Database of Zeolite Structures

Explanatory Notes - Structures

Classically, zeolites are defined as aluminosilicates with open 3-dimensional framework structures
composed of corner-sharing TO4 tetrahedra, where T is Al or Si. Cations that balance the charge of
the anionic framework are loosely associated with the framework oxygens, and the remaining pore
volume is filled with water molecules. The non-framework cations are generally exchangable and the
water molecules removable. This definition has since been expanded to include T-atoms other than Si
and Al in the framework, and organic species (cationic or neutral) in the pores.

Each time a new zeolite framework structure is reported, the members of the Structure Commission of the International Zeolite Association (IZA-SC) check to see if it has a unique framework type. If it does and the structure has been established to the satisfaction of the members of the IZA-SC (see Rules for Framework Type Code Assignment), a unique 3-letter code is assigned (see Origin of zeolite names and codes).

Descriptions of all of the Framework Types that have been assigned codes by the IZA-SC are included in this database. A number of terms that are used in the database to describe zeolite framework structures are defined here.

Each time a new zeolite framework structure is reported, the members of the Structure Commission of the International Zeolite Association (IZA-SC) check to see if it has a unique framework type. If it does and the structure has been established to the satisfaction of the members of the IZA-SC (see Rules for Framework Type Code Assignment), a unique 3-letter code is assigned (see Origin of zeolite names and codes).

Descriptions of all of the Framework Types that have been assigned codes by the IZA-SC are included in this database. A number of terms that are used in the database to describe zeolite framework structures are defined here.

Framework Type Codes

Following the rules set up by an IUPAC Commission on Zeolite Nomenclature in 1978 (R.M.
Barrer, *Pure Appl. Chem.* **51**, 1091 (1979)), a code consisting of three capital letters (in bold face
type) is used to designate a Framework Type. These codes are generally derived from the
names of the Type Materials (see also Origin of 3-Letter Codes) and do not include numbers and
characters other than capital Roman letters. The assignment of Framework Type Codes is
subject to review and clearance by the IZA Structure Commission. Codes are only assigned to
established structures that satisfy the Rules for Framework Type Code Asssignment of the IZA
Structure Commission. For interrupted frameworks, the 3-letter code is preceded by a hyphen.
These mnemonic codes should not be confused or equated with actual materials. They only
describe and define the network of the corner sharing tetrahedrally coordinated framework
atoms (T-atoms). Thus, designations such as NaFAU are untenable. However, a material can be
described using the IUPAC crystal chemical formula (L.B. McCusker, F. Liebau and G.
Engelhardt, *Pure Appl. Chem.* **73**, 381 (2001)), as **|**Na_{58}**| [**Al_{58}Si_{134} O_{384}**]-FAU** or **|**Na-**| [**Al-Si-
O**]-FAU** (Note that the chemical elements must be enclosed within the appropriate (boldface)
brackets, i.e. **| |** for guest species and **[ ]** for the framework host). Framework Types do not
depend on composition, distribution of the T-atoms (Si, Al, P, Ga, Ge, B, Be, etc.), cell

dimensions or symmetry.

The Framework Types have been arranged in alphabetical order according to the Framework Type Code, because structural criteria alone do not provide an unambiguous classification scheme. This also facilitates later insertion of new codes and allows simple indexing.

dimensions or symmetry.

The Framework Types have been arranged in alphabetical order according to the Framework Type Code, because structural criteria alone do not provide an unambiguous classification scheme. This also facilitates later insertion of new codes and allows simple indexing.

Idealized Framework Data

A Framework Type is independent of chemical composition. Therefore, idealized framework data (cell parameters, coordinates of T-atoms) were obtained from a DLS-refinement (Ch. Baerlocher, A. Hepp. and W.M Meier, DLS-76, a program for the simulation of crystal structures by geometric refinement, ETH Zurich (1978)) in the (highest possible) symmetry of the Framework Type. The refinement was carried out assuming a (sometimes hypothetical) SiO_{2} composition and with the following prescribed interatomic distances:

_{2} framework is given as FD_{Si}.

