Copper(II) Complexes with New Polypodal Ligands Presenting Axial−Equatorial Phenoxo Bridges {2-[(Bis(2-pyridylmethyl)amino)methyl]-4-methylphenol, 2-[(Bis(2-pyridylmethyl)amino)methyl]-4-methyl-6-(methylthio)phenol}:  Examples of Ferromagnetically Coupled Bi- and Trinuclear Copper(II) Complexes

Abstract

Two new ligands, 2-[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol (HL) and 2-[(bis(2-pyridylmethyl)amino)methyl]-4-methyl-6-(methylthio)phenol (HSL), were synthesized and were used to prepare the trinuclear copper(II) complex {[CuSL(Cl)]2Cu}(PF6)2.H2O (1) and the corresponding binuclear complexes [Cu2(SL)2](PF6)2 (2) and [Cu2L2](PF6)2 (3). The crystal structure of 1 shows two different coordination environments: two square base pyramidal centers (Cu1 and Cu1a, related by a C2 axes), acting as ligands of a distorted square planar copper center (Cu2) by means of the sulfur atom of the SCH3 substituent and the bridging phenoxo oxygen atom of the ligand (Cu2-S = 2.294 A). Compounds 2 and 3 show two equivalent distorted square base pyramidal copper(II) centers, bridged in an axial-equatorial fashion by two phenoxo groups, thus defining an asymmetric Cu2O2 core. A long copper-sulfur distance measured in 2 (2.9261(18) A) suggests a weak bonding interaction. This interaction induces a torsion angle between the methylthio group and the phenoxo plane resulting in a dihedral angle of 41.4(5) degrees. A still larger distortion is observed in 1 with a dihedral angle of 74.0(6) degrees. DFT calculations for 1 gave a ferromagnetic exchange between first neighbors interaction, the calculated J value for this interaction being +11.7 cm-1. In addition, an antiferromagnetic exchange for 1 was obtained for the second neighbor interaction with a J value of -0.05 cm-1. The Bleaney-Bowers equation was used to fit the experimental magnetic susceptibility data for 2 and 3; the best fit was obtained with J values of +3.4 and -16.7 cm-1, respectively. DFT calculations for 2 and 3 confirm the nature and the values of the J constants obtained by the fit of the experimental data. ESR and magnetic studies on the reported compounds show a weak exchange interaction between the copper(II) centers. The low values obtained for the coupling constants can be explained in terms of a poor overlap between the magnetic orbitals, due to the axial-equatorial phenoxo bridging mode observed in these complexes.

Carboxylic decorated Schiff base complexes as metallotectons for hydrogen bonded 3D networks

“…This superexchange pathway, which does not seem very effective, has been less studied than the equatorial one. In spite of this, there are several examples of this kind of magnetic interaction reported in the literature that indicate that it should promote a small (ferro- [34] or antiferromagnetic [34][35]) or null [36] magnetic exchange. Thus, this is in agreement with the low -2J value found for 1, which does not merit further consideration.…”

Tetranuclear Copper(II) Complexes Bearing Cu4O6 and Cu4O4 Cores: Synthesis, Structure, Magnetic Properties, and DFT Study

“…It has also been stated that when the copper centers are connected axially by a bridging phenoxido group, they exhibit very weak ferro-and antiferromagnetic or no interaction. [26][27][28] Thus, in our case, the magnetic exchange is mediated principally through alkoxido bridges. Both theoretical and experimental studies have shown that the major factor controlling the magnetic exchange interaction in dialkoxido-bridged dicopper(II) complexes is the value of the Cu-O-Cu angle and a linear variation of J with θ (the Cu-O-Cu angle).…”

“…Therefore, the magnetic exchange coupling mediated by the phenoxido-bridge magnetic pathway should be very small. [26][27][28] In view of this, in a first approach, only the J 1 parameter for the alkoxido-bridge pathway was considered. The χ M T versus T data were simulated through a full-matrix diagonalization method by using the MAGPACK [29] program with the above Hamiltonian and J 2 = 0 cm -1 .…”

A Review on Some Trinuclear Copper Complexes

“…9-11 Additionally, there is an increasing interest in studying the cyclic trinuclear copper(II) complexes because they can be geometrically frustrated systems which offer the opportunity to examine magnetic exchange models such as spin frustration, spin delocalization, or antisymmetric exchange. and co-workers 17 as DNA nucleases and cytotoxic agents. Complex 3 shows its DNA cleavage activity in absence of any external coreductant.…”