However, we found significant haemolysis in our second round of assays (Table in SI), which was not observed in the initial CO-ADD screening. A recent study systematically investigated the cytotoxicity of common dimeric metal precursors against a range of human cancer cell lines. For Rh1 the authors found IC50 values in the high µM range except in the case of prolonged (96 h) exposure of the human ovarian carcinoma cell line A2780 to the compound, which resulted in increased toxicity (IC50 = 7.3 ± 1.5 µM). It is possible that hydrolysis of the chloride-rhodium bonds opens up coordination sites where the compound can interact with human red blood cells in unfavourable ways.