Single bond | EPFL Graph Search

In chemistry, a single bond is a chemical bond between two atoms involving two valence electrons. That is, the atoms share one pair of electrons where the bond forms. Therefore, a single bond is a type of covalent bond. When shared, each of the two electrons involved is no longer in the sole possession of the orbital in which it originated. Rather, both of the two electrons spend time in either of the orbitals which overlap in the bonding process. As a Lewis structure, a single bond is denoted as AːA or A-A, for which A represents an element. In the first rendition, each dot represents a shared electron, and in the second rendition, the bar represents both of the electrons shared in the single bond. A covalent bond can also be a double bond or a triple bond. A single bond is weaker than either a double bond or a triple bond. This difference in strength can be explained by examining the component bonds of which each of these types of covalent bonds consists (Moore, Stanitski, and Ju

Covalent attachment of proteins to calcite surface for the single molecule experiments

Two protocols of covalent attachment of proteins onto the calcite surface, viz. one using the metallochelat and second using the aminohexil, are elaborated. Single molecule force spectroscopy method has been used to test their efficiency and practical applicability. Experiments were performed measuring the specific interaction force between bovine serum albumin (BSA) fixed onto the freshly cleaved calcite single crystal surface (procedure under the study here) and its polyclonal antibody (Ab-BSA) immobilized onto an AFM tip using standard and well studied procedure. We found the conditions, when up to 3-3.5% of tip-sample approaches lead to the formation of a single specific bond. (C) 2007 Elsevier B.V. All rights reserved.

2008

Small Molecule Activation by Multimetallic Uranium Complexes

Marta Falcone

The development of new processes for the selective and sustainable transformation of abundant small molecules constitutes one of the major research areas in inorganic and organometallic chemistry. These molecules as CO2, CO, N2 and H2 are abundant reservoirs of chemical energy, readily available sources of carbon, nitrogen and hydrogen. In a patent from 1909, Haber reported that uranium and uranium nitride were very efficient catalysts for ammonia synthesis. In order to perform multi-electron transfer, multimetallic complexes need to be designed. Reactivity of uranium bridging nitride remained unexplored since we investigated the nitride based reactivity of a dinuclear uranium(IV) bridging nitride complex towards small molecules such as CO2, yielding the first example of a uranium complex containing a bridging dicarbamate ligand, or CO, resulting in the complete cleavage in mild conditions of one of the strongest bonds in nature, or H2, yielding one of the few examples in f-elements of metal hydride, which is readily transferred to substrates such as CO2. Beyond the ligand based reactivity, we were interested in reducing the two metal centers to access a diuranium(III) bridging nitride, to pursue nitrogen activation. This complex was shown to have high flexibility, provided by the siloxide ligands, high reducing power and a bridging atom, the nitride, that holds together the uranium centers, with the possibility to bend upon nitrogen activation. This approach led us to the isolation of a hydrazido complex, resulting from the four-electron reduction of dinitrogen by the two metal centers. Moreover, complete cleavage of the NâN single bond was achieved by addition of CO to give two cyanate ligands or by addition of H2 to give ammonia. The nitride atom linker is nonetheless, too reactive to act as a spectator and it is involved in reactivity. Hence, we target the isolation of the analogue dinuclear U(III) complex with an oxide ligand as linker. This complex showed the same reactivity towards nitrogen but DFT revealed a more ionic character of the UâO bond nature with respect to the UâN bond, leading to different reactivity of the hydrazido fragment upon addition of CO and upon addition of H2, showing a smaller extent of activation in the oxo complex with respect to the nitride. The diuranium(III) bridging oxide complex showed interesting reactivity with H2, forming a bis-hydride complex capable of reducing CO2 beyond the formate level, to methanol.

EPFL2019

Four-electron Reduction and Functionalization of N₂ by a Uranium(III) Bridging Nitride

Marta Falcone, Marinella Mazzanti

N2 is a cheap and widely available but very unreactive molecule. Notably, the only industrial process for the conversion of dinitrogen is the Haber-Bosch process to form ammonia, but under very harsh conditions (high temperature and pressure). Here, we review our recent research leading to the reduction of dinitrogen by four electrons, under ambient conditions by a uranium(III) bridging nitride, K3 U-N-U, where two uranium(III) cations are linked by a nitride group and a flexible metal-ligand scaffold. We also show that the bound dinitrogen can be further functionalized under mild conditions: the addition of acid, hydrogen and protons or carbon monoxide to the uranium hydrazido complex yields to the cleavage of the N-N single bond and to the formation of new N-H and N-C bonds.

2018

Small Molecule Activation by Multimetallic Uranium Complexes

Marta Falcone

EPFL2019