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2.3 Basic structure types

Pauling rules: understanding polyhedral structures

Example 4 – Al O *2SiO *2H O (Kaolinite)
3
2
2
2
3+
4+
CN(Al ) = 6, CN(Si ) = 4, sij (Al-O) = 1/2 , sij (Si-O) = 1
CN(O1) = 2(Al), CN(O2) = 2(Al) + 1(Si), CN(O3) = 2

sij (O1) = 1 (!!!), sij (O2) = 2, sij (O3) = 2. Consequence: O1 is OH !!!

Example 5 – Determine possible coordination spheres of O in Na BiO 4
3

5+
• rock salt type structure CN(O) = 6, CN(cations) = 6, O , Na , Bi .
2-
+
• ONa with charge: -2 + 6/6 = -1
6

• ONa Bi with charge: -2 + 5/6 + 5/6 = -1/3
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• ONa Bi with charge: -2 + 4/6 + 10/6 = +1/3
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4
• ONa Bi with charge: -2 + 3/6 + 15/6 = +1
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3
• Composition and frequency of octahedra:

O(Na Bi)/6 + O(Na Bi )/6 = O Na Bi 3/6 = O Na Bi
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4
2
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9/6
2