Tetrazolate bridged dinuclear photo-luminescent zinc(II) Schiff base complex prepared via 1,3-dipolar cycloaddition at ambient condition

Article abstract of DOI:10.1080/00958972.2016.1153078

A bis(-NN′-tetrazolate)-bridged centrosymmetric dinuclear zinc(II) Schiff base complex, [Zn₂(L)₂(PZTZ)₂] (HL is a tridentate Schiff base, 2-(2-(dimethylamino)ethyliminomethyl)-6-ethoxyphenol and HPZTZ is 2-pyrazinyltetrazo

Full text of DOI:10.1080/00958972.2016.1153078

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Tetrazolate bridged dinuclear photo-luminescent
zinc(II) Schiff base complex prepared via 1,3-
dipolar cycloaddition at ambient condition
Satavisha Bhattacharya, Sumit Roy & Shouvik Chattopadhyay
To cite this article: Satavisha Bhattacharya, Sumit Roy & Shouvik Chattopadhyay (2016):
Tetrazolate bridged dinuclear photo-luminescent zinc(II) Schiff base complex prepared via
1,3-dipolar cycloaddition at ambient condition, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2016.1153078
To link to this article: http://dx.doi.org/10.1080/00958972.2016.1153078
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Date: 14 March 2016, At: 09:26

Journal of Coordination Chemistry, 2016
http://dx.doi.org/10.1080/00958972.2016.1153078
Tetrazolate bridged dinuclear photo-luminescent zinc(II) Schiff
base complex prepared via 1,3-dipolar cycloaddition at ambient
condition
Satavisha Bhattacharya, Sumit Roy and Shouvik Chattopadhyay
department of Chemistry, Jadavpur university, Kolkata, india
ARTICLE HISTORY
ABSTRACT
received 1 august 2015
accepted 29 January 2016
A bis(μ-NN′-tetrazolate)-bridged centrosymmetric dinuclear zinc(II) Schiff base
complex, [Zn2(L)2(PZTZ)2] (HL is a tridentate Schiff base, 2-(2-(dimethylamino)
ethyliminomethyl)-6-ethoxyphenol and HPZTZ is 2-pyrazinyltetrazole), has been
synthesized via [3 + 2] cycloaddition of 2-cyanopyrazine and sodium azide in
the presence of zinc(II) acetate dihydrate and HL. The structure of the complex
is confirmed by single-crystal X-ray diffraction analysis. The complex shows
fluorescence.
KEYWORDS
Zinc(ii); schiff base;
1,3-dipolar cycloaddition;
5-pyrazinyltetrazolate
1. Introduction
Di- and polynuclear zinc(II) complexes are widely used in opto-electronic devices [1, 2], catalysis [3–5],
materials science [6, 7], etc. They are also used in biological modeling applications [8–10]. The ability
of zinc(II) to adopt various geometries deserves further exploration of molecular architectures of new
zinc(II) complexes using different bi- or polydentate chelating ligands [11–13]. Among them, tri- and
tetradentate Schiff bases are the most popular for the ease of their synthesis, stability, and versa-
tility [14–18]. Azide is also a very good co-ligand and there are many reports on the synthesis and
CONTACT shouvik Chattopadhyay
© 2016 taylor & francis
shouvik.chem@gmail.com

