Ln-Pt electron polarization effects on the magnetic relaxation of heterometallic Ho- and Er-Pt complexes

O-versus S-Metal Coordination of the Thiocarboxylate Group: An NMR Study of the Two Tautomeric Forms of the Ga(III)-Photoxenobactin E Complex

Photoxenobactin E (1) is a natural product with an unusual thiocarboxylic acid terminus recently isolated from an entomopathogenic bacterium. The biosynthetic gene cluster associated with photoxenobactin E, and other reported derivatives, is very similar to that of piscibactin, the siderophore responsible for the iron uptake among bacteria of the Vibrionaceae family, including potential human pathogens. Here, the reisolation of 1 from the fish pathogen Vibrio anguillarum RV22 cultured under iron deprivation, its ability to chelate Ga(III), and the full NMR spectroscopic characterization of the Ga(III)-photoxenobactin E complex are presented. Our results show that Ga(III)-photoxenobactin E in solution exists in a thiol-thione tautomeric equilibrium, where Ga(III) is coordinated through the sulfur (thiol form) or oxygen (thione form) atoms of the thiocarboxylate group. This report represents the first NMR study of the chemical exchange between the thiol and thione forms associated with thiocarboxylate-Ga(III) coordination, including the kinetics of the interconversion process associated with this tautomeric exchange. These findings show significant implications for ligand design as they illustrate the potential of the thiocarboxylate group as a versatile donor for hard metal ions such as Ga(III).

Experimental assignment of long-range magnetic communication through Pd & Pt metallophilic contacts

Record-breaking magnetic exchange interactions have previously been reported for 3d-metal dimers of the form [M(Pt(SAc)₄)(pyNO₂)]₂ (M = Ni or Co) that are linked in the solid state via metallophilic Pt⋯Pt bridges. This contrasts the terminally capped monomers [M(Pt(SAc)₄)(py)₂], for which neither metallophilic bridges nor magnetic exchange interactions are found. Computational modeling has shown that the magnetic exchange interaction is facilitated by the pseudo-closed shell d⁸⋯d⁸ metallophilic interaction between the filled Pt²⁺ 5d _{z ²} orbitals. We present here inelastic neutron scattering experiments on these complexes, wherein the dimers present an oscillatory momentum-transfer-dependence of the magnetic transitions. This allows for the unequivocal experimental assignment of the distance between the coupled ions, which matches exactly the coupling pathway via the metallophilic bridges. Furthermore, we have synthesized and magnetically characterized the isostructural palladium-analogues. The magnetic coupling across the Pd⋯Pd bridge is found through SQUID-magnetometry and FD-FT THz-EPR spectroscopy to be much weaker than via the Pt⋯Pt bridge. The weaker coupling is traced to the larger radial extent of the 5d _{z ²} orbitals compared to that of the 4d _{z ²} orbitals. The existence of a palladium metallophilic interaction is evaluated computationally from potential surface cuts along the metal stretching direction. Similar behavior is found for the Pd⋯Pd and Pt⋯Pt-systems with clear minima along this coordinate and provide estimates for the force constant for this distortion. The estimated M⋯M stretching frequencies are found to match experimental observed, polarized bands in single-crystal Raman spectra close to 45 cm^-1. This substantiates the existence of energetically relevant Pd⋯Pd metallophilic interactions. The unique properties of both Pt²⁺ and Pd²⁺ constitutes an orthogonal reactivity, which can be utilized for steering both the direction and strength of magnetic interactions.

Unequal sensitivities of energy levels in a high-symmetry Ho3+ complex towards lattice distortions

High-resolution inelastic neutron scattering has been used to study low-energy magnetic transitions in a Ho³⁺ complex. This complex crystallises in the high-symmetry space group P4/m and has near-perfect D_4d symmetry, which has allowed for the determination of all relevant spin-Hamiltonian parameters. Static and dynamic inhomogeneity in the crystal lattice manifests as a temperature-dependent broadening of the observed magnetic excitations. By implementing distributions in the spin-Hamiltonian parameters, it is possible to reproduce with great accuracy the observed magnetic transition spectrum. This reveals the range to which extraneous perturbations of the crystal field affect low-energy electronic states, such as those involved in quantum tunnelling of magnetisation, in atomic clock transitions, or in spintronics.

Ionic-caged heterometallic bismuth-platinum complex exhibiting electrocatalytic CO2 reduction

An air-stable heterometallic Bi-Pt complex with the formula [BiPt(SAc)5]n (1; SAc = thioacetate) was synthesized. The crystal structure, natural bond orbital (NBO) and local orbital locator (LOL) analyses, localized orbital bonding analysis (LOBA), and X-ray absorption fine structure (XAFS) measurements were used to confirm the existence of Bi-Pt bonding and an ionic cage of O atoms surrounding the Bi ion. From the cyclic voltammetry (CV) and controlled potential electrolysis (CPE) experiments, 1 in tetrahydrofuran reduced CO2 to CO, with a faradaic efficiency (FE) of 92% and a turnover frequency (TOF) of 8 s-1 after 30 min of CPE at -0.79 V vs. NHE. The proposed mechanism includes an energetically favored pathway via the ionic cage, which is supported by the results of DFT calculations and reflectance infrared spectroelectrochemistry data.

Importance of Axial Symmetry in Elucidating Lanthanide-Transition Metal Interactions

In this paper, we experimentally study and model the electron donating character of an axial diamagnetic Pd²⁺ ion in four metalloligated lanthanide complexes of formula [PPh₄][Ln{Pd(SAc)₄}₂] (SAc^- = thioacetate, Ln = Tb, Dy, Ho, and Er). A global model encompassing inelastic neutron scattering, torque magnetometry, and dc magnetometry allows to precisely determine the energy level structure of the complexes. Solid state nuclear magnetic resonance reveals a less donating character of Pd²⁺ compared to the previously reported isostructural Pt²⁺-based complexes. Consequently, all complexes invariably show a lower crystal field strength compared to their Pt²⁺-analogues. The dynamic properties show an enhanced single molecule magnet behavior due to the suppression of quantum tunneling, in agreement with our model.

Contribution of 155Gd Mössbauer data to the study of the magnetic interaction in heterodinuclear 3d–Gd (3d = Cu, Ni) coordination complexes

The observed ¹⁵⁵Gd Mössbauer isomer shifts of 3d–Gd complexes give an experimental proof for the participation of 5d Gd orbitals to the magnetic interaction in these 3d–Gd complexes.