Search for: All records

Several new bimetallic and trimetallic complexes containing the [Y(COT)2]- unit in different coordination environments are synthesized and fully characterized using X-ray crystallography and NMR spectroscopy. These complexes include [K([2.2.2]cryptand)][Y(COT)2] (1), [K(18-crown-6)(THF)][Y(COT)2] (2), [Y2K2(COT)4(THF)4] (3), and [YKCa(COT)3(THF)3] (4). In the presence of secondary ligands, bimetallic ionic pairs that comprise a [Y(COT)2]- sandwich and a solvent-wrapped K+ ion are formed in 1 and 2. In contrast, 3 represents a bimetallic tetradecker oligomer with two [Y(COT)2]- units bridged by a K+ ion and a terminal [K(THF)4]+ moiety. Complex 4 is a heterotrimetallic triple-decker with an axial arrangement of three metal centers to form [Y(COT)2K(COT)Ca(THF)3]. Structural analysis shows the Y–COTcentroid distances in the [Y(COT)2]- sandwich are equidistant (1.884(6) Å) in 1 but become asymmetric in 2–4 (1.857(3)–1.952(3) Å), reflecting additional external coordination. The two COT rings are parallel in 1 and become increasingly tilted from 0.8° to 27.5° in 2–4, respectively. Multinuclear NMR spectroscopy measurements reveal solution behavior of the sandwich and heterometallic multi-decker COT-based products. The observed NMR spectroscopic trends corroborate with weak interactions between the [Y(COT)2]- unit and cationic moieties persisting in solutions of 2–4. 

The rectangular cyclobutadiene (CBD, C₄H₄) is a unique moiety for building nonbenzenoid polycyclic conjugated hydrocarbons with interesting electron‐accepting properties. Herein, the investigation on chemical reduction of several CBD‐containing polycyclic hydrocarbons with increasing conjugation length is reported: biphenylene (C₁₂H₈), dimethyl[2]naphthalene (C₂₂H₁₆), and tetramethyl‐dibenzo‐[3]phenylene (C₃₀H₂₂). The two‐step sequential reduction is first demonstrated by in situ spectroscopic investigation and then confirmed by the isolation of single crystals of the reduced products. The X‐ray crystallographic analysis reveals the formation of several mono‐ and doubly reduced products in solvent‐separated and complexed forms. The crystal structures for both neutral parents and corresponding reduced products unravel the changes in bond alternation in each ring of the fused systems. Density functional theory (DFT) and nucleus‐independent chemical shift (NICS) scan calculations reveal that the two‐electron addition reduces the aromatic character in the benzenoid rings but has minor influence on the antiaromatic CBD rings. 

“Redox Properties of Nanographenes”, Y. Zhu, M. A. Petrukhina. Chapter 20 in “Molecular Nanographenes: Synthesis, Properties and Applications”, Edited by N. Martín and C. Nuckols, Wiley-VCH, 2025, 449-482 

Chemical reduction coupled with X-ray crystallographic and spectroscopic analyses reveals the electron accepting abilities of molecular nanographenes with various topological features, further supporting their advanced energy-storage applications. 

An overview of structural responses of helicenes with increasing dimensions and complexity to stepwise electron addition reveals charge- and topology-dependent outcomes ranging from reversible to irreversible core transformations and site-specific reactivity.