![]() ![]() Such changes are often accompanied by a reduction in the electron count as well. A common means of creating the requisite vacant site is by loss of a coordinated ligand or a change in the bonding mode of a ligand (such as conversion of a trihapto allyl ligand to the monohapto form). For example, for an olefin to undergo insertion, metathesis or polymerization, there must be room for the olefin to approach or bond to the metal. Typically, most complexes with a CN of less than 6 fall into this category, although this can vary.Ĭoordinative unsaturation is an important concept in organotransition metal chemistry. We use the term coordinative unsaturation to describe a complex that has one or more open coordination sites where another ligand can be accommodated. let's just say that it is somewhere between one and three. This allows you to count the pi and delta-type orbitals on cyclopentadiene, but ignore the pi-electrons from an imido ligand.Īs far as the number of coordination sites used by a Cp ligand. The way that I suggest is to count each pair of electrons donated to the metal, ignoring any pi-donation that is localized on a single atom. Either way, alkenes are usually considered to occupy only one coordination site. Alkene complexes can be drawn as neutral two electron donors but are sometimes considered dianionic bidentate ligands.Cp 2TiCl 2 would not be considered an 8-coordinate complex by most chemists!.Alkoxide, imido and oxo ligands can donate one, two or three pairs of electrons to a metal center, but in all cases each only occupies one coordination site.While this method seems to alleviate the problem, it adds further complications. The general consensus is to consider ferrocene a six coordinate species because there are six electron pairs on the ligands that participate in bonding (using the ionic formalism). Given the reactivity and bonding of ferrocene, calling it a 2-coordinate complex doesn't seem quite right either. But complications quickly arise when one considers the bonding of alkene or alkenyl fragments such as ethylene and cyclopentadienyl.įor example, in ferrocene all ten cyclopentadienyl carbons are equally bonded to the iron center, but few would call this a 10-coordinate complex. For example, 3+ and 3+ are both 6-coordinate complexes. For simple monodentate and chelating ligands, the coordination number can be defined as the number of atoms or ligands directly bonded to the metal atom. There are many definitions of the term coordination number, but there is no one simple unambiguous definition that works in all cases. Visit our sponsor at Coordination Number and Coordination Chemistry Definitions The Organometallic HyperTextBook: Coordination Number and and Coordination Chemistry Definitions ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |