Molecular structures, DFT studies and their photophysical properties in solution and solid state. Microwave-assisted multicomponent synthesis of organotin bearing Schiff bases

Article abstract of DOI:10.1016/j.molstruc.2018.12.039

A couple of luminescent organotin compounds derivated from ligands-ONO were obtained by multicomponent microwave assisted synthesis in short time (15 min) and good yields: ((E)-8, 8-8-diphenylbenzo[d] naphtho [1,2-h][1,3,6,2] dioxazastannonine (1) and (E)

Full text of DOI:10.1016/j.molstruc.2018.12.039

Journal of Molecular Structure 1180 (2019) 642e650
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Molecular structures, DFT studies and their photophysical properties
in solution and solid state. Microwave-assisted multicomponent
synthesis of organotin bearing Schiff bases*
a
a
b
b
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~
Arelly M. Canton-Díaz , Blanca M. Munoz-Flores , Ivana Moggio , Eduardo Arias ,
Gleb Turlakov b, Casiano Del Angel-Mosqueda c, Pedro I. Ramirez-Montes d,
Víctor M. Jimenez-Perez
Universidad Autonoma de Nuevo Leon, Facultad de Ciencias Químicas, Ciudad Universitaria, Av. Universidad s/n, C. P. 66451, Nuevo Leon, Mexico
Centro de Investigacion en Química Aplicada, Boulevard Enrique Reyna 140, 25294, Coahuila, Mexico
a, *
ꢀ
ꢀ
a
ꢀ
ꢀ
ꢀ
b
c
ꢀ
ꢀ
ꢀ
~
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Universidad Autonoma de Nuevo Leon, Facultad de Odontología, Dr. Eduardo Aguirre Pequeno, Mitras Centro, C. P. 64460, Nuevo Leon, Mexico
d
ꢀ
ꢀ
ꢀ
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Universidad Nacional Autonoma de Mexico, Facultad de Estudios Superiores Cuautitlan, Departamento de Matematicas, Torre Izcalli K5, C. P. 54700,
ꢀ
Cuautitlan Izcalli, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
A couple of luminescent organotin compounds derivated from ligands-ONO were obtained by multi-
component microwave assisted synthesis in short time (15 min) and good yields: ((E)-8, 8-8-
diphenylbenzo[d] naphtho [1,2-h][1,3,6,2] dioxazastannonine (1) and (E)11, 13- di-tert-butyl, 8- diphe-
nylbenzo [d] naphtho [1,2-h][1,3,6,2] dioxazastannonine (2)). Both compounds were fully characterized
by NMR (1H, 13C, and 119Sn; 2D-NMR, HETCOR and COSY), UVeVis, IR, and high-resolution mass spec-
trometry. The X-ray structures of two complexes demonstrate that the tin atoms adopt a bipyramidal
trigonal geometry. The 119Sn NMR chemical shifts of the tin atom in the complexes are also consistent
with the presence of pentacoordinate tin centers. The photophysical properties in solution and solid
state, DFT, and voltammetry the two complexes have been determined.
Received 1 November 2018
Received in revised form
7 December 2018
Accepted 10 December 2018
Available online 14 December 2018
Keywords:
Organotin
Fluorescence
X-ray
© 2018 Published by Elsevier B.V.
Schiff base
Microwave assisted synthesis
1. Introduction
fluorescent properties where the tin derivatives have shown new
and interesting applications in the fabrication of optoelectronic
The fundamental tin chemistry has been well documented as
well as their important role in catalysis, in organic synthesis and
the application of organotin compounds in biology and medicinal
areas [1,2]. Specifically, organotin Schiff bases compounds have
been reported with a plethora of biological activity such as cyto-
toxicity [3,4], antimicrobial [5,6], antioxidant [7,8], antifungal
[9,10], anti-inflammatory [11,12], antibacterial [13,14], antitumor
[15,16], anti-insecticidal [17,18], antitubercular [19], and antifertility
[20,21]. However, in less than a decade, the luminescent organotin
Schiff bases have gained tremendous attention due to easy and fast
chemical synthesis, high atom economy, low E-factor, and their
devices such as OLEDs (Organic light emitting devices, Fig. 1,
compound A) [22] and organic solar [23].
Among other applications, these compounds have been re-
ported as novel cell-staining fluorescent probes, in particular of
cytoplasm in vitro assays with melanoma cells B16F10 (C) [24],
human lung carcinoma cell line A549 (D) [25] and nucleoli/cyto-
plasm marker with melanoma cells B16F10 (E) [26]. Other two
interesting applications are the fluorescent detection of warfare
agents (F) [27] and silk fibroin dyes by using organotin biogenic
Schiff bases (G) [28].
