I'm pretty sure that instead of "metal carbonyl", ions like croconate (CO)5(2-) and squarate (CO)4(2-) are formed when CO reacts with strongly
reducing metals. For example, potassium reacts with carbon monoxide to form hexapotassium benzenehexolate:
https://www.sciencedirect.com/science/article/pii/0022190263... |