Targeted structural modification of spin crossover complexes: pyridine vs pyrazine

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, PZMAT and PZMPT (4-amino- and 4-pyrrolyl-3,5-bis{[(2-pyrazylmethyl)amino]methyl}-4H-1,2,4-triazole, respectively), and two dinuclear complexes of them, [FeII2(PZMAT)2](BF4)4∙MeOH∙2H2O (1∙MeOH∙2H2O) and [FeII2(PZMPT)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.