Crystallographic elucidations of indium(III) porphyrin conformations, morphology and aggregation behaviour: Comparative optical study of free base porphyrins and their indium(III) derivatives at varying pH

Article abstract of DOI:10.1016/j.molstruc.2019.01.064

The supramolecular structural architectures of 5, 10, 15, 20-Tetrakis-(4-methoxyphenylporphyrinato) indium (III) chloride (I) and 5, 10, 15, 20-Tetrakis-(4-methylphenylporphyrinato) indium (III) chloride (II) have been determined from their three dimensio

Full text of DOI:10.1016/j.molstruc.2019.01.064

Accepted Manuscript
Crystallographic elucidations of indium(III) porphyrin conformations, morphology and
aggregation behaviour: Comparative optical study of free base porphyrins and their
indium(III) derivatives at varying pH
Padma Dechan, Gauri Devi Bajju, Puneet Sood, Umar Ali Dar
PII:
S0022-2860(19)30075-4
DOI:
https://doi.org/10.1016/j.molstruc.2019.01.064
MOLSTR 26115
Reference:
To appear in: Journal of Molecular Structure
Received Date: 4 October 2018
Revised Date: 18 January 2019
Accepted Date: 18 January 2019
Please cite this article as: P. Dechan, G.D. Bajju, P. Sood, U.A. Dar, Crystallographic elucidations of
indium(III) porphyrin conformations, morphology and aggregation behaviour: Comparative optical study
of free base porphyrins and their indium(III) derivatives at varying pH, Journal of Molecular Structure
(2019), doi: https://doi.org/10.1016/j.molstruc.2019.01.064.
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ACCEPTED MANUSCRIPT
Crystallographic elucidations of indium(III) porphyrin conformations, morphology and
aggregation behaviour: Comparative optical study of free base porphyrins and their
indium(III) derivatives at varying pH
Padma Dechana, Gauri Devi Bajjua*, Puneet Soodb and Umar Ali Dara
aPostgraduate Department of Chemistry, University of Jammu, Jammu-180006, India
bAdvanced Materials Research Centre, Block- A2, Kamand Campus, Indian Institute of
Technology, Mandi, Himachal Pradesh, 175005, India
Abstract
The supramolecular structural architectures of 5, 10, 15, 20-Tetrakis-(4-
methoxyphenylporphyrinato) indium(III) chloride (I) and 5, 10, 15, 20-Tetrakis-(4-
methylphenylporphyrinato) indium(III) chloride (II) have been determined from their three
dimensional X-ray diffraction data. Complex I crystallizes in the orthorhombic space group,
Pbca with a = 23.0083(4) Å, b = 15.2447(3) Å, c = 23.3737(4) Å, α = β = γ = 90°, V =
8198.5(3) Å3 and Z = 8, whereas complex II crystallizes in the triclinic space group, P-1 with
a = 12.0737(5) Å, b =12.1000(5) Å, c =14.1682(6) Å, α = 88.560(3)°, β = 78.730(3)°, γ =
78.280(3)° V = 1987.40(14) Å3 and Z = 2. The geometries around In+3 ions in both the
complexes are square pyramidal giving dome shaped architectures to the metalloporphyrins.
In their respective crystal lattices, the monomeric units of complex I and II are packed in J-
type (head-to-tail) supramolecular aggregation. These monomers are linked into their three
dimensional supramolecular networks by various non covalent forces. Further the packing of
monomers of each complex in their respective unit cells leaves significant void volumes
(porosities). The optical absorption spectra of complex I and II and their free base analogs
i.e. 5, 10, 15, 20-Tetrakis-(4-methoxyphenyl) porphyrin, H2TMP and 5, 10, 15, 20-Tetrakis-
(4-methylphenyl) porphyrin, H2TTP have also been investigated in CH2Cl2 at different ionic
strengths of the media. The investigations revealed that both the free bases exist as simple
monomers, j-aggregates and dianionic monomers at neutral (pH = 7), acidic (pH = 4 and
lower) and basic (pH = 10) media conditions. Also at high ionic strength of the media, the
free bases undergo charge transfer electronic transitions. The two In3+ porphyrin exists as
simple monomers at pH = 7. However at pH = 5 and lower, the In3+ ions in complex II is
remarkably easily replaced by the protons of the acid to generate the corresponding
protonated free base monomers which simultaneously aggregate in J-type stacking mode. In
contrast to complex II that exhibits low stability in acidic media, the complex I remain intact
in such media reflecting extremely high stability of the complex. The insertion of In3+ ions

