A stannatrane-like [4.4.4.01,6] heterotricyclic stannate anion possessing rhodanide antennae: A chromoreactand for Fe3+, Cu2+ and Co2+ ions

Article abstract of DOI:10.1016/j.ica.2017.04.017

Exploration of an aminotrisphenol ligand (H₃L) to synthesise heterocyclic tin derivatives led to the unexpected formation of a stannatrane-like [4.4.4.0^1,6] heterotricyclic stannate anion [LSnCl₂]^? (1). Further, its metathesis reaction with ammonium thiocyanate provided access to its thiocyanate derivative [LSn(NCS)₂]^? (2), which proved to be a chromophoric probe. The characterization methods applied, such as elemental analysis, various spectroscopic methods (FT-IR, NMR (¹H, ¹³C, ¹¹⁹Sn), UV–Vis, Mass) and X-ray crystallography (for 2) are in accord with the formation of these ionic compounds. The rhodanide functionalized stannatrane-like compound (2) was isolated as triethylammonium salt with distorted octahedral environment around Sn generated by the tripodal O₃N donor system and the N atoms of two cis configured thiocyanates. This particular organization of rhodanides imparted chelator and chromophoric character to 2 and enhanced its colorimetric and optical response towards some metal ions (such as Fe³⁺, Cu²⁺ and Co²⁺ ions) as compared to the free tripodal ligand (H₃L) and ammonium thiocyanate. The role of 2 as a bidentate ligand for the chelation of metal ions may be responsible for the enhanced stability of metal complexes as well as the observed spectral behaviour.

Full text of DOI:10.1016/j.ica.2017.04.017

Accepted Manuscript
Research paper
A stannatrane-like [4.4.4.01,6] heterotricyclic stannate anion possessing rhoda-
nide antennae: A chromoreactand for Fe3+, Cu2+ and Co2+ ions
Neha Srivastav, Raghubir Singh, Varinder Kaur, Jörg Wagler, Edwin Kroke
PII:
S0020-1693(17)30248-7
http://dx.doi.org/10.1016/j.ica.2017.04.017
ICA 17522
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
20 February 2017
7 April 2017
10 April 2017
Please cite this article as: N. Srivastav, R. Singh, V. Kaur, J. Wagler, E. Kroke, A stannatrane-like [4.4.4.01,6]
heterotricyclic stannate anion possessing rhodanide antennae: A chromoreactand for Fe3+, Cu2+ and Co2+ ions,
Inorganica Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.04.017
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A stannatrane-like [4.4.4.01,6] heterotricyclic stannate anion possessing rhodanide
antennae: A chromoreactand for Fe3+, Cu2+ and Co2+ ions
Neha Srivastava, Raghubir Singhb*, Varinder Kaura*, Jörg Waglerc, Edwin Krokec
aDepartment of chemistry, Panjab University, Sector 14, Chandigarh – 160014, India
E-mail: var_ka04@yahoo.co.in
bDepartment of chemistry, DAV College, Sector 10, Chandigarh – 160011, India
E-mail: raghu_chem2006@yahoo.com
cInstitut für Anorganische Chemie, Technische Universität Bergakademie, Freiberg – 09596
Freiberg, Germany
Abstract
Exploration of an aminotrisphenol ligand (H3L) to synthesise heterocyclic tin derivatives
led to the unexpected formation of a stannatrane-like [4.4.4.01,6] heterotricyclic stannate
anion [LSnCl2]¯ (1). Further, its metathesis reaction with ammonium thiocyanate provided
access to its thiocyanate derivative [LSn(NCS)2]¯ (2), which proved to be a chromophoric
probe. The characterization methods applied, such as elemental analysis, various
spectroscopic methods (FT-IR, NMR (1H, 13C, 119Sn), UV-Vis, Mass) and X-ray
crystallography (for 2) are in accord with the formation of these ionic compounds. The
rhodanide functionalized stannatrane-like compound (2) was isolated as triethylammonium
salt with distorted octahedral environment around Sn generated by the tripodal O3N donor
system and the N atoms of two cis configured thiocyanates. This particular organization of
rhodanides imparted chelator and chromophoric character to 2 and enhanced its colorimetric
and optical response towards some metal ions (such as Fe3+, Cu2+ and Co2+ ions) as compared
to the free tripodal ligand (H3L) and ammonium thiocyanate. The role of 2 as a bidentate
ligand for the chelation of metal ions may be responsible for the enhanced stability of metal
complexes as well as the observed spectral behavior.
Keywords: Mannich base, aminotrisphenol, pseudo-stannatrane, thiocyanate, chemosensor,
Fe3+, Cu2+, Co2+.
1

1. Introduction
Fused heterotricyclic metalloorganics (termed as ‘atranes’) and their derivatives have
gained interest due to their diverse reactivities and structural properties, especially when
associated with ligands of varied steric and electronic factors [1-5]. In the past, fused
heterotricyclic metalloorganics with symmetric [3.3.3.01,5] podand systems have been studied
extensively [6-8] due to their distinct structural features, stability and wide spread
applications in catalysis, sol-gel processes, cross-coupling and biological systems [9-12]. In
these compounds, three heterocyclic rings form a ‘propeller’ like structure and the bridgehead
positions are occupied by a central atom (transition metal or main group metal/metalloid) and
nitrogen. Aminoalkanol and aminophenol derived tin compounds of this class are commonly
termed as ‘stannatranes’ or ‘pseudostannatranes’ depending upon the tripodal ligating
systems [13-15]. These are gaining immense interest due to their structural diversity which
includes mono-, di-, tri-, tetra- (ladder like) and penta-nuclear oxo-clusters [13-18].
Generally, heterotricyclic organotin compounds are likely to associate to form oligomeric
units in solid state due to the presence of lone pair donor atoms in their tricyclic ligating
system and the unsaturated tin coordination sphere [14-16]. Generally speaking, the
formation of oligomeric clusters in these compounds is a consequence of low steric
protection induced by flexible arms N(CH2)nO present in the tripodal ligating environment.
Only those heterotricyclic tin compounds are monomeric with distorted trigonal bipyramidal
units, which possess either the steric constraints on the ring skeleton or the bulky exocyclic
substituent or lack lone pair donor groups in the ring skeleton [13,17-19]. Recently, a strategy
to control the ligating environment for the isolation of oligomeric fused [3.3.3.01,5]
heterotricycles has been reported by Zoller et al. [13,14].
In order to stabilize stannatrane moieties as monomeric units, we have chosen
aminotrisphenolate ligands because of the structural rigidity offered by phenolic arms and
achievement of favourable topological control [2]. They feature a central nitrogen atom (of
the tripodal ligand) for the formation of a transannular bond with the central atom to generate
a pseudo 3-fold symmetric environment resulting in a fused [4.4.4.01,6] heterotricycle [20-
24]. In this ligand system, bulkiness of the ring skeleton caused by ortho and para substituted
phenyl rings, can disfavour the interaction between two heterotricyclic molecules and thus
support the formation of monomeric complexes. Numerous reports are available in literature
on effective coordination of aminotrisphenolate ligating systems with transition metals and
main group elements, which confirmed the formation of monomeric units (with exceptions of
2

