Thiocyanate mediated structural diversity in phenol based “end-off” compartmental ligand complexes of group 12 metal ions: Studies on their photophysical properties and phosphatase like activity

Article abstract of DOI:10.1016/j.saa.2017.01.041

The reaction of a pentadentate compartmental ligand LH, namely 4-tert-Butyl-2,6-bis-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol, with group 12 metal ions (Zn^II, Cd^II, Hg^II) followed by addition of NaSCN afforded one discre

Full text of DOI:10.1016/j.saa.2017.01.041

Accepted Manuscript
Thiocyanate mediated structural diversity in phenol based “end-
off” compartmental ligand complexes of group 12 metal ions:
Studies on their photophysical properties and phosphatase like
activity
Jaydeep Adhikary, Prateeti Chakraborty, Sugata Samanta, Ennio
Zangrando, Sanjib Ghosh, Debasis Das
PII:
DOI:
Reference:
S1386-1425(17)30060-4
doi: 10.1016/j.saa.2017.01.041
SAA 14894
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date:
Revised date:
Accepted date:
11 November 2016
30 December 2016
22 January 2017
Please cite this article as: Jaydeep Adhikary, Prateeti Chakraborty, Sugata Samanta, Ennio
Zangrando, Sanjib Ghosh, Debasis Das , Thiocyanate mediated structural diversity in
phenol based “end-off” compartmental ligand complexes of group 12 metal ions: Studies
on their photophysical properties and phosphatase like activity. The address for the
corresponding author was captured as affiliation for all authors. Please check if
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ACCEPTED MANUSCRIPT
‘Revised’
Thiocyanate mediated structural diversity in phenol based “end-off”
compartmental ligand complexes of group 12 metal ions: Studies on
their photophysical properties and phosphatase like activity
Jaydeep Adhikary a,b, Prateeti Chakraborty a,e, Sugata Samanta c, Ennio Zangrando d, Sanjib Ghosh
f*, Debasis Das a*
a Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata-700 009, India, E-
mail: dasdebasis2001@yahoo.com
b Department of Chemical Sciences, Ariel University, Ariel 40700, Israel.
c Department of Chemistry, Presidency University, Kolkata-700073, India.
d
Department of Chemical and Pharmaceutical Sciences, University of Trieste, Via L. Giorgieri
1, 34127 Trieste, Italy.
e Department of Chemistry, Amity University, Newtown, Kolkata, West Bengal 700156 92, India
f
The School of Science, Adamas University, Barasat, West Bengal, India. E-mail:
pchemsg@gmail.com
Keywords : Coordination chemistry . Group 12 metals . Structural diversity . Photophysical
property . Phosphatase like activity.
ABSTRACT
The reaction of a pentadentate compartmental ligand LH, namely 4-tert-Butyl-2,6-bis-[(2-
pyridin-2-yl-ethylimino)-methyl]-phenol, with group 12 metal ions (ZnII, CdII, HgII) followed by
addition of NaSCN afforded one discrete dinuclear complex [Zn2(L)(SCN)3](1), and two
polymeric 1D species [Cd2.5(L)(SCN)3(AcO)]n (2) and [Hg2(L)(SCN)3]n (3). All the complexes
have been structurally characterized by single crystal X-ray diffraction. The crystal structure of
the complexes reveals different coordination modes of thiocyanate anion that affect the different
topology detected in the compounds: the anions are 1-NCS and 1,1-NCS connected in complex
1, while 1,3-NCS bridging mode is observed in 2, and 1-SCN and 1,3-NCS in 3. The polymeric
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Hg complex of the bicompartmental ligand system here reported is unprecedented. Detail study
of their photophysical properties including the phosphorescence spectra at 77 K has been done.
Phosphatase like activity of all the three complexes has been performed in DMSO-H2O medium
and their activity follows the order of 1>2>>3.
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1. Introduction
It is well-known that inorganic-organic hybrids of mono- and dinuclear complexes as well
as of polymeric species, especially those with [d10] metal centers, [1–10] exhibit
photoluminescence and have potential applications as optoelectronic devices[11–13]. Exploiting
the different varieties of coordination geometries around these metal ions, diverse molecular and
crystalline architectures [14,15] of different shapes and sizes [16] may be accessed through
strong metal–ligand covalent bonds [17] and multiple weak non-covalent forces [18–21]. The
presence of the [d10] electronic configuration hampers to apply the analytical techniques such as
Mossbauer, EPR spectroscopy and magnetic susceptibility measurements for their detection. On
the other hand, emission spectroscopy can be fruitfully used because group 12 metal complexes
change the fluorescence intensity of organic fluorophores containing coordinated center [22-26]
and therefore fluorescence spectroscopy [22] has been the most powerful tool to detect these
metal ions [24−26]. Schiff bases [27-29] have recently been focused by coordination chemists
due to their preparative accessibilities, structural varieties and varied denticities. Additionally
pseudohalide anions like ambidentate thiocyanate [8,30–34] result in different molecular
architectures through their versatile ligation modes (Fig. 1). Combining these two features we
have synthesized three thiocyanate bridged Schiff base complexes, namely [Zn2(L)(SCN)3] (1),
[Cd2.5(L)(SCN)3(AcO)]n(2), [Hg2(L)(SCN)3]n(3), where LH= 4-tert-Butyl-2,6-bis-[(2-pyridin-2-
yl-ethylimino)-methyl]-phenol (Scheme 1). All three complexes have been structurally
characterized showing that complex 1 is a discrete dinuclear species, whereas 2 and 3 are
polymeric in nature. The different coordination modes of ambidentate thiocyanate to the [d10]
metal ions lead to diverse complex nuclearity, which may be explained by the age-old hard and
soft acids and bases (HSAB) theory [35]. Comprehensive investigations of photophysical
properties of the complexes in solution as well in solid state have been executed.
The catalytic cleavage of phosphoesters is a fundamental reaction for living organisms,
such as in processing RNA replication and bone metabolism, and it is of ecological significance
in the detoxification of pesticides. Natural phosphatases, which accomplish this hydrolysis,
commonly contain zinc (II) ions in their active sites. Zinc (II) ion is frequently chosen by nature
due to its high Lewis acidity, flexibility of the coordination geometry, and fast ligand exchange.
Therefore, di-zinc (II) complexes have been widely used as artificial model of
phospatases[36,37]. On the other hand di-cadmium (II) complex has recently been used as a
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mimics of organophosphate pesticide degrading enzymes and metallo-β-lactamases [38]. In this
communication our synthesized [d10] complexes have been explored in Phosphatase like activity
using 4-nitrophenyl phosphate (4-NPP) in DMSO-H2O medium and tried to find out whether
decreasing Lewis acidity of the group 12 metals have some influence in the hydrolysis of stable
P-O bond of 4-NPP. Our finding strongly suggests that Phospahatase like activity of the
dinuclear complexes decreases from complex 1 to 3 as Lewis acidity decreases from zinc to
mercury.
