Metal – organic hybrids of tin(IV) with tuneable band gap: Synthesis, spectral, single crystal X-ray structural, BVS and CSM analysis of morpholinium hexahalostannate(IV)

Article abstract of DOI:10.1016/j.molstruc.2020.128489

Self assembled organic - inorganic hybrid materials such as morpholinium hexachlorostannate(IV) (3) and morpholinium hexabromostannate(IV) (4) have been synthesised from morpholinium chloride (1) and morpholinium bromide (2) at room temperature. The hybrids were characterized by elemental analysis, IR, NMR, TG-DTA, DRS and PL spectroscopy and single crystal X-ray diffraction. IR and NMR spectral data of (3) and (4) show very little changes compared to their parent compounds (1) and (2). However, the = NH₂ ⁺ proton signal of the bromide hybrid (4), shows a relatively lower δ value due to extensive hydrogen bonding compared to its chloride analogue (3). Thermal analysis confirmed the proposed formulae of the compounds. Optical absorption measurements showed 3.80 and 2.60 eV as band gaps for (3) and (4) respectively at room temperature implying that the band gaps can be easily tuned by altering the halide ion. Single crystal X-ray structures of compounds (3) and (4) revealed extensive hydrogen bonded interactions between the morpholinium cation and the SnCl₆ ^2? and SnBr₆ ^2? anions in (3) and (4). In (4), two molecules of morpholinium bromide co-crystallized with the hybrid. BVS calculations performed on SnCl₆ ^2? and SnBr₆ ^2? anions (3) and (4) resulted in 4.10 and 4.13 respectively, which clearly established the formal oxidation state of tin in the compounds as 4+. CSM calculation on SnBr₆ ^2? yielded a value of 0.006 signifying a near perfect octahedral geometry of the anion.

Full text of DOI:10.1016/j.molstruc.2020.128489

Journal of Molecular Structure 1218 (2020) 128489
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Metal e organic hybrids of tin(IV) with tuneable band gap: Synthesis,
spectral, single crystal X-ray structural, BVS and CSM analysis of
morpholinium hexahalostannate(IV)
Kuppukkannu Ramalingam *, Thangarasu Rajaraman 1
Department of Chemistry, Annamalai University, Annamalainagar, 608 002, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Self assembled organic - inorganic hybrid materials such as morpholinium hexachlorostannate(IV) (3)
and morpholinium hexabromostannate(IV) (4) have been synthesised from morpholinium chloride (1)
and morpholinium bromide (2) at room temperature. The hybrids were characterized by elemental
analysis, IR, NMR, TG-DTA, DRS and PL spectroscopy and single crystal X-ray diffraction. IR and NMR
spectral data of (3) and (4) show very little changes compared to their parent compounds (1) and (2).
Received 24 March 2020
Received in revised form
3 May 2020
Accepted 19 May 2020
Available online 22 May 2020
However, the ¼ NHþ2 proton signal of the bromide hybrid (4), shows a relatively lower
d value due to
extensive hydrogen bonding compared to its chloride analogue (3). Thermal analysis confirmed the
proposed formulae of the compounds. Optical absorption measurements showed 3.80 and 2.60 eV as
band gaps for (3) and (4) respectively at room temperature implying that the band gaps can be easily
tuned by altering the halide ion. Single crystal X-ray structures of compounds (3) and (4) revealed
extensive hydrogen bonded interactions between the morpholinium cation and the SnCl26ꢀ and SnBr62ꢀ
anions in (3) and (4). In (4), two molecules of morpholinium bromide co-crystallized with the hybrid.
BVS calculations performed on SnCl26ꢀ and SnBr26ꢀ anions (3) and (4) resulted in 4.10 and 4.13 respec-
tively, which clearly established the formal oxidation state of tin in the compounds as 4þ. CSM calcu-
lation on SnBr26ꢀ yielded a value of 0.006 signifying a near perfect octahedral geometry of the anion.
© 2020 Published by Elsevier B.V.
Keywords:
Tin(IV)-Organic hybrid
Morpholinium
Crystal structure
BVS
CSM
Band gap
1. Introduction
in the unit cell and is held together by weak van der Waals forces.
