Synthesis, characterization and UV–visible study of schiff base-acetylene functionalized organosilatrane receptor for the dual detection of Zn2+ and Co2+ ions

Article abstract of DOI:10.1016/j.ica.2021.120465

The present article describes the synthesis of Schiff base-acetylene functionalized organosilatranes (6a–6e) and their characterization by ¹H and ¹³C NMR spectroscopy and ESI-QTOF mass spectrometry. The UV–visible study of the organosilatrane 6a unveiled their high selectivity towards the recognition of Zn²⁺ and Co²⁺ ions without exhibiting any significant interference from other competitive metal ions. The calculated value of association constant with 6a for Zn²⁺ and Co²⁺ ions was 0.11 × 10⁶ M^?1 and 0.24 × 10⁶ M^?1 and the limit of detection was 0.28 × 10^?6 M and 0.82 × 10^?6 M respectively. Furthermore, DFT calculations were performed to get an insight into the interacting behaviour of sensor 6a towards Zn²⁺ and Co²⁺ ions.

Full text of DOI:10.1016/j.ica.2021.120465

Inorganica Chimica Acta 525 (2021) 120465
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journal homepage: www.elsevier.com/locate/ica
Research paper
Synthesis, characterization and UV–visible study of schiff base-acetylene
functionalized organosilatrane receptor for the dual detection of Zn2+ and
Co2+ ions
,
Gurjaspreet Singha *, Sushmaa, Priyankaa, Sumana, Dikshaa, Jashan Deep Kaura,
Anamika Sainia, Anita Devia, Pinky Satijab
a Department of Chemistry, Panjab University, Chandigarh 160014, India
b School of Advanced Chemical Sciences, Shoolini University, Solan, Himachal Pradesh 173212, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
The present article describes the synthesis of Schiff base-acetylene functionalized organosilatranes (6a–6e) and
their characterization by 1H and 13C NMR spectroscopy and ESI-QTOF mass spectrometry. The UV–visible study
of the organosilatrane 6a unveiled their high selectivity towards the recognition of Zn2+ and Co2+ ions without
exhibiting any significant interference from other competitive metal ions. The calculated value of association
constant with 6a for Zn2+ and Co2+ ions was 0.11 × 106 Mꢀ 1 and 0.24 × 106 Mꢀ 1 and the limit of detection was
0.28 × 10ꢀ 6 M and 0.82 × 10ꢀ 6 M respectively. Furthermore, DFT calculations were performed to get an insight
into the interacting behaviour of sensor 6a towards Zn2+ and Co2+ ions.
Schiff-base
Organosilatranes
Acetylene
UV–visible study
Zn2+ and Co2+ ions
1. Introduction
ion is one of the essential metal ion in animals, plants, soils and rocks. It
is the major component of vitamin B12 that helps in the iron meta-
In recent years, the development of chemosensors for the identifi-
cation of metal ions attains great attention in the research field because
metal ions performs significant roles in the functioning of living or-
ganisms and plants [1]. They have been extensively used in energy
storage devices, pharmaceuticals, paper, water, textiles and food in-
dustries [2]. However, the altered level of these metal ions is extremely
harmful to human health and the environment [3].
bolism, DNA synthesis, support formation of myelin and RBCs (Red
Blood Cells) [12,13]. The excess of Co2+ ions in the body causes several
health issues like cardiomyopathy, cardiac failure, asthma, thyroid
damage and diminished pulmonary function while its deficiency causes
pernicious anemia [14]. Apart from their biological imporance, it is also
used to accelerate the O2/H2 production in electrodes, sulphate-radical
induced destruction of contaminants and improve the electrochromic
properties of tungsten oxide nanowires [15–17]. So, the detection of
Zn2+ and Co2+ ions is necessary in every field. A number of methods
(atomic absorption/emission spectroscopy, electrochemical methods
and inductively coupled plasma) have been used for their detection
but optical methods are preferred over these sophisticated instru-
mentation techniques because of their simplicity, excellent selectivity
and high detection accuracy [18].