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NH2
N
+
O
OH
O
1 : 2
Reflux,60oC
MeOH
LH: Hg(OAc)2: NaSCN= 1:2:3
N
OH
N
LH: Zn(OAc)2: NaSCN= 1:2:3
N
N
[Zn2(L) (SCN)3]
Complex 1
[Hg2(L)(SCN)3]n
Complex 3
LH
LH: Cd(OAc)2: NaSCN= 1:2.5: 3
[Cd2.5 (L)(SCN)3(AcO)]n
Complex 2
Scheme 1 Synthetic Route of Complexes 1−3.
2. Results and discussions
2.1. Spectral analyses of the ligand (LH) and the complexes (1-3)
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The ligand LH was characterized by 1H-NMR and 13C-NMR (see section 4.2, Fig. S1-S2,
Supplementary information). All the complexes have been characterized by different spectral
analyses. The FTIR spectra of all complexes show bands due to C=N stretching frequency in the
range of 1635-1650 cm-1 and skeleton vibrations in the range 1569−1605 cm−1. In complex 1,
stretching frequency at 2010 and 2081 cm-1 suggested the presence of two different coordination
modes for SCN- anions. Additional stretching frequencies at 2116 and 2118 cm-1 for complexes 2
and 3, respectively, denoted in both cases the SCN- ligand acting as end-to-end bridging group as
previously reported (Fig. S3−S5, Supplementary information) [39-41]. The three complexes
were also characterized by 1H-NMR (see section 4.2, Fig. S6−S8, Supplementary
information). ESI-MS spectra for 1-3 show the base peaks at m/z = 661.19, 1062.58 and 295.12
amu, and agree well with the species [LZn2(SCN)2]+, [{LCd2(SCN)2 Cd (SCN)2}+ +2K] and
[{LHg2}3+ + Na], respectively (Fig. S9−S11, Supplementary information).
2.2. Description of crystal structures
The X-ray structural analyses of 1–3 confirm the formation of dinuclear entities formed
by compartmental ligand which acts as a pentadentate chelating for the metals. The ORTEP view
with atom labelling scheme of complex 1 is shown in Fig. 2, and a selection of bond lengths and
angles is given in Tables S1(Supplementary information). We already studied zinc (II)
complexes of bi-compartmental ligands in connections with SCN counter anions [42]. In all the
2-
examples reported we obtained Zn(SCN)4 species, while here the anions result coordinated to
the Schiff base complex.
In complex 1 both the ZnII ions have a distorted trigonal bipyramid with a
bridging phenoxy oxygen, two N-donors (from the imine and py donors), and two SCN nitrogen
atoms, of which one acting as bridging towards the metals. Although the coordination geometry
appears comparable, (trigonality τ index of 0.54, 0.63 for the two metal spheres), it is worth of
note the asymmetric behaviour of bridging atoms that lead to significantly different Zn-NCS and
Zn-O(phenol) bond distances for the two metals, at a lower extent for the latter. In fact the Zn(1)-
N(5) and Zn(2)-N(5) bond lengths are of 2.064(3) and 2.355(3) Å, while Zn(1)-O(1) and Zn(2)-
O(1) are of 2.153(2) and 1.992(2) Å, respectively. Another interesting feature is the displacement
of the metals on different side of the phenolate mean plane, of –0.884(2) Å (Zn1) and 0.297(2) Å
(Zn2). The mono coordinated SCN are bound almost linearly to the metals with a Zn-N-S bond
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angle of 162.7°. Simliar type of thiocyanate bridged dinuclear zinc complex was reported
priously [43].
In the cadmium complex 2, the metals bridged by the phenolate ligand have a different
coordination environment with a N3O2S and N2O3S chromophore for the presence of a bridging
acetate anion (Fig. 3). The SCN anions behave as ambidentate ligands, so that Cd1 and Cd2 in
the compartmental ligand are bound to octahedral Cd(SCN)6 units built by metal Cd3, located on
a crystallographic inversion centre, giving rise to a 1D coordination polymer developed along
axis a (Fig. S12, Supplementary information). Of thiocyanates bound to Cd3 ion, four are
coordinated through N, two through S. Selected bond length and angles are presented in Table
S2(Supplementary information). The Cd-S distances relative to metals Cd1, Cd2 present
shorter values [Cd(1)-S(2) = 2.6114(18), Cd(2)-S(3) = 2.612(2) Å] with respect to those
measured for Cd(3)-S(1), of 2.739(2) Å. On the other hand the Cd-NCS bond distances are
almost comparable within their esd’s (range 2.305(8)-2.316(7) Å).The acetate anion assumes the
less frequent chelating-bridgingmode μ2-η2:η1 with Cd-O distances in between 2.476(10) -
2.541(8) Å, which are considerably longer with respect to the Cd-O1 bond lengths, of 2.253(4)
and 2.231(4) Å. The other bond distances appear in the usual range for these types of complexes
[44]. Within the compartmental ligand the metals, separated by 3.717 Å, are displaced from the
phenolato mean plane by –0.962(5) Å (Cd1) and 1.308(4) Å (Cd2). Some examples of cadmium
complexes of Schiff base ligand with end to end bridging thiocyanate ligand are found in
literature [45]. In those cases mononuclear cadmium complexes were polymerised through
thiocyanate ligand. Another example of thiocyanate bridged cadmium complex of end-off
bicompartmental Schiff base ligand has been reported where also mononuclear unit got
polymerised [46]. However, in our case dinuclear cadmium complex of end-off bicompartmental
ligand got polymerise through SCN- ligand.
The structural analysis of compound 3 reveals in the crystal two crystallographic
independent Hg2L(SCN)3 units which are displayed in Fig. 4. The dinuclear fragment Hg1/Hg2
gives rise to a polymeric 1D chain because of the bridging behaviour of one SCN anion, and the
metals have a different coordination environment with a N3OS and N2OS2 donor set for Hg1 and
Hg2, respectively. On the other hand in the second unit Hg3 has a distorted square planar
coordination while Hg4 exhibits a coordination environment similar to Hg2. The data reported in
Table S3 (Supplementary information) show comparable values for the Hg-N(imino) and Hg-
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N(py) bond distances involving the Schiff base, of 2.183(19)- 2.24(2) Å and 2.41(2)- 2.48(2) Å,
respectively, and the Hg-O bond lengths are in the range 2.353(14)-2.477(13) Å. The variation is
likely due to the distortions observed in the dinuclear units and to the different coordination
geometry of the metals. Among the Hg-S bond length values the Hg(2)-S(3), of 2.608(8) Å,
relative to the bridging thiocyanate is the longest, while the others fall in between 2.379(8)-
2.586(7) Å, and all the anions show a comparable C-S-Hg coordination bond angle of 99.5°
(mean value).