dimeric Al complexes and ꢀ-oxo dimeric Ti complexes when the ligand bears less bulky
substituents on the phenolate rings) [2, 25-27].
Aminotrisphenolate showed exclusive monomeric pseudo-atrane chemistry with silicon
[28-32] and germanium [33] as they tend to form fused [4.4.4.01,6] heterotricycles with
trigonal bipyramidal coordination sphere of the central atom (Chart 1a and 1b). Silicon-
trisphenolate compounds can be isolated in water-dichloromethane mixtures without
undergoing hydrolysis because the rigid and bulky ligating system protects the central silicon
from the attack of water molecules [28-32]. In addition to its tetradentate tripodal NO3
-
coordination (as fully deprotonated L3- ligand, aminotrisphenolate can be used as an O3
chelator, as was shown by the synthesis of a zwitterionic Sn(II) compound (Chart 1c), and in
a Zr(IV) complex it was proven capable of acting as HL2- ligand [34].
Chart 1. Pseudoatranes of Group 14 involving a tripodal aminotrisphenolate moiety.
Working on a similar type of ligating systems, recently we reported the formation of
[4.4.3.01,6] pseudostannatranes with a semi-rigid aminobisphenolate ligand having one
flexible ethanolate arm [15]. Interestingly, despite of steric protection induced by two
substituted o-phenylene units in the fused [4.4.3.01,6] heterotricycle, one flexible arm
provided an active site to extend the coordination sphere around Sn. Hence, fused [4.4.3.01,6]
heterotricycles with hexacoordinate tin atoms were isolated.
Utilizing the stability effects offered by a trisphenolate ligating system (H3L) and
hexacoordination of tin, we report herein a triethylammonium salt of fused [4.4.4.01,6]
heterotricyclic derivative of Sn possessing two exocyclic –NCS substituents. It was obtained
in two steps; 1) formation of Et3NH[LSnCl2] (1), and 2) derivatization to Et3NH[LSn(NCS)2]
(2). Single crystal X-ray diffraction studies of Et3NH[LSn(NCS)2] revealed the formation of a
salt with monomeric fused [4.4.4.01,6] heterotricyclic stannate anions. Because of steric
constraints, two cis positions are occupied by –NCS groups as exocyclic substituents and the
rest by the tripodal tetradentate ligating system. The presence of two cis-disposed –NCS
groups imparts both chelating and chromogenic characteristics to Et3NH[LSn(NCS)2].
3

Interestingly, solution of 2 becomes visible to the naked eye immediately on the addition of
metal ions (such as Fe3+, Cu2+ and Co2+ ions). Moreover, the colorimetric and optical
response of this compound is enhanced over corresponding free ligand (H3L), ammonium
thiocyanate as well as combinations thereof. Hence, the compound may act as colorimetric
and optical sensor for detecting the presence of these metal ions. Although,
polydentate/supramolecular ligating systems have been widely used for sensing purposes,
however, this is the first report on sensing metallic species utilizing trisphenolate based
complex anions [35-37].
2. Experimental
2.1. Materials
Synthesis of all compounds was performed under a dry nitrogen atmosphere using
Schlenk technique. Solvents were purchased commercially, dried before use and stored under
nitrogen atmosphere. Triethylamine (CDH) was distilled over KOH pellets. Tin tetrachloride
(Acros), hexamethylentetramine (Merck), 2,4-dimethylphenol (Merck), ammonium
thiocyanate (Merck), ferric nitrate nonahydrate (Merck), copper nitrate trihydrate (Merck),
cobalt nitrate hexahydrate (Merck), manganese acetate (Acros organics), cadmium chloride
(CDH), chromium nitrate nonahydrate (Merck), lead nitrate (Fisher scientific), zinc nitrate
hexahydrate (CDH) and nickel nitrate hexahydrate (CDH) were used as such without any
purification.
2.2. Physical measurements
Infrared spectra were routinely obtained on Thermo scientific NICOLET IS50 FT-IR and
Perkin Elmer RX-I FT-IR spectrophotometers. Mass spectral measurements (ESI source with
capillary voltage 2500 V) were carried out on a VG Analytical (70-S) spectrometer. C, H, N
elemental microanalyses were obtained on a FLASH-2000 organic elemental analyzer. The
solution NMR spectra were recorded at 25 °C on a Bruker Avance II FT NMR (AL 400
MHz) spectrometer (1H, 13C, 119Sn). Chemical shifts in ppm are reported relative to
tetramethylsilane (TMS) for 1H and 13C or tetramethylstannane for 119Sn. Single-crystal X-ray
diffraction data were collected on a Stoe IPDS-2T diffractometer using Mo Kꢁ radiation (ꢂ
0.71073 Å). The structure was solved by direct methods (SHELXS-97) and refined with full-
matrix least-squares method (refinement of F2 against all reflections with SHELXL-97).
Ultraviolet-visible (UV-vis) spectra were recorded using a Jasco V-530 UV-vis
spectrophotometer.
4

