Complete and incomplete spin transitions in 1D chain iron(II) compounds

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Pfaffeneder, Toni ; Thallmair, Sebastian ; Bauer, Wolfgang ; Weber, Birgit:
Complete and incomplete spin transitions in 1D chain iron(II) compounds.
In: New Journal of Chemistry. Bd. 35 (2011) Heft 3 . - S. 691-700.
ISSN 1369-9261
DOI: https://doi.org/10.1039/C0NJ00750A

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Abstract

The synthesis and characterisation of two new octahedral iron(ii) SCO coordination polymers [FeL1(bimm)] (1) and [FeL2(bppa)](MeOH)0.5 (2) (L1 = [3,3[prime or minute]]-[1,2-phenylenebis(iminomethylidyne)bis(4-phenyl-2,4-butanedionato)(2-)-N,N[prime or minute],O2,O2[prime or minute]], L2 = [E,E]-[{diethyl 2,2[prime or minute]-1,2-phenylenebis(iminomethylidyne)bis(3-oxo-3-phenylpropanato)}(2-)-N,N[prime or minute],O3,O3[prime or minute]], bimm = bis(1H-imidazol-1-yl)methane and bppa = 1,3-bis(pyridine-4-yl)propane) is presented. Results from X-ray structure analysis at different temperatures revealed in the case of 1 that the transition from a gradual to a cooperative SCO with a 5 K wide hysteresis is due to an increase of the short intermolecular contacts, which exceed a certain threshold for the cooperative effect. In the case of compound 2 an incomplete spin transition with a 4 K wide hysteresis was observed. The low temperature [small chi]MT product remains constant at a value typical for a mixed HS/LS state in stepwise spin transitions. A quantitative correlation between the cooperative effects of 12 monomer and polymer iron(ii) SCO complexes and their structural properties derived from X-ray structure analysis, the so-called crystal contact index, CCI, is introduced.