Synthesis and characterization of unsymmetrically tetrasubstituted porphyrin and their nickel (II) complexes with the crystal structure of 5,15- bis(4-aminophenyl)- 10, 20-diphenylporphyrinatonickel(II)

Article abstract of DOI:10.1016/S0022-2860(00)00417-8

New unsymmetrically tetrasubstituted porphyrin-Schiff base ligands (8- 10) containing recognition sites for alkali and transition metal quest cations have been synthesized by the condensations of 5-(4-aminophenyl)- 10,15,20-triphenylporphyrin (5) with sal

Full text of DOI:10.1016/S0022-2860(00)00417-8

Journal of Molecular Structure 525 (2000) 215–226
www.elsevier.nl/locate/molstruc
Synthesis and characterization of unsymmetrically
tetrasubstituted porphyrin and their nickel (II) complexes with the
crystal structure of 5,15-bis(4-aminophenyl)-
10, 20-diphenylporphyrinatonickel(II)
a
b
a
a
b,
*
¨
M. Hayvalı , H. Gu¨ndu¨z , N. Gu¨ndu¨z , Z. Kılıc¸ , T. Hokelek
a
ˇ
Department of Chemistry, Ankara University, 06100 Tandogan, Ankara, Turkey
bDepartment of Physics, Hacettepe University, 06532 Beytepe, Ankara, Turkey
Received 7 July 1999; accepted 4 January 2000
Abstract
New unsymmetrically tetrasubstituted porphyrin–Schiff base ligands (8–10) containing recognition sites for alkali and
transition metal quest cations have been synthesized by the condensations of 5-(4-aminophenyl)-10,15,20-triphenylporphyrin
(5) with salycylaldehyde, 2-hydroxy-1-naphthaldehyde and 40-hydroxy-50-formyl-benzo-15-crown-5. Homonuclear crystalline
1:1 [Ni(II): ligand] complexes (8a–10a) of the ligands with Ni(CH3COO)2·4H2O have been obtained. The porphyrin ligands
1
and their complexes have been characterized by elemental analysis, IR, UV–VIS, H , 13C NMR and MS, and the structure of
trans-5,15-bis(4-aminophenyl)-10,20-diphenylporphyrinato-nickel(II) (7a) has been examined crystallographically. It crystal-
ꢀ
lizes in the monoclinic space group C2/c with a ˆ 22:096ꢀ2†; b ˆ 13:455ꢀ1†; c ˆ 15:599ꢀ1† A; b ˆ 134:81ꢀ1†Њ; V ˆ
ꢀ 3
3290:6ꢀ2† A ; Z ˆ 4 and Dx ˆ 1:42 g cmϪ3: The molecule is centrosymmetric and the porphine nucleus is non-planar. The
˚
average value for the diameter of the hole has been estimated as 3.830(4) A. ᭧ 2000 Elsevier Science B.V. All rights reserved.
Keywords: Porphyrins; Unsymmetric tetrasubstituted porphyrins; Porphyrin–Schiff bases; Porphyrin complexes; Crystal structure of porphyrin
1. Introduction
stability of the porphyrin nucleus is well known and
is caused partly by the aromatic nature of this
macrocyclic system [7]. Bis(porphyrin)metal(IV)
complexes [M(porph)2], have been extensively
studied in the recent years due to their structural,
chemical and spectroscopic similarity to the ‘special
pair’ found in the reaction center of photosynthetic
bacteria [8–11]. The kinetics of porphyrin metallation
continues as an active research area, not only for
mechanistic implications of such studies but for a
number of practical applications as well [12,13].
Their unique photochemical properties make
porphyrins [14] important for the development of
molecular optoelectronic gates [15], photoinducible
The porphyrins lie at the focal point formed from
different fields of research, including solar energy
conversion catalysis, spectroscopy and the develop-
ment of organo metals [1,2]. The use of model
porphyrin systems to probe structure–function rela-
tionships in the hemoproteins hemoglobin and
myoglobin has been an active field of research
over the past quarter century [3–6]. The remarkable
* Corresponding author. Tel.: ϩ 90-312-235-2551; fax: ϩ 90-
312-235-2550.
¨
E-mail address: merzifon@eti.cc.hun.edu.tr (T. Hokelek).
0022-2860/00/$ - see front matter ᭧ 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(00)00417-8

216
M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
Scheme 1.
energy [16] or electron-transfer systems [17] and
enzyme models [18]. However the synthesis of such
arrays with a defined photophysical function often
involves multi-step sequences [19] with the introduc-
tion of the porphyrin chromophore as a difficult task.
Porphyrins can be used as radiation sensitive
substances, since they absorb radiation energies at
specified wavelengths. It is found that some of the
porphyrin derivatives are deposited in tumors and
rapidly growing tissues and they can be used as fluor-
escence indicators in determining the carcinogen
tissues in cancerous patients [20]. So, e.g. the Hg or
gamma radiation emitting isotope 57Co metal
complexes of porphyrins can be used as chemoter-
aphic substances [21]. In literature, there are only a
few reports about the porphyrin–Schiff base
derivatives which are the ligands produced from the
reaction of various amines with the porphyrins having
formyl group at b-position of the porphyrin ring [22–
24]. Our research group have also been investigated a
serious of some porphyrin derivatives to understand
the basicity of porphyrin ligands with potentiometric
titration in non-aqueous media [25,26]. In this study,
firstly the porphyrin-nitro derivatives (2–4) are
obtained by the regio-selective nitration of tetraphe-
nylporphyrin (1), later the porhpyrin-nitro derivatives
are reduced with Sn/HCl to get the porphyrin-amine
derivatives (5–7) (Scheme 1) [27]. The new
porphyrin–Schiff base ligands (8–10) and their nick-
el(II) complexes (8a–10a) are synthesized from the
individual reactions of monoamino-porphyrin, 5-(4-
aminophenyl)-10,15,20-triphenylporphyrin (5) and

M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
217
Scheme 2.

