Magnetism and Structure in Chains of Copper Dinuclear Paddlewheel Units

Abstract

An anhydrous copper carboxylate compound of formula [Cu(trans-2-butenoate)(2)](n) has been characterized. X-ray analysis reveals a structure built by paddlewheel units bridged by pairs of Cu...O axial bonds to give infinite chains arranged in a new topological motif. Susceptibility measurements in the 10-300 K temperature range, and isothermal magnetization curves at 2, 5, 10, and 50 K with fields up to 5 T, were obtained. Electron Paramagnetic Resonance (EPR) spectra of powder samples were measured at 33.9 GHz at 300 K, and at 9.60 GHz at temperatures in the range 90 <or= T <or= 350 K. Fitting the susceptibility data to a chain model of alternating paddlewheel and [Cu(mu-O)(2)Cu] dinuclear units yielded exchange interactions J(1) = -330.6(1) cm(-1) and J(2) = 5.9(2) cm(-1). The EPR spectra reflect the usual antiferromagnetic dinuclear behavior, with zero field splitting parameters of the excited spin triplet, D = -0.329(3) cm(-1) and E approximately 0, plus a central peak not expected for isolated dinuclear units. We interpret this peak as arising from the stochastic spin dynamics of the chain introduced by exchange couplings between spins in neighbor dinuclear units, which averages out the zero field splitting. Interactions of the units with the rest of the chain acting as a spin bath give rise to a quantum transition between localized dinuclear states and states of the spin chain. This effect competes with the condensation of the antiferromagnetic dinuclear units into the singlet ground state, producing a characteristic temperature dependence of the shape of the powder EPR spectra. We interpret these features in terms of basic theories of magnetic resonance in coupled spin systems applied to the chain array of dinuclear units.

Significant anti-inflammatory properties of a copper(II) fenoprofenate complex compared with its parent drug: Physical and chemical characterization of the complex

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Temperature dependence of the effective interdimer exchange interaction in a weakly coupled antiferromagnetic dimer copper compound

“…37, 39 Here we prove that its relative signal intensity R (fraction of the sphere of field orientations in the powder sample where the condition δω ≤ ω ex holds) allows evaluating |J ′ eff | (exchange narrowing phenomena do not depend on the sign of the interaction). The observed T -dependence is a consequence of the depopulation with decreasing T of the excited triplet state, and the effective value of J ′ eff becomes zero when the average magnetic moment of the AFM DUs cancels out.…”

“…In a wider Trange, 4-298 K, we obtained equal results from measurements of the relative intensity of the so-called U-peak of the powder spectrum. In a previous work, 39 we proposed that this peak is a consequence of the interdimer coupling |J ′ eff |.…”

EPR and magnetic studies of a carboxylate-bridged dinuclear copper(II) compound: [cu2(flu)4(dmf)2]

“…The two axial ligands (L) are important for the coupling between neighbor units; when they are absent, the units tend to combine in chains or rings. 5,6 The great structural diversity of the "paddle wheel" units reported over ca. 60 years 7 maintained the interest in their magnetic properties.…”

“…Interesting quantum phase transitions produced by randomly distributed interactions between one unit and the "bath" of other units in the lattice have been recently observed by EPR. 6,8 We report here magnetic measurements and singlecrystal and powder EPR spectra of tetrakis( (Figure 1c).…”