In the presence of dioxygen, four cobalt complexes of linear tetrapyrroles, Co(OEB) (OEB is the trianion of octaethylbiliverdin), [Co-II(OEBOx)]I-3 (OEBOx is the monoanion of the oxidized form of octaethylbiliverdin), Co-II(OEFB) (OEFB is the octaethylformylbiliverdin dianion), and Co-II(OEBOMe) (OEBOMe is the dianion of octaethylmethoxybiliverdin) form the bischelate cobalt(II)) complex of the anionic dipyrrole tetraethylpropentdyopent anion, Co-II(TEPD)(2). Both carbon monoxide and carbon dioxide are formed when Co-II(TEPD)(2) is produced by the thermal reactions between Co-II(OEFB) or Co(OEB) and O-2. Three different crystal morphologies of Co-II(TEPD)2 have been analyzed by single-crystal X-ray diffraction. In each case the cobalt atom is coordinated by four nitrogen atoms of the two propentdyopent ligands in a pseudotetrahedral fashion. In each morphology, a common tab/slot intermolecular C-H ... O hydrogen bond interaction that involves the methine C-H unit and two adjacent C-H units of the flanking ethyl groups and the lactam oxygen atom is found. These interactions connect pairs of molecules into extended chains. Co-II(TEPD)2 has been characterized spectroscopically (UV-vis and NMR) and electrochemically.