Crystal structure and characterization of a new chain-like polyrotaxane zinc(II) coordination polymer with mixed pyridine-2,6-dicarboxylate and 1,4-bis(1<i>H</i>-imidazol-1-ylmethyl)benzene ligands

A new chain-like polyrotaxane Zn^II coordination polymer, <i>catena</i>-poly[[[[(pyridine-2,6-di-carboxyl-ato-κ³ <i>O</i>,<i>N</i>,<i>O</i>')zinc(II)]-μ-1,4-bis-(1<i>H</i>-imidazol-1-ylmeth-yl)benzene-κ² <i>N</i> ¹:<i>N</i> ^1'] hemi{bis-[μ-1,4-bis-(1<i>H</i>-imidazol-1-ylmeth-yl)benzene-κ² <i>N</i> ¹:<i>N</i> ^1']bis-[(pyridine-2,6-di-carboxyl-ato-κ³ <i>O</i>,<i>N</i>,<i>O</i>')zinc(II)]}] nona-hydrate], {[Zn(C₇H₃NO₄)(C₁₄H₁₄N₄)][Zn₂(C₇H₃NO₄)₂(C₁₄H₁₄N₄)₂]_0.5·9H₂O} _<i>n</i> or {[Zn₂(2,6-PDC)₂(bix)₂]·9H₂O} _<i>n</i> [where 2,6-PDC = pyridine-2,6-di-carboxyl-ate, C₇H₃NO₄, and bix = 1,4-bis-(1<i>H</i>-imidazol-1-ylmeth-yl)benzene, C₁₄H₁₄N₄], was synthesized and characterized. The mol-ecular structure comprises two Zn^II units. Both Zn^II ions are fivefold coordinated, with the coordination sphere inter-mediate between trigonal-bipyramidal and square-pyramidal, as defined by two bix ligands and one 2,6-PDC tridentate chelating ligand. For one of the units, two Zn^II ions are bridged by <i>gauche</i>-bix ligands, providing a dinuclear [Zn₂(2,6-PDC)₂(bix)₂] macrocycle. The other unit is built by <i>trans</i>-bix bridging ligands, leading to a zigzag chain-like structure. Inter-estingly, these two entities are inter-weaved, leading to a polyrotaxane structure extending parallel to [101]. The crystal structure is consolidated by hydrogen-bonding, π-π and C-H⋯π inter-molecular inter-actions.