The space group, the cell dimensions and the atomic coordinates of a real material will depend upon its chemical composition, but they will be related to the crystallographic data listed for the Framework Type. If the symmetry is different, it will be a subgroup of this space group, and the unit cell parameters will be related by relatively simple geometric considerations. The relationship between the unit cell parameters of the Type Material and those of the Framework Type are indicated where appropriate.

dSi-O = 1.61 Å, weight = 2.0

dO-O = 2.629 Å, weight = 0.41

dSi-Si = 3.07 Å, weight = 0.23

In each case, the coordinates were first optimized within an approximate unit cell, and then the unit cell was also allowed to refine. The resulting DLS reliability index (i.e. how well the assumed geometric parameters are accommodated by the framework structure) is listed. The Framework Density for this SiOdO-O = 2.629 Å, weight = 0.41

dSi-Si = 3.07 Å, weight = 0.23

The space group, the cell dimensions and the atomic coordinates of a real material will depend upon its chemical composition, but they will be related to the crystallographic data listed for the Framework Type. If the symmetry is different, it will be a subgroup of this space group, and the unit cell parameters will be related by relatively simple geometric considerations. The relationship between the unit cell parameters of the Type Material and those of the Framework Type are indicated where appropriate.

Framework Density (FD)

The Framework Density is defined as the number of tetrahedrally coordinated atoms (T-atoms) per 1000 Å^{3}. The figures given refer to the Type Materials. For non-zeolitic framework structures, values of at least 19 to 21 T/1000 Å^{3} are generally obtained, while for zeolites with fully crosslinked frameworks, the observed values range from about 12.1 for structures with the largest pore volume to around 20.6. To date, FD's of less than 12 have only been encountered for the interrupted framework cloverite (**-CLO**), for the silfide UCR-20 (**RWY**), for a few germanosilicates (**IRR**, **-IRY** and **-ITV**), and for hypothetical networks. The FD is obviously related to the pore volume but does not reflect the size of the pore openings. For some of the more flexible zeolite structures, the FD values can vary appreciably. In these cases (e.g. gismondine) values are given for the Type Material and for the framework in its most expanded state. The flexibility of a framework structure is, to some extent, revealed by the possible variation in the FD.

**FD**_{Si}

FD values may also depend on composition. For all Framework Types, the Framework Density calculated for an idealized SiO_{2} composition in the highest possible space group (see idealized framework data) is also given (FD_{Si}).

Topological Denisty (TD)

The Coordination Sequence (CS) can be used to calculate a Topological Density (TD). As might be expected, the CS is a periodic function. This has been established for all observed framework topologies by R.W. Grosse-Kunstleve, G.O. Brunner and N.J.A. Sloane (*Acta Crystallogr. A***52**, 879 (1996)). They showed that the CS of any T-atom can be described exactly by a set of p quadratic equations

**ABW** is exactly described by a set of three quatratic equations (p=3), namely

**SOD** and p = 42 for **FAU** to p = 4,658,179,125,600 for **STT** and 79,357,853,975,400 (!) for **IWW**. With growing index k (the shell number of the CS), the linear and constant coefficients, b_{i} and c_{i}, respectively, become less and less important. Therefore we can define the exact Topological Density TD as the mean of all a_{i} divided by the dimensionality of the topology (i.e. 3 for zeolites)

_{i}> has been approximated as the mean of a_{i} for the last 100 terms of a CS with 1000 terms (TD1000:100), weighted with the multiplicity of the atom position, and divided by three (dimensionality). Click here for a list of these Topological Densities for all Framework Types. There is a simple relationship between TD and TD_{10}: TD_{10} ~ TD *1155. Since TD_{10} is an approximation, i.e. it is 'arbitarily' terminated at N_{10}, the values obtained by this formula deviate by 11% for **-CLO** and 5% for **FAU** but differences are generally below 3%. It seems that for very open framework structures, 10 steps are not sufficient for a satisfatory convergence. The correlation factor between the exact topological density TD and the framework density FD is 0.82.

