Study of the Counter Cation Effects on the Supramolecular Structure and Electronic Properties of a Dianionic Oxamate-Based {Ni} Helicate.

Herein, we describe the synthesis, crystal structure, and electronic properties of {[K(dmso)(HO)][Ni(Hmpba)]·dmso·2HO} () and [Ni(HO)][Ni(Hmpba)]·3CHOH·4HO () [dmso = dimethyl sulfoxide; CHOH = methanol; and Hmpba = 1,3-phenylenebis(oxamic acid)] bearing the [Ni(Hmpba)] helicate, hereafter referred to as {Ni}. SHAPE software calculations indicate that the coordination geometry of all the Ni atoms in 1 and 2 is a distorted octahedron (O) whereas the coordination environments for K1 and K2 atoms in 1 are Snub disphenoid J84 (D) and distorted octahedron (O), respectively. The {Ni} helicate in is connected by K counter cations yielding a 2D coordination network with topology. In contrast to , the electroneutrality of the triple-stranded [Ni(Hmpba)] dinuclear motif in is achieved by a [Ni(HO)] complex cation, where the three neighboring {Ni} units interact in a supramolecular fashion through four (10) homosynthons yielding a 2D array. Voltammetric measurements reveal that both compounds are redox active (with the Ni/Ni pair being mediated by OH ions) but with differences in formal potentials that reflect changes in the energy levels of molecular orbitals. The Ni ions from the helicate and the counter-ion (complex cation) in can be reversibly reduced, resulting in the highest faradaic current intensities. The redox reactions in also occur in an alkaline medium but at higher formal potentials. The connection of the helicate with the K counter cation has an impact on the energy levels of the molecular orbitals; this experimental behavior was further supported by X-ray absorption near-edge spectroscopy (XANES) experiments and computational calculations.