2.3. Synthesis
2.3.1. Synthesis of the aminotrisphenol ligand H3L.
This ligand was synthesized following a method reported in literature [31]. Briefly,
hexamethylenetetramine (3.80 g, 27.1 mmol) and 2,4-dimethylphenol (15.0 mL, 124 mmol)
with a catalytic amount of p-toluenesulfonic acid hydrate (0.10 g) were heated in an oil bath
at 110 °C for 20 h. Then, an additional quantity of 2,4-dimethylphenol (5.00 mL, 41.4 mmol)
was added and heating was continued for a further period of 20 h. The resultant solid was
recrystallized from acetone (100 mL). Yield 72 % (16.4 g, 39.0 mmol); m.p. 174-178 °C; FT-
IR (cm-1): 1153 (C–N), 1211 (C–O), 1482, 1609 (C=C), 2868, 2912, 3011(C–H), 3366, 3517
7
8
(–OH); 1H NMR (400 MHz, DMSO): ꢃ (ppm) 2.14 (s, 9H, Ar–CH3 ), 2.18 (s, 9H, Ar–CH3 ),
3.60 (s, 6H, NCH2), 6.76 (s, 3H, H5), 6.77 (s, 3H, H3), 8.84 (br., 3H, OH).
2.3.2. Synthesis of Et3NH[LSnCl2] (1).
Aminotrisphenol H3L (1.00 g, 2.38 mmol) was dissolved in dry tetrahydrofuran (20 mL)
in the presence of anhydrous triethylamine (1.01 mL, 7.16 mmol), and tin tetrachloride (0.28
mL, 2.38 mmol) was added to it drop wise with stirring. The contents were stirred for about 5
h at room temperature and then filtered to remove the precipitated triethylammonium
chloride. The salt was washed with THF and from the filtrate the solvent was evaporated and
the solid obtained was dried under vacuum. Yield (crude product): 96 % (1.63 g, 2.30 mmol);
m.p.: 195-198 °C. FT-IR (cm-1): 417 (Sn–N), 537 (Sn–O), 1159 (C–N), 1263 (C–O), 1478,
1
1605 (C=C), 2868, 2910, 2949, 2994 (C–H), 3101 (N-H). H NMR (400 MHz, CDCl3): ꢃ
3
(ppm) 1.25 (t, J(1H-1H) = 7 Hz, 9H, triethylammonium CH3), 1.76 (s, 3H, Ar–CH316), 1.95
3
(s, 6H, Ar–CH37,25), 2.08 (s, 6H, Ar–CH38,26), 2.13 (s, 3H, Ar–CH317), 3.09 (q, J(1H-1H) = 7
Hz, 6H, triethylammonium NCH2), 3.16 (d, 2J(1H-1H) = 11 Hz, 2H, NCH29,27), 3.73 (br., 2H,
2
NCH218), 5.25 (d, J(1H-1H) = 11 Hz, 2H, NCH29’,27’), 5.60 (s, 1H, H14), 6.37 (s, 1H, H12),
6.47 (s, 2H, H5,23), 6.59 (s, 2H, H3,21), 9.34 (br., 1H, NH). 13C NMR (100 MHz, CDCl3): ꢃ
(ppm) 8.67 (triethylammonium CH3), 16.61 (Ar–CH37,16,25), 20.38 (Ar–CH38,17,26), 46.32
(triethylammonium NCH2), 55.77 (NCH29,18,27), 116.58 (C6,15,24), 126.60 (C2,11,20), 129.27
(C5,14,23), 129.75 (C3,12,21), 133.93 (C4,13,22), 151.17 (C1,10,19). 119Sn (149 MHz, CDCl3): ꢃ
(ppm) -624. MS: m/z (relative abundance (%) assignment): 135 (14.84) [C9H11O]+, 402
(92.20) [M - Cl - OPh(CH3)2CH]+, 420 (72.06) [L + H]+, 536 (100) [M - 2Cl - (C2H5)3NH]+,
554 (10.84) [M + NH3 - (C2H5)3NH + H]+, 606 (4.04) [M - (C2H5)3NH]+. C33H46Cl2N2O3Sn
(708.35): calcd. C 55.95, H 6.55, N 3.95; found C 55.80, H 6.55, N 4.06.
2.3.3. Synthesis of Et3NH[LSn(NCS)2] (2).
5

A solution of compound 1 (1.00 g, 1.41 mmol) and NH4SCN (0.21 g, 2.82 mmol) in dry
acetonitrile was stirred overnight. The resulting solution was filtered and the solvent was
removed under vacuum to obtain solid. The product was recrystallized from
dichloromethane-hexane to get crystals for single crystal X-ray diffraction studies. Yield
(crude product) 95 % (1.01 g, 1.34 mmol), m.p.: 225-228 °C. FT-IR (cm-1): 418 (Sn–N), 538
(Sn–O), 1160 (C–N), 1241 (C–O), 1476, 1613 (C=C), 2061, 2005, 1978 (–NCS), 2855, 2921,
1
3
2990 (C–H), 3129 (N–H). H NMR (400 MHz, CDCl3): ꢃ (ppm) 1.28 (t, J(1H-1H) = 7 Hz,
9H, triethylammonium CH3), 1.78 (s, 3H, Ar–CH316), 1.94 (s, 6H, Ar–CH37,25), 2.09 (s, 9H,
Ar–CH38,17,26), 3.12 (q, 3J(1H-1H) = 7 Hz, 6H, triethylammonium NCH2), 3.33 (d, 2J(1H-1H) =
2
13 Hz, 3H, NCH29,27), 3.71 (br., 2H, NCH218), 4.81 (d, J(1H-1H) = 13 Hz, 3H, NCH29’,27’),
5.65 (s, 1H, H14), 6.40 (s, 1H, H12), 6.50 (s, 3H, H5,23), 6.63 (s, 3H, H3,21), 8.78 (br., 1H, NH).
13C NMR (100 MHz, CDCl3): ꢃ (ppm) 8.86 (triethylammonium CH3), 16.09, 16.14, 16.44
(Ar–CH37,16,25), 20.13, 20.31, 20.33 (Ar–CH38,17,26), 47.03 (triethylammonium NCH2), 58.47,
63.26 (NCH29,18,27), 120.21, 122.23 (C6,15,24), 125.21, 126.72 (C2,11,20), 127.81, 128.20
(C5,14,23), 129.43, 129.75 (C3,12,21), 131.89, 133.91 (C4,13,22), 151.14, 157.74 (C1,10,19), 172.44
(NCS). 119Sn (149 MHz, CDCl3): ꢃ (ppm) -704. MS: m/z (relative abundance (%)
assignment): 652 (100) [M - (C2H5)3NH]+, 625 (14.72) [M - (C2H5)3NH - 2CH3 + 2H]+, 609
(10.14) [M - (C2H5)3NH - 3CH3 + H]+, 179 (174.41) [OPh(CH3)2CH2N+NH3]+.
C35H46N4O3S2Sn (753.60): calcd. C 55.78, H 6.15, N 7.43, S 8.51; found C 55.77, H 5.89, N
6.88, S 8.34.
2.3.4. Optical studies of 2
Stock solution of compound 2 (5 mM) and metal salts (10 mM) were prepared by
dissolving requisite amounts in methanol and acetone. To study the colorimetric response of
2, 2 mL of its stock solution was mixed with 2 mL of respective metal ion solution (Mn2+,
Cd2+, Cr3+, Fe3+, Cu2+, Co2+, Hg2+, Pb2+, Zn2+, Ni2+; 0.5 mM each). The change in colour of
the solution was recorded immediately. The same solution was used to record the UV-vis
spectrum.
In order to complete the titration and record the response of 2 towards increasing
concentration of Fe3+, Cu2+ and Co2+, 2 mL solution of 2 (0.2 mM) was filled in a quartz
optical cell of 1 cm optical path length, and 0.04 mL of the solution of metal ions (0.2 mM)
were added gradually by using a micropipette. After 2 min of the mixing of metal ions with 2,
UV-vis absorption spectra were measured at room temperature.
6