218
M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
5-(4-aminophenyl)-10,15,20-triphenylporphyrinato-
m-chloroperoxybenzoic acid according to the
published procedure [31].
1
nickel(II) (5a) (Scheme 2). The IR, H-, 13C-NMR
spectroscopic data of the new porphyrin ligands and
their Ni(II) complexes with the crystal structure of
compound (7a) are reported.
2.2.5. 40-Hydroxy-5-formyl-benzo-15-crown-5
40-Hydroxy-50-formyl-benzo-15-crown-5 was synthe-
sized from the reaction of 40-hydroxybenzo-15-
crown-5 and hexamethylenetetramine according to
the published procedure [32].
2. Experimental
2.1. Reagents and techniques
2.2.6. Tetraphenylporphyrin (1)
Pyrrole was purchased from Merck and distilled
over zinc dust. Tetrahydrofuran was distilled and
stored over sodium wire. Infrared absorption spectra
were obtained from a Mattson 100-FTIR spectrometer
in KBr discs and were recorded in cmϪ1 units. UV–
VIS spectra were measured using a UNICAM UV2-
100 series spectrometer. Elemental analyses were
Tetraphenylporphyrin was synthesized from the
reaction of pyrrole and benzaldehyde according to
the published procedure [33,34]. Nitro (2–4) and
amine (5–7) derivatives of tetraphenylporphyrin
were synthesized according to the literature method
of Kruper [27].
1
performed on a LECO CHNS-932 analyzer. The H-
and 13C-spectra were recorded on a Bruker DPX FT-
NMR spectrometer operating at 400 and 101.6 MHz,
2.2.7. trans-5,15-Bis(4-nitrophenyl)-10,20-
diphenylporphyrin (4) and cis-5,10-bis
(4-nitrophenyl)-15,20-diphenylporphyrin (3)
1
respectively. The H- and 13C-chemical shifts were
These compounds are synthesized according to the
modified method of Kruper [27]. Tetraphenylpor-
phyrin (1) (1.0 g, 1.62 mmol) was dissolved in
150 cm3 of freshly distilled CHCl3 and HNO3 (20 g,
0.32 mmol, 100%) was slowly added, during 2 h to
this mixture with vigorous stirring at 2ЊC, with argon
being passed over the reaction mixture. The reaction
was monitored by using TLC, the excess of HNO3 was
separated by adding distilled water of 100 cm3. This
procedure was repeated until the water was being
colorless. The CHCl3 layer was dried over MgSO4
and the CHCl3 was evaporated. The crude product
was chromatographed (silica gel: 100 g, eluent:
CHCl3/CCl4 1:1) and crystallized from methanol.
Compounds (3) and (4) (cis–trans mixture) were
obtained in 0.14 g (12%) yield, m.p. Ͼ300ЊC,
found: C, 73.11; H, 4.19; N, 11.63; C44H28N6O4·H2O
requires C, 73.35; H, 4.41; N, 11.54; Rf: 0.68 (CH2Cl2,
measured using SiMe4 as an internal standard. Fast
atomic bombardment (FAB) mass spectra were
obtained on a VG-ZAPSPEC spectrometer with an
ion source temperature of 240ЊC.
2.2. Synthetic procedures
2.2.1. Tetraethyleneglycoldichloride
Tetraethyleneglycoldichloride was synthesized
from the reaction of tetraethylene glycol and SOCl2
according to the published procedure [28].
2.2.2. Benzo-15-crown-5
Benzo-15-crown-5 was synthesized from the reac-
tion of 1,2-dihydroxybenzene and tetraethylenegly-
coldichloride according to the published procedure
[29].
2.2.3. 40-Formylbenzo-15-crown-5
1
silica gel). H NMR (CDCl3); dppm, Ϫ2.73 (s, 2H,
40-Formylbenzo-15-crown-5 was synthesized from
the reaction of benzo-15-crown-5 in POCl3 and N-
methylformanilide according to the published proce-
dure [30].
internal NH), 7.81 (m, 6H, p–m diphenyl), 8.24 (d,
4H, J ˆ 6:7 Hz; orthophenyl), 8.41 (d, 4H,J ˆ
8:20 Hz; nitrophenyl), 8.86 (d, 4H, J ˆ 8:20; nitro-
phenyl), 8.77 (d, 2H,J ˆ 4:7 Hz; b-pyrrole), 8.81(s,
2H, b-pyrrole), 8.90(s, 2H, b-pyrrole), 8.94(d, 2H,
J ˆ 4:60 Hz; b-pyrrole) UV–VIS (CH2Cl2, nm) 420
(Soret), 516;552;590;646. IR (KBr, cmϪ1); 3317 n
(NH); 1597, 1520 n(NO2 asym.); 972 n(NO2 sym.)
2.2.4. 40-Hydroxybenzo-15-crown-5
40-Hydroxybenzo-15-crown-5 was synthesized
from the reaction of 40-formylbenzo-15-crown-5 and