Essentially, hybrid perovskites are complex materials, and the
Organic-inorganic hybrid materials have received considerable
attention in the recent past [1e5]. Hybrid materials demonstrate
interesting structural, electrical, optical and thermal properties
[6e10]. There has been a surge in the number of publications and
patents in this field of research due to the potential use of hybrid
perovskites as charge carriers in solar cells [11e16]. The hybrid
perovskites with the empirical formula ABX3, comprise a network
of corner-sharing BX6 octahedra, where B ¼ Pb2þ or Sn2þ, X ¼ Cl, Br,
I and A ¼ organic ammonium cation [17e19]. A hybrid ABX3
analogue of B ¼ Pb2þ ion, and A ¼ morpholinium cation with an
Eg ¼ 3.23 eV has been reported from our laboratory [20]. In certain
hybrid compounds, BX6 octahedron exists as well-separated entity
presence of various types of interactions and structural disorder
may play an important role in their properties [21]. Therefore,
modifications in the alkyl groups, metal atoms and halides, alter the
optical and electronic properties of the hybrids [22,23]. The most
workable replacements for Pbþ2 in the perovskite material are Sn
and Ge which are also group 14 metals. However, the stability of the
2þ oxidation state decreases when moving up the group 14 ele-
ments, thus the major problem with the use of these metals is their
chemical instability in the required oxidation state. Under ambient
conditions, the Sn2þ ion is oxidized to Sn4þ and therefore Sn4þ acts
as a p-type dopant within the materials in a self doping process
[24,25]. Sn4þ is an attractive dopant due to the resulting high
mobility, lower conduction band, increased electron density, and
comparable crystal structure [26]. One concern with lead contain-
ing hybrid perovskite is its toxicity, and as such attempts are on to
replace the lead in the perovskite crystal with a less toxic metal
[27,28]. In an effort to identify relatively less toxic tin based hybrid
organic-inorganic materials, the present work on synthesis,
* Corresponding author.
E-mail address: krauchem@yahoo.com (K. Ramalingam).
Currently working as Guest Lecturer, Department of Chemistry, Government
1
Arts and Science College, Manalmedu e 609 202, Mayiladuthurai, Tamilnadu, India.
https://doi.org/10.1016/j.molstruc.2020.128489
0022-2860/© 2020 Published by Elsevier B.V.

2
K. Ramalingam, T. Rajaraman / Journal of Molecular Structure 1218 (2020) 128489
spectral, single crystal X-ray structural, BVS and CSM analysis of
morpholinium hexachlorostannate(IV) and morpholinium hex-
abromostannate(IV) is reported. The iodide analogue could not be
stabilized at room temperature.
stirring for 2 h at 60 ꢁC. Colourless crystals formed from the solu-
tion after one day were filtered, washed with diethylether and
dried in air. Yield: 82%, dec.: 225-226ꢁC. C8H20O2N2SnCl6 (507.65):
cald.: C 18.93; H 3.97; N 5.51%; found: C 18.89; H 3.93; N 5.47%. IR
(KBr):
n
¼ 3415, 3150, 2939, 2856, 2772, 1635, 1560, 1451, 1376,
2. Experimental
1231, 1182, 1102, 1031, 914, 872, 587, 474, 432 cmꢀ1. 1H NMR ([D6]
DMSO, 400MHZ, ppm):
d
¼ 3.761e3.785 (3.669) (t, 4H, 2,6 -CH2,
2.1. Materials and instrumentation
J ¼ 4.4 Hz), 3.070 (2.860) (s, 4H, 3,5 -CH2), 9.263 (2H, br NH2). 13C
NMR ([D6] DMSO,100MHZ, ppm):
(46.61) (3,5-CH2).
d
¼ 63.17 (68.16) (2,6- CH2), 42.64
All solvents (Merck), reagents such as morpholine (Sigma
Aldrich, assay: 99%), tin metal shots (Merck, assay: 99.5%), hydro-
bromic acid (Merck 47%) were commercially available analytical
grade materials and were used without further purification.
