Novel Co(III)/Co(II) mixed valence compound [Co(bapen)Br2]2[CoBr4] (bapen = N,N′-bis(3-aminopropyl)ethane-1,2-diamine): Synthesis, crystal structure and magnetic properties

•Novel Co(III)/Co(II) mixed valence ion pair compound.•Crystal structure containing two crystallographically independent complex cations.•Intermolecular hydrogen bonding interactions.•S = 3/2 behavior of Co(II) with zero-field splitting parameter D/hc = 8.7 cm−1.

Green crystals of Co(III)/Co(II) mixed valence compound [Co(bapen)Br2]2[CoBr4] (bapen = N,N′-bis(3-aminopropyl)ethane-1,2-diamine) were isolated from the aqueous system CoBr2 – bapen – HBr, crystallographically studied and characterized by elemental analysis and IR spectroscopy. Its ionic crystal structure is built up of [Co(bapen)Br2]+ cations and [CoBr4]2− anions. The Co(III) central atoms within the complex cations are hexacoordinated (donor set trans-N4Br2) with bromido ligands placed in the axial positions. The Co(II) atoms exhibit distorted tetrahedral coordination. Beside ionic forces weak NH⋯Br intermolecular hydrogen bonding interactions contribute to the stability of the structure. Temperature variable magnetic measurements confirm the S = 3/2 behavior with the zero-field splitting of an intermediate strength: D/hc = 8.7 cm−1.

Graphical abstractReaction of cobalt(II) bromide with N,N′-bis(3-aminopropyl)ethylenediamine and HBr in aqueous solution under aerobic conditions yielded green crystals of new Co(III)/Co(II) mixed valence compound [Co(bapen)Br2]2[CoBr4]. Compound was characterized by X-ray structure analysis, IR spectroscopy and magnetometry.Figure optionsDownload full-size imageDownload as PowerPoint slide