When the total number for valence electron e s of the metal and ligands is 18, a transition metal organometallic compound usually has hight thermal stability.For example, Cr(CO)6, Fe(CO)5, Ni(CO)4, Fe( 5H5)2, Mo(C6H6)(C )3 etc. satisfy the 18 lectron rule, but the monomeric parts of Mn2(CO)10, Co2(CO)8 or [Fe(C5H5)(CO)2]2 have only 17 electrons and the extra electron comes f by forming a metal-metal bond. 8 Unlike the electron rule in main group compounds, applicability of the 18 electron rule is limited. That is to say, it is a sufficient condition but compounds with hight thermal stability are not electron compounds.
When the total number for valence electron e s of the metal and ligands is 18, a transition metal organometallic compound usually has hight thermal stability.For example, Cr(CO)6, Fe(CO)5, Ni(CO)4, Fe( 5H5)2, Mo(C6H6)(C )3 etc. satisfy the 18 lectron rule, but the monomeric parts of Mn2(CO)10, Co2(CO)8 or [Fe(C5H5)(CO)2]2 have only 17 electrons and the extra electron comes f by forming a metal-metal bond. 8 Unlike the electron rule in main group compounds, applicability of the 18 electron rule is limited. That is to say, it is a sufficient condition but compounds with hight thermal stability are not electron compounds.
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