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In this letter, we report the first infrared spectrum of C762-. This multiply charged anion has been studied in an electrodynamic ion trap held at room temperature using tunable infrared radiation from a free-electron laser. Resonant vibrational excitation is found to cause electron detachment and the resulting singly negatively charged as well as the remaining doubly charged parent ion are monitored as a function of IR wavelength in an experimental scheme that we term infrared multiphoton electron detachment spectroscopy. The obtained IR spectra are contrasted to computed vibrational spectra using density functional theory. The dianionic molecule retains its overall symmetry (i.e., D2 point group) with a 1A1 ground state with respect to the neutral fullerene. Spectral shifts of characteristic tangential modes relative to the neutral cage are shown to originate from the excess charge density. [ABSTRACT FROM AUTHOR]

Differential cross sections and time-of-flight spectra have been measured in a crossed molecular beam apparatus for inelastic scattering and charge transfer in collisions of 30 eV protons with ethylene. High resolution inelastic time-of-flight spectra reveal peaks corresponding to the fundamentals of at least two of the infrared active antisymmetric vibrational modes of ethylene. In the time-of-flight spectra of H atoms resulting from charge transfer energy loss, peaks corresponding to excitation of two electronic states of the ethylene molecular ion are resolved. The H-atom product angular distributions are consistent with a 2.0 eV potential well in the ground state potential energy surface of the charge transfer reaction. The observations for the antisymmetric vibrational modes are explained in terms of an ion-induced dipole mechanism. Excitation of the symmetric modes is attributed to a vibronic coupling mechanism. An appendix provides a detailed account of the vibronic distributions in idealized low energy, high symmetry collisions leading to stable C2H5+ complexes. [ABSTRACT FROM AUTHOR]

Size-selected hydroxide ion water tetramers and pentamers [OH[sup -] (H[sub 2]O)[sub 4,5]], produced by a supersonic expansion, have been investigated using vibrational predissociation spectroscopy in conjunction with ab initio calculations based on density functional theory (DFT). The observed spectra in the frequency range 2650-3850cm [sup -1] show some broad absorption bands attributed to the free and hydrogen bonded OH stretches of OH[sup -] (H[sub 2]O)[sub 4,5] at an estimated cluster temperature of 170 K. DFT calculations performed at the B3LYP/6-31+ G* level reveal five and eight possible low lying isomeric forms for OH[sup -] (H[sub 2]O)[sub 4] and OH (H[sub 2]O)[sub 5], respectively. The global minimum isomer of the tetramer is tri-solvated cyclic, which is energetically more stable than the tetra-solvated wheel-shaped form with an OH ion at its centre. Compact cage-like lowest energy structures are found for the pentamer, in which the water molecules can act either as a single-donor-single-acceptor, as a double-proton-donor, or as a double-donor-single-acceptor in both the first and the second solvation shell of the OH ion core. Interconversion among the isomers appears to be rapid as manifested in the observed spectra dominated by broad and congested absorptions. To understand the nature of spectral broadening and congestion, systemic comparisons of the results are made against those of the corresponding protonated cations, H[sup +](H[sub 2]O)[sub n+1] and the corresponding halide anions, X[sup -] (H[sub 2]O)[sub n], X = F, Cl, Br, and I. It is suggested that the spectral complexities observed for OH[sup -](H[sub 2]O)[sub 4,5] are predominantly a result of sampling configurations with a large distribution of O[sub solvent]-O[sub ion]-O[sub solvent] angles and O[sub solvent] · · · H-O[sub solvent] distances between water molecules in the first and/or second hydration shells, together with the existence of more than one isomer in the supersonic expanson and rapid isomeric interconversion among them. [ABSTRACT FROM AUTHOR]

In this letter, we report the first infrared spectrum of C762-. This multiply charged anion has been studied in an electrodynamic ion trap held at room temperature using tunable infrared radiation from a free-electron laser. Resonant vibrational excitation is found to cause electron detachment and the resulting singly negatively charged as well as the remaining doubly charged parent ion are monitored as a function of IR wavelength in an experimental scheme that we term infrared multiphoton electron detachment spectroscopy. The obtained IR spectra are contrasted to computed vibrational spectra using density functional theory. The dianionic molecule retains its overall symmetry (i.e., D2 point group) with a 1A1 ground state with respect to the neutral fullerene. Spectral shifts of characteristic tangential modes relative to the neutral cage are shown to originate from the excess charge density. [ABSTRACT FROM AUTHOR]