For Job plot analyses, 0.2 mM solution of metal ions (Fe3+, Cu2+ and Co2+) and 0.2 mM of
2 was prepared, and a titration was performed under the condition that mole fraction of metal
ions gradually increases from 0 to 1 in final solution (5 mL).
To compare the chelating behaviour of 2, NH4SCN and H3L, different test solutions were
prepared by mixing their equimolar solutions (1 mM) with the metal ions (Fe3+, Cu2+ and
Co2+; 1 mM each) in different ratios (for details see table S1).
3. Results and discussion
In the present work, a C3 symmetric aminotrisphenolate ligand was used to obtain
monomeric fused [4.4.4.01,6] heterotricyclic tin compounds. The tricyclic cage of H3L was
substituted with bulky phenyl groups, which provided non-flexibility to the arms. Moreover,
the rigidity of tripodal arms transformed the oligomerizable active centres of ligating system
into inactive sites. Owing to the stability offered by trisphenolate ligating system and
formation of monomeric fused heterotricyclic cages in the past, we tried to yield a chloro
derivative of fused [4.4.4.01,6] heterotricycle (i.e LSnCl) to use as a precursor for obtaining its
rhodanide derivative (i.e. LSnNCS). Unexpectedly, the reaction yielded compounds 1 and 2
as triethylammonium salts (Scheme 1). The most interesting feature of these compounds is
incorporation of an extra exocyclic substituent leading to hexcoordination at Sn centre. The
formation of 1 and 2 was confirmed by IR and NMR (1H, 13C, 119Sn) spectroscopy, mass
spectrometry, elemental analysis and single-crystal X-ray diffraction studies (only for 2).
Scheme 1. Synthetic routes to compound 1 and 2 (isolated and expected products).
The solid state FT-IR spectrum of ligand H3L features vibration bands at 3517 and 3362
cm-1 due to free and hydrogen bonded –OH groups, which disappeared in the IR spectra of 1
and 2, thereby confirming its role as L3- ligating system. Apart from this, 1 and 2 showed the
corresponding Sn–O and Sn–N bands in their respective regions, i.e., 537 and 538 cm-1 for
Sn−O, 417 and 418 cm-1 for Sn−N, respectively. The mass spectrum of 1 consisted of peaks
at m/z 606 (1 lacking triethylammonium ion) and 536 (1 lacking triethylammonium and both
chloride substituents) suggesting the presence of the heterotricycle. In the mass spectrum of
7

2, a sharp peak corresponding to the heterotricyclic cage with two –NCS substituents
appeared as a base peak at m/z 652.
1H NMR spectrum of 1 (crude) showed relatively broad signals in the respective regions
for some of the protons either due to the ring inversion of skeleton or flipping between endo
1
and exo form [38,39], however, corresponding signals for 2 were relatively clear. The H
NMR spectrum of compound 1 and 2 supported the formation of the stannatrane-like cage.
1H NMR data revealed that the anion has mirror symmetry, and in compound 2 the SCN
ligands, Sn atom, N1 and the aryl which belongs to O2 are constituents of the mirror plane.
Hence, the N-CH2 protons of this group are chemically equivalent and produce a singlet at
3.73 and 3.71 ppm for 1 and 2, respectively. The other two aryls (at O1 and O3) are
chemically equivalent, but they have two different protons of their NCH2 groups, one of them
points towards the NCS ligand and the other one points towards the aryl which is in the
mirror plane. The presence of two doublets for NCH2, ꢃ = 3.16/5.25 ppm (2J(1H-1H) = 11 Hz)
for 1 and 3.33/4.81 ppm (2J(1H-1H) = 13 Hz), for 2 suggested different environment for the
protons, and are, therefore diastereotopic. This is also supported by the presence of four
signals at 5.60, 6.37, 6.47, 6.59; and 5.65, 6.40, 6.50, 6.63 for aromatic protons as well as
splitting of signals of aryl-methyl groups in ratio 3:6:9 and 3:6:6:3, respectively for 1 and 2.
119Sn spectra in CDCl3 showed signals at -624 for 1 and -709 ppm for 2 corroborating
hexacoordination at Sn. The 119Sn NMR signal for 2 showed splitting due to 119Sn–15N
coupling [40,41] (Fig. S1).
3.1.Crystal Structure
Single-crystal X-ray diffraction analysis of 2 revealed formation of an ionic compound
with fused [4.4.4.01,6] heterocyclic anion (featuring hexacoordinated Sn) and
triethylammonium as cation (Fig. 1). The compound was isolated as monomer with distorted
octahedral geometry of Sn, in which NCS substituents are cis to each other. The tetradentate
L3- is coordinated in such a way that its N atom and one of the oxygen atoms are situated
trans to the –NCS groups. Because of steric constraints, this ligating system indeed
disfavoured the formation of oligomers even in the case of tin where oligomerisation or
formation of clusters is very common. Nonetheless, it still supported the formation of an
octahedral tin coordination sphere with the aid of a small monodentate ligand.
8

