A Nanosized {Ni$^{II}$$_{18}$} Cluster with a ‘Flying Saucer’ Topology Exhibiting Slow Relaxation of Magnetisation Phenomena at Both 15 K and 1.3 K

A high-nuclearity {Ni$_{18}$} complex (1) with a unique ‘flying saucer’ motif has been prepared from the organic chelate, α-methyl-2-pyridine-methanol (mpmH), in conjunction with bridging azido (N$_{3}$) and peroxido (O$_2$$^{-2}$) ligands. Magnetic susceptibility measurements revealed the presence of both ferro- and antiferromagnetic exchange interactions between the metal centres in 1, and the stabilization of spin states with appreciable S values at two different temperature regimes. The end-on bridging azido and alkoxido groups are in all likelihood the ferromagnetic mediators, while the η$^{3}$:η$^{3}$:μ$_{6}$-bridging peroxides most likely promote the antiparallel alignment of the metals’ spin vectors, yielding an overall non-zero spin ground state for the centrosymmetric compound 1. Furthermore, the {{Ni$_{18}$}} nanosized cluster behaves as a single-molecule magnet, exhibiting magnetic hysteresis at low temperatures and two relaxation processes at 15 K and 1.3 K, a very rare phenomenon in polynuclear magnetic 3d-metal clusters.