An organometallic single-ion magnet is synthesized with only 19 non-hydrogen atoms featuring an erbium ion sandwiched by two different aromatic ligands. This molecule displays a butterfly-shaped hysteresis loop at 1.8 K up to even 5 K. Alternating-current (ac) susceptibility measurement reveals the existence of two thermally activated magnetic relaxation processes with the energy barriers as high as 197 and 323 K, respectively.

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A novel end-on azide-bridged homospin 1D chain, Co(bt)(N3)2 (1) (bt = 2,2'-bithiazoline), is constructed by sharing edges of Co(II) distorted octahedrons to form a helix, which shows magnetic hysteresis with steps and slow relaxation below 5-6 K, typical of single-chain magnet behavior.

Size-controllable monodisperse nanomaterials have been studied intensively due to their fundamental scientific interest and potential technological applications. [1] So far, the monodisperse magnetic nanocrystals, such as Fe, Co, FePt, CoPt, Fe 2 O 3 , Fe 3 O 4 , have been synthesized [2] for possible applications in magnetic data storage, ferrofluids, refrigeration systems, medical imaging, drug targeting, and catalysis. [3] Compared with a number of works done on these nanomagnetic metals and metal oxides, sparse work on the preparation and magnetic properties of nanoscale magnetic metallic sulfides has been reported so far. The europium monochalcogenides, EuX (X = O, S, Se, Te), with the rock-salt structure have been studied extensively since the 1960s. The pure, bulk EuO and EuS crystals, whose Curie temperatures (T C ) are 69 and 16.6 K, respectively, are well known to be insulating ferromagnets, in which the Heisenberg model applies. [4] Owing to their wide range of potential applications, such as ferromagnetic semiconductors and magnetoresistance, optomagnetic, and luminescent materials, [4,5] renewed attention has been given to the synthesis and properties of EuO and EuS crystals in the past number of decades. In an earlier study, we synthesized magnetic EuS nanoparticles with an average size of 5.5 nm, [5e] but until now little work on the size-controllable synthesis of monodisperse EuS nanocrystals has been reported. Herein, we report a direct and facile method to synthesize monodisperse EuS nanocrystals with sizes ranging from 2.6 to 20 nm. The EuS nanoparticles were prepared by the thermal decomposition of molecular precursors [Eu(phen)(ddtc) 3 ] and [Eu(bpy)-(ddtc) 3 ] (phen = 1,10-phenanthroline; bpy = 2,2'-pyridine; ddtc = diethyldithiocarbamate), in a way similar to previous work. [5d, e] The as-synthesized nanocrystals have been found to show uniform sizes and could be self-assembled into twodimensional (2D) or three-dimensional (3D) ordered superlattices. It is known that the decrease of the crystal size usually affects the properties of magnetic materials, as the small size usually gives rise to new surfaces, which result in a possible quantum tunneling effect and interparticle interactions. [6] The magnetic behavior of monodisperse EuS nanocrystals with controllable particle sizes was investigated. The magnetic properties were observed to depend strongly on particle size, as found in other nanoscale magnetic materials. [7] These results are interesting and helpful for the synthesis of lanthanide sulfides and in systematically understanding the relationship between size and magnetic properties of nanoscale ferromagnetic samples. On the other hand, a better understanding of the size-dependent properties of magnetic nanoparticles will be helpful to elucidate magnetizing mechanisms and to facilitate the design of magnetic materials.The single molecular precursor was prepared in the way reported by Formanovskii et al. [8] with slight modifications (see Supporting Information). The analysis res...