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Metal–organic frameworks (MOFs) that display photoredox activity are attractive materials for sustainable photocatalysis. The ability to tune both their pore sizes and electronic structures based solely on the choice of the building blocks makes them amenable for systematic studies based on physical organic and reticular chemistry principles with high degrees of synthetic control. Here, we present a library of eleven isoreticular and multivariate (MTV) photoredox-active MOFs, UCFMOF-n, and UCFMTV-n-x% with a formula Ti6O9[links]3, where the links are linear oligo-p-arylene dicarboxylates with nnumber of p-arylene rings and xmol% of multivariate links containing electron-donating groups (EDGs). The average and local structures of UCFMOFs were elucidated from advanced powder X-ray diffraction (XRD) and total scattering tools, consisting of parallel arrangements of one-dimensional (1D) [Ti6O9(CO2)6]∞nanowires connected through the oligo-arylene links with the topology of the edge-2-transitive rod-packed hexnet. Preparation of an MTV library of UCFMOFs with varying link sizes and amine EDG functionalization enabled us to study both their steric (pore size) and electronic (highest occupied molecular orbital–lowest unoccupied molecular orbital, HOMO–LUMO, gap) effects on the substrate adsorption and photoredox transformation of benzyl alcohol. The observed relationship between the substrate uptake and reaction kinetics with the molecular traits of the links indicates that longer links, as well as increased EDG functionalization, exhibit impressive photocatalytic rates, outperforming MIL-125 by almost 20-fold. Our studies relating photocatalytic activity with pore size and electronic functionalization demonstrate how these are important parameters to consider when designing new MOF photocatalysts.

We report herein a series of Cp*Ir complexes containing a rigid 8-aminoquinolinesulfonamide moiety as highly efficient catalysts for the dehydrogenation of formic acid (FA). The complex [Cp*Ir(L)Cl] (HL = N-(quinolin-8-yl)benzenesulfonamide) displayed a high turnover frequency (TOF) of 2.97 × 104h–1and a good stability (>100 h) at 60 °C. Comparative studies of [Cp*Ir(L)Cl] with the rigid ligand and [Cp*Ir(L′)Cl] (HL′ = N-propylpypridine-2-sulfonamide) without the rigid aminoquinoline moiety demonstrated that the 8-aminoquinoline moiety could dramatically enhance the stability of the catalyst. The electron-donating ability of the N,N′-chelating ligand was tuned by functionalizing the phenyl group of the L ligand with OMe, Cl, and CF3to have a systematical perturbation of the electronic structure of [Cp*Ir(L)Cl]. Experimental kinetic studies and density functional theory (DFT) calculations on this series of Cp*Ir complexes revealed that (i) the electron-donating groups enhance the hydrogen formation step while slowing down the β-hydride elimination and (ii) the electron-withdrawing groups display the opposite effect on these reaction steps, which in turn leads to lower optimum pH for catalytic activity compared to the electron-donating groups.

In a conventional lithium-ion battery (LIB), graphite forms the negative electrode or anode. Although Na is considered one of the most attractive alternatives to Li, achieving reversible Na intercalation within graphitic materials under ambient conditions remains a challenge. More efficient carbonaceous anode materials are desired for developing advanced LIBs and beyond Li-ionbattery technologies. We hypothesized that two-dimensional materials with distinct surface electronic properties create conditions for ion insertion into few-layer graphene (FLG) anodes. This is because modification of the electrode/electrolyte interface potentially modifies the energetics and mechanisms of ion intercalation in the thin bulk of FLG. Through first-principles calculations; we show that the electronic, structural, and thermodynamic properties of FLG anodes can be fine-tuned by a covalent heteroatom substitution at the uppermost layer of the FLG electrode, or by interfacing FLG with a single-side fluorinated graphene or a Janus-type hydrofluorographene monolayer. When suitably interfaced with the 2D surface modifier, FLG exhibits favorable thermodynamics for the Li+, Na+, and K+intercalation. Remarkably, the reversible binding of Na within carbon layers becomes thermodynamically allowed, and a large storage capacity can be achieved for the Na intercalated modified FLG anodes. The origin of charge-transfer promoted electronic tunability of modified FLGs is rationalized by various theoretical methods.

