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The synthesis of C∧C∧P pre-ligands based on a dicyclohexylphosphine-substituted biphenyl framework is reported. The pre-ligands form the respective non-palindromic pincer complexes of PtIIand PdIIvia double oxidative addition and subsequent comproportionation or C–H activation. The complexes of PtIIas well as PdIIemit similar green phosphorescence efficiently in the solid state, the former also in solution albeit with less intensity. The most fascinating photophysical feature, however, is a direct singlet–triplet (S0→ T1) excitation of this phosphorescence in the spectral window between the emission and the major singlet–singlet UV absorption. The S0→ T1excitation spectra show a rich vibronic pattern, which is especially pronounced for the solid samples at cryogenic temperatures. The molar extinction of the lowest-energy singlet–triplet absorption band of the homologous Pt and Pd complexes as well as that of the Pt complex with a different (NHC) ancillary ligand were determined in tetrahydrofuran solutions. Quantum efficiencies of triplet formation (by intersystem crossing) via the “standard” excitation pathway S0→ Sn→ T1were determined for the Pt complexes and found to be different in dependence of the ancillary ligand.

The gas-phase laser-induced photoluminescence of cationic mononuclear gadolinium and lutetium complexes involving two 9-oxophenalen-1-one ligands is reported. Performing measurements at a temperature of 83 K enables us to resolve vibronic transitions. Via comparison to Franck–Condon computations, the main vibrational contributions to the ligand-centered phosphorescence are determined to involve rocking, wagging, and stretching of the 9-oxophenalen-1-one–lanthanoid coordination in the low-energy range, intraligand bending, and stretching in the medium- to high-energy range, rocking of the carbonyl and methine groups, and C–H stretching beyond. Whereas Franck–Condon calculations based on density-functional harmonic frequency computations reproduce the main features of the vibrationally resolved emission spectra, the absolute transition energies as determined by density functional theory are off by several thousand wavenumbers. This discrepancy is found to remain at higher computational levels. The relative energy of the Gd(III) and Lu(III) emission bands is only reproduced at the coupled-cluster singles and doubles level and beyond.

The crown-ether coordination compounds ZnX2(18-crown-6), EuX2(18-crown-6) (X: Cl, Br, I), MnI2(18-crown-6), Mn3Cl6(18-crown-6)2, Mn3I6(18-crown-6)2, and Mn2I4(18-crown-6) are obtained by ionic-liquid-based synthesis. Whereas MX2(18-crown-6) (M: Zn, Eu) show conventional structural motives, Mn3Cl6(18-crown-6)2, Mn3I6(18-crown-6)2, and Mn2I4(18-crown-6) exhibit unusual single MnX4tetrahedra coordinated to the crown-ether complex. Surprisingly, some compounds show outstanding photoluminescence. Thus, rare Zn2+-based luminescence is observed and unexpectedly efficient for ZnI2(18-crown-6) with a quantum yield of 54%. Unprecedented quantum yields are also observed for Mn3I6(18-crown-6)2, EuBr2(18-crown-6), and EuI2(18-crown-6) with values of 98, 72, and 82%, respectively, which can be rationalized based on the specific structural features. Most remarkable, however, is Mn2I4(18-crown-6). Its specific structural features with finite sensitizer–activator couples result in an extremely strong emission with an outstanding quantum yield of 100%. Consistent with its structural features, moreover, anisotropic angle-dependent emission under polarized light and nonlinear optical (NLO) effects occur, including second-harmonic generation (SHG). The title compounds and their optical properties are characterized by single-crystal structure analysis, X-ray powder diffraction, chemical analysis, density functional theory (DFT) calculations, and advanced spectroscopic methods.