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into the porphyrinic cores of free bases causes bathochromic shift followed by increase in the
intensities of absorption bands. The appearance of two set of doublets for ortho phenyl
1
protons in the H NMR spectra of each complex is attributed to the magnetic inequivalence
of their ortho phenyl protons caused by the pulling of In+3 ions above the mean porphyrin
planes.
Keywords: dome shaped, mean porphyrin planes, J-type stacking, absorption bands, charge
transfer electronic transitions, magnetic inequivalence
Corresponding author: Gauri Devi Bajju*
E-mail: gauribajju@gmail.com
Contact No.: +91 9419145184
1. Introduction
Porphyrin photosensitizers are widely used in numerous applications such as photodyanamic
therapy (PDT) [1], solar energy harvesting [2, 3], artificial photosynthesis [4], photodynamic
destruction of viruses [5], magnetic resonance imaging (MRI) for the detection of cancer cells
[6] etc. For e.g. 5, 10, 15, 20-Tetraphenylporphyrinato indium(III) chloride, TPPInCl is an
efficient photosensitizer in the photooxidation of L-tryptophan (Trp) and bovine serum
albumin (BSA) [7]. The In3+ ion in TPPInCl induces spin-orbit coupling (heavy atom effect)
favouring long lifetime of the triplet excited state in order to efficiently generate singlet
molecular oxygen [7]. The high photosensitizing ability of TPPInCl suggests that indium
porphyrins can serve as potential photosensitizers in photodyanamic therapy and other photo
responsive devices such as organic light-emitting diodes and organic thin-film transistors. In
order to understand the potential behaviour of π conjugated porphyrins in various biological
and material applications, characterisation of macro rings as an individual molecule and their
crystal packing modes are essential. The first indium derivatives of metalloporphyrins i.e.
TPPInCl, TTPInCl and TMPInCl were reported by Bhatti et al [8]. These
1
metalloporphyrins were characterised by H NMR spectroscopy, Uv-Vis spectroscopy and
elemental analysis. Later, the first single crystal of an indium porphyrin, 5, 10, 15, 20-
tetrakis-(phenylporphyrinato) indium(III) chloride, TPPInCl was reported in 1980 [9].
Eventually many more single crystals of In3+ porphyrins were reported in the literature [10-
14]. In all the reported structures, the In3+ ion is displaced from the core planes due to its
higher ionic radius (0.8 Å). The magnitude of displacement of the metal ion from the core
porphyrinic plane seems to be controlled by various peripheral substitutions around the

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porphyrin ring and axial substitutions on the metal centre. Though, the two In3+ complexes
i.e. TMPInCl and TTPInCl were successfully synthesized by Bhatti et al [8], the single
crystals of these complexes have not been reported in the literature and in fact the complexes
seems not to have given adequate attention. As a result many interesting chemistry of
TMPInCl and TTPInCl are yet to be explored. In an attempt to grow the single crystals of
TMPInCl and TTPInCl, we reiterated the synthesis of TMPInCl and TTPInCl following
the method described by Bhatti et al [8]. After many attempts, we were finally successful in
getting fine needle shaped and violet colored crystals of TMPInCl and TTPInCl. The
complexes crystallized in the orthorhombic and triclinic unit cells. Each complex have highly
ruffled structures with In3+ ion being displaced out of the N4 core planes, giving “dome
shaped” architectures to the metalloporphyrins. The effect of pH on the electronic absorption
spectra of the free base analogues of I and II i.e. H2TMP and H2TTP have also been
investigated in non aqueous media and the results have been discussed in detailed. Porphyrins
are known to undergo dramatic self aggregation under certain conditions [15-17]. Porphyrins
aggregate either in J-type (head-to-tail) fashion or H-type (face-to-face) fashion [18]. The J-
type stacking involves prominent red shift of monomeric absorption bands, in particular the B
band [19, 20] and the H-type stacking involves blue shift of monomeric absorption bands [21,
22]. The J-type molecular alignments have been observed in the three dimensional crystal
lattice of the each synthesized complex and in the aggregated states of H2TMP and H2TTP.
The schematic diagram 1 shows the structures of the two free base porphyrins, under neutral
(a), acidic (b) and basic media conditions (c). The structures of In3+ porphyrins, I and II are
also given in scheme 1 (d).

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(a)
(b)
(c)
(d)
R = -OCH3, -CH3
Scheme 1 Structures of H2TMP and H2TTP at (a) pH = 7 (b) pH = 4 and lower (c) pH = 10
(d) structures of I and II
2. Experimental
2.1 Materials and reagents
The analytical grades chemicals were used for the synthesis of the starting materials i.e.
H2TMP and H2TTP and their In3+ derivatives i.e. I and II. Pyrrole, 4-methoxybenzaldehyde,
4-methylbenzaldehyde, propionic acid, diethylether, glacial acetic acid, sodium acetate,
methanol, dichloromethane, chloroform, basic alumina and silica gel were purchased from
sigma Aldrich as were used as received. InCl3 was also purchased from sigma Aldrich.
2.2 Measurements and Instrumentation
1
UV-Visible spectra were obtained on PG spectrophotometer; model T-90. H NMR spectra
were recorded on Bruker spectrometer, model AV 400 N (400 MHZ), using CDCl3 as solvent
and TMS as internal reference. FT-IR spectra were recorded between 4000 cm-1 to 400 cm-1
using KBr pellets on Perkin Elmer Spectrum.