M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
219
2.2.8. cis-5,10-Bis(4-aminophenyl)-15,20-
diphenylporphyrin (6) and trans-5,15-bis(4-
aminopenyl)-10,20-diphenylporphyrin (7)
2.2.10. 5-[4-(2-Hydroxy-1-
naphthalydenaminophenyl)]-10,15,20-
triphenylporphyrin (9)
2-Hydroxy-1-naphthaldehyde (0.22 g, 1.28 mmol)
in 25 cm3 THF was added to compound (5) (0.5 g,
0.79 mmol) in 100 cm3 THF with vigorous stirring
at 65ЊC, with N2(g) being passed over the reaction
mixture. The work-up procedure was as in compound
(8), the yield 0.23 g (37%), Rf: 0.74 (CH2Cl2, silica
gel) m.p. Ͼ300ЊC, found: C, 84.66; H, 4.81; N, 9.12,
The mixture of (3) and (4) (0.2 g, 0.28 mmol)
was reduced with SnCl2·H2O/HCl (8 equiv./
100 ml) according to the method of Kruper [27],
purple crystals 0.87 g (48%) yield, Rf: 0.43
(CH2Cl2, silica gel) m.p. Ͼ300ЊC, found: C,
81.44; H, 5.22; N, 13.13, calc. for C44H32N6; C,
1
81.96; H, 5.00; N, 13.03. H NMR (CDCl3); dppm
,
1
calc. for C55H37N5O; C, 84.27; H, 4.76; N, 8.93. H
Ϫ2.67 (s, 2H, internal NH), 4.02 (s, 4H, NH2
prim.), 7.07 (d, 4H, J ˆ 7:90 Hz; aminophenyl),
7.78 (m, 6H, p–m diphenyl), 8.02 (d, 4H, J ˆ
8:00 Hz aminophenyl), 8.24 (d, 4H, J ˆ 7:00;
orthophenyl), 8.90 (m, 8H, b-pyrrole). UV–vis
(CH2Cl2, nm) 424 (Soret), 518;556;594;650. IR
(KBr, cmϪ1 3440, 3363 n(NH2), 3325 n(NH),
1512 n(NH2-bend.).
NMR (CDCl3); dppm, Ϫ2.87 (s, 2H, internal NH), 7.21
(d, 1H, J ˆ 9:17 Hz naphthaline rings), 7.40 (t, 1H),
7.59 (t, 1H), 7.77 (d, 2H, J ˆ 8:01 Hz; p-phenyl), 7.81
(m, 9 ϩ 2H, p–m triphenyl and a-naphthaline), 7.88
(d, 1H, J ˆ 9:17 Hz meta), 8.28 (d, 6H orthotri-
phenyl), 8.36 (d, 2H, J ˆ 7:79 Hz meta according to
p-substituted phenyl-NyCH), 8.94 (m, 8H, b-
pyrrole), 9.71 (s, 1H, –HCyN–). 13C NMR(CDCl3);
dppm, 109.6; 119.1; 119.4; 120.7; 120.8; 122.6; 124.1;
127.1; 127.9; 128.2; 128.6; 129.9; 131.7; 133.7;
135.0; 136.2; 137.3; 141.0; 142.6; 145.5; 155.6;
170.6. UV–vis (CH2Cl2, nm) 420 (Soret), 516; 552;
592; 646. IR (KBr, cmϪ1) 3402 n(OH), 3317 n(NH,
internal sec-NH), 1628 n(HCyN–). MS: m/e found:
784.4, calc. 784.4.
2.2.9. 5-[4-(Salycylidene)aminophenyl]-10,15,20-
triphenylporphyrin (8)
Salicylaldehyde (0.4 g, 3.28 mmol) was added to 5-
(4-aminophenyl)-10,15,20-triphenylporphyrin
(5)
(1.0 g, 1.59 mmol) in 100 cm3 THF with vigorous
stirring at 65ЊC, with N2(g) being passed over the reac-
tion mixture. The mixture was boiled during 18.0 h
and monitored by using Kiesel gel 60F254 (silica gel)
precoated TLC plates. The solvent was removed
under reduced pressure. The residue was chromato-
graphed (silica gel: 100 g, eluent: CH2Cl2) and crys-
tallized from CH2Cl2–light petroleum (1:3),
compound (10) was obtained in 0.25 g (21%) yield,
Rf: 0.72 (CH2Cl2, silica gel) m.p. Ͼ300ЊC, found: C,
83.83; H, 5.64; N, 8.93, calc. for C51H35N5O; C, 83.47;
2.2.11. 5-[4-(40-Hydroxy-50-imino-benzo-15-crown-
5-phenyl]-10,15,20-triphenylporphyrin (10)
40-Hydroxy-50-formyl-benzo-15-crown-5 (0.49 g,
1.57 mmol) and compound (5) (0.5 g, 0.79 mmol)
were used for the preparation of (10) as for (8),
the purple crystal, 0.2 g (27%) yield, Rf: 0.18
(CH2Cl2/THF, 3/1 silica gel) m.p. Ͼ300ЊC,
found: C, 76.27; H, 4.77; N, 7.36, calc. for
C59H49N5O7; C, 76.71; H, 5.42; N, 7.58. 1H
NMR (CDCl3); dppm, Ϫ2.76 (s, 2H, internal NH),
3.80–4.22 (m, 16H, crown ether); 6.59 (s, 1H, o,
OH, crown ether phenyl); 7.02 (s, 1H, m, OH,
crown ether phenyl); 7.65 (d, 2H, J ˆ 8:18 Hz;
p-phenyl); 7.77 (m, 9H, p–m triphenyl); 8.24 (m,
6H ϩ 2H, overlapping ortho triphenyl and p-
phenyl); 8.85 (m, 8H ϩ 1H, b-pyrrole and imine
proton); 13.80 (s, 1H, OH proton). UV–vis
(CH2Cl2, nm) 420 (Soret), 516; 550; 590; 646.
IR (KBr, cmϪ1) 3425 n(OH), 3317 n(NH), 2924
and 2862 n(C–H, internal sec-NH), 1628
n(HCyN–) 1281, 1211, 1149 n(C–O–C).
1
H, 4.81; N, 9.54. H NMR (CDCl3); dppm, Ϫ2.66 (s,
2H, internal NH), 7.04 (m, 2H, salicylphenyl), 7.18 (d,
2H, J ˆ 8:03 Hz; salicylphenyl), 7.49 (d, 2H, J ˆ
7:38 Hz p-phenyl), 7.53 (t, 1H, J ˆ 7:27 salicyl-
phenyl), 7.70 (d, 2H, J ˆ 8:1 Hz p-phenyl), 7.81 (m,
9H, p–m triphenyl), 8.30 (m, 6H, o-triphenyl), 8.92
(m, 9H, b-pyrrole and imine proton), 13.46 (s, 1H,
OH), 13C NMR(CDCl3); dppm, 117.8; 119.6; 119.8;
120.7; 120.8; 127.1; 128.2; 131.7; 132.9; 133.8;
135.0; 136.0;141.4; 142.6; 148.5; 161.8; 163.6. UV–
vis (CH2Cl2, nm) 421 (Soret), 516; 550; 592; 646. IR
(KBr, cmϪ1) 3448 n(OH); 3317 n(NH), 1620
n(HCyN, internal sec-NH).