2
S. BHATTACHARyA eT AL.
characterization of various polynuclear transition and non-transition metal Schiff base complexes with
azide co-ligands [14, 19–25]. These metal-ligated azides may be made to undergo 1,3-dipolar cycload-
dition reactions with a suitable alkyl cyanamide to form tetrazolates which are multidentate/bridging
building blocks in metal–organic frameworks [26–29]. Tetrazole functional groups are also used as a
metabolically stable surrogate for a carboxylic acid group in medicinal chemistry [30], as high-density
energy materials in materials science [31–33] and also as versatile ligands in coordination chemistry
[34, 35]. Among a number of coordination modes of tetrazoles, the 1,2-coordination to produce bis(μ-
tetrazolate)-bridged complexes is relatively common [36-38]. Zinc(II) tetrazolate-bridged complexes
did not receive attention to date, possibly because of the lack of magnetic exchange interactions in
them. The importance of zinc(II) complexes lies in their strong luminescence properties.
We report the tandem synthesis of a dinuclear zinc(II) Schiff base complex bridged by a substituted
tetrazolate formed by reaction of 2-cyanopyrazine, sodium azide, zinc(II) acetate dihydrate, and HL
{2-(2-(dimethylamino)ethyliminomethyl)-6-ethoxyphenol} under stirring in methanol. The X-ray dif-
fraction study has confirmed the structure of the complex.
2. Experimental
All starting materials were commercially available, reagent grade, and used as-purchased from
Sigma–Aldrich.
Caution!!! Azide complexes are potentially explosive. Although no problem was encountered in the
present study, only small amounts of the material should be prepared and must be handled with care.
2.1. Synthesis of HL {2-(2-(dimethylamino)ethyliminomethyl)-6-ethoxyphenol}
The tetradentate N2O2 donor Schiff base, HL, was prepared by refluxing N,N-dimethyl-1,2-diaminoethane
(1 mmol, 0.1 mL) and 3-ethoxysalicylaldehyde (1 mmol, 0.166 g) in methanol (20 mL) for ca. 1 h. The
Schiff base was not isolated, but was used directly for preparation of the complex.
2.2. Synthesis of [Zn2(L)2(PZTZ)2] {bis(μ2-5-(pyrazin-2-yl)tetrazolato-N,N′)-bis(2-[([2-
(dimethylamino)ethyl]imino)methyl]-6-ethoxyphenolato)-di-zinc(II)}
A methanol solution of zinc(II) acetate dihydrate (1 mmol, 0.219 g) was added to methanol solution of
HL, followed by addition of a methanol solution of 2-cyanopyrazine (1 mmol, 0.105 g) with stirring. A
methanol solution of sodium azide (1 mmol, 0.065 g) was then added to the solution and stirred for
3 h. The resulting solution was kept at room temperature for several days to get X-ray quality yellow
single crystals of the complex.
yield: 0.20 g (55%). Anal. Calcd for C36H44N16O4Zn2 (FW 895.65): C, 48.28; H, 4.95; N, 28.02. Found: C,
48.22; H, 4.90; N, 28.09%. IR (KBr, cm−1): 1639 (C=N), 2993–2839 (CH), 1447, 1404 (tetrazole). UV–vis, λmax
(nm), [εmax (L mol−1 cm−1)] (DMSO), 282 (5.1 × 104), 380 (2.6 × 104).
2.3. Physical measurements
elemental analysis (carbon, hydrogen, and nitrogen) was performed on a Perkinelmer 240C elemental
analyzer. The infrared spectrum, in KBr (4000–400 cm−1), was recorded using a Perkinelmer Spectrum
Two FTIR spectrophotometer. eSI-MS was recorded on a Qtof Micro yA263 mass spectrometer. The
electronic spectrum in DMSO (800–200 nm) was recorded on a Perkinelmer Lambda 35 UV–vis spec-
trophotometer. The fluorescence spectrum in DMSO was obtained on a Hitachi F-7000 Fluorescence
spectrophotometer at room temperature. Lifetime measurements were recorded using a Hamamatsu
MCP photomultiplier (R3809) and analyzed using IBHDAS6 software.

