Au20 (t Bu3 P)8 : A Highly Symmetric Metalloid Gold Cluster in Oxidation State 0.

Metalloid gold clusters have unique properties with respect to size and structure and are key intermediates in studying transitions between molecular compounds and the bulk phase of the respective metal. In the following, the synthesis of the all-phosphine protected metalloid cluster Au20 (t Bu3 P)8 , solely built from gold atoms in the oxidation state of 0 is reported. Single-crystal X-ray analysis revealed a highly symmetric hollow cube-octahedral arrangement of the gold atoms, resembling gold bulk structure. Quantum-chemical calculations illustrated the cluster can be described as a 20-electron superatom. Optical properties of the compound have shown molecular-like behavior.

Experimental and Theoretical Study of the Ultrafast Dynamics of a Ni2 Dy2 -Compound in DMF After UV/Vis Photoexcitation.

Invited for this month's cover picture are the groups of Wolfgang Hübner (TU Kaiserslautern, Germany), Annie Powell (Karlsruhe Institut of Technology, Germany), and Andreas-Neil Unterreiner (Karlsruhe Institut of Technology, Germany). The cover picture shows the Dy2 Ni2 -molecular magnet being excited with a UV/Vis laser pulse, together with its time-resolved spectrum after the pulse. The comparison of the theoretical and the experimental spectra together with both the observed and the calculated relaxation times reveal, among others, three key points: the intermediate states participating in the laser-induced dynamics, the partial metal-to-oxygen charge-transfer excitations, and the order of magnitude of the coupling of the molecular magnet to the thermal bath of the environment. Read the full text of their Full Paper at 10.1002/open.202100153.

d/f-Polypnictides Derived by Non-Classical Ln2+ Compounds: Synthesis, Small Molecule Activation and Optical Properties.

Reduction chemistry induced by divalent lanthanides has been primarily focused on samarium so far. In light of the rich physical properties of the lanthanides, this limitation to one element is a drawback. Since molecular divalent compounds of almost all lanthanides have been available for some time, we used one known and two new non-classical reducing agents of the early lanthanides to establish a sophisticated reduction chemistry. As a result, six new d/f-polyphosphides or d/f-polyarsenides, [K(18-crown-6)] [Cp''2 Ln(E5 )FeCp*] (Ln=La, Ce, Nd; E=P, As) were obtained. Their reactivity was studied by activation of P4 , resulting in a selective expansion of the P5 rings. The obtained compounds [K(18-crown-6)] [Cp''2 Ln(P7 )FeCp*] (Ln=La, Nd) are the first examples of an activation of P4 by a f-element-polypnictide complex. Additionally, the first systematic femtosecond (fs)-spectroscopy investigations of d/f-polypnictides are presented to showcase the advantages of having access to a broader series of lanthanide compounds.

Understanding the Photoexcitation of Room Temperature Ionic Liquids.

Photoexcitation of (neat) room temperature ionic liquids (RTILs) leads to the observation of transient species that are reminiscent of the composition of the RTILs themselves. In this minireview, we summarize state-of-the-art in the understanding of the underlying elementary processes. By varying the anion or cation, one aim is to generally predict radiation-induced chemistry and physics of RTILs. One major task is to address the fate of excess electrons (and holes) after photoexcitation, which implies an overview of various formation mechanisms considering structural and dynamical aspects. Therefore, transient studies on time scales from femtoseconds to microseconds can greatly help to elucidate the most relevant steps after photoexcitation. Sometimes, radiation may eventually result in destruction of the RTILs making photostability another important issue to be discussed. Finally, characteristic heterogeneities can be associated with specific physicochemical properties. Influencing these properties by adding conventional solvents, like water, can open a wide field of application, which is briefly summarized.

Directed Electron Transfer in Flavin Peptides with Oligoproline-Type Helical Conformation as Models for Flavin-Functional Proteins.