N_{k} = a_{i}k^{2} + b_{i}k + c_{i} for k = i + np, n = 0,1,2,... and i = 1,2,3, ... p

For example, the CS of
N_{k} = 19/9 k^{2} + 1/9 k + 16/9 for k = 1 + 3n, n=0,1,2,...

N_{k} = 19/9 k^{2} - 1/9 k + 16/9 for k = 2 + 3n, n=0,1,2,...

N_{k} = 19/9 k^{2} - 0 k + 2 for k = 3 + 3n, n=0,1,2,...

The number of equations p necessary to calculate all members of a particular coordination sequence varies from p=1 for N

N

TD = <a_{i}>/3 = 1/(3p) Σ(a_{i}) (i=1...p)

This TD is the same for all T atoms in a structure. For some frameworks, this calculation can take quite a long time, so an approximation valid to ± 0.001 has been used to calculate the values for each of the Framework Types. The value for <aChannel dimensionality

There are two different ways the channel dimensionality is defined:

*topological dimensionality* any channel that has a pore opening larger than a 6-ring is considered a channel, irrespectiv of the actual geometric pore opening. In contrast to this, in the *"sorption diemsionality"* only channel directions that have a pore opening larger than 3.4Å in the Type Material are counted . The value of 3.4Å has been choosen to be small enough to allow for certain variation in the actual pore openings of a material, but not too small to be unrealistic. Thus the "sorption dimensionality" will provide a guide whether a small (or slim) organic monecule might be able to diffuse along a channel direction.

(1) Topological dimensionality and

(2) Dimensionality with respect to the sorption of a organic molucule

In the (2) Dimensionality with respect to the sorption of a organic molucule

Maximum diameter of a sphere

To provide more quantitative information about the size of the channel system, the following data is given in angstroms:

*Micropor. Mesopor. Mat.*, **90**,32-38, 2006.

- the diameter of the largest possible included sphere

- the diameter of the largest-free-sphere that can diffuse along a

- the diameter of the largest-free-sphere that can diffuse along b

- the diameter of the largest-free-sphere that can diffuse along c

These maximum sphere diameters were computed geometrically by Delaunay triangulation with the following assumptions:- the diameter of the largest-free-sphere that can diffuse along a

- the diameter of the largest-free-sphere that can diffuse along b

- the diameter of the largest-free-sphere that can diffuse along c

- both the framework T- and O-atoms are hard spheres of diameter 2.7 angstrom

- all extra-framework atoms (i.e. water, organics and cations) are ignored

- the interrupted frameworks are not terminated by hydrogen atoms, i.e. only T and O atoms are considered as hard spheres

- the calculations are based on the coordinates of ideal SiO_{2} frameworks in the highest possible symmetry, as given in the *Atlas*

Details of the calculations can be found in:
"A geometric solution to the largest-free-sphere problem in zeolite frameworks", M.D. Foster, I. Rivin, M.M.J. Treacy and O. Delgado Friedrichs, - all extra-framework atoms (i.e. water, organics and cations) are ignored

- the interrupted frameworks are not terminated by hydrogen atoms, i.e. only T and O atoms are considered as hard spheres

- the calculations are based on the coordinates of ideal SiO

Coordination Sequences

The concept of Coordination Sequences was originally introduced by G.O. Brunner and F. Laves (*Wiss. Z. Techn. Univers. Dresden* **20**, 387 (1971) H2) and first applied to zeolite frameworks by W.M,. Meier and H.J. Moeck ( *J. Solid State Chem.* **27**, 349 (1979)).

In a typical zeolite framework, each T-atom is connected to N_{1} = 4 neighboring T-atoms through oxygen bridges. These neighboring T-atoms are then linked in the same manner to N_{2} T-atoms in the next shell. The latter are connected with N_{3} T-atoms etc. Each T-atom is counted only once. In this way, a Coordination Sequence can be determined for each T-atom of the 4-connected net of T-atoms. It follows that

CS's are listed from N_{1} up to N_{10} for each topologically distinct T-atom in the framework structure along with the vertex symbol. The CS and the vertex symbol together appear to be unique for a particular framework topology, i.e. they can be used to distinguish different zeolite Framework Types unambiguously. In this way, isotypic frameworks can be recognized easily.

In a typical zeolite framework, each T-atom is connected to N

CS's are listed from N

Vertex symbols for zeolite nets

The Vertex Symbol was first used in connection with zeolite-type networks by M. O'Keeffe and S.T. Hyde (*Zeolites* **19**, 370-374 (1997)). This symbol indicates the size of the smallest ring associated with each of the 6 angles of a tetrahedron (T-atom). The symbols for opposite pairs of angles are grouped together. For **FAU**, the Vertex Symbol reads 4·4·4·6·6·12, indicating that one pair of opposing angles contains 4-rings, a second pair a 4-ring and a 6-ring, and the final pair a 6-ring and a 12-ring. It is useful for determining the smallest rings in a framework. In the case of **DOH**, for example, the vertex symbols for the four T-atoms are

so the smallest rings are 4- and 5-rings. Sometimes more than one ring of the same size is found for a single angle. This is indicated with a subscript like 6_{2} or 8_{2}. An asterisk in the vertex symbol indicates that no ring is formed for that angle. The Coordination Sequence and the Vertex Symbol together appear to be unique for a particular Framework Type. That is, they can be used to distinguish different zeolite Framework Types unambiguously. In this way, isotypic frameworks can be recognized easily.

5 · 5 · 5 · 5 · 5 · 6

4 · 5 · 5 · 6 · 5 · 6

5 · 5 · 5 · 5 · 5 · 6

5 · 5 · 5 · 5 · 5 · 5

4 · 5 · 5 · 6 · 5 · 6

5 · 5 · 5 · 5 · 5 · 6

5 · 5 · 5 · 5 · 5 · 5

so the smallest rings are 4- and 5-rings. Sometimes more than one ring of the same size is found for a single angle. This is indicated with a subscript like 6

Natural Tilings

Natural tilings for periodic nets are defined and discussed by V. A. Blatov, O. Delgado-Friedrichs, M. O'Keeffe and D. M. Proserpio, *Acta Crystallogr. A* **63**, 418-425 (2007). The tiling data for the Database were prepared by N. A. Anurova and V. A. Blatov with the program TOPOS (http://www.topos.samsu.ru/) and illustrations made with 3dt (http://gavrog.org/). The data are discussed and analyzed by N. A. Anurova, V. A. Blatov, G. D. Ilyushin and D. M. Proserpio, *J. Phys. Chem. C* **114**, 10160-10170 (2010).

Each page contains important crystallographic and topological information on the natural tiles and tiling. The four integers*pqrs* at the top right hand corner of each page indicate that there are *p* kinds of vertices, *q* kinds of edges, *r* kinds of faces, and *s* kinds of tiles in the tiling. The **Face symbol** shows the list of all rings that define the tile. **V**, **E**, **F** are the numbers of vertices, edges, faces of a tile. The **Symmetry** and **Wyckoff** lines contain the point symmetry and the name of the Wyckoff position where the tile centroid is allocated. If some tiles are combinatorially equal, but crystallographically different, then several **Symmetry** and **Wyckoff** records are given. The **Label** line includes the natural tile symbol conforming to Smith's nomenclature; the asterisk * marks natural tiles that have no corresponding name in Smith's list. The colored rectangle indicates the color of the tile in the **TILING** picture. The section **Special features** indicates whether the natural tiling is simple or has two-face edges, i.e. edges that belong to the faces of only two tiles.

