Tribute To A Numerical Inorganic Icon: Kenneth Wade
University of Durham chemistry professor Kenneth Wade, famously known for the borane electron-counting rule that bears his name, passed away on March 16 at age 81. Chemists at the University of Nottingham, led by big-haired chemistry professor Martyn Poliakoff, have prepared a lovely video tribute to Professor Wade as part of their Periodic Table of Video series.
Chemists use electron-counting rules to determine bonding patterns in different classes of compounds, such as the familiar octet rule for first- and second-row elements, the 18-electron rule for transition metals, and the Hückel 4n + 2 rule for aromatic compounds. However, these rules don’t readily apply to electron-deficient molecules such as boranes that utilize multicentered bonding–a pair of electrons shared between more than two atoms–so other rules have been devised.
In 1971, building on the collective observations of other chemists, Wade formulated his n + 1 rule. Wade’s rule states that a cage molecule with a geometry based on a closed polyhedron constructed of triangles with n vertices will possess n + 1 skeletal bonding electron pairs.
Wade’s rule and its corollaries have been refined and extended by a number of researchers. When coupled with spectroscopic studies and theoretical calculations, these rules have been successful in showing the structural interconnections between boranes, carboranes, other heteroboranes, carbocations, organometallic complexes, and transition-metal cluster compounds.
Hats off to Professor Wade.