Elemental analysis was carried out with Perkin Elmer 2100 Series II
instrument. FTIR spectra (as KBr pellets) were recorded with an
Avatar Nicolet 360 spectrophotometer over the range of 4000-
400 cmꢀ1. NMR spectra were recorded at room temperature using a
400 MHz Bruker AMX-400 spectrometer in DMSO‑d6. 13C NMR
spectra were obtained at 100.6 MHz at room temperature. Thermal
stability studies were carried out using NETZSCH STA 449 F3
JUPITER instrument under nitrogen atmosphere in the range of
room temperature to 1200 ꢁC at a heating rate of 20 K/min. DSC was
carried out with TA-Q20 Differential Scanning Calorimeter. Diffuse
reflectance spectra were recorded on a Varian 5000 UVeVis spec-
trophotometer from 200 to 2500 nm using barium sulphate as
standard with 100% reflectance. Photoluminescence spectra were
2.5. Preparation of morpholinium hexabromostannate(IV)
dimorpholiniumbromide; (C4H10NO)2SnBr6·(C4H10NO)2Br2 (4)
Stannic bromide, SnBr4 was prepared by dissolving tin shots
(0.12 g, 1 mM) in hydrobromic acid (5 mL). To the freshly prepared
stannic bromide solution, ethanolic solution of morpholinium
bromide (0.34 g, 2 mM) was added with constant stirring for 2 h at
60 ꢁC. Yellow crystals formed from the solution after one day were
filtered, washed with diethyl ether and dried in air. Yield: 88%, dec.:
207-208 ꢁC. C16H40N4O4SnBr8 (1110.49): cald. :C 17.31; H 3.63; N
5.05%; found: C 17.28; H 3.60; N 5.01%. IR (KBr):
2939, 2855, 2598, 1654, 1559, 1450, 1397, 1230, 1182, 1104, 910, 871,
587, 434 cmꢀ1 1H NMR ([D6] DMSO, 400MHZ, ppm):
n
¼ 3425, 3185,
.
d
¼ 3.764e3.788 (t, 4H, 2,6 -CH2, J ¼ 4.8Hz), 3.102 (s, 4H, 3,5 -CH2),
8.937 (2H, br NH2). 13C NMR ([D6] DMSO, 100MHZ, ppm):
d
¼ 63.14
recorded at room temperature on
spectrometer.
a FLUOROLOG-FL - 11
(2,6 -CH2), 42.72, (3,5 - CH2).
2.6. Single crystal X-ray crystallography studies
2.2. Preparation of morpholinium chloride; C4H10ONCl (1)
Single crystal X-ray intensity data were collected at ambient
temperature (295 K) using graphite monochromated Mo-K radi-
ation (
¼ 0.71073 Å) on a Bruker SMART 1000 CCD diffractometer.
Morpholinium chloride was prepared by passing hydrogen
chloride gas through morpholine (0.34 mL, 4 mM) in diethyl ether
(6 mL) and the resultant colourless solid was filtered through a
filter paper and dried over anhydrous calcium chloride. Yield: 82%,
m. p.: 174 ꢁC. C4H10ONCl (123.58): cald.: C 38.90; H 8.16; N 11.34%;
a
l
Data were corrected for absorption using SADABS [29]. The struc-
tures were solved by direct methods using SIR97 [30] and were
refined by SHELX2014 [31]. The non-hydrogen atoms were refined
anisotropically and all the hydrogen atoms were fixed geometri-
cally. Molecular plots were obtained with ORTEP-3 and Mercury
programs [32,33].
found: C 38.87; H 8.14; N 11.30%. IR (KBr):
2812, 2776, 2595, 1633, 1565, 1451, 1306, 1225, 1186, 1099, 1035,
869, 595, 435 cmꢀ1. 1H NMR ([D6] DMSO, 400MHZ, ppm):
¼ 3.779
n
¼ 3420, 3282, 2947,
d
(2.860) (d, 4H, 2,6 -CH2), 3.061(3.669) (s, 4H, 3,5 -CH2), 9.367 (2H,
br NH2). 13C NMR ([D6] DMSO, 100MHZ, ppm):
(2,6- CH2); 42.59 (46.61) (3,5-CH2).
d
¼ 63.14 (68.16)
3. Results and discussion
3.1. Infrared spectral studies
2.3. Preparation of morpholinium bromide; C4H10ONBr (2)
IR Spectra were recorded in the range of 4000-400 cmꢀ1 and all
the FTIR spectra including those of the morpholinium chloride (1)
and bromide (2) are included in the electronic supplementary
material. The spectra of morpholinium hexachlorostannate(IV) and
its bromide analogue are quite similar with small variations in the
band positions. The broad bands observed at 3415 and 3425 cmꢀ1
for compounds (3) and (4) respectively correspond to the stretching
vibrations of NH2 group. For the morpholinium chloride and its
bromide analogue, nN-H bands are observed at 3420 and 3418 cmꢀ1
respectively. The NH2 bending vibrations are observed at 1560 and
1559 cmꢀ1 in (3) and (4) respectively. Sharp bands at 1102 and
1104 cmꢀ1 are due to the stretching modes of cyclic C-O-C moiety
[34,35]. The transmittances at 872 and 871 cmꢀ1 are due to the
characteristic C-H rocking vibrations of the morpholine moiety.
