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

•Luminescent and weakly ferromagnetic complexes with tunable ligand environment.•Magneto-structural analysis in cis-[CoIII(en)2(RNH2)Cl]Cl2 using ligand donor strength.•Active emission compounds due to the signature of substituent in ligand moiety.•This investigation accounts on redox active and ferromagnetic cobalt(III) complexes.

Luminescent cis-[CoIII(en)2(RNH2)Cl]Cl2 (where RNH2 = HexnNH2, PennNH2, BuiNH2, BunNH2, PrnNH2, EtNH2, MeNH2, BznNH2) complexes exhibiting ferromagnetism with some rationalization of magneto-structural features have been synthesized. Such characteristics were verified using auxiliary RNH2 ligands. The complexes show emission (λem ~ 411 nm and τ1 ~ 3, τ2 ~ 10, τ3 ~ 0.7 ns) in fluid solutions upon excitation at λex = 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)–HexnNH2 (τ2 = ~ 9.5 ns) < Co(III)–MeNH2 (τ2 = ~ 12.3 ns) due to (i) destabilization of d–d mixed LMCT emitting state, and (ii) smaller HOMO–LUMO gap. The Epc = 357–396 mV values observed for CoIII(en)2(RNH2)Cl2 + in solvents such as DMSO, water and water/PriOH shows metal-centered reduction and a simple one electron transfer process because the current function (Ipc/ν1/2) is independent of sweep rate (50–350 mV s− 1). Importantly, cobalt(III) complex with short chain RNH2 exhibits higher saturation magnetization; Ms = 150.8 × 10− 4 μB/Co3 + than complex with long chain RNH2, in which Ms = 0.5 × 10− 4 μB/Co3 + at 298 K, this indicates the manifestation of ferromagnetic coupling in CoIII(en)2(RNH2)Cl2 + cation. In essence, the effect of RNH2 on luminescence, electrochemical and magnetic properties of cis-[CoIII(en)2(RNH2)Cl]Cl2 has been rationalized. Such correlation provides an outcome on the signature of the substituent, RNH2 moiety in cobalt(III)–alkyl amine complexes.

Graphical abstractLuminescent cis-[CoIII(en)2(RNH2)Cl]Cl2 (λem ~411 nm; τ2 ~10-12 ns) complexes show weak ferromagnetism: Ms = 0.5-150 x 10− 4 µB/Co3 + with some rationalization of magneto-structural features. Cyclic voltammetric study indicates metal-centered reduction (Epc = 357 - 396 mV) through one electron transfer.Figure optionsDownload full-size imageDownload as PowerPoint slide