Cadmium complexes of meso-tetra-(p-chlorophenyl)porphyrin: [meso-tetra-(p-chlorophenyl)porphyrinato](pyridine)cadmium(II) pyridine solvate and [meso-tetra-(p-chlorophenyl)porphyrinato](dimethylformamide)cadmium(II) toluene solvate

Article abstract of DOI:10.1016/j.inoche.2004.09.015

This work reports the porphyrin ring current effect as a tool for the investigation of coordinated pyridine and DMF ligands and X-ray crystals of the two five-coordinate and mononuclear cadmium (II) porphyrin complexes Cd[(p-Cl)₄tpp](py) (5) and Cd[(p-Cl)₄tpp](DMF) (6) with square-based pyramidal geometries. The crystal structures of [meso-tetra-(p-chlorophenyl)porphyrinato](pyridine)cadmium(II) pyridine solvate Cd[(p-Cl)₄tpp](py)·py [or 5·py], and [meso-tetra-(p-chlorophenyl)porphyrinato](dimethylformamide)cadmium(II) toluene solvate Cd[(p-Cl)₄tpp](DMF)·toluene [or 6·toluene] were determined. The ring current effect provides a complementary method for the investigation of coordinated pyridine and DMF ligand in complexes 5 and 6, respectively.

Full text of DOI:10.1016/j.inoche.2004.09.015

Inorganic Chemistry Communications 7 (2004) 1233–1237
www.elsevier.com/locate/inoche
Cadmium complexes of meso-tetra-(p-chlorophenyl)porphyrin:
[meso-tetra-(p-chlorophenyl)porphyrinato](pyridine)cadmium(II)
pyridine solvate and [meso-tetra-(p-chlorophenyl)porphyrinato]
(dimethylformamide)cadmium(II) toluene solvate
a
a,
b,
c
Wun-Sian Wun , Jyh-Horung Chen *, Shin-Shin Wang *, Jo-Yu Tung ,
d
d
e
Feng-Ling Liao , Sue-Lein Wang , Lian-Pin Hwang , Shanmugam Elango
f
a
Department of Chemistry, National Chung-Hsing University, 250 Kuo-Kuang Road, Taichung 40227, Taiwan
b
Union Chemical Laboratories, Hsin-Chu 300, Taiwan
c
Tzu Hui Institute of Technology, Ping Tung 92641, Taiwan
d
Department of Chemistry, National Tsing-Hua University, Hsin-Chu 300, Taiwan
e
Department of Chemistry, Institute of Atomic and Molecular Sciences, National Taiwan University, Academia Sinica, Taipei 107, Taiwan
f
Institute of Chemical and Engineering Sciences, Singapore 627833, Singapore
Received 18 August 2004; accepted 23 September 2004
Available online 19 October 2004
Abstract
The crystal structures of [meso-tetra-(p-chlorophenyl)porphyrinato](pyridine)cadmium(II) pyridine solvate Cd[(p-Cl)4tpp](py) Æ py
[or 5 Æ py], and [meso-tetra-(p-chlorophenyl)porphyrinato](dimethylformamide)cadmium(II) toluene solvate Cd[(p-Cl)4tpp](DMF) Æ
toluene [or 6 Æ toluene] were determined. The ring current effect provides a complementary method for the investigation of coordinated
pyridine and DMF ligand in complexes 5 and 6, respectively.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Crystal structures; Cadmium meso-tetra-(p-chlorophenyl)porphyrin complexes; Ring current effect; Five-coordinate square-based pyra-
midal geometries
Previously, Ellis and coworkers reported the multinu-
1
solvate Cd(tpp) Æ (dioxane)2 (4). The solution 113Cd
NMR is relatively insensitive to the nature of the axial
nitrogen donor ligand in Cd(tpp)L (L = py, pip, etc.)
five-coordinated complexes with a range of 418–438
ppm [2]. Even the very weak oxygen of donor dioxane
at +435 ppm falls into this range. As a result the charac-
teristics of 113Cd NMR spectra of Cd(tpp)L complexes
are dictated by the porphyrin ring system. Hence, the
113Cd chemical shift in solution is unsuitable to probe
the subtle differences in the local environment for cad-
mium in ‘‘free, unliganded’’ Cd(tpp) and in ‘‘liganded’’
Cd(tpp)L [2]. The chemical shifts for the pyridine car-
bons of 2 were observed at 149.3 (py-C2,6), 123.5
(py-C3,5) and 135.8 ppm (py-C4) [2]. This observation
clear (113Cd, 15N, 13C, H) NMR study of the pyridine
adduct of cadmium meso-tetraphenylporphyrin Cd(tpp)
(py) (py = pyridine) (1) and 15N multiply labeled cad-
mium meso-tetraphenylporphyrin Cd([15N4]tpp)(py) (2)
[1]. Amma et al. [3] reported the crystal structures and
113Cd NMR spectra of the piperidine adduct of (5, 10,
15, 20-tetraphenylporphyrinato)cadmium(II) Cd(tpp)
(pip) Æ o-xylene (pip = piperidine) (3) [2] and (5, 10, 15,
20-tetraphenylporphyrinato)cadmium(II)-bis(dioxane)
*
Corresponding authors. Tel.: +88 64 228 40411x606; fax: +88 64
228 62547.