220
M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
Table 1
Experimental data
2.2.13. trans-5,15-Bis(4-aminophenyl)-10,20-
diphenylporphyrinatonickel(II) (7a)
Compound (7) (0.05 g, 0.08 mmol) and Ni(CH3-
COO)·4H2O were used for the preparation of (5a) as
for (7a), the purple crystals, 0.02 g (32%) yield, Rf:
0.40 (CH2Cl2, silica gel). The suitable crystals for X-
ray analysis were obtained from CHCl3–MeOH (1:1)
mixture.
Compound
Color/shape
For. Wt.
Space group
Temp. (K)
Cell constants
C44H30N6Ni
Purple/prismatic
701.48
C2/c
293
a ˆ 22:096ꢀ2†; b ˆ 13:455ꢀ1†;
ꢀ
c ˆ 15:599ꢀ1† A;
b ˆ 134:81ꢀ1†Њ
Cell volume
3290.6(2)
2.2.14. 5-(4-Salicylideneaminophenyl)-10,15,20-
triphenylporphyrinatonickel(II) (8a)
Formula units/unit cell
4
1.42
0.63
Dcalc (Mg mϪ3
)
Compound (8a) was obtained by following two
different methods. Method 1 (appropriate method):
the Ni(II) complex of compound (5) was synthesized
and the product (5a) was used to obtain the
porphyrin–Schiff base complex (8a). Salicylaldehyde
(0.12 g, 0.98 mmol) was added to compound (5a)
(0.5 g, 0.73 mmol) in 100 cm3 boiling THF, with
N2(g) being passed over the reaction mixture. The
mixture was refluxed for 12 h and the solvent removed
under reduced pressure. The residue was chromato-
graphed (silica gel; 120 g, eluent: CH2Cl2) and crys-
tallized from CH2Cl2–light petroleum (1:3), 0.19 g
(33%) yield, Rf: 0.68 (CH2Cl2, silica gel), m.p.
Ͼ300ЊC, found: C, 77.60; H, 4.20; N, 8.96, calc. for
mcalc (mmϪ1
)
Diffractometer/scan
Radiation used,
graphite
monochromator
Max. crystal dimen.
(mm)
Standard reflections
Decay of standard
Reflections measured
2u(max) (Њ)
Enraf-nonius CAD-4/v Ϫ 2u
MoKa (l ˆ 0.71073 A)
˚
0:12 × 0:16 × 0:32 mm
3
Ͻ 1%
1651
27.2
0 Ͻ h Ͻ 17; 0 Ͻ k Ͻ 12;
Ϫ13 Ͻ l Ͻ 8
501
Range of h,k,l
Number of reflections
with Fo Ͼ 2.0 (Fo)
Corrections applied
Computer programs
Lorentz-Polarization
shelxs86 [35] molen[36]
ortep[37]
1
C51H33N5ONi; C, 77.49; H, 4.21; N, 8.86. H NMR
(CDCl3); dppm, 7.04 (t, 1H, J ˆ 8:28 Hz; salicyl-
phenyl), 7.14 (d, 1H, J ˆ 8:12 Hz salicylphenyl);
7.47 (t, 2H, J ˆ 7:38 Hz p-phenyl); 7.53 (d, 1H, J ˆ
7:27 Hz; salicylphenyl); 7.63 (d, 2H, J ˆ 8:1 Hz;
p-phenyl); 7.72 (m, 9H, p–m triphenyl); 8.06 (m,
6H, o-triphenyl); 8.10(d, 2H, p-phenyl);8.79 (m, 8H,
b-pyrrole); 8.94 (s, 1H, imine proton); 13.38 (s, 1H,
OH). 13C NMR (CDCl3); dppm, 117.8; 118.5; 119.5;
119.8; 120.2; 127.3; 128.2; 132.4; 132.6; 132.7;
132.9; 133.8; 134.1; 135.1; 141.1; 141.3; 143.0;
143.1; 143.2; 148.5; 161.7; 163.5. UV–VIS
Source of atomic
scattering factor
Structure solution
Treatment of hydrogen Calculated geometrically and
atoms
No. of parameters var.
Weight
GOF
Int. Table For X-Ray Cryst. Vol.
IV, 1976 [38]
Direct methods
riding model was used
102
v ˆ 1=s2ꢀF†
1.66
R ˆ ͉Fo͉ Ϫ ͉Fc͉=͉Fo͉
0.071
0.063
0.04
Ϫ0.04
Rw
Ϫ3
˚
˚
(Dr) max (eA
(Dr) min (eA
)
Ϫ3
)
(CH2Cl2, nm) 418 (Soret), 526. IR (KBr, cmϪ1
)
3448 n(OH), 1620 n(HCyN–). Method 2: The free
base compound (8) was dissolved in DMF and
Ni(CH3COO)2·4H2O was added to this mixture for
obtaining the complex (8a).
2.2.12. 5-(4-aminophenyl)-10,15,20-
triphenylporphyrinatonickel(II) (5a)
Compound (5) (1.0 g, 1.59 mmol) was dissolved
in 250 cm3 DMF and Ni(CH3COO)2·4H2O (3.96 g,
15.9 mmol) was added to this mixture and boiled
during 1 hours, 0.29 g (27%) yield. IR (KBr,
cmϪ1) 3425, 3364 n(NH2), Rf: 0.52 (CH2Cl2, silica
gel).
2.2.15. 5-[4(2-Hydroxy-1-naphthalydene)aminophenyl]-
10,15,20-triphenylporphyrinatonickel(II) (9a)
Compound (5a) (0.5 g, 0.73 mmol) in 75 cm3 THF
and 2-hydroxy-1-naphthaldeyde (0.25 g, 1.45 mmol)
were used for the preparation of complex (9a) as for