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2.3 Solution and Refinement of the Crystal Structures of I and II
Reflection data were measured at 293(2) K. The crystal was mounted under paratone oil and
to get relative intensity data, the single crystal analysis was collected on a CCD Agilent
SUPERNOVA E (Dual) diffractometer using monochromated Cu-Kα radiation (λ = 0.154184
Å) at 293(2) K. Using Olex2 [23], the structure was solved with the ShelXS [24] structure
solution program using Direct Methods and refined with the ShelXL [24] refinement package
using Least Squares minimisation. The positions of all the atoms were obtained by direct
method. All non hydrogen atoms were refined anisotropically. The remaining H- atoms were
refined with isotropic temperature factors, 1.2 Ueq of their parent atoms. Crystallographic data
(cif) has been deposited with the Cambridge Structural Data Centre with reference numbers-
1584380 and 1584382.
2.4 Synthesis of H2TMP and H2TTP
The two starting compounds i.e. H2TMP and H2TTP were synthesized according to the
modified Adler’s method [25]. Pyrrole (20mmols) and para-substituted benzaldehydes
(20mmols) were added to the propionic acid solutions (50ml) in a 250ml round bottomed
flasks fitted with water condensers. The reaction mixtures were then allowed to reflux for
half an hour at 60˚C, as shown in scheme 2. After the completion of the reaction, the reaction
mixtures were allowed to cool at room temperature and then stored in refrigerator for 2 hours.
The shiny purple crude products of H2TMP and H2TTP were then filtered and the residues
were air dried completely. The crude products were then subjected to their purifications on
basic alumina columns using methanol in case of H2TMP and chloroform in case of H2TTP
as eluting solvents. The purified compounds were finally recovered by the evaporation of the
organic solvents.
H2TMP was obtained as purple solid with 60% yield. FT-IR (KBr, νmax, cm-1): 3317.66 ν(N-
H)pyrrole, 730.46 γ(C-H)ph, 800.04 γ(C-H)pyrrole, 1341.22 ν(C-N), 1595.22 ν(C=N),
2913.18 ν(C-H) OCH3, 1023.84 ν(C-O-C)sym, 1233.98 ν(C-O-C)asym.1H NMR (CDCl3,
400MHz, δ, ppm): -2.74 (s., 2H, NH), 4.12 (s., 12H, OCH3), 7.31-7.33 (d., 8H, ArHm), 8.14-
8.16 (d., 8H, ArHo), 8.89 (s., 8H, βH). UV-Vis (λmax, nm, CH2Cl2): 421 (B band), 519, 555,
594, 651 (Q bands).

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H2TTP was obtained as purple solid with 70% yield. FT-IR (KBr, νmax, cm-1): 3327.35 ν(N-
H)pyrrole, 735.87 γ(C-H)ph, 800.49 γ(C-H)pyrrole, 1352.16 ν(C-N), 1583.63 ν(C=N),
1
2912.64 ν(C-H) OCH3, 1022.32 ν(C-O-C)sym, 1221.96 ν(C-O-C)asym. H NMR (CDCl3,
400MHz, δ, ppm): -2.74 (s., 2H, NH), 2.73 (s., 12H, CH3), 7.57-7.59 (d., 8H, ArHm), 8.11-
8.13 (d., 8H, ArHo), 8.88 (s., 8H, βH). UV-Vis (λmax, nm, CH2Cl2): 420 (B band), 516, 552,
592, 644 (Q bands).
2.5 Synthesis of I and II
The In3+ derivatives of H2TMP and H2TTP i.e. I and II were synthesized by acetate method
according to the procedure described by Bhatti et al [8]. 246 mg (0.4 mmols) of the starting
compounds and 221 mg (1.0mmols) of the metal carriers i.e. InCl3 were added in 250 ml
round bottomed flasks fitted with water condensers and loaded with glacial acetic acids (30
ml) and sodium acetates (0.554 g). The reaction mixtures were then refluxed for 4 hours at
60˚C. The progresses of the reactions were determined spectrophotometrically. After the
completion of the reaction, the reaction mixtures were allowed to cool at room temperature
and then brought to 0˚C by placing the mixtures on ice baths. This method induces rapid
crystallisation of the products so formed. The crude products of I and II were purified on
silica gel columns using dichloromethane as an eluent. The metal complexes were further re-
crystallized from mixed solvent systems of dichloromethane and Hexane (2:1). The needle
shaped single crystals of the metal complexes, I and II were obtained by slow evaporation of
the chloroform solutions.
[In(III)TMP]Cl [I] was obtained as violet solid with 40% yield. FT-IR (KBr, νmax, cm-1):
720.44 γ(C-H)ph, 806.28 γ(C-H)pyrrole, 1339.62 ν(C-N), 1572.05 ν(C=N), 2932.89 ν(C-H)
1
OCH3, 1064.75 ν(C-O-C)sym, 1247.03 ν(C-O-C)asym. H NMR (CDCl3, 400MHz, δ, ppm):
4.14 (s., 12H, OCH3), 7.36-7.38 (d., 8H, ArHm), 8.04-8.06 (d., 8H, ArHo), 8.30-8.32 (d., 8H,
ArHo), 9.12 (s., 8H, βH). UV-Vis (λmax, nm, CH2Cl2): 430 (B band), 563, 606 (Q bands).
[In(III)TTP]Cl [II] was obtained as violet solid with 35% yield. FT-IR (KBr, νmax, cm-1):
723.34 γ(C-H)ph, 800.49 γ(C-H)pyrrole, 1336.73 ν(C-N), 1573.98 ν(C=N), 2923.25 ν(C-H)
1
OCH3, 1069.57 ν(C-O-C)sym, 1251.86 ν(C-O-C)asym. H NMR (CDCl3, 400MHz, δ, ppm):
2.75 (s., 12H, CH3), 7.63-7.65 (d., 8H, ArHm), 8.01-8.03 (d., 8H, ArHo), 8.27-8.29 (d., 8H,
ArHo), 9.10 (s., 8H, βH). UV-Vis (λmax, nm, CH2Cl2): 426 (B band), 560, 601 (Q bands).
3. Results and Discussion