Fig. 1. ORTEP presentation (thermal ellipsoids at 40 % probability whereas hydrogens at 10
% probability) of 2 with partial numbering scheme.
In spite of the different trans-donor situations, the three Sn–O bond lengths are essentially
the same (Sn–O1 2.022(3), Sn–O2 2.021(3) and Sn–O3 2.016(3) Å). The Sn−N(thiocyanate)
bond lengths are more responsive to their different trans-donor situations: Sn–N2 2.155(5)
and Sn–N3 2.178(4) Å. Both thiocyanate units are nearly linear (N2–C28–S1 176.2(6)°, N3–
C29–S2 177.4(5)°) and the Sn–N–C–S tetratomic chains are bent at the nitrogen atoms (Sn1–
N2–C28 128.8(5)°, Sn1–N3–C29 159.6(5)°). The difference in the Sn–N–C bond angles is
accompanied with significant differences in N–C bond lengths in the two –NCS groups (N2–
C28 1.162(8), N3–C29 1.121(7) Å).
Generally, fused heterocycles form propeller like structure with symmetrical orientation
of tripodal arms. However, in the present molecule, propeller-like arrangement is lost due to
the second thiocyanate group, thus furnishing an octahedral coordination sphere about tin.
Interestingly, the transannular Sn–N bond (2.244(4) Å, Table 1) observed in this molecule
belongs to the shortest observed in that kind of tin compounds, together with short
transannular Sn−N bonds in some stannatranes with fused five-membered rings, i.e.,
N(CH2CMe2O)3SnOC6H4NO2 (2.232(2) Å) and N[CH2C(O)O]3Sn(CH2)3N(O)Me2 (2.231(7)
Å)19, while various other stannatranes exhibit longer transannular Sn−N bonds (e.g.,
compounds of the type N(CH2CMe2O)3SnX (X = OR, SR, halogen) (2.248(2)-2.295(3) Å)
[13], [N(CH2CH2O)3SnMe]3 (2.28 Å) [16], [N(CH2CH2O)3SnR] (R = t-Bu, 2.324 Å [18]; R =
C6H4-o-OMe, 2.323(7) Å [17]), N(CH2CH2O)3SnOs(ꢄ2-S2CNMe2)(CO)(PPh3)2 (2.422(4) Å)
[42]
and
psuedostannatranes
with
aminobisphenolate
moiety
of
type
[N{CH2(C6H2Me2)O)}3SnBu]2 (2.256(2) Å) and [{CH2(C6H2Me2)O)}3SnPh·OSnPh2]2
(2.264(2) Å) [15]). This may be attributed to the electron withdrawing effect of –NCS
9

substituents, which is also corroborated by the shortening of transannular Si–N bond
observed in 1-isothiocyanatosilatrane [43].
Table 1. X-ray crystal data of selected bond lengths (Å) and angles (°).
Bond lengths (Å)
Bond Angles (°)
Sn(1)-O(av)
Sn(1)-N(1)
Sn(1)-N(2)
Sn(1)-N(3)
S(1)-C(28)
S(2)-C(29)
N(2)-C(28)
N(3)-C(29)
N(1)-C(9)
N(1)-C(18)
N(1)-C(27)
O(1)-C(1)
O(2)-C(10)
O(3)-C(19)
2.019(3)
2.244(4)
2.155(5)
2.178(4)
1.611(8)
1.612(6)
1.162(8)
1.121(7)
1.501(6)
1.506(6)
1.511(6)
1.343(6)
1.357(6)
1.355(6)
O(1)-Sn(1)-O(2)
O(1)-Sn(1)-O(3)
O(2)-Sn(1)-O(3)
O(1)-Sn(1)-N(2)
O(2)-Sn(1)-N(2)
O(3)-Sn(1)-N(2)
O(1)-Sn(1)-N(3)
O(2)-Sn(1)-N(3)
O(3)-Sn(1)-N(3)
O(1)-Sn(1)-N(1)
O(2)-Sn(1)-N(1)
O(3)-Sn(1)-N(1)
N(2)-Sn(1)-N(3)
N(2)-Sn(1)-N(1)
N(3)-Sn(1)-N(1)
95.7(3)
170.3(3)
93.93(14)
89.01(17)
92.93(17)
91.51(17)
86.10(16)
178.12(17)
84.28(17)
87.90(14)
86.87(13)
91.62(14)
87.69(19)
176.86(18)
92.61(16)
In the crystal structure, the triethylammonium cation is two-fold disordered with nearly
equal occupancy of the two conformations. In spite of this disorder, the N-H groups are in
similar orientation and there are weak interactions between the cation Et3NH+ and anion
[LSn(NCS)2]–. Specifically, the closest contact between cation and [LSn(NCS)2]– involves a
nitrogen atom of thiocyanate and a H atom of the Et3NH+ cation (N2–H4/N2–H4A =
2.424/2.094 Å) and are within the sum of van der Waals radii for nitrogen and hydrogen
(2.75 Å), consistent with weak cation-anion interactions [44]. This interaction can be
interpreted as a contributor to the different Sn-N-C angles encountered with the two NCS
ligands in this tin complex.
The packing of compound consisted of compact arrangement of fused heterotricyclic
anion and triethylammonium cation in a zig-zag fashion owing to the persisting Van der Waal
forces (Fig. S2). These arrangements can be viewed in plane as a group of butterflies moving
in same direction. Selected parameters of data collection and structure refinement are given in
Table S2.
3.2.Chromogenic and optical response of 2
10

A very interesting feature of 2 is its capability to act as a chromoreactand (chromogenic
reactand) towards some metallic species such as Fe3+, Cu2+ and Co2+ ions. A solution of 2
switched its colour immediately to light orange (Fe3+), peach (Cu2+) and blue (Co2+) in
acetone, and pink (Fe3+), and green (Cu2+) in methanol even in the presence of low
concentrations of these metal ions (0.005, 0.115 and 0.214 mM for Fe3+, Cu2+ and Co2+,
respectively). This particular characteristic of 2 was attributed to the presence of rhodanide
antennae, which have high tendency to coordinate metal ions via S, thereby inducing a rapid
colour change. In contrast, other metal ions (0.5 mM) including Mn2+, Cd2+, Cr3+, Hg2+, Pb2+,
Zn2+, Ni2+ did not induce any colour change in 2 (5 mM) (Fig 2).
Fig. 2. Top: Column chart illustrating the optical response of 2 (5 mM) against different
metal ions (0.5 mM) in methanol (λ
= 519 and 391 nm for Fe3+ and Cu2+ ions,
max
respectively) and acetone (λ
= 467, 472 and 623 nm for Fe3+, Cu2+ and Co2+,
max
respectively); Bottom: Chromogenic response of 2 towards different metal ions in methanol
and acetone (Left to right: 2, Mn2+, Cd2+, Cr3+, Fe3+, Cu2+, Co2+, Hg2+, Pb2+, Zn2+, Ni2+).
The UV-Vis spectrum of pure H3L showed an intense band at 286 nm, which was also
observed in case of 2. The colourless solution of 2 (0.2 mM) in methanol showed a split peak
with maxima at 235 and 287 nm with no absorption band in the visible region. After addition
of metal ions to the solution of 2, the consistency of these bands in addition to an extra band
in the visible region suggested the retention of the tricyclic framework of the receptor even
11

