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

Anthony W Addison,Elizabeth A Brayman,Fan Xiao,Mark M Turnbull,Jerry P Jasinski,Stephen J Jaworski,Molly A O'Connor,Matthias Zeller

doi:10.1107/s2056989022001220

Abstract

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 CoCl2 complexes with Ppz, namely, {μ-1,4-bis-[2-(pyridin-2-yl)eth-yl]piperazine}bis-[di-chlorido-cobalt(II)], [Co2Cl4(C18H24N4)] or Co2(Ppz)Cl4, 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 CoCl2 units. Co2(Ppz)Cl4 and {di-chlorido-{4-methyl-1-[2-(pyridin-2-yl)eth-yl]-1,4-di-aza-cyclo-hepta-ne}cobalt(II) [CoCl2(C13H21N3)] or Co(Pmhpz)Cl2, crystallize in the monoclinic space group P21/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(C18H24N4)]ClO4 or [Co(Ppz)Cl]ClO4, are also monoclinic (P21). The complex {1,4-bis-[2-(pyridin-2-yl)eth-yl]-1,4-di-aza-cyclo-hepta-ne}di-chlorido-cobalt(II) [CoCl2(C19H26N4)] or Co(Phpz)Cl2 (P ) is mononuclear, with a penta-coordinated CoII 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)Cl2, [Co(Ppz)Cl]+ and Co(Pmhpz)Cl2 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)Cl2 and Co(Phpz)Cl2, 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.

Highlights

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-1,4bis[2-(pyridin-2-yl)ethyl]piperazine (Pdmpz) and tridentate 4-methyl-1-[2(pyridin-2-yl)ethyl]homopiperazine (Pmhpz)
The CoCl2 complexes with Ppz, namely, {-1,4-bis[2-(pyridin-2-yl)ethyl]piperazine}bis[dichloridocobalt(II)], [Co2Cl4(C18H24N4)] or Co2(Ppz)Cl4, and Pdmpz, are shown to be dinuclear, with the ligands bridging the two tetrahedrally coordinated CoCl2 units
The complex {1,4-bis[2-(pyridin-2-yl)ethyl]-1,4-diazacycloheptane}dichloridocobalt(II) [CoCl2(C19H26N4)] or Co(Phpz)Cl2 (P1) is mononuclear, with a pentacoordinated CoII ion, and entails a Phpz ligand acting in a tridentate fashion, with one of the pyridyl moieties dangling and non-coordinated; its displacement by ClÀ is attributed to the solvophobicity of ClÀ toward MeOH

Summary

Chemical context

Pyridylethylation of amines has previously been used to prepare a variety of chelating agents (Phillip et al, 1970; Profft & Georgi, 1961; Profft & Lojack 1962; Gray et al, 1960; Kryatov et al, 2002; Kryatova et al, 2012; Marsich et al, 1998; Karlin et al, 1984; Anandababu et al, 2020; Muthuramalingam et al, 2019a,b), with an original driver being the generation of biomimetic molecules (Karlin et al, 1984). For Ppz, both copper(II) (Mautner et al, 2008, 2009; O’Connor et al, 2012) and nickel(II) (O’Connor et al, 2012) complexes have been described. In the case of Phpz, there are reports of copper(II) complexes (O’Connor et al, 2012), including their application as oxidation catalysts (Muthuramalingam et al, 2017, 2020). Nickel(II) complexes of Phpz have been studied as catalysts (Muthuramalingam et al, 2019a,b) as has a recent cobalt(II) complex (Anandababu et al, 2020). For Pmhpz, copper and nickel complexes have been characterized (O’Connor et al, 2012), and Muthuramalingam and coworkers have recently examined oxidative catalysis by copper complexes including that of Pmhpz (Muthuramalingam et al, 2021), but there appears to be only the single prior report of Pdmpz (O’Connor et al, 2012). X-ray quality crystals of the Pdmzp complex were not obtained

Structural commentary

Database survey

Methods

Refinement

Funding information