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(Figure 65) is typical of the I : I inclusion complexes; values for I :2
inclusion compounds such as Zn|T(p-CI )PP] - 2Ñ:Í608 (3.90A) were
higher.i:'* Slightly offset stacking of the porphyrin macrocycles in
subsequent layers delined the depth of the cavities. The intermoleeular
Br Br contact distances were reported as 3.837 A for a 1:2 Zn|T(p-Br)PP|-
2CsHxO,4 (methyl salicylate) inclusion material. Thermal gravimetric
analysis (TGA) was reported for ZnlTfp-BiOPPJ^CxH^O^ showing a 21% weight
loss for loss of solvent (theoretical 23%) at ~ 125 C without further
loss to 350 C.14 In the case of the 1:1 Zn|T(p-CI)PP|/nitrobenzene
inclusion compound, the observed helical arrangement of the porphyrin
backbone produced a [polarized cavity environment (Figure 66). Guest
molecules were observed to order in response.1'" The p-xylene clathrate
of Zn[T(p-F)PPJ featured a linear chain structure similar to that noted
in the chloro- and bromo-derivatives. However, the nonbonding F -F
contact distances have increased to 4.1 and 4.2 A, characteristic of a
repulsive interaction rather than an attractive force as observed in
other halogenated porphyrin materials.
A second motif observed by Strouse and coworkers is characterized by
tightly packed herringbone-like layers (Figure 67). Structures of this
type were observed for ZjijT(p-Cl)PP]-C7H7Cl Ubchlorotoluene).11"'
Zn|T(j> Br)PP|-3C,HsN and Zn(T(p-Br)PP]-4C.)l 1 ^ (mesitylene).1''1 In
the p-bronto compounds, ligation of two pyridines to the Zn(ll) ion was
observed. The remaining uncoordinated guest molecules were observed to
occupy voids between the porphyrin moieties.
A third motif, also observed in Strouse's TPP materials, is
characterized by lightly packed corrugated layers in which the guest
molecules intercalate between the layers: Zn|T(p-Br)PP] -4C(,H7N
(aniline) and Zn[T(p-Br)PP| • 2CXH||N (methylbenzylamine) (Figure 68).1,1
2. Hydrogen-Bonded Network Materials
In an effort to synthesize more robust frameworks, hydrogen-bond
interactions have been explored as basis for linking porphyrin molecules.
Hydrogen bonds offer the additional advantages of directionality and
selectivity.1 While hydrogen bonding is certainly a stronger interaction
than the van der Waals interactions that hold the "porphyrin sponge"
solids together, even multiple hydrogen bonds per jwrphyrin still provide
only modest stabilization of the solids in the absence of their solvates.
Chou et al.
Figure 56. A 21-component multiporphyrin array. Reprinted with permission
from Drain, Ñ. Ì.; Lehn, J.-M. /. Chem. Soc., Chem. Commun. 1994, 2313.
Goldberg and coworkers have explored a number of substituted
tetraphenylporphyrins as building blocks for porous solids. Some of the
inclusion compounds of
5,10,15,20-tetra(4-hydroxy)phenyl porphyrins H2[T(p-OH)PP] featured
structures similar to those observed in halogenated species.130 In a
motif similar to the previously observed linear polymeric chains, the
Zn[T(p-OH)PP] ¦ 2-C6H60-2H20 (phenol), Zn[T(p-OH)PP]-2C9H10O • H20
(benzyl acetate) and Zn[T(p-OH)PP] ¦ 2C7H60 ¦ H20 (ben-zaldehyde)
clathrate materials are characterized by dual cis-side OH ¦ OH
intermolecular attractions. There are no intermolecular interactions
between para-substituted hydroxyl groups and /j-pyrrole hydrogen atoms of
adjacent linear chains (as observed in the halogenated materials).
Instead, para-substituted hydroxyl groups hydrogen bond with hydroxyl
groups on adjacent linear chains, forming a two-dimensional porphyrin
network. A guest water molecule
participates in this interchain bonding arrangement (Figure 69). In this
manner, two different guest cavities are formed-voids between porphyrins
in a polymeric chain and between chains in the two-dimensional array.
Layers are stacked in an offset manner, therefore forming pores instead
of channels in which axially coordinated ligands partially occupy the
voids in successive layers.
Similar ñè-side OH • • • OH interactions are observed in the Cu[T(p-
OH)PP] • 4CgHgO (acetophenone), Zn[T(p-OH)PP] • 2CgH]0 ¦ 4CH3OH (o-xylene
and methanol) and Zn[T(p-OH)PP] ¦ 5C7Hg02 (guaiacol) materials. The
linear porphyrinic chains are separated by guest molecules which hydrogen
bond to the hydroxyl groups (Figure 70). In the acetophenone and o-xylene
included materials, porphyrin macrocyclic planes of successive layers are
offset preventing the formation of distinct channels. The parallel
porphyrin macrocycles of successive layers are directly
41 / Porphyrin Materials Chemistry
Figure 57. Porphyrin arrays linked by yne and polyyne units. Reprinted
with permission from Lin, V. S.; DiMagno, S. G.; Therien, M. ). Science
1994, 264, I 105.
aligned in the guaiacol-included material generating ~9A cavities.
"Sandwiched" between layers of porphyrin macrocycles is a single
parallel-orientated guest molecule (Figure 71). There is another guest