Magnetic exchange interactions in transition metal dimers. III. Nickel(II) di-.mu.-cyanato, di-.mu.-thiocyanato, and di-.mu.-selenocyanato complexes and related outer-sphere copper(II) complexes

Abstract

increase the ICB effect. The reactions involving NiEDTA, Ni(trien), and NiBPEDA all have nickel-nitrogen bond rupture as rate determining while the ZnEDTA system involves copper-ligand bond formation as rate determining. Of the three possible explanations for the increased activity due to CuOH+, the first, an increase in the stability of the dinuclear intermediate, cannot explain why CuOH+ reacts at an accelerated rate with ZnEDTA because the dinuclear intermediate forms after the rate-determining step. The second explanation, a transition state, could explain all four systems but is based on the tenuous grounds of an acceleration in copper water loss due to hydroxide. The third possibility, however, fits all four cases since a hydrogen-bonded or hydroxidebridged intermediate would affect the values of Kos, the outer-sphere association constant, to the same extent that it would affect the stability of a dinuclear intermediate. Therefore it is suggested that this is the most likely explanation for the increased reactivity of CuOH+.

Determination of intermolecular copper–copper distances from the EPR half-field transitions and their comparison with distances from X-ray structures: applications to copper(II) complexes with biologically important ligands

“…EPR spectroscopy is a convenient and effective way to probe the electronic structure of paramagnetic molecules [1][2][3][4][5][6][7]. One parameter of interest that is obtainable by EPR in the case of paramagnetic molecules with two separated unpaired electrons is the distance between these two paramagnetic centers [1].…”

“…A simplified energy level diagram is shown in Fig. 1 [7]. In addition to the direct dipole-dipole interaction, an anisotropic exchange interaction can also contribute to D. Which of these two anisotropic effects makes the dominant contribution to D depends mostly on the distance between the spins.…”

Copper complexes with bibracchial lariat ethers: from mono- to binuclear structures

“…The EPR spectrum obtained for complex 6 shows at least seven peaks in the g region, which result from intramolecular magnetic exchange interactions between the two Cu(II) ions in the binuclear complex, as found for outer-sphere Cu(II) dimers [13] or other binuclear Cu(II) complexes bridged by aromatic moieties [14,15]. We were unable to detect DM S = 2 EPR transitions expected for a S% = 1 dimer [13] in any of the dimeric complexes. This could result from their very low intensity found when the Cu-Cu distance is larger than 5 A , , as found in the crystal structure of complex 5.…”

Synthesis, crystal structure and magnetism of a two-dimensional Ni(II) coordination polymer with thiocyanate anion and dehydrogen-1,10-phenanthrolin-2-ol as bridging ligands

“…Generally the magnetic couplings between bridging Ni(II) ions with thiocyanate as end-end bridge show weak ferromagnetic interactions with coupling constants from J ¼ 2.4 cm À1 to J ¼ 6.3 cm À1 [9, [16][17][18][19]. The fact that the present complex exhibits a weak anti-ferromagnetic interaction may indicate that the magnetic interaction between -Pheno bridging Ni(II) ions is a weak anti-ferromagnetic interaction, but its coupling intensity is stronger than that of thiocyanate bridging Ni(II), offsetting the ferromagnetic interaction, making the present complex exhibit a weak anti-ferromagnetic interaction.…”