Among various metal ions, Zn2+ and Co2+ ions are necessary vital
elements for human beings. In humans, Zn2+ is the second most abun-
dant transition metal ion and it helps in several physiological processes
such as gene transcription, protein sequencing and regulation of met-
alloenzymes [4,5]. The surplus of Zn2+ ions causes several neurode-
generative diseases like Alzheimer’s, Parkinson’s, epilepsy,
hypoxia–ischemia, arteriosclerosis and damage the pancreas while its
deficiency causes stomach cramps, diabetes, skin diseases and infantile
diarrhea [6,7]. It also performs important physiological functions in
plants as it is the major component of different cofactors that regulate
the enzyme activity [8,9]. The Zn2+ metal ions are widely employed in
the industry in the protection process of steel and iron and for the
manufacturing of batteries [10,11]. On the other hand, the Co2+ metal
Organosilatranes are trigonal bipyramidal silicon molecules having
three five-membered rings and a transannular dative bond between ni-
trogen and a silicon atom. Generally, they are represented as. Nowadays,
they are attaining great attention because of their peculiar stereo-
electronic and molecular structure which is responsible for their unique
behaviour [19]. They have been popularly used in the field of sensing,
* Corresponding author at: Department of Chemistry and Centre of Advanced Studies, Panjab University, Chandigarh 160014, India.
E-mail address: gjpsingh@pu.ac.in (G. Singh).
https://doi.org/10.1016/j.ica.2021.120465
Received 23 April 2021; Received in revised form 18 May 2021; Accepted 18 May 2021
Available online 20 May 2021
0020-1693/© 2021 Elsevier B.V. All rights reserved.

G. Singh et al.
Inorganica Chimica Acta 525 (2021) 120465
Scheme 1. Schematic representation and reaction condition for the synthesis of Schiff base-acetylene functionalized organosilatranes (6a–6e): toluene, 60 ◦C, 6
h reflux.
nanoscience, biology and coating purposes [20–23]. Schiff base are
represented by R1R2C = NR’(R’∕=H) and show their widespread appli-
cations in various fields like nanoscience, biology, sensing, agriculture
and material chemistry [24–27]. Further, the Schiff base linked acety-
lene moiety enhances their sensing capability and biological utility
[28,29].
Triethanolamine (Aldrich), dry toluene (Merck) and N, N’-dime-
thylformamide (DMF) (Merck) were used as received. Inorganic chloride
salts of sodium, cobalt, barium, nickel, zinc, magnesium, silver, potas-
sium, rubidium, cadmium, calcium, aluminium and cesium were bought
from S.D. fine Chem. Ltd., India. Acetylene functionalized benzaldehyde
and γ-aminopropylorganosilatrane was synthesized by known proced-
ures from literature [30,20]. The Schlenk line was used to create N2
atmosphere for addition purposes. The 1H (400 MHz) and 13C (126 MHz)
NMR spectra were recorded on the BRUKER AVANCE II spectropho-
tometer using CDCl3 as an internal reference, and chemical shifts (δ)
were reported relative to tetramethylsilane. The coupling constant (J)
values are reported in Hz. The following abbreviations are used in NMR:
s = singlet, d = doublet, t = triplet, q = quartet, p = pentet, m =
multiplet. Mass spectral measurements were recorded with XEVO-G2-XS
QTOF mass spectrometer. The UV–visible spectral measurements were
carried out on the JASCO V-530 UV–visible spectrophotometer.
With an aspiration, we have synthesized the organosilatanes that
contain biologically and materially important Schiff base and acetylene
moiety into a single framework. The photophysical properties of the
organosilatrane 6a were examined by employing UV–visible spectros-
copy towards the identification of Zn2+ and Co2+ ions over other metal
ions.
2. Experimental section
2.1. Material and equipments
Propargyl bromide (80% in toluene) (Avra), substituted Hydrox-
ybenzaldehyde (ortho and para) (Avra), Potassium carbonate (Avra),
Potassium hydroxide (Avra), Aminopropyltrimethoxysilane (Aldrich),
2

G. Singh et al.
Inorganica Chimica Acta 525 (2021) 120465
Fig. 1. UV–visible spectra of compoound 6a in the presence of different metal ions in acetonitrile solution.
Fig. 2. The picture of compoound 6a upon addition of different metal ions in acetonitrile solution.