On the other hand, nowadays and take in account the climate
change, the scientific community is facing one of its biggest chal-
lenges where the use of fast, efficient, clean, and environmental
friendly synthetic methods is imperative. However, the green
synthetic methods such as ultrasound, electrosynthesis [29],
mechanosynthesis [30,31], and microwave-assisted synthesis [32]
to obtain organotin derivatives are still quite scarce. Recently, in our
*
Dedicated to Prof. Dr. Carlos Camacho-Camacho for his contribution on orga-
notin chemistry.
* Corresponding author.
ꢀ
ꢀ
E-mail address: victor.jimenezpr@uanl.edu.mx (V.M. Jimenez-Perez).
https://doi.org/10.1016/j.molstruc.2018.12.039
0022-2860/© 2018 Published by Elsevier B.V.

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643
Fig. 1. Fluorescent organotin compounds with different applications.
research group the green synthesis of organotin compounds
derived from Schiff base has been reported [33]. In continuing with
our research, here we report on the multicomponent micro-wave
assisted synthesis and photoluminescent properties of two orga-
notin complexes 1 and 2 (vide infra). The X-ray single crystal
structure, DFT and voltammetry properties were investigated. Both
organotin compounds were fully characterized by NMR (1H, 13C,
and 119Sn), UVevis, IR spectroscopy, high resolution mass spec-
trometry and fluorescence spectroscopy.
hydroxy-1-napthaldehyde 0.1000 g (0.58 mmol), 2-aminophenol
0.0633 g (0.58 mmol), diphenyltin oxide 0.1678 g (0.58 mmol) and
acetonitrile (5 mL) was microwave irradiated at 182 ꢀC for 15 min.
The reaction progress was monitored by thin layer chromatography
every 60 s. After cooling to room temperature, the excess of solvent
was evaporated under reduced pressure, the product was filtered
and washed with hexane, giving 1 as a red solid in 85% yield
(0.31 g). M.p. 213 ꢀC. IRʋmax (ATR) N-H 1476, C]N 1608 C¼CArom
.
1619 cmꢁ1. UV/vis (CHCl3) labs/max (nm) [εmax *104 (Mꢁ1 cmꢁ1)]: 474
[1.32] Fluorescence (CHCl3):
CDCl3)
l
fluor (nm): 560. 1H NMR (400.13 MHz,
d
¼ 6.76 (td, H15, 1H), 7.13 (dd, H13, 1H), 7.23 (dd, H16, 1H),
2. Experimental section
7.24 (d, H3, 1H), 7.34 (td, H7, 1H), 7.37 (m, H-p, 2H), 7.38 (m, 14H, H-
m), 7.41 (d, H14, 1H), 7.52 (td, H8, 1H), 7.72 (dd, H6, 3J ¼ 7.9 Hz, 1H),
7.89 (d, H4, 1H), 7.93 (m, 4H, H-o), 8.02 (d, H9, 3J ¼ 8.5 Hz, 1H), 9.58
2.1. Materials and measurements
(s, 1H, 3J ¼ 60 Hz, N-H), 13C NMR (75.45 MHz, CDCl3)
