page_title: William Lipscomb
section_title: Boron chemistry and the nature of the chemical bond
hierarchical_section_title: William Lipscomb / Scientific studies / Boron chemistry and the nature of the chemical bond
caption_attribution_description: English: Atomic structure of B10H16 a boron hydride. Shown in the middle is the discovery in 1961 of a bond directly between two boron atoms without terminal hydrogens, a feature not previously seen in other boron hydrides.
context_page_description: William Nunn Lipscomb Jr. was a Nobel Prize-winning American inorganic and organic chemist working in nuclear magnetic resonance, theoretical chemistry, boron chemistry, and biochemistry.
context_section_description: In this area Lipscomb originally intended a more ambitious project: "My original intention in the late 1940s was to spend a few years understanding the boranes, and then to discover a systematic valence description of the vast numbers of electron deficient intermetallic compounds. I have made little progress toward this latter objective. Instead, the field of boron chemistry has grown enormously, and a systematic understanding of some of its complexities has now begun."
  Examples of these intermetallic compounds are KHg₁₃ and Cu₅Zn₇.  Of perhaps 24,000 of such compounds the structures of only 4,000 are known (in 2005) and we cannot predict structures for the others, because we do not sufficiently understand the nature of the chemical bond.
  This study was not successful, in part because the calculation time required for intermetallic compounds was out of reach in the 1960s, but intermediate goals involving boron bonding were achieved, sufficient to be awarded a Nobel Prize.
  The three-center two-electron bond is illustrated in diborane (diagrams at right).
  In an ordinary covalent bond a pair of electrons bonds two atoms together, one at either end of the bond, the diboare B-H bonds for example at the left and right in the illustrations.
  In three-center two-electron bond a pair of electrons bonds three atoms (a boron atom at either end and a hydrogen atom in the middle), the diborane B-H-B bonds for example at the top and bottom of the illustrations.
  Lipscomb's group did not propose or discover the three-center two-electron bond,
  nor did they develop formulas that give the proposed mechanism.
  In 1943, Longuet-Higgins, while still an undergraduate at Oxford, was the first to explain
  the structure and bonding of the boron hydrides. The paper reporting the work, written with his tutor R. P. Bell,
   also reviews the history of the subject beginning with the work of Dilthey.
   Shortly after, in 1947 and 1948, experimental spectroscopic work was performed by Price
  that confirmed Longuet-Higgins' structure for diborane. The structure was re-confirmed by electron diffraction measurement in 1951 by K. Hedberg and V. Schomaker, with the confirmation of the structure shown in the schemes on this page. Lipscomb and his graduate students further determined the molecular structure of boranes (compounds of boron and hydrogen) using X-ray crystallography in the 1950s and developed theories to explain their bonds. Later he applied the same methods to related problems, including the structure of carboranes (compounds of carbon, boron, and hydrogen). Longuet-Higgins
  and Roberts
  discussed the electronic structure of an icosahedron of boron atoms and of the borides MB₆. The mechanism of the three-center two-electron bond was also discussed in a later paper by Longuet-Higgins, and an essentially equivalent mechanism was proposed by Eberhardt, Crawford, and Lipscomb.
  Lipscomb's group also achieved an understanding of it through electron orbital calculations using formulas by Edmiston and Ruedenberg and by Boys.
  The Eberhardt, Crawford, and Lipscomb paper discussed above  also devised the "styx number" method to catalog certain kinds of boron-hydride bonding configurations.
  Wandering atoms was a puzzle solved by Lipscomb in one of his few papers with no co-authors.
  Compounds of boron and hydrogen tend to form closed cage structures.
  Sometimes the atoms at the vertices of these cages move substantial distances with respect to each other.
  The diamond-square-diamond mechanism (diagram at left) was suggested by Lipscomb to explain this rearrangement of vertices.
  Following along in the diagram at left for example in the faces shaded in blue,
  a pair of triangular faces has a left-right diamond shape.
  First, the bond common to these adjacent triangles breaks, forming a square,
  and then the square collapses back to an up-down diamond shape
  by bonding the atoms that were not bonded before.
  Other researchers have discovered more about these rearrangements.
  The B₁₀H₁₆ structure (diagram at right) determined by Grimes, Wang, Lewin, and Lipscomb found a bond dire
caption: B10H16 showing in the middle a bond directly between two boron atoms without terminal hydrogens, a feature not previously seen in other boron hydrides.
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