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Abstract Co‐crystallization of the spin‐crossover (SCO) cationic complex, [Fe(1‐bpp)2]2+(1‐bpp=2,6‐bis(pyrazol‐1‐yl)pyridine) with fractionally charged organic anion TCNQδ−(0<δ<1) afforded hybrid materials [Fe(1‐bpp)2](TCNQ)3.5 ⋅ 3.5MeCN (1) and [Fe(1‐bpp)2](TCNQ)4 ⋅ 4DCE (2), where TCNQ=7,7,8,8‐tetracyanoquinodimethane, MeCN=acetonitrile, and DCE=1,2‐dichloroethane. Both materials exhibit semiconducting behavior, with the room‐temperature conductivity values of 1.1×10−4 S/cm and 1.7×10−3 S/cm, respectively. The magnetic behavior of both complexes exhibits strong dependence on the content of the interstitial solvent. Complex1undergoes a gradual temperature‐driven SCO, with the midpoint temperature ofT1/2=234 K. The partial solvent loss by1leads to the increase in theT1/2value while complete desolvation renders the material high‐spin (HS) in the entire studied temperature range. In the case of2, the solvated complex shows a gradual SCO withT1/2=166 K only when covered with a mother liquid, while the facile loss of interstitial solvent, even at room temperature, leads to the HS‐only behavior.
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From spin-crossover to single molecule magnetism: tuning magnetic properties of Co( ii ) bis-ferrocenylterpy cations via supramolecular interactions with organocyanide radical anions
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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- PAR ID:
- 10182410
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 8
- Issue:
- 24
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 8135 to 8144
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Co-crystallization of the prominent Fe( ii ) spin-crossover (SCO) cation, [Fe(3-bpp) 2 ] 2+ (3-bpp = 2,6-bis(pyrazol-3-yl)pyridine), with a fractionally charged TCNQ δ − radical anion has afforded a hybrid complex [Fe(3-bpp) 2 ](TCNQ) 3 ·5MeCN (1·5MeCN, where δ = −0.67). The partially desolvated material shows semiconducting behavior, with the room temperature conductivity σ RT = 3.1 × 10 −3 S cm −1 , and weak modulation of conducting properties in the region of the spin transition. The complete desolvation, however, results in the loss of hysteretic behavior and a very gradual SCO that spans the temperature range of 200 K. A related complex with integer-charged TCNQ − anions, [Fe(3-bpp) 2 ](TCNQ) 2 ·3MeCN (2·3MeCN), readily loses the interstitial solvent to afford desolvated complex 2 that undergoes an abrupt and hysteretic spin transition centered at 106 K, with an 11 K thermal hysteresis. Complex 2 also exhibits a temperature-induced excited spin-state trapping (TIESST) effect, upon which a metastable high-spin state is trapped by flash-cooling from room temperature to 10 K. Heating above 85 K restores the ground-state low-spin configuration. An approach to improve the structural stability of such complexes is demonstrated by using a related ligand 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) to obtain [Fe(bzimpy) 2 ](TCNQ) 6 ·2Me 2 CO (4) and [Fe(bzimpy) 2 ](TCNQ) 5 ·5MeCN (5), both of which exist as LS complexes up to 400 K and exhibit semiconducting behavior, with σ RT = 9.1 × 10 −2 S cm −1 and 1.8 × 10 −3 S cm −1 , respectively.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0tc00830c
