Hydrogen-bonded pillars of alternating chiral complex cations and anions: 1. Synthesis, characterization, X-ray structure and thermal stability of catena-{[Co(H2oxado)3][Cr(C2O4)3]·5H2O} and of its precursor (H3oxado)[Co(H2oxado)3](SO4)2·2H2O

Abstract

Compound (H₃oxado)[Co(H₂oxado)₃](SO₄)₂·2H₂O (1) (H₃oxado⁺ = oxamide dioximemonoximium) reacted metathetically with Ba₆(H₂O)₁₇[Cr(C₂O₄)₃]₄·7H₂O in water to give the one-dimensional complex salt {[Co(H₂oxado)₃][Cr(C₂O₄)₃]·5H₂O}_∞ (2) (H₂oxado = oxamide dioxime). Compounds 1 and 2 were characterized by elemental analysis, FTIR, UV-Vis and by single crystal X-ray structure determination. The structure of 2 consists of infinite pillars of alternating chiral complex cations and anions linked together along [100] by electrostatic and longitudinal O–H⋯O interactions, with an average intrachain Co⋯Cr separation of 4.94 Å. Equatorial N–H⋯O bridges cross-link neighboring pillars (which are of opposite chirality) and consolidate a three-dimensional lattice framework which delineates elliptic nanochannels parallel to the a axis, encapsulating highly disordered water molecules. The thermal stability of both compounds was assessed by TGA, and the effective magnetic moment of 2, checked at room temperature, revealed considerable spin–orbit coupling.