Morpholinium bromide was prepared by adding hydrobromic
acid (2 mL) to morpholine (0.34 mL, 4 mM) in diethyl ether (6 mL)
and then heated at 60 ꢁC for 10 min. On cooling, morpholinium
bromide precipitated out of the solution which was washed with
diethyl ether for three times. Yield: 86%, m. p.: 205-206 ꢁC.
C4H10ONBr (168.03): cald.: C 28.59; H 6.00; N 8.34%; found: C
28.56; H 5.96; N 8.30%. IR (KBr):
2515, 1634, 1562, 1451, 1305, 1186, 1099, 869, 594, 426 cmꢀ1
NMR ([D6] DMSO, 400MHZ, ppm):
¼ 3.765e3.790 (2.860) (t, 4H,
n
¼ 3418, 3112, 2985, 2816, 2716,
.
1H
d
2,6 -CH2), 3.081e3.104(3.669) (t, 4H, 3,5 -CH2), 9.017 (2H, br NH2).
13C NMR ([D6] DMSO, 100MHZ, ppm):
42.67 (46.61) (3,5-CH2).
d
¼ 63.09 (68.16) (2,6- CH2),
2.4. Preparation of morpholinium hexachlorostannate(IV);
(C4H10NO)2SnCl6 (3)
3.2. NMR spectra
Stannic chloride, SnCl4 was prepared by dissolving tin shots
(0.12 g, 1 mM) in concentrated hydrochloric acid (5 mL). To the
freshly prepared stannic chloride solution, ethanolic solution of
morpholinium chloride (0.25 g, 2 mM) was added with constant
1H and 13C NMR spectra of morpholinium hexa-
chlorostannate(IV) and morpholinium hexabromostannate(IV) and
the corresponding morpholinium salts (1H and 13C NMR spectra of

K. Ramalingam, T. Rajaraman / Journal of Molecular Structure 1218 (2020) 128489
3
(1) and (2) are included in the supplementary data) were recorded
in DMSO- d6. The 1H and 13C NMR spectra of (3) are shown in Fig. 1
and the signals are listed in Table 1. It shows four protons of 3, 5
eCH2 protons adjacent to nitrogen observed as a triplet at
3.070 ppm and 2, 6 eCH2 protons adjacent to oxygen observed as a
triplet in the range, 3.761e3.785 ppm respectively. The ¼ NH2þ
proton signal is observed as a weak signal due to coupling with the
quardrupolar 14N nucleus (I ¼ 1) at 9.263 ppm, the integration
corresponding to two protons for (3). In the 13C NMR spectrum of
(3), 3, 5e and 2, 6 -C(H2) signals are observed at 42.64, 63.17 ppm
respectively. For compound (4), the spectra are shown in Fig. 2. In
the 1H NMR spectrum, 2, 6 eCH2 proton signals are observed at
3.764e3.788 ppm and 3, 5 eCH2 proton signals are observed at
3.102 ppm. The ¼ NHþ2 proton signal is observed at 8.937 ppm.
The ¼ NHþ2 proton signal of (3) is observed significantly at a higher
crystallizes in the monoclinic system, with centrosymmetric space
group, P21/c. ORTEP of the molecule is shown in Fig. 3. Sn-Cl bond
distances vary from 2.383(5) e 2.443(11) Å. Cl-Sn-Cl bond angles
vary from 87.52(6)ꢁ to 92.48(6)ꢁ and the chlorine atoms show
disorder. The compound shows extensive hydrogen bonded in-
teractions. However, large thermal parameters associated with the
chlorine atoms preclude any meaningful discussion on the aspect of
hydrogen bonding for (3). Morpholinium hexabromostannate(IV)
ꢀ
(4) crystallized in the triclinic system, with PI space group. Two
molecules of morpholinium bromide co-crystallized with the
hybrid material in the unit cell. Each tin atom is surrounded by six
bromine atoms in an octahedral geometry. ORTEP of the molecule is
shown in Fig. 4. Sn-Br bond distances range from 2.5741(7) Å to
2.5926(7) Å and Br-Sn-Br bond angles vary from 89.12(3)ꢁ to
90.88(3)ꢁ. The SnBr62ꢀ is relatively less distorted than the SnCl26ꢀ
anion. Compound (4) shows extensive hydrogen bonded in-
teractions as shown in Fig. 5 and the relevant parameters are given
in Table 4. ¼ NHþ2 protons of the compound show short hydrogen
bonded distances. H/O, H/Br interactions are responsible for the
stabilization of the compound in the solid state and are less than
the sum of van der Waals radii of the elements (2.80 and 3.10 Å),
indicating their role in the stabilization of the compound (4). In the
bromide analogue, SnBr26ꢀ anion is capped by two morpholinium
cations in the unit cell similar to that observed in (3). Hybrid of
morpholinium bromide with lead (II) showed a Pb/O non bonded
distance of 3.122(3) Å [20]. As a contrast, such a short contact was
not observed in (3) and (4). The diallylammonium hex-
abromostannate(IV) showed perfect octahedral geometry with Sn-
Br distances in the range of 2.5809(9) - 2.6132(10) Å [36]. Packing of
the molecules in the unit cell is compared in Fig. 6. In both (3) and
(4), SnX26ꢀ(X ¼ Cl, Br) anions occupy the apices of the unit cell and in
(3), two additional units of SnCl26ꢀ anions are also present inside the
cuboid.
