Different hydrogen-bonding patterns in two [Zn(ENTPP)] complexes with water or methanol as ligands

Article abstract of DOI:10.1080/00958972.2012.686035

We have synthesized zinc complexes of H₂ENTPP (5-(8-ethoxycarbonyl-1-naphthyl)-10,15,20-triphenyl porphyrin) as a model to study hydrogen-bonding interactions. When water or methanol is a ligand, crystals of [Zn(ENTPP)(CH₃OH)] or [Zn(ENTPP)(H₂O)]C ₆H₅CH₃ were obtained. In both structures, the ligand has hydrogen-bonding interactions, but in different patterns. In [Zn(ENTPP)(CH₃OH)], the methanol oxygen and carboxylate oxygen in the naphthyl group form an intermolecular hydrogen bond. In [Zn(ENTPP)(H ₂O)]·C₆H₅CH₃, there are two independent molecules A and B. In molecule B, there is an intramolecular hydrogen bond between the water oxygen and the carboxylate oxygen, while in molecule A, besides the intramolecular hydrogen bond, there is an intermolecular hydrogen bond between the water oxygen and the carboxylate oxygen. ¹H NMR spectra suggest the binding of methanol or water to zinc are equilibrium processes in solution. Equilibrium constant has been determined by UV-Vis measurements, and it suggests the binding affinity of zinc to methanol has been moderately increased.

Full text of DOI:10.1080/00958972.2012.686035

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Different hydrogen-bonding patterns in
two [Zn(ENTPP)] complexes with water
or methanol as ligands
Weiguang Fang a b , Jiaxun Jiang a , Hong Yu a , Wen Yang a
Xiaoming Ren b & Chuanjiang Hu a a
a Key Laboratory of Organic Synthesis of Jiangsu Province ,
,
College of Chemistry, Chemical Engineering and Materials Science,
Soochow University , Suzhou 215123 , P.R. China
b College of Science , Nanjing University of Technology , Nanjing
210009 , P.R. China
Published online: 10 May 2012.
To cite this article: Weiguang Fang , Jiaxun Jiang , Hong Yu , Wen Yang , Xiaoming Ren &
Chuanjiang Hu (2012) Different hydrogen-bonding patterns in two [Zn(ENTPP)] complexes
with water or methanol as ligands, Journal of Coordination Chemistry, 65:11, 1905-1914, DOI:
10.1080/00958972.2012.686035
To link to this article: http://dx.doi.org/10.1080/00958972.2012.686035
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Journal of Coordination Chemistry
Vol. 65, No. 11, 10 June 2012, 1905–1914
Different hydrogen-bonding patterns in two [Zn(ENTPP)]
complexes with water or methanol as ligands
WEIGUANG FANGyz, JIAXUN JIANGy, HONG YUy, WEN YANGy,
XIAOMING RENz and CHUANJIANG HU*y
yKey Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical
Engineering and Materials Science, Soochow University, Suzhou 215123, P.R. China
zCollege of Science, Nanjing University of Technology, Nanjing 210009, P.R. China
(Received 6 January 2012; in final form 12 March 2012)
We have synthesized zinc complexes of H2ENTPP (5-(8-ethoxycarbonyl-1-naphthyl)-10,15,20-
triphenyl porphyrin) as a model to study hydrogen-bonding interactions. When water or
methanol is a ligand, crystals of [Zn(ENTPP)(CH3OH)] or [Zn(ENTPP)(H2O)] ꢀ C6H5CH3 were
obtained. In both structures, the ligand has hydrogen-bonding interactions, but in different
patterns. In [Zn(ENTPP)(CH3OH)], the methanol oxygen and carboxylate oxygen in the
naphthyl group form an intermolecular hydrogen bond. In [Zn(ENTPP)(H2O)] ꢀ C6H5CH3,
there are two independent molecules A and B. In molecule B, there is an intramolecular
hydrogen bond between the water oxygen and the carboxylate oxygen, while in molecule A,
besides the intramolecular hydrogen bond, there is an intermolecular hydrogen bond between
the water oxygen and the carboxylate oxygen. 1H NMR spectra suggest the binding of
methanol or water to zinc are equilibrium processes in solution. Equilibrium constant has been
determined by UV-Vis measurements, and it suggests the binding affinity of zinc to methanol
has been moderately increased.
Keywords: Porphyrin; Hydrogen bond; Naphthyl; Binding constant
1. Introduction
Hydrogen-bonding interactions are common in biological systems and model systems.
In chiral recognition processes, such interactions play important roles in porphyrin-
based systems, such as in a mono-porphyrin system reported by Ogoshi and coworkers
[1, 2]. This system contains both a coordination site and a hydrogen-bonding site, so the
host is capable of binding amino acid esters, through a two-point fixation mechanism,
i.e., amine/zinc coordination and ester carbonyl/naphthol hydrogen-bonding, leading to
effective chiral recognition of amino acid esters. Hydrogen-bonding can also affect the
recognition ability. For example, in 5,15-bis(2-hydroxy-1-naphthy1) octaethylpor-
phyrin reported by Aoyama et al. [2], there is a remarkable difference in binding
constants between the trans and cis isomers. So it is important to synthesize new
*Corresponding author. Email: cjhu@suda.edu.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.686035