The electronic structure and excited-state dynamics of heterojunctions composed of 2D silicane and germanane-based materials (SiR, GeR; R = H, Me) and anatase or rutile isomorphs of TiO2are investigated. Our calculations reveal a high tunability of the band gaps of these heterostructures: 2.28 eV in SiH/a-TiO2to 0.16 eV in GeMe/r-TiO2. Nonadiabatic molecular dynamic (NA-MD) simulations suggest that electron–hole recombination in SiH/a-TiO2, SiH/r-TiO2, and GeH/a-TiO2occurs within 46.0, 3.6, and 1.2 ns, respectively, which is notably slower than in other analogous materials. The methylation of Si or Ge monolayers and the use of rutile polymorphs increase the nonadiabatic coupling and accelerate the recombination. A simple accelerated NA-MD method is devised in this work to evaluate the time scales for extremely slow dynamics of excited states. On the contrary to the electron–hole recombination, “hot” electrons are found to thermalize within a picosecond time scale, whereas some hot holes thermalize notably slower, on the order of 20.5 ps in SiH/a-TiO2and 65.3 ps in GeH/a-TiO2. High tunability of the band gaps, suitable electron and hole localization, and long recombination time scales suggest that SiH/a-TiO2, SiH/r-TiO2, and GeH/a-TiO2heterostructures may be promising candidates for photocatalytic applications.

The recently synthesized all-cis1,2,3,4,5,6-hexafluorocyclohexane (1) has a large dipole moment (6.2 D) and uniaxial facial polarization. Based on density functional theory (DFT) calculations, it is shown that both the “positive” and “negative” surfaces of 1can recognize flat aromatic molecules (X, X = benzene, pyrene, and coronene), 2D materials (graphene), and their fully hydrogenated analogues through attractive noncovalent interactions. 1can be sandwiched between graphene and graphane layers, where the enhanced polarity of the axial CH and CF bonds leads to the formation of an unusual “triple-decker” complex. Upon adsorption with 1, the band gap of graphane reduces from 3.40 to 2.05 eV, which might be useful for visible-light energy-conversion applications. We demonstrate the controlled tuning of the structural and electronic properties in 1-benzene, 1-cyclohexane, and benzene-1-cyclohexane complexes by the application of an external electric field along the polarization axis. The extended analogue of 1, hydrofluorinated graphene (HFG), which has semiconducting properties (band gap ≈ 3.0 eV), can form strong CH···FC interlayer interactions with graphane to form a stable, metallic bilayer. Our calculations show that the two-dimensional HFG can be realized through the high-pressure topochemical condensation of monofluoroacetylene (C2HF) for which the barrier of activation is 18.7 kcal/mol.

The heavier analogues of graphene, namely silicene and germanene, are known to be buckled. Such buckling leads to interesting properties like direct band gap in hydrogenated germanene, known as germanane. This article shows that the sequential replacement of C by Ge in benzene leads to increasing buckling with the maximal buckling distance (d= 0.61 Å) in Ge6H6. The origin of such buckling induced lowering of symmetry (D6h→ D3d) is traced to pseudo Jahn–Teller (PJT) distortion along the b2gnormal mode arising out of mixing of the nondegenerate (A1g) ground state with low lying (Δ0= 4.36 eV) excited state of B2gsymmetry. Buckling also leads to enhanced chemical reactivity of germanene toward hydrogen to form germanane. The large affinity of germanene toward hydrogenation explains the experimental synthesis of exfoliated layers of germanane by Goldberger and co-workers [ACS Nano2013, 7, 4414−4421]. Germanene → germanane formation leads to the opening up of a large band gap making hydrogenation a chemical route to control the electronic properties in these new 2D materials. The presence of buckling in germanene leads to higher hole reorganization energies than polyaromatic hydrocarbons (PAH) of the same nuclearity.

Na-ion batteries (NIBs) are proposed as a promising candidate for beyondLi-ion chemistries, however, a key challenge associated with NIBs is the inability to achieve intercalation in graphite anodes. This phenomenon has been investigated and is believed to arise due to the thermodynamic instability of Na-intercalated graphite. We have recently demonstrated theoretical calculations showing it is possible to achieve thermodynamically stable Na-intercalated graphene structures with a fluorine surface modifier. Here, we present experimental evidence that Na+intercalation is indeed possible in fluorinated few-layer graphene (F-FLG) structures using cyclic voltammetry (CV), ion-sensitive scanning electrochemical microscopy (SECM) and in situ Raman spectroscopy. SECM and Raman spectroscopy confirmed Na+intercalation in F-FLG, while CV measurements allowed us to quantify Na-intercalated F-FLG stoichiometries around NaC14–18. These stoichiometries are higher than the previously reported values of NaC186in graphite. Our experiments revealed that reversible Na+ion intercalation also requires a pre-formed Li-based SEI in addition to the surface fluorination, thereby highlighting the critical role of SEI in controlling ion-transfer kinetics in alkali-ion batteries. In summary, our findings highlight the use of surface modification and careful study of electrode-electrolyte interfaces and interphases as an enabling strategy for NIBs.