after the addition of metal ions and involvement of thiocyanate antennae in the chromogenic
switch.
The switching of colour may be ascribed to the coordination of metal with 2 via S atoms,
which is also supported by the origin of extra band in the absorption spectrum of methanolic
solution of 2 on the addition of Fe3+ and Cu2+ ions. The band centred at 519 (19269 cm-1) in
the presence of Fe3+ ions can be assigned to LMCT transition (i.e from oxidizable thiocyanate
to oxidizing Fe3+) and the absorption band centred at 391 nm (25575 cm-1) in the presence of
Cu2+ ions may be attributed to the LMCT from π NCS to Cu2+ orbitals [45]. Solvatocromism
studies of the metal complexes showed some interesting changes in the chromogenic and
optical properties of compound 2 in the presence of metal ions. The change in solvent from
methanol to acetone showed both the hypochromic and hypsochromic shift in the absorption
bands of 2 and also ‘turned on’ a colorimetric and optical switch for Co2+ ions (which was
absent in methanol) (Fig. S3). The UV-Vis spectrum of Co2+ ions in acetone exhibited
absorption band at 623 nm (16050 cm-1) with a shoulder at 589 nm (16978 cm-1), which
clearly indicated tetrahedral geometry acquired by rhodanides around Co2+ ions. The origin
4
of bands can be ascribed to d-d transitions from ground state A2 to higher energy levels,
which is also supported by literature [46]. The absorption maxima for Fe3+ and Cu2+ in
acetone were observed at 467 (21413 cm-1) and 472 nm (21186 cm-1), respectively (Fig. 2).
The chromogenic and optical change in 2 at different concentration of metal ions (Fig. 3)
showed a continuous rise in the intensity of colour and corresponding absorption maxima
with increasing concentration of metal ions in methanol (except for Co2+ which was taken in
acetone). It is clear that methanolic solution of 2 did not absorb in the visible region,
however, on adding metal ions it showed a drastic increase in absorption centered at 519, 391
and 623 nm (Fe3+, Cu2+ and Co2+ respectively). On the basis of Job’s plot 1:2 colored
complexes [M{(NCS)2SnL}2] [47-49] can be expected for M = Co2+, Cu2+ and Fe3+ ions (Fig.
4).
12

Fig. 3. UV-vis absorption spectra of 2 (0.2 mM) with different concentration of Fe3+, Cu2+ in
methanol and Co2+ in acetone and the corresponding colour change of the sensor 2 on
increment of metal ion concentration.
Fig. 4. Job plot for complexation of sensor 2 (0.2 mM) with Fe3+, Cu2+ and Co2+ (0.2 mM).
13

Moreover, similar type of studies were accomplished using H3L and ammonium
thiocyanate solutions under similar conditions to confirm the participation of –NCS moieties
in the chromogenic response of 2 (Fig. S4, S5, S6). The studies failed to show significant
chromogenic response of H3L on the addition of metal ions. In contrast, similar type of
absorption bands were observed in case of ammonium thiocyanate but their intensity was low
as compared to 2. A table summarizing the wavelengths, concentration and molar
absorptivity is given below to compare the optical properties of 2, H3L and ammonium
thiocyanate under similar conditions (Table 2). The studies revealed 2 as a better
chromoreactand because it can bind metal ions more effectively as compared to free –NCS
(in ammonium thiocyanate). The effective chelation in 2 may be attributed to the presence of
–NCS in cis positions. The regression plots revealed the linearity of optical response up to
0.0761, 0.0761 and 0.0615 for Fe3+, Cu2+ and Co2+, respectively (Fig 5). The limit of
detection for colorimetric response was found to be 0.005, 0.115 and 0.214 mM for Fe3+,
Cu2+ and Co2+, respectively. Hence, 2 may be used as an alternative for the naked eye and
optical recognition of these metal ions.
Table 2. Comparison of optical response of equimolar solutions (1mM each) of 2 (1 equiv),
NH4SCN (2 equiv) and H3L (1 equiv) towards metal ions (1 mM); see Table S1 for more
details.
Metal Chromogenic Wavelength (nm),
Molar Absorptivity,
ꢅ x 105 (m2/mol)
5.038 (LMCT)
1.161 (LMCT)
3.204
Absorbance
ions
Reactand
2
Wavenumber (cm-1)
527 (18975)
521 (19194)
371 (26954)
390 (25641)
383 (26110)
466 (21459)
623 (16051)
623 (16051)
510 (19608)
0.504
0.232
0.320
0.075
0.059
0.043
0.058
0.074
0.014
Fe3+
NH4SCN
H3L
2
0.755 (LMCT)
0.295 (LMCT)
0.435
Cu2+
Co2+
NH4SCN
H3L
2
0.579 (d-d)
0.371 (d-d)
0.138
NH4SCN
H3L
14

Fig. 5. Regression plot for the variation of optical response of 2 (0.2 mM) towards Fe3+ Cu2+
,
and Co2+ ions at 519 nm, 391 nm and 623 nm, respectively.
4. Conclusions
Fused [4.4.4.01,6] heterotricyclic metallorganic compounds of Sn were successfully
achieved as triethylammonium salts. The compounds were isolated as monomers in which Sn
was hexacoordinated. The hexacoordination in compounds was achieved by incorporation of
an extra exocyclic substituent. The presence of –NCS antennae in 2 made it sensitive towards
metal ions Co2+, Cu2+ and Fe3+, which switched its color immediately on the addition of metal
ions. Therefore, 2 may be used for the recognition of some metal ions, which induce different
colours and show solvatochromism behaviour.
Acknowledgements
Authors are thankful to UGC, New Delhi [17-06/2012 (i) EU-V], DST, New Delhi [Regd
No. CS-099/2012] and PURSE-II for providing financial support.
Appendix A. Supplementary data
CCDC 968635 contains the supplementary crystallographic data for 2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
References
15

