Targeted structural modification of spin crossover complexes: pyridine vs pyrazine

Feltham, Humphrey L.C., Cowan, Matthew G., Kitchen, Jonathan A., Jameson, Guy N.L. and Brooker, Sally (2018) Targeted structural modification of spin crossover complexes: pyridine vs pyrazine. Supramolecular Chemistry, 30 (4), 296-304. (doi:10.1080/10610278.2017.1358449).

Abstract

2-(Aminomethyl)pyrazine has been prepared in five steps from 2-pyrazine carboxylic acid. From this key amine, two new bis-terdentate triazole-based ligands which feature pendant pyrazine groups, P_ZMAT and P_ZMPT (4-amino- and 4-pyrrolyl-3,5-bis{[(2-pyrazylmethyl)amino]methyl}-4H-1,2,4-triazole, respectively), and two dinuclear complexes of them, [Fe^II ₂(P_ZMAT)₂](BF₄)₄∙MeOH∙2H₂O (1∙MeOH∙2H₂O) and [Fe^II ₂(P_ZMPT)₂](BF₄)₄∙3H₂O (2∙3H₂O), have been prepared. A structure determination at 100 K on 2∙3.5MeCN confirmed that the ligands adopt the expected binding mode, providing all twelve donors to the two iron(II) centres and two N¹,N²-triazole bridges between them. Both undergo gradual incomplete spin transitions: at room temperature 1∙MeOH∙2H₂O and 2∙3H₂O are approximately two-thirds to three-quarters [HS-HS], dropping to mostly ‘[HS-LS]’ at 50 K. The structure determination and Mössbauer spectroscopy of 2 qualitatively support this. These findings are consistent with the pendant pyrazines providing a somewhat higher field strength than the pendant pyridines do in the analogous PMRT complexes.

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Contributors

Author: Jonathan A. Kitchen

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