Supramolecular assembly of (methanol)[10,15,20-tris(4-cyanophenyl)-5-(4- pyridyl)porphyrinato]-zinc(II) by intermolecular hydrogen bonding and weak coordination

Article abstract of DOI:10.1107/S0108270106034986

The crystal structure of the title compound, [Zn(C₄₆-H ₂₄N₈)(CH₄O)], consists of two-dimensional supramolecular arrays sustained by O-H...N(pyridyl) hydrogen bonding and weak Zn...NC coordination. The interlayer organization in the crystal structure is characterized by tight stacking of the corrugated layers.

Full text of DOI:10.1107/S0108270106034986

metal-organic compounds
Ê
the central Zn ion deviating by only 0.161 (3) A from the
mean plane of the four pyrrole N atoms towards the methanol
ligand. This value should be compared with a commonly
Acta Crystallographica Section C
Crystal Structure
Communications
Ê
observed deviation of about 0.3 A in otherwise unconstrained
ISSN 0108-2701
®ve-coordinate complexes of zinc porphyrins (e.g. Lipstman &
Goldberg, 2006). An apparent weak coordination to the
central Zn ion from the opposite axial direction (Table 1, see
also below) provides an explanation for this discrepancy.
Supramolecular assembly of
(methanol)[10,15,20-tris(4-cyano-
phenyl)-5-(4-pyridyl)porphyrinato]-
zinc(II) by intermolecular hydrogen
bonding and weak coordination
Sankar Muniappan, Sophia Lipstman and Israel Goldberg*
School of Chemistry, Sackler Faculty of Exact Sciences, Tel-Aviv University,
Ramat-Aviv, 69978 Tel-Aviv, Israel
Correspondence e-mail: goldberg@post.tau.ac.il
Received 24 August 2006
Accepted 30 August 2006
Online 12 September 2006
Fig. 2 depicts the supramolecular interaction scheme for (I),
and the self-assembly process can be best described in a
modular way. Firstly, the strongest intermolecular attraction
that can be utilized in this structure is provided by hydrogen
bonding between the axial methanol ligand of one porphyrin
(acting as H-atom donor) and the pyridyl arm (the strongest
H-atom acceptor) of an adjacent unit (Table 2). Each
porphyrin molecule is involved in two such bonds in opposite
directions, thus creating a hydrogen-bonded zigzag chain of
the porphyrin species. However, adjacent chains combine into
a layered array via additional weak coordinations. These
involve the cyanophenyl substituent trans to the pyridyl group
of one unit and the uncoordinated (slightly concave) face of
the methanol±zinc core of an adjacent glide-related unit
(Table 1). This ZnÁ Á ÁN distance is somewhat longer than
previously observed in coordination polymers of six-co-
The crystal structure of the title compound, [Zn(C46-
H24N8)(CH4O)], consists of two-dimensional supramolecular
arrays sustained by OÐHÁ Á ÁN(pyridyl) hydrogen bonding and
weak ZnÁ Á ÁNC coordination. The interlayer organization in
the crystal structure is characterized by tight stacking of the
corrugated layers.
Comment
The supramolecular chemistry of porphyrins in the context of
crystal engineering has been widely studied during the past
decade or so. Effort has been focused mostly on the
meso-tetra-4-pyridylporphyrin and meso-tetrakis(4-carboxy-
phenyl)porphyrin building blocks in both their free-base and
metallated forms, taking advantage of the square-planar
functionality of these units and the versatile coordination and
hydrogen-bonding capacity of the peripheral pyridyl and
carboxylic acid groups (Goldberg, 2005, and references
therein; Kosal et al., 2002; Diskin-Posner et al., 2000; Diskin-
Posner & Goldberg, 1999; Krupitsky et al., 1994; Abrahams et
al., 1994). Attempts to induce the formation of non-centro-
symmetric materials using moieties of reduced (lower than
D4h) symmetry have been reported as well (George et al., 2006;
George & Goldberg, 2006; Vinodu & Goldberg, 2003). As part
of our systematic investigation of porphyrin-based crystalline
solids, we have been exploring the networking capacity of
porphyrin scaffolds bearing various combinations of periph-
eral functional groups (Goldberg, 2005). We report here on
the self-assembly of the title compound, (I).
Ê
ordinate zinc tetrakis(4-cyanophenyl)porphyrin (2.7±2.8 A;
Krishna Kumar et al., 1998), and in the present case this should
Compound (I) (Fig. 1) is characterized by its low symmetry,
while bearing substituent groups suitable for hydrogen
bonding as well as coordinative interactions. Both types come
into play in the interesting crystal structure of (I). The mol-
ecular structure exhibits a slightly domed conformation, with
Figure 1
The molecular structure of the title compound, showing the atom-
labelling scheme. Displacement ellipsoids are drawn at the 50%
probability level at ca 110 K.
Acta Cryst. (2006). C62, m477±m479
DOI: 10.1107/S0108270106034986
# 2006 International Union of Crystallography m477

