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Observation of the single-ion magnet behavior of d8 ions on two-coordinate Co(i)-NHC complexes.

ABSTRACT: The slow magnetic relaxation typical for single-ion magnets has been known for certain low-coordinate 3d metal complexes with d6, d7, and d9 electronic configurations, but never for d8 complexes. Herein, we report a study on two-coordinate d8 cobalt(i)-N-heterocyclic carbene complexes, for which slow magnetic relaxation behavior was observed for [Co(IMes)2][BPh4] (IMes: 1,3-dimesitylimidazol-2-ylidene) under an applied dc field. The system represents the first d8 single-ion magnet, and features a fitted energy barrier of Ueff = 21.3 cm-1 and pre-exponential factor of ?0 = 6.6 × 10-6 s. The analog two-coordinate cobalt(i) complexes with different NHC ligands, [Co(sIMes)2][BPh4] (sIMes: 1,3-dimesitylimidazolin-2-ylidene) and [Co(IAd)2][BArF4] (IAd: 1,3-dimesitylimidazol-2-ylidene; BArF4: tetra(3,5-ditrifluoromethylphenyl)borate), do not show such single-ion magnet behaviour. Ab initio calculations imply that the dihedral angle between the two NHC planes and the degree of unsaturation of the NHC ligands can dramatically alter the D value of the two-coordinate cobalt(i)-NHC ions, possibly via changing of the Co-NHC ?-interactions, and hence affect the spin-orbit coupling splitting.

SUBMITTER: Meng YS

PROVIDER: S-EPMC5951210 | biostudies-other | 2015 Dec

REPOSITORIES: biostudies-other

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Observation of the single-ion magnet behavior of d8 ions on two-coordinate Co(i)-NHC complexes.

Meng Yin-Shan YS Mo Zhenbo Z Wang Bing-Wu BW Zhang Yi-Quan YQ Deng Liang L Gao Song S

Chemical science 20150910 12

The slow magnetic relaxation typical for single-ion magnets has been known for certain low-coordinate 3d metal complexes with d6, d7, and d9 electronic configurations, but never for d8 complexes. Herein, we report a study on two-coordinate d8 cobalt(i)-N-heterocyclic carbene complexes, for which slow magnetic relaxation behavior was observed for [Co(IMes)2][BPh4] (IMes: 1,3-dimesitylimidazol-2-ylidene) under an applied ...[more]

PMID: 29861952

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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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Observation of the single-ion magnet behavior of d8 ions on two-coordinate Co(i)-NHC complexes.

Publications

Observation of the single-ion magnet behavior of d<sup>8</sup> ions on two-coordinate Co(i)-NHC complexes.

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