An iron(ii) spin-crossover metallacycle from a back-to-back bis-[dipyrazolylpyridine]

The syntheses of 4-mercapto-2,6-di(pyrazol-1-yl)pyridine (bppSH) and bis[2,6-di(pyrazol-1-yl)pyrid-4-yl]disulfide (bppSSbpp) are reported. In contrast to previously published “back-to-back” bis-[2,6-di(pyrazol-1-yl)pyridine] derivatives, which form coordination polymers with transition ions that are usually insoluble, bppSSbpp yields soluble oligomeric complexes with iron(II) and zinc(II). Mass spectrometry and DOSY data show that [{Fe(μ-bppSSbpp)}n]2n+ and [{Zn(μ-bppSSbpp)}n]2n+ form tetranuclear metallacycles in nitromethane solution (n = 4), although 1H NMR and conductivity measurements imply the iron compound may undergo more fragmentation than its zinc congener. Both [{Fe(bppSH)2]2+ and [{Fe(μ-bppSSbpp)}n]2n+ exhibit thermal spin-crossover in CD3NO2 solution, with midpoint temperatures near 245 K. The similarity of these equilibria implies there is little cooperativity between the iron centres in the metallacyclic structures

Data to support study of Iron(II) Complexes of 2,4-Dipyrazolyl-1,3,5-Triazine Derivatives ‒ the Influence of Ligand Geometry on Metal Ion Spin State

Seven derivatives of [FeL2]2+ (L = 2,4-di{pyrazol-1-yl}-1,3,5-triazine) are all high-spin. DFT calculations imply this can be attributed to the geometry of the L ligand

Data to Support Iron(II) Complexes of 2,6-Bis(imidazo[1,2?a]pyridin-2-yl)pyridine and Related Ligands with Annelated Distal Heterocyclic Donors

Complexes of the title ligand and two of its derivatives are mostly high-spin in the solid state, but exhibit thermal spin-crossover equilibria in solution with a ligand-centred room-temperature emission

Insight into structure: function relationships in a molecular spin-crossover crystal, from a related weakly cooperative compound

This is a repository copy of Insight into structure: function relationships in a molecular spin-crossover crystal, from a related weakly cooperative compound. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/83008/ Version: Accepted Version Article: Elhaïk, J, Kilner, C and Halcrow, MA (2014) Insight into structure: function relationships in a molecular spin-crossover crystal, from a related weakly cooperative compound. European Journal of Inorganic Chemistry, 2014 (26). 4250 -4253. ISSN 14344250 -4253. ISSN -1948 https://doi.org/10.1002/ejic.201402623 [email protected] https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. Insight into Compound Jérôme Elhaïk, [a] Colin A. Kilner, [a] and Malcolm A. Halcrow* [a] Abstract: The ClO4 − salt of [FeL2] 2+ (L = 2,6-bis(3-methylpyrazol-1-yl)pyridine) undergoes very gradual thermal spin-crossover centered just below room temperature. In contrast, the BF4 − salt of the same complex exhibits an abrupt and structured spin-transition at lower temperature, with a complicated structural chemistry. The difference can be attributed to a much larger change in molecular structure between the spin states of the complex in the more cooperative BF4 − salt, leading to an increased kinetic barrier for their interconversion. Consistent with that suggestion, the high-spin and low-spin structures of weakly cooperative [FeL2][ClO4]2 are almost superimposable. The continuing interest in thermally and optically switchable spin-crossover (SCO) materials [9] Its thermal spin-transition takes place in two steps, via a re-entrant symmetry-breaking transition to an intermediate crystal phase, with a tripled unit cell containing a mixture of high-spin and low-spin sites. The first of these steps occurs abruptly with hysteresis, but at a temperature that varies according to the water content of the sample (x). In contrast the second step is kinetically slow, and is only achieved when the sample is poised at 100 K for 1.5 hrs. [10] Its excited spin-state trapping (LIESST [11] ) behavior is also unique, in that its thermodynamic high low spin transition and kinetically controlled high low spin-state relaxation exhibit different profiles and are effectively decoupled from each other. [12] Although unexceptional in itself, 1[ClO4]2 provides useful insight into the structural origin of the unusual behavior of the BF4 − salt by providing a rare comparison between strongly and weakly cooperative spin-crossover materials based on the same complex molecule. At 300 K, MT for 1[ClO4]2 is 2.4 cm 3 mol -1 K, lower than expected for a high-spin iron(II) complex with this ligand type (3.4-3.6 cm 3 mol -1 K)

Data to support study of Influence of Ligand Substituent Conformation on the Spin State of an Iron(II)/Di(pyrazol-1-yl)pyridine Complex

The solution-phase spin-crossover temperature in iron(II)/4-alkylsulfanyl-2,6-di{pyrazol-1-yl}pyridine complexes is influenced by the conformation of the SMe, SiPr or StBu alkylsulfanyl substituents

Data to support study of Spin States of Homochiral and Heterochiral Isomers of [Fe(PyBox)2]2+ Derivatives

Homochiral [Fe((R)-LPh)2]2+ (LPh = 2,6-bis{4-phenyloxazolinyl}pyridine) undergoes spin-crossover in CD3CN at 34 K lower temperature than its heterochiral diastereomer [Fe((R)-LPh)((S)-LPh)]2+

Data to support study of Structural transformations and spin-crossover in [FeL2]2+ salts (L = 4-{tertbutylsulfanyl}-2,6-di{pyrazol-1-yl}pyridine) − the influence of bulky ligand substituents

Desolvation of [FeL2][BF4]2·xMeNO2 occurs via an intermediate phase, exhibiting hysteretic spin-crossover (SCO) with a reverse step in its warming branch. Incomplete SCO in the final product phase reflects disorder of an L ligand. [FeL2][BF4]2·yMe2CO contains five complex cations per asymmetric unit, four of which undergo gradual SCO in at least two discrete steps

Data to support study of Iron/2,6-Di(pyrazol-1-yl)pyridine Derivatives with a Discotic Pattern of Alkyl or Alkynyl Substituents

[Fe(1-bpp)2][BF4]2 derivatives with four long chain alkyl substituents show an irreversible low→high-spin conversion near 350 K, which may reflect melting of the complexes' alkyl substituent conformation