JOURNAL OF COORDINATION CHeMISTRy
3
Table 1. Crystal data and refinement details of the complex.
Formula
C36H44N16O4Zn2
formula weight
temperature (K)
Crystal system
space group
a (Å)
895.65
150
monoclinic
P21/n
10.804(5)
14.690(5)
12.622(5)
91.836(5)
2
b (Å)
c (Å)
β (°)
Z
d
calc (g cm−3
)
1.486
1.259
928
μ (mm−1
F(0 0 0)
)
total reflections
unique reflections
observed data [I> 2σ (I)]
no. of parameters
R(int)
26,999
3805
3141
272
0.035
R , wR (all data)
0.0385, 0.0777
0.0286, 0.0725
R11, wR22 [I> 2σ (I)]
2.4. X-ray crystallography
X-ray single-crystal data for the complex was collected at 150 K on a Bruker APeX II diffractometer
equipped with a normal focus, sealed tube X-ray source with graphite monochromated Mo-Kα radi-
ation (λ = 0.71073 Å) operating at 50 kV and 30 mA. The programs SAINT [SMART (V 5.628), SAINT (V
6.45a), XPReP, Bruker AXS Inc., Madison, WI, 2004] were used for integration of diffraction profiles, and
multi-scan empirical absorption corrections were applied to the data using SADABS [39]. The molecular
structure was solved by direct methods and refined by full-matrix least squares on F2 using the SHeLX-
97 package [40, 41] with anisotropic displacement parameters for all non-hydrogen atoms. Hydrogens
were placed in their geometrically idealized positions and constrained to ride on their parent atoms.
The crystallographic and refinement data of the complex are summarized in table 1.
Figure 1. orteP view of the complex with atom numbering scheme. thermal ellipsoids are shown at 30% probability. hydrogens
are omitted for clarity. symmetry transformation: a = 1 − x, 1 − y, 1 − z.

4
S. BHATTACHARyA eT AL.
Table 2. selected bond lengths (Å) of the complex.
Zn(1)–o(1)
Zn(1)–n(1)
Zn(1)–n(2)
Zn(1)–n(3)
Zn(1)–n(4)
Zn(1)a–n(5)
1.9923(17)
2.373(2)
2.0233(19)
2.568(2)
2.0874(19)
2.135(2)
note: symmetry transformation a = 1 − x, 1 − y, 1 − z.
Table 3. selected bond angles (°) of the complex.
o(1)–Zn(1)–n(1)
o(1)–Zn(1)–n(2)
o(1)–Zn(1)–n(3)
o(1)–Zn(1)–n(4)
o(1)–Zn(1)–n(5)a
n(1)–Zn(1)–n(2)
n(1)–Zn(1)–n(3)
n(2)–Zn(1)–n(3)
165.15(16)
n(1)–Zn(1)–n(4)
n(1)–Zn(1)–n(5)a
n(2)–Zn(1)–n(4)
n(2)–Zn(1)–n(5)a
n(3)–Zn(1)–n(4)
n(3)–Zn(1)–n(5)a
n(4)–Zn(1)–n(5)a
91.49(6)
94.08(7)
163.63(7)
98.03(7)
71.90(6)
167.43(6)
95.81(6)
91.38(6)
80.56(6)
95.21(6)
