spin counting
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2021 ◽  
Author(s):  
Nicolaas P. van Leest ◽  
Bas de Bruin

Cobalt-porphyrin complexes are established catalysts for carbene and nitrene radical group transfer reactions. The key carbene, mono- and bis-nitrene radical complexes coordinated to [Co(TPP)] (TPP = tetraphenylporphyrin) have previously been investigat-ed with a variety of experimental techniques and supporting (single-reference) DFT calculations that indicated doublet (S = ½) ground states for all three species. In this contribution we revisit their electronic structures with multireference NEVPT2-CASSCF calculations to investigate possible multireference contributions to the ground state wavefunctions. The carbene ([Co<sup>III</sup>(TPP)(•CHCO<sub>2</sub>Et)]) and mono-nitrene ([Co<sup>III</sup>(TPP)(•NNs)]) radical complexes were confirmed to have uncomplicated doublet ground states, although a higher carbene or nitrene radical character and a lower Co‒C/N bond order was found in the NEVPT2-CASSCF calculations. Supported by EPR analysis and spin counting, paramagnetic molar susceptibility determination and NEVPT2-CASSCF calculations, we report that the cobalt-porphyrin bis-nitrene complex ([Co<sup>III</sup>(TPP•)(•NNs)<sub>2</sub>]) has a quartet (S = 3/2) spin ground state, with a thermally assessable multireference & multideterminant ‘broken-symmetry’ doublet spin excited state. A spin flip on the porphyrin-centered unpaired electron allows for interconversion between the quartet and broken-symmetry doublet spin states, with an approximate 10- and 200-fold higher Boltzmann population of the quartet at room tempera-ture or 10 K, respectively.<br>



2021 ◽  
Author(s):  
Nicolaas P. van Leest ◽  
Bas de Bruin

Cobalt-porphyrin complexes are established catalysts for carbene and nitrene radical group transfer reactions. The key carbene, mono- and bis-nitrene radical complexes coordinated to [Co(TPP)] (TPP = tetraphenylporphyrin) have previously been investigat-ed with a variety of experimental techniques and supporting (single-reference) DFT calculations that indicated doublet (S = ½) ground states for all three species. In this contribution we revisit their electronic structures with multireference NEVPT2-CASSCF calculations to investigate possible multireference contributions to the ground state wavefunctions. The carbene ([Co<sup>III</sup>(TPP)(•CHCO<sub>2</sub>Et)]) and mono-nitrene ([Co<sup>III</sup>(TPP)(•NNs)]) radical complexes were confirmed to have uncomplicated doublet ground states, although a higher carbene or nitrene radical character and a lower Co‒C/N bond order was found in the NEVPT2-CASSCF calculations. Supported by EPR analysis and spin counting, paramagnetic molar susceptibility determination and NEVPT2-CASSCF calculations, we report that the cobalt-porphyrin bis-nitrene complex ([Co<sup>III</sup>(TPP•)(•NNs)<sub>2</sub>]) has a quartet (S = 3/2) spin ground state, with a thermally assessable multireference & multideterminant ‘broken-symmetry’ doublet spin excited state. A spin flip on the porphyrin-centered unpaired electron allows for interconversion between the quartet and broken-symmetry doublet spin states, with an approximate 10- and 200-fold higher Boltzmann population of the quartet at room tempera-ture or 10 K, respectively.<br>





Author(s):  
C. M. Sánchez ◽  
P. R. Levstein ◽  
L. Buljubasich ◽  
H. M. Pastawski ◽  
A. K. Chattah

In this work, we overview time-reversal nuclear magnetic resonance (NMR) experiments in many-spin systems evolving under the dipolar Hamiltonian. The Loschmidt echo (LE) in NMR is the signal of excitations which, after evolving with a forward Hamiltonian, is recovered by means of a backward evolution. The presence of non-diagonal terms in the non-equilibrium density matrix of the many-body state is directly monitored experimentally by encoding the multiple quantum coherences. This enables a spin counting procedure, giving information on the spreading of an excitation through the Hilbert space and the formation of clusters of correlated spins. Two samples representing different spin systems with coupled networks were used in the experiments. Protons in polycrystalline ferrocene correspond to an ‘infinite’ network. By contrast, the liquid crystal N -(4-methoxybenzylidene)-4-butylaniline in the nematic mesophase represents a finite proton system with a hierarchical set of couplings. A close connection was established between the LE decay and the spin counting measurements, confirming the hypothesis that the complexity of the system is driven by the coherent dynamics.



2014 ◽  
Vol 66 ◽  
pp. 115-120 ◽  
Author(s):  
Yuuki Mogami ◽  
Satoru Yamazaki ◽  
Shinya Matsuno ◽  
Kunio Matsui ◽  
Yasuto Noda ◽  
...  




2014 ◽  
Vol 378 (11-12) ◽  
pp. 892-898 ◽  
Author(s):  
JunYan Luo ◽  
Jing Hu ◽  
Xiaoli Lang ◽  
Yu Shen ◽  
Xiao-Ling He ◽  
...  


2013 ◽  
Vol 236 ◽  
pp. 31-40 ◽  
Author(s):  
Gholamhasan Teymoori ◽  
Bholanath Pahari ◽  
Elumalai Viswanathan ◽  
Mattias Edén


2013 ◽  
Vol 53 ◽  
pp. 27-37
Author(s):  
Yelena Zelenova ◽  
Steven W. Morgan ◽  
Gregory S. Boutis
Keyword(s):  


2008 ◽  
Vol 78 (6) ◽  
Author(s):  
Sibylle Braungardt ◽  
Aditi Sen(De) ◽  
Ujjwal Sen ◽  
Roy J. Glauber ◽  
Maciej Lewenstein


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