M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
221
(8a), 0.26 g (43%) yield. 13C NMR (CDCl3) dppm
,
tives (2–4). Later these products are reducted to
obtain the p-aminophenyl derivatives (5–7). On the
other hand; p-mono- (2), p-di- (3,4) and p-trinitrophe-
nylporphyins are obtained as a result of nitration of 1
by changing the solvent type and the nitric acid amount
[24]. p-Mono (5), p-di- (6,7) and p-tri-aminophenylpor-
phyrins are produced as a result of corresponding nitro
derivatives (2–4) by SnCl2/HCl (Scheme 1).
The difficulties, in the separation of the products
forming in the reaction media and the low percentage
of their yield in obtaining the unsymmetrical
porphyrins by reacting two different aldehyde with
pyrrole are well known [33,34]. Especially; the yield
of the products in obtaining these compounds is too
low according to the other substituents, since the nitro
group of p-nitrobenzaldehyde which is used to obtain
p-nitro substituted phenylporphyrin, deactivates the
aldehyde group. The nitration with nitric acid is a
highly advantageous method with respect to the
other ones used in the synthesis of p-nitrosubstituted
phenyl porphyrins, since the change of the amount of
nitric acid specifies the type of the product forming in
the media [25,26]. In the reactions; the other p-nitro-
substituted phenyl porphyrins also form together with
the main product at the same time. But, these
compounds can be separated easily by column
chromatography, since their yields are too low.
In literature, there are only a few reports about the
Schiff base derivatives of porphyrins, which are the
Schiff base products obtained from the reactions of
various amines with the porphyrins having formyl
group at b-position [22–24]. In this study, although
a series of solvents are experienced to obtain product
(10), it was deduced that the most suitable one was
THF and it was used as solvent in the following reac-
tions. Although the reaction time was kept over 48 h,
it was observed that the reaction was not completely
forming the product (10) even in case of the excess
addition of the aldehyde to the media by monitoring
continuously the condensation reaction in THF using
TLC. The forming Schiff base (10) was also dissolved
in THF, where the starting compound (9) was
dissolved. Therefore the separation of the compound
(10) was only possible by column chromatography.
On the other hand, it was observed that, the alcohols
used generally in the crystallization of porphyrins
were transforming the porphyrin–Schiff bases (8–10)
to the starting materials. In addition, although, the
109.6; 119.1; 119.4; 120.7; 120.8; 122.6; 124.1;
127.1; 127.9; 128.2; 128.6; 129.9; 131.7; 133.7;
135.0; 136.2; 137.3; 141.0; 142.6; 145.5; 155.6;
170.6.
2.2.16. 5-[4-(40-Hydroxy-50-imino-benzo-15-crown-
5)-phenyl]-10,15,20-triphenylporphyrinatonickel(II)
(10a)
Compound (5a) (0.5 g, 0.73 mmol) in 75 cm3 THF
and 40-hydroxy-50-formyl-benzo-15-crown-5 (0.39 g,
1.25 mmol) were used for the preparation of complex
(10a) as for (8a), 0.12 g (16%) yield. Rf: 0.68 (CH2Cl2,
silica gel), found: C, 71.10; H, 4.75; N, 7.03, calc. for
1
C59H47N5O7Ni; C, 77.49; H, 4.21; N, 8.86. H NMR
(CDCl3); dppm, 3.77–4.27 (m, 16H, crown ether), 6.63
(s, 1H, crown etherphenyl); 7.04 (s, 1H, crown ether-
phenyl); 7.62 (d, 2H, J ˆ 7:71 Hz; p-phenyl); 7.70
(m, 9H, p–m triphenyl); 8.02 (m, 6H, o-triphenyl);
8.07 (d, 2H, J ˆ 7:97 Hz; p-phenyl); 8.78 (m, 8H,
b-pyrrole); 8.83 (s, 1H, imine proton), 13.85 (s, 1H,
OH). UV–VIS (CH2Cl2, nm) 416 (Soret), 528. IR
(KBr, cmϪ1) 3425 n(OH), 1628 n(HCyN–).
2.3. Crystallography
The suitable crystal of (7a) for X-ray analysis was
obtained by recrystallization from CHCl3–MeOH
(1:1) mixture. Experimental data, methods and the
procedure used to elucidate the structure and other
related parameters are given in Table 1. An empirical
absorption correction based on a series of psi-scans
was applied to the data. The structure was solved by
the Patterson method, shelxs86 [35]. Since the differ-
ence synthesis did not clarify the positions of the H
atoms, they were placed in calculated positions at a
˚
distance of 0.95 A from the corresponding C atoms
and a riding model was used in refinement process of
their geometrically calculated positions.
3. Results and discussion
3.1. Synthesis and reactions
For the preparation of new porphyrin derivatives
(8–10) and their Ni(II) complexes (8a–10a); firstly
tetraphenylporphyrin (1) is synthesized and then
nitrated with HNO3 to get the p-nitrophenyl deriva-

