Polyhedral skeletal electron pair theory
The Wade- rule [ weɪd - ] - a term used in chemistry - was erected in 1971 by Kenneth Wade. Was extended this rule by Robert E. Williams and Ralph W. Rudolph. The rules were taken up by David Michael Patrick Mingos and significantly expanded, which is why they are also called Wade- Mingos rules.
With it, it is easy to recognize the structure of a borane compound from its empirical formula. The geometry of the scaffold of boranes, borane anions and carbaboranes is determined by the ratio of the number of electrons to the frame number n of the backbone atoms.
- Closo Latin clausus, closed
- Nido Latin nidus, nest
- Arachno Greek arachnion, Spider Web
The boron atoms of closo -borane sit on the corners of a polyhedron, which is limited only by triangular surfaces ( deltahedra ). Typical known deltahedra include the trigonal bipyramid (5 corners ), the octahedron ( 6 vertices ) and the icosahedron (12 vertices ). The hydrogen atoms of the borane are covalently bonded to the boron atom and show respective radially outwardly. closo -boranes are known but so far only in the form of dianions ( doubly negatively charged molecules ). As an example, the most stable representative, the closo- Dodecaboranat B12H122 - called. The structures of arachno, nido- boranes and hypho arising from the structures of the closo -boranes in which one, two or three adjacent corners of the closo- polyhedron can not be filled with boron atoms. The resulting bodies have thus increasingly more open structures. The hydrogen atoms of these boranes occupy one hand back all the positions on the boron atoms and additional places on the open parts of the polyhedron radially outward.
Example
The Penta borane B5H9 is according to the Wade's rules, a nido -borane. Compared to closed- closo- body him a corner missing. Its structure derives therefore from a closo- body from which is rich around a corner, that is, from an octahedron. Is lost in a corner of the octahedron - obtained a tetragonal ( four-sided ) pyramid. 5 H - atoms are located at the corners of the pyramid and showing radially outwardly away while the remaining 4-H - atoms have in the open square section.
Hypercloso compounds are not found in the simple hydrido - boranes. One expects a similar framework as for closo- connections for them. However, the theoretical work in this area is not complete. Examples include halogen-substituted boranes as B6Cl6.
Determining the number of electron structure
Example
B5H11
N = 5 ( 5 backbone atoms )
At 16 skeletal electrons is obtained for 5 boron atoms thus 2n 6 = 16 It follows the arachno structure.