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 α-helical fold structure of protein.
The 1D 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 [Cd0.77Zn0.23(CH2(COO)2)(SC(NH2)2)2]n (III), [Cd0.50Zn0.50(CH2(COO)2)(SC(NH2)2)2]n (IV), 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 are self-adjusted to sustain their 1D helical motifs.