Iron(II) Spin Crossover Coordination Polymers Derived From a Redox Active Equatorial Tetrathiafulvalene Schiff-Base Ligand

Two polymorphic Fe-II coordination polymers [(FeL)-L-II (TPPE)(0.5)] 1) and [((Fe3L3)-L-II (TPPE)(1.5))] 2), were obtained from a redox-active tetrathiafulvalene (TTF) functionalized ligand [H2L = 2,2'-(((2-(4,5-bis-(methylthio)-1,3-dithiol-2-ylidene)benzo(d) (1,3) dithiole-5,6-diyl)bis-(azanediyl))bis-(meth anylylidene)) (2E,2E')-bis(3-oxobutanoate)] and a highly luminescent connector {TPPE = 1,1,2,2-tetrakis[4-(pyridine-4-yl)phenyl]-ethene}. Complex 1 has a layered structure where the TPPE uses its four diverging pyridines from the TPPE ligand are coordinated by the trans positions to the flat TTF Schiff-base ligand, and complex 2 has an unprecedented catenation of layers within two interpenetrated frameworks. These coordination polymers reserved the redox activity of the TTF unit. Complex 1 shows gradual spin transition behavior without hysteresis. And the fluorescence intensity of TPPE in 1 changes in tandem with the spin crossover (SCO) transition indicating a possible interplay between fluorescence and SCO behavior.

Automated summary

Two polymorphic Fe-II coordination polymers were obtained using a redox-active tetrathiafulvalene (TTF) functionalized ligand and a highly luminescent connector. These coordination polymers retained the redox activity of the TTF unit, with complex 1 showing gradual spin transition behavior and a correlation between fluorescence intensity of TPPE and spin crossover transition.