–
–
–
–
78.29 (C C-H), 75.77 (C C-H), 65.13 (CH = NCH2), 59.57–57.02
– –
2.2. Synthesis and characterization
(NCH2CH2OSi), 55.82 (OCH2), 51.11 (NCH2CH2OSi), 26.59 (CCH2C),
13.81 (SiCH2). ESI-TOF-MS (m/z) Calcd. for C19H26N2O4Si: 375.51 [M
+ H], Found 375.18.
2.2.1. General procedure for the synthesis of Schiff base-acetylene
functionalized organosilatanes (6a–6e)
To a flame-dried 50 mL two-neck round bottom flask, the acetylene
benzaldehyde (2a-2e) (1 equiv) and γ-aminopropylorganosilatrane (1
equiv) were added into 20 mL toluene under a dry N2 atmosphere. Then
the reaction mixture was refluxed for 6 h at 60 ◦C. After refluxing, the
solvent was removed under reduced pressure using a vacuum pump
resulting in semi-solid organosilatranes (6a-6c).
2.2.1.2. Synthesis of (Z)-3-(2,8,9-trioxa-5aza-1sila-bicyclo[3.3.3]unde-
can-1yl)-N-(3-methoxy ꢀ 4-(prop-2-ynyloxy) benzylidene)propan-1amine
(6b). The quantities used were as: 5 (0.10 g1, 0.43 mmol), 2b (0.08 g,
0.43 mmol). Yellow semi-solid, Yield: 92%. H NMR (500 MHz, Chlo-
roform-d) δ: 8.13 (s, 1H, CH = N), 7.41–6.99 (m, 3H, Ar-H), 4.76 (d, J =
2.4 Hz, 2H, OCH2), 3.89 (s, 3H, OCH3), 3.73 (d, J = 5.8 Hz, 6H,
NCH2CH2OSi), 3.57 – 3.53 (t, J = 7.2 Hz, 2H, CH = NCH2), 2.76 (t, J =
2.2.1.1. Synthesis of (Z)-3-(2,8,9-trioxa-5aza-1sila-bicyclo[3.3.3]unde-
can-1yl)-N-(4-(prop-2-ynyloxy) benzylidene)propan-1amine (6a). The
quantities used were as: 5 (0.10 g, 0.43 mmol), 2a (0.07 g, 0.43 mmol).
Yellow semi-solid, Yield: 96%. 1H NMR (500 MHz, Chloroform-d) δ:
8.15 (s, 1H, CH = N), 7.64 (d, J = 8.5 Hz, 2H, Ar-H), 6.94 (d, J = 8.8 Hz,
2H, Ar-H), 4.69 (d, J = 2.5 Hz, 2H, –OCH2), 3.72 (t, J = 5.8 Hz, 6H,
NCH2CH2OSi), 3.55 (t, J = 7.2 Hz, 2H, CH = NCH2), 2.76 (t, J = 5.8 Hz,
–
–
5.8 Hz, 6H, NCH2CH2OSi), 2.50 (t, J = 2.4 Hz, 1H, C C-H), 1.78–1.75
–
(p, J = 7.5 Hz, 2H, –CCH2C-), 0.41 (t, J = 8.6 Hz, 2H, -SiCH2-). 13C NMR
(126 MHz, Chloroform-d) δ: 159.85 (CH = N), 149.78–109.32 (Ar-C),
–
–
–
–
78.27 (C C-H), 76.16–76.04 (C C-H), 65.09 (CH = NCH2), 57.78
–
–
(OCH3), 56.64–56.04 (NCH2CH2OSi), 55.95 (OCH2), 51.09
(NCH2CH2OSi), 26.58–21.44 (CCH2C), 13.82 (SiCH2). ESI-TOF-MS (m/
z) Calcd. for C20H28N2O5Si: 405.53 [M + H], Found 405.18.
