Electron-rich ligand modified, ferromagnetic luminescent cis-[CoIII(en)2(RNH2)Cl]Cl2 complexes and their electrochemical reduction behavior

Abstract

Abstract Luminescent cis -[Co III (en) 2 ( R NH 2 )Cl]Cl 2 (where R NH 2 = Hex n NH 2 , Pen n NH 2 , Bu i NH 2 , Bu n NH 2 , Pr n NH 2 , EtNH 2 , MeNH 2 , Bz n NH 2 ) complexes exhibiting ferromagnetism with some rationalization of magneto-structural features have been synthesized. Such characteristics were verified using auxiliary R NH 2 ligands. The complexes show emission (λ em ~ 411 nm and τ 1 ~ 3, τ 2 ~ 10, τ 3 ~ 0.7 ns) in fluid solutions upon excitation at λ ex = 360 nm. The manifestation of luminescence is attributed due to ligand-to-metal charge transfer emissive state. Electron rich ligand permits a significant reduction in the lifetime of the prominent emitting state Co(III)–Hex n NH 2 ( τ 2 = ~ 9.5 ns) 2 ( τ 2 = ~ 12.3 ns) due to (i) destabilization of d–d mixed LMCT emitting state, and (ii) smaller HOMO–LUMO gap. The E pc = 357–396 mV values observed for Co III (en) 2 ( R NH 2 )Cl 2 + in solvents such as DMSO, water and water/Pr i OH shows metal-centered reduction and a simple one electron transfer process because the current function (I pc /ν 1/2 ) is independent of sweep rate (50–350 mV s − 1 ). Importantly, cobalt(III) complex with short chain R NH 2 exhibits higher saturation magnetization; M s = 150.8 × 10 − 4 μ B /Co 3 + than complex with long chain R NH 2 , in which M s = 0.5 × 10 − 4 μ B /Co 3 + at 298 K, this indicates the manifestation of ferromagnetic coupling in Co III (en) 2 ( R NH 2 )Cl 2 + cation. In essence, the effect of R NH 2 on luminescence, electrochemical and magnetic properties of cis -[Co III (en) 2 ( R NH 2 )Cl]Cl 2 has been rationalized. Such correlation provides an outcome on the signature of the substituent, R NH 2 moiety in cobalt(III)–alkyl amine complexes.