Molecular tectonics: Zinc coordination networks based on centric and acentric porphyrins bearing pyridyl units

Article abstract of DOI:10.1039/c2dt32051g

Two new ligands, one symmetric 1 and the other acentric 2, based on a porphyrin backbone bearing either two ethynylpyridyl or one pyridyl and one ethynylpyridyl coordinating groups connected to the porphyrin at two opposite meso positions have been designed and prepared. In the presence of a Zn(II) cation, they lead to the formation of neutral metallatectons 1-Zn and 2-Zn which self-assemble into coordination networks in the crystalline phase. Whereas the metallatecton 1-Zn leads exclusively to the formation of grid type 2D networks, 2-Zn generates two types of crystals with rod and rhombic morphologies. The rod type crystals are composed of a 1D zigzag type arrangement whereas crystals with rhombic morphology are composed of directional 2D grid type architecture. The packing of the latter leading to the formation of the crystal occurs in a centrosymmetric fashion causing thus the loss of directionality.

Full text of DOI:10.1039/c2dt32051g

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PAPER
Molecular tectonics: zinc coordination networks based on centric and
acentric porphyrins bearing pyridyl units†
F. Sguerra, V. Bulach* and M. W. Hosseini*
Received 4th September 2012, Accepted 5th October 2012
DOI: 10.1039/c2dt32051g
Two new ligands, one symmetric 1 and the other acentric 2, based on a porphyrin backbone bearing either
two ethynylpyridyl or one pyridyl and one ethynylpyridyl coordinating groups connected to the porphyrin
at two opposite meso positions have been designed and prepared. In the presence of a Zn(II) cation, they
lead to the formation of neutral metallatectons 1-Zn and 2-Zn which self-assemble into coordination
networks in the crystalline phase. Whereas the metallatecton 1-Zn leads exclusively to the formation of
grid type 2D networks, 2-Zn generates two types of crystals with rod and rhombic morphologies. The rod
type crystals are composed of a 1D zigzag type arrangement whereas crystals with rhombic morphology
are composed of directional 2D grid type architecture. The packing of the latter leading to the formation
of the crystal occurs in a centrosymmetric fashion causing thus the loss of directionality.
Here, we report on the design and synthesis of two new
Introduction
porphyrin based tectons and their use for the generation of 1-
Molecular tectonics1 is a general approach dealing with mole-
and 2-D networks in the presence of the Zn(II) cation.
cular crystals for which some or all components called tectons2,3
are interconnected through specific interactions through mole-
Experimental part
cular recognition4 or coordination events, into 1-, 2- or 3-D net-
works.5 Among various possible intermolecular interactions, the
use of a coordination bond leading to coordination polymers6 or
MOFs7–19 has attracted considerable attention over the last two
decades.20 This class of crystalline materials is a subgroup of
molecular networks which are extended architectures presenting
translational symmetry.21 The increasing interest in this type of
hybrid assemblies arises from the endless possibilities that com-
binations of organic tectons and metallic centres or complexes
offer. Furthermore, this class of periodic architectures displays
useful properties such as storage,22 catalysis23 and separation.24
Although over the past few years many examples of coordination
networks have been reported, the domain remains still challen-
ging and of current interest.25
Characterization techniques
1H-NMR and 13C-NMR spectra were recorded at room tempera-
ture on a Bruker (300 MHz) NMR spectrometer. UV-Vis absorp-
tion spectra were collected at room temperature on a UVIKON
XL spectrometer from BIO-TEK instruments. Infrared spectra
were measured on a Shimadzu FTIR-8400s equipped with a Pike
Miracle ATR (Ge).
Mass spectra (ESI-MS) were recorded on a microTOF LC
spectrometer (Bruker Daltonics, Bremen).
Single-crystal studies
Among the many organic coordinating tectons reported so far,
the porphyrin based species are of particular interest.26–28
Indeed, in addition to its biological relevance, the porphyrin
backbone offers photophysical and electrochemical properties
resulting from its peculiar electronic structure. These may be of
interest in materials sciences. Furthermore, its propensity to bind
a vast variety of metal centres allows one to finely tune the
above mentioned properties.
