Cobaltocene has 19 valence electrons, one more than usually found in organotransition metal complexes, such as its very stable relative, ferrocene, in accordance with the 18-electron rule.
kˈoʊbɐltˌoʊsiːn hɐz nˈaɪntiːn vˈeɪləns ᵻlˈɛktɹɑːnz, wˈʌn mˈoːɹ ðɐn jˈuːʒuːəli fˈaʊnd ɪn ɔːɹɡˌænoʊtɹænsˈɪʃən mˈɛɾəl kˈɑːmplɛksᵻz, sˈʌtʃ ɐz ɪts vˈɛɹi stˈeɪbəl ɹˈɛlətˌɪv, fˈɛɹoʊsˌiːn, ɪn ɐkˈoːɹdəns wɪððɪ ˈeɪtiːnᵻlˈɛktɹɑːn ɹˈuːl.