Syntheses, structure and properties of cobalt-(II) and -(III) complexes of pentadentate N4S ligands with appended pyrazolyl groups: evidence for cobalt(II)–dioxygen reversible binding

Abstract

Cobalt-() and -() complexes of pentadentate N 4 S ligands based on methyl 2-aminocyclopent-1-ene-1-carbodithioate with appended pyrazolyl groups (3,5-Me 2 C 3 HN 2 CH 2 ) 2 NCH(R)CH 2 NHC 5 H 6 C(᎐ ᎐ S)SCH 3 (R = H, Hmmecd; CH 3 , Hmmpcd) have been prepared and characterised by IR, 1 H NMR and electronic spectroscopy. Two of these compounds have also structurally been characterised by X-ray single crystal diffraction analyses. Cobalt() in [Co(mmpcd)]ClO 4 , 1, shows a five-coordinate, trigonal bipyramidal geometry while its cobalt() counterpart, [Co(mmpcd)Cl]ClO 4 , 2, reveals a six-coordinated distorted octahedral structure by the inclusion of a chloride ligand in its equatorial plane. In dmf or acetonitrile solution, 1 can bind dioxygen reversibly as indicated by EPR spectra recorded at cryogenic temperatures. Metal-dioxygen binding in 1 appears to be weak, possibly due to its trigonal bipyramidal structure and the presence of a sulfur donor in the ligand framework. Electronic spectra of the cobalt() complexes show two LMCT bands in the near UV region, tentatively assigned to S→Co III charge transfer.

Redox processes as a route for the formation of an unusual structure of the Co(II)/Zn(II) complex isolated from the system: [Co(0)/Zn(II)-1-hydroxymethyl-3,5-dimethylpyrazole]

“…Adach et al / Inorganic Chemistry Communications 13 (2010) 361-364 ature was 4.4 BM, very close to that of the spin-only value expected for trigonal bipiramidal complexes having one Co(II) ion with three unpaired electrons[33][34][35]. The trigonal bipiramidal coordination environment of Co(II) ion in 1 was also confirmed with the electronic spectrum.…”

(1,4,7,10,13-Pentamethyl-1,4,7,10,13-pentaazacyclopentadecane-κ5N)cobalt(II) perchlorate

“…The bond lengths and distances are comparable to those previously reported for cobalt(II) complexes with macrocyclic polyamine ligands (Kueppers et al, 1986;Hubin et al, 2002). The NÐCoÐN angles in the equatorial plane are 142.1 (2), 133.4 (2) and 84.6 (2) , indicating a highly distorted trigonal-bipyramidal coordination geometry (Bhattacharyya et al, 2000;Hubin et al, 2002). The N1ÐCoÐN3 angle for the axial positions is 160.4 (2) , deviating signi®cantly from the ideal 180 .…”

Activation of Co(I) State in a Cobalt-Dithiolato Catalyst for Selective and Efficient CO2 Reduction to CO

“…The Co−S (2.229°) and Co−N (1.967°) bond distances are in good agreement with other high-spin cobalt(II) thiolate complexes known in the literature (Table S1). 49 Electrochemical Investigations and Product Analysis. The cyclic voltammogram (CV) of 1 using glassy carbon (GC) electrode shows two quasi-reversible redox processes at −1.65 V (ΔE p = 240 mV) and −2.12 V (ΔE p = 270 mV) versus Fc +/0 , which corresponds to Co(II/I) and Co(I/0) redox processes in acetonitrile (0.1 M nBu 4 NClO 4 supporting electrolyte; Figure 2a, black).…”