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1. Revealing electronic state-switching at conical intersections in alkyl iodides by ultrafast XUV transient absorption spectroscopy

   https://doi.org/10.1038/s41467-020-17745-w  

   Chang, Kristina F.; Reduzzi, Maurizio; Wang, Han; Poullain, Sonia M.; Kobayashi, Yuki; Barreau, Lou; Prendergast, David; Neumark, Daniel M.; Leone, Stephen R. (August 2020, Nature Communications)

   Abstract Conical intersections between electronic states often dictate the chemistry of photoexcited molecules. Recently developed sources of ultrashort extreme ultraviolet (XUV) pulses tuned to element-specific transitions in molecules allow for the unambiguous detection of electronic state-switching at a conical intersection. Here, the fragmentation of photoexcitediso-propyl iodide andtert-butyl iodide molecules (i-C₃H₇I andt-C₄H₉I) through a conical intersection between³Q₀/¹Q₁spin–orbit states is revealed by ultrafast XUV transient absorption measuring iodine 4dcore-to-valence transitions. The electronic state-sensitivity of the technique allows for a complete mapping of molecular dissociation from photoexcitation to photoproducts. In both molecules, the sub-100 fs transfer of a photoexcited wave packet from the³Q₀state into the¹Q₁state at the conical intersection is captured. The results show how differences in the electronic state-switching of the wave packet ini-C₃H₇I andt-C₄H₉I directly lead to differences in the photoproduct branching ratio of the two systems. 

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2. Intra- and intermolecular C—H...F hydrogen bonds in the crystal structure of 1,2-bis[2-(2,3,4,5-tetrafluorophenyl)ethynyl]benzene

   https://doi.org/10.1107/S2056989024010995  

   Bosch, Eric; Bowling, Nathan P (December 2024, Acta Crystallographica Section E Crystallographic Communications)

   The title molecule, C₂₂H₆F₈, crystallizes in the monoclinic space groupP2₁/cwith two unique molecules in the asymmetric unit andZ= 8. Each molecule features a short intramolecularsp²-C—H...F hydrogen bond with H...F separations at 2.363 (14) and 2.270 (14) Å, corresponding to 91 and 87.5% of the sum of the van der Waals radii, and C—H...F angles of 158.3 (14) and 166.8 (14)°, respectively. Each molecule also forms an intermolecular bifurcated CH...(F)₂interaction with H...F distances ranging from 2.500 (16) to 2.597 (17) Å. 

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3. Synthesis of Square Planar Cu ₄ Clusters

   https://doi.org/10.1002/anie.202209529  

   Osei, Manasseh Kusi; Mirzaei, Saber; Bogetti, Xiaowei; Castro, Edison; Rahman, Mohammad Azizur; Saxena, Sunil; Hernández Sánchez, Raúl (September 2022, Angewandte Chemie International Edition)

   Abstract Template‐assisted synthesis of well‐defined polynuclear clusters remains a challenge for [M₄] square planar topologies. Herein, we present a tetraamine scaffold^RL(NH₂)₄, where L is a rigidified resorcin[4]arene, to direct the formation ofC₄‐symmetric^RL(NH)₄Cu₄clusters with Cu−Cu distances around 2.7 Å, suggesting metal‐metal direct interactions are operative since the sum of copper's van der Waals radii is 2.8 Å. DFT calculations display HOMO to HOMO‐3 residing all within a 0.1 eV gap. These four orbitals display significant electron density contribution from the Cu centers suggesting a delocalized electronic structure. The one‐electron oxidized [Cu₄]⁺species was probed by variable temperature X‐band continuous wave‐electron paramagnetic resonance (CW‐EPR), which displays a multiline spectrum at room temperature. This work presents a novel synthetic strategy for [M₄] clusters and a new platform to investigate activation of small molecules. 

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4. Charge‐Transport Properties of F ₆ TNAP‐Based Charge‐Transfer Cocrystals

   https://doi.org/10.1002/adfm.201904858  

   Dasari, Raghunath_R; Wang, Xu; Wiscons, Ren_A; Haneef, Hamna_F; Ashokan, Ajith; Zhang, Yadong; Fonari, Marina_S; Barlow, Stephen; Coropceanu, Veaceslav; Timofeeva, Tatiana_V; et al (October 2019, Advanced Functional Materials)

   Abstract The crystal structures of the charge‐transfer (CT) cocrystals formed by the π‐electron acceptor 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyanonaphtho‐2,6‐quinodimethane (F₆TNAP) with the planar π‐electron‐donor molecules triphenylene (TP), benzo[b]benzo[4,5]thieno[2,3‐d]thiophene (BTBT), benzo[1,2‐b:4,5‐b′]dithiophene (BDT), pyrene (PY), anthracene (ANT), and carbazole (CBZ) have been determined using single‐crystal X‐ray diffraction (SCXRD), along with those of two polymorphs of F₆TNAP. All six cocrystals exhibit 1:1 donor/acceptor stoichiometry and adopt mixed‐stacking motifs. Cocrystals based on BTBT and CBZ π‐electron donor molecules exhibit brickwork packing, while the other four CT cocrystals show herringbone‐type crystal packing. Infrared spectroscopy, molecular geometries determined by SCXRD, and electronic structure calculations indicate that the extent of ground‐state CT in each cocrystal is small. Density functional theory calculations predict large conduction bandwidths and, consequently, low effective masses for electrons for all six CT cocrystals, while the TP‐, BDT‐, and PY‐based cocrystals are also predicted to have large valence bandwidths and low effective masses for holes. Charge‐carrier mobility values are obtained from space‐charge limited current (SCLC) measurements and field‐effect transistor measurements, with values exceeding 1 cm²V⁻¹s¹being estimated from SCLC measurements for BTBT:F₆TNAP and CBZ:F₆TNAP cocrystals. 

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5. Electron and Spin Delocalization in [Co ₆ Se ₈ (PEt ₃ ) ₆ ] ^0/+1 Superatoms

   https://doi.org/10.1002/cphc.202300064  

   Xu, Yunyao; Chen, Jia; Aydt, Alexander P.; Zhang, Lichirui; Sergeyev, Ivan; Keeler, Eric G.; Choi, Bonnie; He, Shoushou; Reichman, David R.; Friesner, Richard A.; et al (January 2024, ChemPhysChem)

   ChemPhysChem (Ed.)

   Abstract Molecular clusters can function as nanoscale atoms/superatoms, assembling into superatomic solids, a new class of solid‐state materials with designable properties through modifications on superatoms. To explore possibilities on diversifying building blocks, here we thoroughly studied one representative superatom, Co₆Se₈(PEt₃)₆. We probed its structural, electronic, and magnetic properties and revealed its detailed electronic structure as valence electrons delocalize over inorganic [Co₆Se₈] core while ligands function as an insulated shell.⁵⁹Co SSNMR measurements on the core and³¹P,¹³C on the ligands show that the neutral Co₆Se₈(PEt₃)₆is diamagnetic and symmetric, with all ligands magnetically equivalent. Quantum computations cross‐validate NMR results and reveal degenerate delocalized HOMO orbitals, indicating aromaticity. Ligand substitution keeps the inorganic core nearly intact. After losing one electron, the unpaired electron in [Co₆Se₈(PEt₃)₆]⁺¹is delocalized, causing paramagnetism and a delocalized electron spin. Notably, this feature of electron/spin delocalization over a large cluster is attractive for special single‐electron devices. 

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