Azide-rich complexes of cobalt(III) with the rare 5-phenyl-2,2'-bipyridine ligand

Reaction of one or two equivalents of 5-phenyl-2,2′-bipyridine (L) with a mixture of one equivalent of CoCl2 and two equivalents of NaN3 leads to mononuclear heteroleptic cobalt(III) complexes [CoL2(N3)2](N3)0.55Cl0.45·EtOH (1) and [CoL2(N3)2]N3·2.5EtOH (2), respectively. Both structures reveal that cobalt(III) atom is linked to the six nitrogen atoms of two L and two N3− anions. Both structures are stabilized by intermolecular Csingle bondH⋯N and π⋯π stacking interactions. TG and DSC analyses reveal 1 being stable up to 63 °C and decomposing in three steps, 2 on the other hand decomposes at 84 °C in two steps. Both decomposition pathways start with an endothermic loss of the lattice ethanol molecules. The second step in 1 (177 °C) and 2 (196 °C) is related to the jet effect, seen as an abrupt weight loss due to a drastic energy release upon heating. In 2 this is the result of a release of N2 gas from the azides and decomposition of the ligands L followed by the full reduction of cobalt(III) to cobalt(0). In 1 there is a loss of one azide accompanied by the reduction of cobalt(III) to cobalt(II). The final decomposition step of 1 at 215 °C is attributed to the exothermic decomposition of L and remaining azide with the formation of a mixture of CoCl2 and Co2N. DFT calculations are performed in order to shed additional light on possible spin states of cobalt complexes as well as to rationalize the stability of the synthesized materials.

Publication year:2017

Keywords:A1 Journal article

BOF-keylabel:yes

BOF-publication weight:1

CSS-citation score:1

Authors:International

Authors from:Higher Education

Accessibility:Open