The
Atlas of Zeolite Framework Types (Ch. Baerlocher, L.B. McCusker and D.H. Olson, Elsevier,
Amsterdam, 2007) contains 176 topological distinct tetrahedral TO
4 frameworks, where T may be
Si, Al, P, Ga, B, Be etc.. The compiled Framework Types do not depend on composition, distribution of the
various T-atoms, cell dimensions or symmetry. The frameworks exhibit such a diversity of 4-connected
3-dimensional nets, that finite and infinite component units were introduced to describe their topologies.
Finite units were introduced by W.M. Meier (
Molecular Sieves, 1968, pp. 10-27) and J.V. Smith
(
Chem. Rev. 88, 149 (1988)). The secondary building units (SBUs) of Meier, e.g., 4-, 5- or 6-rings,
are invariably non-chiral. This means that only one kind of SBU rather than enantiomeric pairs is needed
to assemble the three-dimensional framework. The assemblage of the structure does not necessarily involve
crystallographic symmetry operations.
The finite structural subunits (SSUs) developed by Smith are often of greater complexity (e.g. polyhedral
cages). The SSUs represent a structural feature. They are not, however, SBUs in the sense just mentioned
because very often the framework cannot be constructed from SSUs alone. Frequently, SSUs need to share
corners, edges or faces to complete the framework. The SBUs, as such, are not meant to describe
precursors from which the zeolite grows. On the other hand, inspection of the systematics in existing
framework types may give clues to choose targets for synthesis because equal segments in different
frameworks, like (some of) the polyhedral cages, may play a role during crystal growth.
Infinite units, e.g. chains and layers, have been discussed extensively by several authors. The 5-ring
zeolites have been described in terms of component chain as well as in terms of component layers.
Building Units
Crystal structures, which are periodically ordered in 3 dimensions, are ordered
structures (regular crystalline solids). In this sense, chemical disorder, e.g. different cations on a
particular site, and dynamic disorder, e.g. rotational disorder of template molecules, is exluded.
Structural disorder within cavities of zeolite frameworks is also excluded. In this Schemes of Building
Zeolite Framework Models (hereafter called Schemes) the frameworks are built from periodic 0-, 1-, or
2-dimensional structurally invariant Periodic Building Units (PerBUs). The PerBUs are built from smaller
units composed of a limited number of T-atoms by applying simple operation(s) to the smaller unit, e.g.
translation, rotation. The zeolite framework types are analyzed in terms of these component PerBUs. The
infinite PerBUs, like (multiple) chains, tubes and layers, and finite PerBUs, like (double) 4-rings,
(double) 6-rings and cages, are far from unique. However, they are common to several zeolite framework
types and allow an easy description of the frameworks. Infinite PerBUs and finite PerBUs can be used to
build the zeolite frameworks. 6-Ring layers are frequently curled up to form tubes of 6-rings.
Many PerBUs can readily be constructed from (infinite) chains shown in Scheme 1. Three of these chains,
with identity periods of ~ m*2.5 Å, are referred to as zigzag (ZZ) chain, sawtooth (SAW) chain and crankshaft
(CRSHFT) chain with m = 2, 3 and 4, respectively. The number of T atoms in the independent repeat unit
along the chain axis equals m. The fibrous zeolites can be built using the natrolite (NAT) chain. The
unit cell dimension in a certain direction very often reflects the presence of ZZ, SAW or CRSHFT chains
in that direction.
Pore Descriptor
According to the IUPAC Recommendations (L.B. McCusker, F. Liebau and G. Engelhardt,
Pure Appl. Chem. 73, 381 (2001)), the pore system is described with the general pore
descriptor
{D [nm]i (Weff)}
where
D is the dimensionality of the pore system. For cages
D = 0, and for channels,
D = 1. For systems of interconnected channels,
D = 2 or 3;
[
nm]
i is the shape of the pore, where
m is the number of
n-rings (or windows) defining the faces of the polyhedral pore and ∑
mi is the
total number of faces;
[
uvw] the direction of the channel. The term [
uvw] can be replaced by <
uvw> to
indicate that all crystallographic equivalent directions are involved;
and (
Weff) is the effective channel width. In a topological
description this is the smallest
n-ring that determines the accessibility of the pore system to
guest species along the dimension of infinite extension.
If more than one pore system is present, the descriptors are separated by a slash(/).
Chains
Zigzag Chains
In the following framework types at least one of the unit cell dimensions is about 5.2 Å, indicating the
presence of zigzag (ZZ) chains: ABW, ATN, ATO, ATS, BCT, BIK,
CAN, CAS, CFI, -CHI, DAC, EPI, EUO, GON, ITW,
JBW, MTT, MTW, NES, NON, NPO, NSI, OSI, SFE,
SFH, SFN, SSY, TON, and VET. A detailed description of the framework
type is given in the building scheme concerned.
All PerBUs consist of ZZ chains connected to 4-rings, of (double) layers of (corrugated) fused 6-rings
with additional zigzag chains or 4-rings, or of tubular pores of rolled-up honeycomb-like sheets of
(fused) 6-rings. These pores are different from the 6-ring pores in which crankshaft chains determine
the cell repeat along the pore axis.