–
–
6H, NCH2CH2OSi), 2.52 (t, J = 2.4 Hz, 1H, C C-H), 1.78–1.74 (p, J =
–
7.5 Hz, 2H, –CCH2C-), 0.40 (t, J = 8.5 Hz, 2H, -SiCH2-). 13C NMR (126
MHz, Chloroform-d) δ: 159.60–159.11 (CH = N), 130.46–114.77 (Ar-C),
3

G. Singh et al.
Inorganica Chimica Acta 525 (2021) 120465
2.2.1.5. Synthesis of (Z)-3-(2,8,9-trioxa-5aza-1sila-bicyclo[3.3.3]unde-
can-1yl)-N-(3-methoxy ꢀ 2-(prop-2-ynyloxy) benzylidene)propan-1amine
(6e). The quantities used were as: 5 (0.10 g, 0.43 mmol), 2e (0.08 g,
0.43 mmol). Pale yellow semi-solid, Yield: 87%. 1H NMR (500 MHz,
Chloroform-d) δ: 8.68 (s, 1H, CH = N), 7.56–6.89 (m, 3H, Ar-H), 4.72 (d,
J = 2.4 Hz, 2H, OCH2), 3.83 (s, 3H, OCH3), 3.71 (t, J = 5.8 Hz, 6H,
NCH2CH2OSi), 2.74 (t, J = 5.8 Hz, 6H, NCH2CH2OSi), 2.57 (t, J = 4.5
–
–
Hz, 2H, CH = NCH2), 2.53 (t, J = 2.4 Hz, 1H, C C-H), 1.80–1.73 (m,
–
2H, –CCH2C-), 0.40 (t, J = 8.3 Hz, 2H, -SiCH2-). 13C NMR (126 MHz,
–
–
Chloroform-d) δ: 156.93 (CH = N), 152.53–113.62 (Ar-C), 78.99 (C C-
–
–
–
H), 76.29 (C C-H), 65.45 (CH = NCH2), 60.54–57.78 (NCH2CH2OSi),
–
55.82 (OCH2), 51.10 (NCH2CH2OSi), 26.56 (CCH2C), 13.92 (SiCH2).
ESI-TOF-MS (m/z) Calcd. for C20H28N2O5Si: 405.53 [M + H], Found
405.18.
2.3. Synthesis of 6a + Zn2+/Co2+complex
The equimolar amount of organosilatrane 6a and zinc chloride/co-
balt chloride was added into the round bottom flask comprising 20 mL
dry acetonitrile and then stirred for 4 h at 25 ◦C. The solvent was then
removed under vacuum, which provides the yellow-colored precipitate.
3. Results and discussion
3.1. Synthetic aspects and characterizations
The route utilized for the synthesis of acetylene functionalized
organosilatranes (6a–6e) is shown in Scheme 1. In the first step, the
terminal alkynes (2a-2e) were prepared by reacting the substituted
benzaldehyde with propargyl bromide in the presence of DMF solvent
and potassium carbonate base. The second step includes the synthesis of
γ-aminopropylorganosilatrane (5) by transesterification reaction be-
tween aminopropyltrimethoxysilane and triethanolamine by using dry
toluene as a solvent and potassium hydroxide pellet as a catalyst. In this
step, a dean stark apparatus was employed for the azeotropically
removal of methanol and byproducts. In the final step, the alkynes
(2a–2e) and γ-aminopropylorganosilatrane (5) were refluxed in dry
toluene which results into the joining of these two compounds through
Schiff-base linkage and formation of desired products (6a–6e). The para
derivatives gave the higher yield (>90%) as compared to the ortho de-
rivatives and among the para derivatives the 6a was obtained with
highest yield (96%). In 1H NMR spectra, the triplet at 3.71–3.73
(NCH2CH2OSi), 2.74–2.76 (NCH2CH2OSi) and 0.39–0.41 (SiCH2)
confirm the formation of organosilatranes. The sharp singlet in the range
Fig. 3. Bar graph representation of interference study of compounds 6a in the
presence of different competitive metal ions.
