9858 | New J. Chem., 2022, 46, 9858–9870 This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2022 Cite this: New J. Chem., 2022, 46, 9858 Multifunctionality of the [C 2 mim][Ln(fod) 4 ] series (Ln = Nd–Tm except Pm): magnetic, luminescence and thermochemical studies† Ana C. Cerdeira, a Joa ˜ o P. Leal, b Joa ˜ o Avo ´ , c Catarina Viola, d Maria H. Casimiro, e Luis M. Ferreira, a Filipe A. A. Paz, f Laura C. J. Pereira, * a Cla ´ udia C. L. Pereira * d and Bernardo Monteiro * g A series of nine tetrakis lanthanide b-diketonate complexes of the type [C 2 mim][Ln(fod) 4 ] (C 2 mim = 1-ethyl-3-methylimidazolium, fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) were prepared, with yields above 80%, and their thermochemical, photophysical and magnetic susceptibilities were evaluated. Thermochemical studies presented a rare and reversible conversion between two solid phases (polymorphism), characteristic of the [Ln(fod) 4 ]  anion. Photophysical and magnetic studies revealed that Dy and Er presented the multifunctionality of being simultaneously SMMs and visible (Dy) or near infra-red (Er) emitters. The Nd, Ho and Tm analogues present characteristic emission bands in the NIR region (800–1200 nm), while Sm, Eu, Tb and Dy present emissions in the visible range. Magnetic susceptibility of Tb, Dy, Ho, Er and Tm salts were measured in the temperature range of 2–300 K, showing paramagnetic behaviour, although with different regimes, with AC susceptibility measurements, at different frequencies in the range of 10–10 000 Hz, providing evidence of slow magnetic relaxation processes for Gd, Dy and Er analogues with SMM behavior. Introduction Until the mid-20th century lanthanides (Ln) had few applica- tions and undergraduate textbooks still implied that the chemistry of the lanthanides was based on Ln 3+ ions, with Ce(IV) as an exception, and the study of one or two ‘‘represen- tative’’ members was enough to extrapolate the behaviour of the whole series. 1 Since then, our knowledge of the chemistry of Ln has changed completely 2 and with it their industrial useful- ness. Nowadays, among many others, Ln find applications in computer hard drives, fluorescent lights, catalysts (petroleum and automotive industries), super magnets (in generators, cars, electrical engines), flat screens and batteries. 3 One of the most important lessons in Ln applications is the requirement of a specific lanthanide in a specific ligand environment for a specific application, completely refuting the idea that Ln chemistry is all the same across the series. 1 Concerning the intrinsic properties of Ln compounds, some properties are still emerging like, for example, stereoisomerism, which is one aspect of lanthanide complexes that has remained hidden until very recently. 4 Two of the most explored properties of the Ln are their optical and magnetic properties. The luminescent properties of the Ln 3+ ions cover a wide range of emissions comprising near- infrared (Pr 3+ , Nd 3+ , Ho 3+ , Er 3+ , Yb 3+ , Tm 3+ ,), visible (Pr 3+ , Sm 3+ , Eu 3+ , Tb 3+ , Dy 3+ , Tm 3+ ) and ultraviolet (Gd 3+ ), which combined to the narrowness and the hypersensitivity of their transitions have allowed their use in many applications including thermometers, 5,6 sensing of gases, vapours or small molecules, 7–10 light-emitting devices, 11,12 biomedical applications, 13,14 forensics, 15 etc. The a Centro de Cie ˆncias e Tecnologias Nucleares (C2TN), DECN, Instituto Superior Te ´cnico, Universidade de Lisboa, Campus Tecnolo ´gico e Nuclear, Estrada Nacional 10, 2695-066 Bobadela, Portugal b Centro de Quı ´mica Estrutural (CQE), Institute of Molecular Sciences, DECN, Instituto Superior Te ´cnico, Universidade de Lisboa, Campus Tecnolo´gico e Nuclear, Estrada Nacional 10, 2695-066 Bobadela, Portugal c Associate Laboratory i4HB–Institute for Health and Bioeconomy and Institute for Bioengineering and Biosciences (IBB), Instituto Superior Te ´cnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lis-boa, Portugal d LAQV-REQUIMTE, Dep. de Quı ´mica, Universidade Nova de Lisboa, 2829-516, Monte de Caparica, Portugal e Centro de Cie ˆncias e Tecnologias Nucleares (C2TN), Instituto Superior Te ´cnico, Universidade de Lis-boa, Campus Tecnolo´gico e Nuclear, Estrada Nacional 10, 2695-066 Bobadela, Portugal f Department of Chemistry, CICECO-Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal g Centro de Quı ´mica Estrutural (CQE), Institute of Molecular Sciences, DEQ, Instituto Superior Te ´cnico, Universidade de Lisboa, Campus Tecnolo ´gico e Nuclear, Estrada Nacional 10, 2695-066 Bobadela, Portugal. E-mail: bernardo.monteiro@ctn.tecnico.ulisboa.pt † Electronic supplementary information (ESI) available. See DOI: https://doi.org/ 10.1039/d2nj01415g Received 22nd March 2022, Accepted 19th April 2022 DOI: 10.1039/d2nj01415g rsc.li/njc NJC PAPER Published on 19 April 2022. Downloaded by Universidade de Lisboa on 5/24/2022 9:53:19 AM. 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