Chloro­cobalt complexes with pyridyl­ethyl-derived di­aza­cyclo­alkanes

Syntheses are described for the blue/purple complexes of cobalt(II) chloride with the tetra­dentate ligands 1,4-bis­[2-(pyridin-2-yl)eth­yl]piperazine (Ppz), 1,4-bis­[2-(pyridin-2-yl)eth­yl]homopiperazine (Phpz), trans-2,5-dimethyl-1,4-bis­[2-(pyridin-2-yl)eth­yl]piperazine (Pdmpz) and tridentate 4-methyl-1-[2-(pyridin-2-yl)eth­yl]homopiperazine (Pmhpz). The CoCl(2) complexes with Ppz, namely, {μ-1,4-bis­[2-(pyridin-2-yl)eth­yl]piperazine}bis­[di­chlorido­cobalt(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 tetra­hedrally coordinated CoCl(2) units. Co(2)(Ppz)Cl(4) and {di­chlorido­{4-methyl-1-[2-(pyridin-2-yl)eth­yl]-1,4-di­aza­cyclo­hepta­ne}cobalt(II) [CoCl(2)(C(13)H(21)N(3))] or Co(Pmhpz)Cl(2), crystallize in the monoclinic space group P2(1)/n, while crystals of the penta­coordinate mono­chloro chelate 1,4-bis­[2-(pyr­id­in-2-yl)eth­yl]piperazine}chlorido­cobalt(II) perchlorate, [CoCl(C(18)H(24)N(4))]ClO(4) or [Co(Ppz)Cl]ClO(4), are also monoclinic (P2(1)). The complex {1,4-bis­[2-(pyridin-2-yl)eth­yl]-1,4-di­aza­cyclo­hepta­ne}di­chlorido­cobalt(II) [CoCl(2)(C(19)H(26)N(4))] or Co(Phpz)Cl(2) (P [Image: see text] ) is mononuclear, with a penta­coordinated 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 penta­coordinate 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.