d
compared to the bromide analogue due to intense hydrogen
bonded interactions. Synthesis, spectral, crystal structure and band
gap determination studies on diallylammonium hex-
abromostannate(IV) has been reported from our laboratory
recently [36]. A similar 1H chemical shift was observed due to
hydrogen
bonding
in
the
diallylammonium
hex-
abromostannate(IV) as well. In the 13C NMR spectrum of (4), 3, 5 e
and 2, 6 -C(H2) signals are observed at 42.72 and 63.14 ppm
respectively whereas the free amine signals are observed at 46.61
and 68.16 ppm [35]. Effectively, NMR spectral data of the two
morpholinium halides and their hybrids show differences in
chemical shifts within the experimental variations. However,
the ¼ NHþ2 proton signal of the bromide hybrid shows a relatively
lower
d value due to extensive hydrogen bonding.
3.3. Single crystal X-ray structure analysis
Single crystals of morpholinium hexachlorostannate(IV) and
morpholinium hexabromostannate(IV) suitable for X-ray analysis
were obtained by slow evaporation of ethanolic solutions of the
reaction mixtures at room temperature. Crystal data, data collec-
tion and refinement parameters and the results of analyses of two
compounds are presented in Table 2. Selected bond parameters are
listed in Table 3. Morpholinium hexachlorostannate(IV) (3)
3.4. Bond valence sum analysis (BVS)
Bond valence sum analysis is used to estimate the valence of the
central atom from the experimentally determined bond distances.
BVS calculations are carried out based on the bond distances
Fig. 1. 1H and 13C NMR spectra of morpholinium hexachlorostannate(IV).

4
K. Ramalingam, T. Rajaraman / Journal of Molecular Structure 1218 (2020) 128489
Table 1
1H and13C NMR chemical shifts (ppm).
C4H10ONCl (1)
C4H10ONBr (2)
C8H20O2N2SnCl6 (3)
C16H40O4N4SnBr8 (4)
1H NMR
2, 6 -CH2 (4H, t)
3, 5 -CH2 (4H, t)
¼ NHþ2 (2H, b)
13C NMR
3.779
3.061
9.367
3.778
3.091
9.017
3.761e3.785
3.070
9.263
3.764e3.788
3.102
8.937
2, 6 -C(H2)
3, 5 - C(H2)
63.14
42.59
63.09
42.67
63.17
42.64
63.14
42.72
Fig. 2. 1H and 13C NMR spectra of morpholinium hexabromostannate(IV).
Table 2
Crystal data, data collection and refinement parameters of (3) and (4).
