Targeted structural modification of spin crossover complexes: pyridine vs pyrazine

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(Z)MAT 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, [Fe-2(II)(P(Z)MAT)(2)](BF4)(4)center dot MeOH center dot 2H(2)O (1 center dot MeOH center dot 2H(2)O) and [Fe-2(II)(PZMPT)(2)](BF4)(4)center dot 3H(2)O (2 center dot 3H(2)O), have been prepared. A structure determination at 100 K on 2 center dot 3.5MeCN confirmed that the ligands adopt the expected binding mode, providing all twelve donors to the two iron(II) centres and two N-1,N-2-triazole bridges between them. Both undergo gradual incomplete spin transitions: at room temperature 1 center dot MeOH center dot 2H(2)O and 2 center dot 3H(2)O are approximately two-thirds to three-quarters [HS-HS], dropping to mostly [HS-LS] at 50 K. The structure determination and Mossbauer 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. [GRAPHICS] .