The structural, spectroscopic, redox properties and also the reactivity toward S-alkylation of a new mononuclear N2S2 dithiolate Co II complex [CoL] ( 1 ), with H 2 L = 2,2′-(2,2′-bipyridine-6,6′-diyl)bis(1,1-diphenylethanethiol), have been investigated. The X-ray structure of 1 has revealed an unusual distorted square planar geometry for a Co II ion within a thiolate environment. The X-band EPR spectrum of 1 displays a rhombic S = 1/2 signal consistent with a low spin configuration for the d 7 Co II ion with a large g -anisotropy ( g x = 2.94, g y = 2.32 and g z = 2.01). By pulsed EPR experiments (HYSCORE), two weak hyperfine couplings (hfc) of 3.2 and 2.2 MHz have been measured and attributed respectively to protons and nitrogen nuclei of the bipyridine unit. In addition, another hyperfine coupling (hfc) of 7.5 MHz has been attributed to the cobalt ion. DFT calculations have successfully reproduced the