Endo- and exohedral complexes of superphane with cations

Quite recently it has been shown in a previous study that superphane, that is, [2.2.2.2.2.2](1,2,3,4,5,6)cyclophane, is a very convenient molecule in the study of endohedral complexes and especially in the study of the influence of the caged entity (i.e., guest) on the structure of the host molecule. This advantage results from the presence of two parallel benzene rings joined together by six quite flexible ethylene bridges (spacers). This article examines the energetic and structural properties of endo- and exohedral complexes of superphane with the following cations: H⁺ , Li⁺ , Na⁺ , K⁺ , Be²⁺ , Mg²⁺ , Ca²⁺ , B³⁺ , Al³⁺ , Ga³⁺ . The stability of endohedral complexes has been shown to be strongly dependent on the charge and radius of the caged cation. The inclusion of the cation inside the superphane molecule causes its 'swelling', which is manifested by an increase in the distance between the benzene rings and elongations of the ring and spacer C-C bonds. In the case of exohedral complexes, three forms are investigated: with the cation above the benzene ring, with the cation interacting with the superphane window in the equatorial position, and with the cation interacting with the center of the C-C spacer bond. The first of these forms has been shown to be preferred. The cation⋯acceptor distance depends on the cation radius. Among the cations investigated, H⁺ and Be²⁺ are particularly reactive and predisposed to induce significant structural changes in the superphane molecule, forming C-H bond or C-Be-C bridges, respectively.

Laser spectroscopic and computational insights into unexpected structural behaviours of sandwich complexes upon ionization

Transition-metal sandwich complexes play key roles in various fields such as fundamental and applied chemistry; many of their unique properties arise from their ability to form stable or reactive ions. The first mass-analyzed threshold ionization (MATI) spectra of mixed sandwich compounds, (Ch)(Cp)Cr and (Cot)(Cp)Ti (Ch = η⁷-C₇H₇, Cp = η⁵-C₅H₅, Cot = η⁸-C₈H₈), presented in this work provide an extremely accurate description of the electron detachment. The ionization energies of the neutrals and stabilization energies of the metal-ligand interactions upon ionization are derived from the MATI data with an accuracy of 0.0006 eV. In combination with DFT calculations, laser threshold ionization spectroscopy reveals surprisingly different structural variations accompanying the detachment of the non-bonding d_z² electron from the sandwich molecules. The geometry of (Ch)(Cp)Cr remains practically unchanged while the ionization of (Cot)(Cp)Ti causes a noticeable shortening of the inter-ring distance, similar to that resulting from the ionization of a typical antibonding orbital. Electron density analysis throws light on the nature of these amazing effects.

Substituent effects on the electronic structures of sandwich compounds: new understandings provided by DFT-assisted laser ionization spectroscopy of bisarene complexes

Recent advances on substituent effects in transition metal bisarene complexes studied with high-resolution threshold ionization spectroscopy are reviewed to demonstrate new aspects of the ligand influence on electronic structures of sandwich molecules. Unprecedented accuracy in the determination of ionization energies provided by the laser techniques makes it possible to reveal and describe quantitatively such fine phenomena as isotope effects, the mutual substituent influence or variations of substituent effects on replacing the central metal atom with its Group analogues. In combination with DFT calculations, laser ionization spectroscopy unveils mechanisms of the ligand influence on unique redox properties of sandwich complexes which are of key importance for their practical use.

Main-group metal cyclophane complexes with high coordination numbers

Density functional theory calculations using the PBE0-D3BJ hybrid functional have been employed to investigate the complexation of main-group metal-cations with [2.2.2]paracyclophane and deltaphane. Geometry optimization under symmetry constraints was performed to observe the mode of coordination that a metal-cation adopts when it resides inside the cyclophane cavity. Thermodynamic properties were investigated to note the trends of stability along a group of metals. To further investigate the bonding properties, Morokuma–Ziegler energy decomposition analysis, natural bond orbital analysis and Bader's analysis were employed. It was observed that most of the main-group metal complexes with cyclophanes prefer an η⁶η⁶η⁶ coordination mode where the metal-cation sits in the centre of the cyclophane cavity. There is an increased thermodynamic stability in [2.2.2]paracyclophane complexes compared to their deltaphane analogues while the reverse is true regarding the strength of coordination based on interaction energy.

Investigation of the complexation of main-group metal-cations with [2.2.2]paracyclophane and deltaphane.

Understanding the interplay between π–π and cation–π interactions in [janusene–Ag]+ host–guest systems: a computational approach

Guiding the development of new systems with increased cation–π interaction capability.

Rydberg state mediated multiphoton ionization of (η7-C7H7)(η5-C5H5)Cr: DFT-supported experimental insights into the molecular and electronic structures of excited sandwich complexes

The first REMPI/DFT study of a mixed sandwich complex reveals fine ligand effects on structural transformations accompanying electronic excitation.

