Synthesis of 4-Hydroxy-2,6-di(pyrazol-1-yl)pyridine, and the Spin State Behaviour of Its Iron(II) Complex Salts

Cook, Laurence J. Kershaw; Halcrow, Malcolm A.

doi:10.3390/magnetochemistry1010003

Cited by 9 publications

(13 citation statements)

References 39 publications

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“…In all cases, the signals of their terpy ligands are more paramagnetically shifted than those in the homoleptic complexes [Co( L′ ) 2 ](ClO 4 ) 2 (or previously reported [Co( L′ ) 2 ](OTf) 2 ), thus hinting on a larger population of the HS state as compared to the latter, which undergo an SCO in their pure solutions in acetonitrile-d 3 . The chemical shifts observed at room temperature for the 3-bpp ligands in the two types of cobalt(II) complexes, of which the homoleptic compounds are always HS, ,,,,,, are inconclusive.…”

Section: Resultsmentioning

confidence: 99%

“…In a search for SCO-active cobalt(II) complexes of 3-bpp that are otherwise HS, ,,,,,, we attempted combining them with terpy coligands known to provide an appropriate ligand field for an SCO of the cobalt(II) ion to occur. By mixing three previously synthesized 3-bpp ( L1 , L2 , and L3 ; Scheme ) ,,,, and two available terpy ( L1′ and L2′ ; Scheme ) ligands in a 1:1 ratio with a cobalt(II) salt in an NMR tube, six new heteroleptic cobalt(II) complexes were obtained in situ (Scheme ) together with five earlier reported homoleptic compounds ,− –the side products of the statistical synthesis–and they were screened for a possible SCO behavior by the NMR spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

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In Situ NMR Search for Spin-Crossover in Heteroleptic Cobalt(II) Complexes

et al. 2020

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Here we report the first successful attempt to identify spin-crossover compounds in solutions of metal complexes produced by mixing different ligands and an appropriate metal salt by variable-temperature nuclear magnetic resonance (NMR) spectroscopy. Screening the spin state of a cobalt(II) ion in a series of thus obtained homoleptic and heteroleptic compounds of terpyridines (terpy) and 2,6-bis(pyrazol-3-yl)pyridines (3-bpp) by using this NMR-based approach, which only relies on the temperature behavior of chemical shifts, revealed the first cobalt(II) complexes with a 3-bpp ligand to undergo a thermally induced spin-crossover. A simple analysis of NMR spectra collected from mixtures of different compounds without their isolation or purification required by the current method of choice, the Evans technique, thus emerges as a powerful tool in a search for new spin-crossover compounds and their molecular design boosted by wide possibilities for chemical modifications in heteroleptic complexes.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

In Situ NMR Search for Spin-Crossover in Heteroleptic Cobalt(II) Complexes

et al. 2020

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“…For instance, the use of BF 4´a s the counterion results into a full SCO transition with a small hysteresis loop [23], whereas the use of ClO 4´r esults in the SCO molecules being kinetically trapped in its HS state [19,24]. Alternatively, modifications of the 1-bpp unit have been recently reported, obtaining (among others [25,26] (5) [27]. Even though the structure of the ligands is similar (see Scheme 1), their SCO properties are remarkably different, with transition temperatures of ca.…”

Section: Introductionmentioning

confidence: 99%

Disclosing the Ligand- and Solvent-Induced Changes on the Spin Transition and Optical Properties of Fe(II)-Indazolylpyridine Complexes

et al. 2016

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Abstract:The family of the spin crossover (SCO) compounds based on the 1-bpp unit has furnished striking examples of how subtle changes in the crystal packing have important consequences in their spin transition. Small modifications of the 1-bpp unit itself have been recently reported, obtaining the indazolyl and pirazolyl derivatives [Fe II . In this work we study the consequences of a change in the ligand structure and solvent on the SCO of 1-5. More specifically, we demonstrate that their different behavior is not due to an intraligand H¨¨¨H contact, as suggested experimentally, but to an unfavorable arrangement of the FeN 6 core that some of the ligands might create, which destabilizes their Low Spin (LS) state structure and, thus, alters the transition temperature. Further, by means of solid state calculations, we disclose the effect of the solvent on the structure and crystal cohesion of the crystals. Finally, we analyze the emission and adsorption properties of 1-5, with special interest in the evolution of the absorption spectroscopy of the ligands upon complexation, and its relation with the spin multiplicity of the iron ion.

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“…The molecular complex [Fe(L1) 2 ]¨2ClO 4 , 1, (L1 = 2,6-bis{3-methylpyrazol-1-yl}pyrazine) is closely related to the family of spin crossover (SCO) active [Fe(bpp) 2 ] 2+ (bpp = 2,6-di{pyrazol-1-yl}pyridine) systems [10]. A previous SQUID magnetometry study of 1 revealed an unusual transition curve, consisting of two steps, separated not by a plateau as is often the case in stepped SCO materials [11], but rather by a change in gradient from an abrupt initial step (on cooling) followed by a much more gradual second step [12], as shown in Figure 1.…”

Section: Introductionmentioning

confidence: 99%