In the dinuclear units the metals are separated by 4.108(1) and 4.044(1) Å and are
considerably displaced with respect to the phenolato mean ring by 0.91(1)/ –1.53(1) and 1.59(1)/
–0.75(1) Å. Fig. S13 (Supplementary information) depicts the 1D coordination polymer
formed by the Hg1/Hg2 units connected by the bridging SCN and the crystal packing
arrangement of the Hg3/Hg4 complexes. The Hg3-N15' of 2.94(4) Å is a distance lower than the
sum of van der Waals radii for the atoms and does not exclude an interaction, thus out lining a
chain similar to that of (Hg1/Hg2)n(Fig. S13, Supplementary information). Both these
polymeric arrangements develop around a crystallographic two-fold screw axis. At our
knowledge this is the first example of a structurally characterized complex with bi-
compartmental ligand containing mercury.
The results show N-bonded thiocyanate in Zn2+ complex, while a preference for S-bonded
in 2 and 3 is in accord with the soft acid character of Cd2+ and Hg2+ ions. Making allowance for
the different coordination geometry and different ligands, these complexes show an increasing
metal-metal distance inside the Schiff base (from 3.277 Å (Zn), 3.717 Å (Cd) to 4.108 and 4.044
Å (Hg), and concomitant increasing displacement with respect to the phenol ring (Fig. S14,
Supplementary information). Both features appear mainly due to the increasing size of the ion,
although crystal packing (polymer formation in Cd and Hg derivatives) is not being excluded to
play a role.
2.3. Photophysical study of the ligand(LH) and the complexes(1-3)
2.3.1. Absorption spectra
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The absorption spectra of the free ligand (LH) and the complexes 1, 2 and 3 in three
different solvents methanol (MeOH), dichloromethane (DCM) and acetonitrile (ACN) at 298K
are shown in Fig. 5. The ligand shows three distinct bands around 445, 343 and 242 nm (Table
1). The band at 343 nm is weaker in MeOH compared with that in ACN and DCM (Fig. 5). The
band positions are practically same in all the three solvents having widely different polarity
supporting the π-π* nature of the transitions. Further proof for the π-π* nature of transitions is
obtained from the time resolved emission studies.
The complexes 1 and 2 exhibit similar absorption spectra in ACN (Fig. 5, Table 1). The
lowest energy band of the ligand observed at 445 nm is shifted to 380 nm for the complexes. The
complex 1 exhibits almost similar spectra in all the three solvents although in ACN, a vibrational
band is apparent around 425 nm. The complex 2, however, exhibits prominent vibrational
structure at 430 nm in DCM and MeOH. In the complex 3, the lowest energy band appears
around 420 nm in DCM and ACN (Fig. 5, Table 1). The complex 3, exhibits a slight red shift for
the lowest energy band in MeOH. The band at 343 nm observed for the ligand is found to be
shifted towards blue and is masked by the most intense band around 256 nm in the complexes 1
and 2. In the complex 3, this band is discernible and is found to appear prominently in MeOH.
The absorption spectra of the complexes transparent KBr pellet are shown in Fig.
S15(Supplementary information).
2.3.2. Steady state and time resolved emission spectra
The emission spectra of the ligand and the complexes 1-3 in acetonitrile and in solid state
(transparent KBr pellet) at 298K are shown in Fig. 6. The excitation is made at the lowest
energy absorption band in each case. The ligand emits strongly peaking around 500 nm in
acetonitrile; the complexes 1 and 2 exhibit blue shifted emission compared with that of the
ligand. The complex 2 shows quenched emission compared to the complex 1 (Table 2). The
complex 3 emits very weakly in the same region as that of the ligand (Fig. 6A). The observed
quenching is predicted to be due to heavy atom effect. In the solid state (KBr pellet) the emission
maxima of the complexes are shifted to the red compared to that observed in solution (Fig. 6B,
Table 1)
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The free ligand exhibits a single component (3.8 ns) in the fluorescence decay (Fig. 7A).
In each of the complexes the fluorescence decay is found to fit with two components (Fig. 7 B).
The average lifetime for the complexes is in accordance with the quenched emission. The
lifetime values clearly suggest the π-π* nature of the emission in all the cases [47,48].
2.3.3. Phosphorescence spectra at 77K
The ligand and the complexes 1-3 exhibit phosphorescence spectra in DCM-MeOH
glassy matrix at 77K (Fig. 8). The ligand phosphorescence is found to be very weak. The
complexes exhibit much enhanced phosphorescence compared to that of the ligand due to larger
population of the triplet state induced by the heavy atom effect. The complex 2 exhibits
enhanced phosphorescence compared to the complex 1 due to heavy atom effect. Table 2 shows
the relative fluorescence quantum yield values along with phosphorescence quantum yield values
confirming the participation of heavy atom effect. The lifetime values of phosphorescence
suggest the π-π* nature of the lowest triplet states (Table 1). The phosphorescence spectra of 1
and 2 also show vibronic structure (Fig. 8).
2.4. Phosphatase like activity
Our synthesized complexes have the capability to cleavage 4-NPP. The kinetic study of
catalytic efficiency to cleave P–O bond of 4-NPP was performed by following the procedure
described in experimental section. Wavelength scan during phosphatase like activity of
complexes 1-3 are represented in Fig. 9 and Fig. S16-S17 (Supplementary information). The
Zn and Cd complexes showed very good activity whereas Hg complex formed an adduct during
catalysis and hence kinetic study was not performed further. As can be observed for Zn and Cd
complexes, the reaction followed a first order kinetics at lower concentration and gradually
differs from unity at higher concentration. The kinetic parameters (Vmax, KM, kcat) for the
catalyzed reactions were determined from the linear plots of 1/kobs versus 1/[4-NPP] values
(Lineweaver–Burk plot) assuming the Michaelis–Menten approach of enzymatic kinetics. The
results remained the same when the experiment was accomplished by varying the complex
concentration and maintaining the [4-NPP] constant during the experiment. All the kinetic
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parameters are given in Table 3 and kinetic plots are provided in Fig. S18-21 (Supplementary
information). Analysis of the experimental data yielded Michaelis binding constant (KM) values
of 1.63 × 10-3 M for 1 and 2.09 × 10-3 M for 2, and Vmax values of 8.5 × 10-6 and 7.59 × 10-6 Ms-1
for 1 and 2, respectively. The turnover number (Kcat) value is obtained by dividing the Vmax by
the concentration of the complex used, and is found to be 17.01 ×10-2 and 11.58 × 10-2 s-1 for 1
and 2, respectively. The spontaneous hydrolysis rate of 4-NPP was too low to be taken into
account in the kinetic measurements. Therefore, the general rate of spontaneous hydrolysis was
not separately determined. Table 4 represents the rate constants (kcat) for the hydrolysis of
various phosphate esters by previously reported zinc complexes [49]. Comparing the Tables 3
and 4, it is evident that both the complexes 1 and 2 belong to high catalytically active group
towards hydrolysis of 4-NPP and the activity is higher for 1. To find out the possible
intermediates during catalysis, the ESI-MS positive spectra were recorded. The ESI-MS positive
spectrum of complex 1 in DMSO-H2O medium has base peak at m/z = 697.53 corresponds to the
[LZn2(SCN)2(H2O)2]+. The ESI-MS positive spectrum of complex 1(as representative) and 4-
NPP (1: 50 mixture) in DMSO-H2O was recorded after 15 minutes of mixing, and the spectrum
is depicted in Fig. S22 (Supplementary information). A major peak at m/z = 843.13 is
II
attributed as 1:1 complex-substrate adduct, namely [L-Zn2 (OH)+ 4-NPP+ Na+]+, which may be
the active intermediate through which the hydrolysis was occurred. However, the base peak
observed at m/z = 162.10 can be assigned to the sodium adduct of 4-nitrophenol. With the help
of some relevant references [49b,50] and the ESI-MS spectral data, we have proposed a plausible
mechanistic pathway of phosphatase like activity of complex 1 (Fig. 10).
