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(PPh3)2X2(
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Abstract Co‐X ; X=Cl, Br, I) reveal rarely observed spin‐phonon coupling as avoided crossings between magnetic andu ‐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 theS =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 ) andg 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 inCo‐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 inmore » -
Abstract The role of hydrogen atoms as surface ligands on metal nanoclusters is of profound importance but remains difficult to directly study. While hydrogen atoms often appear to be incorporated formally as hydrides, evidence suggests that they donate electrons to the cluster's delocalized superatomic orbitals and may consequently behave as acidic protons that play key roles in synthetic or catalytic mechanisms. Here we directly test this assertion for the prototypical Au9(PPh3)8H2+nanocluster, formed by addition of a hydride to the well‐characterized Au9(PPh3)83+. Using gas‐phase infrared spectroscopy, we were able to unambiguously isolate Au9(PPh3)8H2+and Au9(PPh3)8D2+, revealing an Au−H stretching mode at 1528 cm−1that shifts to 1038 cm−1upon deuteration. This shift is greater than the maximum expected for a typical harmonic potential, suggesting a potential governing cluster‐H bonding that has some square‐well character consistent with the hydrogen nucleus behaving as a metal atom in the cluster core. Complexing this cluster with very weak bases reveals a redshift of 37 cm−1in the Au−H vibration, consistent with those typically seen for moderately acidic groups in gas phase molecules and providing an estimate of the acidity of Au9(PPh3)8H2+, at least with regard to its surface reactivity.
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Abstract The role of hydrogen atoms as surface ligands on metal nanoclusters is of profound importance but remains difficult to directly study. While hydrogen atoms often appear to be incorporated formally as hydrides, evidence suggests that they donate electrons to the cluster's delocalized superatomic orbitals and may consequently behave as acidic protons that play key roles in synthetic or catalytic mechanisms. Here we directly test this assertion for the prototypical Au9(PPh3)8H2+nanocluster, formed by addition of a hydride to the well‐characterized Au9(PPh3)83+. Using gas‐phase infrared spectroscopy, we were able to unambiguously isolate Au9(PPh3)8H2+and Au9(PPh3)8D2+, revealing an Au−H stretching mode at 1528 cm−1that shifts to 1038 cm−1upon deuteration. This shift is greater than the maximum expected for a typical harmonic potential, suggesting a potential governing cluster‐H bonding that has some square‐well character consistent with the hydrogen nucleus behaving as a metal atom in the cluster core. Complexing this cluster with very weak bases reveals a redshift of 37 cm−1in the Au−H vibration, consistent with those typically seen for moderately acidic groups in gas phase molecules and providing an estimate of the acidity of Au9(PPh3)8H2+, at least with regard to its surface reactivity.
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Abstract Following the success of Auranofin as an anti‐arthritic drug, search for novel gold drugs has afforded a large number of [L−Au(PPh3)] complexes that exhibit notable salutary effects. Unlike Au(III)‐containing species, these gold complexes with {Au(PPh3)}+moiety are stable in biological media and readily exchange L with S‐ and Se‐containing enzymes or proteins. Such exchange leads to rapid reduction of microbial loads or induction of apoptotic cell death at malignant sites. In many cases the lipophilic {Au(PPh3)}+moiety delivers a desirable toxic L to the specific cellular target in addition to exhibiting its own beneficial activity. Further research and utilization of this synthon in drug design could lead to novel chemotherapeutics for treatment of drug‐resistant pathogens and cancers.
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Abstract Three multi‐shell metalloid gold clusters of the composition Au32(R3P)12Cl8(R=Et,nPr,nBu) were synthesized in a straightforward fashion by reducing R3PAuCl with NaBH4in ethanol. The Au32core comprises two shells, with the inner one constituting a tilted icosahedron and the outer one showing a distorted dodecahedral arrangement. The outer shell is completed by eight chloride atoms and twelve R3P groups. The inner icosahedron shows bond lengths typical for elemental gold while the distances of the gold atoms in the dodecahedral arrangement are in the region of aurophilic interactions. Quantum‐chemical calculations illustrate that the Jahn–Teller effect observed within the cluster core can be attributed to the electronic shell filling. The easily reproducible synthesis, good solubility, and high yields of these clusters render them perfect starting points for further research.
