Proton NMR Spectroscopy and Magnetic Properties of a Solution-Stable Dicopper(II) Complex Bearing a Single μ-Hydroxo Bridge

Abstract

The reaction of copper(II) perchlorate with the macrocyclic ligand [22]py4pz in the presence of base leads to formation of a dinuclear complex [Cu(2)([22]py4pz)(mu-OH)](ClO(4))(3)xH(2)O, in which two copper ions are bridged by a single mu-hydroxo bridge. Each copper ion is further surrounded by four nitrogen atoms of the ligand. The mu-hydroxo bridge mediates a strong antiferromagnetic coupling (2J = -691(35) cm(-1)) between the metal centers, leading to relatively sharp and well-resolved resonances in the (1)H NMR spectrum of the complex in solution. We herein report the crystal structure, the magnetic properties, and the full assignment of the hyperfine-shifted resonances in the NMR spectrum of the complex, as well as the determination of the exchange coupling constant in solution through temperature-dependent NMR studies.

Catecholase Activity of a Copper(II) Complex with a Macrocyclic Ligand: Unraveling Catalytic Mechanisms

“…However, it is liable that in the course of the catalytic reaction the original dicopper(II) core undergoes substantial modification, as the carbonate bridge is likely to be cleaved by the incoming catecholate, as proposed in Scheme 1. Our earlier studies on other dicopper complexes with structurally related macrocyclic ligands [38,39] indicate that the macrocyclic cavity has a sufficient flexibility to bring two copper ions within a short distance of each other, required for a didentate bridging coordination mode of catechol. As a result, in the absence of the rigid carbonate bridge the substrate can bind to both copper(II) ions in a bridging fashion, pushing the catalytic reaction towards the cycle B, whereas the relative influence of mechanistic pathway A becomes negligible after a few minutes of the reaction.…”

A Dissymmetric, Singly Phenoxido-Bridged Cu∥ Dinuclear Coordination Compound: Synthesis, Characterisation, Magnetic and Computational Study

“…[40][41][42] For instance, only one example of a dicopper unit bridged by a single hydroxide-ligand has been reported so far together with its magnetic properties. 43 As mentioned above, the coordination environment around Cu1 is square pyramidal, while Cu2 exhibits a distorted octahedral geometry. In both cases, the unpaired electron occupies mainly the d x 2…”

Self-Assembly of an Infinite Copper(II) Chiral Metallohelicate

“…The value of J 2 is consistent with the value of the hydroxido bridge and the coordination environments of Cu1 and Cu2. 28 Thus, while the high temperature behavior of 1 is dominated by the strong antiferromagnetic interaction through the hydroxide bridge, below ca. 55 K, 1 can be depicted as a unidimensional assembly of antiferromagnetically coupled S ) 1/2 spins.…”

“…A Curie-Weiss fit of the high temperature area (250-350 K, see Figure S6 of the Supporting Information) results in a large negative θ of -290 K and a low Curie-Weiss constant of 1.54 cm 3 mol -1 , both in agreement with strong antiferromagnetic interactions active at these temperatures. The presence in the trinuclear core of 1 of a single hydroxido bridge with a rather large Cu-O-Cu angle [Cu1-47-u2 ) 137.0(2)°] would account for the dominant strong antiferromagnetic coupling observed, 28 while exchange coupling through the Biim 2-bridges is also expected to be antiferromagnetic in nature, albeit weaker. 29 These interactions would then result in an isosceles Cu(II) triangle (considering the Cu1-Cu3 and Cu2-Cu3 pairs to be similar) presenting at low temperatures a doublet ground state, as observed down to 20 K. The further decrease at lower temperatures can then only be ascribed to weak carboxylato bridges along the helix between Cu 3 units.…”