Orange, transparent crystals of [BMIm]2[Mn(CO)3(GeI3)3] (BMIm: 1-butyl-3-methylimidazolium) are obtained by reacting GeI4, [Mn(CO)6][AlCl4], and Ph3GeH in the ionic liquid [BMIm][NTf2]. [Mn(CO)6][AlCl4] and triphenylgermane turn out to be essential as reactive carbonyl precursors and for the reduction of GeI4. According to X-ray structure analysis based on single crystals, the title compound exhibits a novel {MnGe3} cluster unit with Mn–Ge single bonds and surprisingly short distances (236–241 pm). Although sensitive to oxygen/moisture, the carbonyl compound is stable up to a temperature of 150 °C. Mass spectrometry (MS) shows [Mn(CO)3(GeI3)2]−, [Mn(CO)3(GeI3)I]−, and [GeI3]−as decomposition fragments in the gas phase. In addition to crystal structure analysis and MS, the title compound is characterized by energy-dispersive X-ray spectroscopy (EDXS), thermogravimetry (TG), optical spectroscopy (UV–visible), infrared spectroscopy (FT-IR), and density functional theory (DFT) calculations.

We present a study of the structural effects of hydrogen adsorption on Ru14–investigated by a combination of trapped ion electron diffraction and density functional computations. While the bare Ru14–forms a double layer hexagonal structure, the adsorption of hydrogen initiates an evolution of the metal core toward an icosahedral structure. The structural rearrangement is driven by the difference in mean hydrogen adsorption energies, gradually stabilizing the icosahedral cluster core structure for higher hydrogen coverage. Detailed temperature dependent measurements reveal a crossover between the two structure motifs and indicate a structural phase equilibrium. Accompanying free energy computations confirm the chemical equilibrium and identify a hydrogen coverage instability region where the cluster hydrides decompose into the two core isomers with different hydrogen coverage.

The individual interaction energy terms in symmetry-adapted perturbation theory (SAPT) not only have different physical interpretations but also converge to their complete basis set (CBS) limit values at quite different rates. Dispersion energy is notoriously the slowest converging interaction energy contribution, and exchange dispersion energy, while smaller in absolute value, converges just as poorly in relative terms. To speed up the basis set convergence of the lowest-order SAPT dispersion and exchange dispersion energies, we borrow the techniques from explicitly correlated (F12) electronic structure theory and develop practical expressions for the closed-shell Edisp(20)-F12 and Eexch–disp(20)-F12 contributions. While the latter term has been derived and implemented for the first time, the former correction was recently proposed by Przybytek [J. Chem. Theory Comput.2018, 14, 5105−5117] using an Ansatz with a full optimization of the explicitly correlated amplitudes. In addition to reimplementing the fully optimized variant of Edisp(20)-F12, we propose three approximate Ansätze that substantially improve the scaling of the method and at the same time avoid the numerical instabilities of the unrestricted optimization. The performance of all four resulting flavors of Edisp(20)-F12 and Eexch–disp(20)-F12 is first tested on helium, neon, argon, water, and methane dimers, with orbital and auxiliary basis sets up to aug-cc-pV5Z and aug-cc-pV5Z-RI, respectively. The double- and triple-ζ basis set calculations are then extended to the entire A24 database of noncovalent interaction energies and compared with CBS estimates for Edisp(20)and Eexch–disp(20)computed using conventional SAPT with basis sets up to aug-cc-pV6Z with midbond functions. It is shown that the F12 treatment is highly successful in improving the basis set convergence of the SAPT terms, with the F12 calculations in an X-tuple ζ basis about as accurate as conventional calculations in bases with cardinal numbers (X+ 2) for Edisp(20)and either (X+ 1) or (X+ 2) for Eexch–disp(20). While the full amplitude optimization affords the highest accuracy for both corrections, the much simpler and numerically stable optimized diagonal Ansatz is a very close second. We have also tested the performance of the simple F12 correction based on the second-order Møller–Plesset perturbation theory, SAPT-F12(MP2) [Frey, J. A.; Chem. Rev.2016, 116, 5614−5641] and observed that it is also quite successful in speeding up the basis set convergence of conventional Edisp(20)+ Eexch–disp(20), albeit with some outliers.