2.2.1.3. Synthesis of (Z)-3-(2,8,9-trioxa-5aza-1sila-bicyclo[3.3.3]unde-
can-1yl)-N-(3-ethoxy-4-(prop-2-ynyloxy)
benzylidene)propan-1amine
(6c). The quantities used were as: 5 (0.10 g, 0.43 mmol), 2c (0.09 g,
1
0.43 mmol). Yellow semi-solid, Yield: 91%. H NMR (500 MHz, Chlo-
roform-d) δ: 8.12 (s, 1H, CH = N), 7.39–7.01 (m, 3H, Ar-H), 4.76 (d, J =
2.4 Hz, 2H, OCH2), 4.12 (q, J = 7.0 Hz, 2H, OCH2CH3), 3.73 (t, J = 5.8
Hz, 6H, NCH2CH2OSi), 3.54 (t, J = 7.2 Hz, 2H, CH = NCH2), 2.76 (t, J =
–
–
5.8 Hz, 6H, NCH2CH2OSi), 2.49 (t, J = 2.4 Hz, 1H, C C-H), 1.79–1.73
–
(m, 2H, –CCH2C-), 1.43 (t, J = 7.0 Hz, 3H, OCH2CH3), 0.39 (t, J = 8.3
Hz, 2H, -SiCH2-). 13C NMR (126 MHz, Chloroform-d) δ: 159.91 (CH =
–
–
–
–
N), 149.28–110.85 (Ar-C), 78.53 (C C-H), 75.93 (C C-H), 65.13 (CH
–
–
= NCH2), 64.42 (OCH2CH3), 59.52–56.95 (NCH2CH2OSi), 56.84
(OCH2), 51.13 (NCH2CH2OSi), 26.60 (CCH2C), 14.81 (CH3), 13.83
(SiCH2). ESI-TOF-MS (m/z) Calcd. for C21H30N2O5Si: 419.56 [M + H],
Found 419.20.
of 8.15–8.68 and 2.49–2.53 confirms the presence of Schiff base protons
–
–
(HC = N) and alkyne protons (C C-H) respectively. The methoxy pro-
–
tons showed a triplet around 3.83–3.89 while the ethoxy protons
showed triplet and quartet at 1.43 and 4.12 respectively. In the 13C NMR
of all the organosilatranes (6a-6e), the highly deshielded imine carbon
appeared in the region of 156.10–159.91 while the highly shielded
methylene carbon (SiCH2) appeared around 13.81. The carbons of the
organosilatrane cage appeared in the range of 51.07–59.92. In the mass
spectra, the base peak for all the compounds received at [M + H]. The
obtained NMR (1H and 13C) and mass spectra match well with the
structure of synthesized organosilatranes (6a–6e).
2.2.1.4. Synthesis of (Z)-3-(2,8,9-trioxa-5aza-1sila-bicyclo[3.3.3]unde-
can-1yl)-N-(2-(prop-2-ynyloxy) benzylidene)propan-1amine (6d). The
quantities used were as: 5 (0.10 g, 0.43 mmol), 2d (0.07 g, 0.43 mmol).
Brown semi-solid, Yield: 86%. 1H NMR (500 MHz, Chloroform-d) δ: 8.64
(s, 1H, CH = N), 7.93–6.97 (m, 4H, Ar-H), 4.71 (d, J = 2.4 Hz, 2H,
OCH2), 3.71 (t, J = 5.8 Hz, 6H, NCH2CH2OSi), 2.74 (t, J = 5.8 Hz, 6H,
NCH2CH2OSi), 2.55 (t, J = 4.5 Hz, 2H, CH = NCH2), 2.52 (t, J = 2.4 Hz,
–
–
1H, C C-H), 1.80–1.73 (m, 2H, –CCH2C-), 0.41 (t, J = 8.3 Hz, 2H,
–
-SiCH2-). 13C NMR (126 MHz, Chloroform-d) δ: 156.67–156.10 (CH =
–
–
–
–
N), 131.13–112.76 (Ar-C), 78.44 (C C-H), 75.33 (C C-H), 65.57 (CH
–
–
3.2. UV–visible study
=
NCH2), 59.37–57.00 (NCH2CH2OSi), 56.39 (OCH2), 51.07
(NCH2CH2OSi), 26.68 (CCH2C), 13.86 (SiCH2). ESI-TOF-MS (m/z)
Calcd. for C19H26N2O4Si: 375.51 [M + H], Found 375.17.