Parameters
(3)
(4)
Empirical formula
Formula weight
Colour
C8H20Cl6N2O2Sn
507.65
Colourless
C16H40Br8N4O4Sn
1110.49
Yellow
Crystal dimension(mm)
Crystal system
Habit
Space group
a(Å)
0.15 ꢂ 0.10 ꢂ 0.10
0.20 ꢂ 0.15 ꢂ 0.10
Monoclinic
Triclinic
Block
P21/c
8.0967(7)
9.0589(6)
12.7149(9)
90
96.346(2)
90
Block
ꢀ
PI
8.3041(5)
10.0745(6)
11.2721(7)
70.671(4)
71.103(3)
73.314(3)
824.63(9)
1
b(Å)
c(Å)
a
b
g
(deg)
(deg)
(deg)
V(Å3)
926.89(12)
2
Z
T(K)
293(2)
1.819
2.241
293(2)
2.236
10.493
Dcalc (g cmꢀ3
)
m
(mmꢀ1
)
F(000)
range (deg)
Diffractometer
500
2.531e28.000
Bruker axs Kappa apex2 CCD
526
q
1.979e24.999
Bruker axs kappa apex2 CCD
Scan type
u
and
f
scan
u and f scan
Index range
ꢀ10 ꢃ h ꢃ 10,-11 ꢃ k ꢃ 11,-16 ꢃ l ꢃ 16
ꢀ9 ꢃ h ꢃ 9, ꢀ11 ꢃ k ꢃ 11, ꢀ13 ꢃ l ꢃ 13
Reflection collected
Unique reflection
Observed reflections [I > 2
Weighting scheme
11192
2236
1761
23822
2895
2220
s
(I)]
w ¼ 1/[
s
2 (Fo2)þ(0.0162 P)2 þ1.5838P] where P¼(Fo2 þ2F2c)/3
W ¼ 1/[ s2 (Fo2)þ(0.0308p)2 þ4.1805p] where p¼(Fo2 þ2F2c)/3
Number of Parameters refined
117
152
Final R, RW(observed data)
0.029, 0.059
0.0393, 0.0855
obtained from the single crystal X-ray structural analysis. There-
fore, BVS studies indirectly prove the correctness of the crystal
structures determined [37]. The method depends on the Rij value
for an i-j bond which is primarily ionic [38e40]. In a compound, the
oxidation state of a central atom ‘i’ bonded to ‘j’ match up to the
bond valence, V and the total valence of the central atom is its
oxidation state, V ¼ Svij ¼ exp[(Ro - Rij)/b] where Ro is used as
reported for a large number of ionic compounds [41] and Rij is the
experimentally determined bond distance. The constant b can be
assumed to be 0.37 [42]. Bond valence sums of (3) and (4) are 4.10

K. Ramalingam, T. Rajaraman / Journal of Molecular Structure 1218 (2020) 128489
5
Table 3
Selected bond distances (Å) and bond angles (ꢁ) of (3) and (4).
(3)
(4)
bond distances
Sn-Cl1
Sn-Cl2
Sn-Cl3
C1-N1
C1-C2
C2-O1
C3-O1
2.425 (3)
Sn1-Br1
Sn1-Br2
Sn1-Br2
C1-N2
C1-C2
C2-O2
2.5780(9)
2.5926(7)
2.5741(7)
1.465(11)
1.485(11)
1.398(10)
1.391(11)
2.413(1)
2.413(1)
1.487 (5)
1.499 (6)
1.404 (5)
1.411 (5)
C3-O2
Angles
Cl1eSn1eCl2
Cl2eSn1eCl3
Cl1eSn1eCl3
N1eC1eC2
N2eC4eC3
O1eC2eC1
O1eC3eC4
90.42 (7)
91.60 (7)
92.48 (6)
108.7 (3)
109.7 (3)
112.4 (3)
111.8 (3)
Br1-Sn1-Br2
Br2-Sn1-Br3
Br1-Sn1-Br3
N2-C1-C2
N2-C4-C3
O1-C5-C6
89.12(3)
90.88(3)
90.44(3)
109.0(7)
108.5(7)
110.6(7)
111.6(7)
O1-C2-C1
Symmetry transformations used to generate equivalent atoms: (3) ꢀxþ2, ꢀy, ꢀzþ2; (4) 1 -xþ2,-y,-z.
þ
Fig. 3. ORTEP of the capped unit of 2[C8H20N2 O2] SnCl26ꢀ (3) (Thermal ellipsoids are with 50% probability).
þ
Fig. 4. ORTEP of 2[C4H10N O] SnBr26ꢀ (4) (Thermal ellipsoids are with 50% probability) Two molecules of co crystallized [C4H10N O] Br are not included.
and 4.13 respectively which established the formal oxidation state
of tin as 4þ unequivocally as shown in Table 5.
assessed by symmetry measures. CSM methodology has been
successful in such quantification in dealing with transition metal
complexes and metal oxides. In the case of hexacoordinated atom,
the idyllic geometries are ideal octahedron (iOh) or ideal trigonal
prism (itp). In a scale of 0 (iOh) to 100 (itp), the geometrical devi-
ation of an octahedral molecule can be calculated. In this investi-
gation, SnCl26ꢀ anion showed disorder with respect to three chloride
ions and therefore CSM of the ion could not be computed. CSM
calculation on SnBr26ꢀ anion depicted in Fig. 7 showed a CSM value
of 0.006, clearly indicating the near perfect octahedral geometry
associated with it.
