Binucleating Jäger-type {(N 2 O 2 ) 2 } 4− ligands : magnetic and electronic interactions of Fe( ii ), Ni( ii ) and Cu( ii ) across an in-plane TTF-bridge †

The simultaneous presence of different electrophores provides an interesting playground for responsive materials. Herein, we present the incorporation of a twice-reversibly oxidizable tetrathiafulvalene (TTF) unit into a binucleating ligand, bridging two metal centers in a fully conjugated plane. A two-step synthesis scheme gave the D 2h symmetric Schiff base-like ligand H 4 L in moderate yields from which the corresponding copper( ii ) [Cu 2 L] , nickel( ii ) [Ni 2 L] , [Ni 2 L(py) 4 ] and iron( ii ) complexes [Fe 2 L(py) 4 ] , [Fe 2 L(dmap) 4 ] and [Fe 2 L(bpee) 2 ]·1 Tol could be obtained. Characterization was performed through 1 H-NMR, IR, UV-vis and 57 Fe-Mössbauer spectroscopy, SQUID magnetometry and cyclic voltammetry, supported by density functional theory (DFT) calculations. Single crystal X-ray analysis of [Ni 2 L(py) 4 ] revealed six-coordinate paramagnetic centers, whereas [Ni 2 L] underwent gradual coordination induced spin state switching (CISSS) in solution. The magnetic independence of both metal centers is echoed by close-to-ideal Curie-plots of the [Cu 2 L] system and the gradual spin crossover of all iron( ii ) compounds. By contrast, cyclic voltammetry measurements in solution indicated oxidation-dependent TTF–metal interactions, as well as metal–metal interactions. The reversible TTF-borne events in H 4 L and [Ni 2 L] are overlaid with metal-borne events in the case of [Fe 2 L(py) 4 ] , as is corroborated by an analysis of the frontier orbital landscapes and through diagnostic spectral features upon chemical oxidation.