UV–visible spectroscopy was employed to examine the photo-
physical properties of the compound 6a in the absence and presence of
various metal ions (Na+, Co2+, Ba2+, Ni2+, Zn2+, Mg2+, Ag+, K+, Rb2+
,
Cd2+, Ca2+, Al3+, Cs+,). Firstly, the solution of 6a (10ꢀ 6 M) and metal
4

G. Singh et al.
Inorganica Chimica Acta 525 (2021) 120465
Fig. 4. UV–visible study of compound 6a (a) titration profile with varying concentration of Zn2+ ions from 10 to 100 µL (b) BH-plot at λ = 260 nm (c) linear
calibration curve.
ions (10ꢀ 2 M) were prepared in acetonitrile and sufficient time was
given for their complete mixing. After that, 10 µL of each metal solution
was added one by one with the help of micropipette into the 3 mL of
10ꢀ 6 M 6a solution taken into quartz cuvette and their respective
UV–visible spectra were recorded. The 6a spectra alone showed three
interference experiment was performed. In this experiment, we
sequentially added the 100 µL of each competitive metal ion solution
into the solution of 6a (3 mL) and Zn2+/Co2+ ions (10 µL) and recorded
their UV–visible responses. Careful investigation of the spectra at λ =
312 nm showed no significant interference by the presence of other
metal ions indicating the highly sensitive nature of 6a towards the
identification of Zn2+ and Co2+ ions (Fig. 3).
absorption bands at 218 nm, 260 nm and 312 nm due to π-π* electronic
transitions. The spectra showed significant changes only in the presence
of Zn2+ and Co2+ ions while the other metal ions did not bring any
notable change in the spectra (Fig. 1). The selective recognition of Zn2+
and Co2+ ions may be due to the size of the cavity generated by silatrane
6a is similar to the size of these ions and both the ions fit into this cavity.
A visible color change in the solution of 6a was also noticed in the
presence of Co2+ ions (Fig. 2) and this change was also supported by the
appearance of a band at 462 nm, which lies in the visible region.
To test the sensitivity of 6a towards Zn2+ and Co2+ ions, an
For the UV–visible titration experiment, we dilute the solution of
Zn2+ and Co2+ ions up to 10-4 M and then 10–100 µL was added into the
6a solution. After each successive addition, the spectra were recorded.
The successsive addition of both these metal ions displays
hypochromic shift at 260 nm and hyperchromic shift at 312 nm, but
at 218 nm, the addition of Zn2+ ions exhibits the hypochromic shift
while the addition of Co2+ ions exhibits hyperchromic shift (Figs. 4(a)
and 5(a)). Also, no visible color change was noticed at this
5

G. Singh et al.
Inorganica Chimica Acta 525 (2021) 120465
Fig. 5. UV–visible study of compound 6a (a) titration profile with varying concentration of Co2+ ions from 10 to 100 µL (b) BH-plot at λ = 260 nm (c) linear
calibration curve.
concentration.
a high correlation coefficient value (R2 > 0.99), which concludes that
1:1 stoichiometry of the complex. The association constant, Ka =
intercept/slope value for Zn2+ and Co2+ ions were 0.11 × 106 Mꢀ 1 and
0.24 × 106 Mꢀ 1 respectively which indicates the binding strength of 6a
towards Co2+ ions was almost double as compared to Zn2+ ions.
Furthermore, the limit of detection, LOD = 3 × standard deviation/slope
was calculated by plotting the linear calibration curves (Figs. 4(c) and 5
(c)). The LOD values obtained for 6a towards Zn2+ and Co2+ ions were
0.28 × 10ꢀ 6 M and 0.82 × 10ꢀ 6 M respectively which is less than the
permissile value of Zn2+ (70 µM) and Co2+ (1.7 µM) ions in drinking
water allowed by WHO (World Health Organisation) and EPA (Envi-
ronmental Protection Agency) [6,13]. Table 1 shows that the synthe-
sized organosilatrane 6a is a better chemsensor for the detection of Zn2+
and Co2+ ions in comparison to the previously reported sensors because
of its high association constant and low detection limit value.
Further, the stoichiometry and binding ability of 6a with Zn2+ and
Co2+ ions were examined by using the Benesi and Hildebrand (B-H)
graphical method. In this methodology, by assuming 1: n stoichiometry
between compound 6a and metal ions, the equilibrium is expressed by
the following Eq. (1).
[
]
6a + Nm2+⇌ Analyte∙M2+
(1)
n
[
]
Analyte⋅M2+
ꢀ
)
M = Co2+, Zn2+
n
[
]
Assosiation constant, Ka =
[Analyte] M2+
n
A graph is plotted between [A-AO]ꢀ 1 vs. [Zn2+ n
]
and [Co2+ n
]
by
using the UV–visible titration data at λ = 260 nm (Figs. 4(b) and 5(b)).