3.5. Continuous symmetry measure (CSM)
Continuous symmetry measure (CSM) computes the distance of
a given structure from the desired ideal symmetry or from a
reference shape [43e46]. Various geometries associated with
molecules have been described as ‘slightly distorted’ or ‘severely
distorted’ with reference to a polyhedron. Extent of distortion of a
particular molecular structure from an ideal polyhedron can be

6
K. Ramalingam, T. Rajaraman / Journal of Molecular Structure 1218 (2020) 128489
Fig. 5. Hydrogen bonded interactions of the bromine atoms in (4) and the H atoms identified in the adjacent morpholium cations.
3.6. Thermal analysis
Table 4
Hydrogen bonded distances (Å), bond angles (ꢁ) in (4).
Thermal stability is an important quality of the application of
organic-inorganic hybrid perovskites. Fig. 8(a) shows thermogra-
vimetric and differential thermal analysis of morpholinium hexa-
DdH
H$$$A
D$$$A
DdH$$$A
C(1)-H(1A)...Br(3)
C(1)-H(1B)/Br(1)
C(2)-H(2A)...Br2)
C(3)-H(3B)/Br(4)
C(4)-H(4B)/Br(1)
C(6)-H(6A)...Br(4)
C(6)-H(6B)/O(2)
C(7)-H(7A)...Br(2)
C(8)-H(8A)...O(1)
N(1)-H(1C)-...Br(2)
N(1)-H(1D)...Br(3)
N(1)-H(1D)...Br(4)
N(2)-H(2C)/Br(4)
N(2)-H(2D)...Br(4)
0.97
0.97
0.97
0.97
0.97
0.97
0.97
0.97
0.97
0.97
0.97
0.97
0.97
0.97
2.92
2.95
2.86
3.12
3.09
3.12
2.43
3.13
2.50
2.53
2.99
2.35
2.31
2.42
3.653(8)
3.884(9)
3.672(8)
3.868(9)
3.966(9)
3.742(8)
3.363(10)
3.794(8)
3.293(10)
3.404(6)
3.466(6)
3.249(6)
3.254(6)
3.299(7)
132.7
161.9
141.8
135.2
151.6
123.3
161.1
127.4
138.8
149.5
111.4
153.5
165.2
150.8
chlorostannate(IV)
and
8(b)
shows
morpholinium
hexabromostannate(IV). Thermogravimetric analysis was carried
out in an atmosphere of nitrogen at a heating rate of 20 K/min.
Morpholinium hexchlorostannate(IV) shows a mass loss of 10.4%
corresponding to the loss of NH4Cl (calcd.: 10.5%) before 100 ꢁC
associated with an endothermic signal in the DTA. In the second
step of thermal decomposition between 300 and 380 ꢁC, a total
mass of 66.0% comprising of all the organic components along with
the five chlorine atoms (cald.: 66.1%) are lost in an exothermic
process. Above 380 ꢁC, free tin metal corresponding to 23.3%
(calcd.: 23.4%) evaporated continuously leaving no significant res-
idue in an exothermic process.
Symmetry transformations used to generate equivalent atoms: (4)
i ꢀxþ2, ꢀy, ꢀzþ2; ii x, ꢀyþ1/2, zþ1/2; iii x, ꢀyꢀ1/2, zþ1/2; iv ꢀxþ3, yþ1/2, ꢀzþ5/
2; v ꢀxþ2, yþ1/2, ꢀzþ5/2.
Morpholinium hexabromostannate(IV) shows its first thermal
decomposition above 280 ꢁC, as an exothermic process corre-
sponding to the loss of 2 mol of co-crystallized morpholinium
Fig. 6. Unit cell packing of (3) and (4) along ‘a’ axis.
Table 5
Bond valence sums of (3) and (4).
Compound
C N
Ro (Snþ4-X)
Bond distances (Rij)
V ¼ S vij
(3)
6
2.276
Sn1-Cl1
2.425
Sn1-Cli1
Sn1-Cl2
2.4133
Sn1-Br2
2.5926
Sn1-Cli2
2.4133
Sn1-Bri2
2.5926
Sn1-Cl3
2.4123
Sn1-Br3
2.5741
Sn1-Cli3
2.4127
Sn1-Bri3
2.5741
4.10
2.425
(4)
6
2.444
Sn1-Br1
2.5780
Sn1-Bri1
2.5780
4.13

K. Ramalingam, T. Rajaraman / Journal of Molecular Structure 1218 (2020) 128489
7
28.6% (calcd.: 28.8%):
Such a loss of bromine atoms from SnBr4 at elevated tempera-
tures has been documented [47,48]. In the last stage of decompo-
sition above 600 ꢁC, tin metal evaporates continuously in an
exothermic process. Thermal analysis of the two hybrids clearly
supports their proposed formulae and establishes the fact that the
thermal stability of the chloride compound (3) is less than its
bromide analogue (4).
