Synthesis, solution properties, and solid-state structural analysis of [Mn(κ4-N,N,S,N-dpktsc)Br]2·nCH3CN (n = 1 or 0 and dpktsc = di-2-pyridyl ketone thiosemicarbazone)

Ultrasonic radiation of a mixture of [Mn(CO)5Br], [dpktsc], and CH3CN gave [Mn(κ4-N,N,S,N-dpktsc)Br]2·nCH3CN (n = 0 or 1). Under reflux, a mixture of [Mn(CO)5Br], [dpktsc], and CH3CN gave [Mn(κ3-N,N,S-dpktsc-H)2]·2H2O. Crystals of [Mn(κ4-N,N,S,N-dpktsc)Br]2 were obtained by the evaporation of CH3CN from crystals of [Mn(κ4-N,N,S,N-dpktsc)Br]2·CH3CN. The solid-state structures of [Mn(κ4-N,N,S,N-dpktsc)Br]2·nCH3CN (n = 0 or 1) reveal two independent centrosymmetric dimers in the unit cell of each crystal and one CH3CN in the case of solvated crystal. Crystals of [Mn(κ4-N,N,S,N-dpktsc)Br]2·nCH3CN are stabilized by a network of non-covalent interactions that include hydrogen bonds and π–π interactions. Spectroscopic measurements reveal sensitivity of protophilic solutions of [Mn(κ4-N,N,S,N-dpktsc)Br]2 and [Mn(κ3-N,N,S-dpktsc-H)2]·2H2O to changes in their surroundings, as manifested by changes in the intensity of electronic absorption spectral properties in the presence and absence of external stimulus (acid or base). Electrochemical measurements in DMF reveal two closely spaced reduction/oxidation couples due to MnI → Mn0 and MnI → MnII of the dimer. In the case of [Mn(κ3-N,N,S-dpktsc-H)2]·2H2O, two well-separated reductions appeared due to MnII → MnI and MnI → Mn0. Electrochemical reactions of [Mn(κ4-N,N,S,N-dpktsc)Br]2 and [Mn(κ3-N,N,S-dpktsc-H)2]·2H2O show the monomer to be more active toward CO2 than the dimer.