Each page contains important crystallographic and topological information on the natural tiles and tiling. The four integers

Loop Configurations of T-atoms

The Loop Configuration is a simple graph showing how many 3- or 4-rings a given T-atom is involved in (List). Solid lines represent T-O-T linkages whereas dotted lines indicate non-connected T-O bonds found in interrupted frameworks. M. Sato (Proc. 6th IZC, Reno (Butterworth, 1984), p. 851) used the term "second coordination networks". Loop Configurations are likely to be of interest to spectroscopists. These data can also be used for classification purposes and for deducing rules relating to these structures which might be of predictive value (G.O. Brunner, *Zeolites*, **13**, 88 (1993)). The information given in the loop configuration is a subset of the vertex symbol.

Secondary Building Units (SBU's)

Zeolite frameworks can be thought of as consisting of finite or infinite (i.e. chain- or layer-like) component units. These Secondary Building Units^{a}, which contain up to 16 T-atoms, are derived assuming that the entire framework is made up of one type of SBU only. It should be noted that SBU's are invariably non-chiral^{b}. A unit cell always contains an integral number of SBU's. As far as practicable, all possible SBU's have been listed for Framework Type Codes assigned up to 2007. The codes given below the drawings are used on the data page to describe the SBU's. If more than one SBU is possible for a given framework type, all are listed.

The number of observed SBU's increased from 16 in 1992 to 23 in 2007 and an increasing number of frameworks required combinations of SBU's. These have not been listed in extenso because this can be arbitrary. Listing of SBU's for new Framework Type Codes was discontinued in 2007 in favor of CBU's and Tilings.

Please note:The SBU's are only theoretical topological building units and should not be considered to be or equated with species that may be in the solution/gel during the crystallization of a zeolitic material.

^{a}The primary building units are single TO_{4} tetrahedra.

^{b} This means that SBU's in the isolated state of highest possible symmetry are neither left- nor right-handed.

The number of observed SBU's increased from 16 in 1992 to 23 in 2007 and an increasing number of frameworks required combinations of SBU's. These have not been listed in extenso because this can be arbitrary. Listing of SBU's for new Framework Type Codes was discontinued in 2007 in favor of CBU's and Tilings.

Please note:The SBU's are only theoretical topological building units and should not be considered to be or equated with species that may be in the solution/gel during the crystallization of a zeolitic material.

Composite Building Units (CBU's)

Some units (e.g. double 6-ring, cancrinite cage, sodalite cage, alpha cavity) appear in several different framework structures, and can be useful in identifying relationships between Framework Types. Smith has compiled an exhaustive list of such units, not only for zeolite structures but also for hypothetical 3-dimensional 4-connected nets (Landolt-Boörnstein, Vol. 14, Subvolume A, Springer, Berlin, 2000). In his *Compendium of Zeolite Framework Types. Building Schemes and Type Characteristics*, van Koningsveld has also included an extensive list of them (Elsevier, Amsterdam, 2007). Here we have arbitrarily selected just 58 Composite Building Units and five chains that are found in at least two different Framework Types. These are different from secondary building units in that they are not required to be achiral, and cannot necessarily be used to build the entire framework. To facilitate communication, each unit has been assigned a lower case italic three-character designation. With the exception of the double 4-, 6- and 8-rings (*d*4*r*, *d*6*r* and *d*8*r*, respectively), a code corresponding to one of the Framework Types containing the CBU has been used for this purpose.

Type Material

The type material is the species first used to establish the framework type and is indicated with an asterisk (*) in the list of related materials and in the references.

The composition, expressed in terms of cell contents, has been idealized where necessary for simplicity. The chemical formula is given according to the new IUPAC rules. The space group and cell parameters listed for each type material are those taken from the reference cited. In many instances, further refinement of the structure taking into account ordering etc. would yield a lower symmetry. It should also be noted that the space group and other crystallographic data related to the type material structure do not necessarily apply to isotypes.

In some cases, the space group setting of the type material differs from that of the framework type. In these cases, the relationship between the unit cell orientation of the type material with respect to that of the framework type is given. This relationship is important when comparing the orientation of the channel direction and the viewing direction of ring drawings (which are both given for the axis orientation of the type material) with that of the framework drawing.

Isotypic species are very frequent and are listed under "Related materials".