1906
W. Fang et al.
porphyrin-based hydrogen-bonding systems and study the corresponding hydrogen-
bonding interactions.
We are interested in hydrogen-bonding interactions in model systems [3] and have
recently studied the intramolecular hydrogen-bonding on the structure of a porphyrin
[Zn(SATPP)(CH3OH)] (SATPP, dianion of 5-(2-salicylideneaminophenyl)-10,15,20tri-
phenylporphyrin) [4]. One of our ongoing projects is to study chiral recognition in
porphyrin systems containing hydrogen-bonding interactions. Recently, we designed a
porphyrin, 5-(8-ethoxycarbonyl-1-naphthyl)-10,15,20-triphenyl porphyrin (H2ENTPP),
as shown in scheme 1 [5]. Its metal complex could provide a coordination site, a
hydrogen-bonding site and a steric interaction site, as a potential host in chiral
recognition. In this article, we have synthesized two zinc complexes,
[Zn(ENTPP)(CH3OH)] and [Zn(ENTPP)(H2O)] ꢀ C6H5CH3, and studied hydrogen-
bonding interactions in their solid structures. Binding constant of zinc to methanol has
also been determined by UV-Vis measurements.
2. Experimental
2.1. General procedures
2.1.1. Materials and general methods. All reagents were of analytical grade and used
1
without purification. All solvents were used as received. H NMR spectra were carried
out using a Bruker AVANCE 400 spectrometer.
2.2. Synthesis of [Zn(ENTPP)]
[Zn(ENTPP)] was prepared according to literature procedure [6]. A solution of
Zn(CH3COO)2 ꢀ 2H2O (0.125 g, 0.57 mmol) in methanol (5 mL) was added to the
solution of H2ENTPP (0.21 g, 0.28 mmol) in chloroform (50 mL). The mixture was
refluxed for 3 h. After completion of the reaction, the solution was washed with water
(3 ꢁ 100 mL). The organic layer was collected, then dried over magnesium sulfate, and
concentrated under reduced pressure. The residue was purified on silica gel with
methylene chloride/hexane (1 : 1) to give light purple solid. Yield 0.20 g (89%).
hydrogen bonding site
steric hindered group
O
R'
X
coordination site
R
N
N
M
N
N
Scheme 1 A potential host for chiral recognition.