[1] O. Wichmann, R. Sillanpää, A. Lehtonen, Structural properties and applications of
multidentate [O, N, O, Xꢆ] aminobisphenolate metal complexes, Coord. Chem. Rev. 256
(2012) 371-392.
[2] G. Licini, M. Mba, C. Zonta, Amine triphenolate complexes: synthesis, structure and
catalytic activity, Dalton Trans. (2009) 5265-5277.
[3] L.G. Hubert-Pfalzgraf, Some aspects of homo and heterometallic alkoxides based on
functional alcohols, Coord. Chem. Rev. 178-180 (1998) 967-997.
[4] A. Singh, R.C. Mehrotra, Novel heterometallic alkoxide coordination systems of polyols
(glycols, di- and tri-ethanolamines) derived from the corresponding homometallic
moieties, Coord. Chem. Rev. 248 (2004) 101-118.
[5] J.G. Verkade, Main group atranes: chemical and structural features, Coord. Chem. Rev.
137 (1994) 233-295.
[6] M.G. Voronkov, V.P. Baryshok, Metallatranes, J. Organomet. Chem. 239 (1982) 199-
249.
[7] J.G. Verkade, Atranes: new examples with unexpected properties, Acc. Chem. Res. 26
(1993) 483-489.
[8] M.G. Voronkov, V.M. Dyakov, S.V. Kirpichenko, Silatranes, J. Organomet. Chem. 233
(1982) 1-147.
[9] J.K. Puri, R. Singh, V.K. Chahal, Silatranes: a review on their synthesis, structure,
reactivity and applications, Chem. Soc. Rev. 40 (2011) 1791-1840.
[10]N. Srivastav, R. Singh, V. Kaur, Carbastannatranes: a powerful coupling mediators in
Stille coupling, RSC Adv. 5 (2015) 62202-62213.
[11]M.G. Voronkov, V.P. Baryshok, Antitumor activity of silatranes, Pharm. Chem. J. 38
(2004) 3-9.
[12]M.S. Jensen, C. Yang, Y. Hsiao, N. Rivera, K.M. Wells, J.Y.L. Chung, N. Yasuda, D.L.
Hughes, P.J. Reider, Synthesis of an anti-methicillin-resistant staphylococcus aureus
(MRSA) carbapenem via stannatrane-mediated stille coupling, Org. Lett. 2 (2000) 1081-
1084.
[13]T. Zoller, C .Dietz, L.I.-Berends, O. Karsten, G. Bradtmoller, A.-K. Wiegand, Yu Wang,
V. Jouikov, K. Jurkschat, Novel stannatranes of the type N(CH2CMe2O)3SnX (X = OR,
SR, OC(O)R, SP(S)Ph2, Halogen). Synthesis, molecular structures, and electrochemical
properties, Inorg. Chem. 51 (2012) 1041-1056.
[14]T. Zoller, K. Jurkschat, Novel Trialkanolamine derivatives of tin of the type
[N(CH2CMe2O)2(CH2)nOSnOR]m (m = 1, 2; n = 2, 3; R = t Bu, 2,6-Me2C6H3) and
16

related tri- and pentanuclear tin(IV) oxoclusters. Syntheses and molecular structures,
Inorg. Chem. 52 (2013) 1872-1882.
[15]N. Srivastav, R. Mutneja, N. Singh, R. Singh, V. Kaur, J. Wagler, E. Kroke, Diverse
molecular architectures of Si and Sn [4.4.3.01,6] tridecane cages derived from a mannich
base possessing semi-rigid unsymmetrical podands, Eur. J. Inorg. Chem. 2016 (2016)
1730-1737.
[16]R.G. Swisher, R.O. Day, R.R. Holmes, The first complete crystal structure of a
stannatrane. Trimeric Methyl(2,2’,2”-nitrilotriethoxy)stannane Hexahydrate, Inorg.
Chem. 22 (1983) 3692-3695.
[17]Y. Ovchinnikov, Y. Struchkov, V. Baryshok, M. Voronkov, Crystal and molecular
structure of 1-(2ꢆ-methoxyphenyl)-3,7,10-trimethylstannatrane, J. Struct. Chem. 35
(1994) 750-753.
[18]A. Tzschach, K. Jurkschat, Aspects of pentacoordinated tin compounds, Comments
Inorg. Chem. 3 (1983) 35-50.
[19]D. Dakternieks, G. Dyson, K. Jurkschat, R. Tozer, E.R.T. Tiekink, Utilization of
hypervalently activated organotin compounds in synthesis. Preparation and reactions of
Me2N(CH2)3SnPh3, J. Organomet. Chem. 458 (1993) 29-38.
[20]Y. Takii, P.M. Gurubasavaraj, S. Katao, K. Nomura, Effect of terminal aryloxo ligands
in ethylene polymerization using titanatranes of the type, [Ti(OAr){(O-2,4-R2C6H2)-6-
CH2}3N]: Synthesis and structural analysis of the heterobimetallic complexes of
titanatranes with AlMe3, Organometallics 31 (2012) 8237-8248.
[21]A. Lehtonen, R. Sillanpää, Alkoxo, chlorido, and methyl derivatives of
oxidomolybdenum (VI) complexes with tetradentate [O3N]-type ligands, Polyhedron 26
(2007) 5293-5300.
[22]N.V. Timosheva, A. Chandrasekaran, R.R. Holmes, Atrane and phosphorane formation
with aminotriphenols, Z. Anorg. Allg. Chem. 631 (2005) 2683-2690.
[23]D.J. Kim, Y. Hong, S.H. Kim, K.M. Lee, S. Muna, S. Yoon, J. Lee, Y. Do, Y. Kim,
Boratranes with all six-membered rings or with two different ring sizes: Synthesis,
characterization, and X-ray crystal structures, Inorg. Chim. Acta 378 (2011) 311-314.
[24]M. Kol, M. Shamis, I. Goldberg, Z. Goldshmit, S. Alfi, E. Hayut-Salant, Titanium(IV)
complexes of trianionic amine triphenolate ligands, Inorg. Chem. Commun. 4 (2001)
177-179.
17

