Disorder of the dimeric TCNQ–TCNQ unit in the crystal structure of [Ni(bpy)(3)](2)(TCNQ–TCNQ)(TCNQ)(2)·6H(2)O (TCNQ is 7,7,8,8-tetra­cyano­quinodi­methane)

Crystallization from an aqueous methanol system composed of Ni(NO(3))(2), 2,2′-bipyridine (bpy) and LiTCNQ (TCNQ is 7,7,8,8-tetra­cyano­quinodi­methane) in a 1:3:2 molar ratio yielded single crystals of bis­[tris­(2,2′-bi­pyridine-κ(2) N,N′)nickel(II)] bis­(7,7,8,8-tetra­cyano­quinodi­methane radical anion) bi[7,7,8,8-tetra­cyano­quino­dimethanide] hexa­hydrate, [Ni(C(10)H(8)N(2))(3)](2)(C(24)H(8)N(8))(C(12)H(4)N(4))(2)·6H(2)O or [Ni(bpy)(3)](2)(TCNQ–TCNQ)(TCNQ)(2)·6H(2)O. The crystal structure comprises [Ni(bpy)(3)](2+) complex cations, two centrosymmetric crystallographically independent TCNQ(·−) anion radicals with π-stacked exo groups, and an additional dimeric TCNQ–TCNQ unit which comprises 75.3 (9)% of a σ-dimerized (TCNQ–TCNQ)(2−) dianion and 24.7 (9)% of two TCNQ(·−) anion radicals with tightly π-stacked exo groups. The title complex represents the first example of an Ni(II) complex containing a σ-dimerized (TCNQ–TCNQ)(2−) dianion. Disordered solvent water mol­ecules present in the crystal structure participate in hydrogen-bonding inter­actions.