Hydrogen bonding patterns
1907
Anal. Calcd for C51H34N4O2Zn ꢀ 0.5H2O (%): C, 75.69; H, 4.36; N, 6.92. Found:
C, 75.54; H, 4.29; N, 6.87.
2.3. X-ray crystallography
Suitable crystals of [Zn(ENTPP)(CH3OH)] for X-ray diffraction were grown from
diffusion of methanol into the toluene solution in 8 mm diameter glass tubes. When
methanol was replaced by hexane, X-ray quality crystals of [Zn(ENTPP)H2O]ꢀ C6H5CH3
were obtained.
X-ray data collection was made on a Rigaku Mercury CCD X-ray diffractometer
using graphite monochromated Mo-Kꢀ radiation (ꢁ ¼ 0.071073 nm) at 223(2) K for
[Zn(ENTPP)(CH3OH)] and at 293 K for [Zn(ENTPP)(H2O)] ꢀ C6H5CH3. Both crystals
were solved by direct methods and refined on F2 using full-matrix least-squares with
SHELXTL version 97 [7]. Anisotropic thermal parameters were refined for non-
hydrogen atoms. Hydrogen atoms, H(1 S) in [Zn(ENTPP)CH3OH], H(1WA), H(2WA),
H(1WB), and H(2WB) in [Zn(ENTPP)(H2O)] ꢀ C6H5CH3, were found in Fourier maps,
their coordinates and isotropic temperature factors were refined; other hydrogen atoms
were theoretically added riding on their parent atoms. In the structure of
[Zn(ENTPP)(H2O)] ꢀ C6H5CH3, toluene was disordered over two positions and both
were refined as rigid groups. After the final refinement the occupancy of the major
orientation was 64%. Crystal data for [Zn(ENTPP)CH3OH] and [Zn(ENTPP)(H2O)] ꢀ
C6H5CH3 are listed in table 1.
2.5. Equilibrium constant determination
UV-Vis spectra were measured on a Shimadzu UV-3150 spectrometer. Microliter
amounts of freshly distilled methanol were added to 1.78 ꢁ 10ꢂ6 mol Lꢂ1 [Zn(ENTPP)]
in CH2Cl2. The concentrations of methanol for UV-Vis measurements ranged from
1.85 ꢁ 10ꢂ3 to 1.23 ꢁ 10ꢂ1 mol Lꢂ1. Absorbance changes were monitored by observing
the increase in intensity of the Soret band at 422 nm.
3. Results and discussion
3.1. Molecular structure
The porphyrin complex has been synthesized by mixing H2ENTPP with methanol
solution of Zn(CH3COO)2 ꢀ 2H2O. In the presence of methanol, X-ray quality crystals
of [Zn(ENTPP)(CH3OH)] were crystallized; while in the absence of methanol, crystals
of [Zn(ENTPP)(H2O)] ꢀ C6H5CH3 were obtained, such coordinated water is probably in
the original toluene/hexane solvent. Both structures have been determined by X-ray
crystallography.
The crystal structure of [Zn(ENTPP)(CH3OH)] has been solved in the P2(1)/c space
group, and one asymmetric unit consists of one zinc porphyrinate molecule. The crystal
ꢀ
structure of [Zn(ENTPP)(H2O)] ꢀ C6H5CH3 has been solved in the P1 space group, and
one asymmetric unit consists of two independent zinc porphyrinate molecules and two

