Oligomeric approach to 2D materials modeling

Oligomeric approach has been originally developed to study electronic properties of conjugated polymers. This approach allows to access electronic properties of 1D systems otherwise difficult to calculate. We successfully extended this method to study electronic properties of 2D materials. In this review we summarize our recent work in this area. It has been established that large graphene nanoflake possess multiconfigurational singlet or even high spin ground state. Doping of 2D systems has also been explored and it has been demonstrated that doping allows to tune their electronic properties, including ionization potentials, electron affinities, reorganization energies and the very nature of the ground state. The electronic properties of novel 2D allotropies of carbon, phosphorus, germanium and silicon have been studied as well as their complexes with Li. Heterostructures, of different 2D allotropies are readily formed. This is an alternative method for tuning of their electronic properties.

Unexpected Light-Induced Thermal Hysteresis in Matrix Embedded Low Cooperative Spin Crossover Microparticles

The embedding of spin-crossover micro- or nanocrystals in various surroundings dramatically changes their functionalities based on first-order spin transitions. The dampening of their internal cooperativity, together with introducing a new kind of interactions occurring at interfaces between spin-crossover particles and their environment, results in spectacular effects, as an enhanced hysteresis with non-cooperative transitions. In this work, we deal with the influence of the embedding matrix on the light-induced thermal hysteresis (LITH) in the case of spin-crossover microparticles of Fe(phen)2(NCS)2. Despite the low cooperativity of this compound, the competition between the continuous photoexcitation towards the metastable high spin state and the relaxation down to low spin ground state leads to a light-induced thermal hysteresis, with a quasi-static width of around 10 K. This unexpected hysteresis is explained by considering a switch-on/cutoff mechanism of the particle–matrix interactions in the framework of a mean-field approach based on negative external pressures, with Gaussian distributed variations and of an Ising-like model with various interactions with the environment. Additional first-order reversal curves measurements and corresponding calculated distributions are in line with relaxations under light and confirm the existence of a non-kinetic LITH.

Revisiting the Electronic Structure of Cobalt-Porphyrin Nitrene and Carbene Radicals with NEVPT2-CASSCF Calculations: Doublet versus Quartet Ground States

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^III(TPP)(•CHCO₂Et)]) and mono-nitrene ([Co^III(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^III(TPP•)(•NNs)₂]) 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>

Revisiting the Electronic Structure of Cobalt-Porphyrin Nitrene and Carbene Radicals with NEVPT2-CASSCF Calculations: Doublet versus Quartet Ground States

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^III(TPP)(•CHCO₂Et)]) and mono-nitrene ([Co^III(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^III(TPP•)(•NNs)₂]) 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>

Controlled Synthesis, Characterization and Magnetic Properties of Unsymmetrical Heterodinuclear CuIIMII (M = Co, Mn and Cd) Complexes in Alkoxo Bridged Acyclic Ligand Environment

This work reports the syntheses of heterodinuclear Cu(II)-Co(II), Cu(II)-Mn(II) and Cu(II)-Cd(II) complexes following a convenient single-pot synthetic procedure using the two asymmetric binucleating ligands. Site-specificity offered by one of the ligands' arms towards Cu(I) center has been successfully exploited here, avoiding all sorts of impending scrambling reactions. X-ray crystallography and ESImass spectral studies have been used to prove the exclusivity of these products. Magnetic studies at variable temperatures (4-300 K) have been proved inadequate to assign any spin-ground state for Cu(II)-Co(II) and Cu(II)-Mn(II) compounds.

Deciphering the origin of variation in the spin ground state and oxidation state of a {Mn19} cluster on a Au(111) surface: is the Au(111) surface innocent?

Modeling the structure of a {Mn19} cluster on an Au(111) surface reveals that exchange coupling constants vary grossly upon adsorption due to surface-induced structural distortions. This leads to significant variations in the ground state S values.

A triple-triangle cluster derived from a simple tridentate ligand

An iron(iii) complex [Fe7] with a corner-shared triple-triangle core structure shaped like a three-leaf clover has S = 19/2 spin ground state.