Electron self-exchange study of the coordination-number-invariant pentacoordinate copper(I/II) couple [CuI,II((5-meimidh)2DAP)]+/2+

Ligand dynamics in tetracoordinate copper(I) complexes of bis(pyrazolyl)pyridine ligands †

“…However, the variable temperature 1 H NMR studies in solution indicate the inequivalence of the methylene protons with a weak coupling between them (δ > J). [18][19][20] Exchange narrowing at high temperatures reveals the equivalence of two protons of the methylene group due to dynamic exchange. Coalescence occurs at 298 (±2) K for all these compounds though the chemical shifts for the methylene protons are different (cf.…”

“…As a result, there is little variation in the coalescence temperature and hence the thermodynamic parameters in the different solvents. [18][19][20] Simulation and estimation of energy barrier and thermodynamic parameters. Line shape analyses have been carried out using a modified version of DNMR 5.…”

“…Though no quantitative comparison of thermodynamic parameters can be made, a gross look at the derived parameters shows that they are comparable to such data obtained for similar compounds. 20 The increase in activation barrier energy in the order 4 < 3 < 2 is understandable since the replacement of phenyl by Bu n should facilitate the Cu᎐P free rotation. As expected this energy for 6 is much less than that for 2 because of the absence of a methyl group in the former.…”

Electron exchange kinetics in a tetrahedrally coordinated copper(II)/(I) couple

“…The ligand exchange rate data in Table 2 are presented as rate constants k, with the assumption that the exchange is first order with respect to each of Cu(dpym),-and Hdpym (i.e., a = b = 1 in eq. [6]). The useful ranges of Hdpym and Cu(dpym); concentrations were limited on the one hand by the need to have enough solute to give accurately measurable spectra, and on the other by the narrowing of the linewidth with increasing concentrations when working at the fast exchange limit of the NMR linewidth technique.…”

“…If, however, the coordination environments of the CU' and CU" partners are constrained to be similar, the intermediates of the square scheme become virtually identical, the Marcus cross relationship (2) should be valid, and the CU"" self-exchange should be fast. In synthetic CU" couples, this is most readily achieved when five-coordination is enforced in both the CU' and CU" partners (kex >lo4 L mol-I s-l) (6). The efficacy of Cubased biological redox reagents may be understood on this basis -except that in the case of the type I or "blue" copper proteins (azurins, plastocyanins, stellacyanins, etc.)…”