Here [A-AO] denotes the change in absorbance intensity of compound 6a
upon the addition of metal ions. These graphs come out to be linear with
6

G. Singh et al.
Inorganica Chimica Acta 525 (2021) 120465
chain and somewhat on Schiff-base moiety. Hence, with the change in
metal ions, there is a change in electronic distribution and molecular
stability. It is noticed that the energy of both HOMO and LUMO de-
creases from 6a to 6a-Zn2+/Co2+ system and the resulting decrease in
energy gap (ΔE = ELUMO-EHOMO) from 0.1840 a.u. for 6a to 0.1810 a.u.
for 6a-Zn2+ ions, 0.0632 a.u. for the alpha of 6a-Co2+ ions and 0.0116 a.
u. for the beta of 6a-Co2+ ions indicating the higher stability of the
complex molecule. Further, the experimental evidence was taken into
account by collecting the 1H NMR of synthesized the 6a-Zn2+/Co2+
complex which showed a major shift in the organosilatrane protons from
3.72 ppm to 3.89 ppm (6a-Zn2+), 3.72 ppm to 3.65 ppm (6a-Co2+) and
Schiff base protons from 8.15 ppm to 9.85 ppm, 8.15 ppm to 10.24 ppm
indicating that the binding majorly occurs through these bonds (Fig. S16
and S17). Based on these, the proposed binding mechanism was shown
in Scheme 2.
Table 1
Comparative study of the analytical performance of newly synthesized sensor
(6a) with the previously reported sensors.
Sensors
Metal
Ka
LOD
(M)
References
ions
(Mꢀ 1
)
Thiophene-diocarbohydrazide
derivative
Zn2+
Zn2+
Co2+
Co2+
1.15 ×
0.15 ×
6
104
10ꢀ 6
Phenanthroline based sensor
1.30 ×
106
0.84 ×
10ꢀ 6
9
Hexabodipy functionalized
cyclotriphosphazenes
Amide based sensor
2.95 ×
0.84 ×
12
13
15
106
10ꢀ 6
8.90 ×
105
0.99 ×
10ꢀ 6
Quinoline and N’, N’
–dimethylethane-1,2-diamine
based sensor
Zn2+
Co2+
1.30 ×
0.01 ×
105
10ꢀ 6
4.0 ×
104
6.89 ×
10ꢀ 6
Schiff base-acetylene
Zn2+
Co2+
0.11 ×
0.28 ×
Present
work
functionalized organosilatrane
106
10ꢀ 6
4. Conclusions
0.24 ×
106
0.82 ×
10ꢀ 6
In this article, we have been successfully synthesized the acetylene
functionalized organosilatranes (6a–6e) and well-characterized them
with 1H and 13C NMR spectroscopy and mass spectrometry. The
UV–visible study of organosilatrane 6a manifests their high selectivity
and sensitivity towards the dual ion sensing of Zn2+ and Co2+ metal ions
with detection limit 0.82 × 10ꢀ 6 M and 0.28 × 10ꢀ 6 M respectively. We
expect that the synthesized chemosensor may offer opportunity for their
applications in the field of industry and living sciences.
3.3. Binding study by DFT and 1H NMR
To understand the binding interactions between receptor 6a and
metal ions (Zn2+ and Co2+) theoretical DFT (Density Functional Theory)
calculations were conducted on Gaussian 03 software. Firstly, the
structure of 6a was optimized in the absence and presence of Zn2+ and
Co2+ ions by employing the B3LYP functional level and 6-31G(d) basis
set for C, H, N, O atoms and LAN2DZ basis set for Zn2+ and Co2+ ions
respectively (Fig. 6). Then highest occupied molecular orbit (HOMO)
and lowest unoccupied molecular orbit (LUMO) was also created at the
same level of theory and their respective energy values were noted
(Fig. 7). Fig. 7 shows the electron density of HOMO and LUMO in 6a and
6a-Zn2+, mainly delocalized over Schiff-base, phenyl ring and slightly
on propyl chain. In the case of 6a-Co2+ complex, singly occupied mo-
lecular orbitals (SOMO) and singly unoccupied molecular orbitals
CRediT authorship contribution statement
Gurjaspreet Singh: Supervision, Project administration. Sushma:
Conceptualization, Investigation. Priyanka: Methodology. Suman:
Writing - original draft. Diksha: Writing - review & editing. Jashan
Deep Kaur: Resources. Anamika Saini: Data curation. Anita Devi:
Validation. Pinky Satija: Visualization.
