Planar polycubane single-molecule magnet [Ni-6(Pymeid)(6)Ni-12(OH)(6)(mu 3OH)(16)Cl-2 (H2O)(2)]center dot 38H(2)O: Experiment and theory

Abstract

Comprehensive experimental and theoretical study of atomic and magnetic structure of the 18-nuclei complex [Ni-6(Pymeid)(6)Ni-12(OH)(6)(mu 3OH)(16)Cl-2 (H2O)(2)] 38H(2)O (H(2)pymeid - N-(2-pyridyl)methyliminodipropionic acid) with rare polycubane planar architecture is reported. Magnetic moments of Ni-II ions (S = 1) in the sectional metal-oxygen Ni-18 core are coupled ferro- and antiferromagnetically, so that the complex is a single-molecule magnet (SMM) with the total spin in the ground state S = 10, and the blocking temperature T-b = 14.3 K. The ac - susceptibility, chi '', obeys the Arrhenius law with the effective barrier U-eff = 18.9 cm(-1) (27.2 K). QTM regime is observed at T <= 8 K. Magnetic anisotropy is characterized by remanent magnetization M-0 = 0.7 mu(B) and coercive field H-c = 340 Oe. Electronic structure and values of the local moments and the exchange constants are calculated in the LDA + U DFT approach. Two complementary 3-nuclei cubane fragments are linked antiferromagnetically to the main 12-nuclei ferromagnetic core. The ligands moderate the exchange couplings in the adjacent cubanes by shifting respective 3d DOS peaks of peripheral Ni ions towards lower energies.