3. Conclusions
The fifty years old HSAB principle becomes the guiding line of structural diversity in
coordination complexes of d10 metal systems demonstrate in the present work. We have
investigated the reaction of ligand, 4-tert-butyl-2,6-bis-[(2-pyridin-2-yl-ethylimino)-methyl]-
phenol (LH) with group 12 metal ions (ZnII, CdII, HgII) followed by addition of NaSCN. This
provided three structurally diverse complexes and the X-ray structural analyses indicate the
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different coordination ability of SCN in the metal group, from nitrogen donor (isothiocyanate)
with zinc(II) to sulfur (thiocyanate) with mercury(II) ions. Zinc complex is dinuclear whereas
cadmium and mercury complexes are polymeric in nature due to the bridging coordination mode
of SCN. Photophysical properties of ligand and of complexes have been studied exclusively. π-π*
transition for all the complexes and the ligand are further confirmed by life time calculation. The
ligand is fluorescent, but the fluorescence intensity increases upon complexation with zinc, most
probably due to the increasing rigidity of the molecule. But for cadmium and mercury complexes
the florescence intensity decreases, may be for heavy metal effect. ZnII and CdII complexes are
capable to hydrolyze p-nitrophenyl phosphate in DMSO-H2O medium, while HgII complex
results inactive toward Phosphatase like activity, most probably due to the least Lewis acidity of
this metal.
4. Experimental section
4.1. Physical methods and materials
Elemental analyses (carbon, hydrogen and nitrogen) were performed using a Perkin-
Elmer 240C elemental analyzer. Infrared spectra (4000–500cm-1) were recorded at 27 °C using a
1
13
Perkin-Elmer RXI FT-IR spectrophotometer with KBr pellets. H and C NMR spectra (300
MHz) were recorded in CDCl3 solvent at 298 K on a Bruker AC 300 NMR spectrometer using
the solvent signal as the internal standard in a 5mm BBO probe. All chemicals were obtained
from commercial sources and used as received. Solvents were dried according to standard
procedure and distilled prior to use.
4.2. Syntheses
4.2.1. Synthesis of ligand [LH]
A methanolic solution (10 mL) of 2-(2-aminoethyl)pyridine (0.488 g, 4mmol) was added
drop wise to a hot methanolic (40 mL) solution of 4-tert-butyl-2,6-diformyl-phenol (0.412 g, 2
mmol) and the resulting solution was refluxed for 30 minutes and allowed to cool. Then the
solution was evaporated obtaining a yellow sticky mass which was further purified with ether-
water mixture. Yield 85%.C, 75.36; H, 7.24; N, 13.52; Found: C, 75.28; H, 7.18; N, 13.48.1H-
NMR (300MHz, CDCl3) : 6.990-7.090(2H, m, Ar-H), 8.442-8.456 (1H, s, -CH=N-), 7.450-
7.496(4H, s, Pyridine-H), 3.055-3.102 and 3.899-3.945(4H, two t, -N-CH2-CH2-N-),1.122-1.212
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(9H, s, -C(CH3)3).13C NMR (300 MHz, CDCl3): 165.59 (−CH=N−),159.95 (Ar−C−OH),
121.36−149.41 (Ar−C and Py-C), 39.48 and 60.05(N−CH2−CH2−N), 29.67-34.08
(−C(CH3)3)UV λmax (CH3CN)/nm445, 343, 242 (ε/dm3mol-1cm-1 1028, 2968,15212).
4.2.2. Synthesis of [Zn2(L)(SCN)3](1)
A methanolic solution (5 mL) of 2-(2-aminoethyl)pyridine (0.244 g, 2 mmol) was added
drop wise to a hot methanolic (20 mL) solution of 4-tert-Butyl-2,6-bis-[(2-pyridin-2-yl-
ethylimino)-methyl]-phenol (0.206 g, 1 mmol) and the resulting mixture was refluxed for half an
hour. Then, a methanolic solution (10 mL) of zinc(II)acetate hexahydrate (0.437 g, 2 mmol) was
added under continuous refluxing condition for 30 minutes. Then solution was cooled and an
aqueous solution (5 mL) of sodium thiocyanate (0.244 g, 3 mmol) was added to it. A yellow
precipitate, deposited after 15 minutes was dissolved in dry acetonitrile and the solution filtered.
After few days yellow single crystals of complex 1 suitable for X-ray analysis were obtained
from the filtrate. Yield 62%. C, 48.97; H, 4.24; N, 14.74; Found: C, 48.90; H, 4.18; N, 14.64. 1H-
NMR (300MHz, d6-DMSO): 8.497-8.962 (1H, m, -CH=N-), 7.297-8.040(2H, m, Ar-H and 4H, s,
Pyridine-H), 2.873-3.159 and 3.962(4H, two t, N-CH2-CH2-N),1.289 (9H, s, -C(CH3)3).IR:
(SCN) = 2010, 2081 cm-1, (C=N) = 1645 cm-1, (skeletal vibration) = 1556 cm-1. UV
λmax(CH3CN)/nm 380, 257 (ε/dm3mol-1cm-1 2509, 13583 ).
4.2.3. Synthesis of [Cd2.5(L)(SCN)3(AcO)]n(2)
Complex 2 was prepared following the same procedure as for 1 where cadmium(II)
acetate dihydrate (0.665 g, 2.5 mmol) was used in place of zinc(II) salt. Resulting solution was
filtered and yellow single crystals of complex 2 grew in the resulting solution after one weak.