Sawtooth Chains
In the following framework types at least one of the unit cell dimensions is about
n*7.6 Å, indicating the presence of (twisted) sawtooth (SAW) chains. Sawtooth chains can be
connected into several PerBUs. A detailed description of the framework types obtained is given in the
building schemes of ATT, ATV, AWO, CDO, DAC, EON, EPI, FER,
JBW, LTL, MAZ, MFS, MOR, OFF, RWR and UEI.
Crankshaft Chains
In the following framework types at least one of the unit cell dimensions is between
8.3 and 9.9 Å, indicating the presence of crankshaft (CRSHFT) chains. Crankshaft chains can be connected
into several PerBUs. A detailed description of the framework types obtained is given in the building
schemes of
ACO,
AEL/,
AET,
AFI,
AFO,
AHT,
APC,
APD,
ATT,
ATV,
AWO,
DFT,
DON,
GIS,
‑LIT,
MER,
PHI,
GME,
UEI and
VFI.
Several PerBUs consist of pores of rolled-up honeycomb-like sheets of (fused) 6-rings. These pores are
different from the 6-ring pores in which ZZ chains determine the cell repeat along the pore axis.
Rings
Single 3- and/or 4-rings
Single 3- and/or 4-rings (S3/4R) can be connected into several PerBUs. In some cases
additional T-atoms are needed to build the PerBU. A detailed description of the framework types obtained
is given in the building schemes of EDI, ITE, LOV, MEI, MON, NAB,
NAT, NPO, OBW, OSO, -PAR, PON, ‑RON, RSN, RTH,
RWY, THO, VNI, VSV and WEI.
Double 4-rings
Double 4-rings (D4Rs) can be connected in several ways. In some cases the 4-rings
of the D4Rs are not 4-fold connected and/or additional T atoms are needed to build the framework. A
detailed description of the framework types obtained is given in the building schemes of ACO,
AFI, AFN, AFR, AFS, AFY, APC, APD, AST, ASV,
BOG, BPH, BRE, CGF, CGS, ‑CLO, DFO, DFT, ETR,
GIS, GOO, HEU, ITW, LAU, LTA, MEI, MER, OWE,
PHI, RRO, SAS, SFO, STI, TER, UOZ, USI, YUG
and ZON.
5-rings
5-Rings (5RINGS) can be connected into several PerBUs. In all cases additional
T-atoms, connected to the 5-rings, are needed to build the PerBU. A detailed description of the
framework types obtained is given in the building schemes of BIK, CAS, CDO,
CFI, ‑CHI, CON, DAC, DON, EPI, ESV, FER, GON,
IWR, MAZ, ME, MFI, MFS, MOR, MTF, MTT, MTW,
NSI, RTE, SFE, SFF, SFH, SFN, SGT, SSY, STF,
STT and TON.
Double 6-rings
Double 6-rings (D6Rs) can be connected into several PerBUs. In some cases the
6-rings of the D6Rs are not 6-fold connected and/or additional T atoms are needed to build the
PerBU.
A detailed description of the framework types obtained is given in the building schemes of
AEI,
AEN,
AFI,
AFO,
AFT,
AFX,
ATT,
ATV,
AWO,
AWW,
BOG,
CGS,
CHA,
EMT,
ETR,
FAU,
GME,
IFR,
KFI,
LAU,
‑LIT,
MSO,
RTE,
RUT,
SAO,
SAS,
SAV,
SOS,
TSC and
UEI.
Cages
A polyhedron whose maximum window is a 6-ring is called a cage. All other polyhedra
are called cavities.
Cages or cavities can be connected in several ways. A detailed description of the
framework types obtained is given in the building schemes of (in alphabetic order):
AST,
ATN,
AWW,
‑CLO,
DDR,
DOH,
EMT,
FAU,
KFI,
LTA,
LTN,
MEP,
MER,
MTN,
PAU,
RHO,
SBE,
SBS,
SBT,
SOD and
TSC.
Families
ABC-6 family
A large number of framework types can be constructed using a hexagonal PerBU
consisting of an array of non-connected 6-rings. They all belong to the so-called ABC-6-family. In these
framework types the unit cell dimension along the hexagonal axis is about n*2.55 Å (where
n = number of PerBUs along the hexagonal axis). A detailed description of the framework types is
given in the building schemes of AFG, AFT, AFX, CAN, CHA, EAB,
ERI, FRA, GIU, GME, LEV, LIO, LOS, MAR, OFF,
SAT and SOD.
Beta(like) family
The framework types *BEA, BEC, CON, ISV, ITH,
IWR and IWW can be built using chains that resemble each other.
Clathrasils
The famework types DDR, DOH, MEP and MTN belong to the
clathrasil family and can be built using units that consist of 30 T-atoms. These T30-units can be
connected in a periodic manner in 2-dimensions to form layers. Additional 6-ring layers are sometimes
needed.
Miscellaneous
A detailed description of the miscellaneous framework types is given in the building
schemes of ANA, CZP, SFG, UFI and UTL.
last updated: 4-August-2023