Slow magnetic relaxation of a ferromagnetic Ni(II)5 cluster with an S = 5 ground state.

Complex [Ni 5{pyCOpyC(O)(OMe)py} 2(O 2CMe) 4(N 3) 4(MeOH) 2].2MeOH.2.6H 2O ( 1.2MeOH.2.6H 2O) was synthesized by the reaction of Ni(O 2CMe) 2.4H 2O with pyCOpyCOpy and NaN 3 in refluxing MeOH. It crystallizes in the monoclinic C2/ c space group and consists of five Ni (II) atoms in a helical arrangement. Direct current magnetic susceptibility studies reveal ferromagnetic interactions between the Ni (II) ( S = 1) ions, stabilizing an S = 5 ground state. Alternating current susceptibility experiments revealed the existence of out-of-phase signals indicative of slow magnetic relaxation. Analysis of the signals showed that they are composite, suggesting more than one relaxation process, while analysis of their magnitudes suggests not all molecules undergo slow magnetic relaxation. Magnetization field-sweep experiments revealed hysteresis at 1.8 K, and magnetization decay experiments clearly verified the appearance of slow magnetic relaxation at that temperature.