222
M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
Table 2
with Ni(II) ion in DMF at room temperature to specify
the most suitable active center in the metal
coordination. The complexes; 5-(4-aminophenyl)-
10,15,20-triphenyl porphyrinatonickel(II) (5a), and
5-(4-salicylideneaminophenyl)-10,15,20-triphenyl-
porphyrinato-nickel(II) (8a), were determined. The
loss of the peak at 3317 cmϪ1 in the IR spectrum of
the complex (8a) was the evidence of the diffusion of
the metal into the porphyrin skeleton. This determina-
tion was clarified that porphyrin skeleton was more
appropriate to give complexes easily with respect to
the Schiff base side. Porphyrinato–Schiff base
complexes (8a–10a) were reacted with Ni(II), Cu(II)
and Fe(III) ions in THF, CHCl3 and C6H6, but the
expected complexes could not have been obtained
from Schiff base side. Thus it was understood that the
Schiff base side was not appropriate to form complexes.
Consequently; as it was given in Section 2, the
appropriate method (method 1) for the preperation
of the porpyhrin Schiff base Ni(II) complexes (8a–
10a) was to obtain the porphyrin Ni(II) complex (7a)
and then to make the condensation reaction of 7a with
corresponding aromatic aldehydes (Scheme 2).
Atomic coordinates and isotropic displacement parameters with
e.s.d’s in parentheses (starred atoms were refined isotropically)
2
˚
Atom
x
y
Z
B (A )
Ni
N1
N2
N3
C1
C2
C3
C4
C5
C6
C7
C8
0.500
0.1251(3)
0.128(1)
0.121(1)
0.234(5)
0.154(1)
0.157(1)
0.128(1)
0.113(1)
0.090(1)
0.065(1)
0.250
6.54(8)*
6.4(3)*
6.8(3)*
10(2)*
0.4401(5)
0.3938(5)
0.634(2)
0.4690(6)
0.4001(7)
0.3309(6)
0.3526(7)
0.2929(7)
0.2054(7)
0.0843(7)
0.2064(7)
Ϫ0.143(3)
0.0328(9)
Ϫ0.098(1)
Ϫ0.125(1)
Ϫ0.016(1)
Ϫ0.010(1)
Ϫ0.124(1)
Ϫ0.181(1)
Ϫ0.291(1)
Ϫ0.350(1)
Ϫ0.291(1)
Ϫ0.180(1)
0.0952(9)
0.1021(9)
0.215(1)
0.281(1)
0.095(1)
0.033(1)
0.052(1)
Ϫ0.005(1)
Ϫ0.080(1)
Ϫ0.100(1)
Ϫ0.047(1)
6.2(4)*
8.0(5)*
7.8(4)*
7.3(4)*
6.3(4)*
7.1(5)*
9.1(5)*
9.5(6)*
10.4(6)*
8.5(5)*
8.7(5)*
6.4(4)*
7.4(5)*
8.0(5)*
7.3(4)*
6.8(5)*
7.7(5)*
9.1(5)*
9.6(6)*
8.5(5)*
9.2(5)*
9.1(5)*
0.1864(8) Ϫ0.027(1)
0.1029(8) Ϫ0.050(1)
C9
0.0328(8)
0.0557(7)
0.1387(7)
0.3145(7)
0.2511(7)
0.2957(7)
0.3830(7)
0.5536(7)
0.5797(7)
0.6173(8)
0.6434(8)
0.6304(8)
0.5963(7)
0.5666(7)
0.017(1)
0.106(1)
0.133(1)
0.097(1)
0.092(1)
0.120(1)
0.137(1)
0.160(1)
0.187(1)
0.277(1)
0.305(1)
0.236(1)
0.143(1)
0.121(1)
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
3.2. IR and NMR spectroscopies
The characteristic internal n(NH) absorption band
was observed at 3317 cmϪ1 for all of the porphyrin
ligands, but this band disappears in all of the porphyr-
inatonickel(II) complexes. The stretching frequencies
of n(OH), n(NH2) and n(CyN) were observed at
3425–3448; 3440, 3363 and 1620–1628 cmϪ1 values,
in porphyrin ligands and their complexes, respec-
tively. The observation of n(Ar–O) and n(C–O–C)
bands at 1281; 1211–1149 cmϪ1 for compounds (10)
and (10a) was the evidence for the existence of crown
ether groups. The molecular ion peaks (m/e) were
Schiff base was formed from the reaction of 40-formyl-
benzo-15-crown-5 and 5-(4-aminophenyl)-10,15,20-
triphenylporphyrin (5) in THF, and the mixture was
separated by column chromatography (silica gel,
100 g, eluent: CH2Cl2/THF (10:1)), it was observed
that the product taken from the column was trans-
forming to the starting compounds in the eluent.
Hence, the Schiff base formed from 40-formyl-benzo-
15-crown-5 was not obtained purely. But, the
porphyrin crown ether Schiff base (10) was obtained
from the condensation reaction of 40-hydroxy-50-
formyl-benzo-15-crown-5 and the compound (5).
Consequently, the Schiff bases (8–10) obtained from
2-hydroxy substituted aromatic aldehydes and
porphyrin amine (5) were stable in CH2Cl2.
1
observed at 784.4 for compound (9). The H NMR
chemical shifts of the new compounds were given in
the experimental part. The characteristic internal NH,
b-pyrrol and HCyN– chemical shifts were found at
(Ϫ2.66)–(Ϫ2.87); 8.76–8.95 and 8.83–9.71 ppm,
respectively. Compound (9) with an internal NH
value of Ϫ2.87 has the most basic porphyrin hole
among the other porphyrin ligands. The ethyleneoxide
groups, –OCH2–CH2O–, resonate between 3.80–4.22
and 3.77–4.27 ppm in compounds (10) and (10a),
respectively, which are the evidences of the formation
Compound (8) which is a porphyrin–Schiff base
derivative, has two active centers appropriate for
coordination. One of them is the porphyrin skeleton
and the other one is the Schiff base side with
o-hydroxy substituent. This compound is reacted

M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
223
Fig. 1. An ortep [37] drawing of (7a) with the atom-numbering scheme. The thermal ellipsoids are drawn at the 50% probability level.
of the porphyrin–crown ether ligand (12) and porphyrin–
crown ether complex (10a).
reported to further corroborate the structure assign-
ments. The final coordinates and equivalent isotropic
displacement parameters are given in Table 2. The
molecular structure with the atom-numbering scheme
is shown in Fig. 1. The molecular packing is shown in
Fig. 2. The packing of the molecules in the unit cell is
purely due to van der Waals forces of interaction. The
bond lengths and angles with some selected torsion
angles are given in Table 3. The molecule has a center
of symmetry. The distances between neighboring
phenyl and pyrrole H atoms (H3···H7 3.161(8),
The 13C NMR data of some of the new porphyrin
ligands and their complexes were given in the experi-
mental part. However; due to the low solubility of the
compounds, precise values could not have been
obtained and the expected amount of the carbon
signals could not have been observed. The observed
peaks between 416–424 nm (Soret bands) in the UV–
VIS spectra for all of the porphyrin ligands and their
complexes were the characteristic peaks for the
porphyrin core, concerned.
˚
H2···H22 2.723(8), H11···H13 2.817(8) A) cause a
great deal of steric crowding. These steric effects tilt
the phenyl rings out of the molecular plane. Devia-
tions from perpendicularity of the porphine and
phenyl rings can be correlated with the degree of
3.3. Crystal study
Single crystal X-ray structure of compound (7a) is

224
M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
Fig. 2. The molecular packing of (7a).
planarity of porphine ring. The phenyl rings seem to
be rotated considerably out of the plane of the macro-
cycle. An examination of the deviations from
the individual pyrrole and phenyl least-squares
planes shows that the rings B(N1,C1,C2,C3,C4),
C(C6,C7,C8,C9,C10,C11), and D(N2,C12, C13,
C14, C15) are planar (the maximum distances to
the least-squares planes are 0.021(17), Ϫ0.006(19)
are probably the result of repulsion effects arising
from the close contacts between the nearest H atoms
of the phenyl and pyrrole rings. It is greatly increased
when the molecules are packed closely in the crystals.
Organic molecules tend to pack in crystals as closely
as their geometry allows [39]. The porphine nucleus
will remain planar, if possible, in order to increase
overlap of p orbitals. When there are substituents
bent at a sharp angle to the porphine nucleus, the
molecules can not be close packed and remain planar
at the same time [40]. Consequently, the shape of a
particular porphyrin in a crystal appears to depend on
the substituents and the type of packing. The N3 atom
has distortion. In the refinement process, although
some constraints were applied, the C20–N3 distance
˚
and Ϫ0.022(14) A, respectively), while ring A
(C17,C18,C19,C20,C21,C22) is not planar (maximum
˚
deviation of C21 Ϫ0.035(15) A from the least-squares
plane). The rings are also twisted with respect to
each other. The porphine nucleus E(N1,C4,C5,C12,
N2,C15,C160,C10,N10,C40,C50,C120,N20,C150, C16,C1)
˚
is non-planar (maximum deviation of C5 0.47(2) A
˚
from the least-squares plane). The dihedral angles
between the least-squares planes are A–B 119.9(6), A–
C 81.3(5), A–D 53.2(7), A–E 140.4(9), B–C 98.4(6),
B–D 158.0(7), B–E 91.2(9), C–D 61.0(7), C–E 120.5(9)
and D–E 105.8(9)Њ.
was reached to a value of 1.04 A, which is chemically
unacceptable. In fact, the withdrawing of the nitrogen
electrons to the porphine nucleus can also be effective
in the shortening of the C20–N3 bond. The behaviors
of the bond angles of the two different pyrroles show
that C1–N1–C4 (103.(1)Њ) angle is 3.(1)Њ less than the
Deviations from planarity in the porphine nucleus

