The structure of a potassium-copper complex with six-membered macrocyclic ethylsiloxanolate ligands

The structure of K2{[EtSiO2]6K2Cu4[O2SiEt]6} · 4n-BuOH, a novel mixed sandwich-like complex of K+ and Cu2+ with two 6-membered macrocyclic ethylsiloxanolate ligands, was established by means of X-ray study. The ligands have an all-cis configuration and a crown conformation. Four Cu2+ and two K+ ions form a planar hexagon sandwiched between antiparallel coaxial macrocyclic ligands. The K+ ions occupy two opposite apices of the hexagon. The Cu2+ ions have square-planar coordination with four siloxanolate OM atoms, while the K+ ions, are coordinated with two O atoms of the solvating butanol molecules, in addition to four OM atoms. The electric neutrality of the whole complex is due to the two outer-sphere K+ counter-ions, each located over one of the two siloxanolate macrocycles, i.e., over the «decks» of the sandwich and coordinated with endocyclic siloxane OSi atoms, as in crown-ether complexes.