acid and 3d ions gives rise to a chiral 2D layered structure, showing intriguing long‐range weak ferromagnetic ordering, mainly in the case of the CoII counterpart. Long‐range ordering is suppressed by magnetically diluting the sample into a ZnII‐based homologue, in such a way that the resulting material behaves as a bifunctional single‐ion magnet and long‐lasting phosphor.