Valence tautomerism interconversion triggers transition to stable charge distribution in solid polymeric cobalt–polyoxolene complexes

Abstract

The reaction of 3,3,3',3'-tetramethyl-5,5',6,6'-tetrahydroxy-1,1'spiro-bis(indane), L, with cobalt salts in the presence of diazine ligands affords polymeric derivatives of general formula [CoL(diazine)]infinity . nH2O, L being coordinated as a mixed-valence SQ-Cat species. The bipiridyl and o-phenantroline derivatives have been characterised by means of magnetic, EPR and calorimetric measurements. The characterisation showed that both systems are obtained in a metastable charge distribution, presumably trapped due to the class I character of the mixed valence form of the ligand. The occurrence of entropy-driven valence tautomeric interconversion induces the transition to the most stable charge distribution. The photomagnetic characterisation evidenced that valence tautomeric process can be photoinduced and that the lifetime of the photoinduced metastable state, obtained in low yield, is of ca. 2 x 10(5) s at 9 K.

Synthesis, crystal structure and valence tautomerism of a 4,4′-bipyridine-bridged one-dimensional chiral cobalt complex

“…The temperature dependent reversible valence tautomeric behavior for complex 1 was shown in Scheme 1. The magnetic properties of the title complex also agree well with the previously observed for polymeric complexes with similar donor ligands [26][27][28][29].…”

Valence‐Tautomeric Metal–Organic Nanoparticles

“…[24] The magnetic properties of nanoparticles of different sizes all exhibited similar dependence on temperature. Therefore, the variation of the slope mostly likely can be correlated with the presence of two different relaxation mechanisms associated with different network environments and/or the presence of an additional structural transition, as recently reported by Dei et al [25,26] In summary, we have demonstrated that precipitation/ coordination polymerization is a suitable approach for the fabrication of pre-synthesized units into functional metalorganic nanoparticles. Size-tunable nanoparticles that exhibit valence tautomerism have been obtained by using electroactive [Co III (3,5-dbsq)(3,5-dbcat)] units and the appropriate bridging ligand.…”

Valence Tautomeric Transitions of Three One-Dimensional Cobalt Complexes

“…28 Interestingly, it showed not only photoswitchable interconversion between the two tautomers but also a pressure effect on the VT transition. Besides, using bis-bidentate tetraoxolene ligand could also lead to the formation of 1D VT complexes, as exemplified by [Co(L)(spiro)]·3H 2 O (L = 2,2′-bipyridine or 1,10-phenanthroline, spiroH 4 = 3,3,3′,3′-tetramethyl-5,5′,6,6′-tetrahydroxy-1,1′-spirobisindane), 29 which showed time-dependent changes of the magnetic susceptibilities and displayed thermally and photoinduced VT transitions.…”