New Series of Triply Bridged Dinuclear Cu(II) Compounds: Synthesis, Crystal Structure, Magnetic Properties, and Theoretical Study

Abstract

Five new triply bridged dinuclear Cu(II) compounds have been synthesized, and their magnetic properties have been measured and characterized. The magnetic coupling constants (J) of these compounds plus a previously structurally characterized compound of the same type have been derived by appropriate fitting of the experimentally measured molar susceptibility variation with the temperature. Two of the compounds are ferromagnetically coupled, and three are antiferromagnetically coupled with J values in the [+150, -40] cm(-1) range. The validity of the structural aggregate Addison's parameter as a qualitative magneto-structural correlation is confirmed. The origin of the magnetic interactions and the magnitude of the magnetic coupling have been analyzed by means of density functional theory-based calculations using a variety of state of the art exchange-correlation potentials. It is shown that the long-range separated LC-ωPBE provides the overall best agreement with experiment for this family as well as for a set of previously reported hetero triply bridged dinuclear Cu(II) compounds, especially for ferromagnetic systems.

Hetero triply-bridged dinuclear copper(ii) compounds with ferromagnetic coupling: a challenge for current density functionals

“…The DFT calculations have revealed that, for ferromagnetic class B compounds, the calculated J values almost quantitatively correlate with the sum of Addison's t parameter 13 of each Cu(II) ion. The calculated and experimental J values of all compounds are in agreement, 12 especially for the long-range separated hybrid LC-oPBE method. 14 In particular, the DFT calculations properly reproduce the magnitude of the magnetic coupling constants in the whole range of topologies studied.…”

“…The electron density was described either explicitly considering all electrons or using small core (LANL2) effective core potential (ECP) for the Cu atoms which allows one to take scalar relativistic effects into account. For the all electron calculations we used a rather large standard basis set of Gaussian Type Orbitals (GTO) which is the same as in previous works 11,12 and is defined as follows: 6-3111+G…”

“…S1-S6 (ESI †). For comparison purposes, the structural data of compounds 1-7 and of some other relevant hetero triply-bridged dinuclear Cu(II) compounds previously studied 10,12 are summarized in Table 1.…”

“…Clearly, compounds with strong ferromagnetic coupling are of great interest for potential technological applications. [4][5][6][7][8][9][10][11][12] Among the different Cu(II) families with ferromagnetic properties, previous work has focused on the design, magnetic properties and magneto-structural correlations of the hetero triply-bridged dinuclear Cu(II) systems because this particular type of compound exhibits moderate to strong ferromagnetic interactions. [6][7][8][9][10] In this type of system, the magnetic interaction occurs via bridging ligands, although various pathways are possible, 10 which depend on the coordination geometry of the Cu(II) ion, the CuÁ Á ÁCu separation, the bond angles involving the bridging atoms, the dihedral angle between the planes containing the Cu(II) ions and the distance from the Cu(II) to the bridging ligands.…”

“…10 However, to obtain more quantitative relationships it is necessary to go beyond the semiempirical EH method and to make use of more reliable electronic structure methods as demonstrated by recent studies on other triply bridged dinuclear Cu(II) compounds which employed state of art density functional theory (DFT) based methods. 11,12 Six different exchange-correlation functionals have been used in order to fully understand the magnetostructural correlation and also to accurately predict the broad range of magnetic coupling constant (J) values exhibited by class B and class F compounds with ferro-and antiferromagnetic behavior, respectively. The DFT calculations have revealed that, for ferromagnetic class B compounds, the calculated J values almost quantitatively correlate with the sum of Addison's t parameter 13 of each Cu(II) ion.…”