Yield 67%. C, 40.09; H, 3.47; N, 10.56; Found: C, 40.01; H, 3.38; N, 10.54. 1H-NMR (300MHz,
d6-DMSO): 8.444-8.578 (1H, m, -CH=N), 7.495-7.718 (2H, m, Ar-H), 7.917(4H, s, Pyridine-H),
3.144-3.162 and 3.887-4.148(4H, two t, -N-CH2-CH2-N-),1.166-1.856 (9H, m, -C(CH3)3). IR:
(SCN) = 2007, 2073, 2116 cm-1, (C=N) = 1639 cm-1, (skeletal vibration) = 1569 cm-1. UV
λmax(CH3CN)/nm 381, 256 (ε/dm3mol-1cm-1 2178, 9224).
4.2.4. Synthesis of [Hg2(L)(SCN)3]n(3)
Complex 3 was prepared similarly as 1, with mercury(II) acetate (0.636 g, 2 mmol)
instead of zinc(II) salt. Light yellow block shaped single crystals suitable for X-ray diffraction
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was obtained on overnight standing. The crystals were isolated by filtration and air dried. Yield
1
72%. C, 35.19; H, 2.95; N, 9.91; Found: C, 35.13; H, 2.88; N, 9.84. H-NMR (300MHz, d6-
DMSO): 8.290-8.557(1H, m, -CH=N-), 7.174-7.796(2H, m, Ar-H and 4H, s, Pyridine-H), 2.642-
3.168 and 4.058(4H, one multiplet and one singlet, -N-CH2-CH2-N-),1.139 (9H, s, -C(CH3)3).
IR: (SCN) = 2088, 2118 cm-1, (C=N) = 1630 cm-1, (skeletal vibration) = 1529 cm-1. UV
λmax(CH3CN)/nm 419, 255 (ε/dm3mol-1cm-1 2026, 10095).
4.3. Crystal structure determination
Intensities data for crystal structure analyses of compounds 1−3 were collected on a
Bruker Smart Apex diffractometer equipped with CCD. In all cases measurements were
conducted at room temperature with Mo Kα radiation (λ = 0.71073 Å). Cell refinement,
indexing, and scaling of the data sets were done using the programs Bruker Smart Apex, and
Bruker Saint packages[51]. All structures were solved by direct methods and subsequent Fourier
analyses [52] and refined by the full-matrix least-squares method based on F2 with all observed
reflections[52]. Likely due to the quality of the crystal of 3, unreliable thermal ellipsoids were
obtained for the carbon atoms, which were isotropically refined. The t-butyl group of 1 was
found disordered over two positions (refined occupancies of 0.48(1)/0.52(1)). In addition the ΔF
maps of 1 revealed the presence of a lattice CH3CN molecule. Hydrogen atoms were placed at
calculated positions and included in final cycles of refinement. All calculations were performed
using the WinGX System, Ver 1.80.05 [53]. Crystal data and details of refinements are given in
Table S4(Supplementary information).
4.4. Photophysical properties
UV−Vis absorption spectra were recorded on a Hitachi U-4010 spectrophotometer at 298
K. The steady state emission measurements were carried out using a Hitachi Model F-7000
spectrofluorimeter equipped with a 150 W xenon lamp, at 298 K using a stopper cell of 1 cm
path length. Emission studies were performed using a Dewar system having a 5 mm OD quartz
tube and freezing of all the samples to 77 K was achieved at the same rate. Phosphorescence
spectra were recorded with a Hitachi Model F-7000 spectrofluorimeter equipped with
phosphorescence accessories at 77 K.
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Fluorescence quantum yield () was determined in each case by comparing the corrected
emission spectrum of the samples with that of anthracene in MeOH ( 0.20) [54] using equation
(1),[55] taking into account the total area under the emission curve.
n2
n2
F ODR
Q = QR
(1)
OD
FR
R
Where Q is the quantum yield of the compounds, F is the integrated fluorescence
intensity (area under the emission curve), OD is the optical density, and n is the refractive index
of the medium. It is assumed that the reference and the unknown samples are excited at the same
wavelength (360 nm). The subscript R refers to the reference fluorophore (anthracene in this
case) of known quantum yield. The standard quantum yield value was used for the calculation of
radiative and non-radiative rate constants of the system.
Singlet state lifetimes were measured by a Time Master Fluorimeter from Photon
Technology International (PTI, USA). The system consists of a pulsed laser driver PDL-800-B
with interchangeable sub-nanosecond pulsed LEDs and pico-diode lasers (PicoQuant, Germany)
with a TCSPC set-up (PTI, USA). The lifetimes of the free ligand and complexes were measured
by using a diode laser LDH-405 (pulse width 200 ps) and PLS-370 (pulse width 600 ps) from
PicoQuant, Germany, at a repetition frequency of 10 MHz. Instrument response functions (IRF)
were measured at the respective excitation wavelengths of 370 nm (for LED source) and 405 nm
(for diode laser) using slits with a band pass of 1-3 nm using Ludox silica as scatterer. Intensity
decay curves were fitted as summation of exponential terms:
F (t) = iexp(-t/i)
The decay parameters were recovered using a non-linear iterative fitting procedure based on the
Marquardt algorithm[56]. A deconvolution technique was used to determine the lifetime up to
150-200 ps with LED, while the time resolution was 100 ps with diode laser. The quality of fit
has been assessed over the entire decay, including the rising edge, and tested with a plot of
weighted residuals and other statistical parameters e.g., the reduced χ2 ratio and the Durbin–
Watson (DW) parameters[57].
The decay times of the three complexes in milli-seconds or longer range were also
acquired by phosphorescence time-based acquisition mode in which emission intensity was
measured as a function of time in the QM-30 fluorimeter (PTI, USA) using a gated detection
15

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system with start and end window time of 200 and 2000 s, respectively. The decay parameters
were recovered using a non-linear iterative fitting procedure based on the Marquardt algorithm
[57].
4.5. Phoshphatase like activity and kinetics studies
Kinetic measurements of (4-nitrophenyl)phosphate (4-NPP) hydrolysis were performed
by using similar procedure as reported earlier [49e,49f,58]. Disodium 4-NPP hexahydrate was
used as the substrate and 97.5% (v/v) DMSO-H2O medium was taken for the catalysis. The
solutions of substrate 4-NPP and complexes in the mixed solvent were freshly prepared, and the
total volume of the reaction mixture was maintained as 2 mL. An initial screening of the
hydrolytic tendencies of all the metal complexes was performed till 2% formation of p-
nitrophenolate (2h) and then their kinetic data were determined. The hydrolysis rate of 4-NPP
in the presence of complexes were measured by an initial rate method following the increase in
the 441 nm absorption due to the released 4-nitrophenolate ion in aqueous DMSO (ε, 18500 M−1
cm−1) at 30 °C. For wavelength scan, spectra were recorded from a solution having 1 mmol 4-
NPP and 0.05 mmol complex for 2 h. Kinetic experiments were done with excess of substrate
and excess of complex keeping the other constant. Herein we report only the former data. The
study comprised 5 sets with the catalyst concentration of 0.05 mmol and substrate of 0.5 (10
equiv), 0.7 (14 equiv), 1.0 (20 equiv), 1.2 (24 equiv) and 1.5 (30 equiv) mmol. The reactions
were initiated by injecting 0.04 mL of complex (2.5 × 10−3 M) into 1.96 mL of 4-NPP solution,
and the spectrum was recorded only after fully mixing at 30 °C. The visible absorption increase
was recorded in a time span of 30 min at intervals of 5 min. All measurements were performed in
triplicate, and the average values were adopted. The reactions were corrected for the degree of
ionization of 4-nitrophenol at 30 °C using the molar extinction coefficient for the 4-
nitrophenolate at 441 nm. The final A∞ values for each set were obtained after 2 days at 30 °C.