E-mail address: jyhhchen@dragon.nchu.edu.tw (J.-H. Chen).
1387-7003/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2004.09.015

1234
W.-S. Wun et al. / Inorganic Chemistry Communications 7 (2004) 1233–1237
indicates that only free pyridine is found in 2 while axi-
ally coordinated pyridine is absent. Furthermore, the
1H and 15N chemical shifts of coordinated pyridine in 2
remain unreported. Apparently more spectroscopic data
would be necessary to identify the pyridine being coordi-
nated to cadmium in 1 or 2 in the solution state. The elec-
tron density and the donating ability of the pyrrole
nitrogen, which is the first bonding atom toward the cad-
mium ion in the cadmium porphyrin complex, are con-
sidered to be lowered in the case of H2(p-Cl)4tpp, as it
contains electron-withdrawing chlorine atom. Upon
replacing tpp2ꢀ with (p-Cl)4tpp2ꢀ, the complex 1 became
[meso-tetra-(p-chlorophenyl)porphyrinato](pyridine)cad-
mium(II) Cd[(p -Cl)4tpp](py) (5), and further replace-
ment of the pyridine fragment in 5 by N,N-dimethylfor-
mamide (DMF) ligand, it became [meso-tetra-(p-chloro-
phenyl)porphyrinato](dimethylformamide)cadmium(II)
Cd[(p-Cl)4tpp](DMF) (6). The upfield shifts of the axial
ligand due to the porphyrin ring current might provide
a strategy to observe the coordinated pyridine and DMF
in 5 and 6, respectively by 1H NMR spectroscopic studies.
We report herein, X-ray structures of two new complexes
namely 5 and 6 and resolved unambiguously the binding
mode of pyridine and DMF to the cadmium atom in 5
The molecular framework is depicted in Fig. 1a for
compound 5 Æ py and in Fig. 1b for 6 Æ toluene. 1, 2 Their
structures are five-coordination Cd(II) metalloporphy-
rin complexes, having four nitrogen atoms of the por-
phyrins in common, but they are different with a
˚
pyridine for 5 and a DMF for 6 [4]. Bond distance (A)
for Cd(1)–N(5) is 2.315(4) and the mean Cd–N(p) for
5 Æ py is 2.203(3); for 6 Æ toluene the values are Cd(1)–
O(1) = 2.28(2) and the mean Cd–N(p) = 2.197(8) [5].
˚
The Cd–N (axial) distance of 2.315(4) A in 5 is compa-
˚
rable to that of Cd–N(3) = 2.387(3) A in bis[tetrakis(1-
pyrazoly)borato]cadmium(II)[B(pz)4]2Cd [6] and is also
˚
smaller than the upper limit 2.54(1) A for the typical
covalent
bond
distance
of
Cd–N(13)
in
Cd(C32H34N5)(C7H6N2)NO3 Æ CHCl3 [7]. Hence N(1),
N(2), N(3), N(4) and N(5) are bonded strongly as well
as covalently to Cd atom in 5 Æ py. The Cd(1)–O(1)(ax-
˚
ial) distance of 2.28(2) A in 6 is smaller than those of
˚
Cd(2)–O(1) = 2.379(4) and Cd(2)–O(2) = 2.391(4) A in
[(bmnpaCd)2(l-CO3)](ClO4)2 Æ CH3CN [8]. Hence N(1),
N(2), N(1A), N(2A) and O(1) are covalently bonded
to Cd in 6 Æ toluene.