Data were collected on a Bruker APEX8 CCD Diffractometer
equipped with an Oxford Cryosystem liquid N2 device at
173(2) K using a molybdenum microfocus sealed tube generator
with mirror-monochromated Mo-Kα radiation (λ = 0.71073 Å),
operated at 50 kV/600 mA. The structures were solved using
SHELXS-97 and refined by full matrix least-squares on F2 using
SHELXL-97 with anisotropic thermal parameters for all non-
hydrogen atoms.29 The hydrogen atoms were introduced at
calculated positions and not refined (riding model).
Laboratoire de Chimie de Coordination Organique, UMR CNRS 7140,
Université de Strasbourg, Institut Le Bel, 4, rue Blaise Pascal, F-67000
Strasbourg, France. E-mail: hosseini@unistra.fr
†CCDC 899822–899825 (Crystallographic data for 1-Zn·CH2Cl2, 1-Zn,
2-Zn·CHCl3 and 2-Zn in CIF format). For crystallographic data in CIF
or other electronic format see DOI: 10.1039/c2dt32051g
Synthesis
General: All reagents were purchased from commercial sources
and used without further purification. Compounds 4 and 9 are
commercially available.
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Compounds 3,30 5–731 and 832 were prepared according to
reported procedures.
chromatography (Al2O3, CH2Cl2 to CH2Cl2–acetone 97 : 3). The
compound was obtained as a purple solid (100 mg, 68%).
1H-NMR (300 MHz, CDCl3) δ: −2.82 (s, br, 2H, NH), 1.92
(s, 12H, CH3ortho), 2.71 (s, 6H, CH3para), 7.38 (s, 4H, Hmeta),
8.25 (dd, J = 4.4 and 1.7 Hz, 4H, Hpyridyl), 8.86 (m, 4H, Hβpyr),
8.92 (d, J = 4.6 Hz, 2H, Hβpyr), 9.09 (dd, J = 4.4 and 1.7 Hz,
4H, Hpyridyl), 9.33 (d, J = 4.6 Hz, 2H, Hβpyr), 10.20 (s, 1H,
Compound 1. In a Schlenck tube, a solution of 5,15-dimesi-
tyl-10,20-dibromoporphyrin 6 (100 mg, 0.14 mmol, 1 equiv.),
4-ethynyl pyridine 8 (42 mg, 0.42 mmol, 3 equiv.), Pd2dba3
(64 mg, 0.07 mmol, 0.5 equiv.) and AsPh3 (85.7 mg, 0.28 mmol,
2 equiv.) in degassed triethylamine (3 mL) and dry THF (7 mL)
was heated at 75 °C for 1 h. The mixture was cooled to room
temperature and the solvent was evaporated under reduced
pressure. The product was washed with methanol (3 × 10 mL)
and purified by column chromatography (Al2O3, CH2Cl2) to
afford the pure compound as a green solid (84 mg, 80%).
H
meso); 13C-NMR (90 MHz, CDCl3) δ: 21.5 (CH3), 21.7 (CH3),
104.9 (CH), 116.0 (C), 118.2 (C), 127.9 (C), 129.4 (CH), 130.3
(CH), 130.5 (CH), 130.9 (CH), 131.8 (CH), 137.8 (C), 138.0
(C), 139.4 (C), 148.2 (CH), 150.7 (C). UV-Vis. (CH2Cl2) λmax
/
nm (ε × 104/L mol−1 cm−1): 419 (39.13), 508 (1.61), 539 (0.28),
582 (0.46), 637 (0.11). IR(ATR)/cm−1 νmax: 1597, 1558, 1464,
1440, 1334, 1270, 1244, 1218, 1193, 1174, 1072 1051, 997,
961, 844, 797, 784, 736, 705, 696. m/z (HRM+) calc.: 624.312
[M + H+], found: 624.311.
