Proton and deuterium magnetic resonance study of the aqueous nickelous complex

Abstract

The absorption signals of protons and deuterons in bound and nonbound water molecules in the aqueous nickelous system were observed. From the PMR and DMR measurements, the hyperfine coupling constants were calculated and found to be (1.3±0.1)×105 and (2.0±0.2)×104 Hz, respectively. The spin density at the proton (and deuteron) nuclei was calculated to be (2.9±0.3)×10−5 electrons/a.u.3, in accordance with theoretical expectations. The rate constant at 298°K for the exchange of water was found to be 3×104 sec−1, and the activation energy 12 kcal/mole. The relaxation time of the electron at 243°K, assuming T1e =T2e was found to be 1.9×10−12 sec and the activation ernergy 0.8 kcal/mole. The temperature dependence of the proton transverse relaxation rate was studied. It is suggested that in the absence of chemical exchange the transverse relaxation rate is governed both by the relaxation of the nickelous unpaired electrons and by the diffusional motion of the water molecules. Methods of estimating the diffusional correlation time are discussed.

Magnetic Properties of Ni2+(aq) from First Principles

“…The overall conclusion is that the signs and orders of magnitude are well-defined across the different levels of theory used, for the presently relevant HFC parameters other than A con ( 1 H). In light of these results, the agreement between the results from the experiment [ A con ( 1 H) = −0.13 MHz] and PBE (COSMO/COSMO for properties/structure; – 0.15 MHz; Table S2) should be considered rather fortuitous. The results show that it is important to account for solvation effects on the underlying molecular structures.…”

“…The same value was later adopted also in an EPR relaxation study of the aqueous solution of Ni 2+ . The values of 2.25 and 2.3 have been also used in NMR studies of aqueous Ni 2+ solutions (refs and , respectively). Our static DFT calculations using different ECFs as well as the dynamic simulation point to significantly smaller g values.…”

“…The results listed in Table 2 indicate that in the presence of the Ni 2+ ion the calculated 17 O shielding constant agrees with the experimental data of Neely and Connick 35 and to a somewhat lesser extent also with those of Fiat and Chmelnick, 38 whereas the simulated 1 H shielding constant does not reproduce the experimental data of Granot. 31 Table 5 lists the simulated contributions of the various physical mechanisms of pNMR shielding to the principal values σ ii (i = 1, 2, 3) of the shielding tensor. There are important contributions to the principal values beyond those that are significant for the isotropic values.…”

Kinetics and mechanism of oxidation of nickel(II) tetraazamacrocycles by the peroxydisulphate anion in aqueous and binary aqueous mixtures

“…The values fall in the range of 3-30 x lo3 s-I, which is close to the solvent exchange rate for water at Ni2+(aq) of 3 x lo4 s-' (23). It is reasonable to assume that like Ni2+(aq), interchange at the bis-aquo nickel(I1) tetraazamacrocycle will be dissociative, with an exchange rate that is fast relative to the rate- determining peroxy-bond fissure in our system.…”

Spin dynamics simulation of electron spin relaxation in Ni2 +(aq)

“…The lled circles correspond to simulations done without the uctuating part of the g tensor. The stars represent the available experimental results: T 1 = T 2 = 2.9 ps (blue) at B = 0 T [1], T 1 = 5.7 ps (blue) at 1.39 T at the temperature of 223 K [2], and T 1 = 3.4 ps (blue) (if T 1 T 2 ) and T 1 = 1.9 ps (red) (if T 1 = T 2 ) at 2.11 T and 243 K [3].…”