Acknowledgements
We are thankful to University Grants Commission (UGC), New Delhi, India, for the Senior
Research Fellowship to J.A[UGC/197/Jr. Fellow (enhancement) dated 26.02.2013].
Appendix A. Supplementary data
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CCDC 1025963-1025965 contains the supplementary crystallographic data for the complexes 1-
3 reported in this paper. These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www. ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found in the online version, at doi:
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References
[1] P. Comba, T.W. Hambley, B. Martin, Molecular Modeling of Inorganic Compounds, 3rd
ed., Wiley-VCH, Wienheim, (2009).
[2] J.N. Lalena, D.A. Cleary, Principles of Inorganic Materials Design, second ed., John Wiley
& Sons Inc., Hoboken, New Jersey, (2010).
[3] C. Janiak, Coord. Chem. Rev. 250 (2006) 66.
[4] G.A. Hembury, V.V. Borovkov, Y. Inoue, Chem. Rev. 108 (2008) 1.
[5] P. Jiang, Z. Guo, Coord. Chem. Rev. 248 (2004) 205.
[6] W. Huang, H.-B. Zhu, S.-H. Gou, Coord. Chem. Rev. 250 (2006) 414.
[7] H. Zhang, X. Wang, K. Zhang, B.K. Teo, Coord. Chem. Rev. 183 (1999) 157.
[8] H. Deng, Y.-C. Qiu, Y.-H. Li, Z.-H. Liu, R.-H. Zeng, M. Zeller, S.R. Batten, Chem.
Commun. (2008) 2239.
[9] A. Morsali, M.Y. Masoomi, Coord. Chem. Rev. 253 (2009) 1882.
[10] G. Mahmoudi, A. Morsali, M. Zeller, Inorg. Chim. Acta 362 (2009) 217.
[11] V. Balzani, A. Credi, M. Venturi, Molecular Devices and Machines, Wiley-
VCH,Weinheim, (2003).
[12] M. Petty, Molecular Electronics: From Principles to Practice, Wiley, Chichester, (2008).
[13] J. Otsuky, T. Akasaka, K. Araki, Coord. Chem. Rev. 252 (2008) 32.
[14] B. Mohapatra, S. Verma, Cryst. Growth Des. 13 (2013) 2716.
[15] W. Yang, C. Wang, Q. Ma, C. Liu, H. Wang,J. Jiang, Cryst. Eng. Comm. 16 (2014) 4554.
[16] O.M. Yaghi, M. O’Keeffe, M. Kanatzidis, J. Solid State Chem. 152 (2000) 1.
[17] J.W. Steed, J.L. Atwood, Supramolecular Chemistry, second ed., John Wiley &Sons, New
York, (2009).
[18] S.T. Hyde, B. Ninham, S. Anderson, Z. Blum, T. Landh, K. Larsson, S. Liddin, The
Language of Shape, Elsevier, Amsterdam, (1997).
[19] P.J. Steel, Acc. Chem. Res. 38 (2005) 243.
[20] G.R. Desiraju (Ed.), Crystal Design: Structures and Function, Perspectives in
Supramolecular Chemistry, vol. 7, John Wiley & Sons, Chichester, (2003).
[21] M.J. Zaworotko, Cryst. Growth Des. 7 (2007) 4.
[22] D. Natale, J.C. Mareque-Rivas, Chem. Commun. (2008) 425.
[23] P. Jiang, Z. Guo, Coord. Chem. Rev. 248 (2004) 205.
18

ACCEPTED MANUSCRIPT
[24] (a) C.H. Hung, G.F. Chang, A. Kumar, G.F. Lin, L.Y. Luo, W. M. Ching, E. W.G. Diau,
Chem. Commun. (2008) 978. (b) J.-F. Zhu, H. Yuan, W.H. Chan, A. W. M. Lee, Org.
Biomol. Chem. (2010) 3957. (c) G. Buncic, P. S. Donnelly, B. M. Paterson, J. M. White,
M. Zimmermann, Z. Xiao, A.G. Wedd, Inorg. Chem. 49 (2010) 3071.(d) H.Chen, Y. Wu,
Y. Cheng, H. Yang, F. Li, P. Yang, C.Huang, Inorg. Chem. Commun. 10 (2007) 1413. (e)
S. Mizukami, S. Okada, S. Kimura, K.Kikuchi, Inorg. Chem. 48 (2009) 7630. (f) K.
Kikuchi, K. Komatsu, T.Nagano, Curr. Opin. Chem. Biol. 8 (2004) 182.(g) E. Kimura,
S.Aoki, BioMetals 14 (2001) 191.(h) J.H. Hu, J.B. Li, J. Qi, J.J. Chen, New J. Chem. 39
(2015) 843.
[25] (a) K. Komatsu, K. Kikuchi, H. Kojima, Y. Urano, T.Nagano, J. Am. Chem. Soc. 127
(2005) 10197. (b) T. Hirano, K.Kikuchi, Y. Urano, T.Nagano, J. Am. Chem. Soc. 124
(2002) 6555. (c) T. Hirano,K. Kikuchi, Y. Urano, T. Higuchi, T. Nagano, J. Am. Chem.
Soc. 122 (2000) 12399. (d) S. Maruyama, K. Kikuchi, T. Hirano, Y. Urano,T.Nagano, J.
Am. Chem. Soc. 124 (2002) 10650. (e) T. Hirano, K. Kikuchi, Y. Urano, T. Higuchi, T.
Nagano, Angew. Chem., Int. Ed., 39 (2000) 1052. (f) K. Hanaka, K. Kikuchi, H. Kojima,
Y. Urano, T. Nagano, J. Am. Chem. Soc. 126 (2004) 12470. (g) Y. Zhao, Z. Lin, C. He, H.
Wu,. C.Duan, Inorg. Chem. 45 (2006) 10013.
[26] (a) Y. Mikata, M. Wakamatsu, A. Kawamura, N. Yamanaka, S. Yano, A. Odani, K.
