Homochiral column structure of rac- and Λ-[MIII(tn)3]P3O9 (M = Co, Cr; tn = 1,3-diaminopropane; P3O9 = cyclotriphosphate(3−)) produced by multiple hydrogen bonds

Abstract

The crystal structures of rac- and Λ-[M^III(tn)₃]P₃O₉·nH₂O (M = Co, Cr; tn = 1,3-diaminopropane = trimethylenediamine; P₃O₉ = cyclotriphosphate(3−)) were determined by single-crystal X-ray analyses. In rac-[Co(tn)₃]P₃O₉·7.3H₂O, the [Co(tn)₃]³⁺ cations with the same absolute configuration (Δ or Λ) and the P₃O₉³⁻ anions are alternately arrayed and connected by multiple NH⋯O hydrogen bonds to form a homochiral columnar structure. Adjacent homochiral columns with opposite chirality are connected by intercolumn hydrogen bonds to form a racemic pair of columns. The crystal structure of rac-[Cr(tn)₃]P₃O₉·7.5H₂O is similar to that of the Co complex; however, there exist two types of racemic pairs of columns. In the crystal of Λ-[Co(tn)₃]P₃O₉·2.5H₂O, a pair of columns consisting of alternately stacked Λ-[Co(tn)₃]³⁺ cations and P₃O₉³⁻ anions are linked by hydrogen bonds. Neighboring column pairs are further linked by hydrogen bonds to form a three-dimensional (3-D) sheet structure. The crystal structure of Λ-[Cr(tn)₃]P₃O₉·2.5H₂O is isomorphous with the Co complex. The circular dichroism (CD) spectra of aqueous solutions of Λ-[M(tn)₃]Br₃ (M = Co, Cr) change when P₃O₉³⁻ is added, and the changes were explained by ion pair formation through hydrogen bonds.