Crystal engineering: Synthesis and structural analysis of coordination polymers with wavelike properties

Supramolecular coordination polymers with wavelike structures have been synthesized by self-assembly and their structures analyzed using the sine trigonometric function. Slow evaporation of a methylene chloride-methanol solution of a 1:1 molar mixture of [M(tmhd) ₂], where M = Co or Ni, and quinoxaline; a 1:2:1 molar mixture of [M(acac) ₂], where M = Co or Ni, 2,2,6,6-tetramethyl-3,5-heptadione and quinoxaline; or a 1:2:1 molar mixture of [Co(acac) ₂], dibenzoylmethane, and quinoxaline, yielded the crystalline coordination polymers. In the presence of the nitrogenous base, ligand scrambling occurs yielding the most insoluble product. The synthesis and structures of the following wavelike polymers are reported: trans-[Co(DBM) ₂(qox)] _n nH ₂O (2), trans-[Co(tmhd) ₂(qox)] _n (3), trans-[Ni(tmhd) ₂(qox)] _n (4), where DBM ^-=dibenzoylmethanate, tmhd ^- = 2,2,6,6-tetramethyl-3,5-heptadionate, and qox=quinoxaline. The wavelike structures are generated by intramolecular steric interactions and crystal packing forces between the chains. Some of the tert-butyl groups show a two-fold disorder. The sine function, φ=A sin 2πx/λ, where φ=distance (Ǻ) along the polymer backbone, λ = wavelength (Ǻ), A = amplitude (Ǻ), x = distance (Ǻ) along the polymer axis, provides a method to approximate and visualize the polymer structures.