Electron-spin delocalization in antiferromagnetic dimeric copper(II) benzoates

Abstract

The copper(II) salts of benzoic acid, o-, m-, and ^-methylbenzoic acid, and 2,6-dimethyl-and 3,5-dimethylbenzoic acid exist as dimers with reduced magnetic moments in acetone solution at room temperature. The solution nmr spectra of these compounds, as well as of [Cu(formate)z•urea]2 and [CuiacetateVureaL, exhibit quite large contact shifts of the proton resonances, consistent with a superexchange mechanism for the spin exchange. The pattern of signs of the contact shifts suggests that spin delocalization from the copper ions is into the bonding system of the carboxylate groups, although finite spin densities also appear in the systems of the aromatic rings, possibly via hyperconjugation.

Paramagnetic Properties of the Halide‐Bound Derivatives of Oxidised Tyrosinase Investigated by 1H NMR Spectroscopy

“…[9][10][11][12][13][14] ), as well as Cu 2 + -substituted aminopeptidase, [9] appear to give relatively sharp NMR signals. As in the case of Ty, these Cu 2 compounds carry two closely spaced magnetically coupled copper atoms.…”

Synthesis, Structure, Magnetic Properties, and 1H NMR Studies of a Moderately Antiferromagnetically Coupled Binuclear Copper(II) Complex

“…Although NMR spectroscopy has been successfully used to investigate the structural and bonding properties of metal complexes, NMR studies of paramagnetic copper(II) complexes are fewer due to their inherent slow electronic relaxation time, leading to broadened signals . On the other hand, antiferromagnetically coupled copper(II) complexes are expected to give relatively narrow NMR signals. − However, there are still few reports that demonstrate the usefulness of NMR spectra of binuclear Cu(II) complexes in solution. − …”

Characterization of the Structural and Electronic Properties of Spin-Coupled Dinuclear Copper(II) Centers by Proton NMR Spectroscopy

“…13,141 H NMR spectra have been reported for antiferromagnetically and ferromagnetically coupled systems and both provide relatively sharp, hyperfine shifted 1 H NMR signals. 13,[15][16][17][18][19][20][21][22][23] However, the majority of the studies reported to date have relied on laborious synthetic methods such as substitution or deuteration to assign only a portion of the observed isotropically shifted signals. Therefore, 1 H NMR spectroscopy has been of little utility as a structural or magnetic probe of dicopper(II) centers.…”