Preparation, characterization, and X-ray crystal structures of helical and syndiotactic zinc-based coordination polymers.

Abstract

The reactions of (facac)2Zn.2H2O (facac = 1,1,1,5,5,5-hexafluoroacetylacetonate) with 2,5-bis(4-ethynylpyridyl)furan (1) and 1,2-bis(4-ethynylpyridyl)benzene (2) yield, upon crystallization, coordination polymers. The former polymer, ((facac)2Zn.1)n, has an isotactic, helical structure in the solid state [monoclinic space group P2(1)/n; a = 11.0374(3) A, b = 24.2179(10) A, c = 14.3970(4) A, beta = 92.880(2) degrees; Z = 4]. The latter polymer, ((facac)2Zn.2)n, adopts a syndiotactic structure in the solid state [monoclinic space group P2(1)/n; a = 9.1344(1) A, b = 21.7985(5) A, c = 16.0322(4) A, beta = 99.6680(11) degrees; Z = 4]. The solution structures of the corresponding oligomers have been studied by low-temperature 1H and 19F NMR spectroscopy. Chiral polymers were prepared using the fragment [(+)-tfc]2Zn ((+)-tfc = 3-((trifluoromethyl)hydroxymethylene)-(+)-camphorate). A linear, zigzag structure was found for ([(+)-tfc]2Zn.1)n [triclinic space group P1; a = 7.4833(2) A, b = 14.1563(5) A, c = 21.21230(5) A, alpha = 78.4440(15) degrees, beta = 81.5644(15) degrees, gamma = 76.4976(13) degrees; Z = 1]. Reaction with tris(4-pyridyl)methanol (3) yielded a homochiral, helical polymer, ([(+)-tfc]2Zn.3)n [monoclinic space group C2; a = 25.0633(12) A, b = 11.8768(7) A, c = 17.1205(9) A, alpha = 90 degrees, beta = 117.954(3) degrees, gamma = 90 degrees; Z = 4].