98.40(6)
78.87(7)
88.99(6)
94.53(6)
note: symmetry transformation a = 1 − x, 1 − y, 1 − z.
2.5. Hirshfeld surface analysis
Hirshfeld surfaces [42–44] and the associated 2-D fingerprint [45–47] plots were calculated using Crystal
explorer [48] with bond lengths to hydrogens set to standard values [49]. For each point on the Hirshfeld
isosurface, two distances, de (the distance from the point to the nearest nucleus external to the surface)
and di (the distance to the nearest nucleus internal to the surface), are defined. The normalized contact
distance (dnorm) based on de and di is given by:
Table 4. selected zinc(ii)–npyrazinyl distances (Å) in some reported complexes.
Complex
Distance (Å)
Ref.
[Zn2(l)2(PZtZ)2]
2.568(2)
2.214(2)
2.087(3)
2.049(3)
2.214(2)
2.184(2)
2.130(4), 2.065(2)
2.103(1)
2.217(2)
2.037(2)
2.332(3)
2.229(4)
2.19(1)
this work
[55]
[56]
[57]
[58]
[59]
[60]
[61]
[62]
[63]
[64]
[64]
[65]
[66]
[66]
[67]
[68]
[69]
[70]
[71]
[72]
[Zn(sac)2(μ-pyz)(h2o)2]n
[Zn(phen)(dPZda)(h2o)]·2h2o
Zn(2,6-PZdC)(h2o)2
{[Zn(pyzn)(sCn)(h2o)2]·h2o}∞
(h3o)2[Zn(2,3PZdC)2]
[Zn2(h2o)4(dipic)2(μ-apyz)]
[(Zn(dmPZ)2Cl2]
1aZnCl2
[Zn(n3)2(amPyZ)2]
[Zn2(pztc)(phen)4]·12h2o
[Zn2(pz25dc)(phen)4](no3)2·10h2o
Zn(pyz)(nCme)2[auBr2(Cn)2]2
[Zn(ptp)(h2o)]2
[Zn(ptp)]n
[Zn(pzta)2(h2o)2]
2.131(3)
2.228(3)
2.197(2)
2.058(1)
2.213(3)
2.185(2)
2.241(2)
2.194(2)
[ZnCl2(amPyZ)2]
Zn(l1)2(h2o)2
Zn(l2)2(h2o)2
Zn(l3)2(Cl)2
[Zn(PZtZ)2(h2o)2]
notes: hl = 2-(2-(dimethylamino)ethyliminomethyl)-6-ethoxyphenol; hPZtZ = 2-pyrazinyltetrazole; Pyz = pyrazine, and sac =
saccharinate; Phen = 1,10-phenanthroline; h2dPZda = 3,5-dimethyl-2,6-pyrazinedicarboxylic acid; Pyzn = pyrazine-2-carbox-
ylic anion; 2,6-PZdC = pyrazine-2,6-dicarboxylate; 2,3-PZdC = pyrazine-2,3-dicarboxylate; dipich2 = dipicolinic acid; apyz =
2-aminopyrazine; dmPZ = 2,5-dimethylpyrazine; 1a = 2-(6′,2″-bipyrid-2′-yl)-3-(2-pyridyl)pyrazine; pz25dc = pyrazine-2,5-dicar-
boxylate; phen = 1,10-phenanthroline; h4pztc = pyrazine-2,3,5,6-tetracarboxylic acid; h2ptp = 2,3-bis(pyridine-2-yl)-5,6-di-1h-
tetrazol-5-ylpyrazine; pzta = pyrazinyl tetrazolate; amPyZ = 2-aminopyrazine; hl1 = 5-(pyrazin-2-yl)-3-(pyridin-4-yl)-1h-1,2,4-
triazole; hl2 = 5-(pyrazin-2-yl)-3-(pyridin-3-yl)-1,2,4-triazolide; l3 = 2-(1-hydrazinylideneethyl)pyrazine.

