Binuclear and chain-structure zinc(II) complexes constructed from 3,4-di­meth­oxy-trans-cinnamic acid and N-donor coligands 4-(1H-pyrazol-3-yl)pyridine and 4,4′-bipyridine

3,4-Dimeth­oxy-trans-cinnamic acid (Dmca) reacts with zinc sulfate in the presence of 4-(1H-pyrazol-3-yl)pyridine (L₁) or 4,4′-bipyridine (L₂) under hydro­thermal conditions to afford two mixed-ligand coordination complexes, namely tetra­kis­(μ-3,4-dimeth­oxy-trans-cinnamato-κ²O:O′)bis­[[4-(1H-pyrazol-3-yl)pyridine]­zinc(II)] hepta­hydrate, [Zn₂(C₁₁H₁₁O₄)₄(C₈H₇N₃)₂]·7H₂O or [Zn₂(Dmca)₄(L₁)₂]·7H₂O, (I), and catena-poly[[bis­(3,4-dimeth­oxy-trans-cinnamato-κO)zinc(II)]-μ-4,4′-bipyridine-κ²N:N′], [Zn(C₁₁H₁₁O₄)₂(C₁₀H₈N₂)]_n or [Zn(Dmca)₂(L₂)]_n, (II). The Zn^II centres in the two compounds display different coordination polyhedra. In complex (I), the Zn^II cation is five-coordinated with a pseudo-square-pyramidal geometry, while in complex (II) the Zn^II cation sits on a twofold axis and adopts a distorted tetra­hedral coordination environment. Complex (I) features a centrosymmetric binuclear paddle-wheel-like structure, while complex (II) shows a chain structure. This study emphasizes the significant effect of the coordination mode of both carboxyl­ate-group and N-donor coligands on the formation of complex structures.