Hypho structures

For a B Hm borane based on an anion B H 8-, a hypho-structure is preferred. B is at n vertices of an (n + 3) vertices polyhedron requiring (n + 4) pairs of framework bonding electrons. 

These results indicate, that reduction of 15 leads to the trishomoaromatic compounds 16a and 16b as tetrameric units bridged by Li centers. Alternatively, the tetrameric units may be described as commo-lithiacarboranes. The (hyphothetic) monomeric unit [(MeCH)3(BMe)3 Li3(thp)e]e should have a hypho structure. 

Hydrogen migration. 709 Hydrolysis constants, and charge-size functions, 328 Hydrometallurgy. 382-383, 384 Hydron, and proton, 318, A49 Hypho structures, 798-800, A77... 

S = N + A hypho structure (closed polyhedron - three vertices)... 

Say the number of BH groups that exist in a given compound and for which we have to find vertices is x. Hien if the number of vertices v called for by W-M rules also happens to equal x, each vertex will be occupied and we will have a closo structure. On the other hand, if x is (v - 1), one vertex will be empty and a nido structure will result. If x is (v - 2) or (v — 3), then the resulting arachno and hypho structures have two or three empty vertices. In such a case, the empty vertices prefer to be adjacent. 

Nido-cluster (a nest) a deltahedral structure with one missing vertex. Arachno-cluster (a spider-web) a deltahedral structure with two missing vertices. Hypho-cluster (a net) a deltahedral structure with three missing vertices. 

The hypho (Gr.. net ) series of boranes, with electronic formula 2n + 8, has beer suggested to augment the closo, nido, and arachno series. Although no neutral boranes fit this scheme, some borane derivatives do. It is also passible to construct units consisting of more than one of the above types. These are called cmjuncio (Latin, joined subunits ) structures. 

For boranes and carboranes, the terms do so, nido, arachno, and hypho are used to describe their molecular skeletons with reference to a series of increasingly open deltahedra. Boranes of the nido, arachno, and hypho types are compounds based on formulas B H +4, B H +6, and B Il +8, respectively. The structures... 

Molecular structures of some hypho cluster systems (a) B5H9(PMe3)2 (b) (NCCH2)C3B6Hj 2 (c) [/u,2- C(CN)2 2]C2B7H12. In carboranes (b) and (c), for clarity only bridging and extra H atoms are included, and all exo H atoms attached to the vertices are omitted. 

The polyhedra which represent the c/ow-boranes also serve as the basis for the structures of the nido-, arachno- and hypho-boranes. The term nido, as mentioned... 

Finally, several authors including Lipscomb himself, have pointed out the relationship of the styx rules (see above) to Wade s rules55,87,88. The sum of the digits in the topological styx formula for a borane structure gives the number of skeletal electron pairs in the molecule since both approaches factor out the bonds to exopolyhedral substituents. Thus, in the general formula BpHp+q used in the styx rules, q values of 2, 4, 6 and 8 are identified with closo-, nido-, arachno-and hypho-borane structures, respectively. 

This section presents the structure of the boron hybrides and is arranged in accordance with the relationship defined by Wade s Rules and expressed by Williams and Rudolph. Thus for the boranes containing six or more pairs of skeletal bonding electrons, the relationship between the structures of the closo-, nido-, arachno-and hypho-species is described. In cases where the parent borane does not exist, examples from heteroboranes with the correctly predicted structure based on Williams coordination number pattern recognition theory (CNPR) of borane structures will be described 70. Treated separately will be mono- and diborane species and also species with more than 12 boron atoms. Although there have been several reviews on the structures of the boranes in recent years none have used the current approach89. ... 

A hypho-borane adduct, B3H53P(CH3)3 has been prepared recently which belongs to the N = 7 class 1U). Boron-11 NMR data support the structure shown in Fig. 14. 

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