¼ 109.30 [C1,
d
All starting materials were purchased from Aldrich Chemical
Company. Solvents were used without further purification. The 4,6-
di-tert-butylaminophenol was prepared as previously reported
(Scheme 1) [34]. Melting points were carried out on an Electro-
thermal Mel-Temp apparatus and are uncorrected. Infrared spectra
were recorded using a Bruker Tensor 27 FT-IR spectrophotometer
equipped with a Pike Miracle™ ATR accessory with single reflection
ZnSe ATR crystal. High resolution mass spectra were acquired by
LC/MSD TOF on an Agilent Technologies instrument with APCI as
ionization source. 1H, 13C and 119Sn-NMR spectra were recorded in
CDCl3 and (CD3)2SO on a Bruker advance DPX 400. Chemical shifts
(ppm) are relative to (CH3)4Si for 1H and 13C and to (CH3)4Sn for
119Sn. The new preparation of tin compounds 1 and 2 was per-
formed on a microwave reactor Anton Paar Monowave 300 rated at
40 W and 20 bars designed for small scale microwave synthesis.
2J(13C-119Sn) ¼ 24 Hz], 114.91 (C14), 117.22 (C15), 118.83 (C13),
118.90 (C9), 123.83 (C7), 125.04 (C3), 127.47 [C5,
2J(13C-119Sn) ¼ 16 Hz],
128.72
(C8),
128.86
[C-m,
3J(13C-119Sn) ¼ 86 Hz], 129.58 (C6), 129.67 (C13), 130.47 [C-p,
2J(13C-119Sn) ¼ 16 Hz],
132.77
(C10),
134.25
[C-i,
1J(13Ce119Sn) ¼ 299 Hz], 136.57 [C-o, 2J(13C-119Sn) ¼ 54 Hz], 139.13
(C17), 139.37 (C4), 156.26 [C11, 2J(13C-119Sn) ¼ 21 Hz], 158.64 [C12,
2J(13C-119Sn) ¼ 28 Hz], 172.78 [C2, 2J(13C-119Sn) ¼ 25 Hz] ppm. 119Sn
NMR (100.7 MHz, C6D6)
d
¼ ꢁ324.82 ppm. HETCOR [dH
/dC]: 7.93/
136.57 (H-o/C-o), 7.38/128.86 (H-m/C-m), 7.37/130.47 (H-p/C-p),
7.24/125.04 (H3/C3), 7.72/129.58 (H6/C6), 7.41/114.91 (H14/C14),
7.13/118.83 (H13/C13), 7.34/123.83 (H7/C7), 7.52/128.72 (H8/C8),
9.58/156.26 (H11/C11), 7.89/139.37 (H4/C4), 7.23/129.67 (H16/C16),
6.76/117.22 (H15/C15), 8.02/118.90 (H9/C9). COSY [dH/dH]: 7.34/7.52
(H7/H8), 7.13/7.89 (H3/H4), 7.72/7.34(H6/H7), 6.76/7.24 (H15/H16),
7.38/7.93 (H-m/H-o), 7.41/6.76 (H14/H15) HRMS (APCI/TOF-Q)
Calcd. For C29H21NO2Sn [Mþ] 535.0600 u.m.a; Found 536.069977
u.m.a. (Error: 0.267854 ppm).
2.2. Synthesis of (E)-8, 8-8-diphenylbenzo[d] naphtho [1,2-h]
[1,3,6,2] dioxazastannonine (1)
A microwave vial containing a homogeneous mixture of 2-

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Scheme 1. Multicomponent microwave-assisted synthesis of organotin compounds 1 and 2.
2.3. Synthesis of (E)11, 13- di-ter-butyl, 8- diphenylbenzo [d]
naphtho [1,2-h][1,3,6,2] dioxazastannonine (2)
3. Methods for evaluation
3.1. Cyclic voltammetry
Preparation of 2 was accomplished following the same pro-
cedure of 1 from 2-hydroxynalthaldehyde 0.1 g (0.58 mmol) and
4,6-di-tert-butyl1-phenol-2eamine 0.1284 g (0.58 mmol), diphe-
nyltin oxide 0.1447 g (0.58 mmol), at 182 ꢀC for 15 min. The product
was obtained as a red solid in 91% yield (0.32 g). M.p. 219 ꢀC. IRʋmax
The electrochemical properties of both compounds were
investigated by cyclic voltammetry in a C3 cell Stand from Basi
coupled to a potentiostat/galvanostat ACM Gill AC. All of the ex-
periments were performed at room temperature in CH2Cl2 con-
taining Bu4NPF6 (0.1 M) as the supporting electrolyte, glassy carbon
as a working electrode (GCE), Pt wire electrode as the counter
electrode, Ag/AgCl electrode as the reference electrode and ferro-
cene/ferrocenium (FOC) as external reference (Eox ¼ 5.1 V,
Ered ¼ 3.8 V); value of ꢁ4.8 eV below the vacuum level. The ex-
periments were carried out under nitrogen atmosphere at a scan-
ning rate of 50 mV/s between ꢁ3.0 and þ 3.0 V. The molecular
orbital energies HOMO and LUMO were calculated from the first
oxidation (Eox) and reduction (Ered) potentials with the relation-
ship: EHOMO[LUMO] ¼ -exp(E(Ox[red]vs. Ag/AgCl))-4.80. In our
electrochemical experiments, ferrocene exhibited an formal po-
tential (Eꢀ) of 0.436 V. The electrochemical energy gap (Eg) was the
difference between LUMO-HOMO.
(ATR) N-H 1528, C-H 2964-2852, C]N 1610, C¼CArom 1600 cmꢁ1
.
