Cooperative redox and spin activity from three redox congeners of sulfur-bridged iron nitrosyl and nickel dithiolene complexes

Abstract

The synthesis of sulfur-bridged Fe–Ni heterobimetallics was inspired by Nature’s strategies to “trick” abundant first row transition metals into enabling 2-electron processes: redox-active ligands (including pendant iron–sulfur clusters) and proximal metals. Our design to have redox-active ligands on each metal, NO on iron and dithiolene on nickel, resulted in the observation of unexpectedly intricate physical properties. The metallodithiolate, (NO)Fe(N 2 S 2 ), reacts with a labile ligand derivative of [Ni II (S 2 C 2 Ph 2 )] 0 , Ni DT , yielding the expected S-bridged neutral adduct, FeNi , containing a doublet {Fe(NO)} 7 . Good reversibility of two redox events of FeNi led to isolation of reduced and oxidized congeners. Characterization by various spectroscopies and single-crystal X-ray diffraction concluded that reduction of the FeNi parent yielded [FeNi] − , a rare example of a high-spin {Fe(NO)} 8 , described as linear Fe II (NO – ). Mössbauer data is diagnostic for the redox change at the {Fe(NO)} 7/8 site. Oxidation of FeNi generated the 2 [FeNi] + ⇌ [Fe 2 Ni 2 ] 2+ equilibrium in solution; crystallization yields only the [Fe 2 Ni 2 ] 2+ dimer, isolated as PF 6 − and BArF − salts. The monomer is a spin-coupled diradical between {Fe(NO)} 7 and Ni DT + , while dimerization couples the two Ni DT + via a Ni 2 S 2 rhomb. Magnetic susceptibility studies on the dimer found a singlet ground state with a thermally accessible triplet excited state responsible for the magnetism at 300 K (χ M T = 0.67 emu·K·mol −1 , µ eff = 2.31 µ B ), and detectable by parallel-mode EPR spectroscopy at 20 to 50 K. A theoretical model built on an H 4 chain explains this unexpected low energy triplet state arising from a combination of anti- and ferromagnetic coupling of a four-radical molecular conglomerate.

Magnetic coupling between Fe(NO) spin probe ligands through diamagnetic NiII, PdII and PtII tetrathiolate bridges

“…13 Consistently, the two reductions of the [FeMFe] 2+ series are {Fe(NO)} 7/8 based, with the first process leading to a mixed valence {Fe(NO)} 7 –M II –{Fe(NO)} 8 unit, and the second event producing the fully reduced {Fe(NO)} 8 –M II –{Fe(NO)} 8 complex. In prior studies, we observed the rare {Fe(NO)} 8 unit in the case of doubly reduced [Fe–Ni] + , 10,11 but attempts to isolate the one- and two-electron reduction products of the [FeMFe] 2+ complexes have thus far been unsuccessful.…”

Development of (NO)Fe(N2S2) as a Metallodithiolate Spin Probe Ligand: A Case Study Approach

“…Thus, the sulfur-bridged Fe–Ni bimetallics of this study with NO on iron and dithiolene on nickel were found to produce heterobimetallics with unusual and unexpectedly intricate physical properties . Good reversibility in two redox events of the as isolated neutral bimetallic complex FeNi at −0.24 and −1.18 V led to isolation of oxidized and reduced congeners, respectively; see Figure .…”

“…Magnetic data (SQUID) on the dimer dication, spin topology shown in Figure 7A, found a singlet ground state with a thermally accessible triplet state that is responsible for the magnetism at 300 K (χ M T = 0.61 emu K ) explains this unexpected ferromagnetic low-energy triplet state arising from antiferromagnetic coupling of a four-radical molecular conglomerate. 2 The R 1 and R 2 distances were adjusted and benchmarked to match the DFT computed energies (Figure 7B). With both energy profiles the PHI program was used to fit J 1 and J 2 , the dominant exchange pathways.…”

“…Inset shows the CV of FeNi displaying two fully reversible redox events. Adapted with permission from ref . Copyright 2022 The Author(s).…”

Sulfur Lone Pairs Control Topology in Heterotrimetallic Complexes: An Experimental and Theoretical Study

“…The nitrosylated (N 2 S 2 )­Fe­(NO) and Co­(NO) derivatives offer the possibility of exploiting the aggregative ability of sulfur to generate polymetallic products containing the redox, vibrational, and magnetic activity of the NO ligand. , In view of the numerous hydrocarbon connectors possible within the N 2 S 2 scaffold, an almost unlimited design space is conceivable. An application of these strategies toward derivatives of molybdenum, expected to be analogous to a class of [(bis-diphosphine) 2 M­(NO)­X] n + molecules, led to an unusual, asymmetric version of the basket structure of Figure .…”