1H-NMR (300 MHz, CDCl3) δ: −1.89 (s, br, 2H, NH), 1.87
(s, 12H, CH3ortho), 2.66 (s, 6H, CH3para), 7.32 (s, 4H, Hmeta),
7.84 (d, J = 6.0 Hz, 4H, Hpyridyl), 8.72 (d, J = 4.8 Hz, 4H,
H
βpyr), 8.82 (d, J = 6.0 Hz, 4H, Hpyridyl), 9.59 (d, J = 4.8 Hz,
4H, Hβpyr); 13C-NMR (90 MHz, CDCl3) δ: 21.6 (CH3), 30.9
Compound 11. 5,15-Dimesityl-10-(pyridin-4-yl)porphyrin 10
(85 mg, 0.136 mmol, 1 equiv.) in CHCl3 (65 mL) and pyridine
(65 μL) was treated with NBS (27 mg, 1.1 equiv.) at 0 °C for
30 min. The mixture was quenched with acetone (15 mL). The
solvent was evaporated under reduced pressure and the product
was purified by column chromatography (Al2O3, CH2Cl2–
acetone 95 : 5). The pure product was obtained as a purple solid
(80 mg, 84%).
(CH3), 94.2 (C), 125.4 (CH), 128.0 (CH), 138.2 (CH), 139.1
(CH), 148.4 (C), 148.3 (C), 150.1 (CH). UV-Vis. (CH2Cl2) λmax
/
nm (ε × 104/L mol−1 cm−1): 441 (34.17), 526 (0.91), 596 (3.39),
624 (1.85), 687 (2.09). IR (ATR)/cm−1 νmax: 2205, 1734, 1591,
1558, 1538, 1524, 1491, 1471, 1452, 1399, 1368, 1344, 1315,
1261, 1213, 1194, 1159, 1001, 976, 947, 925, 858, 811, 796, 726,
704. m/z (HRM+): calc.: 749.339 [M + H+], found: 749.338.
1H-NMR (300 MHz, CDCl3) δ: −2.58 (s, br, 2H, NH), 1.85
(s, 12H, CH3ortho), 2.66 (s, 6H, CH3para), 7.32 (s, 4H, Hmeta),
8.18 (dd, J = 4.4 and 1.5 Hz, 2H, Hpyridyl), 8.72 (s, 4H, Hβpyr),
8.78 (d, J = 4.8 Hz, 2H, Hβpyr), 9.04 (dd, J = 4.4 and 1.5 Hz,
2H, Hpyridyl), 9.64 (d, J = 4.8 Hz, 2H, Hβpyr); 13C-NMR
(90 MHz, CDCl3) δ: 21.5 (CH3), 21.6 (CH3), 103.0 (CBr), 116.4
(C), 119.5 (C), 127.9 (CH), 129.3 (CH), 137.8 (C), 138.1 (CH),
139.3 (C), 148.3 (CH), 150.0 (C). UV-Vis. (CH2Cl2) λmax/nm
(ε × 104/L mol−1 cm−1): 419 (42.60), 517 (1.70), 551 (0.72),
595 (0.49), 651 (0.41). IR(ATR)/cm−1 νmax: 3342, 3075, 2919,
2360, 2343, 1594, 1578, 1472, 1400, 1348, 1213, 1188, 1068,
971, 881, 846, 815, 801, 788, 737, 723, 657, 642. m/z (HRM+)
calc.: 702.223 [M + H+], found: 702.223.
Compound 2. In a Schlenck tube, a solution of 5,15-dimesi-
tyl-10-(pyridin-4-yl)-20-bromoporphyrin
11
(100
mg,
0.143 mmol, 1 equiv.), 4-ethynyl pyridine 8 (21.8 mg,
0.22 mmol, 1.5 equiv.), Pd2dba3 (32.7 mg, 0.036 mmol, 0.25
equiv.) and AsPh3 (43.8 mg, 0.143 mmol, 1 equiv.) in degassed
Et3N (3 mL) and dry THF (7 mL) was heated at 75 °C for 2 h.
The mixture was cooled to room temperature and the solvent
was evaporated under reduced pressure. The product was washed
with MeOH (3 × 10 mL) and purified by column chromato-
graphy (Al2O3, CH2Cl2) to afford the pure compound as a
purple solid (70 mg, 68%).