1908
W. Fang et al.
Table 1. Crystallographic data for [Zn(ENTPP)(CH3OH)] and [Zn(ENTPP)(H2O)] ꢀ C6H5CH3.
Crystal
[Zn(ENTPP)(CH3OH)]
C52H38N4O3Zn
832.23
Monoclinic
P2(1)/c
223(2)
[Zn(ENTPP)(H2O)] ꢀ C6H5CH3
C116H88N8O6Zn2
1820.68
Triclinic
ꢀ
P1
Empirical formula
Formula weight
Crystal system
Space group
Temperature (K)
Unit cell dimensions (A,
293(2)
ꢃ
˚
)
a
b
c
ꢀ
ꢂ
ꢃ
14.525(3)
11.125(2)
25.615(5)
90
100.82(3)
90
4065.2(14), 4
1.360
0.655
1728
21,995
13.078(3)
17.370(4)
22.840(5)
77.39(3)
73.74(3)
76.12(3)
4771.6(17), 2
1.267
3
˚
Volume (A ), Z
Calculated density (g cmꢂ3
)
Absorption coefficient (mmꢂ1
F(000)
)
0.564
1896
Reflections collected
Independent reflections
Parameters
Goodness-of-fit
R1 [I 4 2ꢄ(I)]
wR2 (all data)
44,281
16,711 [R(int) ¼ 0.0304]
7078 [R(int) ¼ 0.0521]
543
1.079
1317
1.072
0.0774
0.1982
0.0594
0.1518
2 1/2
]
R1 ¼ Æ(||Fo| ꢂ | Fc||)/{Æ|Fo}, wR2 ¼ Æw(|Fo|2 ꢂ |Fc|2)2/[Æw(|Fo|2)
.
Figure 1. ORTEP view for [Zn(ENTPP)(CH3OH)] at 50% probability thermal ellipsoids. The hydrogen
atoms except H(1S) have been omitted for clarity.
toluene solvates. Their ORTEP diagrams are presented in figures 1 and 2. In the
porphyrin, there are three phenyl groups and one naphthyl group at mesopositions.
Zinc is five-coordinate in both cases, the axial ligands are methanol and water,
˚
respectively. The corresponding distance Zn–O is 2.155(4) A for [Zn(ENTPP)
˚
˚
(CH3OH)], 2.145(2) A and 2.233(2) A for [Zn(ENTPP)(H2O)] ꢀ C6H5CH3; other related
distances are listed in table 2. These distances are similar to the corresponding distances
in [Zn(SATPP)(CH3OH)] [4], [Zn(TPP)(CH3OH)] [8], [Zn(TPP)(H2O)] [9],
[Zn(C45H28N4O2)(H2O)] ꢀ 2C6H5NO2 [10], (C45H28N4O2, dianion of 20-(4-carboxyphe-
nyl)-5,10,15-triphenylporphyrin)), [Zn(C48H48N4O3)(H2O)] [11], (C48H48N4O3, dianion

Hydrogen bonding patterns
1909
(a)
molecule A
(b)
molecule B
Figure 2. ORTEP view for [Zn(ENTPP)(H2O)] ꢀ C6H5CH3 at 50% probability thermal ellipsoids: (a)
molecule A consisting of Zn(1); (b) molecule B consisting of Zn(2). The hydrogen atoms except H(1S),
H(1WA), H(1WB), H(2WA), and H(2WB) have been omitted for clarity.
˚
Table 2. Selected bond lengths (A) for [Zn(ENTPP)(CH3OH)] and [Zn(ENTPP)(H2O)] ꢀ C6H5CH3.
[Zn(ENTPP)(CH3OH)]
[Zn(ENTPP)(H2O)] ꢀ C6H5CH3
Zn–N(1)
Zn–N(2)
Zn–N(3)
Zn–N(4)
Zn–O(1)
C(1)–C(18)
C(2)–C(3)
C(1)–O(1)
C(1)–O(2)
C(2)–O(2)
C(1S)–O(1S)
2.049(4)
2.066(4)
2.054(4)
2.063(4)
2.155(4)
1.511(8)
1.483(8)
1.207(6)
1.334(7)
1.461(6)
1.415(7)
Zn(1)–N(11)
Zn(1)–N(12)
Zn(1)–N(13)
Zn(1)–N(14)
Zn(1)–O(1W)
C(11)–C(118)
C(12)–C(13)
C(11)–O(11)
C(11)–O(12)
C(12)–O(12)
2.064(3)
2.061(3)
2.066(3)
2.059(3)
2.145(2)
1.502(5)
1.487(6)
1.198(4)
1.326(4)
1.446(5)
Zn(2)–N(21)
Zn(2)–N(22)
Zn(2)–N(23)
Zn(2)–N(24)
Zn(2)–O(2W)
C(21)–C(218)
C(22)–C(23)
C(21)–O(21)
C(21)–O(22)
C(22)–O(22)
2.051(3)
2.063(3)
2.054(3)
2.053(3)
2.233(2)
1.499(4)
1.503(6)
1.212(4)
1.330(4)
1.466(6)
of 5-(5-carboxy-9,9-dimethyl-(9H)-xanthen-4-yl)-2,8,13,17-tetraethyl3,7,12,18-tetra-
methylporphyrin). As five-coordinate species, zinc is not within the porphyrin plane,
˚
but out of four pyrrole nitrogen plane with displacements 0.26 A for
˚
˚
[Zn(ENTPP)(CH3OH)], 0.27 A for molecule A, and 0.24 A for molecule B in

