organic moieties are introduced into open-framework architectures. These are different from the materials discussed previously in that the organic molecule is now
a part of the framework rather than simply occupying space in a pore system. A
major research theme in this field concerns coordination polymers, which we define
as extended arrays composed of metal atoms or clusters bridged by polyfunctional
organic molecules. Initial strategies focused on using rigid organic linkers to connect individual metal ions or clusters into extended networks, but more recent
efforts have clearly shown that flexible linkers can also be used to great effect. The
development of the coordination polymer area can be traced back to the work of
Gravereau, Garnier and Hardy in Poitiers in the late 1970s, in which zeolitic materials exhibiting ion-exchange properties were made by linking hexacyanoferrates
units with (tetrahedrally coordinated) Zn
2þ cations [118]. Charge balance is provided by sodium ions. The concept gained fresh impetus in 1994/5 with the work
of Robson [119] and Moore [120], who used rigid organic building blocks (e.g.
porphyrins) to construct three-dimensional networks with the topologies of known
structure types such as PtS and ThSi 2 . Much work in this area has been devoted
to crystal engineering, or the ability to rationally tailor reaction conditions and organic ligands to generate a predetermined network [121], often related to a classical, high-symmetry inorganic structure [122].
A second class of materials contains infinite metal–oxygen–metal (M–O–M) arrays as a part of their structures. Some of this work can trace its roots to a strategy
that was originally used by Alberti to increase the inter-layer spacing in layered
compounds [123]. The approach took advantage of monophosphonates, which
acted as spacers between the layers, albeit with no bonding connection between
them. In order to build open, three-dimensional frameworks, Johnson and Jacobson, showed that is possible to create connections between the layers by using
diphosphonates [124]. It is now known that hybrid frameworks can be made not
only with layered metal oxide structures, but also with systems in which the
metal–oxygen–metal (M–O–M) linkages are one- or three-dimensional. We shall
collectively refer to this class of materials as hybrid metal oxides. These two classes
of hybrid materials are discussed below in separate sections.
18.6.1
Coordination Polymers
Robson [119] chose as a geometrical/topological model one of a number of simple
three-dimensional nets such as diamond, a-Po, and PtS, and then tried to devise
ways of chemically linking together the building blocks with a functionality and
a stereochemistry appropriate to the chosen parent net. Using this approach,
he linked metalloporphyrines like Cu(II)(tcp) or Cu(II)(tpp) via Cu(I) complexes
to generate open frameworks in which the tunnels were occupied by disordered molecules of solvent. The first success of Lee and Moore [120] concerned
[Ag(TCB)(CF 3 SO 3 )] (TCB ¼ 1,3,5-tricyanobenzene). TCB has threefold symmetry
and its terminal nitrogens serve as ligating groups for the soft Ag(I) cation. The
combination of TCB and Ag(I) triflate leads to a honeycomb lattice in which tri18.6 Hybrid Nanoporous Materials 609
a part of the framework rather than simply occupying space in a pore system. A
major research theme in this field concerns coordination polymers, which we define
as extended arrays composed of metal atoms or clusters bridged by polyfunctional
organic molecules. Initial strategies focused on using rigid organic linkers to connect individual metal ions or clusters into extended networks, but more recent
efforts have clearly shown that flexible linkers can also be used to great effect. The
development of the coordination polymer area can be traced back to the work of
Gravereau, Garnier and Hardy in Poitiers in the late 1970s, in which zeolitic materials exhibiting ion-exchange properties were made by linking hexacyanoferrates
units with (tetrahedrally coordinated) Zn
2þ cations [118]. Charge balance is provided by sodium ions. The concept gained fresh impetus in 1994/5 with the work
of Robson [119] and Moore [120], who used rigid organic building blocks (e.g.
porphyrins) to construct three-dimensional networks with the topologies of known
structure types such as PtS and ThSi 2 . Much work in this area has been devoted
to crystal engineering, or the ability to rationally tailor reaction conditions and organic ligands to generate a predetermined network [121], often related to a classical, high-symmetry inorganic structure [122].
A second class of materials contains infinite metal–oxygen–metal (M–O–M) arrays as a part of their structures. Some of this work can trace its roots to a strategy
that was originally used by Alberti to increase the inter-layer spacing in layered
compounds [123]. The approach took advantage of monophosphonates, which
acted as spacers between the layers, albeit with no bonding connection between
them. In order to build open, three-dimensional frameworks, Johnson and Jacobson, showed that is possible to create connections between the layers by using
diphosphonates [124]. It is now known that hybrid frameworks can be made not
only with layered metal oxide structures, but also with systems in which the
metal–oxygen–metal (M–O–M) linkages are one- or three-dimensional. We shall
collectively refer to this class of materials as hybrid metal oxides. These two classes
of hybrid materials are discussed below in separate sections.
18.6.1
Coordination Polymers
Robson [119] chose as a geometrical/topological model one of a number of simple
three-dimensional nets such as diamond, a-Po, and PtS, and then tried to devise
ways of chemically linking together the building blocks with a functionality and
a stereochemistry appropriate to the chosen parent net. Using this approach,
he linked metalloporphyrines like Cu(II)(tcp) or Cu(II)(tpp) via Cu(I) complexes
to generate open frameworks in which the tunnels were occupied by disordered molecules of solvent. The first success of Lee and Moore [120] concerned
[Ag(TCB)(CF 3 SO 3 )] (TCB ¼ 1,3,5-tricyanobenzene). TCB has threefold symmetry
and its terminal nitrogens serve as ligating groups for the soft Ag(I) cation. The
combination of TCB and Ag(I) triflate leads to a honeycomb lattice in which tri18.6 Hybrid Nanoporous Materials 609