(SUMO) were produced as
α-HOMO or β-HOMO and α-LUMO or
Declaration of Competing Interest
β-LUMO rather than simple HOMO-LUMO according to their respective
spin states. In 6a-Co2+ complex, the
α, β-HOMO electron density was
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
mainly distributed over silatranyl moiety and metal ions while the α,
β-LUMO electron density was mainly distributed over metal ion, propyl
Fig. 6. Optimized structure of 6a and its complex with Zn2+ and Co2+ ions.
7

G. Singh et al.
Inorganica Chimica Acta 525 (2021) 120465
Fig. 7. DFT computed HOMO-LUMO diagram of (a) organosilatrane 6a, (b) 6a + Zn2+, (c) alpha MO of 6a + Co2+, (d) beta MO of 6a + Co2+
.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.ica.2021.120465.
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Dr. Gurjaspreet Singh is a Professor in the Department of
Chemistry at Panjab University, Chandigarh, India. He has
[18] Y. Feng, G. Ying, Z. Yang, K. Shih, H. Li, D. Wu, Chemosphere Sulfate radical-
induced destruction of emerging contaminants using traces of cobalt ions as
catalysts, Chemosphere. 256 (2020), 127061, https://doi.org/10.1016/j.
chemosphere.2020.127061.
more than 22 years of experience in teaching as well as in
research. He is highly expertise in Organometallics, Bio-
Inorganic, Organotransition chemistry. His research work is
primarily based on the Chemistry of Organosilicon compounds
[19] K. Shen, K. Sheng, Z. Wang, J. Zheng, C. Xu, Cobalt ions doped tungsten oxide
nanowires achieved vertically aligned nanostructure with enhanced
electrochromic properties, Appl. Surf. Sci. 501 (2020), 144003, https://doi.org/
10.1016/j.apsusc.2019.144003.
focusing precisely on the design, synthesis, characterization
and properties of new organic compounds especially the bio-
logical activity of bonded metals. He had published more than
100 research papers in various internationally peer reviewed
[20] G. Singh, S. Rani, A. Arora, H. Sanchita, D.M. Duggal, Organic-inorganic nano-
hybrid decorated by copper (II) incarceration: A versatile catalytic assembly for the
swift reduction of aromatic nitro and dye compounds, Mol. Catal. 431 (2017)
15–26, https://doi.org/10.1016/j.mcat.2017.01.026.
journals. He had the privilege in introducing Click Silylation
term in Organosilicon chemistry and using this term he has
published more than 30 papers in Internationally peer reviewed
journals. Till date, 21 students had completed their doctorate degree under his supervi-
sion. Apart from Ph.D students, till date, he had also acted as a supervisor of the M.Sc
students (more than 80) for their dissertation work. He had successfully completed UGC,
DST SERB ans CSIR major research projects with 80 publications. A lot of his research work
has been presented in various conferences and in professional meetings. He is a Life
member of Chemical Research Society of India and of the Indian Science Congress Asso-
ciation. He has been reviewing the research articles for the various international peer
reviewed journals.
[21] G. Singh, A. Arora, P. Kalra, I.K. Maurya, C.E. Ruizc, M.A. Estebanc, S. Sinha,
K. Goyal, R. Sehgal, A strategic approach to the synthesis of ferrocene appended
chalcone linked triazole allied organosilatranes: Antibacterial, antifungal,
antiparasitic and antioxidant studies, Bioorg. Med. Chem. 27 (2019) 188–195,
https://doi.org/10.1016/j.bmc.2018.11.038.
[22] G. Singh, A. Sanchita, G. Singh, P. Sharma, P.S. Kalra, S. Diksha, V.V. Soni, Ester
appended organosilatranes: Paradigm for the detection of Cu2+, Pb2+ and Hg2+
9