Frustrated Lewis pairs (FLPs) are combinations of Lewis acids and Lewis bases in solution that are deterred from strong adduct formation by steric and/or electronic factors. This opens pathways to novel cooperative reactions with added substrates. Small-molecule binding and activation by FLPs has led to the discovery of a variety of new reactions through unprecedented pathways. Hydrogen activation and subsequent manipulation in metal-free catalytic hydrogenations is a frequently observed feature of many FLPs. The current state of this young but rapidly expanding field is outlined in this Review and the future directions for its broadening sphere of impact are considered.

Frustrated Lewis pair chemistry: development and perspectives.

Ionic liquids (IL) and hydrogen bonding (H-bonding) are two diverse fields for which there is a developing recognition of significant overlap. Doubly ionic H-bonds occur when a H-bond forms between a cation and anion, and are a key feature of ILs. Doubly ionic H-bonds represent a wide area of H-bonding which has yet to be fully recognised, characterised or explored. H-bonds in ILs (both protic and aprotic) are bifurcated and chelating, and unlike many molecular liquids a significant variety of distinct H-bonds are formed between different types and numbers of donor and acceptor sites within a given IL. Traditional more neutral H-bonds can also be formed in functionalised ILs, adding a further level of complexity. Ab initio computed parameters; association energies, partial charges, density descriptors as encompassed by the QTAIM methodology (ρBCP), qualitative molecular orbital theory and NBO analysis provide established and robust mechanisms for understanding and interpreting traditional neutral and ionic H-bonds. In this review the applicability and extension of these parameters to describe and quantify the doubly ionic H-bond has been explored. Estimating the H-bonding energy is difficult because at a fundamental level the H-bond and ionic interaction are coupled. The NBO and QTAIM methodologies, unlike the total energy, are local descriptors and therefore can be used to directly compare neutral, ionic and doubly ionic H-bonds. The charged nature of the ions influences the ionic characteristics of the H-bond and vice versa, in addition the close association of the ions leads to enhanced orbital overlap and covalent contributions. The charge on the ions raises the energy of the Ylp and lowers the energy of the X–H σ* NBOs resulting in greater charge transfer, strengthening the H-bond. Using this range of parameters and comparing doubly ionic H-bonds to more traditional neutral and ionic H-bonds it is clear that doubly ionic H-bonds cover the full range of weak through to very strong H-bonds.

Hydrogen bonding in ionic liquids

Bismuth vanadate (BiVO4) is a promising visible-light driven semiconductor photocatalyst with various benefits such as low production cost, low toxicity, high photostability, resistance to photo-corrosion and narrow band gap with a good response to visible-light excite. However, the fast recombination of photoinduced charge carriers restricts their photocatalytic activity. In the past decades, many attempts were adopted to enhance the photocatalytic activity of BiVO4. Significant advances in understanding the fundamental issues and the development of an efficient photocatalyst have been made in current years. In this review, we have provided a comprehensive overview of the latest progress on the morphology control and growth mechanism of BiVO4 micro/nano-structures, doping with metal and non-metal elements and semiconductor coupling along with some highlights in the photodegradation of organic pollutants under visible-light illumination. This review may benefit the researchers and engineers in the arena of material chemistry for designing new BiVO4 based photocatalysts with low production cost and high efficiency.

A review on BiVO4 photocatalyst: Activity enhancement methods for solar photocatalytic applications

Der Begriff “frustrierte Lewis-Paare” (FLPs) bezeichnet Kombinationen von Lewis-Sauren und Lewis-Basen in Losung, die aufgrund sterischer oder elektronischer Faktoren an der Bildung eines stabilen Addukts gehindert werden. Die verbleibende Lewis-Aziditat und -Basizitat ermoglicht den Zugang zu neuen kooperativen Reaktionen mit zugesetzten Substraten. Die Fixierung und Aktivierung von kleinen Molekulen durch FLPs fuhrte zur Entdeckung einer Vielzahl von neuen Reaktionen und ungewohnlichen Reaktionswegen. Die Aktivierung von Diwasserstoff und die anschliesende Umsetzung in metallfreien katalytischen Hydrierungsreaktionen ist ein haufig beobachtetes Merkmal von FLPs. In diesem Aufsatz wird der aktuelle Stand dieses jungen Forschungsgebietes der Chemie beschrieben und die zukunftige Ausrichtung des sich rasch weiterentwickelnden Konzepts der frustrierten Lewis-Paare betrachtet.