The performance of the Bethe–Salpeter equation (BSE) approach for the first-principles computation of singlet and triplet excitation energies of small organic, closed-shell molecules has been assessed with respect to the quasiparticle energies used on input, obtained at various levels of GWtheory. In the corresponding GWcomputations, quasiparticle energies have been computed for allorbital levels by means of using full spectral functions. The assessment reveals that, for valence excited states, quasiparticle energies obtained at the levels of eigenvalue-only self-consistent (evGW) or quasiparticle self-consistent theory (qsGW) are required to obtain results of comparable accuracy as in time-dependent density-functional theory (TDDFT) using a hybrid functional such as PBE0. In contrast to TDDFT, however, the BSE approach performs well not only for valence excited states but also for excited states with Rydberg or charge-transfer character. To demonstrate the applicability of the BSE approach, computation times are reported for a set of aromatic hydrocarbons. Furthermore, examples of computations of ordinary photoabsorption and electronic circular dichroism spectra are presented for (C60)2and C84, respectively.

Theoretical description of phosphorescence lifetimes in the condensed phase requires a method that takes into account both spin–orbit coupling and solvent–solute interactions. To obtain such a method, we have coupled our recently developed two-component coupled-cluster method with singles and approximated doubles to a polarizable environment. With this new method, we investigate how different solvents effect the electronic phosphorescence energies and lifetimes of 4H-pyran-4-thione.

The strength of interactions between CO2and 23 building blocks of metal–organic frameworks are reported in this paper. This theoretical study is based on an incremental, explicitly correlated coupled-cluster scheme with interference effects. This scheme allows the accurate calculation of molecular complexes such as zinc acetate (32 non-hydrogen atoms) at the CCSD(T) level, close to the basis set limit. Higher CO2affinity for complexes with nitrogen-containing heterocycles is predicted from the calculated interaction energies. The good agreement between the interaction energies obtained from the CCSD(T) scheme and DFT-D3 is discussed.

Excited-state calculations in finite magnetic fields are presented in the framework of spin-noncollinear linear-response time-dependent density functional theory. To ensure gauge-origin invariance, London atomic orbitals are employed throughout. An efficient implementation into the Turbomolepackage, which also includes the resolution of the identity approximation, allows for the investigation of excited states of large molecular systems. The implementation is used to investigate the magnetic circular dichroism spectra of sizable organometallic molecules such as a zinc tetraazaporphyrin with two fused naphthalene units, which is a molecule with 57 atoms.

A molecular containerfor a single water molecule was obtained by chemical transformation of a [60]fullerene cage. A phosphate moiety acts as an effective “stopper” in the orifice (see picture).

Ein molekularer Behälterfür ein einzelnes Wassermolekül wurde durch chemische Umwandlung eines [60]Fulleren‐Käfigs erhalten. Eine Phosphatgruppe dient als ein effektiver Behälterverschluss.

Formulae are derived and implemented for the analytic calculation of first-order molecular properties at the level of explicitly-correlated second-order Møller-Plesset perturbation theory. In this theory, which is denoted as MP2-F12 theory, Slater-type geminals are used to expand the first-order wave function. A second-order perturbation theory correction for single excitations into a complementary auxliary basis set is also included. At the MP2-F12 level, it seems sufficient to restrict the analytic calculation of energy derivatives to the level of standard approximation A of MP2-F12 theory and to assume the extended Brillouin condition to hold. Smooth and rapid convergence towards the basis-set limit is observed for the dipole moments of a selection of small closed- and open-shell molecules when calculated at the RI-MP2-F12/2A*[T+V] + CABS singles level in augmented correlation-consistent polarized valence double-, triple-, and quadruple-zeta basis sets that have been optimized especially for use in MP2-F12 theory.