Dimedone and its derivates are used as selective probes for the nucleophilic detection of sulfenic acids in biological samples. Qualitative analyses suggested that dimedone also reacts with cyclic sulfenamides. Furthermore, under physiological conditions, dimedone must compete with the highly concentrated nucleophile glutathione. We therefore quantified the reaction kinetics for a cyclic sulfenamide model peptide and the sulfenic acids of glutathione and a model peroxiredoxin in the presence or absence of dimedone and glutathione. We show that the cyclic sulfenamide is stabilized at lower pH and that it reacts with dimedone. While reactions between dimedone and sulfenic acids or the cyclic sulfenamide have similar rate constants, glutathione kinetically outcompetes dimedone as a nucleophile by several orders of magnitude. Our comparative in vitro and intracellular analyses challenge the selectivity of dimedone. Consequently, the dimedone labeling of cysteinyl residues inside living cells points towards unidentified reaction pathways or unknown, kinetically competitive redox species., Competing Interests: Declaration of competing interest None., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

We investigate small tantalum clusters Tan+, n = 2-4, for their capability to cleave N2 adsorption spontaneously. We utilize infrared photon dissociation (IR-PD) spectroscopy of isolated and size selected clusters under cryogenic conditions within a buffer gas filled ion trap, and we augment our experiments by quantum chemical simulations (at DFT level). All Tan+ clusters, n = 2-4, seem to cleave N2 efficiently. We confirm and extend a previous study under ambient conditions on Ta2+ cluster [Geng et al., Proc. Natl. Acad. Sci. U. S. A. 115, 11680-11687 (2018)]. Our cryo studies and the concomitant DFT simulations of the tantalum trimer Ta3+ suggest cleavage of the first and activation of the second and third N2 molecule across surmountable barriers and along much-involved multidimensional reaction paths. We unravel the underlying reaction processes and the intermediates involved. The study of the N2 adsorbate complexes of Ta4+ presented here extends our earlier study and previously published spectra from (4,m), m = 1-5 [Fries et al., Phys. Chem. Chem. Phys. 23(19), 11345-11354 (2021)], up to m = 12. We confirm the priory published double activation and nitride formation, succeeded by single side-on N2 coordination. Significant red shifts of IR-PD bands from these side-on coordinated μ2-κN:κN,N N2 ligands correlate with the degree of tilting towards the second coordinating Ta center. All subsequently attaching N2 adsorbates onto Ta4+ coordinate in an end-on fashion, and we find clear evidence for co-existence of end-on coordination isomers. The study of stepwise N2 adsorption revealed adsorption limits m(max) of [Tan(N2)m]+ which increase with n, and kinetic fits revealed significant N2 desorption rates upon higher N2 loads. The enhanced absolute rate constants of the very first adsorbate steps kabs(n,0) of the small Ta3+ and Ta4+ clusters independently suggest dissociative N2 adsorption and likely N2 cleavage into Ta nitrides., (© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

We present an IR-PD study of tantalum cluster adsorbate complexes [Tan(N2)m]+, abbreviated (n,m), n = 5-8. We utilize infrared spectroscopy of isolated and size selected clusters as prepared and characterized by a cryogenic tandem ion trap setup, and we augment our experiments with quantum chemical simulations at the level of density functional theory. The cluster adsorbate complexes (n,m) reveal vibrational bands above 2000 cm-1, which indicate end-on coordinated μ1-N2 oscillators, and bands below 2000 cm-1, which indicate side-on μ2-κN:κN,N coordinated ones. We observe a general increase in spectral complexity and an inhomogeneous broadening, mainly towards the red, at certain points of N2 loading m, which originates from an increasingly higher amount of double and triple N2 coordination at Ta sites, eventually at all of them. Other than the small tantalum clusters Tan+, n = 2-4, the IR-PD spectra of the initial N2 adsorbate species (n,1), n = 5-8, provide strong evidence for a lack of spontaneous N2 cleavage. Spontaneous N2 cleavage by Tan+, n = 5-8, seems suppressed. Therefore, the ability of a small Ta cluster to cleave dinitrogen disappears with one more tantalum core atom. The study of stepwise N2 adsorption on size selected Tan+, n = 5-8 clusters revealed adsorption limits m(max) of [Tan(N2)m]+ that are independent of cluster size within this size range. Cryo-adsorption kinetics at 26 K allowed for kinetic fits to consecutive N2 adsorption steps, and the fits revealed significant N2 desorption rates upon higher N2 loads, and the cluster adsorbate complexes eventually reached equilibrium. Some enhanced N2 desorption rates point towards likely adsorbate shell reorganization, and there is also some evidence for the coexistence of isomeric cluster adsorbate complexes., (© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

