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Rotaxane Co^II Complexes as Field-Induced Single-Ion Magnets.

ABSTRACT: Mechanically chelating ligands have untapped potential for the engineering of metal ion properties. Here we demonstrate this principle in the context of Co^II -based single-ion magnets. Using multi-frequency EPR, susceptibility and magnetization measurements we found that these complexes show some of the highest zero field splittings reported for five-coordinate Co^II complexes to date. The predictable coordination behaviour of the interlocked ligands allowed the magnetic properties of their Co^II complexes to be evaluated computationally a priori and our combined experimental and theoretical approach enabled us to rationalize the observed trends. The predictable magnetic behaviour of the rotaxane Co^II complexes demonstrates that interlocked ligands offer a new strategy to design metal complexes with interesting functionality.

SUBMITTER: Cirulli M

PROVIDER: S-EPMC8361961 | biostudies-literature | 2021 Jul

REPOSITORIES: biostudies-literature

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Rotaxane CoII Complexes as Field-Induced Single-Ion Magnets.

Cirulli Martina M Salvadori Enrico E Zhang Zhi-Hui ZH Dommett Michael M Tuna Floriana F Bamberger Heiko H Lewis James E M JEM Kaur Amanpreet A Tizzard Graham J GJ van Slageren Joris J Crespo-Otero Rachel R Goldup Stephen M SM Roessler Maxie M MM

Angewandte Chemie (International ed. in English) 20210614 29

Mechanically chelating ligands have untapped potential for the engineering of metal ion properties. Here we demonstrate this principle in the context of CoII -based single-ion magnets. Using multi-frequency EPR, susceptibility and magnetization measurements we found that these complexes show some of the highest zero field splittings reported for five-coordinate CoII complexes to date. The predictable coordination behaviour of the interlocked ligands allowed the magnetic pro ...[more]

PMID: 33901329

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Project description:Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)2](ClO4)2∙4H2O (1) and [Ni(terpyepy)2](ClO4)2 MeOH (2) [terpyCOOH = 4'-carboxyl-2,2':6',2″-terpyridine and terpyepy = 4'-[(2-pyridin-4-yl)ethynyl]-2,2':6',2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel-nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9-200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χMT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to -6.0 (1) and -4.7 cm-1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0-5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2.

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Rotaxane Co^II Complexes as Field-Induced Single-Ion Magnets.

Publications

Rotaxane Co<sup>II</sup> Complexes as Field-Induced Single-Ion Magnets.

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