1H-NMR (300 MHz, CDCl3) δ: −2.20 (s, br, 2H, NH), 1.88 (s,
12H, CH3ortho), 2.67 (s, 6H, CH3para), 7.33 (s, 4H, Hmeta), 7.85
(br, 2H, Hpyridyl), 8.17 (br, 2H, Hpyridyl), 8.71 (s, 4H, Hβpyr),
8.78–8.88 (m, 4H, Hpyridyl and Hβpyr), 9.04 (s, br, Hpyridyl), 9.68
(d, J = 4.2 Hz, 2H, Hβpyr); 13C-NMR (90 MHz, CDCl3) δ: 21.9
(CH3), 22.1 (CH3), 77.7 (C), 94.2 (C), 96.8 (C), 97.9 (C), 118.5
(C), 120.6 (CH), 125.8 (C), 128.4 (CH), 129.6 (CH), 132.4, 138.0
(CH), 138.6 (C), 139.7 (CH), 148.8 (CH), 150.4 (CH), 150.5 (C).
UV-Vis. (CH2Cl2) λmax/nm (ε × 104/L mol−1 cm−1): 433
(44.71), 531 (1.26), 572 (2.66), 602 (0.74), 665 (1.17). IR
(ATR)/cm−1 νmax: 3326, 2964, 2919, 2539, 2323, 2200, 1591,
1561, 1536, 1472, 1536, 1472, 1454, 1404, 1377, 1345, 1218,
1193, 1151, 1070, 999, 977, 970, 929, 883, 850, 800, 789, 736,
728. m/z (HRM+) calc.: 725.339 [M + H+], found: 725.335.
Crystallisation conditions
1-Zn: in a crystallization tube (4 mm diameter, 15 cm height),
upon slow diffusion at room temperature of a MeOH solution
(2 mL) of Zn(OAc)2 (2 mg, 4 mmol L−1) into a CH2Cl2 solution
(0.5 mL) of compound 1 (0.38 mg, 1 mmol L−1) purple crystals
of 1-Zn were obtained after 14 days.
2-Zn: in a crystallization tube (4 mm diameter, 15 cm height),
upon slow diffusion at room temperature of a MeOH solution
(2 mL) of Zn(OAc)2 (2 mg, 4 mmol L−1) into a CHCl3 solution
(0.5 mL) of compound 2 (0.36 mg, 1 mmol L−1) two types
of purple crystals (rod and rhombic morphologies representing
ca. 90% and 10% respectively) were obtained after 10 days.
Compound
10. 5,15-Dimesityl-10-bromoporphyrin
7
(147 mg, 0.235 mmol, 1 equiv.), 4-pyridine boronic acid 9
(60 mg, 0.5 mmol, 2.1 equiv.) and Na2CO3 (60 mg, 0.7 mmol, 3
equiv.) in a mixture of toluene (8 mL), MeOH (5 mL) and water
(0.5 mL) were degassed with argon for 15 min. Then Pd(PPh3)4
(13.5 mg, 0.01 mmol, 0.05 equiv.) was added and the mixture
was refluxed at 95 °C for 3 days. The solvent was evaporated
under reduced pressure and the dark solid was purified by column
Results and discussion
Design of ligands 1 and 2
The majority of the reported coordination networks is often
based on two or three component systems. Furthermore, since
14684 | Dalton Trans., 2012, 41, 14683–14689
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Scheme 2
Scheme 1
reported procedure by Lindsey et al.31 upon condensation of the
dipyrrin 330 with the mesitylaldehyde 4.
The porphyrin 5 may be selectively mono- or dibrominated at
the unsubstituted meso positions 10 and 20 using 1 or 2 equiv.
of NBS respectively.31
usually coordination networks are obtained upon combining
metal cations and organic tectons, if the charge neutrality is not
ensured by the organic tecton, the crystal contains anions as
counter ions. In order to reduce the number of components and
to avoid the presence of anions, one may use a self-complemen-
tary neutral metallatecton comprising a metal centre and an
organic moiety bearing peripheral coordinating sites. It has been
shown that this may be achieved by using metaloporphyrin
For the synthesis of compound 1, a Sonogashira coupling
reaction between the dibromo derivative 6 and 4-ethynylpyridine
8 was used. Two types of conditions have been tested for this
coupling reaction. The first one was based on the use of
Pd(PPh3)Cl2 and copper iodide as catalysts.47 Although under
these conditions compounds 1 could be obtained in 90% yield,
unfortunately the ligand was contaminated with 8% of the 1-Cu
complex and the separation was found to be rather difficult and
tedious. In order to avoid the metallation of the porphyrin back-
bone, another route based on a mixture of Pd2(dba)3 and AsPh3
as the catalyst was explored.48 Under this copper free condition,
compound 1 could be obtained although with lower yields
(60–80%).
