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Issue 16, 2020
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Exchange couplings and quantum phases in two dissimilar arrays of similar copper dinuclear units

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Abstract

To investigate the magnetic properties and the spin entanglement of dinuclear arrays, we prepared compounds [{Cu(pAB)(phen)H2O}2·NO3·pABH·2H2O], 1, and [Cu2(pAB)2(phen)2pz]n, 2 (pABH = p-aminobenzoic acid, phen = 1,10-phenanthroline and pz = pyrazine). The structure of 1 is known and we report here that of 2. They contain similar dinuclear units of CuII ions with 1/2-spins S1 and S2 bridged by pairs of pAB molecules, with similar intradinuclear exchange Image ID:d0dt00567c-t1.gif and fine interactions Image ID:d0dt00567c-t2.gif, but different 3D crystal arrays with weak interdinuclear exchange J′, stronger in 2 than in 1. To investigate the magnetic properties and the spin entanglement produced by J′, we collected the powder spectra of 1 and 2 at 9.4 GHz and T between 5 and 298 K, and at 34.4 GHz and T = 298 K and single-crystal spectra at room T and 34.4 GHz as a function of magnetic field (B0) orientation in three crystal planes, calculating intradinuclear magnetic parameters J(1)0 = (−75 ± 1) cm−1, J(2)0 = (−78 ± 2) cm−1, |D(1)| = (0.142 ± 0.006) cm−1, |D(2)| = (0.141 ± 0.006) cm−1 and E(1)E(2) ∼ 0. Single crystal data indicate a quantum entangled phase in 2 around the crossing between two fine structure EPR absorption peaks within the spin triplet. This phase also shows up in powder samples of 2 as a U-peak collecting the signals of the entangled microcrystals, a feature that allows estimating |J′|. Transitions between the two quantum phases are observed in single crystals of 2 changing the orientation of B0. We estimate interdinuclear exchange couplings |J(1)| < 0.003 cm−1 and |J(2)| = (0.013 ± 0.005) cm−1, in 1 and 2, respectively. Our analysis indicates that the standard approximation of a spin Hamiltonian with S = 1 for the dinuclear spectra is valid only when the interdinuclear coupling is large enough, as for compound 2 (|J(2)/J(2)0| ∼ 1.7 × 10−4). When J′ is negligible as in 1, the real spin Hamiltonian with two spins 1/2 has to be used. Broken-symmetry DFT predicts correctly the nature and magnitude of the antiferromagnetic exchange coupling in 1 and 2 and ferromagnetic interdinuclear coupling for compound 2.

Graphical abstract: Exchange couplings and quantum phases in two dissimilar arrays of similar copper dinuclear units

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Supplementary files

Article information


Submitted
15 Feb 2020
Accepted
12 Mar 2020
First published
02 Apr 2020

This article is Open Access

Dalton Trans., 2020,49, 5228-5240
Article type
Paper

Exchange couplings and quantum phases in two dissimilar arrays of similar copper dinuclear units

R. P. Sartoris, V. T. Santana, E. Freire, R. F. Baggio, O. R. Nascimento and R. Calvo, Dalton Trans., 2020, 49, 5228
DOI: 10.1039/D0DT00567C

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