From field-induced to zero-field SMMs associated with open/closed structures of bis(ZnDy) tetranuclear complexes: a combined magnetic, theoretical and optical study†
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Zabala Lekuona, Andoni; Lopez de Pariza, Xabier; Díaz Ortega, Ismael Francisco; Cepeda, Javier; Nojiri, Hiroyuki; Gritsan, Nina P.; Dmitriev, Alexey A.; López-Ortega, Alberto; Rodríguez Diéguez, Antonio; Seco, Jose Manuel; Colacio Rodríguez, EnriqueEditorial
Royal Society of Chemistry
Date
2024-04-12Referencia bibliográfica
Zabala Lekuona, A. et. al. Dalton Trans., 2024, 53, 7971. [https://doi.org/10.1039/D4DT00148F]
Sponsorship
Spanish Ministry of Science, Innovation and Universities (MCN/AEI/FEDER, UE) (PGC2018-102052-A-C22, PGC2018-102052-B-C21, MCIN/ AEI /10.13039/501100011033/ FEDER “Una manera de hacer Europa”); University of the Basque Country (GIU 20/028); Gobierno Vasco/Eusko Jaurlaritza (IT1755-22); Red Guipuzcoana de Ciencia, Tecnología e Innovación (FA385/2023, DG23/16); Junta de Andalucía (FQM-195, FQM-394, A-FQM-172-UGR18 and B-FQM-734-UGR20 and ProyExcel_00386); GIMRT and ICC-IMR programs of the Institute for Materials Research, Tohoku University. HN acknowledges the support by KAKENHI19H00647; Grants PID2021-122613OB-I00 funded by MCIN/AEI/ 10.13039/501100011033 and PJUPNA2020 from Universidad Pública de Navarra; Russian Science Foundation (project no. 22-13-00077)Abstract
We have prepared a bis(compartmental) Mannich base ligand H4L (1,4,8,11-tetraaza-1,4,8,11-tetrakis(2-
hydroxy-3-methoxy-5-methylbenzyl)cyclotetradecane) specifically designed to obtain bis(TMIILnIII) tetranuclear
complexes (TM = transition metal). In this regard, we have succeeded in obtaining three new
complexes of the formula [Zn2(μ-L)(μ-OAc)Dy2(NO3)2]·[Zn2(μ-L)(μ-OAc)Dy2(NO3)(OAc)]·4CHCl3·2MeOH
(1) and [TM2(μ-H2L)2(μ-succinate)Ln2(NO3)2] (NO3)2·2H2O·6MeOH (TMII = Zn, LnIII = Dy (2); TMII = Co,
LnIII = Dy (3)). Compound 1 contains two different bis(ZnDy) tetranuclear molecules that cocrystallize in
the structure, in which acetato bridging ligands connect the ZnII and DyIII ions within each ZnDy subunit.
This compound does not exhibit slow magnetic relaxation at zero field, but it is activated in the presence
of an applied dc magnetic field and/or by Dy/Y magnetic dilution, showing two relaxation processes
corresponding to each of the two different bis(ZnDy) units found in the structure. As revealed by the
theoretical calculations, magnetic relaxation in 1 is single-ion in origin and takes place through the first
excited state of each DyIII ion. When using the succinato dicarboxylate bridging ligand instead of acetate,
compounds 2 and 3 were serendipitously formed, which have a closed structure with the succinate anion
bridging two ZnDy subunits belonging to two different ligands. It should be noted that only compound 2
exhibits slow relaxation of magnetization in the absence of an external magnetic field. According to
experimental and theoretical data, 2 relaxes through the second excited Kramers doublet (Ueff = 342 K).
In contrast, 3 displays field-induced SMM behaviour (Ueff = 203 K). However, the Co/Zn diluted version of
this compound 3Zn shows slow relaxation at zero field (Ueff = 347 K). Ab initio theoretical calculations
clearly show that the weak ferromagnetic coupling between CoII and DyIII ions is at the origin of the lack
of slow relaxation of this compound at zero field. Compound 2 and its diluted analogues 2Y and 3Zn show
hysteresis loops at very low temperature, thus confirming their SMM behaviour. Finally, compounds 1 and
2 show DyIII based emission even at room temperature that, in the case of 2, allows us to extract the splitting
of the ground 6H15/2 term, which matches reasonably well with theoretical calculations.