arachno-borane

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June 18, 2026

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The term "arachno-borane" refers to a specific structural classification within the broader family of boranes, which are compounds of boron and hydrogen. Boranes are known for their complex polyhedral structures, which differ significantly from the chain and ring structures of carbon compounds. The nomenclature system for boranes uses prefixes like closo, nido, and arachno to describe the arrangement of boron atoms within these polyhedrons.12

An arachno-borane is characterized by a structure where the boron atoms occupy n contiguous corners of an (n + 2)-cornered polyhedron, essentially a closo-polyhedron with two missing vertices. These structures are more open than nido-boranes and are generally more reactive and less thermally stable than their closo-borane counterparts. The study of these structures has been crucial in understanding chemical bonding, particularly the concept of multicenter bonding in electron-deficient compounds.12

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borane
Structure and bonding of boranes
…with one missing vertex; (3) arachno- (Greek, meaning “spider’s web”), clusters that are even more open, with boron atoms occupying n contiguous corners of an (n + 2)-cornered polyhedron—i.e., a closo-polyhedron with two missing vertices; (4) hypho- (Greek, meaning “to weave” or “a net”), the most open clusters, with boron…
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…with one missing vertex; (3) arachno- (Greek, meaning “spider’s web”), clusters that are even more open, with boron atoms occupying n contiguous corners of an (n + 2)-cornered polyhedron—i.e., a closo-polyhedron with two missing vertices; (4) hypho- (Greek, meaning “to weave” or “a net”), the most open clusters, with boron…
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chemical bonding
Boranes
…and some resembling spiderwebs (the arachno-boranes). Which type of structure is obtained correlates with the number of valence electrons in the molecule, and the correlation is expressed by Wade’s rules. These rules are empirical, but they can be justified by a consideration of the numbers of 3c,2e and ordinary 2c,2e…
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…and some resembling spiderwebs (the arachno-boranes). Which type of structure is obtained correlates with the number of valence electrons in the molecule, and the correlation is expressed by Wade’s rules. These rules are empirical, but they can be justified by a consideration of the numbers of 3c,2e and ordinary 2c,2e…
Read More