The reactions of [RuCl2(η6-C6H6)]2with chiral aroylthiourea ligands yielded pseudo-octahedral half-sandwich “piano-stool” complexes. All the Ru(ii) complexes were characterized by analytical and spectral (UV-visible, FT-IR, 1H NMR and 13C NMR) studies. The molecular structures of the ligands (L2 and L4) and the complexes (2, 4and 5) were confirmed by single crystal XRD. All the complexes were successfully screened as catalysts for the asymmetric transfer hydrogenation (ATH) of ketones using 2-propanol as the hydrogen source in the presence of KOH. The ATH reactions proceeded with excellent yields (up to 99%) and very good enantioselectivity (up to 99% ee). The scope of the present catalytic system was extended to substituted aromatic ketones and few hetero-aromatic ketones. Density functional theory (DFT) calculations predicted non-classical, concerted transition states for the ATH reactions. The catalytic activity of Ru–benzene complexes toward asymmetric reduction of ketones was significantly higher compared to that of p-cymene complex analogues. Such enhanced efficiency and product selectivity of Ru–benzene complexes compared to those of Ru–p-cymene complexes were rationalized by the computational study.

The ground-state structures, HOMO–LUMO gaps, singlet–triplet splitting, and the UV–vis absorption spectra for Si, Ge-substituted analogues of the recently synthesized disk-like π-conjugated molecules, like octathio[8]circulene, popularly termed “sulflower”, and 2H-benzo[cd]pyrene, popularly termed “olympicene”, are studied using density functional theory. Unlike their pure organic counterparts, these molecules are found to be nonplanar with substantial puckering from the high symmetric structures. The origin of puckering is traced to pseudo Jahn–Teller (PJT) distortions due to favorable mixing of the occupied molecular orbitals (OMO) and unoccupied molecular orbitals (UMO). Even though the HOMO–LUMO and singlet–triplet gaps for these molecules are smaller than their organic counterparts, the reorganization energies (both hole, λh, and electron, λe) for the Si, Ge analogues of sulflower and olympicene are much higher. Therefore, these molecules are expected to be rather inefficient for field effect transistor (FET) device fabrication.

The mechanisms for the C–I bond dissociation in iodoethane, iodobenzene, and iodoethene over the subnanometer sized gold clusters were studied using density functional theory. Au3, Au4, Au14, and Au20clusters and their cations were used as the models to investigate the effects of the size, geometry, and electronic charge on the catalysis of the reaction. Our calculations predict that both iodoethane and iodobenzene interact with the gold through the lone pair on iodine with the small planar clusters activating the reaction more effectively through the formation of strong adducts and low barrier heights. Clusters with large HOMO–LUMO gaps act as poor catalysts owing to the quantum size effects. Even though the cationic clusters bind to the reactants more strongly due to their enhanced Lewis acidity, they also require higher activation energy. However, the catalysis by cations and 3D clusters has a smaller endergonicity which would be desirable in the subsequent steps in cross/homo coupling reactions. In the case of iodoethene, gold binds through the π electrons instead of the lone pair on iodine which fine-tunes the bond dissociation process.

The chemical basis (electronic and steric factors) through which [Au(TPP)]Cl acts as a highly efficient chemoselective catalyst (even more than other homogeneous Au(III) catalysts like AuCl3and [Au(salen)]Cl) in the conversion of allenone to furan is elucidated. The planar aromatic structure of porphyrin unit stabilizes the transition state for ring closure through symmetric orbital interactions between allenone and the catalyst to create a lower energy cyclization pathway. Even though AuCl3catalyzes the cyclization of allenone very efficiently, the inability for the reaction to terminate and the possibility for further reactions that lead to oligomerization of allenone through new C−C bond formation reduce its synthetic utility. A detailed mechanistic investigation on the dimerization of allenone in the presence of AuCl3provides a theoretical rationale for the previous experimental results. In the case of the [Au(salen)]+-catalyzed reaction, the higher activation energy required to cross the barrier for cyclization reduces its efficiency.