Abstract
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·nH2O (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.
Highlights
Molding coordination polymers within the crystal environment to obtain structures of the desired shape is an endeavor which requires the development of synthetic methods using compounds which on reaction produce chains, where the forces directed within and between the polymer chains produce the desired structures
Two different mixtures of starting materials were employed: the metal(II) complex, β-diketone, and dinitrogenous base or the metal(II) β-diketonate, and dinitrogenous base. In the former, the desired polymeric β-diketonate which is coordinated to the metal in the polymer chain is added in the keto form, while in the latter, the desired β-diketonate is added as the metal(II) complex
When quinoxaline is employed as the dinitrogenous base, a slightly basic solution is required for rearrangement and self-assembly to occur
Summary
Molding coordination polymers within the crystal environment to obtain structures of the desired shape is an endeavor which requires the development of synthetic methods using compounds which on reaction produce chains, where the forces directed within and between the polymer chains produce the desired structures. The research is directed toward obtaining coordination polymers with wavelike structural characteristics. The structures of the wavelike polymers were determined by single-crystal X-ray diffraction and the wave characteristics analysed using the sine trigonometric function. Wavelike characteristics of some coordination polymers have been noted previously [1-12]; we have been unable to find any references where trigonometric functions were used to analyze the structural data. The synthesis and structures of the following wavelike polymers are reported: trans-[Co(DBM)2(qox)]n·nH2O (2), trans-[Co(tmhd)2(qox)]n (3), trans-[Ni(tmhd)2(qox)]n (4), where. A number of recent studies have reported the synthesis of cobalt(II) and nickel(II) complexes with DBM−. A linear polymeric structure of the complex trans-[Co(acac)2(pz)]n has been reported [18]. Trans-[Co(acac)2(qox)]n, trans-[Ni(acac)2(qox)]n, and trans-[Co/Ni(acac)2(qox)]n are reported to have a zigzag polymeric chain [19]
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