UV/vis (CHCl3) labs/max (nm) [εmax *104 (Mꢁ1 cmꢁ1)]: 489 [1.48]
Fluorescence (CHCl3): l
fluor (nm): 594 1H NMR (400.13 MHz, CDCl3)
d
¼ 1.29 (s, H-19, 9H, CH3), 1.52 (s, H-18, 9H, CH3), 7.24 (t-d, H3, 1H),
7.27 (d, H15, 1H), 7.32 (t-d, H7, 1H), 7.34 (m, 4H, H-m), 7.35 (m, 2H,
H-p), 7.51 (d, H8, 1H), 7.69 (DMSO‑d6, H6, 1H), 7.86 (DMSO‑d6, H4,
1H), 7.93 (m, H-o, 4H), 7.96 (d, H9, 1H), 9.50 (S, 1H, N-H). 13C NMR
(75.45 MHz, CDCl3)
d
¼ 109.39 [C1/C15, 2J(13Ce119Sn) ¼ 30 Hz],
118.77 (C9), 123.63 (C13), 123.86 (C7), 125.08 (C3), 127.48 (C5),
128.62 (C8), 128.70 [C-m, J(13Ce119Sn) ¼ 84 Hz], 128.76 (C14),
129.64 (C6), 130.25 [C-p, J(13Ce119Sn) ¼ 34 Hz], 131.86 (C10),
134.30
[C-i,
J(13Ce119/117Sn) ¼ 253/209 Hz],
136.58
[C-o,
J(13Ce119Sn) ¼ 55 Hz], 138.57 (C4), 138.72 (C16), 139.80 (C17),
155.11 (C12), 156.38 (C11), 172.25 [C2, 2J(13Ce119Sn) ¼ 29 Hz]. 119Sn
NMR (100.7 MHz, C6D6)
d
¼ ꢁ324.82 ppm. HETCOR correlation [dH
/
3.2. Photophysical studies
dC]: 7.24/125.08 (H3/C3), 7.86/138.57 (H4/C4), 7.69/129.64 (H6/C6),
7.32/123.86 (H7/C7), 7.51/128.62 (H8/C8), 7.96/118.77 (H9/C9),
9.50/156.38 (H11/C11), 7.32/123.63 (H13/C13), 7.27/109.39 (H15/
C15), 1.52/31.03 (H18/C18), 1.29/31.08 (H19/C19), 7.93/136.6 (H-o/C-
The photophysical studies were carried out as previously re-
ported [23,33] in freshly prepared chloroform solutions: absorption
spectra were obtained on a Shimadzu 2401 PC spectrophotometer,
while fluorescence and excitation spectra with a Perkin-Elmer LS
50B spectrofluorimeter. The determination of the fluorescence
o), 7.35/128.64 (H-m/C-m), 7.34/130.18 (H-p/C-p) COSY [dH/dH]:
7.51/7.96 (H8/H9), 7.86/7.24 (H4/H3), 7.32/7.51 (H7/H8), 7.27/7.32
(H15/H13), 7.93/7.35 (H-o/H-m) HRMS (APCI/TOF-Q) Calcd. For
quantum yields in solution (
procedure [35] relative to quinine sulfate in H2SO4 0.1 M
¼ 0.54 at 310 nm), by exciting at 450 nm and under temperature
f) was realized following the literature
C
37H37NO2Sn 647.1800 [Mþ] 648.192291 u.m.a. (Error:
0.453697 ppm).
(f

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645
control of 25.0 0.5 ꢀC with a water circulating bath. The quantum
yield was averaged among the value obtained for three solutions
with absorbance at the excitation wavelength lower than 0.1.
Fluorescence spectra of powders were recorded as the solutions
using a powder sample holder and at ambient conditions. Fluo-
di-tert-butylaminophenol and diphenyltin oxide providing the
new 1 and 2 pentacoordinate tin complexes in high yields (85 and
91%) after common recrystallization technique (Scheme 1). Both
compounds were soluble in common organic solvents such as
chloroform, tetrahydrofuran, methanol.
f
rescence lifetimes (
t
) were obtained by time-correlated single
The 1H NMR spectra of compounds 1 and 2 exhibit one signal
between 9.43 and 9.58 ppm with coupling constants 3J(1H,119Sn) of
60 and 64 Hz respectively, which are indicative of the formation of
both, the new N]C bond and the N/Sn coordination. The 1H
signals of the H-ortho [3J(1H,119Sn) ¼ 54 and 55 Hz] from the Ph2Sn
moiety show a deshielding effect due to their intramolecular
interaction with their corresponding neighbor oxygen atoms, as
was corroborated by X-ray diffraction analysis (vide infra) (C(25)-
Ho$$$O(2) 1: 2.671(3) C(19)-Ho$$$O(2) 1: 3.071(3), Å, (C(25-
Ho$$$O(2) 2: 2.886 (3) Å, (C(19-Ho$$$O(2) 2:2657(3) Å. :: C-
H/O 1: 103.54ꢀ, 120.61 2: 11717ꢀ, 116.82 ꢀC(28)-Ho$$$O(1) 1: 2.491,
C(23)-Ho$$$O(1) 1: 2.997 (3) Å, C(29)-Ho$$$O(1) 2: 2.567 Å; C(23)-
Ho$$$O(1) 2: 2.729 Å; : C-H/O 1: 126.30ꢀ, 110.44ꢀ 2: 110.58ꢀ,
120.28ꢀ suggesting that complexes with phenyl susttuted Sn atoms
are stable in solution [40].
