Mononuclear nickel(II) and dinuclear palladium(II) complexes of a redox-active iminophenolate-based O,O,N,N,S,S ligand - experimental and theoretical vision

"A new potentially hexadentate redox-active schiff base ligand, H2L = 2-((Z)-(2-(2-(2-((Z)-3,5-di-tert-butyl-2hydroxybenzylideneamino)phenylthio)ethylthio)phenylimino)methyl)-4,6-di-tert-butylphenol, reacts with Ni-II(O2CCH3)(2)center dot 4H(2)O and PdCl2 in CH3OH in the presence of air and Et3N affording isolation of yellow and red crystalline solids of composition [Ni(L)] (1) and [Pd-2(L)Cl-2].2CH2Cl2 (2), respectively. When examined by cyclic voltammetry (CV), 1 exhibits three quasireversible responses at E-1/2 = 0.60 V (peak-to peak separation,Delta E-p = 80 mV), 0.96 V (Delta E-p = 80 mV) and 1.16 V (Delta E-p = 160 mV) vs SCE (saturated calomel electrode); while 2 exhibits one quasireversible response at E-1/2 = 1.185 V (peak-to peak separation,Delta E-p = 130 mV). One electron oxidized species showed EPR spectrum correspond to ferromagnetically coupled system, S = 3/2 (S = 1 for NiII and S = 1/2 for phenoxyl radical). Structural analysis revealed that 1 is discrete mononuclear and 2 is discrete dinuclear coordination complex. In complex 1, each Ni-II is in distorted octahedral NiN2O2S2 environment where coordination is satisfied by two nitrogen atoms, two oxygen atoms and two sulfur atoms of the ligand. In complex 2, each Pd is in distorted square planner PdNOSCl environment where coordination is satisfied by one each nitrogen, oxygen and sulfur atoms of the ligand, and a chloride ion. DFT calculations at B3LYP-level of theory adequately describe the electronic structures of 1 and 2, containing a spin-unpaired d(8)Ni(II) ion and spin-paired d(8)Pd(II) ion. Time-dependent-DFT calculations on 1 and 2 shed light on the origin of UV vis NIR spectral absorptions.