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The titanium mediated trimerization of pyrazine leads to the formation of a tris−chelate complex employing a 4a,4b,8a,8b,12a,12b-hexahydrodiyprazino[2,3-f:2′,3′-h]quinoxaline ligand (HATH6, 3). The driving force in the formation of the (Cp*2Ti)3(HATH6) complex 2is attributed to the formation of six Ti−N bonds. We show that density functional theory (DFT) fails to predict quantitatively correct results. Therefore, post-Hartree−Fock methods, such as second-order Møller−Plesset perturbation theory (MP2), in combination with coupled-cluster (CC) methods must be used. Both MP2 and CCSD(T) levels of theory provide endothermic trimerization energies, showing that the plain pyrazine trimer is not stable with respect to decomposition into its monomers. Complete basis set (CBS) results for the MP2 level of theory were computed using explicitly correlated wave functions. With these, we estimate the CCSD(T) CBS limit of the hypothetical trimerization energy to be +0.78 eV. Thus, the trimerization is facilitated by the formation of six Ti−N bonds with a calculated formation energy of −1.32 eV per bond.

Supersonic jet Raman spectroscopy reveals an increasing bathochromic shift of the OH stretching vibration in the most stable conformation of propanol with increasing extent of argon nanocoating. It falls short of the bulk matrix limit of 17 cm−1even at large nozzle distances. Quantum chemical harmonic frequency calculations up to the CCSD(T) level show that this shift cannot be accounted for by individual Ar atoms or even a first solvation layer but instead requires several layers of Ar atoms around the molecule to be explained. It is shown that the stability of Ar−propanol clusters correlates with the number of close O and C contacts to the Ar and that bathochromic shifts are largely caused by backbone solvation. Hydrogen-bonding OH solvation tends to slightly increase the OH stretching frequency but is very sensitive to the computational level.

Ge, whiz!A detailed study of the synthesis, structure, redox chemistry, and bonding properties of pentagerma1.1.1propellane 1, see picture examines fundamental aspects of the interactions between the bridgehead germanium atoms. DFT and CASSCF calculations unravel the biradicaloid characteristics of 1, and preliminary reactivity studies indicate that 1features some radicaltype behavior.

Fast radikal: Bei einer detaillierten Studie zur Synthese, Struktur, Redoxchemie und den Bindungseigenschaften von Pentagerma1.1.1propellan 1; siehe Bild wurden grundlegende Aspekte der Wechselwirkungen zwischen den BrückenkopfGermaniumatomen untersucht. DFT und CASSCFRechnungen erklären den Diradikaloidcharakter von 1, und erste Reaktivitätsstudien lassen darauf schließen, dass 1radikalähnliches Verhalten zeigt.

Initiated by ongoing experimental work in the field of subvalent aluminium compounds and by recent results on isoelectronic Mg2R2s1states species, detailed theoretical work was necessary to explain the unusual bonding situation in some Al2R4isomers R = PtBu2, of a dimeric Al4R′8R′ = OtBu as well as of subhalides Al2F4, Al2Cl4, Mg2Cl2and some of their oligomers. These results are presented in this contribution. Especially the different isomers of the fourmembered heterocyclic RAlR2AlR molecule needed careful theoretical investigation, since on the way from monomeric AlR2radicals to the most stable RAlR2AlR isomer with a butterfly shape, intermediates with different Al–Al interactions – exhibiting diradical as well as diradicaloid character – have to be considered. The presented results on the unusual bonding in these AlP2Al fourmembered heterocyclic systems are an important contribution to a better understanding of the bonding situations in many inorganic molecules containing, for example, B2P2, C2P2, Ge2N2, Sn2N2and Si4entities, which recently have drawn considerable interest. In analogy to the AlIIcompounds some isoelectronic MgIspecies have been investigated. Regarding the obtained results, special attention is drawn to MgCl oligomers, since we found unexpectedly high oligomerisation energies in our calculations. This high stabilisation is based on direct Mg–Mg bonding as well as on Mg–Cl–Mg bridging bonds. These mixed bonding motifs may also be present in the so far unknown solid MgCl. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

