EPR Data on Ni(II) Doped Cu(II) Acetate Monohydrate Single Crystals: Evidence of Ni²⁺ — Cu²⁺ Exchange-Coupled Pairs

Abstract

Electron paramagnetic resonance measurements on nickel(II) doped copper(II) acetate monohydrate single crystals have been made. In the liquid helium temperature range, spectra have been observed which may be assigned to Ni2+-C u2+ strongly coupled mixed pairs in the state of total spin S= 1/2. This result represents a definite difference of magnetic behaviour from the case of the nickel(II) doped dicopper(II) tetra(J u-benzoato-0.0')bis(quinoline) complex, which has the same sandwich dimeric structure but shows spectra indicative of a S=3/2 state. Apart from this difference, unusual EPR data are found such as pronounced misalignments of g with respect to the relevant pair axes and very large values of the hyperfine coupling constant of the copper nucleus, which characteristically recall that case.

Synthesis and Characterization of Cu–Ni Mixed Metal Paddlewheels Occurring in the Metal–Organic Framework DUT-8(Ni0.98Cu0.02) for Monitoring Open-Closed-Pore Phase Transitions by X-Band Continuous Wave Electron Paramagnetic Resonance Spectroscopy

“…For an interpretation of the observed S = 3/2 species as ferromagnetically coupled Cu 2+ S A = 1/2 and Ni 2+ S B = 1 electron spins, , selective signals were simulated with EasySpin using the fundamental spin Hamiltonian , Here, Ĥ S A and Ĥ S B are the single ion Hamiltonians of the Cu 2+ and Ni 2+ . The parameter J AB is a scalar describing the isotropic spin–spin interaction, d AB is a polar vector describing the antisymmetric spin–spin interaction and D AB is a symmetric traceless tensor describing the anisotropic spin–spin interaction.…”

“…Consequently, one expects that bimetallic Ni 2+ -Cu 2+ units have either an electron spin S = 1/2 or S = 3/2, which can be detected by EPR. 50,51 Also dimeric Cu 2+ -Cu 2+ species are expected to be EPR active. EPR spectra of antiferromagnetically coupled Cu 2+ -Cu 2+ paddlewheel units in several MOFs have already been reported.…”

“…Monomeric Cu 2+ has a 3d 9 electron configuration and therefore an electron spin S = 1/2. Consequently, one expects that bimetallic Ni 2+ -Cu 2+ units have either an electron spin S = 1/2 or S = 3/2, which can be detected by EPR. , Also dimeric Cu 2+ -Cu 2+ species are expected to be EPR active. EPR spectra of antiferromagnetically coupled Cu 2+ -Cu 2+ paddlewheel units in several MOFs have already been reported. − Accordingly, we also present first EPR results obtained for the pure DUT-8­(Cu) MOF.…”

“…spins,50,51 selective signals were simulated with EasySpin 56 using the fundamental spin Hamiltonian61,62 …”