Dominance of broken bonds and nonbonding electrons at the nanoscale

Abstract

Although they exist ubiquitously in human bodies and our surroundings, the impact of nonbonding lone electrons and lone electron pairs has long been underestimated. Recent progress demonstrates that: (i) in addition to the shorter and stronger bonds between under-coordinated atoms that initiate the size trends of the otherwise constant bulk properties when a substance turns into the nanoscale, the presence of lone electrons near to broken bonds generates fascinating phenomena that bulk materials do not demonstrate; (ii) the lone electron pairs and the lone pair-induced dipoles associated with C, N, O, and F tetrahedral coordination bonding form functional groups in biological, organic, and inorganic specimens. By taking examples of surface vacancy, atomic chain end and terrace edge states, catalytic enhancement, conducting-insulating transitions of metal clusters, defect magnetism, Coulomb repulsion at nanoscale contacts, Cu(3)C(2)H(2) and Cu(3)O(2) surface dipole formation, lone pair neutralized interface stress, etc, this article will focus on the development and applications of theory regarding the energetics and dynamics of nonbonding electrons, aiming to raise the awareness of their revolutionary impact to the society. Discussion will also extend to the prospective impacts of nonbonding electrons on mysteries such as catalytic enhancement and catalysts design, the density anomalies of ice and negative thermal expansion, high critical temperature superconductivity induced by B, C, N, O, and F, the molecular structures and functionalities of CF(4) in anti-coagulation of synthetic blood, NO signaling, and enzyme telomeres, etc. Meanwhile, an emphasis is placed on the necessity and effectiveness of understanding the properties of substances from the perspective of bond and nonbond formation, dissociation, relaxation and vibration, and the associated energetics and dynamics of charge repopulation, polarization, densification, and localization. Finding and grasping the factors controlling the nonbonding states and making them of use in functional materials design and identifying their limitations will form, in the near future, a subject area of "nonbonding electronics and energetics", which could be even more challenging, fascinating, promising, and rewarding than dealing with core or valence electrons alone.

Deep melting reveals liquid structural memory and anomalous ferromagnetism in bismuth

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Magnetic, X-ray and Mössbauer studies on magnetite/maghemite core–shell nanostructures fabricated through an aqueous route

“…As the crystal dimension decreases, the surface area-to-volume ratio increases resulting in a increased broken bond density at the surface causing the remaining bonds to contract spontaneously with an associated increase in bond strength, which in turn produces localized strain. 56 A decrease in the lattice parameter to 8.3596Å was observed when the particle size increased from 7.3 to 8.4 nm as a result of possible higher surface oxidation of magnetite crystals to g-Fe 2 O 3 . The cell constant decreased slightly further to $8.3544Å on increasing size to 9.7 nm and remained almost constant thereaer.…”

Experimental and theoretical approach of nanocrystalline TiO2 with antifungal activity

“…As a consequence, nanoparticles with increased surface-tovolume ratio are expected to be more reactive due to the dominance of the undercoordinated atoms; i.e. broken bonds and nonbonding electrons at the nanoscale [14]. Thus, following the seminal sentence of Pauli: ''God made the bulk; surfaces were invented by the devil'', very recently, Mudunkotuwa and Grassian [15] emphasized the impact of surface structure and surface energetics on the environmental behavior of nanomaterials.…”