TCNQ (7,7,8,8-tetracyanoquinodimethane) anion-radical derivatives were used to fine tune the magnetic properties of the [Co II (Fctp) 2 ] 2+ (Fctp = 4′-(2-ferrocenyl)-2,2′:6′2′′-terpyridine) cation in the solid state. The cocrystallization of [Co II (Fctp) 2 ] 2+ with TCNQ˙ − yielded the two pseudo-polymorphic products [Co II (Fctp) 2 ] (TCNQ) 2 ( 1 ) and [Co II (Fctp) 2 ] (TCNQ) 2 ·MeCN ( 2 ) whereas the analogous reaction with TCNQF˙ − (TCNQF = 2-fluoro-7,7,8,8-tetracyanoquinodimethane) exclusively yielded [Co II (Fctp) 2 ] (TCNQF) 2 ·MeCN ( 3 ). Compound 1 exhibits slow relaxation of magnetization under an applied DC field with U eff = 19.1 K and τ 0 = 9.8 × 10 −6 s. Compounds 2 and 3 are isostructural but exhibit different spin-crossover behavior with transition temperatures of T 1/2 = 336 K and 226 K, respectively. Investigations of the solid state structures by DFT calculations indicate that the differences in magnetic properties of the cationic moiety, [Co II (Fctp) 2 ] 2+ , are induced by supramolecular interactions between [Co II (Fctp) 2 ] 2+ and tunable TCNQ˙ − /TCNQF˙ − anion-radical derivatives.
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Switching on single-molecule magnet properties of homoleptic sandwich tris(pyrazolyl)borate dysprosium( iii ) cations via intermolecular dipolar coupling
Two new homoleptic Dy III compounds [Dy(Tp Me2 ) 2 ][DyCl 3 (Tp Me2 )]·CH 2 Cl 2 ( 1 ) and [Dy(Tp Me2 ) 2 ]I ( 3 ) as well as a heteroleptic (NMe 4 )[DyCl 3 (Tp Me2 )] ( 2 ) (Tp Me2 = tris(3,5-dimethylpyrazolyl)borate) species are reported. Magnetic studies revealed that 1 is a single-molecule magnet (SMM) with an energy barrier of U eff = 80.7 K with τ 0 = 6.2 × 10 −7 s under a zero applied field. Compound 3 exhibits a U eff of 13.5 K with τ 0 = 1.6 × 10 −6 s under a 0.08 T applied field. Ab initio CASSCF + RASSI-SO calculations were performed to further investigate the magnetic behavior of complexes 1–3 . The results support experimental magnetic data for 1 and 3 and indicate that an intermolecular dipolar interaction of ( zJ = −0.1 cm −1 ) is responsible for the SMM behavior of 1 .
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- Award ID(s):
- 1808779
- NSF-PAR ID:
- 10108546
- Date Published:
- Journal Name:
- Dalton Transactions
- Volume:
- 48
- Issue:
- 28
- ISSN:
- 1477-9226
- Page Range / eLocation ID:
- 10610 to 10618
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Utilizing a terphenyl bisanilide ligand, two Dy( iii ) compounds [K(DME) n ][L Ar Dy(X) 2 ] (L Ar = {C 6 H 4 [(2,6- i PrC 6 H 3 )NC 6 H 4 ] 2 } 2− ), X = Cl ( 1 ) and X = I ( 2 ) were synthesized. The ligand imposes an unusual see-saw shaped molecular geometry leading to a coordinatively unsaturated metal complex with near-linear N–Dy–N (avg. 159.9° for 1 and avg. 160.4° for 2 ) angles. These compounds exhibit single-molecule magnet (SMM) behavior with significant uniaxial magnetic anisotropy as a result of the transverse coordination of the bisanilide ligand which yields high energy barriers to magnetic spin reversal of U eff = 1334 K/927 cm −1 ( 1 ) and 1278 K/888 cm −1 ( 2 ) in zero field. Ab initio calculations reveal that the dominant crystal field of the bisanilide ligand controls the orientation of the main magnetic axis which runs nearly parallel to the N–Dy–N bonds, despite the identity of the halide ligand. Analysis of the relaxation dynamics reveals a ca. 14-fold decrease in the rate of quantum tunneling of the magnetisation when X = I ( 2 ). Most notably, the relaxation times were on average 5.6× longer at zero field when the heavier group 17 congener was employed. However, no direct evidence of a heavy atom effect on the Orbach relaxation was obtained as the height of the barrier is defined by the dominant bisanilide ligand.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9dt00597h
