Low-dimensional copper(II) complexes triply bridged with azide/carboxylate/DMSO showing very strong ferromagnetic interaction and influence of dipolar fields at low temperatures: a quantum Monte Carlo magnetic study.

Two one-dimensional (1D) azido, carboxylato and DMSO triply bridged coordination polymers of formula [Cu(mu1,1-N3)(mu1,3-(C4H3S-CH2COO))(mu-DMSO)]n (1) and [Cu3(mu1,1-N3)4(mu1,3-(C4H3S-COO)2)(mu-DMSO)2]n (2) have been synthesized, structurally characterized, and their magnetic properties have been studied. Cu(II) atoms 1 in are triply bridged by an EO type azide, a syn-syn carboxylate and a mu-O from a DMSO molecule. Complex 2 presents a trinuclear repeating unit in which the Cu(II) atoms are triply bridged in a fashion identical to 1, while the trinuclear moieties are linked through two centrosymmetrically related EO azides. The variable-temperature magnetic susceptibilities of complexes 1 and 2 have been measured in the range 2-300 K under various external fields in the range 0.02-1.0 T. Both curves are almost superimposable with small differences in the low temperature range and reflect the same ferromagnetic behaviour in almost all the temperature range. Quantum Monte Carlo (QMC) studies were carried out in order to fit the susceptibility curves of the two compounds. The simulated parameters are J = 126(2) cm(-1), g = 2.15(1) for compound and J1 = 126(2) cm(-1), J2 = 80(3) cm(-1)g = 2.17(1) for compound 2, proving that large ferromagnetic interactions exist in both compounds. EPR studies showed the temperature dependence of g-factors. The important g shift in the temperature range 4-100 K is attributed to internal dipolar magnetostatic fields.