JOURNAL OF COORDINATION CHeMISTRy
5
Scheme 1. the proposed route to the complex.
(di − rivdw
)
(de − revdw
)
dnorm
=
+
rivdw
revdw
where rivdw and revdw are the van der Waals radii of the atoms. The value of dnorm is negative or positive
depending on intermolecular contacts being shorter or longer than the van der Waals separations. The
parameter dnorm displays a surface with a red–white–blue color scheme, where bright red spots highlight
shorter contacts, white areas represent contacts around the van der Waals separation, and blue regions
are devoid of close contacts. For a given crystal structure and set of spherical atomic electron densities,
the Hirshfeld surface is unique [50], and thus, it suggests the possibility of gaining additional insight
into the intermolecular interactions of molecular crystals.

6
S. BHATTACHARyA eT AL.
Table 5. absorption and emission spectral data of some selected dizinc complexes.
Complex
λexcitation
λemission
Ref.
[Zn2(l)2(PZtZ)2]
380
371
363
365
379
375
375
370
370
370
370
344
370
326
315
382
384
380
432
415
403
407
469
475
475
495
445
445
448
505
489
370, 430
485
450
452
481
this work
[54]
[54]
[54]
[75]
[21]
[21]
[21]
[16]
[16]
[16]
[76]
[77]
[78]
[78]
[79]
[79]
[79]
[Zn2(hl1)4](Clo4)4
[(hl2)Zn2(l2)(dca)2]Clo4
[(hl3)Zn2(l3)(nCs)2]Clo4 Ch3oh
[Zn2l4(oac)2(h2o)]
[Zn(l5)(μ1,1-n3)Zn(l)(n3)]·1.5h2o
[Zn(l5)(μ1,1-nCo)Zn(l)(nCo)]·1.5h2o
[Zn(l5)(μ1,1-nCs)Zn(l)(nCs)(oh2)]
[Zn2(l6)2Cl2]
[Zn2(l6)2Br2]
[Zn2(l6)2i2]
[(n3)Zn(l7)(μ1,1-n3)]2
[Zn2(hl8)2]
[Zn2(l9)2(μ-tp)](Clo4)2
[Zn2(l9)2(μ-tp)](Pf6)2
[Zn2l10Cl3]
[Zn2l11Cl3]
[Zn(h)l12Cl2]·h2o
notes: see table 4 for some abbreviations; hl1 = [2-(-(3-(dimethylamino)propylimino)methyl)-4-bromophenol]; hl2 = [2-(-(3-(di-
methylamino)propylimino)methyl)-6-methoxyphenol];
hl3 = [2-(-(3-(dimethylamino)propylimino)methyl)-6-ethoxyphenol];
h2l4 n,n′-bis(salicylidene)cyclohexane-1,2-diamine; h2l5
2-(2-(dimethylamino)ethylimino)methyl)-6-methoxyphenol;
=
=
h2l6 = 2-(2-(2-pyridyl)ethyl)imino)methyl]phenol; l7 = n-(4,6-dimethylpyrimidin-2-yl)- n′-(1-pyridin-2-yl-ethylidine)-hydra-
zine; h3l8 = 2,6-diformyl-4-methylphenol-di(benzoylhydrazone; l9 = n,n′-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine,
tp = terephthalate dianion; hl10 = 2,6-bis[1-(2-aminoethyl)pyrolidine-iminomethyl]-4-methyl-phenol; hl11 = 2,6-bis[1-(2-ami-
noethyl)piperidine-iminomethyl]-4-methyl-phenol; hl12 = n-{1-(2-aminoethyl)pyrolidine}salicylideneimine.
3. Results and discussion
3.1. Synthesis
The potential tetradentate Schiff base (HL) was prepared by condensation of 3-ethoxysalicylaldehyde
with N,N-dimethyl-1,2-diaminoethane following the literature methods [51, 52]. The ligand is not iso-
lated and was used directly for the preparation of the complex. The methanol solution of HL was then
combined with zinc(II) acetate dihydrate. Addition of 2-cyanopyrazine and sodium azide in this solution
with constant stirring produced the 2-pyrazinyl tetrazolate complex of zinc(II) containing a Schiff base
via [2 + 3] cycloaddition. The synthesis of the complex is shown in scheme 1.
Addition of zinc(II) is essential for synthesis in that the cyclization does not occur under ambient
conditions in the absence of suitable transition metals. Use of nickel(II)/cadmium(II) produces similar
Figure 2. excitation and emission spectra of the complex in dmso solution.

JOURNAL OF COORDINATION CHeMISTRy
7
Figure 3. lifetime decay profile of the complex.
Table 6. the detailed data of the photoluminescence and time-resolved photoluminescence decays of the complex.
λex (nm)
λem (nm)
A1 (%)
τ1 (ns)
A2 (%)
τ2 (ns)
τav (ns)
χ2
380
432
62.59
2.24
37.41
11.48
9.20
1.10304
Figure 4. hirshfeld surfaces mapped over dnorm (a), shape index (b), and curvedness (c) of the complex.
complexes [36, 37, 53]. However, in the absence of suitable transition metals, tetrazoles could not be
isolated from the reaction mixture, as confirmed by the HRMS spectra of the reaction mixtures.
We have repeated the reaction changing the sequence of the addition of the reagents. Mass spec-
tra of the reaction mixture do not support the formation of [Zn2(L)2(PZTZ)2]. Thus, we conclude that
the sequence of addition of different ligands is necessary for [Zn2(L)2(PZTZ)2] formation. The following
mechanism may be proposed for formation of the complex. Three coordination sites at zinc(II) are coor-
dinated with the tridentate Schiff base, while the fourth and fifth coordination sites are occupied by the
2-cyanopyrazine and azide. Coordination to zinc(II) makes azide a better electrophile and it undergoes
a 1,3-dipolar cycloaddition with the nitrile group of 2-cyanopyrazine under ambient conditions to
form the tetrazolate, which binds another zinc(II) to form [Zn2(L)2(PZTZ)2]. The proposed mechanism is
shown in scheme 1.