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The two free base porphyrins and their corresponding In3+ derivatives were synthesized
according to the methods provided in the literature [25, 8] (scheme 2).
Scheme 2 Synthetic routes for H2TMP, H2TTP and their In3+ complexes, I and II
3.2 Crystal structures
I and II crystallizes in the orthorhombic and triclinic unit cells. The Ortep representations of I
and II along with their crystallographic labelling schemes are given in Fig. 1. The

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asymmetric unit in each complex consists of single porphyrin molecule. The geometries
around the In3+ ions in both the metalloporphyrins are regular square pyramidal type, with
N(1)/N(2)/N(3)/N(4) and N(6)/N(10)/N(14)/N(18) lying in the basal planes. The 24 atoms
porphyrin cores in I and II are nearly planar [dihedral angle ̴ 5.07˚ (I) and ̴ 5.03˚ (II)]. In each
complex, the In3+ ion due to its large ionic radius (0.8 Å) is pulled upward towards the axial
chlorine atom and above the mean N4 core plane as shown in Fig. 2. Such phenomenon is
known as “doming” of the macrocyclic rings. The average In−N bond distances are 2.146 Å
(I) and 2.153 Å (II). This measured bond distances in I and II are smaller than that observe in
case of TPPInCl. The average In−N bond distance in TPPInCl was found to be 2.156 (6) Å
[9]. Similarly the average N−N distances are 2.916 Å (I) and 2.931 (II). The larger In−N and
N−N bond distances in II compared with that of I might be attributed to greater expansion of
the porphyrin core in II than I. The In−Cl bond distances are 2.381 Å in both the metal
complexes which is slightly larger than that observe in case of TPPInCl i.e. the In−Cl bond
distance in TPPInCl was found to be 2.369 (2) Å [9]. The four phenyl rings in each complex
are twisted by ̴ 45˚ with respect to the mean N4 core plane showing significant out of plane
distortions. The dihedral angles between the mean plane of 4N and the planes of the phenyl
groups are 44.94˚ [C(24)], 45.57˚ [C(31)], 45.38˚ [C(38)] and 45.05˚ [C(45)] in (I) and 44.51˚
[C(51)], 44.85˚ [C(44)], 44.47˚ [C(35)] and 45.86˚ [C(28)] in (II). The greater out of mean
plane distortion of the peripheral p-substituted phenyl rings in each metal complex might be
attributed to two factors i.e. distortion of In3+ ion above the mean N4 plane and steric
interactions between the neighbouring phenyl protons and beta pyrrole protons [H29···H8
3.673 Å, H33···H4 3.589 Å, H36···H9 2.560 Å, H26···H3 3.440 Å, H22···H19 3.012 Å,
H47···H18 2.843 Å, H43···H14 2.813 Å , H40···H13 2.923 Å] (I) and [H30···H22 3.593 Å,
H37···H21 2.968 Å, H33···H39 3.014 Å, H40···H42 3.581 Å, H46···H23 3.689 Å,
H53···H24 2.497 Å, H49···H20 2.682 Å, H19···H26 3.886 Å] (II) (Fig. 3). The phenyl rings
in both I and II are twisted to a lesser extends than that observe in case of InTPPCl [9].
The porphyrin monomers in I are packed in an offset-stacked geometrical fashion. Such type
of stacking is typical of J-type stacking exhibited by certain dye molecules [26-28]. In
general a face centred stacking is preferred when electron-rich aromatics (donors) interact
with electron-deficient aromatics (acceptors) [29]. Such interactions can be better described
as ‘‘aromatic donor–acceptor interactions’’ [30]. In the offset packing modes of I, the eight
porphyrin monomers of the orthorhombic unit cell acts remarkably as four set of offset
porphyrin pairs (Fig. 4). The two offset porphyrin pairs lying towards the centre of the unit