photon counting (TCSPC) with a Tempro Horiba instrument with a
455 nm nanoLED. A 0.01% suspension of Ludox AS40 (Aldrich) in
ultrapure water was used for the prompt signal. Calibration of the
equipment was realized with a POPOP [1,4-Bis(4-methyl-5-fenil-2-
oxazolyl)benzene] methanol solution (optical density <0.1 and
lifetime of 0.93 ns [36]) Data were fit in the software DAS6 available
in the equipment. Nanosecond transient absorption experiments
were realized by using laser flash photolysis technique with a
LP920 instrument (Edinburgh Ltd). The third harmonic (355 nm)
frequency of a flashlamp pumped Q-switched Nd:YAG laser (Con-
tinuum Minilite II, pulse width ca. 5 ns) was used for laser excita-
tion. CHCl3 was deoxygenated by bubbling nitrogen into the
solution by 30 min. Probe and fluorescence spectra have been
subtracted during measurements by the equipment software.
For the unambiguous assignment of the proton and carbon
resonant signals, it was essential to achieve HETCOR and COSY
correlation experiments (see ESI). The 119Sn NMR spectra of the
complex 1 and 2 in CDCl3 exhibit a single resonance signal char-
acteristic in the five-coordinated compounds in ꢁ320
and ꢁ324 ppm (Table 1), respectively. The pentacoordinated tin
atoms show a trigonal bipyramidal distorted geometry [41,42]. The
13C NMR spectra for both compounds, the imine carbon signals
(C11) appear in 154 and 156 ppm, respectively, shifted to higher
frequencies respect to the free ligands, due to the N/Sn coordi-
nation bond. The experimental value for C(18)-Sn-C(24) 1: 111.16
(2)ꢀ, 2: 121.82 (14)ꢀ suggests that the tin atom has a slightly dis-
torted trigonal bipyramid geometry. C-ipso, C-ortho, C-meta, and C-
para from Ph2Sn were unambiguously assigned by their corre-
sponding nJ(119Sn, 13C) values (See ESI).
3.3. Theoretical calculations
The geometry of the equilibrium conformer at ground state was
found at AM1 level and then further optimized through Density
Functional Theory (DFT) calculations at the restricted B3LYP level
with the relativistic effective core potential standard basis set
Lanl2dz [37] for Sn atom and 6-31G(d,p) for H,C,N and O atoms.
Frequency calculations were carried out to ensure the absence of
the imaginary frequencies and to confirm the minimized struc-
tures. The coordinates generated during the DFT optimization
processes were used as input for the electronic excited state cal-
culations and the first 30 singlet and triplet electronic excited states
were calculated in vacuum and with solvent (chloroform) by Time
Dependent Density Functional Theory (TDDFT) with the same
combined basis set at the restricted and unrestricted methods. The
state-specific nonequilibrium solvation approach was applied by
saving the solvent reaction field from the ground state. Solvent
effects in the ground and excited states were taken into account
with the polarizable continuum model (PCM). All theoretical
studies were realized with Gaussian09 program.
IR spectroscopic analysis showed stretching bands at 1608 to
1610 cmꢁ1, which belong to the C]N bond and at 1600 to
1624 cmꢁ1 assigned to the C]C double bond in both organotin
complexes; the n(C]N) absorption is shifted towards lower fre-
quencies with respect to the ligands (1628-1597 cm1) [6] because of
the coordination of the azomethine nitrogen with the diorganotin
moiety (C]N/Sn) [43]. The high resolution mass spectra of
organotin compounds confirmed the expected molecular ion for 1:
536.0665 uma and 2: 647.1800 uma; likewise the ion peak corre-
sponds to its molecular ion.
3.4. X-ray crystallography
The crystal data of 1 and 2 were recorded on an Enraf Nonius
Kappa-CCD
(
l
MoKa ¼ 0.71073 Å, graphite monochromator,
T ¼ 293 K-CCD rotating images scan mode). The crystal was
mounted on a Lindeman tube. Absorption correction was per-
formed using the SHELX-A [38] program. All reflection data sets
were corrected for Lorentz and polarization effects. The first
structure solution was obtained using the SHELXS-97 program and
then SHELXL-97 program was applied for refinement and output
data. All software manipulations were done under the WIN-GX
environment program set [39]. All heavier atoms were found by
Fourier map difference and refined anisotropically. Some hydrogen
atoms were found by Fourier map differences and refined iso-
tropically. The remaining hydrogen atoms were geometrically
modelled and are not refined.
