Insights Into Metal−π Arene Interactions of the Highly Lewis Acidic Rh24+ Core with a Broad Set of π-Ligands: From Ethylene to Corannulene and C60-Fullerene

A computational study on a multimode spin conductance switching by coordination isomerization in organometallic single-molecule junctions

Single-molecule junctions provide the additional flexibility of tuning the on/off conductance states through molecular design. Here, we focus on a family of organometallic complexes with a conjugated curved buckybowl as the ligand. Using first-principles calculations, a multi-mode reversible spin switching based on the CpFe·corannulene complex is predicted by the temperature control of the CpFe+ coordination position in corannulene. The different spin conductance states for three coordinated modes are ascribed to the different electronic spin states of the organometallic complex due to crystal field effects. The predicted relative stabilities of isomers and the energy barriers of isomerization reactions can ensure that the conversion among the three isomers can occur quickly and, at a specific temperature, a dominant isomer has a higher proportion than the other two isomers. This provides a new framework for understanding transport in organometallic complexes with localized d states. This presents an exciting opportunity for exploiting junctions involving molecular spin switching.

Ion-π interaction in impacting the nonlinear optical properties of ion-buckybowl complexes

Ion-buckybowl complexes have received considerable attention in modern chemical research due to its fundamental and practical importance. Herein, we performed density functional theory (DFT) to calculate the geometical structure, binding interactions, dipole moments and the first hyperpolarizabilities (βtot) of ion-buckybowl complexes (ions are Cl(-) and Na(+), buckybowls are quadrannulene, corannulene and sumanene). It is found that the stabilities of ion-buckybowl compounds primarily originate from the interaction energy, which was proved by a new isomerization energy decomposition analysis approach. Plots of reduced density gradient mirror the ion-π weak interaction has been formed between the ions and buckybowls. Significantly, the buckybowl subunits cannot effectively impact the nonlinear optical (NLO), but the kind of ion has marked influence on the second-order NLO responses. The βtot values of Cl(-)-buckybowl complexes are all larger as compared to that of Na(+)-buckybowl complexes, which is attributed to the large charge-transfer (CT) from Cl(-) to buckybowl. Our present work will be beneficial for further theoretical and experimental studies on the NLO properties of ion-buckybowl compounds.

Functionalized corannulene carbocations: a structural overview

A detailed structural overview of a family of bowl-shaped polycyclic aromatic carbocations of the type [C20 H10 R](+) with different R functionalities tethered to the interior surface of corannulene (C20 H10 ) is provided. Changing the identity of the surface-bound groups through alkyl chains spanning from one to four carbon atoms and incorporating a different degree of halogenation has led to the fine tuning of the bowl structures and properties. The deformation of the corannulene core upon functionalization has been revealed based on X-ray crystallographic analysis and compared for the series of cations with R=CH3 , CH2 Cl, CHCl2 , CCl3 , CH2 CH3 , CH2 CH2 Cl, and CH2 CH2 Br. The resulting carbocations have been isolated with several metal-based counterions, varying in size and coordinating abilities ([AlCl4 ](-) , [AlBr4 ](-) , [(SnCl)(GaCl4 )2 ](-) , and [Al(OC(CF3 )3 )4 ](-) ). A variety of aggregation patterns in the solid state has been revealed based on different intermolecular interactions ranging from cation-anion to π-π stacking and to halogen⋅⋅⋅π interactions. For the [C20 H10 CH2 Cl](+) ion crystallized with several different counterions, the conformation of the R group attached to the central five-membered ring of corannulene moiety was found to depend on the solid-state environment defined by the identity of anions. Solution NMR and UV/Vis investigations have been used to complement the X-ray diffraction studies for this series of corannulene-based cations and to demonstrate their different association patterns with the solvent molecules.

SO₂--yet another two-faced ligand

Experimentally known adducts of SO2 with transition metal complexes have distinct geometries. In the present paper, we demonstrate by a bonding analysis that this is a direct consequence of sulfur dioxide acting as an acceptor in one set, square-planar complexes of d(8) and linear two-coordinated complexes of d(10) transition metals, and as a donor with other compounds, well-known paddle-wheel [Rh2(O2CCF3)4] and square-pyramidal [M(CO)5] (M = Cr, W) complexes. Bonding energy computations were augmented by the natural bond orbital (NBO) analysis and energy decomposition analysis (EDA). When the SO2 molecule acts as an acceptor, bonding in the bent coordination mode to the axial position of the d(8) or the d(10) metal center, the dominant contributor to the bonding is LAO(S) (Lewis Acidic Orbital, mainly composed of the px-orbital of the S atom) as an acceptor, while a dz(2) orbital centered on the metal is the corresponding donor. In contrast, the distinct collinear (or linear) coordination of the SO2 bound at the axial position of [Rh2(O2CCF3)4] and/or [M(CO)5] is associated with a dominant donation from a lone pair localized on the sulfur atom, σ*(Rh-Rh) and/or empty LAO(M) (mainly composed of the dz(2) orbital of the metal), respectively, acting as an acceptor orbital. The donor/acceptor capabilities of the SO2 molecule were also checked in adducts with organic Lewis acids (BH3, B(CF3)3) and Lewis bases (NH3, N(CH3)3, N-heterocyclic carbene).