Synthesis and structure of pseudotetrahedral Co(II) zwitterionic complexes: trichloro(1-methylpiperazin-1-ium-N~4)cobalt(II) and trichloro(1,4-dimethylpiperazin-1-ium-N~4)cobalt(II)

摘要

The pseudotetrahedral cobalt(II) zwitterionic complexes, [CoCl_3(H_2Meppz)] (1) [H_2Meppz~+ = 1-methylpiperazin-1-ium cation] and [CoCl_3(HMe_2ppz)] (2), [HMe_2ppz~- = 1,4-dimethylpiperazin-1-ium cation] have been synthesized and characterized in the solid state by X-ray single crystal analysis, IR spectra, magnetic measurements and electronic spectra. In both the compounds the cobalt(II) center is coordinated in a distorted tetrahedral fashion by the three chloride ions and by one nitrogen of the piperazine ring that retains the more stable chair conformation. The distorted coordination polyhedron in complex 1 preserves the C_(3v) symmetry while in complex 2 it retains only the m symmetry. In complex 1. the (H_2Meppz)~+ cation binds the Co(II) ion in the equatorial position of the piperazine ring using the unmethylated N1-H nitrogen atom that is less hindered than the methylated one. Complex 2. on the contrary, is a novelty being the first example of a Co(II) ion bound in the axial position of a piperazine ring, this produces a long Co(II)-N bond, 2.108(4) A. Electronic spectra in the solid state are in perfect accordance with the X-ray crystallographic results indicating a C_(3v) symmetry for complex 1 and a C_s(m) symmetry for complex 2. These complexes present strong two-center and three-center hydrogen bonds of N~+ -H...Cl type.