Reactions of Fe(II) precursors with the tetradentate ligand S,S'-bis(2-pyridylmethyl)-1,2-thioethane (bpte) and monodentate NCE(-) coligands afforded mononuclear complexes [Fe(bpte)(NCE)2] (1, E = S; 2, E = Se; 3, E = BH3) that exhibit temperature-induced spin crossover (SCO). As the ligand field strength increases from NCS(-) to NCSe(-) to NCBH3(-), the SCO shifts to higher temperatures. Complex 1 exhibits only a partial (15%) conversion from the high-spin (HS) to the low-spin (LS) state, with an onset around 100 K. Complex 3 exhibits a complete SCO with T1/2 = 243 K. While the γ-2 polymorph also shows the complete SCO with T1/2 = 192 K, the α-2 polymorph exhibits a two-step SCO with the first step leading to a 50% HS → LS conversion with T1/2 = 120 K and the second step proceeding incompletely in the 80-50 K range. The amount of residual HS fraction of α-2 that remains below 60 K depends on the cooling rate. Fast flash-cooling allows trapping of as much as 45% of the HS fraction, while slow cooling leads to a 14% residual HS fraction. The slowly cooled sample of α-2 was subjected to irradiation in the magnetometer cavity resulting in a light-induced excited spin state trapping (LIESST) effect. As demonstrated by Mössbauer spectroscopy, an HS fraction of up to 85% could be achieved by irradiation at 4.2 K.

The discovery of ferrocene nearly 70 years ago marked the genesis of metallocene chemistry; although the ferrocenium cation was discovered soon afterwards, a derivatized ferrocenium dication was only isolated in 2016 and the monoanion of ferrocene has only been observed in low temperature electrochemical studies. Here we report the isolation of a derivatized ferrocene anion in the solid state as part of an isostructural family of 3 d metallocenates which consist of anionic complexes of a metal centre (manganese, iron or cobalt) sandwiched between two bulkyCp ttt ligands (where Cp ttt is {1,2,4-C 5 H 2 t Bu 3 }). These air- and thermally-sensitive complexes rapidly decompose above -30 °C, however, we were able to characterise all metallocenates by a wide range of physical techniques and ab initio calculations. These data have allowed us to map the electronic structures of this metallocenate family, including an unexpected high-spin S = 3/2 ground state for the 19e - derivatized ferrocene anion.

Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single-molecule magnets (SMMs). Spin-phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin-phonon coupling in molecules is challenging. We have found that far-IR magnetic spectra (FIRMS) of Co(PPh 3 ) 2 X 2 (Co-X; X = Cl, Br, I) reveal rarely observed spin-phonon coupling as avoided crossings between magnetic and u-symmetry phonon transitions. Inelastic neutron scattering (INS) gives phonon spectra. Calculations using VASP and phonopy programs gave phonon symmetries and movies. Magnetic transitions among zero-field split (ZFS) levels of the S = 3/2 electronic ground state were probed by INS, high-frequency and -field EPR (HFEPR), FIRMS, and frequency-domain FT terahertz EPR (FD-FT THz-EPR), giving magnetic excitation spectra and determining ZFS parameters (D, E) and g values. Ligand-field theory (LFT) was used to analyze earlier electronic absorption spectra and give calculated ZFS parameters matching those from the experiments. DFT calculations also gave spin densities in Co-X, showing that the larger Co(II) spin density in a molecule, the larger its ZFS magnitude. The current work reveals dynamics of magnetic and phonon excitations in SMMs. Studies of such couplings in the future would help to understand how spinphonon coupling may lead to magnetic relaxation and develop guidance to control such coupling.

To successfully establish an infection, Acinetobacter baumannii must overcome the iron starvation and oxidative stress imposed by the human host. Although previous studies have shown that ATCC 19606 T cells acquire iron via the acinetobactin-mediated siderophore system, little is known about intracellular iron metabolism and its relation to oxidative stress in this pathogen. Screening of an insertion library resulted in the isolation of the ATCC 19606 T derivative 1644, which was unable to grow in iron-chelated media. Rescue cloning and DNA sequencing showed that the insertion inactivated a gene coding for an NfuA Fe-S cluster protein ortholog, without any effect on the expression of the acinetobactin system. The nfuA mutant was also more sensitive to hydrogen peroxide and cumene hydroperoxide than the parental strain. The iron chelation- and oxidative-stress-deficient responses of this mutant were corrected when complemented with either the ATCC 19606 T parental allele or the Escherichia coli MG1655 nfuA ortholog. Furthermore, electron paramagnetic resonance (EPR) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses showed that the ATCC 19606 T NfuA ortholog has iron-binding properties compatible with the formation of [Fe-S] cluster protein. Ex vivo and in vivo assays using human epithelial cells and Galleria mellonella , respectively, showed that NfuA is critical for bacterial growth independent of their capacity to acquire iron or the presence of excess of free iron. Taken together, these observations indicate that the A. baumannii NfuA ortholog plays a role in intracellular iron utilization and protection from oxidative-stress responses that this pathogen could encounter during the infection of the human host.

The nitroxyl radical 1-methyl-2-azaadamantane N-oxyl (Me-AZADO) exhibits magnetic bistability arising from a radical/dimer interconversion. The transition from the rotationally disordered paramagnetic plastic crystal, Me-AZADO, to the ordered diamagnetic crystalline phase, (Me-AZADO)2, has been conclusively demonstrated by crystal structure determination from high-resolution powder diffraction data and by solid-state NMR spectroscopy. The phase change is characterized by a wide thermal hysteresis with high sensitivity to even small applied pressures. The molecular dynamics of the phase transition from the plastic crystal to the conventional crystalline phase has been tracked by solid-state (1H and 13C) NMR and EPR spectroscopies.

We report two low-spin diphosphametallocenates [K(2.2.2-crypt)][M(PC4Me4)2] (M = Cr, Fe) and propose structural features that allow spin-control in 3d metallocenates.

The molecular tetravalent oxidation state for praseodymium is observed in solution via oxidation of the anionic trivalent precursor [K][Pr3+(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] (1-Pr(NP*)) with AgI at -35 C. The Pr4+ complex is characterized...

The zero-field splitting parameters D and E in the iron(ii) complex [Fe(C3S5)2]2– are shown to be remarkably resistant to a twist of the inter-ligand dihedral angle (θd) from 90 to 70°.