From a SciAm article on the discovery of new magnetic organic molecules:
The discovery was partly accidental. The researchers were mixing organic nitrogen-rich compounds with nickel atoms and water. Normally during s uch reactions, multiple organic molecules will attach to each metal ion, so a relatively small amount of nickel should have been needed. But Hicks says his postdoc, Rajsapan Jain, noticed that the chemicals were not completely used up in the reaction, so they kept adding nickel to see what would happen. They ended up with a mudlike powder in their test tubes.
To quote Isaac Asimov: “The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ (I found it!) but ‘That’s funny …'”