For the synthesis of 2, the monopyridyl derivative 10 was first
prepared using a Suzuki coupling reaction between monobromo-
porphyrin 7 and 4-pyridine boronic acid 9 in the presence of
Pd(PPh3)4 and sodium carbonate.49 The reaction under reflux in
toluene or in DMF at 120 °C failed and led to the dehalogenation
of porphyrin 7. However, in a biphasic medium (toluene/metha-
nol/water),50 the desired compound 10 was obtained in 68%
yield. The latter was transformed into its brominated derivative
11 in 84% yield upon treatment with NBS in CHCl3 at 0 °C.
Finally, using the copper free conditions mentioned above for
the synthesis of 1, compound 2 was obtained in 68% yield upon
a Sonogashira coupling between bromo derivative 11 and
4-ethynylpyridine 8.
derivatives.33–40 Along this idea, compounds
1 and 2
(Scheme 1) were designed. These compounds are ligands
offering three coordinating poles,41 i.e. the tetraaza core of a
porphyrin and two peripheral monodentate pyridyl units. The
binding of metal centres such as the Zn(II) cation, adopting the
penta- or hexa-coordination mode, by 1 and 2 leads to the
formation of 1-Zn and 2-Zn neutral complexes which, owing to
the presence of two divergently oriented peripheral pyridyl units
and the coordination extension possibility offered by the metal
centre located within the core of the porphyrin, must behave as
self-complementary metallatectons, leading thus to the formation
of infinite neutral coordination networks.
Compounds 1 and 2 are symmetric and unsymmetrical
porphyrin based ligands bearing two peripheral pyridyl units at
the meso positions 10 and 20. The remaining two meso positions
are occupied by two mesityl groups for solubilisation purposes.
For compound 1, an ethynyl spacer is used to connect the
pyridyl group to the porphyrin backbone. Examples of porphyrin
derivatives bearing ethynylpyridyl units have been reported.42,43
For compound 2 whereas one of the two pyridyl units is directly
connected, for the other one, an ethynyl spacer is used. In prin-
ciple, owing to the centric nature of the self-complementary
metallatecton 1-Zn, one would expect the formation of centro-
symmetric architectures, whereas for the acentric tecton 2-Zn,
directional architectures may be expected.44–46
Structural investigations of coordination networks formed by
1-Zn and 2-Zn
Synthesis of ligands 1 and 2
The generation of coordination networks was achieved by self-
assembly processes by reacting ligand 1 or 2 with zinc acetate.
At room temperature, upon slow diffusion of a MeOH solution
of Zn(OAc)2 into a CH2Cl2 or CHCl3 solution of porphyrin 1 or
The synthetic strategy adopted for the preparation of ligands 1
and 2 is based on the common 5,15-dimesitylporphyrin pre-
cursor 5 (Scheme 2). The latter was synthesised following a
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2, suitable crystals were obtained. Under the crystallisation
process, ligands 1 and 2 were metallated affording thus the
metallatectons 1-Zn and 2-Zn respectively (Scheme 1). The
crystalline materials thus obtained (see the experimental section)
were structurally studied using X-ray diffraction methods on
single crystals (Table 1).
For 1-Zn, the structural investigation revealed that the crystal
(monoclinic, P2(1)/n) is composed of 1-Zn and CH2Cl2 solvent
molecules which were found to be disordered over two positions.
For the solvent molecules, occupying the empty space, no
specific interactions with the tecton are observed.
Fig. 1 A portion of the structure of the 2D grid-type architecture gen-
erated by the self-complementary metallatecton 1-Zn showing the orien-
tation of the mesityl and pyridyl groups and the location of the N atom
of the two pyridyl units above and below the mean plane of the por-
phyrin. H atoms are not represented for clarity. For distances and angles
see text.
The porphyrin backbone is quasi-planar. The two N atoms of
the two ethynylpyridine units are located above and below the
mean plane of the porphyrin by 1.18 Å (Fig. 1). The two mesityl
units and pyridyl groups are tilted with respect to the porphyrin
plane by 80.2° and 35.7° respectively.
