Synthesis, Structure, and Physical Properties of Tetraalkylammonium Bis(5,6‐dihydro‐1,4‐dithiin‐2,3‐diselenolato)nickelate, (R 4 N)[Ni(ddds) 2 ] (R = Me, Et, and n Bu), and Neutral Complex [Ni(ddds) 2 ] 2

Novel metal complexes (R 4 N)[Ni(ddds) 2 ] (R = Me, Et and n Bu, ddds = 5,6‐dihydro‐1,4‐dithiin‐2,3‐diselenolate) have been prepared and their crystal structures determined. The intraligand Se–Se distance is longer than that between the inner sulfur atoms of the five‐member ring of the M(dddt) 2 − sulfur analogue and is almost equal to the S–S distance in the six‐member ring. Consequently, two‐dimensional intermolecular close contacts are expected, and observed in Ni(ddds) 2 complexes. The neutral Ni(ddds) 2 species was obtained by electrochemical oxidation from the monoanionic ( n Bu 4 N)[Ni(ddds) 2 ] complex. X‐Ray crystal structure analyses of this neutral species show that two Ni(ddds) 2 are connected by the two Ni–Se bonds. Thus, the Ni(ddds) 2 entities form [Ni(ddds) 2 ] 2 dimers which are arranged face‐to‐face and rotated by about 90° with respect to each other. The electrochemical behavior of ( n Bu 4 N)[Ni(ddds) 2 ] indicates the possible formation of cation‐radical species. The room temperature magnetic susceptibility measurements showed that the (R 4 N)[Ni(ddds) 2 ] complexes are paramagnetic with μ eff = 1.77–1.83 μ B , corresponding to one unpaired electron per molecular formula. The temperature dependence of the magnetic susceptibility of (Et 4 N)[Ni(ddds) 2 ] is indicative of weak long‐range antiferromagnetic ordering below 9 K. The dimerization in [Ni(ddds) 2 ] 2 results in a strong antiferromagnetic spin coupling within the dimer, and explain the non magnetic state observed for this compound.