Magnetic properties and exchange couplings of one-dimensionally arrayed 4f-3d heterometallic [Ln2Cu2]n compounds

Heterometallic polymeric coordination compounds [{Ln(hfac)(2)(CH3OH)}(2){Cu(dmg)(Hdmg)}(2)](n) ([Ln(2)Cu(2)](n); Ln = Tb, Ho, and Er; H(2)dmg = dimethylglyoxime; Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) were synthesized, and the X-ray crystallographic analysis shows that their structures are isomorphous to those of the known ferrimagnetic [Gd2Cu2](n) and [Dy2Cu2](n) analogs. The exchange couplings in [Tb2Cu2](n), [Ho2Cu2](n), and [Er2Cu2](n) were precisely evaluated by high-frequency EPR and pulsed-field magnetization studies, giving J(Tb-Cu)/k(B) = -0.77(2)K, J(Ho-Cu)/k(B) = -0.250(12)K and J(Er-Cu)/k(B) = -0.149(15) K. They were comparable to those of the Gd and Dy analogs. The absolute value of the exchange coupling parameter monotonically decreases in the order of Gd, Tb, Dy, Ho, and Er. (C) 2008 Elsevier Ltd. All rights reserved.