Synthetic approaches to cobalt(III) complexes [Co(L)(L′)2] containing the bidentate dialkylating nitrogen mustard N,N-bis(2-chloroethyl)-1,2-ethanediamine (L = dce) together with anionic ancilliary ligands (L′) which are either carbonato (CO32−), oxalato (ox2−), bis(2-hydroxyethyl)dithiocarbamato (bhedtc−), 2-pyridine carboxylato (pico−) or 2-pyrazine carboxylato (pyzc−) were investigated. Synthetic routes were developed using the related amines N,N-diethyl-1,2-ethanediamine (dee) and 1,2-ethanediamine (en). The complexes [Co(CO3)2(L)]− (L = dee 1, dce 2), [Co(ox)2(L)]− (L = dee 3, dce 4), [Co(bhedtc)2(dee)]+5, [Co(bhedtc)2(en)]+6, mer-[Co(pico)3], mer-[Co(pyzc)]37 and [Co(pico)2(dee)]+8 were prepared and were characterised by IR, UV-Vis, 1H and 13C{1H} NMR spectroscopy, mass spectrometry and cyclic voltammetry. [Co(bhedtc)2(en)]BPh46b and trans(O)-[Co(pico)2(dee)]ClO48 were characterised by X-ray crystallography. In vitro biological tests were carried out on complexes 1–4 in order to assess the degree to which coordination of the mustard to cobalt attenuated its cytotoxicity, and the differential toxicity in air vs. nitrogen.
