A novel α-helix-liked metallohelicate series and their structural adjustments for the isomorphous substitution

A novel metallohelical motif is well designed and synthesized by mimicking the alpha-helical fold structure of protein. The ID helical structures of [Cd(CH2(COO)(2))(SC(NH2)(2))(2)](n) (I) and [Zn(CH2(COO)(2)) (SC(NH2)(2))(2)](n) (II) are primarily induced and stabilized by the multiple long-range intrahelix hydrogen bonds. Malonate dianion acts as a bidentate ligand coordinated with metal ions to form the backbone of the helix, and thiourea molecules that bend into the helical turn are involved in the intrahelix hydrogen-bond system. The metal ion occupations in the helix of I and II can be freely substituted by simply controlling the initial ratio of those two metal ions. Single crystals of three mixed metal ion complexes of [Cd0.77Zn0.79(CH2(COO)(2))(SC(NH2)(2))(2))(n) (III) [Cd0.50Zn0.50(CH2(COO)(2))(SC(NH2)(2))(2)](n) (TV), and [Cd0.21Zn0.79(CH2(COO)(2))(SC(NH2)(2))(2)](n) (V) were synthesized from systems with an initial Cd/Zn mole ratio of 1:1 for III, 1:2 for IV, and 1:8 for V. They are isomorphous as confirmed by X-ray characterization. When the metal ion is substituted, the multiple intrahelix hydrogen interaction motifs of the coordination polymer structure an self-adjusted to sustain their 1D helical motifs.