Tetranuclear lanthanide complexes display significant slow magnetic relaxation with an open hysteresis loop and the magnetocaloric effect

Two tetranuclear lanthanide complexes with the formulas [Dy-4(HL)(4)(OAc)(2)(H2O)(2)]& BULL;2Et(3)NH & BULL;2CH(3)CN (1) and [Gd-4(HL)(4)(OAc)(2)(H2O)(2)]& BULL;2Et(3)NH & BULL;2CH(3)OH & BULL;4CH(3)CN (2) (H4L = N,N & PRIME;-bis(3-hydroxylsalicylidene)benzene-1,2-diamine) were structurally and magnetically characterized. Dynamic magnetic studies revealed that complex 1 exhibits two distinct slow magnetic relaxation processes under a zero direct current (dc) field and the extracted energy barriers (U-eff) of the low-temperature and high-temperature relaxation processes reach 207(2) K and 353(3) K, respectively, which are among the highest U-eff values of reported tetranuclear dysprosium molecular nanomagnets. More strikingly, as for complex 1, the open hysteresis loop behavior is detected until 5 K (6.5 K for the diluted sample), and a coercive field of 453 Oe is observed at 1.8 K, which is unusually seen in tetranuclear lanthanide single-molecule magnets. Further magnetic studies of diluted samples combined with ab initio calculation indicate that the Dy-III-Dy-III interactions play a crucial role in suppressing quantum tunneling of magnetization and consequently resulted in the bulk magnet-like hysteresis behavior. Additionally, the Gd-congener 2 displays the magnetocaloric effect (MCE) with a magnetic entropy change (-& UDelta;S-m) of 20.8 J kg(-1) K-1 at 2 K for & UDelta;H = 7 T.