The fivefold coordination geometry adopted may be
quantified by using the s descriptor for five-coordination
as suggested by Addison et al. [9]. This distortion index
is defined as s = (bꢀa)/60, where b is the largest and a is
the second largest of the Lbasal–M–Lbasal angles. For an
ideal C4v sp, s = 0; for a C3v tbp, s = 1. In the present
case, we find b = 145.9(1)ꢁ [N(3)–Cd(1)–N(1)] and
a = 145.3(1)ꢁ [N(4)–Cd(1)–N(2)] for 5, and b =
143.1(4)ꢁ [N(1)–Cd(1)–N(1A)] and a = 142.3(5)ꢁ [N(2)–
Cd(1)–N(2A)] for 6. Thus the value s = 0.01 is obtained
for both 5 and 6. Hence, the geometries around Cd(II)
for both complexes are best described as a square-based
pyramid with N(1), N(2), N(3) and N(4) [or N(1),
N(1A), N(2), and N(2A)] lying in the basal plane for 5
1
and 6 through the H and 13C NMR measurements.
1
A mixture of H2(p-Cl)4tpp (0.1 g, 1.4 · 10ꢀ4 mol) and Cd(OAc)2 Æ
2H2O (0.079 g, 0.6 · 10ꢀ4 mol) in DMF (50 cm3) was refluxed for 30
min. After concentration, the residue was dissolved in pyridine and
collected by filtration to remove the excess Cd(OAc)2 Æ 2H2O. The
pyridine layer was concentrated to dryness affording a bluish-purple
precipitate of 5 (0.13 g, 78%). Compound 5 was dissolved again in
pyridine to crystallize out purple crystals for a single-crystal X-ray
analysis. 1H NMR (599.95 MHz, pyridine-d5, 20 ꢁC):d 9.06 [s, Hb,
j J(Cd–H)j = 4.2 Hz]; 8.30 [d, ortho-H, 3J(H–H) = 8 Hz]; 7.79 [d, meta-H,
4
3J(H–H) = 8 Hz]; 8.70 (m, free py-H2,6); 7.56 (m, free py-H4); 7.19 (m,
free py-H3,5). 13C NMR (150.87 MHz, pyridine-d5, 20 ꢁC): d 151.2 (s,
Ca); 142.6 (s, C1); 136.5 (s, C2,6); 133.8 (s, C4); 132.4 (s, Cb); 127.0 (s,
(or 6). Because of the larger size of Cd2+ (r = 1.01A),
˚
˚
Cd lies 0.65(1) A above the 4N plane toward the pyri-
C
3,5); 121.0 (s, Cm); 149.9 (m, free py-C2,6); 135.5 (m, free py-C4); 123.5
dine nitrogen [i.e., N(5)] for 5 Æ py compared to 0.70(2)
(m, free py-C3,5). 13C NMR (150.87 MHz, toluene-d8, 20 ꢁC): d 151.3
(s, Ca); 142.7 (s, C1); 136.3 (s, C2,6); 134.1 (s, C4); 132.3 (s, Cb); 126.9 (s,
C3, 5); 120.9 (s, Cm); 146.9 (s, coordinated py-C2,6); 135.8 (s,
coordinated py-C4); 122.9 (s, coordinated py-C3,5). 113Cd (133.1
MHz, pyridine-d5, 20 ꢁC): d 435.0 (s, 113Cd). FAB-MS, m/z (assign-
ment, relative intensity): 154 ([NBA + H]+, 100); 752 ([H2(p-Cl)4tpp]+,
42.89); 862 ([Cd (p-Cl)4tpp]+, 36.99); 863 ([Cd (p-Cl)4tpp + H]+, 32.45).
UV/Visible spectrum [k, nm (10ꢀ4 e, Mꢀ1 cmꢀ1)] in CH2Cl2: 609 (1.4),
567 (1.8), 433 (31.0).