The Zn(II) cation, located in the centre of the porphyrin back-
bone, is hexacoordinated with a deformed octahedral coordi-
nation geometry. Its coordination sphere is composed of 6 N
atoms, among which four belong to the porphyrin tetraaza core
with a Zn–N distance of ca. 2.06 Å and the remaining two
apical positions are occupied by two N atoms of two pyridyl
units belonging to two consecutive metallatectons 1-Zn with a
Zn–N distance of 2.380 (5) Å. The two pyridyl groups are not
perpendicular to the porphyrin mean plane but tilted with an
angle of 63.7°. Owing to the hexacoordination of the Zn cation,
the overall architecture is a 2D coordination network of the grid
type (Fig. 2). The distance between two consecutive Zn(II)
cations within the grid is 12.51 Å. The dihedral angle between
consecutive porphyrin units is 77.6°.
Fig. 2 A portion of the 2D coordination network generated by 1-Zn
showing the connectivity pattern between consecutive units. The grid
type architecture is generated owing to the hexacoordination of the Zn
cation allowing thus the interconnection of consecutive units. H atoms
and CH2Cl2 solvent molecules are not represented for clarity. For bond
distances and angles see text.
Consecutive sheets are packed in a parallel fashion. They are
not eclipsed but staggered (space group P21/n). The distance
between consecutive sheets is 8.02 Å. The shortest distance
between Zn atoms belonging to two consecutive 2D grids is
8.02 Å. The packing mode leads to the formation of channels
Table 1 Crystallographic parameters recorded at 173 K for 1-Zn and 2-Zn
1-Zn·CH2Cl2
53H40Cl2N6Zn
1-Zn
2-Zn·CHCl3
2-Zn
Empirical formula
Molecular weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C
C52H38N6Zn
812.25
Monoclinic
P2(1)/n
10.7971(19)
14.170(3)
14.493(2)
90
C51H39Cl3N6Zn
907.60
Orthorhombic
Pccn
19.7276(4)
30.6924(6)
14.4077(3)
90
C50H38N6Zn
788.23
Orthorhombic
Pccn
16.1357(7)
32.4593(14)
15.6512(7)
90
897.18
Monoclinic
P2(1)/n
11.3103(9)
13.8466(12)
15.1616(12)
90
α (°)
β (°)
102.876(4)
90
2314.7(3)
2
109.694(4)
90
2087.7(6)
2
90
90
8723.7(3)
8
90
90
8197.4(6)
8
γ (°)
V (Å3)
Z
Colour
Purple
0.14 × 0.12 × 0.07
1.287
928
0.688
Purple
0.14 × 0.12 × 0.07
1.292
844
0.632
Purple
0.12 × 0.08 × 0.04
1.382
3744
0.791
Purple
0.12 × 0.12 × 0.08
1.277
3280
0.642
Crystal dim (mm3)
Dcalc (g cm−3
F(000)
)
μ (mm−1
)
Wavelength (Å)
Number of data meas.
Number of data with I > 2σ(I) 6496 [R(int) = 0.0921]
0.71073
25 988
0.71073
18 727
4637 [R(int) = 0.0550]
0.71073
124 534
9810 [R(int) = 0.0402]
0.71073
21 642
9049 [R(int) = 0.0703]
R
Rw
GOF
R1 = 0.1061, wR2 = 0.2744 R1 = 0.0503, wR2 = 0.0844 R1 = 0.0674, wR2 = 0.1809 R1 = 0.0782, wR2 = 0.2045
R1 = 0.1676, wR2 = 0.3070 R1 = 0.0970, wR2 = 0.0886 R1 = 0.0864, wR2 = 0.1978 R1 = 0.1488, wR2 = 0.2434
1.106
1.000
1.029
1.031
14686 | Dalton Trans., 2012, 41, 14683–14689
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filled with CH2Cl2 solvent molecules. Furthermore, the available
space is occupied by the mesityl groups belonging to consecu-
tive layers (Fig. 3).
solvate to 69.3°. Finally, the removal of the solvent molecules
leads to the shrinking of the consecutive sheets by ca. 1 Å.
Consequently, the volume of 2087 Å3 observed for the de-
solvated crystal represents a ca. 10% decrease when compared to
the solvated crystal (2314 Å3).
