Crystal chemical formulae

Question 1

How are the linkage type of the overall structure written for different types of structures?

Answer 1

3D linked structure: 3 over ∞
2D sheet structure: 2 over ∞
1D fibre structure: 1 over ∞
Finite molecule: []

Question 2

How are shapes of molecules characterised in crystal chemical formulae?

Answer 2

^ for a chain structure of finite length
O for a cyclic structure
Ⓥ for a cage molecule

E.g.Ⓥ[P4] - white phosphorus

Question 3

How are the linkage type of a partial structure written when a certain atom has a certain linkage with another atoms of the same type?

Answer 3

^ for a chain structure of finite length
O for a cyclic structure
Ⓥ for a cage molecule

Then the atoms in questions are placed in brackets.

E.g. Na4Ⓥ[Si4]

Question 4

How are coordination notated in crystal chemical formulas?

Answer 4

In superscripted brackets after the unique atom. Number indicates how many atoms it is coordinated by, letter indicates what type of coordination (e.g. o = octahedral, t = tetrahedral, s = square planar)

E.g. CaTiO3

Ca[8,12;]Ti[8,6o;]O3[4,2;]

Question 5

Which coordination polyhedron does the symbol 2l denote?

Answer 5

Two atoms collinear with A

Question 6

Which coordination polyhedron does the symbol 2n denote?

Answer 6

Two atoms, non-collinear with A

Question 7

Which coordination polyhedron does the symbol 3l denote?

Answer 7

Triangle, coplanar with A

Question 8

Which coordination polyhedron does the symbol 3n denote?

Answer 8

Triangle, non-coplanar with A

Question 9

Which coordination polyhedron does the symbol 4s denote?

Answer 9

Square, coplanar with A

Question 10

Which coordination polyhedron does the symbol 4n denote?

Answer 10

Square, non-coplanar with A

Question 11

Which coordination polyhedron does the symbol 4t denote?

Answer 11

Tetrahedron

Question 12

Which coordination polyhedron does the symbol 4y denote?

Answer 12

Triangular pyramid with A at centre of base.

Question 13

Which coordination polyhedron does the symbol 5l denote?

Answer 13

Pentagon

Question 14

Which coordination polyhedron does the symbol 5y denote?

Answer 14

Tetragonal pyramid

Question 15

Which coordination polyhedron does the symbol 5by denote?

Answer 15

Trigonal bipyramid

Question 16

Which coordination polyhedron does the symbol 7by denote?

Answer 16

Pentagonal bipyramid

Question 17

Which coordination polyhedron does the symbol 6o denote?

Answer 17

Octahedron (trigonal antiprism)

Question 18

Which coordination polyhedron does the symbol 6p denote?

Answer 18

Trigonal prism

Question 19

Which coordination polyhedron does the symbol 6p1c denote?

Answer 19

Monocapped trigonal prism

Question 20

Which coordination polyhedron does the symbol 6p2c denote?

Answer 20

Bicapped trigonal prism

Question 21

Which coordination polyhedron does the symbol 6p3c denote?

Answer 21

Tricapped trigonal prism

Question 22

Which coordination polyhedron does the symbol 8cb denote?

Answer 22

Cube (tetragonal prism)

Question 23

Which coordination polyhedron does the symbol 8ap denote?

Answer 23

Square antiprism (tetragonal antiprism)

Question 24

Which coordination polyhedron does the symbol 8ap1c denote?

Answer 24

Monocapped square antiprism

Question 25

Which coordination polyhedron does the symbol 8ap2c denote?

Answer 25

Bicapped square antiprism

Question 26

Which coordination polyhedron does the symbol 8by denote?

Answer 26

Hexagonal bipyramid

Question 27

Which coordination polyhedron does the symbol 12co denote?

Answer 27

Cuboctahedron

Question 28

Which coordination polyhedron does the symbol 12aco denote?

Answer 28

Anticuboctahedron

Question 29

Which coordination polyhedron does the symbol 12i denote?

Answer 29

Icosahedron

Question 30

Which coordination polyhedron does the symbol 12p denote?

Answer 30

Hexagonal prism

Question 31

Which coordination polyhedron does the symbol 14FK denote?

Answer 31

14-vertex Frank-Kasper polyhedron

Question 32

Which coordination polyhedron does the symbol 15FK denote?

Answer 32

15-vertex Frank-Kasper polyhedron

Question 33

Which coordination polyhedron does the symbol 16FK denote?

Answer 33

16-vertex Frank-Kasper polyhedron

Question 34

What does the symbol t mean for polyhedra?

Answer 34

Tetrahedron

Question 35

What does the symbol s mean for polyhedra?

Answer 35

Square

Question 36

What does the symbol o mean for polyhedra?

Answer 36

Octahedron

Question 37

What does the symbol cb mean for polyhedra?

Answer 37

Cube

Question 38

What does the symbol do mean for polyhedra?

Answer 38

Dodecahedron with triangular faces

Question 39

What does the symbol co mean for polyhedra?

Answer 39

Cuboctahedron

Question 40

What does the symbol i mean for polyhedra?

Answer 40

Icosahedron

Question 41

What does the symbol l mean for polyhedra?

Answer 41

Linear/planar

Question 42

What does the symbol n mean for polyhedra?

Answer 42

Non-linear/non-planar

Question 43

What does the symbol y mean for polyhedra?

Answer 43

Pyramidal

Question 44

What does the symbol p mean for polyhedra?

Answer 44

Prismatic

Question 45

What does the symbol a mean for polyhedra?

Answer 45

anti-

Question 46

What does the symbol b mean for polyhedra?

Answer 46

bi-

Question 47

What does the symbol c mean for polyhedra?

Answer 47

Capped. 1c = monocapped, 2c = bicapped, 3c = tricapped

Question 48

How can non-bonding orbitals be described in crystal chemical formulae?

Answer 48

With heavy bar under the element symbol.

Question 49

What is the Frank-Kasper method for deteremining coordination?

Answer 49

You create a Wigner-Seitz cell around the atom in question. This is done by drawing a line between all neighbouring atoms, and cutting it in half, and finding the smallest volume that encapsulates these half-way points. All atoms emerging from the faces of this domain is part of the coordination polyhedron.

Question 50

Which three balances must be met for crystal chemical formulae?

Answer 50

For compound: C_m ^c+[C] A_n ^a-[A] 1. Electroneutrality: m * c = n * a 2. Connectivity: m * C = n * A 3. Bond valence: c/C = a/A

Question 51

What is the gap method for determining coordination?

Answer 51

When plotting bond distances from A to neighbouring atoms as a histogram, there usually is a large gap after a cluster of bonds. The gap method counts all the bonds occuring before the gap as part of the coordination polyhedron.