What to do about unpaired electrons? A hydrocarbon hexaradical with three Closs diradicals linked by 1,3,5-trimethylbenzene as ferromagnetic coupler

2002 ◽  
Vol 117 (15) ◽  
pp. 7147-7152 ◽  
Author(s):  
Michael S. Schuurman ◽  
Chaeho Pak ◽  
Henry F. Schaefer
Keyword(s):  
Unpaired Electrons

Explaining the magnetism of gold

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Gas Phase ◽  
Computational Study ◽  
Formation Enthalpy ◽  
Gold Atom ◽  
Orbital Energy ◽  
Knudsen Effusion ◽  
Energy Diagram ◽  
Unpaired Electrons ◽  
The Difference ◽  
Good Agreement

<p>In the present work, a computational study is performed in order to clarify the possible magnetic nature of gold. For such purpose, gas phase Au<sub>2</sub> (zero charge) is modelled, in order to calculate its gas phase formation enthalpy. The calculated values were compared with the experimental value obtained by means of Knudsen effusion mass spectrometric studies [5]. Based on the obtained formation enthalpy values for Au<sub>2</sub>, the compound with two unpaired electrons is the most probable one. The calculated ionization energy of modelled Au<sub>2</sub> with two unpaired electrons is 8.94 eV and with zero unpaired electrons, 11.42 eV. The difference (11.42-8.94 = 2.48 eV = 239.29 kJmol<sup>-1</sup>), is in very good agreement with the experimental value of 226.2 ± 0.5 kJmol<sup>-1</sup> to the Au-Au bond<sup>7</sup>. So, as expected, in the specie with none unpaired electrons, the two 6s<sup>1</sup> (one of each gold atom) are paired, forming a chemical bond with bond order 1. On the other hand, in Au<sub>2</sub> with two unpaired electrons, the s-d hybridization prevails, because the relativistic contributions. A molecular orbital energy diagram for gas phase Au<sub>2</sub> is proposed, explaining its paramagnetism (and, by extension, the paramagnetism of gold clusters and nanoparticles).</p>

A decomposition of the number of effectively unpaired electrons and its physical meaning

2009 ◽  
Vol 476 (1-3) ◽  
pp. 101-103 ◽  
Author(s):  
Luis Lain ◽  
Alicia Torre ◽  
Diego R. Alcoba ◽  
Roberto C. Bochicchio
Keyword(s):  
Physical Meaning ◽  
Unpaired Electrons

Delocalization of unpaired electrons in acceptor-bridge-donor molecular structures as monitored by CW-EPR spectroscopy

1996 ◽  
Vol 225 (3-4) ◽  
pp. 258-264 ◽  
Author(s):  
R. Krzyminiewski ◽  
A. Bielewicz ◽  
J. Kudynska ◽  
H.A. Buckmaster ◽  
B. Brycki
Keyword(s):  
Epr Spectroscopy ◽  
Molecular Structures ◽  
Unpaired Electrons

scholarly journals Supramolecular Complexes of Graphene Oxide with Porphyrins: An Interplay between Electronic and Magnetic Properties

Molecules ◽  
2019 ◽  
Vol 24 (4) ◽  
pp. 688 ◽  
Author(s):  
Kornelia Lewandowska ◽  
Natalia Rosiak ◽  
Andrzej Bogucki ◽  
Judyta Cielecka-Piontek ◽  
Mikołaj Mizera ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Graphene Oxide ◽  
Hybrid Materials ◽  
Π Stacking ◽  
Drastic Increase ◽  
Unpaired Electrons ◽  
The Difference ◽  
The Fourier Transform ◽  
Supramolecular Aggregates ◽  
Selection Of

Graphene oxide (GO) was modified by two modified porphyrins (THPP and TCPP) to form GO–porphyrin hybrids. Spectroscopic measurements demonstrated the formation of stable supramolecular aggregates when mixing two components in solution. The Fourier transform infrared (FTIR) and Raman scattering measurements confirm π-stacking between hydrophobic regions of GO nanoflakes and porphyrin molecules. On the number and the kind of paramagnetic centers generated in pristine GO samples, which originate from spin anomalies at the edges of aromatic domains within GO nanoflakes. More significant changes in electronic properties have been observed in hybrid materials. This is particularly evident in the drastic increase in the number of unpaired electrons for the THPP-GO sample and the decrease in the number of unpaired electrons for the TCPP-GO. The difference of paramagnetic properties of hybrid materials is a consequence of π-stacking between GO and porphyrin rings. An interesting interplay between modifiers and the surface of GO leads to a significant change in electronic structure and magnetic properties of the designed hybrid materials. Based on the selection of molecular counterpart we can affect the behavior of hybrids upon light irradiation in a different manner, which may be useful for the applications in photovoltaics, optoelectronics, and spintronics.

scholarly journals The electron density function of the Hückel (tight-binding) model

2018 ◽  
Vol 474 (2210) ◽  
pp. 20170721 ◽  
Author(s):  
Ernesto Estrada
Keyword(s):  
Density Matrix ◽  
Electron Density ◽  
Tight Binding ◽  
High Dimensional ◽  
Spin Interaction ◽  
Tight Binding Model ◽  
Solid State Physics ◽  
Binding Model ◽  
Conjugated Molecules ◽  
Unpaired Electrons

The Hückel (tight-binding) molecular orbital (HMO) method has found many applications in the chemistry of alternant conjugated molecules, such as polycyclic aromatic hydrocarbons (PAHs), fullerenes and graphene-like molecules, as well as in solid-state physics. In this paper, we found analytical expressions for the electron density matrix of the HMO method in terms of odd-powers of its Hamiltonian. We prove that the HMO density matrix induces an embedding of a molecule into a high-dimensional Euclidean space in which the separation between the atoms scales very well with the bond lengths of PAHs. We extend our approach to describe a quasi-correlated tight-binding model, which quantifies the number of unpaired electrons and the distribution of effectively unpaired electrons. In this case, we found that the corresponding density matrices induce embedding of the molecules into high-dimensional Euclidean spheres where the separation between the atoms contains information about the spin–spin repulsion between them. Using our approach, we found an analytic expression which explains the bond length alternation in polyenes inside the HMO framework. We also found that spin–spin interaction explains the alternation of distances between pairs of atoms separated by two bonds in conjugated molecules.

Entropy and heat capacity in the generalized Bose–Einstein condensation theory of superconductors

2019 ◽  
Vol 33 (26) ◽  
pp. 1950311
Author(s):  
L. A. García ◽  
M. de Llano
Keyword(s):  
Heat Capacity ◽  
Energy Gap ◽  
Coupling Parameter ◽  
Bcs Theory ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Total Electron ◽  
Bose Einstein Condensation ◽  
Unpaired Electrons ◽  
Bose Einstein

The new generalized Bose–Einstein condensation (GBEC) quantum-statistical theory starts from a noninteracting ternary boson-fermion (BF) gas of two-hole Cooper pairs (2hCPs) along with the usual two-electron Cooper pairs (2eCPs) plus unpaired electrons. Here we obtain the entropy and heat capacity and confirm once again that GBEC contains as a special case the Bardeen–Cooper–Schrieffer (BCS) theory. The energy gap is first calculated and compared with that of BCS theory for different values of a new dimensionless coupling parameter n/n[Formula: see text] where n is the total electron number density and n[Formula: see text] that of unpaired electrons at zero absolute temperature. Then, from the entropy, the heat capacity is calculated. Results compare well with elemental-superconductor data suggesting that 2hCPs are indispensable to describe superconductors (SCs).

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