Chloro-cobalt complexes with pyridyl-ethyl-derived di-aza-cyclo-alkanes.

Syntheses are described for the blue/purple complexes of cobalt(II) chloride with the tetra-dentate ligands 1,4-bis-[2-(pyridin-2-yl)eth-yl]piperazine (Ppz), 1,4-bis-[2-(pyridin-2-yl)eth-yl]homopiperazine (Phpz), trans -2,5-dimethyl-1,4-bis-[2-(pyridin-2-yl)eth-yl]piperazine (Pdmpz) and tridentate 4-methyl-1-[2-(pyridin-2-yl)eth-yl]homopiperazine (Pmhpz). The CoCl 2 complexes with Ppz, namely, {μ-1,4-bis-[2-(pyridin-2-yl)eth-yl]piperazine}bis-[di-chlorido-cobalt(II)], [Co 2 Cl 4 (C 18 H 24 N 4 )] or Co 2 (Ppz)Cl 4 , and Pdmpz (structure not reported as X-ray quality crystals were not obtained), are shown to be dinuclear, with the ligands bridging the two tetra-hedrally coordinated CoCl 2 units. Co 2 (Ppz)Cl 4 and {di-chlorido-{4-methyl-1-[2-(pyridin-2-yl)eth-yl]-1,4-di-aza-cyclo-hepta-ne}cobalt(II) [CoCl 2 (C 13 H 21 N 3 )] or Co(Pmhpz)Cl 2 , crystallize in the monoclinic space group P 2 1 / n , while crystals of the penta-coordinate mono-chloro chelate 1,4-bis-[2-(pyr-id-in-2-yl)eth-yl]piperazine}chlorido-cobalt(II) perchlorate, [CoCl(C 18 H 24 N 4 )]ClO 4 or [Co(Ppz)Cl]ClO 4 , are also monoclinic ( P 2 1 ). The complex {1,4-bis-[2-(pyridin-2-yl)eth-yl]-1,4-di-aza-cyclo-hepta-ne}di-chlorido-cobalt(II) [CoCl 2 (C 19 H 26 N 4 )] or Co(Phpz)Cl 2 ( P ) is mononuclear, with a penta-coordinated Co II ion, and entails a Phpz ligand acting in a tridentate fashion, with one of the pyridyl moieties dangling and non-coordinated; its displacement by Cl - is attributed to the solvophobicity of Cl - toward MeOH. The penta-coordinate Co atoms in Co(Phpz)Cl 2 , [Co(Ppz)Cl] + and Co(Pmhpz)Cl 2 have substantial trigonal-bipyramidal character in their stereochemistry. Visible- and near-infrared-region electronic spectra are used to differentiate the two types of coordination spheres. TDDFT calculations suggest that the visible/NIR region transitions contain contributions from MLCT and LMCT character, as well as their expected d-d nature. For Co(Pmhpz)Cl 2 and Co(Phpz)Cl 2 , variable-temperature magnetic susceptibility data were obtained, and the observed decreases in moment with decreasing temperature were modelled with a zero-field-splitting approach, the D values being +28 and +39 cm -1 , respectively, with the S = 1/2 state at lower energy.