Pere Alemany

Broken symmetry approach to calculation of exchange coupling constants for homobinuclear and heterobinuclear transition metal complexes

The application of broken symmetry density functional calculations to homobinuclear and heterobinuclear transition metal complexes produces good estimates of the exchange coupling constants as compared to experimental data. The accuracy of different hybrid density functional theory methods was tested. A discussion is presented of the different methodological approaches that apply when a broken symmetry wave function is used with either Hartree–Fock or density functional calculations. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1391–1400, 1999

About the calculation of exchange coupling constants in polynuclear transition metal complexes

The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H · · · He and CH2 · · · He units to compare with Hartree–Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data.

Exchange Coupling in Carboxylato-Bridged Dinuclear Copper(II) Compounds: A Density Functional Study

A computational study of the exchange coupling is presented for a selected sample of carboxylato-bridged dinuclear copper(II) compounds. Model calculations have been used to examine the influence of several factors on the coupling constants: a) the electron-withdrawing power of the bridging ligands; b) the nature of the axial ligands; c) the number of bridging carboxylato groups; d) some structural distortions frequently found in this family of compounds; and e) the coordination mode of the carboxylato bridge. Coupling constants calculated for some complete structures, as determined by X-ray diffraction, are in excellent agreement with experimental data, confirming the ability of the computational strategy used in this work to predict the coupling constant for compounds for which experimental data are not yet available.

Exchange Coupling in Oxalato-Bridged Copper(II) Binuclear Compounds: A Density Functional Study

A recently developed computational strategy is applied to examine the influence of several factors on the exchange coupling constants of oxalato-bridged copper(II) binuclear complexes (shown schematically here); molecular topology, the nature of terminal ligands and selected structural parameters are discussed.

Density functional study of magnetostructural correlations in cubane complexes containing the Cu4O4 core

A study of the magnetostructural correlations in polynuclear complexes containing a Cu4O4 cubane structure has been carried out employing theoretical calculations based on Density Functional Theory. We have analyzed independently the magnetic properties of three different families of cubane complexes, classified according to the number of short and long Cu⋯Cu distances as 2 + 4, 4 + 2 or 6 + 0. The results indicate that coupling through four short Cu–O bridges can be from weakly ferromagnetic to strongly antiferromagnetic, while that through two or three short bridges can be from moderately ferromagnetic to weakly antiferromagnetic.

Calculation of exchange coupling constants in solid state transition metal compounds using localized atomic orbital basis sets

Abstract The application of theoretical methods based on density functional theory using hybrid functionals and localized, atomic orbital type basis sets is shown to provide good estimates for exchange coupling constants in non-metallic, solid state transition metal compounds with relatively complex crystal structures. The accuracy of the calculated exchange coupling constants is similar to that previously obtained for dinuclear and polynuclear molecular compounds. As an application of this procedure, the magnetic properties of the high-temperature phase of CuGeO 3 , the recently synthesized silver copper oxide Ag 2 Cu 2 O 3 , and the family of M [N(CN) 2 ] 2 ( M =Cr(II), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II)) compounds are analyzed via the computation of their most relevant exchange coupling constants.

Density functional study of the exchange coupling in distorted cubane complexes containing the Cu4O4 core

A density functional study of the exchange coupling in two complexes with cubane structure is presented. One of them can be considered as a pair of binuclear hydroxo-bridged Cu(II) complexes and the second one is an alkoxo-bridged distorted cubane with S4 symmetry. In the former complex, the ferromagnetic coupling is due to the nature of the hydroxo bridges, whereas in the latter the distortion of the Cu4O4 core induces ferromagnetic couplings despite the usual antiferromagnetic behavior expected for the alkoxo bridges.

Continuous chirality measures in transition metal chemistry

The definition of the continuous chirality measure(CCM) is provided and its applications are summarized in this tutorial review, with special emphasis on the field of transition metal complexes. The CCM approach, developed in recent years, provides a quantitative parameter that evaluates the degree of chirality of a given molecule. Many quantitative structural correlations with chirality have been identified for most of the important families of metal complexes. Our recent research has shown that one can associate the chirality measures with, e.g., enantioselectivity in asymmetric catalysis. We also explore a fragment approach to chirality in which we investigate which part of a molecule is responsible for the chirality-associated properties of a given family of compounds.

Analytical Methods for Calculating Continuous Symmetry Measures and the Chirality Measure

We provide analytical solutions of the Continuous Symmetry Measure (CSM) equation for several symmetry point‐groups, and for the associated Continuous Chirality Measure (CCM), which are quantitative estimates of the degree of a symmetry‐point group or chirality in a structure, respectively. We do it by solving analytically the problem of finding the minimal distance between the original structure and the result obtained by operating on it all of the operations of a specific G symmetry point group. Specifically, we provide solutions for the symmetry measures of all of the improper rotations point group symmetries, Sn, including the mirror (S1, CS), inversion (S2, Ci) as well as the higher Sns (n > 2 is even) point group symmetries, for the rotational C2 point group symmetry, for the higher rotational Cn symmetries (n > 2), and finally for the Cnh symmetry point group. The chirality measure is the minimal of all Sn measures.

Symmetry operation measures

We introduce a new mathematical tool for quantifying the symmetry contents of molecular structures: the Symmetry Operation Measures. In this approach, we measure the minimal distance between a given structure and the structure which is obtained after applying a selected symmetry operation on it. If the given operation is a true symmetry operation for the structure, this distance is zero; otherwise it gives an indication of how different the transformed structure is from the original one. Specifically, we provide analytical solutions for measures of all the improper rotations, S  np , including mirror symmetry and inversion, as well as for all pure rotations, C  np . These measures provide information complementary to the Continuous Symmetry Measures (CSM) that evaluate the distance between a given structure and the nearest structure which belongs to a selected symmetry point‐group.