˚
A for Cd(1) in 6 [cf. 0.65(2) A for Cd(II) in 3 [2],
˚
˚
˚
0.03(1) A for Cd(II) in 4 [2], and 0.578(6) A for Cd(II)
in Cd(tpp) [10]]. The dihedral angles between the mean
plane of 4N and the planes of the phenyl groups are
80.3ꢁ [C(24)], 61.2ꢁ [C(30)], 66.1ꢁ [C(36)] and 89.1ꢁ
[C(42)] for 5 Æ py and the corresponding angles are
79.4ꢁ [C(14)], 75.8ꢁ [C(20)], 79.4ꢁ [C(14A)] and 75.8ꢁ
[C(20A)] for 6. The radii of the central ꢀholeꢁ [Ctꢁ ꢁ ꢁN,
the distance from the geometrical center (Ct) of the
mean plane of the 4N-atom core to the porphyrinato-
2
A bluish-purple crystals of 6 in 76% yield was prepared in the
same way as described for 5 Æ py except that the solvent pyridine was
replaced by DMF–toluene [1:1 (v/v)].1H NMR (599.95 MHz, toluene-
4
3
d8, 20 ꢁC): d 8.86 [s, Hb,j J(Cd–H)j = 5.4 Hz]; 7.79 [d, ortho-H, J(H–
˚
˚
3
core N atoms] are 2.10 A for 5 and 2.08 A for 6 which
H) = 8 Hz]; 7.49 [d, meta-H, J(H–H) = 8 Hz ]; 6.78 (s, DMF–CHO);
1.96 (s, DMF–NCH3); 1.71 (s, DMF–NCH3). 13C NMR (150.87 MHz,
toluene-d8, 20 ꢁC): d 161.4 (s, DMF–CO); 151.0 (s, Ca); 142.5 (s, C1);
136.2 (s, C2,6); 134.1 (s, C4); 132.4 (s, Cb); 126.9(s, C3,5); 120.8(s, Cm);
34.9 (s, DMF–CH3); 30.3 (s, DMF–CH3). FAB-MS, m/z (assignment,
rel. intensity): 154 ([NBA + H]+, 100); 861 ([Cd (p-Cl)4tpp-H]+, 64.23);
862 ([Cd (p-Cl)4tpp)]+, 85.24); 863 ([Cd (p-Cl)4tpp + H)]+, 78.73). The
UV/Visible data for compound 6 is similar to that of 5.
˚
are larger than 2.01 A as suggested by Collin and Hoard
[11]. The cadmium(II) is bonded in a modestly expanded
porphyrinato core (C20N4) for both the complexes.
The Hb of 5 (or 6) in toluene-d8 at 20 ꢁC was observed
4
at d = 8.90 (or 8.86 ppm) having j J(Cd–Hb)j = 4.8 Hz
(or 5.4 Hz), respectively (Fig. 2). This coupling satellites

W.-S. Wun et al. / Inorganic Chemistry Communications 7 (2004) 1233–1237
1235
Fig. 1. Molecular configuration and atom-labeling scheme for (a) 5 Æ py, (b) 6 Æ toluene, with ellipsoids drawn at 30% probability. Hydrogen atoms
for all compounds and solvent pyridine for 5 Æ py and toluene for 6 Æ toluene are omitted for clarity.
4
of Hb in 5 and 6 is comparable to the j J(Cd- Hb)j
value of 4.8 Hz for Hb protons in Cd(N–Me-tpp)Cl
[chloro(N-methyl-meso-tetraphenylporphyrinato)cadmi-
um(II)] [12] and that of 5 Hz for Hb protons in
(py-H2,6) for 5. Due to the porphyrin ring current effect,
1
upfield shifts for the H resonances of coordinated py-
H
2,6, py-H3,5 and py-H4 for 5 in toluene-d8 are
Dd = ꢀ3.28 [from 8.59 (obtained for free pyridine) to
5.31 ppm], ꢀ1.74 (from 7.23 to 5.49 ppm) and ꢀ1.59
ppm (from 7.62 to 6.03 ppm), respectively (Fig. 2) [13].
The similar ring current effect for the 1H resonances
of coordinated DMF–CHO, DMF–NCH3, and
1
Cd(tpp)(py) (py = pyridine) (1) [1]. The H NMR spec-
trum (Fig. 2) reveals that the protons of the coordinated
pyridine appear as two triplets at 6.03 ppm (py-H4) and
5.49 ppm (py-H3, 5) and as one broad singlet at 5.31 ppm

1236
W.-S. Wun et al. / Inorganic Chemistry Communications 7 (2004) 1233–1237
Fig. 2. 1H NMR spectra for 5 at 599.95 MHz in toluene-d8 at 20 ꢁC.
1
DMF–NCH0 for 6 in toluene-d8 are Dd = ꢀ1.24 (from
by H and 13C NMR method which are hitherto unre-
ported for the cadmiun(II) porphyrin complexes.
In conclusion, we have investigated two pentacoordi-
nate, diamagnetic, mononuclear cadmium complexes of
meso-tetra-(p-chlorophenyl)porphyrin, i.e., 5 and 6 and
established their X-ray structures. The value s = 0.01 is
obtained for these compounds indicating that the geom-
etry around Cd(II) in 5 and 6 is described as a square-
based pyramid. The coordinated pyridine and DMF in
5 and 6 are clearly identified in toluene-d8 by the por-
phyrin ring current effect.
