Impact of Positional Isomers on the Selective Isolation of cis-trans Isomers in Cobaltdioxolene Chemistry and Solvation Effects on the Valence Tautomerism in the Solid State
Résumé
Three new mononuclear cobalt compounds, trans-[Co(3,5-dbcat)(3,5-dbsq)(4-Etpy) 2 ]•CH 3 CN (1), cis-[Co(3,5-dbcat)(3,5-dbsq)(3-NH 2 py) 2 ]•DMF (2) and trans-[Co(3,5dbcat)(3,5-dbsq)(4-NH 2 py) 2 ]•2DMF (3) (3,5-dbcat 2and 3,5-dbsq •− stand for 3,5-di-tertbutyl-catacholate and 3,5-di-tert-butyl-semiquinonate, respectively), derived from a redoxactive o-dioxolene ligand in presence of 4-ethylpyridine (4-Etpy), 3-aminopyridine (3-NH 2 py), and 4-aminopyridine (4-NH 2 py), respectively, have been synthesized and investigated with a view to examine possible influence of pyridine derivatives and solvation on the valence tautomeric (VT) process. Single crystal X-ray diffraction data for all compounds at room temperature suggest Co(III)(3,5-dbcat)(3,5-dbsq) charge distribution in these complexes. Further insight into the crystal structures discloses the diverse noncovalent interactions offered by the isomers of aminopyridine in 2 and 3, leading to the first example 2 of selective isolation of cis and trans isomers in cobalt-dioxolene chemistry induced by the positional isomers of the ancillary ligands. Variable temperature magnetic susceptibility data for all compounds between 2 and 300 K are consistent with the structural studies. At elevated temperatures, complex 1 exhibits a VT interconversion from low spin Co(III)-(3,5-dbcat)(3,5dbsq) to high spin Co(II)-(3,5-dbsq)(3,5-dbsq), triggered by the loss of lattice solvent molecules, while a partial interconversion is observed for complex 3 even heating up to 430 K. The present report overall highlights the impact of positional isomers on the selective isolation of cis-trans isomers in cobalt-dioxolene chemistry and solvation effects on the valence tautomerism in the solid state.
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