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cell are shown by blue and green colours, where as the other two offset porphyrin pairs lying
partly inside and partly outside the orthorhombic unit cell are shown as pink for clarity (Fig.
5). The two offset porphyrin pairs (blue and green) are interlinked by four types of close non
covalent intermolecular forces of which C···C, C−H···π, In−Cl···H and C−O···H interactions
are present (Fig. 6 and Fig. 7). The closest C···C, In−Cl···H and C−O···H distances are
found to be 3.433, 3.249 and 2.527 Å. The In−Cl···H and C−O···H intermolecular hydrogen
bonding interactions are induced by Cl atoms attached axially to the metal centres and the O
atoms of para methoxy substituents of four peripheral phenyl rings. The monomeric subunits
of each of the two porphyrin pairs (blue and green) are bound to each other by C···C,
C−H···π and C−O···H interactions. The absence of In−Cl···H interactions in this case is
attributed to the non directional orientations of In−Cl and C−H bonds of the interlinked
monomers. Though the monomeric subunits of each of the two offset porphyrin pairs (shown
as pink) due to their greater centroid to centroid distance (11.83 Å) exhibits no inter
porphyrin molecular interactions. However, they are able to interact with their neighbouring
porphyrin moieties belonging to other two offset porphyrin pairs (blue and green) by all the
four non covalent forces discussed earlier. The hydrogen bonds in I are listed in Table 2. The
3D crystal packing in II is relatively simpler as compared to 3D packing in I. In the triclinic
unit cell of II, the two porphyrin macrocyles are stacked in an offset (J-type) supramolecular
fashion similar to I. The two macrocycles are held together by C···C and C−H···π
interactions with closest atom to atom of distances (C···C 3.661 Å) as shown in Fig. 8. The
centroid to centroid and vertical distances between the porphyrin monomers are 6.36 Å and
4.23 Å. In their respective three dimensional crystal lattices, the “dome-shaped" macrocycles
in each complex are packed in such a manner, so that the top of “domes” of the non
covalently interlinked porphyrin subunits are facing outwards, thereby leaving many empty
spaces in their respective crystals. As a result, clear porosities can be observed in the packing
diagrams of I and II (Fig. 9).
Table 1 Numerical details of the solution and refinement of I and II
I
II
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
b/Å
c/Å
α/°
C48H36ClInN4O4
883.08
293(2)
orthorhombic
Pbca
23.0083(4)
15.2447(3)
23.3737(4)
90.00
C48H36ClInN4
819.08
293(2)
triclinic
P-1
12.0737(5)
12.1000(5)
14.1682(6)
88.560(3)

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β/°
90.00
78.730(3)
γ/°
90.00
8198.5(3)
78.280(3)
1987.40(14)
Volume/Å3
Z
8
2
ρcalcg/cm3
1.431
5.610
1.369
5.663
ꢀ/mm-1
F(000)
3600.0
0.407 × 0.117 × 0.098
7.68 to 133.74
-19 ≤ h ≤ 27, -18 ≤ k ≤ 8, -27 ≤ l ≤ 26
16444
7211 [Rint = 0.0308, Rsigma = 0.0385]
1.085
R1 = 0.0383, wR2 = 0.1047
R1 = 0.0484, wR2 = 0.1122
0.78/-1.14
836.0
0.106 × 0.09 × 0.085
7.62 to 133.86
-14 ≤ h ≤ 11, -12 ≤ k ≤ 14, -16 ≤ l ≤ 16
12513
6972 [Rint = 0.0260, Rsigma = 0.0379]
1.038
R1 = 0.0289, wR2 = 0.0739
R1 = 0.0333, wR2 = 0.0771
0.50/-0.44
Crystal size/mm3
2Θ range for data collection/°
Index ranges
Reflections collected
Independent reflections
Goodness-of-fit on F2
Final R indexes [I>=2σ (I)]
Final R indexes [all data]
Largest diff. peak/hole / e Å-3
Table 2 Hydrogen bonds for I
D—H···A
d(D-H)
d(H···A)
d(D···A)
<(DHA)
C27—H27B···Cl1
C25—H25···Cl1
0.960
0.930
3.301
3.389
4.076
4.306
139.15
169.37
C34—H34C···Cl1
C30—H30···Cl1
C41—H41A···Cl1
C48—H48C···Cl1
C34—H34C···O4
C48—H48B···O2
C14—H14···O2
C13—H13···O2
C29—H29···O3
0.960
0.930
0.960
0.960
0.960
0.960
0.930
0.930
0.930
3.011
2.913
3.363
3.249
2.726
2.779
2.486
3.395
2.527
3.711
130.84
178.33
120.81
135.22
128.83
127.85
135.49
101.45
165.74
3.842
3.942
3.988
3.411(7)
3.452(7)
3.216(4)
3.597
3.436(5)
Symmetry code: x, y, z
Table 3 Selected bond lengths (Å) and bond angles (˚) in I and II
I
II
I
II
C11-C35
C16-C42
C21-C1
O3-C38
O4-C45
C20-C1
O2-C31
C28-C6
O1-C24
C12-C11
C7-C6
1.485(4)
1.506 (5)
1.501(5)
1.361(4)
1.369(5)
1.409(5)
1.364(4)
1.493(5)
1.366(4)
1.404(5)
1.396(5)
1.409(5)
1.415(5)
1.401(5)
C17-C16
C9-C8
C12-C41
C5-C4
C51-C54
C3-C4
C8-C32
C8-C7
C11-C12
C28-C31
C16-C48
C16-C15
C13-C12
C35-C38
1.416(4)
1.405(4)
1.509(3)
1.407(4)
1.516(4)
1.401(4)
1.500(4)
1.405(4)
1.399(4)
1.518(4)
1.499(3)
1.398(4)
1.408(4)
1.510(5)
C17-C16 C15 125.7(3)
C11-C12-C13 126.0(2)
C2-C1-C20
C2-C1-C20
C38-O3-C41
C31-O2-C34
C24-O1-C27
C45-O4-C48
125.5(3)
125.5(3)
118.2(3)
117.6(3)
117.2(3)
117.0(5)
C7-C8-C9
C15-C16-C17 125.6(2)
C3-C4-C5 125.8(2)
125.8(2)
C12-C11-C10 125.6(3)
C7-C6-C5 126.0(3)
C10-C11
C15-C16
C1-C2

