Invarioms are aspherical atomic scattering factors that enable structure refinement of more accurate and more precise geometries than refinements with the conventional independent atom model (IAM). The use of single-crystal X-ray diffraction data of a resolution better than sin / = 0.6 Å À1 (or d = 0.83 Å ) is recommended. The invariom scatteringfactor database contains transferable pseudoatom parameters of the Hansen-Coppens multipole model and associated local atomic coordinate systems. Parameters were derived from geometry optimizations of suitable model compounds, whose IUPAC names are also contained in the database. Correct scattering-factor assignment and orientation reproduces molecular electron density to a good approximation. Molecular properties can hence be derived directly from the electron-density model. Coverage of chemical environments in the invariom database has been extended from the original amino acids, proteins and nucleic acid structures to many other environments encountered in organic chemistry. With over 2750 entries it now covers a wide sample of general organic chemistry involving the elements H, C, N and O, and to a lesser extent F, Si, S, P and Cl. With respect to the earlier version of the database, the main modification concerns scattering-factor notation. Modifications improve ease of use and success rates of automatic geometry-based scatteringfactor assignment, especially in condensed hetero-aromatic ring systems, making the approach well suited to replace the IAM for structures of organic molecules.

For the first time, the potential of noble‐metal‐free iron‐based photosensitizers for photocatalytic water reduction by using homo‐ and heteroleptic carbene complexes was proven. The development of a facile synthesis route for such carbene complexes was delineated. The complexes were investigated by UV/Vis and fluorescence spectroscopy, DFT calculations, cyclic voltammetry, and X‐ray absorption spectroscopy. Their catalytic performance was compared to that of established noble‐metal‐containing photosensitizers such as [Ir(ppy)2(bpy)][PF6] (Hppy = 2‐phenylpyridine, bpy = 2,2′‐bipyridine).

Dispersion interactions are omnipresent in intermolecular interactions, but their respective contributions are difficult to predict. Aromatic ethers offer competing docking sites for alcohols: the ether oxygen as a well known hydrogen bond acceptor, but also the aromatic π system. The interaction with two aromatic moieties in diphenyl ether can tip the balance towards π binding. We use a multi-spectroscopic approach to study the molecular recognition, the structure and internal dynamics of the diphenyl ether-methanol complex, employing infrared, infrared-ultraviolet and microwave spectroscopy. We find that the conformer with the hydroxy group of the alcohol binding to one aromatic π cloud and being coordinated by an aromatic C-H bond of the other phenyl group is preferred. Depending on the expansion conditions in the supersonic jet, we observe a second conformer, which exhibits a hydrogen bond to the ether oxygen and is higher in energy.

a Aromatic ethers such as diphenyl ether (DPE) represent molecules with different docking sites for alcohols leading to competing OH-O and OH-p interactions. In a multi-spectroscopic approach in combination with quantum chemical calculations the complex of DPE with tert-butyl alcohol (t-BuOH) is investigated in the electronic ground state (S 0 ) and the electronically excited state (S 1 ). FTIR, microwave as well as mass-and isomer-selective IR/R2PI spectra are recorded, revealing co-existing OH-O and OH-p isomers in the S 0 state. Surprisingly, they are predicted to be of almost equal stability in contrast to the previously investigated DPE-MeOH complex, where the OH-p structure is preferred by both theory and experiment. The tert-butyl group in t-BuOH allows for a simultaneous optimization of hydrogen-bonding and dispersion interactions, which provides a sensitive meeting point between theory and experiment. In the electronically excited state of DPE-t-BuOH, vibrational spectra could be recorded separately for both isomers using UV/IR/UV spectroscopy. In the S 1 state the same structural binding motifs are obtained as in the S 0 state with the OH-O bond being weakened for the OH-O arrangement and the OH-p interaction being strengthened in the case of the OH-p isomer compared to the S 0 state.

Invarioms are aspherical atomic scattering factors that enable structure refinement of more accurate and more precise geometries than refinements with the conventional independent atom model (IAM). The use of single-crystal X-ray diffraction data of a resolution better than sin / = 0.6 Å À1 (or d = 0.83 Å ) is recommended. The invariom scatteringfactor database contains transferable pseudoatom parameters of the Hansen-Coppens multipole model and associated local atomic coordinate systems. Parameters were derived from geometry optimizations of suitable model compounds, whose IUPAC names are also contained in the database. Correct scattering-factor assignment and orientation reproduces molecular electron density to a good approximation. Molecular properties can hence be derived directly from the electron-density model. Coverage of chemical environments in the invariom database has been extended from the original amino acids, proteins and nucleic acid structures to many other environments encountered in organic chemistry. With over 2750 entries it now covers a wide sample of general organic chemistry involving the elements H, C, N and O, and to a lesser extent F, Si, S, P and Cl. With respect to the earlier version of the database, the main modification concerns scattering-factor notation. Modifications improve ease of use and success rates of automatic geometry-based scatteringfactor assignment, especially in condensed hetero-aromatic ring systems, making the approach well suited to replace the IAM for structures of organic molecules.

No abstract

Dispersion interactions can play an important role in understanding unusual binding behaviors. This is illustrated by a systematic study of the structural preferences of diphenyl ether (DPE)-alcohol aggregates, for which OH⋅⋅⋅O-bound or OH⋅⋅⋅π-bound isomers can be formed. The investigation was performed through a multi-spectroscopic approach including IR/UV and microwave methods, combined with a detailed theoretical analysis. The resulting solvent-size-dependent trend for the structural preference turns out to be counter-intuitive: the hydrogen-bonded OH⋅⋅⋅O structures become more stable for larger alcohols, which are expected to be stronger dispersion energy donors and thus should prefer an OH⋅⋅⋅π arrangement. Dispersion interactions in combination with the twisting of the ether upon solvent aggregation are key for understanding this preference.

Diphenyl ether offers competing docking sites for methanol: the ether oxygen acts as a common hydrogen-bond acceptor and the π system of each phenyl ring allows for OH-π interactions driven by electrostatic, induction, and dispersion forces. Based on investigations in the electronic ground state (S ), we present a detailed study of the electronically excited state (S ) and the ionic ground state (D ), in which an impact on the structural preference is expected compared with the S state. Dispersion forces in the electronically excited state were analyzed by comparing the computed binding energies at the coupled-cluster-singles (CCS) and approximate coupled-cluster-singles-doubles levels of theory (CC2 approximation). By applying UV/IR/UV spectroscopy, we found a more strongly bound OH-π structure in the S state compared with the S state, in agreement with spin-component-scaled CC2 calculations. A structural rearrangement into a non-hydrogen-bonded structure takes places upon ionization in the D state, which was revealed by using IR photodissociation spectroscopy and confirmed by theory.