Exchange couplings in one-dimensionally arrayed 4f–3d heterometallic [Ln2Cu2]n compounds: A chemical trend of the coupling parameter

Heterometallic polymeric coordination compounds [{Ln(hfac)2(CH3OH)}2{Cu(dmg)(Hdmg)}2]n (abbreviated as [Ln2Cu2]n) involving light lanthanoid ions, Pr, Nd, Sm, and Eu, were synthesized, where H2dmg and Hhfac stand for dimethylglyoxime and 1,1,1,5,5,5-hexafluoropentane-2,4-dione, respectively. The X-ray crystallographic analysis shows that their structures are isomorphous to those of the known heavy lanthanoid analogs. The exchange couplings were evaluated by high-frequency electron paramagnetic resonance and pulsed-field magnetization studies, giving ferromagnetic exchange parameters: JPr–Cu/kB = 0.039(1) K, JNd–Cu/kB = 0.38(1) K, JSm–Cu/kB = 0.95(2) K, and no interaction between Eu and Cu ions. A significant trend is found in the order of the periodic table. The ferro- and antiferromagnetic 4f–3d couplings were characterized for the light and heavy lanthanoid derivatives, respectively. The magnitude of JLn–Cu decreases with a decrease of the 4f-spin portion, i.e., the number of unpaired electrons, whether the coupling is ferro- or antiferromagnetic.

Graphical abstractThe exchange couplings in [Ln2Cu2]n (Ln = Pr, Nd, Sm, Eu), which are light lanthanoid analogs of the known heavy analogs, were evaluated by high-frequency EPR and pulsed-field magnetization studies. The magnitude of the magnetic coupling decreases with a decrease of 4f-spin, whether the coupling is ferro- or antiferromagnetic.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The exchange couplings were evaluated by high-frequency EPR and magnetization studies. ► A significant trend of the exchange coupling parameter is found in the order of the periodic table. ► The coupling is ferromagnetic for light lanthanoid compounds. ► On the other hand, the coupling is antiferromagnetic for heavy ones. ► The absolute coupling parameter decreases with a decrease of the 4f-spin portion.