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The reaction of Ni(NO3)2·6H2O with Na2SeO3 in the presence of tetramethylethylenediamine (TMEDA) in a water/ethanol mixture yielded the heteroleptic complex [{Ni(TMEDA)SeO3}2] (1). Single-crystal X-ray diffraction analysis showed that complex 1 consists of a dinuclear species in which the two nickel atoms are held together by two bridging selenito anions. The crystal packing of 1 is determined by networks of hydrogen bonds, involving cocrystalized water molecules and the oxygen atoms of the bridging SeO32– groups. The two nickel ions in 1 exhibit antiferromagnetic coupling with J = –25.7 ± 0.1 cm–1, in good agreement with DFT calculations. In addition, when a less sterically hindered ancillary ligand, such as ethylenediamine (en), was used, the homoleptic complex [Ni(en)3](SeO3) (2) was obtained.

We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF5. The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C60(AsF6)2, indicates that the highly reactive C602+ units are arranged according to a novel 1D “zigzag” polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single C−C bonds. The long awaited high-Tc superconductivity and magnetism, expected in a hole-doped C60 compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) su...