Hydrogen-Bonded Porphyrinic Solids: Supramolecular Networks of Octahydroxy Porphyrins

Symmetrically substituted octahydroxy porphyrins,
tetrakis(3‘,5‘-dihydroxyphenyl)porphyrin,
H2T(3‘,5‘-DHP)P, tetrakis(2‘,6‘-dihydroxyphenyl)porphyrin,
H2T(2‘,6‘-DHP)P, and their Zn(II) and
Mn(III) derivatives have
been developed as building blocks for supramolecular hydrogen-bonded
networks. The crystal structures of a series
of these porphyrins exhibit unique structural features through assembly
of porphyrin networks by means of directional
hydrogen bonding. The position of the peripheral hydroxyl groups,
the choice of metallo- or free base porphyrin,
and the nature of the solvate (i.e., guest) dramatically influence
structural features. A one-dimensional, columnar
structure is found for H2T(3‘,5‘-DHP)P·5EtOAc.
With benzonitrile as solvate, the structure of
H2T(3‘,5‘-DHP)P·7C6H5CN changes substantially to a three-dimensional corrugated-sheet
structure in order to accommodate a larger pore
size. When the hydroxyl substituents are simply changed from
the m- to the o-phenyl
positions, an essentially
two-dimensional layered structure is formed for
H2T(2‘,6‘-DHP)P·4EtOAc.
Zn[T(2‘,6‘-DHP)P](EtOAc)2·2EtOAc
has a two-dimensional layered structure, similar to that of its free
base H2T(2‘,6‘-DHP)P interaction between the
aryl
rings of the adjacent layers. The crystal structures of both
Zn[T(3‘,5‘-DHP)P] and Mn[T(3‘,5‘-DHP)P](Cl)
exhibited
three-dimensional hydrogen-bonding features.
Zn[T(3‘,5‘-DHP)P](THF)2·2THF·3CH2Cl2
has a three-dimensional
interconnected layered structure with metalloporphyrins arranged in a
slipped stack orientation within the layers. In
the structure of
Mn[T(3‘,5‘-DHP)P](THF)2·Cl·2THF·5C6H5CH3,
a chloride anion dictates the three-dimensional packing
by bridging four metalloporphyrin molecules through Cl···HO
bonding interactions. In all of these structures,
large
solvate-filled channels are present with cross-sections as large as 42
Å2. The pore volumes of these channels
are
exceptionally large:  as much as 67% of the unit cell
volume.