Chemie frustrierter Lewis‐Paare: Entwicklung und Perspektiven

Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

Review on nanoscale Bi-based photocatalysts

To determine the structure of aqueous sodium hydroxide solutions, results obtained from x-ray diffraction and computer simulation (molecular dynamics and Car-Parrinello) have been compared. The capabilities and limitations of the methods in describing the solution structure are discussed. For the solutions studied, diffraction methods were found to perform very well in describing the hydration spheres of the sodium ion and yield structural information on the anion’s hydration structure. Classical molecular dynamics simulations were not able to correctly describe the bulk structure of these solutions. However, Car-Parrinello simulation proved to be a suitable tool in the detailed interpretation of the hydration sphere of ions and bulk structure of solutions. The results of Car-Parrinello simulations were compared with the findings of diffraction experiments.

The structure of aqueous sodium hydroxide solutions: a combined solution x-ray diffraction and simulation study.

Ion pairing in aqueous calcium chloride solution: Molecular dynamics simulation and diffraction studies

We introduce a unique material ensemble to boost the photocatalytic activity of m-BiVO4 by creating dual heterojunction of bismuth oxybromide nanosheets and Pd nanodomains. The m-BiVO4/BiOBr/Pd ternary composite demonstrates substantially higher photocatalytic activity compared to pure m-BiVO4. We demonstrate for the first time the use of such visible light photocatalyst in highly efficient degradation of polychlorinated biphenyls.

Pd-decorated m-BiVO4/BiOBr ternary composite with dual heterojunction for enhanced photocatalytic activity

Networks are increasingly recognized as important building blocks of various systems in nature and society. Water is known to possess an extended hydrogen bond network, in which the individual bonds are broken in the sub-picosecond range and still the network structure remains intact. We investigated and compared the topological properties of liquid water and methanol at various temperatures using concepts derived within the framework of graph and network theory (neighbour number and cycle size distribution, the distribution of local cyclic and local bonding coefficients, Laplacian spectra of the network, inverse participation ratio distribution of the eigenvalues and average localization distribution of a node) and compared them to small world and Erdős–Renyi random networks. Various characteristic properties (e.g. the local cyclic and bonding coefficients) of the network in liquid water could be reproduced by small world and/or Erdős–Renyi networks, but the ring size distribution of water is unique and none of the studied graph models could describe it. Using the inverse participation ratio of the Laplacian eigenvectors we characterized the network inhomogeneities found in water and showed that similar phenomena can be observed in Erdős–Renyi and small world graphs. We demonstrated that the topological properties of the hydrogen bond network found in liquid water systematically change with the temperature and that increasing temperature leads to a broader ring size distribution. We applied the studied topological indices to the network of water molecules with four hydrogen bonds, and showed that at low temperature (250 K) these molecules form a percolated or nearly-percolated network, while at ambient or high temperatures only small clusters of four-hydrogen bonded water molecules exist.

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Hydrogen bond network topology in liquid water and methanol: a graph theory approach

Explicit solvent molecular dynamics simulations of the (tBu)3P/B(C6F5)3 pair in toluene allowed the estimation of the degree of intermolecular association and the population of encounter complex states in solution phase.

Szabolcs Bálint

Papers

The structure of aqueous sodium hydroxide solutions: a combined solution x-ray diffraction and simulation study.

Ion pairing in aqueous calcium chloride solution: Molecular dynamics simulation and diffraction studies

Pd-decorated m-BiVO4/BiOBr ternary composite with dual heterojunction for enhanced photocatalytic activity

Hydrogen bond network topology in liquid water and methanol: a graph theory approach

Association of frustrated phosphine–borane pairs in toluene: molecular dynamics simulations