The reaction of cobalt(III) complexes alpha-cis-[Co(EDDA)L](+) containing both amino acid (EDDA, ethylenediamine: N,N'-diacetate) and bidentate amine ligands (L = en, ethylenediamine; Men, N-methylethylenediamine; BEE N,N'-diethylethylenediamine; DEE, N,N-diethylethylenediamine) with formaldehyde under basic conditions has been investigated. For L = en, the product is [Co(L-1)](+), which contains a macrocyclic ligand (L-1 = 1,4-bis(carboxymethyl)-6,13-dioxacyclam) formed by linking the primary nitrogens on the en ligand with the secondary nitrogens on the EDDA ligand through two CH2OCH2 bridges. For L = Men and DEE, which each contain only one primary nitrogen, the reaction gives complexes [Co(L-2)](+) and [Co(L-3)](+) bearing hexadentate acyclic ligands (L-2 = 1,4-bis(carboxymethyl)-11-ethyl-6-oxa-1,4,8,11-tetraazatridecane; L-3 = 1,4-bis(carboxymethyl)-6-oxa-1,4,8,11-tetraazadodecane) each resulting from formation of one new CH2OCH2 linkage. All complexes have been characterized by H-1 and C-13 NMR, IR, and UV-visible spectroscopy and cyclic voltammetry. The X-ray crystal structures of [Co(L-1)]Cl . 3H(2)O and [Co(L-3)]PF6 . NH4PF6 . H2O have been determined. [Co(L-1)]Cl . 3H(2)O is monoclinic, P2(1)/n, with a = 14.792(3) Angstrom, b = 3.766(1) Angstrom, c = 16.520(4) Angstrom, beta = 99.54(2)degrees, V = 1871.5(6) Angstrom(3), Z = 4, R = 0.042: [Co(L-3)]PF6 . NH4PF6 . H2O is monoclinic, P2(1)/n, with a 13.353(6) Angstrom, b = 11.595(2) Angstrom, c = 16.900(5) Angstrom, beta = 95.59(3)degrees, V = 2604(2) Angstrom(3), Z = 4, R = 0.107.