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C5-C6
C17-C16
1.406(5)
1.397(5)
C25-C4
C44-C43
1.498(3)
1.333(7)
Fig. 1 ORTEP representations of the molecular structures with atom-labeling schemes for I
(left) and II (right). Ellipsoids are shown at 50% probability level. Hydrogen atoms are
omitted for clarity
Fig. 2 Ortep views of I (left) and II (right) illustrating the pulling of indium atoms above the
N4 core planes. Hydrogen atoms are omitted for clarity

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Fig. 3 Steric interactions between the neighbouring phenyl protons and beta pyrrole protons
of I (left) and II (right) causing the twisting of phenyl rings
Fig. 4 Capped stick (left) and space filled (right) models in the crystal packing of I showing
the offset or slipped face-to-face stacking arrangements of monomeric units

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Fig. 5 Capped stick (left) and space filled (right) models in the crystal packing of I, showing
the alignment of monomeric units as dimeric porphyrin pairs
(a)

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(b)
Fig. 6 Offset or slipped face-to-face stacking geometry in the crystal lattice of I stabilised
by C···C (a) and C−H···π (b) interactions. The atoms involved in directional interactions
are shown by orange (C) and purple (H) spheres
(a)

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(b)
Fig. 7 Offset or slipped face-to-face stacking geometry in the crystal lattice of I stabilised
by In−Cl···H (a) and C−O···H (b) interactions. The atoms involved in directional
interactions are shown by purple (H), yellow (Cl) and red (O) spheres
Fig. 8 Offset or slipped face-to-face stacking geometry in the crystal lattice of II stabilised
by C···C (left) and C−H···π (right) interactions. The atoms involved in directional
interactions are shown by orange(C) and purple (H) spheres

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(a)
(b)
Fig. 9 Spacefilling models of I (a) and II (b) illustrating, the porosities in the crystal
packings. Carbon atoms are shown in gray, oxygens in red, nitrogens in blue, and chlorine
atoms in green
3.3 1H NMR spectroscopy
1
The selected regions of the H NMR spectra of I and II and their corresponding free base
1
analogues i.e. H2TMP and H2TTP are given in Fig. 10 and Fig. 11. H NMR experiments
were carried to better understand the influence of In3+ ion insertion into the porphyrinic cores
of H2TMP and H2TTP. The displacement of In3+ ion above the mean porphyrinic planes as

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observed in the crystal structures of I and II, generates asymmetric environment above and
below the plane of the macrocycles which resulted in the “magnetic inequivalence” of ortho
aryl protons [9]. Hence one can easily observe two sets of doublets for ortho aryl protons
(Hc) in the 1H NMR spectrum of the each synthesized complex. The detection of two sets of
doublets for ortho aryl protons by the pmr spectrometer becomes possible due to the slow
rotation of the aryl rings about the (C−C) single bonds which connects the aryl rings to the
porphyrin rings at their meso (=CH−) positions. The “magnetic inequivalence” of ortho
phenyl protons was earlier arbitrarily assigned to “nonequivalence of phenyls in pairs” [1],
presumably due to lack of crystal data of I and II at that time. The doublets appearing at
7.31/7.33 ppm in I and 7.57/7.59 ppm and 8.11/8.13 in II might be attributed to the presence
1
of some unreacted free base compounds. The H NMR spectra further demonstrates that the
resonance signals corresponding to beta pyrrole protons (Ha), meta phenyl protons (Hb) and
para methoxy protons (He) in case of I and beta pyrrole protons (Ha), meta phenyl protons
(Hb) and para methyl protons (He) in II exhibits downfield shift, compared with the
corresponding resonance signals of their free base analogues i.e. H2TMP and H2TTP. This
indicates that the insertion of In3+ ion into the porphyrinic cores of H2TMP and H2TTP
resulted in the de-protection of the phenyl as well as β-pyrrolic protons. The signals at δ -2.74
in H2TMP and -2.76 ppm in H2TTP are due to the resonances of the inner NH protons.

