Next generation QTAIM for the design of quinone-based switches

The National Natural Science Foundation of China is acknowledged, project approval number: 21673071. The One Hundred Talents Foundation of Hunan Province is also gratefully acknowledged for the support of S.J. and S.R.K. The Royal Society is thanked by S.J., S.R.K, T.X, T.v.M and H.F. for support through an International Exchanges grant. We thank EaStCHEM for computational support via the EaStCHEM Research Computing Facility.Investigation of the hydrogen transfer tautomerization process yielded metallic hydrogen bonds in the benzoquinone-like core of the switch. Bond-path framework sets B and Bσ, comprising a three-stranded, non-minimal 3-D bond, which included the familiar QTAIM bond-path and two additional paths defining the least and most preferred directions of electron density motion, were used with QTAIM and the stress-tensor respectively. The B and Bσ were visualized and uncovered the destabilizing effects on the hydrogen bond of the presence of an Fe atom. The lengths of B and Bσ quantified this effect and the dependence on the position of a fluorine substituent.PostprintPostprintPeer reviewe

The cis-effect explained using next generation QTAIM

The National Natural Science Foundation of China is gratefully acknowledged, project approval number: 21673071. The One Hundred Talents Foundation of Hunan Province is also gratefully acknowledged for the support of S.J. and S.R.K. H.F. and T.v.M. gratefully acknowledge computational support via the EaStCHEM Research Computing Facility.We used next-generation QTAIM (NG-QTAIM) to explain the cis-effect for two families of molecules: C2X2 (X = H, F, Cl) and N2X2 (X = H, F, Cl). We explained why the cis-effect is the exception rather than the rule. This was undertaken by tracking the motion of the bond critical point (BCP) of the stress tensor trajectories Tσ(s) used to sample the Uσ-space cis- and trans-characteristics. The Tσ(s) were constructed by subjecting the C1-C2 BCP and N1-N2 BCP to torsions ± θ and summing all possible Tσ(s) from the bonding environment. During this process, care was taken to fully account for multi-reference effects. We associated bond-bending and bond-twisting components of the Tσ(s) with cis- and trans-characteristics, respectively, based on the relative ease of motion of the electronic charge density ρ(rb). Qualitative agreement is found with existing experimental data and predictions are made where experimental data is not available.Publisher PDFPeer reviewe

Quinone-based switches for candidate building blocks of molecular junctions with QTAIM and the stress tensor

The National Natural Science Foundation of China is acknowledged, project approval number: 21673071. The One Hundred Talents Foundation of Hunan Province and the aid program for the Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province are gratefully acknowledged for the support of S.J. and S.R.K. The Royal Society is thanked by S.J., S.R.K, T.X, T.v.M and H.F. for support through an International Exchanges grant.The current work investigates candidate building blocks based on molecular junctions from hydrogen transfer tautomerization in the benzoquinone-like core of an azophenine molecule with QTAIM and the recently introduced stress tensor trajectory analysis. We find that in particular the stress tensor trajectories are well suited to describe the mechanism of the switching process. The effects of an Fe-dopant atom coordinated to the quinone ring, as well as F and Cl substitution of different ring-hydrogens, are investigated and the new QTAIM and stress tensor analysis is used to draw conclusions on the effectiveness of such molecules as molecular switches in nano-sized electronic circuits. We find that the coordinated Fe-dopant greatly improves the switching properties, both in terms of the tautomerisation barrier that has to be crossed in the switching process and the expected conductance behavior, while the effects of hydrogen substitution are more subtle. The absence of the Fe-dopant atom led to impaired functioning of the switch ‘OFF’ mechanism as well coinciding with the formation of closed-shell H–––H bond critical points that indicated a strained or electron deficient environment.  Our analysis demonstrates promise for future use in design of molecular electronic devices.PostprintPeer reviewe

Organophosphorus Chemistry 2018

Organophosphorus chemistry is an important discipline within organic chemistry. Phosphorus compounds, such as phosphines, trialkyl phosphites, phosphine oxides (chalcogenides), phosphonates, phosphinates and >P(O)H species, etc., may be important starting materials or intermediates in syntheses. Let us mention the Wittig reaction and the related transformations, the Arbuzov- and the Pudovik reactions, the Kabachnik–Fields condensation, the Hirao reaction, the Mitsunobu reaction, etc. Other reactions, e.g., homogeneous catalytic transformations or C-C coupling reactions involve P-ligands in transition metal (Pt, Pd, etc.) complex catalysts. The synthesis of chiral organophosphorus compounds means a continuous challenge. Methods have been elaborated for the resolution of tertiary phosphine oxides and for stereoselective organophosphorus transformations. P-heterocyclic compounds, including aromatic and bridged derivatives, P-functionalized macrocycles, dendrimers and low coordinated P-fragments, are also of interest. An important segment of organophosphorus chemistry is the pool of biologically-active compounds that are searched and used as drugs, or as plant-protecting agents. The natural analogue of P-compounds may also be mentioned. Many new phosphine oxides, phosphinates, phosphonates and phosphoric esters have been described, which may find application on a broad scale. Phase transfer catalysis, ionic liquids and detergents also have connections to phosphorus chemistry. Green chemical aspects of organophosphorus chemistry (e.g., microwave-assisted syntheses, solvent-free accomplishments, optimizations, and atom-efficient syntheses) represent a dynamically developing field. Last, but not least, theoretical approaches and computational chemistry are also a strong sub-discipline within organophosphorus chemistry