1910
W. Fang et al.
ꢃ
˚
Hydrogen-bonds lengths (A) and angles ( ) for [Zn(ENTPP)(CH3OH)] and [Zn(ENTPP)
Table 3.
(H2O)] ꢀ C6H5CH3.
D–H ꢀ ꢀ ꢀ A
d(D–H)
d(H ꢀ ꢀ ꢀ A)
d(D ꢀ ꢀ ꢀ A)
ff(DHA)
[Zn(ENTPP)(CH3OH)]
O(1 S)–H(1 S) ꢀ ꢀ ꢀ O(1 S#1)
0.820(4)
2.019(6)
2.788(6)
155(8)
[Zn(ENTPP)(H2O)] ꢀ C6H5CH3
O(2W)–H(2WB) ꢀ ꢀ ꢀ O(21)
O(1W)–H(1WA) ꢀ ꢀ ꢀ O(11)
O(1W)–H(1WB) ꢀ ꢀ ꢀ O(21#2)
0.850(10)
0.848(10)
0.849(10)
2.023(12)
2.045(16)
1.981(12)
2.861(4)
2.835(3)
2.818(3)
168(4)
155(3)
169(3)
Symmetry operator #1: x, 1.5 ꢂ y, 0.5 þ z; #2: ꢂx, ꢂy, 1 ꢂ z.
[Zn(ENTPP)(H2O)] ꢀ C6H5CH3, respectively. Diagrams showing atomic displacements
from the mean plane of the four nitrogen core are given in the ‘‘Supplementary
material.’’
Our focus is the role of axial ligand in their structures. The methanol (or water)
molecule is not only coordinated to zinc, but also involved in hydrogen-bonding
interactions. In [Zn(ENTPP)(CH3OH)], the methanol forms an intermolecular hydro-
gen bond with the carboxylate oxygen in a symmetry related molecule (symmetry
operator #1: x, 1.5 ꢂ y, 0.5 þ z). The corresponding O(3)ꢀ ꢀ ꢀO(1#1) distance is
˚
2.788(6) A. Related distances and angles are listed in table 3. Because of this hydrogen
bond, one porphyrin packs with its symmetry related neighboring molecule to build a
dimer as shown in figure 3(a).
For [Zn(ENTPP)(H2O)] ꢀ C6H5CH3, the hydrogen-bonding pattern is more compli-
cated. Water in the two independent molecules is involved in different hydrogen-
bonding interactions. For molecule B, there is an intramolecular hydrogen bond
between water oxygen and carboxylate oxygen in the naphthyl group with
˚
O(2W) ꢀ ꢀ ꢀ O(21) distance 2.835(3) A, while in molecule A, instead of one hydrogen
bond, the coordinated water is involved in two hydrogen bonds, one an intramolecular
hydrogen bond between water oxygen and carboxylate oxygen in the naphthyl group
and the other is an intermolecular hydrogen bond between water oxygen and
carboxylate oxygen of an adjacent molecule (symmetry operator #2: ꢂx, ꢂy,1 ꢂ z).
˚
The corresponding distance of O(1W) ꢀ ꢀ ꢀ O(11) is 2.861(4) A and O(1W) ꢀ ꢀ ꢀ O(21#2) is
˚
2.818(3) A. These two molecules form a dimer through such hydrogen bonds as shown
in figure 3(b). The above structural results suggest that ENTPP is capable of forming
hydrogen bonds with a coordinated ligand.
In these [Zn(ENTPP)] complexes, the hydrogen-bonding patterns are much different
from that in [Zn(SATPP)(CH3OH)]. Considering the structural features of ENTPP,
steric effect causes the O(1)–C(1)–O(2) plane to be nearly parallel to the porphyrin
plane. This geometry makes the carbonyl oxygen tilt away from porphyrin center, close
to the porphyrin edge. Such arrangement could weaken the intramolecular hydrogen
bond between the carboxylate oxygen and the coordinated ligand. On the other hand,
such arrangement allows the carboxylate oxygen to have more space to form
intermolecular hydrogen bonds with neighboring molecule. That is also a possible
reason to form dimers through hydrogen-bonding in these [Zn(ENTPP)] species.