Morihiro, S. Tamotsu, Inorg. Chem. 45 (2006) 9262. (b) X.A. Zhang, K. S. Lovejoy, A.
Jasanoff, S. J. Lippard, Proc. Natl. Acad. Sci. 104 (2007) 10780. (c) Z.c. Liu, B.d. Wang,
Z-y. Yang, T-r. Li, Y. Li,Inorg. Chem. Commun. 13 (2010) 606. (d) J.F. Zhu, H. Yuan,
W.H.Chan, A. W. M. Lee, Org. Biomol. Chem. 8 (2010) 3957. (e) Y. Mikata, A.
Yamanaka, A. Yamashita, S. Yano, Inorg. Chem. 47 (2008) 7295. (f) A. Sarkar, A. K.
Ghosh, V. Bertolasi, D. Ray, Dalton Trans. 41 (2012) 1889. (g) X. Peng, X. Tang, W. Qin,
W. Dou, Y. Gou, J. Zheng, W. Liu, D. Wang, Dalton Trans. 40 (2011) 5271. (h) Y. Wu, X.
Peng, B. Guo, J. Fan, Z. Zhang, J. Wang, A. Cui, Y. Gao, Org. Biomol. Chem. 3 (2005)
1387. (i) U. C. Saha, B. Chattopadhyay, K. Dhara, S. K. Mandal, S. Sarkar, A. R. Khuda-
Bukhsh, M.Mukherjee, M. Helliwell, P. Chattopadhyay, Inorg. Chem. 50 (2011) 1213. (j)
H. Sasaki, K. Hanaoka, Y. Urano, T. Terai, T. Nagano, Biorg. Med. Chem. 19 (2011)
1072. (k) S. Majumder, L. Mandal, S. Mohanta, Inorg. Chem. 51 (2012) 8739.
[27] C. P. Pradeep, S. K. Das, Coord. Chem. Rev. 257 (2013)1699.
19

ACCEPTED MANUSCRIPT
[28] P.A. Vigato, S. Tamburini, L. Bertolo, Coord. Chem. Rev. 251 (2007) 1311.
[29] J. Adhikary, P. Kundu, S. Dasgupta, S. Mukherjee, S. Chattopadhyay, G.Aullón,D. Das,
Polyhedron 101 (2015) 93.
[30] A.M. Golub, H. Kohler, V.V. Skopenko (Eds.), Chemistry of Pseudohalides,Elsevier,
Amsterdam, (1986).
[31] D.A. Buckingham, Coord. Chem. Rev. 135–136 (1994) 587.
[32] M. Dakovic, Z. Popovic, G. Giester, M. Rajic-Linaric, Polyhedron 27 (2008) 465.
[33] Y. Bai, W.-L. Shang, D.-B. Dang, H. Gao, X.-F. Niu, Y.-F. Guan, Inorg. Chem. Commun.
11 (2008) 1470.
[34] T. Ghosh, J. Adhikary, P. Chakraborty, P.K. Sukul, M.S. Jana, T.K. Mondal, E.
Zangrando, D. Das, Dalton Trans. 43 (2014) 841.
[35] R. G. Pearson, J. Am. Chem. Soc. 85 (1963) 3533.
[36] M. Jarenmark, E. Csapo, J. Singh, S. Wockel, E. Farkas, F. Meyer, M. Haukka, E.
Nordlander, Dalton Trans. 39 (2010) 8183.
[37] G. Schenk, N. Mitiꢀ, G. Hanson, P. Comba, Coord. Chem. Rev. 257 (2013) 473.
[38] L. J. Daumann, L. R. Gahan, P. Comba, G. Schenk, Inorg. Chem. 51 (2012) 7669.
[39] P. Bhowmik, S. Chattopadhyay, M. G.B. Drew, C. Diaz, A. Ghosh, Polyhedron 29 (2010)
2637.
[40] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, vol.
3, Wiley, New York, (1978) pp. 270–274.
[41] S. Chattopadhyay, M.G.B. Drew, C. Diaz, A. Ghosh, Dalton Trans. (2007) 2492.
[42] (a) P. Maiti, A. Khan, T. Chattopadhyay, S. Das, K. Manna, D. Bose, S. Dey, E.
Zangrando, D. Das, J. Coord. Chem. 64 (2011) 3817–3831. (b) P. Chakraborty, J.
Adhikary, S.Samanta, I. Majumder, C.Massera, D. Escudero, S. Ghosh,A. Bauza, A.
Frontera, D. Das, Dalton Trans. 44 (2015) 20032.
[43] K. Abe, J. Izumi, M. Ohba, T. Yokoyama, H. Okawa, Bull. Chem. Soc. Jpn.74(2001)85.
[44] (a) J-C. Jiang, Z-L. Chu, W. Huang, G. Wang,X-Z. You, Inorg.Chem. 49 (2010) 5897. (b)
P.Roy, J. Coord. Chem. 62 (2009) 2003.
[45] (a) Z.-L. You, Q.-Z. Jiao, S.-Y. Niu, and J.-Y. Chi, Z. Anorg. Allg. Chem. 632(2006) 2486.
(b) S. Roy, S. Chattopadhyay, Inorg. Chim. Acta 433 (2015) 72. (c) S. Roy, K. Harms, S.
20

ACCEPTED MANUSCRIPT
Chattopadhyay, doi.org/10.1016/j.poly.2016.10.008. (d) Z.-L. You, H.-L. Zhu, Acta Cryst.
C61 (2005) m397.
[46] A. Sarkar, V. Bertolasi, D. Ray, Polyhedron 44 (2012) 113.
[47] Lakowicz, J.R. (Eds.) “Principles of Fluorescence Spectroscopy”, 3rd Edition, Kluwer
Academic/ Plenum Publishers: New York, (2003).
[48] Nicholas Turro, “Modern Molecular Photochemistry of Organic Molecules”,
UniversityScience Books, Sausalito, California (2010) 1110 pp.
[49] (a)L. J. Daumann, L. Marty, G. Schenk and L. R. Gahan, Dalton Trans. 42 (2013) 9574.(b)
S. Bosch, P.Comba, L. R. Gahan, and G. Schenk, Inorg. Chem. 53 (2014) 9036. (c)
S.Anbu, S.Kamalraj, B. Varghese, J.Muthumary, and M.Kandaswamy, Inorg. Chem. 51
(2012) 5580. (d) H. Arora, S.K. Barman, F.Lloret, and R.N. Mukherjee, Inorg. Chem. 51
(2012) 5539. (e) R. Sanyal, X. Zhang, P. Kundu, T. Chattopadhyay, C. Zhao, F. A.
Mautner, D. Das, Inorg. Chem. 54 (2015) 2315. (f) P. Chakraborty, J. Adhikary, R. Sanyal,
A. Khan, K. Manna, S. Dey, E.Zangrando, A. Bauzá, A. Frontera, D. Das, Inorg. Chim.
Acta 421 (2014) 364.