The reversibility of the solvation/desolvation process was also
studied. Unfortunately, upon diffusion of CH2Cl2 vapours into
desolvated crystals, an amorphous powder was obtained.
The unsymmetrical ligand 2 in the presence of the zinc(II)
cation leads to the metallatecton 2-Zn (Scheme 1). As for com-
pound 1, the metallation process takes place during the crystalli-
sation process. However, whereas in the case of 1 only one type
of crystal is formed, for 2, two types of crystals with distinct
morphologies are obtained (Fig. 6).
The rod type crystals (Fig. 6 left) dominate and represent the
major component of the mixture (ca. 80–90%) whereas the
rhombic crystals (Fig. 6 right) are the minor component.
X-ray diffraction analysis on crystals with rod type morpho-
logy revealed the formation of a 1D zigzag type architecture
(Table 1) (Fig. 7). The crystal, in addition to the 2-Zn entity, con-
tains a CHCl3 solvent molecule. In marked contrast with the 2D
network formed by 1-Zn and resulting from the hexacoordination
of metal centres, for the 1D network, the zinc cation is penta-
coordinated. The coordination geometry of the cation is square
based pyramidal and its coordination sphere is composed of four
N atoms belonging to the porphyrin backbone occupying the
square base with an average Zn–N distance of ca. 2.06 Å. The
apical position is occupied by the N atom (dZn–N = 2.177(3) Å)
of a pyridyl unit belonging to the consecutive 2-Zn complex
indicating that only one out of the two pyridyl units of 2 is
engaged in the connectivity pattern. It is worth noting that
among the two types of pyridyl groups, only the one directly
connected to the meso position of the porphyrin is bound to the
metal centre whereas the pyridyl of the ethynylpyridine moiety
remains unbound. However, the latter interacts with consecutive
1D networks by π–π interactions.
The desolvation of crystals of 1-Zn was studied on the same
crystal. The removal of the CH2Cl2 molecules was achieved at
room temperature over a period of 24 h. An X-ray diffraction
study revealed a single-crystal-to-single-crystal transformation.
While both the space group (monoclinic, P2(1)/n) and the con-
nectivity pattern (grid type architecture) are conserved upon
removal of the solvent, the metrics however undergoes signifi-
cant changes. The Zn(II) cation remains hexacoordinated with a
deformed octahedral coordination geometry (Fig. 4).
For the organic tecton, the dihedral angle of 24.3° between the
porphyrin mean plane (24 atoms) and the ethynylpyridine
moieties is considerably smaller than the one observed for the
solvated crystal (35.7°). However, the orientation of the two
mesityl groups remains almost unchanged.
The deviation from planarity of tecton 1 is enhanced. Indeed,
the distance (1.84 Å) between the N atoms of the pyridyl units
and the mean plane of the porphyrin backbone is considerably
larger than the one observed for the solvate (1.18 Å) (Fig. 5).
The tilt angle between the ethynylpyridine units and the
porphyrin mean plane is slightly enhanced from 63.7° for the
Fig. 3 A portion of the structure of the 2D coordination network gen-
erated by 1-Zn showing the packing of consecutive sheets as well as the
localisation of the CH2Cl2 solvent molecules in the channels. H atoms
are not represented for clarity. The carbon atoms of consecutive sheets
are differentiated by colour for clarity. For distances and angles see text.
The porphyrin backbone is slightly domed and the Zn cation
is located above the porphyrin mean plane with a distance of
Fig. 5 A portion of the structure of the desolvated crystal of 1-Zn
showing the orientation of the mesityl and pyridyl groups. H atoms are
not represented for clarity. For distances and angles see text.
Fig. 4 A portion of the structure of the desolvated crystals of 1-Zn
showing the deformation of the grid type architecture upon removal of
CH2Cl2 solvent molecules. H atoms are not represented for clarity. For
bond distances and angles see text.
Fig. 6 Photographs of the two types of crystals with rod (left) and
rhombic morphologies obtained upon combining compound 2 with the
Zn cation.
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Fig. 7 A portion of the structure of 2-Zn showing the formation of a
1D zigzag type arrangement. Among the two peripheral pyridyl units,
only the one directly connected to the porphyrin backbone is engaged in
the connectivity pattern. H atoms and CHCl3 solvent molecules are not
represented for clarity. For bond distances and angles see text.