Hydrogen bonding patterns
1911
Figure 3. (a) Diagram of dimer in [Zn(ENTPP)(CH3OH)] formed by intermolecular hydrogen-bonding
interactions and (b) diagram of dimer in [Zn(ENTPP)(H2O)] ꢀ C6H5CH3 formed by both intermolecular and
intramolecular hydrogen-bonding interactions.
3.2. 1H NMR spectra
For porphyrins, NMR provides a very useful probe of intramolecular interactions due
1
to the ring current effect [12]. The H NMR spectra of [Zn(ENTPP)(CH3OH)] in the
selected region in CDCl3 are shown in figure 4(a). Binding of methanol and water to
zinc are verified by 1H NMR studies in solution. When methanol is coordinated to zinc,
methanol protons are in the shielding region and the ring current effect will cause a
remarkable upfield shift. Such shift is evidenced by the resonances of methanol proton
at 2.44 and 0.24 ppm as shown in figure 4(b). Compared with free methanol, these
resonances shift upfield by 1.05 and 0.85 ppm, respectively. Notably, there is another
signal at 1.06 ppm, which is assigned to the water protons. In CDCl3, H2O is a common
impurity which usually has a resonance at 1.56 ppm. But in our case, when it is
coordinated to zinc in solution, its resonance shifts upfield by 0.50 ppm. So there are
two equilibria involved in the solution as shown in scheme 2. The resonances observed

1912
W. Fang et al.
Figure 4. 1H NMR spectra of [Zn(ENTPP)(CH3OH)] ꢀ C6H5CH3 in the selected region in CDCl3: (a) the
concentrated solution and (b) the diluted solution.
K1
(1)
(2)
[Zn (ENTPP)(CH3OH)]
[Zn (ENTPP)(H2O)]
[Zn (ENTPP)]
[Zn (ENTPP)]
CH3OH
H2O
K2
Scheme 2. The equilibria between four-coordinate and five-coordinate porphyrin complexes in solution.
are actually the average contribution from both coordinated and uncoordinated
CH3OH (or H2O). These equilibria are further confirmed by concentration-dependent
1H NMR spectra. The spectrum of the diluted solution is shown in figure 4(b). The
resonances of methanol shift downfield by 0.34 and 0.22 ppm and that of water shifts
downfield by 0.18 ppm. It can be explained as the following reason: the equilibrium (1)
will be driven to the reverse reaction when the concentrations of both reactants
decrease; it will eventually increase the ratio of uncoordinated to coordinated methanol,
which causes the corresponding proton resonances to shift downfield. In the case of
water, because the ratio of uncoordinated to coordinated water increases as the amount
of uncoordinated H2O increases, the average H2O resonance shifts downfield.
3.3. UV-Vis spectra
The binding constant K1 for equilibrium (1) can be measured by UV-Vis spectroscopy
according to a method in the literature [13]. Titration of [Zn(ENTPP)] with methanol
has been performed and is shown in figure 5. The following double reciprocal
relationship can be defined [14]:
1
1
1
1
¼
ꢁ
þ
,
ð3Þ
DA KDA
½CH3OHŠ DA
1
1
where l/DA is the reciprocal of the change in absorbance observed after the addition of
methanol to a [Zn(ENTPP)] solution and DA is the reciprocal of the y-intercept
1
obtained in equation (1) yielding the absorbance change observed at infinite ligand
concentrations. l/DA is plotted versus the reciprocal of the added ligand concentration,
l/[L]. The linear least-squares analysis [15] is used to evaluate the slope and y-intercept
of the plotted data, given in figure S3. The obtained slope is 0.0788 which gives the K1
for the equilibrium as 40.6 L molꢂ1. Such binding constant is over four times larger than
the corresponding value for [Zn(TPP)] [13]. Considering the hydrogen-bonding