Exploring novel and existing design principles to tune the photochemical and photophysical properties of transition-metal complexes is an important goal in contemporary research. Here, we highlight the influence of constitutional isomers of pyridyl-1,2,3-triazolylidene mesoionic carbene (MIC) ligands on the photophysical and photochemical properties of the corresponding tetracarbonyl group 6 metal complexes (M = Cr, Mo, W). All new complexes [M( C-C )] presented herein incorporate a C-C linked pyridyl-MIC ligand and were fully characterized by X-ray diffraction analysis, elemental analysis, and 1 H NMR and IR spectroscopy. Detailed photophysical investigations reveal a single emission in the VIS region, which extends into the NIR with lifetimes of up to 3.5 μs in the solid state at lower temperatures. The quantum yields were determined for all three complexes, and, in particular, the W 0 complex shows an unusually high quantum yield of 29% compared to the values of 0.02% obtained for the [M( C-N )] isomers investigated in earlier works. Beyond this, the investigated W 0 complex also exhibits an emission at 717 nm in a fluid solution. The combination of luminescence and FTIR-step scan spectroscopy with theoretical calculations reveals an emissive 3 MLCT state. Irradiation of the presented complexes leads to a clean cleavage of one axial CO ligand. A metastable 16 VE species with a vacant axial coordination site was detected in the solid state at low temperatures. In solution, the respective solvato complexes are formed. A dark reverse reaction is observed, as previously described for the [M( C-N )] analogues. The increased electron density induced by the C-C linked pyridyl-MIC ligand leads to an increased kinetic rate constant for the reformation of the starting species and is also reflected in the lower photodissociation quantum yields.

Photoactive complexes with earth-abundant metals have attracted increasing interest in the recent years fueled by the promise of sustainable photochemistry. However, sophisticated ligands with complicated syntheses are oftentimes required to enable photoactivity with nonprecious metals. Here, we combine a cheap metal with simple ligands to easily access a photoactive complex. Specifically, we synthesize the molybdenum(0) carbonyl complex Mo(CO) 3 (tpe) featuring the tripodal ligand 1,1,1-tris(pyrid-2-yl)ethane (tpe) in two steps with a high overall yield. The complex shows intense deep-red phosphorescence with excited state lifetimes of several hundred nanoseconds. Time-resolved infrared spectroscopy and laser flash photolysis reveal a triplet metal-to-ligand charge-transfer ( 3 MLCT) state as the lowest excited state. Temperature-dependent luminescence complemented by density functional theory (DFT) calculations suggest thermal deactivation of the 3 MLCT state via higher lying metal-centered states in analogy to the well-known photophysics of [Ru(bpy) 3 ] 2+ . Importantly, we found that the title compound is very photostable due to the lack of labilized Mo-CO bonds (as caused by trans -coordinated CO) in the facial configuration of the ligands. Finally, we show the versatility of the molybdenum(0) complex in two applications: (1) green-to-blue photon upconversion via a triplet-triplet annihilation mechanism and (2) photoredox catalysis for a green-light-driven dehalogenation reaction. Overall, our results establish tripodal carbonyl complexes as a promising design strategy to access stable photoactive complexes of nonprecious metals avoiding tedious multistep syntheses.

In this report, we present the dinuclear copper(II) dimethylglyoxime (H 2 dmg) complex [Cu 2 (H 2 dmg)(Hdmg)(dmg)] + (1), which, in contrast to its mononuclear analogue [Cu(Hdmg) 2 ] (2), is subject to a cooperativity-driven hydrolysis. The combined Lewis acidity of both copper centers increases the electrophilicity of the carbon atom in the bridging μ 2 -O-N=C-group of H 2 dmg and thus, facilitates the nucleophilic attack of H 2 O. This hydrolysis yields butane-2,3-dione monoxime (3) and NH 2 OH that, depending on the solvent, is then either oxidized or reduced. In ethanol, NH 2 OH is reduced to NH 4 + , yielding acetaldehyde as the oxidation product. In contrast, in CH 3 CN, NH 2 OH is oxidized by Cu II to form N 2 O and [Cu(CH 3 CN) 4 ] + . Herein are presented the combined synthetic, theoretical, spectroscopic and spectrometric methods that indicate and establish the reaction pathway of this solvent-dependent reaction., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