[50] (a) V. K. Bhardwaj, A. Singh, Inorg. Chem. 53 (2014) 10731. (b) R. E. H. M. B. Osꢁrio, R.
A. Peralta, A. J. Bortoluzzi, V. R. de Almeida, B. Szpoganicz, F. L. Fischer, H. Terenzi, A.
S. Mangrich, K. M. Mantovani, D. E. C. Ferreira, W. R. Rocha, W. Haase, Z. Tomkowicz,
A. Anjos, A. Neves, Inorg. Chem. 51 (2012) 1569.
[51] Bruker, SMART, SAINT. Software Reference Manual Bruker AXS Inc. Madison,
Wisconsin, USA, (2000).
[52] G. M. Sheldrick, Acta. Crystallogr. Sect A. 64 (2008) 112.
[53] L. J. Farrugia, J. Appl. Crystallogr. 45 (2012) 849.
[54] P. Hrdlovic, J.Donovalova, H. Stankovicova, A.Gaplovsky, Molecules 15 (2010) 8915.
[55] J.R. Lakowicz, Principles of Fluorescence Spectroscopy, 2nd ed.;Kluwer Academic/
Plenum Publishers: New York, (1999).
[56] P. R. Bevington, Data Reduction and Error Analysis for the Physical Sciences; McGraw
Hill: New York, (1969) pp 235−237.
[57] (a) FELIX 32, version 1.1; Photon Technology International, Inc.: Edison, NJ, (2003). (b)
FELIX GX, version 2.0.1; Photon Technology International, Inc.: Edison, NJ, (2003).
21

ACCEPTED MANUSCRIPT
[58] R. Sanyal, A. Guha, T. Ghosh, T.K. Mondal, E. Zangrando, D. Das, Inorg. Chem. 53
(2014) 85.
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Table 1 Absorption, fluorescence and phosphorescence data of the free ligand and of complexes
1-3 in acetonitrile and in solid state (KBr medium).
System
Fluorescence
흀(풎푭풂)풙 (nm)
Singlet state lifetimes monitoring the Phosphorescence
emission maxima in ACN and in solid data in 1:1 (v/v)
Absorption
흀(풎푨풂)풙 (nm)
state (KBr Pellet)
(For free Ligand λex-470 nm & for glassy matrix at
complexes λex-405 nm) 77K
DCM-MeOH
[(M-1cm-1)]
χ2
흀(풎푷풂)풙
In MeCN
In Solid
State
In
MeCN
In Solid
State
τp(s)
τ 1(ns)
τ2 (ns)
<τ> (ns)
[<τ> in Solid
(nm)
State]
445 [1028],
343 [2968],
242 [15212]
3.80
1.2
568
0.01
Ligand
-
495
450
-
-
-
380 [2509],
257 [13583]
2.74
0.66
0.82
1.0
473
0.22
Complex 1
388,
261
498
(7.3%)
(92.7%)
[1.96]
[1.0]
381 [2178],
256 [9224]
440
500
1.62
0.31
0.56
1.0
485
550
0.30
0.03
Complex 2
Complex 3
387,
259
501
537
(19.4%)
(80.6%)
[1.03]
[1.0]
419 [2026],
255 [10095]
4.30
0.24
0.37
1.0
438,
257
(3.4%)
(96.6%)
[0.65]
[1.0]
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Table 2 Fluorescence and phosphorescence quantum yield ratio.
Fluorescence quantum yield ratio
Phosphorescence quantum yield ratio
MeOH
DCM
ACN
1:1 (v/v) DCM –
MeOH
2.9
8.8
1.8
6.7
2.3
8.9
1.3
I/II
II/I
49.8
L/III
III/L
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Table 3 Kinetic parameters of complex 1 and 2 for the hydrolysis of 4-NPP.
Catalyst
Vmax (Ms-1)
KM(M)
kcat (s-1)
8.5010-6
1.6310-3
17.0110-2
1
2
5.7910-6
2.0910-3
11.5810-2
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Table 4 Rate constants (kcat) for the hydrolysis of various phosphate esters by previously reported zinc complexes.
Catalysta
Substrateb
Condition
kcat(s-1)
Ref.year
46a2013
46b2014
46c2012
46d2012
46e2015
46f2014
0.9710-3
5.08× 10−3
2.82 × 10−2
3.4410-4
9.97
1) [Zn2(CH3L5)-(CH3COO)2]BPh4
2) [Zn2(L1)(OAc)2]+
2,4-BDNPP acetonitrile–water (2.5% (v/v)), pH 7.6,25°C
2,4-BDNPP 1:1 acetonitrile/buffer, pH 8.5, 25°C
3) [Zn2L3(H2O)2](ClO4)2(H2O)3
4)[Zn2(L2)(μ-O2CMe)2(MeCN)2][PF6]
5)[Zn2L2Cl2]
4-NPP
HPNP
4-NPP
4-NPP
acetonitrile–water (2.5% (v/v), pH 6.8,25°C
methanol–water (33% (v/v)), pH 8.5, 30°C
97.5% DMF, 25°C
6) [Zn3L1(OAc)4]
MeOH–water (7:3, v/v) at 25 °C
7.11 × 10−2
a
(1)
CH3HL5
=
2-(((2-methoxyethyl)(pyridine-2-ylmethyl)amino)-methyl)-4-methyl-6-(((pyridin-2-ylmethyl)(4-
vinylbenzyl)amino)methyl)phenol); (2) HL1=2,6-bis{[bis(pyridin-2-ylmethyl)amino]methyl}-4-methylphenol (3) L3= 11,24-
Dimethyl-16,19-dioxa-3,7,15,20-tetraaza-tricyclo[20.3.1.19,13]heptacosa-1(26),2,7,9(27),10,12,14,20,22,24-decaene-26,27-diol;
(4)
H2L2= 4-Methyl-2,6-bis-(3-pyridin-2-yl-pyrazol-1-ylmethyl)-phenol; (5) L= 2-[bis(2-methoxyethyl)aminomethyl]-4-isopropylphenol;
(6) HL1= 4-Chloro-2-[(2-morpholin-4-ylethylimino)-methyl]-phenol.
b4-NPP= p-nitrophenylphosphate; 2,4-BDNPP = bis(2,4-dinitrophenyl)phosphate;HPNP = 2-hydroxypropyl-p-nitropenylphosphate.
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Fig. 1 Different bridging modes of SCN- group.
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Fig. 2 ORTEP drawing (30% probability ellipsoids) of complex Zn2L1(SCN)3 (1) (CH3CN
solvent molecule not shown, of t-butyl only one of disordered positions is shown).
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Fig. 3 ORTEP drawing (30% probability ellipsoids) of the crystallographic independent unit of
complex 2. Metal ion Cd3, located on a center of symmetry, gives origin to a 1D coordination
polymer.
29