The interactions of molecular hydrogen with Li containing benzene molecules were studied by means of density functional theory (DFT), second-order Møller−Plesset perturbation theory (MP2), and coupled-cluster theory including all single and double excitations in conjunction with a perturbative estimate of triple excitations [CCSD(T)]. At the DFT and MP2 levels the resolution of the identity (RI) approximation was invoked in the framework of the approaches RI-DFT and RI-MP2. The benzene derivatives studied in this work are lithium benzide (C 6H 5Li), lithium phenoxide (C 6H 5OLi) and lithium benzoate (C 6H 5COOLi). By extrapolating the MP2 and CCSD(T) energies to the complete basis set limit, the interaction energy of dihydrogen with these benzene species is found to be 2.54, 2.66 and 2.57 kcal/mol respectively. In all cases, the H 2molecule takes a side-on position on the Li atom. The interactions are larger than typical van der Waals (vdW) forces and can be attributed to dipole···induced dipole electrostatic forces. Therefore, the organolithium structures studied can perhaps be used as building units for potential hydrogen storage materials.

Conjugate additions of nucleophiles (e.g. enolates, amines and malonate anions) to bis(p‐tolylsulfinyl)alkenes, alkylidene‐1,3‐dithiane‐1,3‐dioxides and alkylidene‐1,3‐dithiolane‐1,3‐dioxides have recently been published. Reasons for different selectivities and reaction rates will be discussed by consideration of steric and electronic effects. The preferred mode of attack can be explained by stereoelectronic effects (hyperconjugation) in the primarily carbanion, which is stabilized by n→S‐O‐σ* interaction with an antiperiplanar SO group. Calculation of the transition states [BP86/aug‐TZVP] for the addition of acetone enolate to the dithiane‐derived alkylidene bis(sulfoxide) revealed that 6.6–7.3 kJ mol−1more energy is needed for an attack leading to a less‐stabilized carbanion. Two axial SO groups in dithiolane‐derived alkylidene bis(sulfoxides) lead to a higher reactivity towards nucleophiles.

Equilibrium geometries and binding energies with respect to the interaction of a methanol molecule (MeOH) with single-walled carbon nanotubes (SWCNTs) of various diameter are calculated by means of density-functional theory including an empirical energy correction for dispersion (DFT-D). This theory is validated by comparing DFT-D results for the model systems benzene−MeOH and coronene−MeOH with corresponding results from high-level wave function-based theory. DFT-D potential energy surface (PES) scans along the intermolecular distance using different functionals are compared with spin-component scaled second-order Møller−Plesset perturbation theory (SCS-MP2) energies and reveal a consistent mutual agreement between the two approaches. Hydrogen-terminated tube sections are used to represent the armchair (4,4), (5,5), (6,6), (8,8), and (10,10) SWCNTs. Similar binding energies are found for the armchair (4,4) and the zigzag (7,0) tubes with similar diameter, but the methanol−SWCNT distance is strongly dependent on the tube type (armchair or zigzag). The interaction energy is found to be diameter-dependent ranging from −15.0 kJ mol-1for the smallest diameter tube to −20.0 kJ mol-1for graphene, which represents the limit of a tube with infinite diameter. Calculating the binding energies for differently curved coronene−MeOH models that could be used in a QM/MM approach shows that >90% of the methanol−tube interaction can be captured with this small model. Furthermore, the electronic properties of zigzag tube sections are examined. Because of the termination of the dangling bonds with hydrogen atoms, orbitals arise that are localized at the tube ends and that are not present in the infinitely long SWCNTs. Nevertheless, an approach is presented to extrapolate the band gaps of SWCNTs from gaps calculated within the cluster approach using tube sections of increasing length.

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