4.2. Single crystal X-ray diffraction analysis
The structure of compounds 1 and 2, is represented by the
ellipsoid plot in Fig. 2. Crystal data were determined by single
crystal X-ray diffraction analysis (Table 2). Selected bond length and
angles are listed in Table 3. In all cases, the central tin atoms are five
coordinated, and five-ring-fused skeletons are formed with N/Sn
coordination bond with lengths around of 1: 2.585 (6), 2: 2.171(3)
Å. The tin atom adopts a distorted trigonal bipyramidal molecular
geometry, where the axial position is occupied by oxygen atom
(1:Sn-O1 1.958 (4), Sn-O2 1.927 (4), 2: Sn-O1 2.101 (2), Sn-O2 074
(2) Å) and the equatorial positions are occupied by nitrogen and
Cipso atoms (1: Sn-C(18) 2.392(7) (7), Sn-C(24) 1.887(4), 2: Sn-C(18)
4. Results and discussion
2.127(4), Sn-C(24) 2.125(4)).
Also, organotin complex 1 crystallizes with two chemically
similar but symmetry-independent molecules in the symmetry
unit, for 2 we can see intermolecular interaction as hydrogen bonds
in the ortho-protons of the aromatic ring with the oxygen atoms
unshared pairs of electrons of the phenolic group (See electronic
4.1. Synthesis and characterization
The multicomponent microwave-assisted synthesis was ach-
ieved in 15 min for 2-hydroxynaphtalehyde, aminophenol or 4,6-

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646
Table 1
Chemical shifts 1H,13C,119Sn and coupling constant [nJ(13C,119Sn)].
Comp.
1H
13C
C-1
119Sn
IR
H-11
CH-o
C-2
C-12
C-i
C-o
C-m
C-p
C¼N
1
2
9.58 [60]
9.43 [64]
7.96
7.86
109.22
109.39
172.82 [25]
172.25 [30]
158.66 [28]
155.12 [21]
134.29 [299/257]
134.31 [253/209]
136.58 [54]
136.59 [55]
128.87 [86]
128.70 [84]
130.48
130.26
ꢁ324.8
ꢁ324.8
1608
1610
Fig. 2. Molecular structures deduced by X-ray crystallography for: 1 (a) and 2 (b).
supporting information Figs. S15eS16). The two molecules show
multiple -stacked molecules in form of columns with a distance of
dp ¼ 3.704 and 4.101 Å for 1 and 2 respectively [44]. (Fig. 3).
Fig. 4a and c.
p
The experimental HOMO and LUMO values for both complexes
are very close each other of c.a. 5.9 eV and 3.7 eV, respectively,
suggesting that there is no marked difference in the electronic
properties of the complexes by changing the eH per tert-butyls.
While the calculated HOMO values are close to the experimental
one of ca. 5.2 eV, the LUMO energies are less negatives, being of
ca. ꢁ2.2 eV. This is understood as calculations were achieved based
on an equilibrium conformer. The HOMO and LUMO frontier orbital
distribution along the Sn-complexes are shown in Fig. 5c. In gen-
eral, it can be seen that there are no significant differences in both
complexes, both HOMO and LUMO orbitals are extendedly
distributed from the naphthalene through the imine-Sn-
coordination center up to the phenyl and tert-phenyls. It was also
observed that phenyls of the Sn ligands do not participate in the
orbital distribution, neither in the HOMO-1 nor in the HOMO-2,
likely because they are out of the plane.
ep
4.3. Electrochemical properties
Both complexes present three oxidation and three reduction
peaks, as can be seen in the representative voltammogram of 1
Fig. 4a. According to the electrostatic potential maps, which are
almost the same for both complexes, Fig. 4b, it could be identified
three high electronegative sites susceptible to redox process visu-
alized in red: on the eOH of the anthracene, on the (tert-butyl-
phenyl)-O- or (phenyl)-O- and on the C]N/Sn-O of the
phenylimine. A slight electronegative density sites, colored in yel-
low, could be also identified, on, the phenylimine or tert-
phenylimina, on the antracene and on the phenyl ligands of the
-Sn-. We recently reported that phenyls induce a slight inductive
effect to the Sn-complex instead for instances when ligands are
butyls [23]. The HOMO and LUMO orbital values were determined
experimentally from the first oxidation and reduction potential
peaks, at the maxima potential and compared with the calculated
values obtained from the optimized geometries; Table inserted in
4.4. Photophysical properties in solution
In general, the photophysical properties in chloroform of the tin
complexes synthesized in this work (Table 4 and Fig. 5) are similar

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647
Table 2
main band in the visible that was previously ascribed to metal-to-
ligand electronic transition (MLT), and less intense bands at around
350 nm due to intraligand electronic transitions (IT). The experi-
mental values are very close to the theoretical ones, Table 5. The
calculations reveal that the MLT bands corresponds to the HOMO-
/LUMO electronic transition and the IT to electronic transitions
from underlying orbitals to LUMO. The maximum shifts from
474 nm to 489 passing from 1 to 2, suggesting that the two tert-
butyls in the phenyl slightly increases the effective conjugation
length. This is in agreement with the electrochemical studies
(HOMO, LUMO) and the fact that the electronic delocalization ex-
tends from the naphthalene through the Sn center up to the
functionalized phenyl as shown in the electronic distribution
observed in the theoretical frontier orbitals. 2) The fluorescence
spectra exhibit a broad band at 560 and 594 nm, following the same
trend of the absorption maxima. 3) The corresponding excitation
spectra (ESI) match well the absorption ones and 4) the fluores-
cence decay (Fig. 5, inset) is monoexponential with fluorescence
Crystal data of compounds 1 and 2.