This work tackles the photochemistry of a series of mononuclear Cr 0 , Mo 0 and W 0 carbonyl complexes containing a bidentate mesoionic carbene ligand of the 1,2,3-triazol-5-ylidene type. FTIR spectroscopy, combined with density functional theory calculations, revealed a clean photo-induced reaction in organic solvents (acetonitrile, pyridine, valeronitrile) to give mainly one photoproduct with monosubstitution of a carbonyl ligand for a solvent molecule. The highest photodissociation quantum yields were reached for the Cr 0 complex under UV irradiation (266 nm). Based on previous investigations, the kinetics of the dark reverse reactions have now been determined, with reaction times of up to several hours in pyridine. Photochemical studies in the solid state (KBr matrix, frozen solution) also showed light-induced reactivity with stabilization of the metastable intermediate with a free coordination site at very low temperature. The identified reactive species emphasizes a mechanism without ligand-sphere reorganization., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

In this study, we present a slight but surprisingly successful structural modification of the previously reported heteroleptic Cu(I) photosensitizer Cubiipo ([(xantphos)Cu(biipo)]PF 6 ; biipo = 16 H -benzo-[4',5']-isoquinolino-[2',1':1,2]-imidazo-[4,5- f ]-[1,10]-phenanthrolin-16-one). As a key feature, biipo bears a naphthalimide unit at the back, which is directly fused to a phenanthroline moiety to extend the conjugated π-system. This ligand was now altered to include two additional methyl groups at the 2,9-positions at the phenanthroline scaffold. Comparing the novel Cudmbiipo complex to its predecessor, ultrafast transient absorption spectroscopy reveals the efficient suppression of a major deactivation pathway by stabilization of a transient triplet state. Furthermore, quantitative measurements of singlet oxygen evolution in solution confirmed that a larger fraction of the excited-state population is transferred to the photocatalytically active ligand-centered triplet 3 LC state with a much longer lifetime of ∼30 μs compared to Cubiipo (2.6 μs). In addition, Cudmbiipo was compared with the well-established reference complex Cubcp ([(xantphos)Cu(bathocuproine)]PF 6 ) in terms of its photophysical and photocatalytic properties by applying time-resolved femto- and nanosecond absorption, step-scan Fourier transform infrared (FTIR), and emission spectroscopies. Superior light-harvesting properties and a greatly enhanced excited-state lifetime with respect to Cubcp enable Cudmbiipo to be more active in exemplary photocatalytic applications, i.e ., in the formation of singlet oxygen and the isomerization of ( E )-stilbene.

Cr(ppy) 3 , a structural analog of the green phosphorescent Ir(ppy) 3 , emits even in solution at room temperature from a weakly distorted spin-flip state at 910 nm (Hppy = 2-phenylpyridine). The low energy arises from an enhanced covalence of the Cr-C bonds as compared to Cr-N bonds. Lower temperature reduces thermally activated decay increasing the emission intensity.

We report the N 2 cryo adsorption kinetics of selected gas phase mixed rhodium-iron clusters [Rh i Fe j ] + in the range of i = 3-8 and j = 3-8 in 26 K He buffer gas by the use of a cryo tandem RF-hexapole trap-Fourier transform ion cyclotron resonance mass spectrometer. From kinetic data and fits, we extract relative rate constants for each N 2 adsorption step and possible desorption steps. We find significant trends in adsorption behavior, which reveal adsorption limits, intermittent adsorption limits, and equilibrium reactions. For those steps, which are in equilibrium, we determine the Gibbs free energies. We conclude on likely ligand shell reorganization and some weakly bound N 2 ligands for clusters where multiple N 2 adsorbates are in equilibrium. The relative rate constants are transferred to absolute rate constants, which are slightly smaller than the collision rate constants calculated by the average dipole orientation (Langevin) theory. The calculated sticking probabilities increase, in general, with the size of the clusters and decrease with the level of N 2 adsorption, in particular, when reaching an adsorption/desorption equilibrium. We receive further evidence on cluster size dependent properties, such as cluster geometries and metal atom distributions within the clusters through the accompanying spectroscopic and computational study on the equiatomic i = j clusters [Klein et al., J. Chem. Phys. 156, 014302 (2022)].