To mimic the charge separation in functional proteins we studied flavin-modified peptides as models. They were synthesized as oligoprolines that typically form a polyproline type-II helix, because this secondary structure supports the electron transfer properties. We placed the flavin as photoexcitable chromophore and electron acceptor at the N-terminus. Tryptophans were placed as electron donors to direct the electron transfer over 0-3 intervening prolines. Spectroscopic studies revealed competitive photophysical pathways. The reference peptide without tryptophan shows dominant non-specific ET dynamics, leading to an ion pair formation, whereas peptides with tryptophans have weak non-specific ET and intensified directed electron transfer. By different excitation wavelengths, we can conclude that the corresponding ion pair state of flavin within the peptide environment has to be energetically located between the S1 and S4 states, whereas the directed electron transfer to tryptophan occurs directly from the S1 state. These photochemical results have fundamental significance for proteins with flavin as redoxactive cofactor.

Photoexcitation of Ge9- Clusters in THF: New Insights into the Ultrafast Relaxation Dynamics and the Influence of the Cation.

We present a comprehensive femtosecond (fs) transient absorption study of the [Ge9(Hyp)3]- (Hyp = Si(SiMe3)3) cluster solvated in tetrahydrofuran (THF) with special emphasis on intra- and intermolecular charge transfer mechanisms which can be tuned by exchange of the counterion and by dimerization of the cluster. The examination of the visible and the near infrared (NIR) spectral range reveals four different processes of cluster dynamics after UV (267/258 nm) photoexcitation related to charge transfer to solvent and localized excited states in the cluster. The resulting transient absorption is mainly observed in the NIR region. In the UV-Vis range transient absorption of the (neutral) cluster core with similar dynamics can be observed. By transferring concepts of: (i) charge transfer to the solvent known from solvated Na- in THF and (ii) charge transfer in bulk-like materials on metalloid cluster systems containing [Ge9(Hyp)3]- moieties, we can nicely interpret the experimental findings for the different compounds. The first process occurs on a fs timescale and is attributed to localization of the excited electron in the quasi-conduction band/excited state which competes with a charge transfer to the solvent. The latter leads to an excess electron initially located in the vicinity of the parent cluster within the same solvent shell. In a second step, it can recombine with the cluster core with time constants in the picosecond (ps) timescale. Some electrons can escape the influence of the cluster leading to a solvated electron or after interaction with a cation to a contact pair both with lifetimes exceeding our experimentally accessible time window of 1 nanosecond (ns). An additional time constant on a tens of ps timescale is pronounced in the UV-Vis range which can be attributed to the recombination rate of the excited state or quasi conduction band of Ge9-. In the dimer, the excess electron cannot escape the molecule due to strong trapping by the Zn cation that links the two cluster cores.

The influence of the FeCp(CO)2+ moiety on the dynamics of the metalloid [Ge9(Si(SiMe3)3)3]- cluster in thf: synthesis and characterization by time-resolved absorption spectroscopy.

A neutral tetrasubstituted Ge9 cluster with a covalently bound transition metal substituent was synthesized successfully via a salt metathesis reaction. Photoexcitation of [Ge9(Si(SiMe3)3)3FeCp(CO)2] induces excited state dynamics of the compound that was analysed by extended broadband fs absorption spectroscopy in the UV-Vis-NIR region. After UV or Vis excitation, an electron is detached from the [Ge9(Si(SiMe3)3)3]--entity and localizes within few hundred fs. Recombination of this cluster-electron-pair occurs in about 7-9 ps. Finally, a third component can be attributed to complete ground state recovery within roughly 150 ps. This is much shorter compared to a longer-lived component within Li[Ge9(Si(SiMe3)3)3], whose transient absorption exceeds the ns timescale after UV excitation. This observation emphasizes a strong influence of the Fe moiety.

Phenanthroline-A Versatile Ligand for Advanced Functional Polymeric Materials.

The controlled incorporation of phenanthroline moieties into polymers is introduced, demonstrating their application as metal-ion complexing ligands for the construction of advanced macromolecular structures. Specifically, two phenanthroline-containing monomers based on acrylate and styrene functionalities, were synthesized. Each monomer was readily copolymerized with either N,N-dimethylacrylamide or styrene via nitroxide-mediated polymerization, resulting in narrowly distributed polar or non-polar copolymers. To demonstrate the versatility of the established polymer systems, the polar polymer was employed for transition metal induced single-chain nanoparticle formation, verified by diffusion-ordered NMR and UV/Vis spectroscopy. Furthermore, the non-polar polymer allows facile incorporation of lanthanide ions, creating luminescent metallo-polymers, in-depth characterized by advanced photophysical experiments and 2D NMR measurements.