Fig. 9 A portion of the 2D coordination network generated by 2-Zn
(crystals with rhombic morphology) showing the connectivity pattern
between consecutive units. The grid type architecture is directional. The
C atoms of the ethynyl units are differentiated by colour (blue) and
H atoms are not represented for clarity. For bond distances and angles
see text.
Fig. 8 A portion of the crystal structure of 2-Zn showing the orien-
tation of the mesityl and pyridyl groups. H atoms and CHCl3 solvent
molecules are not represented for clarity. For distances and angles see
text.
0.31 Å. The dihedral angles between the mesityl and ethynyl-
pyridyl units and the porphyrin mean plane are ca. 80° and 14°
respectively (Fig. 8).
Whereas the N atom of the ethynylpyridine unit is slightly
above the mean plane of the porphyrin backbone with a distance
of 0.14 Å, the N atom of the pyridine moiety directly connected
to the porphyrin is located below with a distance of 0.48 Å
(Fig. 8). The dihedral angle between the porphyrin and the
pyridyl group bound to the Zn cation is 76.4° which is slightly
higher than the one observed for the grid type structures dis-
cussed above.
The X-ray diffraction study on crystals with rhombic morpho-
logy revealed the formation of a directional grid type architecture
(Fig. 9). The crystal (orthorhombic, Pccn, Table 1) is only com-
posed of 2-Zn complexes.
The Zn cation, as in the case of 1-Zn, is hexacoordinated with
a distorted octahedral coordination geometry. The square base of
the latter is occupied by four N atoms of the porphyrin core with
an average Zn–N distance of ca. 2.05 Å. The two apical posi-
tions are occupied by two N atoms belonging to a pyridyl and an
ethynylpyridyl unit belonging to consecutive tectons 2-Zn with
again an average Zn–N distance of ca. 2.35 Å.
Fig. 10 A portion of the crystal structure of 2-Zn (rhombic morpho-
logy) showing the orientation of the mesityl and pyridyl groups.
H atoms are not represented for clarity. For distances and angles see text.
It is worth noting that, owing to the presence of one pyridyl
and one ethynylpyridyl unit located at the axial positions of the
metal centre, the grid type layer is directional, i.e. within a single
grid, the connectivity sequence is of the type (Py, Py, ethynyl-
pyridyl, ethynylpyridyl).
Consecutive grids are packed in a parallel fashion in the
AABB mode. They are not eclipsed but staggered (space group
Pccn). The distance between consecutive sheets is 8.22 Å. This
mode of packing leads to the occupation of empty spaces by
mesityl groups belonging to consecutive 2D networks (Fig. 11).
Although the grid type structure is directional, owing to the
centrosymmetric packing of consecutive grids following the
AABB mode, the overall crystal is not directional (Fig. 11).
The macrocyclic part of tecton 2 is slightly deformed.
However, the deformation is more pronounced than the one
observed for the 1-D network discussed above. In contrast with
all three structures mentioned above, i.e. the 2D grid type archi-
tectures obtained with 1-Zn (both the solvated and desolvated
crystals) and the 1D network observed for 2-Zn, the N atoms of
both the pyridyl and ethynylpyridyl units are located above the
mean plane of the porphyrin with distances of 0.74 Å and
1.27 Å respectively (Fig. 10). The pyridyl and ethynylpyridyl
units are tilted with respect to the porphyrin backbone by 65.7°
and 19.5° respectively. The distance between two adjacent
Zn cations within the grid type structure is 10.06 Å.
Conclusions
In conclusion, the two centric and acentric ligands 1 and 2 based
on a porphyrin backbone bearing two peripheral pyridyl coordi-
nating groups at two opposite meso positions lead in the pres-
ence of a Zn(II) cation to the formation of two metallatectons
1-Zn and 2-Zn. The latter being self complementary building
blocks self-assemble into coordination networks. Whereas in the
case of 1, a 2D grid type architecture is formed, for 2, two types
of crystals with rod or square type morphology are obtained.
Interestingly, the square type crystals are formed upon packing
14688 | Dalton Trans., 2012, 41, 14683–14689
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We thank the University of Strasbourg, the Institut Univer-
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Research in Chemistry (icFRC), the C.N.R.S. and the Ministry
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