MAGNETIC ANOMALIES IN POLYMERIC CHAIN COMPLEXES Cu(hfac)2 WITH SPIN-LABELED DIALKYLPYRAZOLES

High-field EPR of copper(ii)–nitroxide compound exhibiting three-step phase transition: structural insights from the field-induced sample orientation

“…3) confirmed the previously reported stepwise behavior. 32 However, the study revealed that the low temperature transition is divided into two sub-steps ( T LT1 = 46 K and T LT2 = 41 K) with a narrow plateau (<5 K) between them. It was observed that approximately 40% of the nitroxide–Cu 2+ –nitroxide exchange clusters are involved in the high-temperature magnetostructural transition (∼87 K), while approximately 50% are involved in the low-temperature magnetostructural transition (∼41 K).…”

“…The results reveal significant changes in the Cu–O bond lengths within the nitroxide–Cu 2+ –nitroxide exchange-coupled clusters during the magnetostructural transition at T HT = 87 K (with a change of approximately 0.16 Å in Cu–O NO distances from 120 K to 75 K). 32 The interpretation of XRD data collected in the mid-temperature range is rather challenging. While the crystallographic cell of the mid-temperature state is the same as that of the high-temperature state, the elongation of the CuO 6 octahedra in the intermediate phase is considerably reduced compared to the high-temperature phase (Cu–O NO distances of 2.18 Å, Cu–O hfac distances of 1.86 Å and 2.039 Å at 75 K, versus Cu–O NO distances of 2.36 Å, Cu–O hfac distances of 1.96 Å and 1.94 Å at 120 K).…”

“…This suggests the coexistence of weakly-coupled and strongly-coupled spin triads, where the axial and equatorial coordination of the NO groups to the Cu 2+ ions determines the type and the magnitude of exchange interaction. 19,20,30,32 Unfortunately, it was not impossible to determine the low-temperature structure of Cu(hfac) 2 L MeMe due to crystal cracking during the low-temperature magnetostructural transition (at ∼41 K).…”

“…2) and magnetometry techniques. 32 DC SQUID magnetometry revealed two distinct steps in the temperature dependence of the effective magnetic moment: the first occurs at approximately ∼85 K, followed by a second step at around 40 K. XRD analysis confirmed the occurrence of the high-temperature structural transition, but the low-temperature transition resulted in the crystal destruction, making a single-crystal XRD study impossible. Thus, the structure of the material at low temperatures has remained unidentified.…”

“…Thus, the structure of the material at low temperatures has remained unidentified. Furthermore, the previously obtained experimental data 32 is lacking systematic characterization of the two-step magnetostructural transition in Cu (hfac) 2 L MeMe .…”