Bis(μ-3-hydroxy­benzoato)-κ(2) O (1):O (3);κ(2) O (3):O (1)-bis­[bis­(1H-benzimidazole-κN (3))(3-hydroxy­benzoato-κO)nickel(II)] bis­(1H-benzimidazole-κN (3))bis­(3-hy­droxy­benzoato-κO (1))nickel(II) hexa­hydrate

The title compound, [Ni(2)(C(7)H(5)O(3))(4)(C(7)H(6)N(2))(4)][Ni(C(7)H(5)O(3))(2)(C(7)H(6)N(2))(2)]·6H(2)O, is a mononuclear/dinuclear nickel(II) cocrystal, the two mol­ecular species inter­acting through hydrogen bonds that involve the uncoordinated water mol­ecules. In the mononuclear species, the Ni(II) ion, located on an inversion center, is coordinated by two 1H-benzimidazole (bzim) ligands and two 3-hydroxy­benzoate (hba) anions in a square-planar geometry. In the centrosymmetric dinuclear species, the Ni(II) ion is coordinated by two bzim ligands and three hba anions in a square-pyramidal geometry; of the two independent hba anions, one bridges two Ni(II) ions with both carboxylate and hydroxyl groups whereas the other coordin­ates in a unidentate manner to the Ni(II) ion. The apical Ni—O(hydrox­yl) bond is 0.39 Å longer than the basal Ni—O(carbox­yl) bonds. The face-to-face separation of 3.326 (9) Å indicates the existence of π–π stacking between parallel bzim ligands of adjacent dinuclear entities. Extensive N—H⋯O and O—H⋯O hydrogen bonds help to stabilize the crystal structure.