[25]C. Zonta, A. Kolarovic, M. MBA, M. Pontini, E.P. Kundig, G. Licini, Enantiopure
Ti(IV) Amino Triphenolate Complexes as NMR Chiral Solvating Agents, Chirality 23
(2011) 796-800.
[26]C.J. Whiteoak, B. Gjoka, E. Martin, M.M. Belmonte, E.C. Escudero-Adán, C. Zonta, G.
Licini, A.W. Kleij, Reactivity control in iron(III) amino triphenolate complexes:
Comparison of monomeric and dimeric complexes, Inorg. Chem. 51 (2012) 10639–
10649.
[27]C. Martín, C.J. Whiteoak, E. Martin, E.C. Escudero-Adán, J.R. Galán-Mascarós, A.W.
Kleij, Synthesis and structural features of Co(II) and Co(III) complexes supported by
aminotrisphenolate ligand scaffolds, Inorg. Chem. 53 (2014) 11675–11681.
[28]A. Chandrasekaran, R.O. Day, R.R. Holmes, A new class of silatranes:ꢇ Structure and
dynamic NMR behavior, J. Am. Chem. Soc. 122 (2000) 1066-1072.
[29]N.V. Timosheva, A. Chandrasekaran, R.O. Day, R.R. Holmes, Synthesis of trioxy- and
tetraoxysilatranes with all six-membered rings. Structure and dynamic NMR Behavior,
Organometallics 19 (2000) 5614-5622.
[30]A. Chandrasekaran, R.O. Day, R.R. Holmes, Synthesis and structure of cyclic phosphate,
phosphoramidate, phosphonates, and phosphonium salts. Phosphatrane Formation, Inorg.
Chem. 39 (2000) 5683-5689.
[31]N.V. Timosheva, A. Chandrasekaran, R.O. Day, R.R. Holmes, Synthesis of silatranes
with all six-membered rings. Influence of steric effect on structure and NMR behaviour,
Organometallics 20 (2001) 2331-2337.
[32]N.V. Timosheva, A. Chandrasekaran, R.O. Day, R.R. Holmes, Conversion of
tricoordinate to hexacoordinate phosphorus. Formation of a phosphorane-phosphatrane
system, J. Am. Chem. Soc. 124 (2002) 7035-7040.
[33]A.J. Chmura, C.J. Chuck, M.G. Davidson, M.D. Jones, M.D. Lunn, S.D. Bull, M.F.
Mahon, A germanium alkoxide supported by a C3-symmetric ligand for the
stereoselective synthesis of highly heterotactic polylactide under solvent-free conditions,
Angew. Chem. Int. Ed. 46 (2007) 2280-2283.
[34]M.G. Davidson, C.L. Doherty, A.L. Johnson, M.F. Mahon, Isolation and characterisation
of transition and main group metal complexes supported by hydrogen-bonded
zwitterionic polyphenolic ligands, Chem. Commun. (2003) 1832-1833.
[35]E.V. Anslyn, Supramolecular Analytical Chemistry, J. Org. Chem. 72 (2007) 687–699.
[36]J. Wu, B. Kwon, W. Liu, E. V. Anslyn, P. Wang, J.S. Kim, Chromogenic/Fluorogenic
Ensemble Chemosensing Systems, Chem. Rev. 115 (2015) 7893–7943.
18

[37]E.V. Anslyn, Synthetic receptors as sensors, Tetrahedron 60 (2004) 11055–11056.
[38]M. Zeldin, J. Ochs, Synthesis and characterization of organostannatranes, J. Organomet.
Chem. 86 (1975) 369-382.
1
[39]A. Zschunke, A. Tzschach, K. Ponicke, H-NMR-untersuchung zur innermolekularen
beweglichkeit in pentakoordinierten zinnverbindungen, J. Organomet. Chem. 51 (1973)
197-201.
[40]S.J. Blunden, P.A. Cusack, D.G. Giclies, Observation of 117,119Sn-14N coupling in the
Sn(NCS)62- Anion, J. Magn. Reson. 60 (1984) 114-117.
[41]K.C. Molloy, K. Quill, S.J. Blunden, R. Hill, Tin-119 and nitrogen-14 nuclear magnetic
resonance and tin-119 variable temperature mossbauer spectroscopic study of
tricyclohexyltin lsothiocyanate including the first observation of resolved 117,119Sn-14N
coupling in an organotin Compound, J. Chem. Soc., Dalton Trans. (1986) 875-877.
[42]C.E.F. Rickard, W.R. Roper, T.J. Woodman, L. James Wright, The synthesis and crystal
structure of the first metal-bound stannatrane complex Os(Sn[OCH2CH2]3N)(ꢄ2-
S2CNMe2)(CO)(PPh3)2: structural comparisons with the analogous silatrane complex
Os(Si[OCH2CH2]3N)(ꢄ2-S2CNMe2)(CO)(PPh3)2, Chem. Commun. (1999) 837-838.
[43]S.P. Narula, R. Shankar, M. Kumar, R.K. Chadha, C. Janai, Structure and reactivity of 1-
Isothiocyanatosilatrane:ꢇꢈꢉꢊꢋꢈꢌꢍꢎꢏꢐꢈꢏꢍꢑꢒꢐꢎꢒꢓꢋꢈꢔꢍꢐꢊꢈꢒꢈꢕꢍꢎꢋꢖꢐꢈꢗꢍꢘꢙꢚꢗꢈꢛꢜꢓꢕꢝꢈInorg. Chem. 36
(1997) 1268-1273.
[44]A. Bondi, van der waals volumes and radii, J. Phys. Chem. 68 (1964) 441-451.
[45]A.B.P. Lever, Inorganic Electronic Spectroscopy, second ed., Oxford, New York, 1984.
[46]S. Osborne, S. Wellens, C. Ward, S. Felton, R. Bowman, K. Binnemans, M. Swadzba-
Kwasny, N. Gunaratne, P. Nockemann, Thermochromism and Switchable
Paramagnetism of Cobalt(II) in Thiocyanate Ionic Liquids, Dalt. Trans. (2015) 2–5.
[47]Y.-J. Wei, F.-W. Wang, Q.-Y. Zhu, Synthesis, crystal structures, and antimicrobial
activity of a pair of isostructural dinuclear copper(II) complexes derived from 4-nitro-2-
[(2-diethylaminoethylimino)methyl]phenol, Transition Met. Chem. 33 (2008) 543-546.
[48]M. Mousavi, V. Bereau, C. Duhayon, P. Guionneauc, J.-P. Sutter, First magnets based on
thiocyanato-bridges, Chem. Commun. 48 (2012) 10028-10030.
[49]M. Zhang, D.-M. Xian, N. Zhang, Z.-L. You, Synthesis, structures, and fluorescence of
azido-bridged dinuclear and thiocyanato-bridged tetranuclear cadmium(II) complexes
derived from N-isopropyl-N9-(1-pyridin-2-ylethylidene)ethane-1,2-diamine, J. Coord.
Chem. 65 (2012) 1837-1846.
19

20

21

22

23

24

Highlights
•
Synthesis of noval fused [4.4.4.01,6] heterotricyclic metallorganic compounds of Sn as
triethylammonium salts using phenolic ligand [Tris(2-hydroxy-4,6-
dimethylbenzyl)amine] H3L.
•
•
Rhodanide tailored hexacoordinated psuedostannatrane (2) with –NCS antennae act as
one of the rare examples of chromophoric probes
Rapid, sensitive and selective colorimetric sensing of Fe3+, Cu2+ and Co2+ ions
25