The composition, expressed in terms of cell contents, has been idealized where necessary for simplicity. The chemical formula is given according to the new IUPAC rules. The space group and cell parameters listed for each type material are those taken from the reference cited. In many instances, further refinement of the structure taking into account ordering etc. would yield a lower symmetry. It should also be noted that the space group and other crystallographic data related to the type material structure do not necessarily apply to isotypes.

In some cases, the space group setting of the type material differs from that of the framework type. In these cases, the relationship between the unit cell orientation of the type material with respect to that of the framework type is given. This relationship is important when comparing the orientation of the channel direction and the viewing direction of ring drawings (which are both given for the axis orientation of the type material) with that of the framework drawing.

Isotypic species are very frequent and are listed under "Related materials".

Channels

A shorthand notation has been adopted for the description of the channels in the various frameworks. Each system of equivalent channels has been characterized by

the channel direction (relative to the axes of the Type Material structure),
the number of T atoms (bold) forming the rings controlling diffusion through the channels, and
the crystallographic free diameters of the channels in Angstrom units.

The number of asterisks in the notation indicates whether the channel system is one-, two- or three-dimensional. Interconnecting channel systems are separated by a double arrow (↔). A vertical bar (|) means that there is no direct access from one channel system to the other. The examples below have been selected to illustrate the use of this notation. Cancrinite | [001] 12 5.9 x 5.9* |

Offretite | [001] 12 6.7 x 6.8* ↔ ⊥[001] 8 3.6 x 4.9** |

Mordenite | [001] 12 6.5 x 7.0* ↔ {[010] 8 3.4 x 4.8 ↔ [001] 8 2.6 x 5.7} |

Zeolite Rho | <100> 8 3.6 x 3.6*** | <100> 8 3.6 x 3.6*** |

Gismondine | {[100] 8 3.1 x 4.5 ↔ [010] 8 2.8 x 4.8}*** |

Cancrinite is characterized by a 1-dimensional system of channels parallel to [001] or *c* with circular 12-ring apertures. In offretite the main channels are similar but they are interconnected at right angles by a 2-dimensional system of 8-ring channels, and thus form a 3-dimensional channel system. The channel system in mordenite is essentially 1-dimensional with somewhat elliptical 12-ring apertures. The 8-ring limiting diffusion in the [001] direction is extremely narrow, and this effectively prevents diffusion between adjacent 12-ring channels. Zeolite rho is an example of a Framework Type containing two non-interconnecting 3-dimensional channel systems that are displaced with respect to one another (<100> means there are channels parallel to all crystallographically equivalent axes of the cubic structure, i.e., along *x*, *y* and *z*.). In gismondine, the channels parallel to [100] together with those parallel to [010] give rise to a 3-dimensional channel system, which can be pictured as an array of partially overlapping tubes.

Please note: The channel direction is given for the axis orientation of the type material. This orientation may be different from the orientation given in the framework drawing (see the cell relationship give under "crystal chemical data" for these cases.

The free diameter values given in the channel descriptions and on the ring drawings are based upon the atomic coordinates of the type materials and an oxygen radius of 1.35 Å. Both minimum and maximum free diameter values are given for non-circular apertures. In some instances, the corresponding interatomic distance vectors are only approximately coplanar, in other cases the plane of the ring is not normal to the direction of the channel. Close inspection of the framework and ring drawings should provide qualitative evidence of these factors. Some ring openings are defined by a very complex arrangement of oxygen atoms, so in these cases other short interatomic distances that are not listed may also be observed. It should be noted that crystallographic free diameters may depend upon the hydration state of the zeolite, particularly for the more flexible frameworks. It should also be borne in mind that effective free diameters can be affected by non-framework cations and may also be temperature dependent.

Related Materials

Under the heading "Related Materials" as-synthesized materials that have the same framework type but different chemical composition or have a different laboratory code are listed. Materials obtained by post synthesis treatment (e.g. ion exchange, dealumination, etc.) are generally not included. The type material is given first and marked with an asterisk. Isotypic species, which have sometimes been termed "homeotypic", are very frequent.