The phenomenon of single molecule magnet (SMM) behavior of mixed valent Mn 12 coordination clusters of general formula [Mn III 8 Mn IV 4 O 12 (RCOO) 16 (H 2 O) 4 ] had been exemplified by bulk samples of the archetypal [Mn III 8 Mn IV 4 O 12 (CH 3 COO) 16 (H 2 O) 4 ] (4) molecule, and the molecular origin of the observed magnetic behavior has found support from extensive studies on the Mn 12 system within crystalline material or on molecules attached to a variety of surfaces. Here we report the magnetic signature of the isolated cationic species [Mn 12 O 12 (CH 3 COO) 15 (CH 3 CN)] + (1) by gas phase X-ray Magnetic Circular Dichroism (XMCD) spectroscopy, and we find it closely resembling that of the corresponding bulk samples. Furthermore, we report broken symmetry DFT calculations of spin densities and single ion tensors of the isolated, optimized complexes [Mn 12 O 12 (CH 3 COO) 15 (CH 3 CN)] + (1), [Mn 12 O 12 (CH 3 COO) 16 ] (2), [Mn 12 O 12 (CH 3 COO) 16 (H 2 O) 4 ] (3), and the complex in bulk geometry [Mn III 8 Mn IV 4 O 12 (CH 3 COO) 16 (H 2 O) 4 ] (5). The found magnetic fingerprints - experiment and theory alike - are of a remarkable robustness: The Mn IV 4 core bears almost no magnetic anisotropy while the surrounding Mn III 8 ring is highly anisotropic. These signatures are truly intrinsic properties of the Mn 12 core scaffold within all of these complexes and largely void of the environment. This likely holds irrespective of bulk packing effects., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

We investigated the N 2 adsorption behavior of bimetallic rhodium-iron cluster cations [Rh i Fe j (N 2 ) m ] + by means of InfraRed MultiplePhotoDissociation (IR-MPD) spectroscopy in comparison with density functional theory (DFT) modeling. This approach allows us to refine our kinetic results [Ehrhard et al., J. Chem. Phys. (in press)] to enhance our conclusions. We focus on a selection of cluster adsorbate complexes within the ranges of i = j = 3-8 and m = 1-10. For i = j = 3, 4, DFT suggests alloy structures in the case of i = j = 4 of high (D 2d ) symmetry: Rh-Fe bonds are preferred instead of Fe-Fe bonds or Rh-Rh bonds. N 2 adsorption and IR-MPD studies reveal strong evidence for preferential adsorption to Rh sites and mere secondary adsorption to Fe. In some cases, we observe adsorption isomers. With the help of modeling the cluster adsorbate complex [Rh 3 Fe 3 (N 2 ) 7 ] + , we find clear evidence that the position of IR bands allows for an element specific assignment of an adsorption site. We transfer these findings to the [Rh 4 Fe 4 (N 2 ) m ] + cluster adsorbate complex where the first four N 2 molecules are exclusively adsorbed to the Rh atoms. The spectra of the larger adsorbates reveal N 2 adsorption onto the Fe atoms. Thus, the spectroscopic findings are well interpreted for the smaller clusters in terms of computed structures, and both compare well to those of our accompanying kinetic study [Ehrhard et al., J. Chem. Phys. (in press)]. In contrast to our previous studies of bare rhodium clusters, the present investigations do not provide any indication for a spin quench in [Rh i Fe j (N 2 ) m ] + upon stepwise N 2 adsorption.

We present a study of stepwise cryogenic N 2 adsorption on size-selected Fe n + (n = 8-20) clusters within a hexapole collision cell held at T = 21-28 K. The stoichiometries of the observed adsorption limits and the kinetic fits of stepwise N 2 uptake reveal cluster size-dependent variations that characterize four structural regions. Exploratory density functional theory studies support tentative structural assignment in terms of icosahedral, hexagonal antiprismatic, and closely packed structural motifs. There are three particularly noteworthy cases, Fe 13 + with a peculiar metastable adsorption limit, Fe 17 + with unprecedented nitrogen phobia (inefficient N 2 adsorption), and Fe 18 + with an isomeric mixture that undergoes relaxation upon considerable N 2 uptake.