3
8.02 (obtained for free DMF) to 6.78 ppm), ꢀ1.01 (from
2.97 to 1.96 ppm) and ꢀ1.17 ppm (from 2.88 to 1.71
ppm), respectively. The observation of these upfield
shifts indicate that as the protons of the coordinated
pyridine for 5 or the coordinated DMF for 6 in tolu-
ene-d8 become closer to the Ct, the shielding increases.
The ring current effect indicates that the pyridine and
DMF are axially bonded to Cd in 5 and 6, respectively.
This bonding argument is further supported by the re-
sult that the upfield shift of ꢂ3.0 ppm [from 149.9 (ob-
tained for free pyridine) to 146.9 ppm] was observed for
1
the coordinated py-C2,6 of 5 in toluene-d8. The ring
current effects seldom exceed 2 ppm for 13C NMR
[14,15]. Hence, the ring current contribution is relatively
less important in determining the 13C chemical shifts
than proton shifts. Herein, this upfield shift of ꢂ3.0
ppm is due to the shift of 13C being controlled by the
paramagnetic term and not by the ring current effect
[14,16]. Such paramagnetic contribution has arisen from
the covalent bonding between pyridine and Cd atom
and causes a decrease in the bond order between N(5)
and C(45) [or C(49)] for compound 5 [14,17]. Notably,
we unambiguously analyze the coordinated pyridine of
5 and the coordinated DMF of 6 in solvent toluene-d8
Acknowledgements
Financial support from the National Research Coun-
cil of the ROC under Grant NSC 92-2113-M-005-014 is
gratefully acknowledged.
Appendix A. Supplementary material
Crystallographic data in CIF format for 5 and 6 have
been deposited with Cambridge Data Centre as CCDC
225194 and 225195.

W.-S. Wun et al. / Inorganic Chemistry Communications 7 (2004) 1233–1237
1237
˚
For complex 6 Æ toluene: Cd(1)–N(1) = 2.214(8) A, Cd(1)–N(2) =
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˚
˚
2.18(1) A, Cd(1)–O(1) = 2.28(2) A, C(23)–O(1) = 1.26(3) A.
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[4] Crystal data. For complex 5 Æ py: C54H34Cl4N6Cd, Mr = 1021.07,
˚
monoclinic, P2(1)/c, a = 11. 5926(8) A, b = 33.703(2) A,
˚
[11] D.M. Collins, J.L. Hoard, J. Am. Chem. Soc. 92 (1970) 3761.
[12] F.A. Yang, J.H. Chen, H.Y. Hsieh, S. Elango, L.P. Hwang,
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[13] Dd = d (ligated) ꢀ d (unligated), the 1H chemical shift difference
between the coordination compounds and its own free ligand.
[14] E. Breitmaier, W. Voelter, Carbon-13 NMR Spectroscopy, third
ed., VCH Publishers, New York, 1990, pp. 110, 116–117, 285–286.
[15] R.K. Harris, Nuclear Magnetic Resonance Spectroscopy, Pitman,
London, 1983, p. 192.
˚
c = 13.0888(9) A, a = 90ꢁ, b = 114.041(1)ꢁ, c = 90ꢁ, V = 4670.2(6)
A , Z = 4, Dc = 1.452 g cmꢀ3, l(Mo Ka) = 0.741 mmꢀ1, 1.21 <
3
˚
h < 28.28ꢁ, GOF on F2 = 0.669, R1[I>2r(I)] = 0.0392, wR2[I>2r(I)] =
0.0669. For complex 6 Æ toluene: C54H39CdCl4N5O, Mr = 1028.10,
˚
monoclinic, C2, a = 20.096(2) A, b = 9.2653(7) A, c = 15.633(1) A,
˚
˚
3
˚
a = 90ꢁ, b = 128.864(1)ꢁ, c = 90ꢁ, V = 2266.4(3) A , Z = 2,
Dc = 1.507 g cmꢀ3, l(Mo Ka) = 0.765 mmꢀ1, 1.67 < h < 28.30ꢁ,
GOF on F2 = 1.169, R1[I>2r(I)] = 0.0861, wR2[I> 2r(I)] =
0.2088.
[16] S.J. Lin, T.N. Hong, J.Y. Tung, J.H. Chen, Inorg. Chem. 36
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[17] R.J. Pugmire, D.M. Grant, J. Am. Chem. Soc. 90 (1968) 697.
[5] The metal–ligand bond distances. For complex 5 Æ py: Cd(1)–
˚
N(1) = 2.202(3) A, Cd(1)–N(2) = 2.212(3) A, Cd(1)–N(3) =
˚
˚
2.190(3) A, Cd(1)–N(4) = 2.206(3) A, Cd(1)–N(5) = 2.315(4) A.
˚
˚