1
2
Empirical formula
Formula weight
Temperature, K
Wavelength
Crystal system
Space group
a, Å
b, Å
C29H21NH4Sn
534.19
293(2)
0.71073
Monoclinic
P21/c
15.6910(2)
18.789(3)
15.762(2)
90
89.97(10)
90
4647.00(11)
8
1.126
1.13
3.088 -33.237
ꢁ22 ꢂ h < 24,
ꢁ20 ꢂ k ꢂ 20,
- 20 ꢂ l < 19
38311
9590
0.1012
1.046
0.0585/0.1573
0.0693/0.1724
C37H37NO2Sn
646.36
293(2)
0.71073
Orthorhombic
Pbca
12.0196(6)
19.2549(7)
26.9805(13)
90
90
90
6244.3(5)
8
1.375
c, Å
a
b
g
V, Ǻ3
Zꢁ3
rcalc, mg.cm
m
, mmꢁ1
0.851
2
q
range for data
3.020e27.515
ꢁ15 ꢂ h < 14,
ꢁ21 ꢂ k ꢂ 24,
ꢁ34 ꢂ l < 35
28840
6750
0.0612
0.0827
0.0439/0.0956
0.0826/0.1127
Index ranges
lifetimes t, in the nanosecond region. 5) Both complexes present a
low fluorescence quantum yield, with a bit higher value for 1 cor-
responding to the lower Stokes' shift (Dn) value. Nevertheless the
Dn are not so large to ascribe this poor emission properties only to
internal conversion. According to the electrochemical and theo-
retical studies, the electronic distribution is distributed on the
entire molecule so that internal charge transfer is also discarded.
The theoretical calculation of excitations, however, gives a triplet
state with low energy, at around 573 nm (Table 5), associated with
the IL electronic transition and with larger oscillator strength of the
triplet state corresponding to the MLT electronic transition and that
is at higher energy.
No. of reflns collected
No. of indep reflns
[Rint
Goodness of fit
R1, wR2 (I > 2
R1, wR2 (All Data)
]
s(I))
Table 3
Selected bond distances (Ǻ) and angles (ꢀ) for 1 and 2.
1
2
This was confirmed by fash photolysis spectroscopy, in degassed
chloroform solutions. The absorption ns transient spectra (Fig. 6)
reveals the presence of the negative peak relative to the absorption
maxima at 472 (1) and 489 (2) together with positive bands at 374
(1)/379 (2) and at 558 (1)/567 (2), in agreement with the calculated
values for the triplet states. These results indicate that intersystem
crossing is a de-activation pathway, which contributes to the low
fluorescence quantum yield.
Sn(1)eO(1)/Sn(1)eO(2)
Sn(1)eC(18)/Sn(1)eC(24)
Sn(1)eN(1)/C(2)eO(1)
C(1)eC(11)/C(17)eO(2)
O(1)-Sn(1)-O(2)/N(1)Sn(1)C(18)
N(1)Sn(1)eC(24)
O(1)-Sn(1)-C(18)/O(1)-Sn(1)-C(24) 84.4(2)/113.1(2)
O(2)-Sn(1)-C(18)/O(2)-Sn(1)-C(24) 108.05(19)/90.1(2) 97.31(13)/96.48(12)
O(1)-Sn(1)-N(1)/O(2)Sn(1)N(1)
C(10)-C(1)-C(11)-N(1)
C(1)-C(11)-N(1)-C(12)
1.958(4)/1.927(4)
2.101(3)/2.074(2)
2.392 (7)/1.887(4) 2.127(4)/2.125(4)
2.586(6)/1.330 (8) 2.171(3)/1.318(4)
1.398(8)/1.570 (9) 1.434(5)/1.345(4)
148.2(2)/150.04(16) 157.15(10)/115.11(13)
98.8(2)
ꢁ123.05(12)
96.72(13)/91.32(12)
85.19(16)/69.36(18) 80.89(10)/76.85(10)
179.3(4)
175.7(4)
ꢁ177.4(4)
ꢁ168.2(3)
179.4(3)
4.5. Fluorescence properties in powders
C(11)-N(1)-C(12)-C(17)
ꢁ158.2(3)
The emission properties of 1, 2 were also investigated in pow-
ders and compared with those of the butyl homologues (Fig. 7). In
general, the four compounds present very weak emission that
could be detected only with the more opened slits (15 nm; as term
to those of other Sn complexes of naphthaldeyde Schiff bases,
previously studied [23]: 1) the UVeVis absorption spectra present a
Fig. 3. Intermolecular
p-
p
interactions of 1 (a) and 2 (b).