M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
225
Table 3
The bond lengths (A) and angles (Њ) with some selected torsion angles (Њ)
˚
Ni–N1
Ni–N2
N1–C1
N1–C4
N2–C12
N2–C15
C1–C2
C1–C16
C2–C3
C3–C4
C4–C5
C5–C6
C5–C12
C6–C7
C6–C11
N1–Ni–N2
Ni–N1–C1
Ni–N1–C4
C1–N1–C4
Ni–N2–C12
Ni–N2–C15
C12–N2–C15
N1–C1–C2
N1–C1–C16
C2–C1–C16
C1–C2–C3
C2–C3–C4
N1–C4–C3
N1–C4–C5
C3–C4–C5
C4–C5–C6
C4–C5–C12
C6–C5–C12
C5–C6–C7
C5–C6–C11
C7–C6–C11
C6–C7–C8
N2–Ni–N1–C1
N1–Ni–N2–C12
Ni–N2–C12–C5
Ni–N2–C15–C14
Ni–N1–C1–C16
Ni–N1–C4–C5
1.90(1)
1.93(1)
1.38(2)
1.40(1)
1.38(1)
1.36(2)
1.45(2)
1.37(2)
1.33(2)
1.42(2)
1.42(3)
1.47(1)
1.36(2)
1.41(2)
1.40(2)
90.7(5)
129.3(6)
127.(1)
103.(1)
127.(1)
126.7(6)
106.(1)
112.(1)
124.(1)
123.(2)
105.(2)
109.(1)
111.(1)
125.(1)
124.1(9)
118.(1)
121.(1)
121.(2)
121.(1)
121.(1)
118.(1)
121.(1)
163.2(1.4)
17.5(1.4)
Ϫ14.0(2.3)
Ϫ175.7(1.2)
17.5(2.3)
Ϫ2.2(2.5)
C7–C8
C8–C9
C9–C10
C10–C11
C12–C13
C13–C14
C14–C15
C16–C17
C17–C18
C17–C22
C18–C19
C19–C20
C20–C21
C20–N3
C21–C22
C7–C8–C9
C8–C9–C10
C9–C10–C11
C6–C11–C10
N2–C12–C5
N2–C12–C13
C5–C12–C13
C12–C13–C14
C13–C14–C15
N2–C15–C14
C1–C16–C17
C16–C17–C18
C16–C17–C22
C18–C17–C22
C17–C18–C19
C18–C19–C20
C19–C20–C21
C19–C20–N3
C21–C20–N3
C20–C21–C22
C17–C22–C21
1.41(1)
1.43(2)
1.37(2)
1.42(1)
1.48(3)
1.34(2)
1.43(2)
1.49(3)
1.38(2)
1.38(3)
1.40(3)
1.36(3)
1.39(3)
1.04(6)
1.40(3)
123.(2)
113.(1)
127.(1)
118.(2)
126.(2)
110.(1)
123.0(9)
103.(1)
111.(2)
109.(1)
121.(1)
122.(2)
120.(1)
118.(2)
123.(2)
116.(2)
124.(2)
137.(4)
99.(4)
118.(2)
120.(2)
Ni–N1–C1–C2
Ni–N1–C4–C3
N2–Ni–N1–C4
N1–Ni–N2–C15
Ni–N2–C12–C13
–173.6(1.1)
176.1(1.2)
–9.8(1.5)
–166.5(1.5)
173.5(1.0)
0
˚
C12–N2–C15 (106.(1)Њ) angle. The bond lengths and
angles around C atoms on pyrrole rings are affected to
a lesser extent. The average C–N distance is
mated as 4.06 A. In compound (7a), the N1···N10
˚
distance (3.799(3) A) is smaller than the N2···N2
˚
distance (3.860(4) A), in 5,10,15,20-p-ClTPP, the
corresponding distances are determined as 4.060(5)
and 4.154(5) A, respectively [43]. In compound (7a)
Ni–N average distance (1.92 A) and Ca–N–Ca
˚
1.39(2) A. The average C–C bond distances in the
˚
two phenyl rings (A and C) are 1.41(2) and
˚
˚
1.39(3) A, respectively. The optimum value for the
diameter of the hole of triclinic TPP [41] and an
undistorted porphyrin complex [42] has been esti-
average bond angle (104.5(1)Њ) can be compared
with the values (1.952(4) and 1.952 A) and
˚