Helicenes as Molecular Tweezers in the Formation of Cation-π Complexes. Bonding and Circular Dichroism Properties from Relativistic DFT Calculations

Helicene ligands possess a unique helicoidal π-conjugated framework providing high optical rotation values. This has stimulated a growing interest in helicene derivatives as building blocks, which has triggered the development of simple strategies to tune their properties. In this context, we evaluated the formation of cation-π complexes derived from [6]- and [7]helicene, involving Sn²⁺ , Cd²⁺ , and In⁺ in addition of Ag⁺ , which appears as a plausible modification of such helicoidal structure. The nature of the cation-π interaction in the studied helicene complexes exhibits a covalent character, accounting for ligand π-donation to 5 s and 5p empty orbitals of the involved cations. Furthermore, the evaluation of their optical activity exhibits notorious modification patterns in the circular dichroism spectrum, suggesting that the modifications of the optical activity are dependent on the nature of the cation and its related charge state. Thus, the plausible formation of new cation-π complexes derived from helicene ligands, as discussed here, may lead to the characterization of novel species expanding the chemistry of helicene metal complexes to even to larger helicene units. We believe that the present study may open new avenues in the formation of cation-π helicene complexes.

TD DFT insights into unusual properties of excited sandwich complexes: structural transformations and vibronic interactions in Rydberg-state bis(η6-benzene)chromium

TD DFT calculations reveal specific features of the Jahn–Teller effect in the lowest Rydberg p state of a prototypical sandwich molecule.

Synthesis of heteroatomic bridged paracyclophanes

Heteroatomic bridged paracyclophanes were obtained by two independent synthetic approaches. The required precursors consist of para R₂SiCl (R = Me, iPr) substituted aromatic rings (2 and 4). They were subsequently functionalised by using NH₃, [LiPH₂(dme)] or LiAl(PH₂)₄. In the case of the Me-substituted species 2, the reaction with NH₃ directly yielded the Si₂N bridged paracyclophane 5. The Si₂P incorporated derivative 10 was obtained by lithiation of p-C₆H₄(SiiPr₂PH₂)₂ (9) and subsequent salt metathesis with the chlorosilane 4. The second approach involves the use of GaEt₃ in the formation of four membered (GaPn)₂ cycles (Pn = N, P). p-[C₆H₄{SiiPr₂N(H)GaEt₂}₂]₂ (11) and p-[C₆H₄{SiiPr₂P(H)GaEt₂}₂]₂ (12) represent the first examples of stable (GaPn)₂cis isomers as the trans species did not appear in solution. Although 11 and 12 show a similar coordination pattern, they differ in the orientation of the aromatic systems: in the solid structure, 11 adopts a - for paracyclophanes so far unique - T-shape conformation of the phenyl rings, while 12 shows the predominant coplanar orientation. All cyclophanes were characterized by X-ray diffraction, elemental analysis, NMR and IR spectroscopy.

Interlocked benzenes in triangular π-architectures: anchoring groups dictate ion binding and transmission

Graphynes and graphenylenes – potential materials for lithium ion batteries.

How the electron-deficient cavity of heterocalixarenes recognizes anions: insights from computation

The nature of bridging heteroatoms in a heterocalixarene structure has a crucial role in anion recognition.

in/out Isomerism of cyclophanes: a theoretical account of 2,6,15-trithia-[34,10][7]metacyclophane and [34,10][7]metacyclophane as well as their halogen substituted analogues

What are the effects responsible for cyclophane isomer stability?

A silver coordination cage assembled from [Ag2(bis(isoxazolyl))3]: DFT approach to the binding forces within the host–guest interactions

The storage and detection of different types of molecules using porous materials such as metal–organic frameworks (MOFs) have currently become an area of interest in chemistry.

Influence of Ag(+) on the Magnetic Response of [2.2.2]Paracyclophane: NMR Properties of a Prototypical Organic Host for Cation Binding Based on DFT Calculations

The complexation of metal cations into a host-guest situation is particularly well exemplified by [2.2.2]paracyclophane and Ag(I), which leads to a strong cation-π interaction with a specific face of the host molecule. Through this study we sought a deeper understanding of the effects the metal center has on the NMR spectroscopic properties of the prototypical organic host, generating theoretical reasons for the observed experimental results with an aim to determine the role of the cation-π interaction in a host-guest scenario. From an analysis of certain components of the induced magnetic field and the (13)C NMR shielding tensor under its own principal axis system (PAS), the local and overall magnetic behavior can be clearly described. Interestingly, the magnetic response of such a complex exhibits a large axis-dependent behavior, which leads to an overall shielding effect for the coordinating carbon atoms and a deshielding effect for the respective uncoordinated counterparts, evidence that complements previous experimental results. This proposed approach can be useful to gain further insight into the local and overall variation of NMR shifts for host-guest pairs involving both inorganic and organic hosts.

Role of the cation formal charge in cation–π interaction. A survey involving the [2.2.2]paracyclophane host from relativistic DFT calculations

Of charge and cations. Isoelectronic cation–π complexes unravel the nature of variation of the interaction.