General Rules for Silicate Anion Topology

Abstract

A survey of the known anions containing tetrahedrally coordinated silicon shows that the topology of the vast majority of these anions obeys five general rules:

• 1) [SiO₄] tetrahedra are linked to other [SiO₄] tetrahedra via corners rather than edges or faces.

• 2) One oxygen atom can belong to no more than two [SiO₄] tetrahedra.

• 3) If s is the connectedness, i.e., the number of oxygen atoms of an [SiO₄] tetrahedron shared with other [SiO₄] tetrahedra, then for a given silicate anion the difference, Δs, between the s values of all [SiO₄] tetrahedra tends to be small.

• 4) The dimensionality D of a silicate anion, i.e., the number of dimensions in which the anion is infinitely extended, tends towards the highest value possible for a given O : Si ratio.

• 5) Bond lengths and bond angles tend to vary as little as possible from the mean values

  • <d(Si-O)> = 1.62Å;

  • <⊀(O-Si-O)> = 109.47°;

  • <⊀(Si-O-Si)> = 140°.