Planar polycubane single-molecule magnet [Ni^sub 6^(pymeid)^sub 6^Ni^sub 12^(OH)^sub 6^(µ^sub 3^OH)^sub 16^Cl^sub 2^ (H^sub 2^O)^sub 2^]·38H^sub 2^O: Experiment and theory

Comprehensive experimental and theoretical study of atomic and magnetic structure of the 18-nuclei complex [Ni6(pymeid)6Ni12(OH)6(µ3-OH)16Cl2 (H2O)2] 38H2O (H2pymeid – N-(2-pyridyl)methyliminodipropionic acid) with rare polycubane planar architecture is reported. Magnetic moments of NiII ions (S = 1) in the sectional metal-oxygen Ni18 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 Tb = 14.3 K. The ac – susceptibility, χ’’, obeys the Arrhenius law with the effective barrier Ueff = 18.9 cm−1 (27.2 K). QTM regime is observed at T ≤ 8 K. Magnetic anisotropy is characterized by remanent magnetization M0 = 0.7 µB and coercive field Hc = 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.