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

Triggering near‐infrared luminescence of vanadyl phthalocyanine by charging

Probing electrofluorochromism (EFC) at the molecular level remains challenging. Here we study the strongly charge state‐dependent photoluminescence of vanadyl phthalocyanine. We report vibrationally resolved absorption and laser‐induced fluorescence (LIF) spectra of samples comprising both the mass‐selected neutral molecule (VOPc⋅, a stable radical) and its cation produced upon electron ionization (EI) isolated in 5 K neon matrices. Ionization of the essentially non‐emissive VOPc⋅ forms a high‐spin diradical cation (VOPc(+..)) which shows profound photoluminescence (PL) in the NIR range. This unique phenomenon is potentially of interest for NIR‐emitting electro‐optic devices

Bi- and trinuclear coinage metal complexes of a PNNP ligand featuring metallophilic interactions and an unusual charge separation

A selective synthesis of bi- and trinuclear complexes featuring a tetradentate monoanionic PNNP ligand is presented. The binuclear coinage metal complexes show a typical fourfold coordination for Cu and Ag, which changes to a bifold coordination for Au. The latter is accompanied by an unusual charge separation. Optical properties are investigated using photoluminescence spectroscopy and complemented by time-dependent density-functional-theory calculations. All compounds demonstrate clearly distinguished features dependent on the metals chosen and differences in the complex scaffold

Ditopic Hexadentate Ligands with a Central Dihydrobenzo-diimidazole Unit Forming a [2x2] Zn4_{4} Grid Complex

Ditopic ligands are appropriate candidates for homo‐ and hetero‐metallic supramolecular complexes. Two ditopic hexadentate ligands, which are highly interconvertible, are separated from a single ligand L by blocking tautomerism. They form remarkable divergent tetra‐nuclear grid complexes with Zinc(II) showing luminescence properties. A family of ditopic hexadentate ligands based on the parent compound 2,6‐bis(6‐(pyrazol‐1‐yl)pyridin‐2‐yl)‐1,5‐dihydrobenzo[1,2‐d:4,5‐d’]diimidazole (L) was developed and synthesized by using a straightforward condensation reaction, which forms the interlinking central benzo[1,2‐d:4,5‐d’]diimidazole bridge in the ligand backbone. The two secondary amine groups of the benzodiimidazole unit tautomerize and allow the formation of two tauto‐conformers, which upon treatment with metal salts forms different isomeric coordination complexes. Here we report six new derivatives (1–6) that can tautomerize (varying the pyrazolylpyridine part) and 14 derivatives (7–13) with different alkyl and benzyl substitution on secondary amino groups (of L) that prevent the tautomerization. This way, it is possible to study the properties of isomeric coordination complexes and their intrinsic cooperativity by the example of [2x2] grid complexes in the future. A [2x2] Zn$_{4}$ complex of the ligand L was synthesized and structurally characterized

A highly stable, Au/Ru heterobimetallic photoredox catalyst with a [2.2]paracyclophane backbone

We report the synthesis and catalytic application of a highly stable distance-defined Au/Ru heterobimetallic complex. [2.2]Paracyclophane serves as a backbone, holding the two metal centers in a spatial orientation and metal-metal fixed distance. The Au/Ru heterobimetallic complex is highly stable, easily accessible and exhibits promising catalytic activity in a visible-light mediated dual Au/Ru Meyer-Schuster rearrangement.Peer reviewe

Influence of Dispersion Interactions on the Thermal Desorption of Nonplanar Polycyclic Aromatic Hydrocarbons on HOPG

A combination of low energy ion beam deposition and mass resolved thermal desorption spectroscopy is applied to analyze the binding behavior of two nonplanar polycyclic aromatic hydrocarbons (PAHs) to highly oriented pyrolytic graphite (HOPG) surfaces—also concerning their lateral dispersion interactions. In particular, the fullerene precursor C60H30 (FPC) and rubrene C42H28 are studied. Due to their smaller contact areas, both molecules exhibit significantly weaker binding energies to the HOPG surface compared to planar PAHs of similar size: C60H30 is bound to the surface by 3.04 eV, which is 0.6 eV lower than for a fully planar homologue. For rubrene, an isolated molecule–substrate binding energy of 1.59 eV is found, which is about 1 eV less than that of the corresponding planar homologue hexabenzocoronene C42H18. In contrast to FPC, rubrene shows a significant (intermolecular) lateral dispersion contribution to the binding energy as the submonolayer coverage increases