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1
Fig. 10 The selected regions of the H NMR spectra (400 MHz pulse FT) of H2TMP (olive
green, ̴ ̴
4.0 X 10-5 M) and [In(III)TMP]Cl (blue, 5 X 10-3 M) in CDCl3. Extra peaks at δ
7.2 ppm and 1.5-1.6 ppm are due to presence of undeuterated chloroform and water
molecules
Fig. 11 The selected regions of the 1HNMR spectra (400 MHz pulse FT) of H2TTP (red,
X 10-5 M) and [In(III)TTP]Cl (blue, 5 X 10-3 M) in CDCl3. Extra peaks at δ 7.2 ppm and
̴ 4.0
̴
1.5-1.6 ppm are due to presence of undeuterated chloroform and water molecules
3.4. UV-Visible spectroscopy
The electronic absorption spectra of H2TMP and H2TTP are highly sensitive to processes
such as protonation (pH = 4), deprotonation (pH = 10) and metallation. The subtle variations
in optical absorption spectra of the synthesized porphyrins have been monitored by using
UV-Vis spectroscopy.
Fig. 12 shows the optical absorption spectra of H2TMP and H2TTP in dichloromethane
under neutral (pH = 7) and acidic (pH = 4) media. Under neutral environment (pH = 7) at
̴
4.0 x 10-6 M, each of the free base macrocycle [scheme 1 (a)] exhibits one higher intensity
soret or B band centred around λmax 400nm and four weaker Q bands lying between λmax 500
to 680nm range characteristic of a regular or normal porphyrin molecules. The B and Q bands
arise due to the (S0 to S2) and (S0 to S1) transitions within the highly conjugated π systems
[31]. The absorption spectra of the two free bases measured under the neutral conditions at
̴

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4.0 x 10-6 M corresponds to the spectra of non aggregated or monomeric porphyrin moieties,
since no variations were observed upon subsequent dilutions of the solutes. At high ionic
strength of the media (pH = 4), the two inner imino nitrogen atoms of the N4 cores of
H2TMP and H2TTP undergoes protonation [32] [scheme 1 (b)]. The protonation induces
partial positive charge in the centre of the molecules thereby producing dicationic type
species. The dication generations led to the appearance of a narrow higher energy and red
shifted band (known as J-band), followed by reduction in the number of Q bands and
appearance of a single higher intensity Q band in each free base porphyrin (Fig. 12). From the
literature data, it is found that J-band for H2TMP appears at λmax 451nm in THF-aqueous
solution at pH = 4 and lower [32]. This indicates that the media in which the protonation of
porphyrins occurs at low pH plays significant role in deciding the positions of absorption
bands of porphyrins under aggregated conditions. The dramatic change in the spectra of
H2TMP and H2TTP under acidic conditions (pH = 4) are attributed to the prominent self
aggregation of the monomers induced by protonation of inner imino nitrogen atoms. The
prominent red shift of absorption bands, especially, the B bands strongly signifinies that both
the free bases undergo J-type supramolecular aggregation [33]. The decrease in the number of
Q bands is attributed to increase of the D2h symmetry of the free base porphyrins to D4h by
protonation. The symmetry group of the free-base porphyrins are D2h due to the two
hydrogen atoms located diagonally on the pyrrolic nitrogens, the porphyrins without these
protons are of higher symmetry [34]. Another important phenomenon observed under acidic
conditions is the appearance of charge transfer electronic bands (hyperporphyrin effects) in
both the free bases. The charge transfer optical bands were found at λmax 326 and 366nm for
H2TMP and H2TTP. The charge transfer spectra arise due to transition from peripheral para
substituted phenyl groups to empty π∗ orbitals of porphyrins [35]. Because of the charge
transfer transitions, the color of the solutions changes from purple to green. At pH = 10, the
porphyrin rings of H2TMP and H2TTP undergoes deprotonation [36] and produces dianionic
type moieties [scheme 1 (c)]. Though the pattern of absorption band spectra of an electrically
neutral and dianion porphyrins remains same, the dianion generations induces profound
increase in the intensities of B as well as Q bands (Fig. S1). The hyperporphyrin effects have
not been observed for the two free bases under basic media (pH = 10). It can be observed
from Fig. 12 that the absorption bands of H2TMP are slightly red shifted in comparison with
H2TTP. The red shift is due to the greater electron donating tendency of the para methoxy
substituents as compared to para methyl substituents resulting in the increase in π conjugation
and reduction of the HOMO–LUMO energy gap [37].

