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An iron(ii) spin-crossover metallacycle from a back-to-back bis-[dipyrazolylpyridine]†
Laurence J. Kershaw Cook,Julie Fisher,Lindsay P. Harding,Malcolm A. Halcrow
Dalton Transactions Pub Date : 04/16/2015 00:00:00 , DOI:10.1039/C5DT00732A
Abstract

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.

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