The preparation and characterizaton by single crystal X-ray diffraction and electron paramagnetic resonance studies of (C 6H 5) 4As[Ni(S 2C 2(COOCH 3) 2) 2] is described. Crystals of the complex belong to the triclinic space group P 1 , with a = 10.968(3) Å, b = 11.218(3) Å, c = 15.561(5) Å, α = 86.07(4)°, β = 82.71(4)°, γ = 82.07(3)°, and ϱ calcd = 1.509 g cc −1 for Z = 2. The asymmetric unit contains the entire tetraphenylarsonium cation and two half anions; the nickel atoms being located on the inversion centers at (0,0,0) and (1/2,1/2,1/2). The salient structural features include and average NiS distance of 2.129(6) Å, an average intraligand SNiS angle of 92.3(2)°, and intra- and interligand S⋯S separations of 3.060(9) Å and 2.965(8) Å, respectively. The two unique anions in the unit cell are nearly orthogonal and are separated by 12.14 Å. Although the two independent anions are only crystallographically required to be centrosymmetric, the immediate coordination geometry for both closely approximates D 2h symmetry, and the point symmetry for one complete anion is close to C 2h. The principal molecular g values determined from the single crystal EPR measurements are g x = 2.063, g y = 2.151, g z = 1.986, where x and y bisect the intraligand and interligand SNiS angles respectively. These values are in accord with the electronic structural features previously described for such square planar species.