Iron(II) Complexes of Tridentate Indazolylpyridine Ligands: Enhanced Spin-Crossover Hysteresis and Ligand-Based Fluorescence

Abstract

ReuseUnless 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. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. ABSTRACTReaction of 2,6-difluoropyridine with 2 equiv indazole and NaH at room temperature affords a mixture of 2,6-bis(indazol-1-yl)pyridine (1-bip), 2-(indazol-1-yl)-6-(indazol-2-yl)pyridine (1,2-bip) and 2,6-bis(indazol-2-yl)pyridine (2-bip), which can be separated by solvent extraction. A two-step procedure using the same conditions also affords both 2-(indazol-1-yl)-6-(pyrazol-1-yl)pyridine (1-ipp) and 2-(indazol-1-yl)-6-(pyrazol-2-yl)pyridine (2-ipp). These are all annelated analogues of 2,6-di(pyrazol-1-yl)pyridine, an important ligand for spin-crossover complexes.Iron (

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

“…Second, when in the complex, the three binding nitrogen are necessarily in the same side of the molecule, whereas in the free ligand four conformations are possible (in-in, out-in/in-out, out-out, see Scheme 2), depending on whether the coordinating nitrogen atoms of each of the two lateral groups is in the same side (in) to that of the central pyridine, or not (out). For all cases, the out-out conformation is the most stable in agreement with the experimental crystal structures [27]. However, the energy differences between the different conformers remain small (see Table 5) especially for in-in and in-out.…”

“…Given that the out-out conformation is the most stable in solution, the absorption spectra of ligands 1-5 were computed on these structures (see Figure 3). As experimentally observed [27] all ligands exhibit a strong absorption around 300 nm with small shoulders around 350 nm (2-ipp for example). Strong absorption peaks lie at smaller wavelength but they are not represented in the experimental spectra (cut at 300 nm).…”

“…In addition to compound 3, other ligands were investigated in solvent conditions when forming a complex with iron(II) [27]. Compounds 2, 3, 4 and 5 have different ligands based on a central pyridine and two lateral aromatic groups attached to it (see Scheme 1).…”

“…Table 6. Lowest experimental and calculated emission wavelength (nm) computed for each ligand in chloroform in the out-out conformation [27].…”

“…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.…”