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A.M. Canton-Díaz et al. / Journal of Molecular Structure 1180 (2019) 642e650
648
Fig. 4. a) Three voltammograms cycles of complex 1 in CH2Cl2 at scan rate of 50 mV/s, (V vs Ag/AgCl) and GC as working electrode, the inserted table summarizes the electro-
chemical parameters determined for both compounds. b) Electrostatic potential map for both ligands. c) Calculated HOMO-LUMO and HOMO-2(1)-LUMO frontier molecular orbitals
for both complexes.
Table 4
Photophysical properties of compounds 1e2 in CHCl3.
Comp
1
2
labs, exp
348, 474
335, 489
ε
lem
560
594
Dn
3240
3615
F
1.25
0.16
t
1.17
0.31
Krx1010
0.01
0.005
Knrx109
0.84
3.22
1.32
1.48
of comparison the solutions were measured with slit of 2.5 nm).
Under the same experimental conditions, compounds 1 and 2 have
emission maximums almost in the same position of the butyl
conterparts: lemis ¼ 600 nm for the
H
complexes and
lemis ¼ 619 nm for the complexes with tert-butyls on the phenyl of
the Schiff base, as found in solution. This suggests that the mole-
cules self-assembly in solid state in similar way, independently on
the Sn ligand. Indeed, X ray studies in single crystals have evi-
denced
tained in the powders.
p p intermolecular interactions, which likely are main-
ꢁ
However, 1, 2 exhibit more intense fluorescence, contrary to
what found in solution where the fluorescence quantum yield were
Fig. 5. UVeVis (full symbols) and fluorescence (empty symbols) spectra of 1 (squares)
and 2 (cyrcles) in CHCl3. Inset: Fluorescence decays (symbols) and fitted curves (dotted
lines).
practically the same. Other authors reported
p aggregates emission

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A.M. Canton-Díaz et al. / Journal of Molecular Structure 1180 (2019) 642e650
649
Table 5
Calculated properties of compounds 1 and 2 in CHCl3.
Comp
1
labs, th [nm]
470.66
336.60
501.08
392.11
Oscillator strength f
H/L transitions
HOMO/LUMO (97%) HOMO-2-LUMO (91%)
ltr [nm]
405.35
573.19
399.57
572.54
Oscillator strength f
0.262
0.106
0.253
0.166
0.065
0.174
0.135
0.178
2
HOMO-LUMO (98%)
HOMO-1/LUMO (97%)
According to the electrochemical and theoretical studies, both
HOMO and LUMO frontier orbitals present the electronic delocal-
ization extended in the entire molecules, i.e. from the naphthalene
to the phenyl group through the imine-Sn center, but the phenyl
ligands are not involved, likely because are out of the plane. The
two compounds exhibit practically identical phophysical properties
of previously reported homologues with butyl; instead of phenyl as
ligand, with very low fluorescence quantum yield (f < 2%). Despite
that internal conversion is surely occurring as indicated by the
medium values of the Stoke's shift, nevertheless the low fluores-
cence quantum yields are mainly ascribed to intersystem crossing.
Indeed, the energy for the triplet excited state obtained by both,
experimentally by flash photolysis and theoretically, is lower than
the singlet excited state. Interestingly, despite to be still very low
and lower than solutions, the solid state emission is larger for the
phenyl substituted tin complexes studied here with respect to the
butyl conterparts. The investigation of this enhancement requires
to start with materials with larger fluorescence quantum yields at
least in solution, but it is an interesting issue for chemical optimi-
zation of the emission properties of tin complexes derived from
Schiff bases.
Fig. 6. Nanosecond transient absorption spectra of 1 (squares) and 2 (cyrcles) in CHCl3.
Acknowledgments
This research was financially supported by Consejo Nacional de
Ciencia y Tecnología (CONACYT, Mexico, grant: 240011). A. M. C. D.
wants also to thank CONACYT for the Ph. D. scholarship. Authors
thanks to Marco Leyva and Geiser Cuellar from CINVESTAV-CDMX
for the X-ray diffraction and HRMS determinations, respectively.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molstruc.2018.12.039.
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