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

• Published in: Dalton transactions : an international journal of inorganic chemistry 2024-05, Vol.53 (21), p.9092-9105
• Main Authors: Schreck, Constantin, Schönfeld, Sophie, Liebing, Phil, Hörner, Gerald, Weber, Birgit
• Format: Article
• Language: English
• Subjects: Copper; Density functional theory; Electrons; Imines; Iron; Ligands; Magnetic measurement; Mossbauer spectroscopy; NMR; Nuclear magnetic resonance; Oxidation; Playgrounds; Single crystals; Superconducting quantum interference devices; Voltammetry; X ray analysis
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d4dt00479e

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 symmetric Schiff base-like ligand H L in moderate yields from which the corresponding copper(II) [Cu2L], nickel(II) [Ni2L], [Ni2L(py)4] and iron(II) complexes [Fe2L(py)4], [Fe2L(dmap)4] and [Fe2L(bpee)2]·1 Tol could be obtained. Characterization was performed through H-NMR, IR, UV-vis and Fe-Mössbauer spectroscopy, SQUID magnetometry and cyclic voltammetry, supported by density functional theory (DFT) calculations. Single crystal X-ray analysis of [Ni2L(py)4] revealed six-coordinate paramagnetic centers, whereas [Ni2L] 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 [Cu2L] 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 L and [Ni2L] are overlaid with metal-borne events in the case of [Fe2L(py)4], as is corroborated by an analysis of the frontier orbital landscapes and through diagnostic spectral features upon chemical oxidation.