Magnetostructural correlation in isolated trinuclear iron(iii) oxo acetate complexes

Can the Rate of a Catalytic Turnover Be Altered by Ligands in the Absence of Direct Binding Interactions?

Second sphere coordination effects ubiquitous in enzymatic catalysis occur through direct interactions, either covalent or non-covalent, with reaction intermediates and transition states. We present herein evidence of indirect second sphere coordination effects in which ligation of water/alkanols far removed from the primary coordination sphere of the active site nevertheless alter energetic landscapes within catalytic redox cycles in the absence of direct physicochemical interactions with surface species mediating catalytic turnovers. Density functional theory, in situ X-ray absorption and infrared spectroscopy, and a wide array of steady-state and transient CO oxidation rate data suggest that the presence of peripheral water renders oxidation half-cycles within two-electron redox cycles over μ3-oxo-bridged trimers in MIL-100(M) more kinetically demanding. Communication between ligated water and the active site appears to occur through the Fe-O-Fe backbone, as inferred from spin density variations on the central μ3-oxygen 'junction'. Evidence is provided for the generality of these second sphere effects in that they influence different types of redox half-cycles or metals, and can be amplified or attenuated through choice of coordinating ligand. Specifically in the case of MIL-100(M) materials, the Cr isostructure can be made to kinetically mimic the Fe variant by disproportionately hindering oxidation half-cycles relative to the reduction half-cycles. Kinetic and spectroscopic inferences presented here significantly expand both the conceptual definition of second sphere effects as well as the palette of synthetic levers available for tuning catalytic redox performance through chemical ligation.

Advancing Inorganic Coordination Chemistry by Spectroscopy of Isolated Molecules: Methods and Applications

A unique feature of the work carried out in the Collaborative Research Center 3MET continues to be its emphasis on innovative, advanced experimental methods which hyphenate mass-selection with further analytical tools such as laser spectroscopy for the study of isolated molecular ions. This allows to probe the intrinsic properties of the species of interest free of perturbing solvent or matrix effects. This review explains these methods and uses examples from past and ongoing 3MET studies of specific classes of multicenter metal complexes to illustrate how coordination chemistry can be advanced by applying them. As a corollary, we will show how the challenges involved in providing well-defined, for example monoisomeric, samples of the molecular ions have helped to further improve the methods themselves thus also making them applicable to many other areas of chemistry.

Application of continuous wave quantum cascade laser in combination with CIVP spectroscopy for investigation of large organic and organometallic ions

Rapidly developing mid-infrared quantum cascade laser (QCL) technology gives easy access to broadly tunable mid-IR laser radiation at a modest cost. Despite several applications of QCL in the industry, its usage for spectroscopic investigation of synthetically relevant organic compounds has been limited. Here, we report the application of an external cavity, continuous wave, mid-IR QCL to cryogenic ion vibrational predissociation spectroscopy to analyze a set of large organic molecules, organometallic complexes, and isotopically labeled compounds. The obtained spectra of test molecules are characterized by a high signal-to-noise ratio and low full width at half-maximum-values, allowing the assignment of two compounds with just a few wavenumber difference. Data generated by cw-QCL and spectra produced by another standard Nd:YAG difference-frequency generation system are compared and discussed.

Li4Ru2OCl10·10H2O: crystal structure, magnetic properties and bonding interactions in ruthenium-oxo complexes

The results of the structural determination, magnetic characterization, and theoretical calculations of a new ruthenium-oxo complex, Li₄[Ru₂OCl₁₀]·10H₂O, are presented. Single crystals were grown using solvent methods and the crystal structure was characterized by single crystal X-ray diffraction. Li₄[Ru₂OCl₁₀]·10H₂O crystallizes into a low-symmetry triclinic structure (P1) due to the much smaller Li⁺ cation compared to K⁺ cation in the tetragonal complex K₄[Ru₂OCl₁₀]·H₂O. The X-ray photoelectron spectra confirm only the single valent Ru⁴⁺ in Li₄[Ru₂OCl₁₀]·10H₂O even though two distinct Ru sites exist in the crystal structure. Magnetic measurements reveal the diamagnetic property of Li₄[Ru₂OCl₁₀]·10H₂O with unpaired electrons existing on Ru⁴⁺. Furthermore, the molecular orbital analysis matches well with the observed UV and magnetic measurements.

Accurate Magnetic Couplings in Chromium-Based Molecular Rings from Broken-Symmetry Calculations within Density Functional Theory

We present a comprehensive analysis of magnetic coupling in a group of three popular chromium-based molecular rings, the homometallic Cr₈ ring and the heterometallic Cr₇Ni and Cr₇Zn molecules. We show conclusively that the broken symmetry approach within density functional theory (DFT), based on suitable conventional or range-separated hybrid functionals, provides a quantitatively reliable tool to extract magnetic exchange coupling parameters in all rings considered, which opens a window for additional applications in molecular magnetism. We further show that a nonempirical model spin Hamiltonian, based on the parameters extracted from DFT, leads to excellent agreement with experimental susceptibility data and energy spectra. Moreover, based on an optimally tuned range-separated hybrid functional approach, we find that gas-phase gaps of the studied molecular rings are much larger than previously calculated and discuss the implications of the revised electronic structure to potential applications in molecular spintronics.

Comment on “Magnetostructural correlations in isolated trinuclear iron(iii) oxo acetate complexes” by J. Lang, J. M. Hewer, J. Meyer, J. Schuchmann, C. van Wüllen and G. Niedner-Schatteburg, Phys. Chem. Chem. Phys., 2018, , 16673

We present a diagram indicating the areas of allowed ground state total spin numbers, emphasizing the significance of the Lieb–Mattis theorem for the frustrated complexes studied.

Reply to the 'Comment on "Magnetostructural correlations in isolated trinuclear iron(iii) oxo acetate complexes"' by M. Antkowiak, G. Kamieniarz and W. Florek, Phys. Chem. Chem. Phys., 2018, 20, DOI: 10.1039/C8CP04691C

This reply acknowledges comments by Antkowiak et al. and it announces the outcome of new experiments which are in support of the initial findings by Lang et al.