An iron(ii) spin-crossover metallacycle from a back-to-back bis-[dipyrazolylpyridine].
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 (1)H 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.
School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, UK LS2 9JT. m.a.halcrow@leeds.ac.uk.
Laurence J
LJ
Kershaw Cook
Julie
J
Fisher
Lindsay P
LP
Harding
Malcolm A
MA
Halcrow