226
M. Hayvalı et al. / Journal of Molecular Structure 525 (2000) 215–226
[17] C.H. Drain, K.C. Russell, J.M. Lehn, Chem Commun. (1996) 337.
[18] H.A. Wagenknecht, W.D. Woggon, Angew. Chem. Int. Ed.
Engl. 36 (1997) 390.
[19] A. Osuka, S. Marumo, N. Mataga, S. Taniguchi, T. Okada, I.
Yamazaki, Y. Nishimura, T. Ohno, K. Nozaki, J. Am. Chem.
Soc. 118 (1996) 155.
[20] G.M. Badger, R.A. Jones, R.L. Laslett, Aust. J. Chem. (1964) 1028.
[21] N.D. Gupta, T.J. Bardos, J. Heterocyclic Chem. 3 (1966) 495.
[22] B. Ward, P.M. Callahan, R. Young, G.T. Babcock, C.K.
Chang, J. Am. Chem. Soc. 105 (1983) 634.
[23] J.D. Petke, G.M. Maggiora, J. Am. Chem. Soc. 106 (1984) 3129.
[24] L.K. Hanson, C.V. Chang, B. Ward, P.M. Callahan, G.T.
Babcock, J.D. Head, J. Am. Chem. Soc. 106 (1984) 3950.
[25] T. Gu¨ndu¨z, N. Gu¨ndu¨z, M. Hayvalı, Anal. Chim. Acta. 278
(1993) 243.
(104.1(4) and 104.8Њ), in NiOEP and NiTPP, respec-
tively. It is observed that, if the Ca–N–Ca angles
increase, the core size of the substituted porphyrines
increase [44]. Numerous porphyrin complexes have
been synthesized [44–46]; the porphyrin cores are,
in general non-planar and can be further distorted
when the porphyrin molecules accommodate metal
cation that are larger or smaller than the central
holes. These distortions are referred to as “saddled”
and “ruffled”, respectively [45,46]
Acknowledgements
[26] N. Gu¨ndu¨z, T. Gu¨ndu¨z, M. Hayvalı, Talanta 48 (1999) 71.
[27] W.J. Kruper, T.A. Chamberlin, M. Kochanny, J. Org. Chem.
54 (1989) 2753.
[28] M.J. Calwerley, J. Dale, Acta Chem. Scand. B 36 (1982) 241.
[29] C.J. Pedersen, J. Am. Chem. Soc. 89 (1967) 7017.
[30] E.M. Hyde, B.L. Shaw, I. Shepherd, J. Chem. Soc. Dalton
Trans. (1978) 1695.
The authors wish to acknowledge the purchase of
CAD-4 diffractometer under Grant DPT/TBAG1 of the
Scientific and Technical Research Council of Turkey and
Ankara University Research Fund, grant number CHE
93250015, for financial support of this work.
[31] F.C. Camps, J. Coll, S. Ricart, J. Heterocyclic Chem. 20
(1983) 249.
¨
ˇ
References
[32] S. Can, O. Bekaroglu, J. Chem. Soc. Dalton Trans. (1988) 2831.
[33] G.H. Barnett, M.F. Hudson, K.M. Smith, J. Chem. Soc. Perkin
Trans. I (1975) 1401.
[1] S. Fukuzumi, K. Miyamoto, T. Suenobu, E.V. Caemelbecke,
K.M. Kadish, J. Am. Chem. Soc. 120 (1998) 2880.
[2] L.R. Milgrom, J. Chem. Soc. Perkin Trans I (1984) 1483.
[3] G.B. Jameson, J.A. Ibers, Comments Inorg. Chem. 2 (1983) 97.
[4] M. Momenteau, C.A. Reed, Chem. Rev. 94 (1994) 659.
[5] G.B. Jameson, J.A. Ibers, in: I. Bertini, H.B. Gray, S.J.
Lippard, J.S. Valentine (Eds.), Bioinorganic Chemistry,
University Science Books, Mill Valley, CA, 1994, p. 167.
[6] B.A. Springer, S.G. Sligar, J.S. Olson, J. Phillips, N. George,
Chem. Rev. 94 (1994) 699.
[34] J.S. Lindsey, I.C. Schriman, H.C. Hsu, P.C. Keraney, A.M.
Marguerettaz, J. Org. Chem. 52 (1987) 827.
[35] G.M. Sheldrick, Acta Cryst. A 46 (1990) 467.
[36] C.K. Fair, molen an Interactive Intelligent System for Crystal
Structure Analysis, Enraf-Nonius, Delft, The Netherlands,
1990.
[37] C.K. Johnson. ortep II, Report ORNL-5138. Oak Ridge
National Laboratory, TN, 1976.
[38] International Tables for X-Ray Crystallography, Vol. IV,
Kynoch Press, Birmingham (Present distributor Kluwer
Academic Publishers, Dordrecht) 1974.
[7] K.M. Smith (Ed.), Porphyrins and Metalloporphyrins Elsevier,
Amsterdam, 1975.
[39] A.I. Kitaigorodskii, Organic Chemical Crystallography,
Consultants Bureau, New York, 1955.
[8] J. Diesenhofer, O. Epp, K. Miki, R. Huber, H. Michel, J. Mol.
Biol. 180 (1984) 385.
[40] E.B. Fleischer, C.K. Miller, L.E. Webb, J. Am. Chem. Soc. 86
(1964) 2342.
[9] T.O. Yeates, H. Komiya, A. Chirino, D.C. Rees, J.P. Allen, G.
Feher, Proc. Natl. Acad. Sci. USA 85 (1988) 7993.
[10] O. El-Kabbani, C.H. Chang, D. Tiede, J. Norris, M. Schiffer,
Biochemistry 30 (1991) 5361.
[11] C. Kirmaier, D. Holten, Photosynth. Res. 13 (1987) 225.
[12] R.F. Pasternack, E.J. Gibbs, R. Santucci, S. Schaertel, P.
Ellmas, S.C. Mah, J. Chem. Soc. Chem. Commun. (1987) 1771.
[13] J.C. Roberts, S.L. Newmyer, J.A. Mercer-Smith, S.A. Schray,
D.K. Lavallee, Appl. Radiat. Isotopes 40 (1989) 775.
[14] H. Kurreck, M. Huber, Angew. Chem. Int. Ed. Engl. 34 (1995) 849.
[15] R.W. Wagner, J.S. Lindsey, J. Seth, V. Palaniappan, D.F.
Bocian, J. Am. Chem. Soc. 118 (1996) 3996.
[41] S.J. Silvers, A. Tulinsky, J. Am. Chem. Soc. 89 (1967) 3331.
[42] A.M. Shacter, E.B. Fleischer, R.C. Haltiwanger, Acta Cryst. C
43 (1987) 1876.
¨
¨
¨
¨
¨
[43] T. Hokelek, D. Ulku, N. Gunduz, M. Hayvalı, Z. Kılıc¸, Acta
Cryst. C 49 (1993) 1667.
[44] J.A. Shelnutt, C.J. Medforth, M.D. Berber, K.M. Barkigia,
K.M. Smith, J. Am. Chem. Soc. 113 (1991) 4077.
[45] C.J. Medforth, M.O. Senge, K.M. Smith, L.D. Sparks, J.A.
Shelnutt, J. Am. Chem. Soc. 114 (1992) 9859.
[46] L.D. Sparks, C.J. Medforth, M.S. Park, J.R. Chamberlain,
M.R. Ondrias, M.O. Senge, K.M. Smith, J.A. Shelnutt, J.
Am. Chem. Soc. 115 (1993) 581.
[16] J.L. Sessler, B. Wang, A. Harriman, J. Am. Chem. Soc. 117
(1995) 704.