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The optical absorption spectra of I and II at pH = 7 at very low concentrations ̴
4.0 x 10-6M
reflects that both the complexes exists as simple monomers consisting of one sharp soret band
and only two Q bands characteristics of porphyrin coordinated to a metal ion through the four
Nitrogen atoms. The reduction in the number of Q bands in metalloporphyrins is attributed to
the increase in the symmetry (D2h) of the free base porphyrins to D4h by metallation [38].
The most striking feature is the absorption spectral data of the two In3+ complexes at high
ionic strength of the media. The two metalloporphyrins exhibits completely different stability
in acidic environments. The measurement of absorption spectrum of I in CH2Cl2 [Fig. 14
(left)] at pH = 5 and lower exhibits no change in the positions and number of absorption
bands of the metalloporphyrin indicating remarkably high stability of the complex in media
of high ionic strength. This further reflects that the protons of the acid could not replace the
In3+ ion from the macrocyclic ring of H2TMP which may be attributed to relatively strong
coordination of In3+ to the four Nitrogen atoms of the porphyrinic core of H2TMP. On the
contrary, metalloporphyrin II exhibits extremely low stability even in slight acidic media. At
pH ̴ 5, the purple colour of the dichloromethane solution of II changes to dark green followed
by changes in the number and positions of the absorption bands. The soret band undergoes
bathochromic shift and the two Q bands reduces to only one higher energy red shifted band.
An additional band due to charge transfer transition is also observed at λmax ̴ 369nm [Fig. 14
(right)]. This band is red shifted by λmax 3nm compared with that of free base porphyrin
measured under acidic media [Fig. 12 (right)]. All these spectral changes in complex II
indicates that In3+ ions are being easily replaced by the protons of the acid to give the
corresponding protonated free base compounds. The protonated species thus generated
simultaneously undergoes J-type molecular aggregation giving one higher energy J-band and
one Q band. The extremely low stability of complex II in acidic media may be due to weak
coordination of In3+ ion to the four nitrogens of H2TTP. The relatively strong and weak
coordination of the In3+ ions to the nitrogen atoms of the two free bases is also reflected from
the average In−N bond distance parameters which are found to be 2.146 Å [I] and 2.153 Å
[II]. Although the difference in the average In−N bond distances in I and II is very low, there
may be some additional factors that accounts for the different stability of the two
metalloporphyrins in acidic media. The insertion of In3+ ions into the porphyrinic cores of
H2TMP and H2TTP resulted in the bathochromic shift of B as well as Q bands (Fig. 14). The
red shift of absorption bands in In3+ porphyrins (heavy metal porphyrins) can be attributed to
the fact that the metal orbitals are closer in energy to the antibonding π* molecular orbitals
(lowest unoccupied molecular orbitals, LUMOs) than to the bonding, π molecular orbitals

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(highest occupied molecular orbital, HOMO) of porphyrin, so that the perturbation they
generate reduces the energy of the LUMOs more than that of the HOMO, resulting in the
bathochromic shift of π-π* transitions [39].
Fig. 12 The UV/Vis absorption spectra of H2TMP at (a) pH = 7 (magenta) and (b) pH = 4
(green) [left] and H2TTP at (a) pH = 7 (olive green) and (b) pH = 3 (blue) [right] in CH2Cl2

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Fig. 13 The UV/Vis absorption spectra of H2TMP (blue) and [In(III)TMP]Cl (olive green)
[left ] and H2TTP (olive green) and [In(III)TTP]Cl (purple) [right] in CH2Cl2 at pH = 7 at
̴
4.0 x 10-6M
Fig. 14 The UV/Vis absorption spectra of [In(III)TMP]Cl [left ] and [In(III)TTP]Cl [right]
in CH2Cl2 at pH = 5 and lower at ̴
4.0 x 10-6M
4. Conclusions
In summary we have reported the single crystal molecular structures of I and II. Both the
macrocycles have “dome shaped” structures due to the pulling of In3+ ions above the mean
planes of four nitrogen atoms. Further the two metal complexes exhibit J-type stacking of
their monomeric rings. From the absorption measurement data, it is confirmed that both
H2TMP and H2TTP exist as distinct monomers in neutral media at lower molar
concentrations ̴
4.0 x 10-6M. However, under high ionic strength of the media, they tend to
aggregate in J-type molecular alignments. Also under such media both the metal free
compounds undergoes charge transfer transitions characteristics of a hyper porphyrin dye
materials. A tremendous increase in the intensities of the absorption bands of H2TMP and
H2TTP is observed under the basic media. The two metal complexes exist as simple
monomers in neutral media at lower molar concentrations
ionic strength (pH = 5 and lower), the In3+ ion in metalloporphyrin I remain intact with the
̴
4.0 x 10-6M. In media of high

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macrocyclic ring thereby reflecting high stability of the complex. However in II, In3+ ion is
easily demetallated from the macro ring to give the protonated free base species which
undergoes simultaneous J-type aggregation. The insertion of In3+ ions within the porphyrinic
cores of H2TMP and H2TTP induces bathochromic shifts and increase in the intensities of the
absorption bands. In the end, the displacement of In3+ ion above the mean porphyrin plane in
each complex result in the “magnetic inequivalence” of ortho phenyl protons.
Acknowledgments
This research was supported by Council of Scientific and Industrial Research (CSIR) India
(grant No. 09/100(0190)/2016-EMR-I).
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•
•
•
•
Insertion of In3+ ions within the porphyrin cores of H2TMP and H2TTP causes dome-
type structures of the macrocyclic rings.
Absorption bands in two In3+ porphyrins are bathochromically shifted as compared to
their free base analogs.
In basic media, the two In3+ porphyrins exhibit significant increase of their absorption
band intensities.
The In3+ derivative of H2TMP is fairly stable under acidic environment. However, the
In3+ ion is easily released from the porphyrin core of H2TTP under such media.