8
S. BHATTACHARyA eT AL.
Figure 5. fingerprint plots of the complex: full (a) and resolved into n⋯h/h⋯n (b) and o⋯h/h⋯o (c) contacts showing the
percentages of contacts contributed to the total hirshfeld surface area of the complex.
3.2. Description of the structure of [Zn2(L)2(PZTZ)2]
The complex crystallizes in the monoclinic space group P21/n. The perspective view is shown in
figure 1. Selected bond lengths and angles are given in tables 2 and 3, respectively. The complex
features a double μ-NN′-tetrazolate-bridged zinc(II) dinuclear core, in which two distorted octahedral
zinc(II) centers are bridged by two centrosymmetrically related tetrazolate ions. Within the dinuclear
unit, each distorted octahedral zinc(II) center is coordinated meridionally by O(1), N(1), and N(2) of a
deprotonated tridentate L− and N(3) and N(4) of the 2-pyrazinyltetrazolate (PZTZ)−. A symmetry related
nitrogen, N(5)a (symmetry transformation a = 1−x, 1−y, 1−z), from a bridging (PZTZ)− coordinates to
complete the distorted octahedral geometry of zinc(II).
The Zn(1)–Nimine distance (2.0233(19) Å) is shorter than the Zn(1)–Namine distance (2.373(2) Å), as
observed in similar systems [54]. However, Zn(II)–Npyrazinyl distances (2.568(2) (Å)) for this complex are
longer than distances in related zinc complexes [55–72] (table 4). The long Zn(II)–Npyrazinyl bond is prob-
ably a result of the bond angles with respect to chelation of the tetrazolate/pyrazine ring about zinc(II)
and the bridging nature of the tetrazolate itself which prevents that portion of the ligand from “mov-
ing”to accommodate a shorter Zn(II)–Npyrazinyl bond length. It should be noted that the μ-NN′ bridging
geometry of (PZTZ)− is asymmetric, which can be seen from the inequality in the bridging angles
Zn–N(4)–N(5)=134.2°(1) and Zna–N(5)–N(4)=129.1°(1), as observed in similar complexes [38]. The sat-
urated five-membered ring Zn–N(1)–C(3)–C(4)–N(2) assumes a half-chair conformation with puckering
parameters q(2)=0.445(3) Å and ϕ(2)=92.1(2)° [73]. The N(1)–Zn(1)–N(2) angle is 78.87(7)°, typical of
a five-membered chelate ring [74]. There are no other significant interactions present in the complex.
3.3. IR, electronic and fluorescence spectra
Formation of a tetrazole group is further supported by the appearance of sharp bands at 1447 and
1404 cm−1 [37]. The IR band corresponding to the imine (C=N) stretch appears at 1639 cm−1 [51]. Absence
of an azide peak at ~2100 cm−1 in the IR spectrum of the complex supports the proposed reaction
between the nitrile and the azide. Bands at 2993–2839 cm−1 due to alkyl C–H bond stretching vibrations
are in the spectrum of the complex [52]. The electronic spectrum was recorded in DMSO from 200 to
800 nm. The complex shows intense absorptions at 282 and 380 nm which may be assigned as π–π*
and n–π* transitions, respectively [54]. The complex exhibits luminescence at 432 nm upon excitation
at 380 nm, assigned as an intra-ligand (π–π*) fluorescence. Absorption and emission spectral data of
some selected dizinc complexes [16, 21, 54, 75–79] are provided in table 5 in order to have a better
understanding of the photoluminescence properties of dizinc complexes. The excitation and emission
spectrum of the complex is shown in figure 2. The mean lifetime of the excited state is 9.2 ns at room
temperature. The decay profile (figure 3) has been fitted to a multi-exponential model:

JOURNAL OF COORDINATION CHeMISTRy
9
Table 7. hirshfeld surface analysis of some related complexes showing the percentages of contacts contributed to the total hirsh-
feld surface area.
Complex
H⋯H (%)
N⋯H/H⋯N (%)
O⋯H/H⋯O (%)
Ref.
[Zn2(l)2(PZtZ)2]
50.8
50.5
53.9
48.8
49.5
49.3
58.5
47
21.9
17.1
16.5
18.1
14.9
19.9
12.6
28.3
8.1
7.1
6.5
4.9
11
13.9
6.1
6
4
18.8
11.8
this work
[53]
[53]
[53]
[36]
[36]
[37]
[38]
[37]
[Cd(PrtZ)(l1)(oh2)]
[Cd(PrtZ)(l2)(oh2)]
[Cd(PZtZ)(l2)(oh2)]·0.25h2o
[ni2(l3)2(PZtZ)2]·2(Ch3)2so·2.69h2o
2[ni2(l4)2(PZtZ)2]·3h2o
[ni2(l6)2(PrtZ)2]
[ni2(l5)2(PZtZ)2]·2h2o·2Ch3Cn
[ni2(l4)2(PrtZ)2na(h2o)]Clo4·h2o
[ni(l3)(PrtZ)]2
37.8
60.4
6.2
[81]
note: see tables 4 and 5 for abbreviations.
ꢀ
( )
ꢀi exp −t∕ꢁi
I(t) =
i
where bi-exponential functions are used to fit the emission of the complex, obtaining χ2 close to
1. The detailed data of the photoluminescence and time-resolved photoluminescence decay of the
complex are given in table 6.
3.4. Hirshfeld surface analysis
The Hirshfeld surfaces of the complex, mapped over dnorm, shape index, and curvedness are illustrated
in figure 4. The surfaces are shown as transparent to allow visualization of the molecular moiety around
which they are calculated. The dominant interaction between N⋯H and O⋯H atoms can be seen in
the Hirshfeld surfaces as red spots on the dnorm surface in figure 4(a). Other visible spots in the Hirshfeld
surfaces correspond to H⋯H contacts. The small extent of area and light color on the surface indicates
weaker and longer contacts other than hydrogen bonds. The H⋯H, N⋯H, and O⋯H interactions appear
as distinct spikes in the 2-D fingerprint plot (figure 5). Complementary regions are visible in the finger-
print plots where one molecule is a donor (de<di) and the other an acceptor (de>di). The fingerprint plots
can be decomposed to highlight particular atom pair close contacts [80]. This decomposition enables
separation of contributions from different interaction types, which overlap in the full fingerprint. The
proportion of N⋯H/H⋯N and O⋯H/H⋯O interactions comprise 21.9 and 7.1% of the Hirshfeld sur-
faces for each molecule. We have compared Hirshfeld surface analysis of some related metal tetrazolate
complexes with similar ligands [36–38, 53, 81] and gathered the results in table 7. The interactions also
appear as two distinct spikes in the 2-D fingerprint plot (figure 5). The upper spike corresponding to the
donor spike represents the H⋯N interactions (di = 1.09, de = 1.68 Å) and H⋯O interactions (di = 1.13,
de = 1.48 Å). The lower spike being an acceptor spike represents the N⋯H interactions (de = 1.1, di = 1.7 Å)
and O⋯H interactions (de = 1.12, di = 1.5 Å) in the fingerprint plot.
4. Conclusion
We prepared a bis(tetrazolate)-bridged dinuclear zinc(II) complex with a Schiff base as the blocking
ligand under non-hydrothermal and non-microwave reaction conditions. Participation of the tetrazolate
in a (μ-NN′) fashion forms a dinuclear zinc(II) complex. The facile synthesis of the complex affords a
convenient synthetic route for this type of complex and opens up new possibilities for the synthesis of
tetrazolate-bridged zinc(II) complexes with Schiff base co-ligands. Work is in progress to improve the
yield of the reaction and to develop more systems based on this strategy to generalize the concept.

10
S. BHATTACHARyA eT AL.
Supplementary material
Crystallographic data for the analysis have been deposited with the Cambridge Crystallographic data Center, CCDC No.
1408321. The data can be obtained free of charge from CCDC via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgment
Crystallographic data were collected at the DST-FIST, India-funded single crystal diffractometer facility at the Department
of Chemistry, Jadavpur University.
Disclosure statement
No potential conflict of interest was reported by the authors.
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