metal-organic compounds
be attributed to the bias introduced by the markedly stronger
methanol binding to the Zn, as is also re¯ected in the slighly
domed conformation of the porphyrin species. However, the
ZnÁ Á ÁNC attraction creates an interporphyrin `linkage' along
an axis nearly perpendicular to the O55ÐH55Á Á ÁN28
hydrogen-bonding direction, thus affording a supramolecular
porphyrin array of two-dimensional connectivity.
The crystal structure of (I) naturally consists of a stacked
arrangement of the two-dimensional arrays. The corrugated
surfaces of neighbouring layers seem to ®t effectively into one
another, and no solvent is included between them. Two of the
cyanophenyl substituents (related trans to each other) are
directed at the interlayer interface from above and below,
contributing stabilizing dipolar attractions between these CN
dipoles of adjacent layers that point in opposite directions
(Fig. 3). However, the structure of (I) is not centrosymmetric.
This is consistent with our earlier correlations between the
symmetry of the individual building blocks and that of the
resulting crystalline architectures in porphyrin solids (George
& Goldberg, 2006; Vinodu & Goldberg, 2003). The use of
metalloporphyrin scaffolds of D4h symmetry almost uniformly
leads to centrosymmetric crystal structures, while the presence
of directional inter-porphyrin interactions combined with
lateral and/or axial asymmetry of the individual building
blocks may afford non-centrosymmetric architectures
(George et al., 2006; George & Goldberg, 2006; Vinodu &
Goldberg, 2003). In summary, the structure of (I) consists of
uniquely assembled two-dimensional multi-porphyrin arrays,
via a combination of hydrogen bonding and weak coordina-
tion.
Experimental
The free-base porphyrin compound was synthesized according to a
standard literature procedure (Adler et al., 1970), by condensation of
a 3:1 mixture of 4-cyanobenzaldehyde and pyridine-4-carbaldehyde
with distilled pyrrole in hot propionic acid. It was then separated
from the mixture of the various possible substitutional isomers by
elution with 2% methanol on a silica-gel column, and subsequently
metallated with zinc. Both the free-base and the metalloporphyrin
species were fully characterized by 1H NMR, UV±vis and mass
spectroscopic techniques. Crystallization of the title porphyrin was
carried out by evaporation of a solution in a mixture of methanol and
N,N0-dimethylacetamide (1.5 v/v).
Crystal data
[Zn(C46H24N8)(CH4O)]
Mr = 786.14
Monoclinic, Pn
Z = 2
Dx = 1.412 Mg m
Mo Kꢁ radiation
ꢂ = 0.72 mm
T = 110 (2) K
Prism, red
0.30 Â 0.20 Â 0.20 mm
3
1
Ê
a = 9.2505 (4) A
Ê
b = 9.6600 (5) A
Ê
c = 21.1032 (10) A
ꢀ = 101.422 (3)ꢀ
V = 1848.43 (15) A
3
Ê
Figure 2
A stereoview of the speci®c intermolecular interaction scheme in (I). Zn,
Data collection
N and O atoms are shown as darkened spheres. The methanol-to-pyridyl
Ê
Nonius KappaCCD area-detector
diffractometer
1ꢀ ' and ! scans
17749 measured re¯ections
7371 independent re¯ections
6328 re¯ections with I > 2ꢃ(I)
Rint = 0.032
ꢄmax = 27.9ꢀ
OÐHÁ Á ÁN hydrogen bonds [OÁ Á ÁN = 2.751 (6) A] and the ZnÁ Á ÁNC
Ê
contacts [ZnÁ Á ÁN = 3.020 (5) A] are indicated by thin lines. Note the two-
dimensional assembly that forms with a corrugated surface. H atoms have
been omitted for clarity, except for the hydroxylic H atoms in four of the
porphyrin units (in the lower left corner) which are involved in hydrogen
bonding.
Re®nement
Re®nement on F2
R[F2 > 2ꢃ(F2)] = 0.063
wR(F2) = 0.139
w = 1/[ꢃ2(Fo2) + (0.0348P)2
+ 3.736P]
2
where P = (Fo + 2Fc2)/3
S = 1.11
7371 re¯ections
517 parameters
H-atom parameters constrained
(Á/ꢃ)max = 0.013
3
Ê
Áꢅmax = 0.83 e A
3
Ê
1.55 e A
Áꢅmin
=
Absolute structure: Flack (1983),
with 2936 Friedel pairs
Flack parameter: 0.381 (17)
Table 1
Selected geometric parameters (A, ).
ꢀ
Ê
ZnÐN21
ZnÐN22
ZnÐN23
2.062 (5)
2.042 (4)
2.059 (4)
ZnÐN24
ZnÐO55
ZnÐN46i
2.044 (4)
2.226 (4)
3.020 (6)
Figure 3
A stereoview of the crystalline architecture of (I), projected approxi-
mately down the b axis. Zn, N and O atoms are shown as darkened
spheres. Note the tight solvent-free organization of the layered
assemblies (three layers are viewed edge-on). The OÐHÁ Á ÁN hydrogen
bonds and weak ZnÁ Á ÁNC coordination in each layer are indicated by thin
lines. H atoms have been omitted, except for the hydroxylic H atoms of
the three central molecular units which are involved in hydrogen
bonding.
N21ÐZnÐN22
N21ÐZnÐN23
N21ÐZnÐN24
N22ÐZnÐN23
N22ÐZnÐN24
89.86 (17)
171.0 (2)
89.09 (17)
89.61 (17)
171.0 (2)
N23ÐZnÐN24
N21ÐZnÐO55
N22ÐZnÐO55
N23ÐZnÐO55
N24ÐZnÐO55
90.02 (17)
95.96 (16)
95.93 (16)
93.07 (17)
93.07 (16)
Symmetry code: (i) x ‡ 12; y ‡ 1; z ‡ 21.
ꢁ
m478 Muniappan et al. [Zn(C46H24N8)(CH4O)]
Acta Cryst. (2006). C62, m477±m479

metal-organic compounds
Table 2
Hydrogen-bond geometry (A, ).
References
ꢀ
Ê
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DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
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O55ÐH55Á Á ÁN28ii
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1.00
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175
1
2
1
;
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.
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Ê
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Ê
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È
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This research was supported in part by the Israel Science
Foundation (grant No. 254/04).
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GD3047). Services for accessing these data are
described at the back of the journal.
ꢁ
Acta Cryst. (2006). C62, m477±m479
Muniappan et al. [Zn(C46H24N8)(CH4O)] m479