Hydrogen bonding patterns
1913
Wavelength
Figure 5. Spectral changes occurring upon titration of a [Zn(ENTPP)] solution with methanol. Porphyrin
concentration: 1.78 ꢁ 10ꢂ5 mol Lꢂ1. Spectrum recorded at 25ꢃC with dichloromethane as the solvent. In the
titration, each step represents the following ligand concentrations (mol Lꢂ1) increasing in the direction of the
arrow: 0, 1.85 ꢁ 10ꢂ3, 3.70 ꢁ 10ꢂ3, 6.16 ꢁ 10ꢂ3, 1.23 ꢁ 10ꢂ2, 1.85 ꢁ 10ꢂ2, 0.41 ꢁ 10ꢂ2, 1.37 ꢁ 10ꢂ1, and
1.23 ꢁ 10ꢂ1. The absorbance intensities at 422 nm were used for the linear least-squares analysis.
interactions, it is possible that the hydrogen bond moderately increases the binding
ability of methanol to zinc in [Zn(ENTPP)(CH3OH)].
The attempt to measure binding constant K2 for the equilibrium (2) has also been
performed in toluene. But there was no observable shift. The possible reason could be
the limited solubility of water and small binding constant.
4. Conclusion
We have synthesized two mononaphthyl porphyrin complexes, [Zn(ENTPP)(CH3OH)]
and [Zn(ENTPP)(H2O)] ꢀ C6H5CH3. X-ray crystallography shows that in the structure
of [Zn(ENTPP)(CH3OH)], the methanol oxygen and the carboxylate oxygen in the
naphthyl group form an intermolecular hydrogen bond. In molecule B of
[Zn(ENTPP)(H2O)] ꢀ C6H5CH3, there is an intramolecular hydrogen bond between
the water oxygen and the carboxylate oxygen; while in molecule A, besides the
intramolecular hydrogen bond, there is an intermolecular hydrogen bond between the
water oxygen and the carboxylate oxygen. The structural result proves that such
naphthyl substituted porphyrin is capable of forming a hydrogen bond with a
coordinated molecule. For [Zn(SATPP)] species, the phenol oxygen is located along the
center position, which could make it much closer to the ligand, leading to strong
intramolecular hydrogen bonds. While in both [Zn(ENTPP)] structures, the carbonyl
oxygen is tilted away from the porphyrin center, weakening the intramolecular
hydrogen bonds with the ligand and making carbonyl oxygen much easier to form
intermolecular hydrogen bonds with neighboring molecules. This is consistent with a
smaller binding constant for [Zn(ENTPP)] than for [Zn(SATPP)].

1914
W. Fang et al.
Supplementary material
Figures S1 and S2 display the displacements from four pyrrole nitrogen plane. Figures
S3 and S4 display the full 1H NMR spectra at different concentrations. Figure S5 gives
the linear fit for equation (1). Tables S1 and S2 give complete crystallographic details,
atomic coordinates, bond distances and angles, anisotropic temperature factors, and
fixed hydrogen atom positions. CCDC 860474 and 860475 contain the supplementary
crystallographic data. These data can be obtained free of charge via www.ccdc.cam.
ac.uk/conts/retrieving.html or by application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK; Fax: (þ44) 1223 336 033; E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgments
This work was supported by the Natural Science Foundation of China (No. 20971093)
and the Priority Academic Program Development of Jiangsu Higher Education
Institutions.
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