3.7. DSC analysis
DSC traces of (3) and (4) are shown in Fig. 9. In morpholinium
hexachlorostannate(IV) during the heating process up to 160 ꢁC, no
heat change was observed. On cooling, an exothermic process is
observed at 145 ꢁC indicating a phase change. In the case of mor-
pholinium hexabromostannate(IV), an endothermic peak was
observed at 167 ꢁC on heating while an exothermic peak appeared
on cooling at 165 ꢁC. The observed heat changes in (3) and (4) are
characteristic of the chloro- and bromo-analogues of the hybrid.
Fig. 7. Near perfect octahedral geometry of SnBr26ꢀ anion with a CSM value of 0.006.
3.8. Diffuse reflectance spectroscopy
bromide accounting for a mass loss of 30.1% (cald.: 30.3%) and in the
following step another set of morpholinium bromide molecules
were lost accounting for 60.4% (calcd.: 60.6%) of total loss of mass
within 340 ꢁC. The above two stages show a gradation in the slope
of the mass loss indicating the stage wise loss. In the next stage,
with in the temperature range of 340e600 ꢁC, the following reac-
tion takes place corresponding to the loss of four bromine atoms
Diffuse reflectance spectra of (3) and (4) are shown in Fig. 10.
The reflectance increased above 300 nm for (3). Similarly for (4),
the reflectance increased above 450 nm. The absorptions below
450 nm are of organic origin in the hybrids. The band gap was
determined to be 3.80 eV and 2.60 eV for (3) and (4) using a plot of
(F(R) hv)2 versus (hv) as shown in Fig. 11 (a) and (b) respectively.
Fig. 8. Thermal analyses of compound (a) morpholinium hexachlorostannate(IV) (3) and (b) morpholinium hexabromostannate(IV) (4).
Fig. 9. Differential scanning calorimetric analysis of (a) morpholinium hexachlorostannate(IV) and (b) morpholinium hexabromostannate(IV).

8
K. Ramalingam, T. Rajaraman / Journal of Molecular Structure 1218 (2020) 128489
Fig. 10. Diffuse reflectance spectra of (a) morpholinium hexachlorostannate(IV) and (b) morpholinium hexabromostannate(IV).
Fig. 11. Determination of band gap energies of (a) morpholinium hexachlorostannate(IV) and (b) morpholinium hexabromostannate(IV).
Fig. 12. PL spectra of (a) morpholinium hexachlorostannate(IV) and (b) morpholinium hexabromostannate(IV).
The bromo hybrids show lower band gap compared to chloro-
hybrids as reported earlier [15,49]. Interestingly, the dia-
llylammonium hexabromostannate(IV) reported earlier from our
laboratory showed a band gap of 2.70 eV [36]. Therefore, the band
gaps associated with these hybrids can be easily tuned by altering
the halide ion.
emission bands as shown in Fig. 12. The maxima appeared at 490
and 495 nm for (3) and (4) respectively. Relatively low FWHM
associated with the emission bands show the good quality of epi-
layers in the semiconductors. In addition, the proximity of emission
maxima of the two compounds (3) and (4) show the identical na-
ture of photoluminescence process responsible for the emission
[50].
3.9. P L spectra
4. Conclusions
On excitation of morpholinium hexachlorostannate(IV) (3) and
morpholinium hexabromostannate(IV) (4) with 326 nm and
479 nm radiations respectively, the compounds exhibited narrow
Metal
e
organic hybrids of morpholinium hexa-
chlorostannate(IV) and its bromide analogues have been

K. Ramalingam, T. Rajaraman / Journal of Molecular Structure 1218 (2020) 128489
9
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synthesised and characterized by spectroscopic and single crystal
X-ray diffraction techniques. IR spectral analysis of the compounds
show that different vibrational bands of the organic moiety show
very little change on hybrid formation with tin. 1H NMR spectrum
of morpholinium hexabromostannate(IV) shows significant
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X-ray structural analysis showed the octahedral nature of the
hexahalo dianions. Morpholinium cations capped the central hex-
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teractions in both the hybrids stabilize the solids and contribute to
the effective band gap. BVS established the formal oxidation state of
tin as 4þ. CSM analysis of the SnBr26ꢀ indicated its near perfect
octahedral geometry.
5
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