Coordination of expanded terpyridine ligands to cobalt

The tridentate expanded terpyridine-like ligand N,N′-dimethyl-N,N′-dipyridin-2-yl-pyridin-2,6-diamine (ddpd) and [Co(H2O)6](BF4)2 give the high-spin complex mer-[Co(ddpd)2](BF4)2 with a tetragonally compressed CoN6 coordination geometry according to X-ray diffraction and SQUID measurements. UV–Vis–NIR spectra indicate a large ligand field splitting close to the high-spin/low-spin crossover point. Oxidation of the CoII complex to CoIII is achieved with silver triflate. The self exchange between high-spin CoII and low-spin CoIII is slow on the NMR time scale.

Graphical abstractThe tridentate expanded terpyridine-like ligand N,N’-dimethyl-N,N’-dipyridin-2-yl-pyridin-2,6-diamine (ddpd) and [Co(H2O)6](BF4)2 give the high-spin complex mer-[Co(ddpd)2](BF4)2 with a tetragonally compressed CoN6 coordination geometry (X-ray diffraction and SQUID measurements). UV-Vis-NIR spectra indicate a large ligand field splitting close to the high-spin/low-spin crossover point. The self exchange between high-spin CoII and low-spin CoIII is slow on the NMR time scale.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of high-spin mer-[Co(ddpd)2](BF4)2 (X-ray diffraction, SQUID). ► The ligand field splitting is close to the high-spin/low-spin crossover point. ► The self exchange between CoII and CoIII is slow on the NMR time scale.