IM-18: DO Family

Periodic Building Unit (PerBU):

Layer of isolated zig-zag chains

Layer symmetry

2D cell parameters

a = 10.48 Å

b = 7.55 Å

gamma = 90°

To facilitate understanding of the connectivity patterns shown below, O atoms that connect to a single row of d4r units have been highlighted in the layer of isolated zig-zag chains shown to the right.

Intergrowth Family IM-18

2-dimensional disorder of the units connecting ordered layers

Periodic Building Unit

Connecting unit

	Connecting unit	d4r

References


		Cichocka, M.O., Lorgouilloux, Y., Smeets, S., Su, J., Wan, W., Caullet, P., Bats, N., McCusker, L.B., Paillaud, J.L. and Zou, X.D.
			"Multidimensional disorder in zeolite IM-18 revealed by combining transmission electron microscopy and X-ray powder diffraction analyses"
			Crystal Growth Des., 18, 2441-2451 (2018)

Connectivity pattern

Each layer of zig-zag chains is generated from the previous one by a mirror plane (or a shift of 1/4a). The zig-zag layers themselves are fully ordered in 3 dimensions. However, the rows of d4r unit connectors can be disordered along both b and c, making the disorder in this family 2-dimensional.

Examples

Positions of d4r unit connectors in a row
There are two possible positions for a row of d4r units above two neighboring zig-zag chains in the layer. The position of the first d4r unit (along a) determines the positions of all the other d4r units in that row.

Symmetry Operations	Translation	Comment	Image
	0	d4r units in position 1
	1/2a	d4r units in position 2

Examples

Disorder along b: layers formed by the rows d4r unit connectors
The arrangement of the rows of d4r units is not necessarily periodic along b. Each row can be the same as the neighboring one or shifted by 1/2a.

First row	Next row	Comment	Image
position 1	position 1	shift of 0a^*
position 1	position 2	shift of 1/2a^*

^* relative to the previous row of connectors

Examples

Disorder along c: stacking of the layers of connectors
The d4r units in the connecting layers can also be disordered along c. The ordered zig-zag chains are shifted by 1/4a in adjacent layers. The rows of d4r unit connectors can be stacked along the [001] direction using either of the following connectivity patterns.

First layer	Second layer	Comment	Image
position 1	position 1	shift of 1/4a^*
position 1	position 2	shift of 1/4a^*

^* relative to the previous row of connectors

Effect on channel system
The disorder can block one or both of the straight 10-ring channels (e.g. those present in polymorphs A and B) when both d4r positions are present in a single layer of d4r units (see polymorph C).